摘要:

J. MATER. CHEM., 1991 1(4), 531-537 531 Copper-Cobalt Hydroxysalts and Oxysalts: Buik and Surface Characterization Piero Porta,* Roberto Dragone, Giuseppe Fierro, Marcello Inversi, Mariano Lo Jacono and Giuliano Moretti Centro CNR su 'Struttura e Attivita Catalitica di Sistemi di Ossidi' (SACSO), c/o Dipartimento di Chimica, Universita di Roma 'La Sapienza', Piazzale A. Moro 5,00185 Roma, Italy Copper-cobalt oxysalts of various Cu : Co atomic ratios (100 :0. 92:8,85: 15, 77 :23,67 :33,15: 85,0:100) have been prepared by coprecipitation, at constant pH, from solutions of copper and cobalt nitrates added to a solution of NaHCO,; the structure and chemical nature of the Cu-Co oxysalts have been investigated by several complementary techniques such as X-ray diffraction (XRD), magnetic susceptibility, reflectance spectroscopy and X-ray photoelectron spectroscopy (XPS) to obtain information both on their bulk and on their surface pro pert ies.In the range of Cu :Co atomic ratios from 100 :0 to 67 :33 the materials consist of Co-containing malachite, Cu,~,Co,CO,(OH),, while for Cu : Co equal to 0: 100 and 15:85 the products are CoCO,, spherocobaltite, and Cu-containing spherocobaltite Coo,,,Cuo~,,CO,, respectively. From both reflectance spectroscopy and magnetic susceptibility measurements the presence of only Cu2+ and Co2+ species has been ascertained in all materials. Antiferromagnetic interactions are strong at high copper content and become weaker at increasing cobalt loading. The observed decrease in volume of the malachite monoclinic unit cell with incorporation of Co2' ions, in spite of the larger Co2+ ion radius with respect to that of Cu2+, indicates that distortion of the MO, polyhedra at the cation site of the malachite lattice is less when Cu2' is replaced by Co2+.The presence of Cu2+ in the spherocobaltite trigonal lattice shows a small cell volume decrease as expected from ionic radii difference. XPS has confirmed the presence of only Cu2+ and Co2+ species at the surface of the materials. It is also shown that the local nature of the chemical bond is essentially determined by the nature of the first-neighbour ligands. At higher copper content, where the materials are cobalt-containing malachite, the surface is enriched in cobalt.Keywords: Copper-cobalt oxysalt; Mixed oxide precursor; Catalyst 1. Introduction It is essential that the initial precursor homogeneity is maintained during the transformation steps of the solid. One Mixed copper-cobalt oxides, especially those with the spinel of the most promising preparation methods for such multic- structure, are active catalysts for the oxidation of CO by 02.1 Cu-Co oxides (containing also A1 or Cr, Zn and an alkali omponent materials to satisfy the above requirements is the metal) are also used for the conversion of synthesis gas (CO/ coprecipitation technique, by which oxysalt precursors such C02/H2) to higher alcohol^.^-^ The composition of these as hydroxycarbonates, carbonates, oxalates, acetates, etc., are materials, developed mainly at the Institut Francais du produced and where all the metals are possibly in the same Petrole,s corresponds to that of conventional copper-based crystalline structure.methanol synthesis catalysts modified by the addition of This paper follows studies (both bulk and surface charac- cobalt. Mixed Cu-Co-Zn-Cr oxides have also been tested terization) performed in our laboratory on Cu-Zn hydroxy-as useful catalysts for the synthesis of hydrocarbons.6 carbonate precursors and on derived Cu-Zn mixed ~xides,~ It is well known that the chemical and physical properties as well as on Cu-Mn (hydr0xy)carbonate precursors and on of mixed oxide catalysts depend on the mode of preparation derived Cu-Mn mixed oxides." In this work we present the and on their thermal history since these effect the component results of the bulk and surface characterization of some Cu- interdispersion and definite m~rphology.~ Co precursors for mixed oxide systems.In a following paper To this end, many considerable efforts have been made in finding preparative we will report the results of the bulk and surface characteriz- methods that are capable of giving precursors where two or ation of the Cu-Co mixed oxides obtained by calcination of more metals are in the same or parent crystalline structure the precursors in air and in NZ, and of their behaviour under and which, after calcination at low temperature, may provide H2 reduction. well interdispersed mixed oxides of required specific surface area and particle size.Note that the solid-state reactions of interest are mainly 2. Experimental topotactic transformations, which lead to oxide products that 2.1 Sample Preparation and Analysis inherit certain structural and morphological features of the precursors; at low temperature the topotactic reactions require Compounds with Cu :Co atomic ratios of 100 :0,92 :8,85 :15, constrained mobility of species and limited structural 77 :23, 67 :33, 15 :85 and 0 :100 were prepared by coprecipi- rearrangement during calcination.* [For the definition of tation at a constant pH of 8 from Cu and Co nitrate solutions topotaxy see ref. 8(b).] As a consequence of their useful in suitable proportions with NaHCO, in excess by the same interdispersed state, the different oxide materials may interact, method described for Cu-Mn salts [see ref.10(a) for details]. favouring synergetic effects; they may act as multicomponent All the precipitates were repeatedly washed with cold water promotion compounds, manifesting a wide variety of electric, to eliminate the presence of nitrate ions and sodium. After electronic and structural properties, and they display several washing, the sodium content was analysed by atomic absorp- reactivity properties under subsequent treatments (under inert, tion and found to be 100 ppm. Once washed, the solids were reducing or oxidising atmosphere). heated in an oven at 383 K for 24 h and finely ground in an 532 agate mortar. The colour ranged from light green to grey- green for samples with Cu: Co atomic ratios of 100-67 :33, was pink for the 0: 100 composition, and light violet for the 15:85 compound. Elemental copper and cobalt analyses were performed by atomic absorption with a Varian SpectraAA-30 instrument.The percentage of water loss from the samples was also determined by weight loss after heating them at 443 K for 4 h. Table 1 lists the prepared compounds, the analytical data and other features. 2.2 X-Ray Diffraction The powder diffraction patterns were obtained with a Philips automated PW 1729 diffractometer equipped with an IBM PS2 computer for data acquisition and analysis (software APD-Philips) and an HP plotter. Scans were taken with a 20 step size of 0.01", using Co-Ka (iron-filtered) radiation.The intensities of the reflections were estimated by evaluation of the integrated peaks. Structural data for reference compounds were taken from the literatures.' 2.3 Reflectance Spectra Diffuse reflectance spectra were carried out by utilizing a Cary 2300 spectrometer equipped with a diffuse reflectance accessory and an IBM PS2 computer for data acquisition and analysis (software Spectra Ca1c.-Galactic Industries Corp.), in the wavelength range 200-2500 nm, covering the UV, visible and near-infrared regions. 2.4 Magnetic Susceptibility Magnetic susceptibilities were measured by the Gouy method over the temperature range 100-300 K. A check that the susceptibilities were independent of magnetic field strength was made. Correction was made for the diamagnetism of the samples.Then the mean magnetic susceptibility values, xat= xsp(x,,rncu+xcornco), where xsprepresents the magnetic suscep- tibility per gram of paramagnetic species, and x and rn are the relative molar fraction and atomic weight of Cu and Co, were evaluated for each precursor. An example of the linearity on the l/xat us. T plot is shown in Fig. 1 for the sample with atomic ratio Cu :Co =85 :15. From the intercepts of the line on the temperature axis the value of the Weiss temperature, 0 (which accounts for the strength of antiferromagnetic inter- actions among paramagnetic ions in the lattice), can be inferred. From the slope of the l/xat us. T plot the value of the Curie constant C=xat(T+0)can be obtained.The values of the magnetic moment ~~2.83 JC were calculated for all 4ooL 300-/* 1 -$ 200-8' -1 00 0 100 200 300 TIK Fig. 1 Reciprocal atomic susceptibility, 1/xat, us. temperature, T, for the Cu :Co =85 : 15 composition J. MATER. CHEM., 1991, VOL. 1 the samples studied. Table 1 reports the data obtained from the magnetic measurements. 2.5 X-ray Photoelectron Spectroscopy 2.5.1 Qualitative Analysis The X-ray photoelectron and X-ray excited Auger spectra were obtained using both Mg-Ka (hv= 1253.6 eV) and A1-Ka (hv = 1486.6 eV) radiations with a Leybold-Heraeus LHS-10 spectrometer operating at constant transmission energy (E, = 50 eV), and connected to an HP 21 13 computer for data acquisition and analysis. The spectrometer was calibrated by using the following photoemission lines (with reference to the Fermi level): EB Cu 2p,,, =932.8 eV; EB Ag 3d5,, =368.3 eV; and EB Au 4f7,, = 84.0 eV.The instrumental resolution expressed by the full- width at half maximum (FWHM) of the Au 4f,,, peak was 1.2 and 1.4 eV using Mg and A1 sources, respectively. The analysis chamber during the experiments was evacuated to better than 1 x10-* mbar. The spectra were recorded at room temperature and at low X-ray fluxes (anode operating at 10 kV and 20 mA with Mg-Ka, and at 12 kV and 10 mA with Al-Ka), and with an acquisition time of ca. 1 h (0.05 eV per channel, dwell time 50ms) to avoid X-ray induced reduction of Cu2 + species, as verified for experiments with longer acquisition time.The data analysis procedure generally involved smoothing, background substraction by a linear or 'S-type' integral profile and a curve-fitting procedure, using a mixed Gaussian-Lorentzian function, by a least-squares method (software DS4,X by Leybold Heraeus). The spectra were analysed in terms of the relative peak area intensity, the FWHM of the peaks, the chemical shifts of the 2p,,, and L3M45M45 tran- sitions of copper and cobalt, and the 0 1s transition. The experimental errors were estimated to be kO.2 eV for the photoelectron peak; and f0.2 and k0.5 eV for the Auger peaks of copper and cobalt, respectively. For cobalt the FWHM of the Auger peak is ca. 10 eV and the maximum is taken as the centre of the broad square line.The samples were pressed into a grooved tantalum sample holder. Charging effects were corrected using the C 1s peak relative to the carbonate group which was fixed for all the samples at EB =289.1 eV. Note that the use of A1-Ka radiation produces interference in the Co spectral region (at the lowest binding energies) by the Co L3M23M45 Auger transition, which causes the absolute Co 2p3,, integrated intensity to be overestimated by ca. 15%.12 On the other hand, when Mg-Kcr excitation is used the Auger peak interferes with the 0 1s photoelectron peak. Note also that, as reported by Dillard and K~ppelman'~ and verified by us, when the Mg source is used there is a partial overlap between the oxygen Auger KLL peaks and the low- energy region of the Co 2p,,, which modifies its background lineshape.The data reported in Table 2 were obtained with the Al-Kcr radiation. 2.5.2 Quantitative Surface Analysis The surface compositions of the compounds were obtained on the basis of the peak area intensities of the Cu 2p3,, and Co 2p3/, levels using the sensitivity-factor approach.gd The relative atomic sensitivity factor was determined from exper- imental measurements on Cu2C03(0H), and CoCO,, using the data obtained with the A1-Ka radiation. The following expression was applied to obtain the surface atomic ratio from the XPS intensity ratio (c~/co)xPs=0.76CI(CU 2P,,,)/I(CO 2P3/2)1 Where I represent the peak areas and 0.76 is the relative Table 1 Phases present detected by XRD" phases cu:co cu:co (XRD) CU% CO% H,O% ('4'4) (XPS) xcu Ccalc Cexp NPB O/K a/A blA CIA PI" 55.6 -2.9 --1.o -0.6 2.19 200 9.518 11.947 3.249 98"45' 50.9 3.9 2.4 11.9 5.4 0.93 0.86 0.8 2.53 110 9.471 12.019 3.220 97"55' 46.7 7.5 4.1 5.8 4.5 0.85 1.08 1.o 2.83 75 9.410 12.038 3.210 97" 10 43.4 11.1 5.6 3.6 2.5 0.78 1.30 1.28 3.20 80 9.400 12.082 3.198 97'05' 38.8 16.3 6.8 2.2 1.5 0.69 1.59 1.6 3.57 55 9.398 12.121 3.185 97" 8.2 37.3 5.2 0.2 0.2 0.16 3.25 3.7 5.40 70 4.660 14.949 -48.8 2.5 ----3.77 5.50 60 4.668 14.991 malachite-like, S =spherocobaltite-like.Copper and cobalt weight percent (by atomic absorption, accuracy within 2%); weight percent of water obtained by weight loss at 443 K (accuracy atomic ratios determined by atomic absorption (AA)and by XPS (accuracy within 15%); copper molar fractions, Xcu; nominal and experimental copper molar fractions, Xcu; Curie and experimental, Cexp),magnetic moments (accuracy within 2%); Weiss temperature (K) (accuracy within 10%); lattice parameters calculated for Co-malachite (monoclinic (trigonal cell).Table 2 Binding energies of 0 Is, Cu 2p,,,, Co 2p3/, and Auger kinetic energies for CU(L~M~~M~~, 'G)and Co (L3M45M45) transitions" Eb (0 Is)/eV E,(C Is; COi-531.2 (2.4) 933.8 (4.5) -916.9 -289.1 (2.5) 531.1 (2.7) 933.8 (4.8) 781.1 (4.8) 9 16.8 769.4 289.1 (2.4) 531.3 (2.8) 933.8 (4.5) 781.1 (4.8) 9 16.8 769.4 289.1 (2.4) 53 1.2 (2.7) 933.5 (4.3) 781.3 (4.8) 9 16.4 769.4 289.1 (2.4) 531.3 (3.0) 933.7 (4.5) 781.5 (4.8) 916.3 769.7 289.1 (2.9) 531.2 (2.8) 933.5 (4.4) 781.3 (4.8) 916.4 770.0 289.1 (2.4) 531.2 (2.7) 781.2 (4.8) 770.4 289.1 (2.4) ~~ the full width at half maximum of the photoelectron peaks are reported. For all the samples the charging was corrected with reference to the C Is peak of the COi-group fixed 534 atomic sensitivity factor obtained using the intensity ratios [(metal 2p3/,/(oxygen 1 s)] recorded on the pure precursors by the expression Sco/Sc, =3(Ic0/10)/~Icu/~~)=8.09/10.7=0.76 Note that the measured intensity for Cu 2p3/2 and Co 2p3/2 peaks takes into account both the satellite and the main peaks.The water content of the compounds (see Table 1) does not influence the sensitivity factor appreciably (0.75 instead of 0.76). The surface Cu:Co ratios are reported in Table 1, column 7.3. Results and Discussion 3.1 Phase Analysis The X-ray pattern of the sample with atomic ratio Cu :Co = 1OO:O shows exclusively the reflections of the mineral mala- chite, CU~CO~(OH)~, hereafter labelled M." The precursors with Cu :Co compositions in the range 92 :8-67 :33 also give XRD spectra similar to malachite, at least in the sequence of the X-ray lines. Fig.2 shows as an example the observed spectrum for the compound with Cu :Co =85 :15, and super- imposed the lines of malachite." This observation, together with the evidence that no extra lines of other phases are detectable, points out that solid solutions of cobalt-containing malachite of chemical formula Cu2 -xCo,C03(0H)2 (hereafter labelled CoM) are formed in the range of Cu:Co= 92 :8-67 :33.It should be recalled that cobalt-containing malachites have indeed been found to exist also as natural products.'" The samples with Cu :Co atomic ratios 0 : 100 and 15 :85 give XRD patterns corresponding to that of the mineral spherocobaltite, CoCO3," hereafter labelled S. The XRD pattern of the precursor with Cu :Co = 15:85 (Fig. 3) matches very well with that of S, no other phases being detectable. It is inferred that Coo~ssCuo, 15co3copper-containing spheroco- baltite, hereafter labelled CuS, is achieved. 3.2 Diffuse Reflectance Spectroscopy The reflectance spectrum performed on the Cu :Co = 100:0 sample shows [Fig. 4(a)] two absorption bands at ca.8000 (1250) and 12 500 cm-' (800 nm). These bands are character- istic of Cu2+ (3d9 electronic configuration) in a distorted 1600 1400 -1 1200 I 1000 B 3 800 0 600 400 200 0 20 40 60 80 2810 Fig. 2 X-Ray pattern (Co-Kcr, radiation) of the Cu :Co =85 :15 com-position. The X-ray lines (26' and relative intensities) of the reference spectrum for malachite (ref. 1I) are also shown J. MATER. CHEM., 1991, VOL. 1 I6O0 1400 I 1200 I000 (I).L C5 800 0 600 400 i II IIIII Ill 10 20 40 60 80 201" Fig. 3 X-Ray pattern (Co-Ka, radiation) of the Cu :Co = 15:85 com-position. The X-ray lines (26' and relative intensities) of the reference spectrum for spherocobaltite (ref. 11) are also shown 1 I I 40 000 30 000 20 000 10 000 wavenumbers/cm-' Fig.4 Reflectance spectra of Cu-Co precursors.(a) Spectrum of Cu: Co = 100:0; (b) spectrum of Cu :Co =85 : 15; (c) spectrum of cu:co=o: 100 octahedral co-ordinati~n~"~~~-'~and attributed to the +dX2-y2 and dxy,xz,yz-+dx2 transitions, respectively.d,~ -,,z Another strong absorption starting at ca. 25 000 cm-' (400 nm) is due to the charge-transfer transitions from primar- ily ligand orbitals (bonding and non-bonding) to the highest dX2-y~orbital of copper.17 The reflectance spectrum of the Cu :Co =0 : 100 compound shows [Fig. 4(c)] two bands at ca. 8300 (1200) and 20 000 cm-' (500 nm) typical of Co2+ (3d7 electronic con- figuration) in octahedral symmetry and assigned to the tran- sitions "T1,+"T2, and 4T1, ("F)+"T,, ("P), respectively.18 Large absorption is exhibited for wavelengths shorter than 300 nm (33 000 cm-'). For the intermediate Cu:Co compositions all d-d tran-+ +sition bands, corresponding to both Cu2 and Co2 species are visible in all the materials. The spectrum for the Cu :Co = 85: 15 compound is shown in Fig.qb), as an example. It should be pointed out that with the increase of cobalt content, especially up to Cu:Co=67:33, the band of copper at 8000 cm-' is shifted towards higher energy owing to the superposition of a band of Co2+ at 8300 cm- ',and the peak of Cu2+ at 12 500 cm-' is shifted towards lower energy. The latter observation seems to signify that the presence of cobalt J. MATER.CHEM., 1991, VOL. I in the same structure of malachite induces a certain lengthen- ing in the Cu-0 bonds. 3.3 Magnetic Properties The experimental values of the Curie constants, C, magnetic moments, p, and Weiss temperatures, 8, for each Cu:Co composition are reported in Table 1. The values of C for pure malachite (Cu :Co = 100:0) and spherocobaltite (Cu :Co-0: 100) are 0.6 and 3.8, respectively, as expected for Cu and Co in the oxidation state of +2 (Cu2+ being in distorted- octahedral symmetry'" and Co2 + in nearly octahedral co- ordination"). The above C values for Cu2 + and Co2 +,and the respective copper and cobalt analytical molar fractions (Xcuis reported in Table 1, column 8) were used to calculate the relative C values for each intermediate composition by applying the additivity law formula: C =Cc,X +Cco(1 -X).All the calcu- lated C values (except that for the 15 :85 composition) agree fairly well with the experimental ones (Table l).This assures the presence of Cu2+ and Co2+ species in the mixed precursors. Table 1 shows also that the Weiss temperature, 8, (which specifies antiferromagnetic interactions present within the solid and is directly proportional to the average number of nearest-neighbour magnetic ions surrounding each magnetic ion) has the highest negative value (-200 K) in the pure malachite, and becomes less negative at the increase of cobalt content. This implies that Cu-0-Cu exchange interactions are magnetically stronger than those of Cu-0-Co or co-0-co.3.4 Structural Bulk Properties It was observed from the XRD spectra that many X-ray lines of the CoM and CuS solid-solution phases, in addition to having different intensities with respect to pure M and S, were systematically displaced with increasing concentration of for- eign atoms within the host malachite or spherocobaltite lattices (see Fig. 2 and 3 as examples of displacement). The unit-cell parameters, reported in Table 1, were determined for all compounds using the observed d spacings and the relative hkl Miller indices for each given reflection. It is evident from Table 1 that (i) the incorporation of Co2+ ions in the malachite monoclinic lattice gives a decrease of the cell volume, I/. In particular, with increasing Co content, both a and c parameters decrease and b increases.Since the p angle progressively decreases this means that the lattice becomes less and less distorted at the increase of Co content, i.e. comes nearer to 90" and the lattice approaches an orthorhombic one. This behaviour has been found by us also for the Zn-containing'" and Mn-containing" malachites. (ii) The introduction of Cu2 + in the spherocobaltite trigonal lattice gives a slight decrease of both a and c parameters, which provides an overall slight decrease in cell volume. As regards point (i) recall that the monoclinic lattice of M contains two types of non-equivalent Cu2+ ions: Cu of type I (Cu,) is surrounded by four oxygens belonging to C03 groups and two OH ions, whereas Cu of type I1 (Cull) is surrounded by two oxygens of the carbonate anion and four OH ions2' Both CU, and CuII are in distorted octahedral co- ordination, the mean values of the four coplanar and two apical interatomic Cu-0 distances being for Cu, 1.98 and 2.71 A, and for Cull 2.01 and 2.41 A.Both CuI06 and CulI06 distorted octaedra form strings in the c direction linked by edges. Co2+ can be present in the mineral mala~hite,'~ as we found also for Zn2+ and for Mn2+.'"910 Our study has demonstrated that, up to 33% cobalt content, monophasic solid solutions with a malachite structure are formed. It must be added that beyond the above value other metastable phases (the characterization of which is in progress) are produced.The observed decrease of the cell volume of the CoM samples with increasing cobalt content seems in contrast with expectations based on the isomorphous substitution of Cu2 + by Co2+ ions within the malachite lattice, since the octahedral ionic radii for Cu2 + and Co2 + (high-spin configuration) are 0.73 and 0.745 A, respectively.21 The unexpected volume shrinkage of the malachite monoclinic unit cell with incorpor- ation of Co2 + ions (bigger than Cu2 +)indicates that distortion of the MeO, polyhedra at the cation site of the malachite lattice is less when Cu2+ is replaced by Co2+. The decrease of local octahedral distortion (with a consequent overall decrease in the cell volume) is linked, in our opinion, to the different electron configuration of Cu d9 and Co d7 ions, the latter having less tendency than copper to give elongation of the oxygen octahedra.22 Recall that in the corresponding oxides, CuO and COO, Cu2+ and Co2+ are co-ordinated differently to oxygens, having nearly square-planar and octa- hedral symmetry, re~pectively.~~ It should be noticed that similar behaviour has been observed in zinc malachites'" and manganese malachites"" (in this case we observed a lower increase in the cell volume than that expected on the basis of a pure ionic radii difference).The presence of Co2+ in CoM solid solutions should increase the structural and thermal stability of the malachite structure, as already observed for ZnM'" and MnM." Some preliminary thermogravimetric (TG, DTG and DTA) findings confirm this hypothesis; CoM materials show a displacement (ca.80" for the 92: 8 compound) of decomposition to higher temperature with respect to pure M.As for point (ii) the lower volume observed for the Coo~85Cuo,15C03compound with respect to spherocobaltite, C0C03 (whose structure is similar to calcite and contains cations in nearly octahedral ~o-ordination)~~ agrees with ionic radii considerations since the substitution of slightly larger Co2+ ions (ionic radius=0.745 A) by Cu2+ (0.73 A) induces an overall shrinkage of the lattice. 3.5 Surface Properties The presence of Cu2 + and Co2 + species has been ascertained by X-ray photoelectron spectroscopy (XPS) at the surface of the materials. Table 2 reports the binding energies and the kinetic energies of the 2p33,2 photoemission and L3M45M45 Auger transitions for both copper and cobalt.In the same table the binding energies of 0 1s and C 1s (carbon atom of the carbonate group) and the full width at half maximum, FWHM, for all photoelectron peaks (in parentheses) are reported. The 2p3,2 transitions of Cu2+ and Co2+ ions present, beside the main peak, a satellite peak at higher binding energy. The origin of such satellites has been the subject of much discussion in the literature. For Cu2+ the satellite and the main peaks are related, respectively, to the 2p53d9 and 2p53d"L electronic configurations in the final state, where L refers to a ligand hole [see ref. 9 (d) and references therein].For Co2+ the interpretation of both satellite and main peaks should be similar and related to the 2p53d7 and 2p53d8L electronic configurations in the final state, respe~tively.~~-~~ It has also been reported that for Cu2 +-containing compounds the satel- lite-main peak energy separation increases and the satellite- main peak intensity ratio decreases with increasing covalent character of the metal-ligand bond.24 The presence of the satellites (at ca. 9 and 5 eV from the main peaks, respectively, for copper and cobalt)27in the XP spectra of the pure malachite and spherocobaltite as well as of the solid solutions (both Cu, -xCoxC03(OH)z and co~~8~c~o~~~co3)thus becomes clear evidence of the oxi-dation state of +2 for cobalt and copper in all the studied materials.The 2p3,, satellite-main peak separation and their relative intensity ratio (ca.0.7 and 0.5 for Cu2+and Co2+,respectively) remain constant, within experimental error, for both Cu and Co in all compounds. Table2 shows that the 0 1s binding energy is constant within experimental error. These results suggest that the local nature of the metal-oxygen bond is essentially determined only by the nature of the first-neighbour ligands. In Fig. 5 the Cu:Co atomic ratios in the surface region (XPS) as well as in the bulk (chemical analysis by atomic absorption) are reported for the hydroxycarbonate-carbonate solid solutions. In the figure the straight line with slope equal to unity indicates that the surface composition reflects bulk composition for both cobalt and copper. The results reported in Table 1 and Fig.5 clearly show that up to Cu:Coz6 (sample 85:15)the surface region is slightly enriched in cobalt, whereas for the sample 92 :8 there is strong evidence for high cobalt enrichment at the surface. We interpret these results in terms of strain-energy effects.The Co2+ions are bigger than the Cu2+ and prefer less distorted octahedral symmetry (highly distorted MeOs polyhedra are present in the pure malachite). As a consequence, Co2+ ions tend to segregate at the surface, the driving force being the strain energy term of the segregation enthalpy. However, the hypothesis of higher reactivity of Co2+ ions with moisture cannot be excluded (chemical driving force).For the sample with atomic ratio Cu: Co =15:85 (Cu2+ incorporated into the spherocobaltite lattice) high homogen-eity between surface and bulk has been observed. 4. Conclusions The results obtained can be summarized as follows. (1) At high Cu:Co atomic ratios (up to 67:33) single phases of Cu, -xCoxC03(0H), malachite-like solid solutions are formed; the incorporation of Co2 ions into the malachite+ 12110 / 92:8 0 : p 3 , , , , I 15 :85 2 4 6 8 1012 Cu : Cu (AA) Fig. 5 Cu: Co compositions at the surface (XPS) and in the bulk (chemical analysis by atomic absorption) for hydroxycarbonate mala-chite-like compounds. The straight line (slope= 1) represents the homogeneous distribution between surface and bulk J.MATER. CHEM., 1991, VOL. 1 lattice produces less distortion in the MeOs polyhedra, higher structural and thermal stability, and Cu-0-Co exchange antiferromagnetic interactions weaker than the initial Cu-0-Cu ones. (2) Spherocobaltite, C0C03, and coO~~~c~o~~~co3copper-containing spherocobaltite are formed at high cobalt loading. (3) The surface is enriched in cobalt (much more at low Co content) in the malachite-like solid solutions owing to the strain-energy contribution, arising from size and electronic effects (Co2+ is bigger than Cu2+, and prefers less distorted octahedral symmetry). (4) Surface composition reflects bulk composition for both copper and cobalt in the Cuo.15Coo.s5compound. We gratefully acknowledge support from the Italian CNR 'Progetto Finalizzato Chimica Fine 11'. References 1 S.Angelov, D. Mehandjiev, B. Piperov, V. Zarkov, A. Terlecki-Baricevic, D. Jovanovic and Z. Jovanovic, Appl. Catal., 1985, 16, 431. 2 K. Fujimoto and T. Oba, Appl. Catul., 1985, 13, 289. 3 X. Xiaoding, E. B. M. Doesburg and J. J. F. Scholten, Catal. Today, 1987,2, 125. 4 J. E. Baker, R. Burch and S. E. Golunski, Appl. Catal., 1989, 53, 279, and references therein. 5 (a) A. Sugier and E. Freund, US.Pat., 4 122 110, 1987; (b) P. Courty, D. Durand, E. Freund and A. Sugier, J. Mol. Catal., 1982, 17, 241. G. Fornasari, S. Gusi, F. Trifiro and A. Vaccari, Znd. Eng. Chem. Res., 1987, 26, 1500, and references therein. D. Waller, D. Stirling, F.S. Stone and M. S. Spencer, Faraday Discuss. Chem. SOC.,1989, 87, 107. (a)L. Volpe and M. Boudart, Catal. Reu. Sci. Eng., 1985, 27, 515; (b) H. R. Oswald and J. R. Gunter, in Crystal Growth and Materials, ed. E. Kaldis and H. J. Scheel,North-Holland, Nether-lands, 1977, p. 415. 9 (a) P. Porta, S. De Rossi, G. Ferraris, M. Lo Jacono, G. Minelli and G. Morreti, J. Catal., 1988, 109, 367; (b) P. Porta, G. Fierro, M. Lo Jacono and G. Moretti, Catal. Today, 1988, 2, 675; (c) P. Porta, R. Dragone, M. Lo Jacono, G.Minelli and G. Moretti, Solid State Zonics, 1989, 32/33, 1019; (d) G. Moretti, G. Fierro, M. Lo Jacono and P. Porta, Surf. Interface Anal., 1989, 14, 325: (e) G. Moretti and P. Porta, J. Phys. Condens. Matter, 1989, 1, 193; (f)G.Moretti and P. Porta, Surf. Interface Anal., 1990, 15, 47. 10 (a) P. Porta, G. Moretti, M. Lo Jacono, M. Musicanti and A. Nardella, J. Mat. Chem., 1991, 1, 129; (b) P. Porta, G. Moretti,M. Musicanti and A. Nardella, Catal. Today, 1991, 2, 21 1. 11 X-ray Powder Data File, ASTM 10-399, malachite; ASTM 11-692, spherocobaltite. 12 N. G. Farr and H. J. Griess, J. Electr. Spectrosc. Relat. Phenom., 1989, 49, 293. 13 J. G. Dillard and M. H. Koppelman, J. Coll. Interface Sci., 1982, 87, 46. 14 M. Deliens, R. Oosterbosch and T. Verbeek, Bull. SOC. Fr. Mineral. Cristallogr., 1973, 96, 371. 15 V. F. Anufrienko, T. M. Yurieva, F. S. Hadzieva, T. P. Minyukova and S. Yu. Burylin, React. Kinet. Catal. Lett., 1985, 27-1, 201. 16 F. H. Chapple and F. S. Stone, Proc. Br. Ceram. SOC.,1964, 1, 45. 17 (a) R. D. Willet, L. Liles Jr. and C. Michelson, Znorg. Chem., 1967, 6, 1885: (b) P. Porta and A. Mazzarano, in Reactivity of Solids, ed. P. Barret and L. C. Dufour, Elsevier, Amsterdam, 1985, Part B, p. 1053. 18 F. Pepe, M. Schiavello, G. Minelli and M. Lo Jacono, 2.Physik. Chem. NF, 1979, 115, 7, and references therein. 19 A. Cimino, M. Lo Jacono, P. Porta and M. Valigi, 2. Physik. Chem. NF, 1970,70, 166. 20 A. F. Wells, Acta Crystallogr., 1951, 4, 200. 21 R. D. Shannon, Acta Crystallogr., Sect. A., 1976, 32, 751. 22 J. D. Dunitz and L. E. Orgel, Nature (London) 1957, 179, 462. 23 L. Bragg and G. F. Claringbull, in Crystal Structures ofMinerals, Bell, London, 1965. J. MATER. CHEM., 1991, VOL. 1 537 24 25 26 G. van der Laan, C. Westra, C. Haas and G. A. Sawatzky, Phys. Rev. B, 1984, 29,4401. B. W. Veal and A. P. Paulikas, Phys. Rev. B, 1985,31, 5399. T. A. Carlson, J. C. Carver, L. J. Saethre, F. G. Santiba’nez and 27 C. D. Wagner, in Practical Surface Analysis by Auger and Photoelectron Spectroscopy, ed. D. Briggs and M. P. Seah, Wiley, Chichester, 1983, pp. 477-509. G. A. Vernon, J. Electron. Spectrosc. Relat. Phenom., 1974, 5, 247. Paper 0/05767C; Received 27th December, 1990

ISSN:0959-9428    

DOI:10.1039/JM9910100531

出版商:RSC    

年代:1991

数据来源: RSC

摘要:

J. MATER. CHEM., 1991, 1(4), 539-543 Magnesium Oxide as a Support Material for Dehydrogenation Catalysts Dick E. Stobbe," Frederik R. van Buren," Peter E. Groenendijk," Adrianus J. van Dillenb and John W. Geusb a Dow Benelux N.V., P.O. Box 48, 4530 AA Terneuzen, The Netherlands Department of Inorganic Chemistry, State University of Utrecht, P.O. Box 80083, 3508 TB Utrecht, The Netherlands Two commercial preshaped magnesium oxides, viz. pellet-shaped magnesium oxide (Engelhard, Mg-0601) and spherical magnesium oxide (Sud-Chemie, T-4403), have been evaluated for use as carrier material in supported dehydrogenation catalysts. The influences of temperature and steam atmosphere on the textures of the support materials have been studied. The texture of the pellet-shaped support has been found to be well controlled by thermal treatment in air.Upon thermal treatment the B.E.T. surface area of this magnesium oxide decreases, while the average pore radius increases. Typically, a B.E.T. surface area of 6 m2 g-' and an average pore radius of 1000 A is obtained upon treatment at 1173 K. Spherical magnesium oxide (Sud-Chemie, T-4403) has a very low surface area of 0.18 m2 g-' and an average pore radius of 40 000 A. Calcination in air at temperatures up to 1473 K does not affect the texture. In 4.8 bar of steam at 423 K both magnesium oxides react completely to magnesium hydroxide. This is accompanied by a drastic increase of the B.E.T. surface area and a decrease of the mechanical strength. At 973 K and a steam pressure of 1 bar no reaction with water is observed.Keywords: Magnesium oxide; Catalyst support; Catalyst; B.E.T. surface area At present, the commercial dehydrogenation of ethylbenzene to styrene is carried out industrially in the presence of steam over unsupported iron oxide catalysts promoted with potass- ium and chromium compounds.' The alkali promotor is added mainly to suppress carbon deposition on the catalyst. Major problems arising with these unsupported iron oxide catalysts are connected with the reduction of the iron oxide phase and migration of the potassium promotor under process conditions.'-'The migration of the potassium promotor and the lattice transformation which is coupled to the reduction of the iron oxide phase cause a degradation of the mechanical strength of the catalyst bodies.The disintegration of the catalyst bodies will lead to an increased pressure drop over the reactor, which may be unfavourable for high styrene selectivity and yield. Additionally, transport of potassium leads to a drop in the effectiveness of the suppression of coking in regions of the catalyst where potassium has been depleted. These problems are obviated by applying iron oxide homogeneously and finely divided onto a preshaped support materiaL5 Magnesia, being a basic oxide, has been selected as support material for an iron oxide dehydrogenation catalyst. Since carbon formation is enhanced by the acidic character of a catalyst, an acidic support material, such as Si02 or y-A1203, is undesirable.6 A neutral or basic support, such as ceA1203 or MgO would be more appropriate.Moreover, as long as alkali is used as a promotor the support should not react with the alkali compound. After reaction with the support, the alkali is no longer active in blocking acidic sites and in gasification of carbon deposits, because it has penetrated into the support. Inasmuch as this is the case with cr-A1203 and not with MgO,' MgO is the most suitable carrier to be used. On the other hand magnesium oxide is unique among catalyst supports, since it can react extensively with water to form brucite, Mg(OH),, which could hamper its use for the envis- aged reaction.8p12 A first step in the development of a magnesia-supported dehydrogenation catalyst is the characterization of the texture of commercially available preshaped magnesium oxide sup- ports.Besides the nature of the active phase, the texture of a catalyst system is generally of utmost importance in determin- ing its activity and selectivity in an industrial process. Since commercial reactors contain considerable amounts of catalyst the mechanical strength is also of great importance. It is therefore very advantageous to be able to control the final texture and the mechanical strength of a catalyst system. As such, the process of ethylbenzene dehydrogenation requires small catalyst bodies with relatively wide pores and a relatively small surface area in order to establish fast transport of reactants and products.' Small pores are detri- mental to styrene selectivity and yield.' The catalyst bodies should have sufficient thermal conductivity to avoid tempera- ture gradients within the bodies, and the catalyst bodies should not be too small, since the pressure drop over the catalyst bed must remain limited.Starting from powdered supports, the texture and mechan- ical strength of a catalyst system are very difficult to control. Therefore preshaped support bodies are used. Preshaped support bodies, such as pellets or spheres, enable one to choose beforehand a known and fixed texture. Furthermore, the mechanical strength of these preshaped support bodies is generally expected to be larger if compared with catalysts prepared from powdered supports.The availability of commercial preshaped magnesium oxide supports is very limited. Only two supports were at our disposal, viz. small pellets (Engelhard, Mg-0601, T 1/8 in?) and spheres (Girdler Sud-Chemie, T-4403, 18-20 mm). The textures and structures of both supports are characterized with commonly used techniques, such as scanning electron microscopy, X-ray diffraction, thermogravimetric analysis and B.E.T. measurements. Since (thermo)stability of the used sup- port is a prereq~isite,'~ it is also important to investigate its behaviour under reaction conditions, i.e. high temperatures and steam atmospheres. tl in =2.54 cm Experimental To investigate the effect of treatment at high temperatures on the texture of the preshaped magnesium oxides, they were calcined in air.First, the magnesium oxides were calcined at 1173 K for different periods of time to determine the time required to attain a stable specific surface area. Next, the magnesium oxides were calcined in air at different tempera- tures ranging from 423 to 1473 K for this period of time. The influence of steam on the texture of the magnesium oxides was also investigated. For this purpose, the magnesium oxides were heated at 423 K in saturated steam (4.8 bar,14 in an autoclave. The magnesium oxides were treated in a steam flow (1 bar) at 973 K for 144 h. B.E.T. surface areas both before and after thermal or steam treatment were determined by nitrogen physisorption using a Quantasorb instrument (Quantachrome Corp.).Nitrogen adsorption was measured dynamically at 77 K with a thermal conductivity detector. The magnesium oxides were fragmented into particles of sizes between 0.5 and 0.85 mm. Prior to the physisorption experiments, the samples were outgassed in nitrogen at 393 K for 1 h. Pore size distributions were studied using mercury porosi- metry (Carlo Erba Porosimeter 2000). Pore radii in the range 38-75 000 A could be determined. For calculations a contact angle of 14 1.3" and a surface energy of 480 x 10-J m -were used. It was assumed that the pores were non-intersecting and of cylindrical shape. X-Ray diffraction measurements were performed with a Philips powder diffractometer mounted on a Philips PW 1140 X-ray generator with Mo-Ka ,2 radiation (12 =0.7 10 73 A). Thermogravimetric analysis (DuPont 951-TGA cell coupled to a DuPont 1090 unit) was performed in a nitrogen flow with a heating rate of 20 K min-'. The analysis was performed with mass-spectrometry to identify evolved gases. Finally, the materials were characterized using a scanning electron microscope (Philips SEM 505) equipped with an X-ray microanalyser (EDAX 9900 system) to determine the chemical composition of the magnesium oxides.Results and Discussion Elemental Analysis The compositions of the Mg-0601 and the T-4403 magnesium oxides are given in Table 1 expressed as weight percentage of the elements. The Mg-0601 magnesium oxide contained minor amounts of Si, Ca, and C1.Also ca. 1.5 wt.% S was found, which is equivalent to a sulphur-content in magnesium oxide of 0.9 wt.%. The sulphur was present as magnesium sulphate. The pellets were bluish owing to the presence of graphite, which had been used in the manufacturing process. The graphite could be removed by calcination above 973 K. T-4403 Table 1 Compositions of the magnesium oxides element wt.% (Mg-0601) MgSi 94.3 1.2 S 1.5 Cac1 2.2 0.8 MgSi (T-4403) 76.5 13.8 Ca 6.0 Fe 3.0 A1 0.7 J. MATER. CHEM., 1991, VOL. 1 magnesium oxide contained ca. 14 wt.% Si, 6 wt.% Ca, and ca. 3 wt.% Fe. No sulphur was detected. Thermal Treatment Fig. 1 shows the B.E.T. surface area of MgO (Mg-0601) after calcination at 1173 K in air as a function of the calcination time.The B.E.T. surface area of the fresh MgO is 14.7m2 g-'. This value decreases rapidly upon calcination at 1173 K. The decrease is completed within 10 h. Then the B.E.T. surface area reaches a stable value of 6 m2 g-'.To eliminate the risk that treatments at other temperatures should require longer equilibration times, thermal treatments of ca. 23 h have been used for further sinter experiments. In Fig. 2 the B.E.T. surface area of Mg-0601 after calcination for 23 h is represented as a function of the temperature. After an initial decrease at 423 K the surface area increases to 16.4m2 g-' at 573 K. At higher temperatures the area rapidly decreases again to 0.35 m2 g-' at 1473 K. The increase at 573 K can be explained with the help of the thermogravimetric analysis diagram of fresh MgO shown in Fig.3. From ca. 523 to 623 K a slight weight decrease is observed. This is probably due to the decomposition of some magnesium hydroxide or magnesium hydroxycarbonate that is present in the fresh MgO. This decomposition must have brought about the intermediate increase of the B.E.T. surface area. Connected with the decrease in the surface area, a shift in the pore-size distribution to higher values is observed with mercury porosimetry. The results represented in Fig. 4 clearly show that the fresh Mg-0601 support has an average pore radius of 300 A. The average pore radius increases to 900 A upon calcination in air at 1173 K. After calcination at still higher temperatures the average pore radius rapidly rises to values over 10 000 A.Simultaneously, the cumulative pore I 0 "E $9 Q) sr6 rn 0 10 20 30 40 50 60 70 time/h Fig. 1 B.E.T. surface area of Mg-0601 magnesium oxide after calci- nation in air at 1173 K as a function of the calcination time 4i----Lh0 273 473 673 873 1073 1273 1473 TIK Fig. 2 B.E.T. surface area of Mg-0601 magnesium oxide after calci- nation in air for 23 h as a function of the calcination temperature J. MATER. CHEM., 1991, VOL. 1 54 1 .-C E Fig. 3 Thermogravimetric analysis of fresh Mg-0601 magnesium oxide performed in nitrogen at a heating rate of 20 K min-' 410' 10 lo3 10 radius/!+ Fig. 4 Pore size distributions of Mg-0601 magnesium oxide after calcination at different temperatures in air, obtained with mercury intrusion.The dotted line indicates the lower limit of the detection range. (a) Fresh; (b) 1173K; (c) 1473 K volume increases from 0.248 to 0.294 cm3 g- ' after calcination at 1173 K and decreases to 0.143 cm3 g- ' after calcination at 1473 K. This decrease is associated with a shrinkage of the magnesium oxide pellets. Moreover, the shrinkage will lead to a gain in mechanical strength due to an increase of the density of the pellets. The process of sintering, which causes a decrease of the surface area and an increase of the average pore size, is confirmed by scanning electron microscopy. Fig. 5 shows micrographs Of the fracture surface Of fresh and calcined Mg-0601 magnesium oxide pellets- The fresh mag- nesium oxide consists of small spherical Particles with an average diameter of ca.500 A [Fig. 5(a)]. Upon calcination a gradual increase of the particle size is observed. The small spherical particles sinter to larger spherical particles of ca. 1000-2000 A in diameter at I173 K [Fig. 5(b)]. Beyond 1173 K the growth of the particles is more drastic [Fig. 5(c)]. At 1473 K the particles apparently have coalesced. The size of the particles after treatment at 1473 K is ca. 20 000 A. The T-4403 magnesium oxide has a very dense structure, comparable to that of the Mg-0601 magnesium oxide after treatment at 1473 K. The scanning electron micrograph of the fracture surface of a T-4403 magnesium oxide sphere is shown in Fig.6. The B.E.T. surface area of this magnesium oxide is only 0.18 m2 g-'. Fig. 7 shows the pore size distri- bution as determined with mercury porosimetry. The average pore radius is ca.40000A. The cumulative pore volume is 0.105 cm3 g-'. No change in morphology is observed for the T-4403 magnesium oxide upon treatment in air at temperatures up to 1473 K. Evidently, the T-4403 support has undergone a treatment at temperatures above 1473 K already in the manu- facturing process, which explains the sintered structure. Fig. 5 Scanning electron micrographs of the fracture surface of Mg-0601 magnesium oxide pellets after calcination in air at different temperatures (bars indicate 1 pm): (a)Fresh; (b) 1173 K; (c) 1473 K Fig.6 Scanning electron micrographs of the fracture surface of a T-4403 magnesium oxide sphere (bars indicate 10 pm) 30-i h s I Y :1f 20' 1 n-0. I 1 2 3 4 510 10 10 10 10 radius/A Fig. 7 Pore size distributions of fresh T-4403 magnesium oxide obtained with mercury intrusion. The dotted line indicates the lower limit of the detection range Steam Treatment When the Mg-0601 magnesium oxide support is treated in an autoclave in 4.8 bar steam at 423 K, magnesium oxide is transformed into brucite, Mg(OH),. This is in accordance with what is thermodynamically expected." In Fig. 8 the stability sectors for periclase and brucite, i.e. MgO and Mg(OH)2,respectively, are shown with regard to the reaction MgO+H,O Mg(OH)2 (1) The curve of Fig.8 represents the thermodynamic equilibrium (AG=O) between MgO and Mg(OH)2. The X-ray patterns show that in 4.8 bar saturated steam at 423 K the transformation of MgO into Mg(OH)2 is fairly complete. The (200) and (220) MgO peaks at 19.4 and 27.7" 20, respectively, in the fresh material have disappeared com-pletely after the treatment. The diffraction pattern after treat-ment points to fairly well crystallized brucite. After the steam treatment, thermogravimetric analysis coupled to mass-spectrometry was performed, and showed a decrease in weight of 26.0% between 600 and 750 K. This is ascribed to the decomposition of the Mg(OH), back to MgO. From the weight decrease of 26% it can be calculated that 85% of the magnesium oxide has been transformed into magnesium hydroxide during the steam treatment.Mass--8 i -10 012345 103 KIT Fig. 8 Plot of logarithmic steam pressure as a function of reciprocal temperature for the coexistence of MgO and Mg(OH)2. Data taken from ref. (18) J. MATER. CHEM., 1991, VOL. 1 spectrometric measurements showed that evolved gases con-tain, besides water, some C02.This originates from the fresh Mg-0601 material. The transformation of MgO into Mg(OH)2 is coupled to a large increase of the B.E.T. surface area. It increases from 14.7m2g-' for the fresh material to 25.0m2 g-' after the steam treatment. The scanning electron micrograph of the external edge of a different, treated Mg-0601 pellet, represented in Fig.9, shows the cause of the increase of the surface area. The treatment in steam causes a phase transformation of the cubic MgO into hexagonal platelets of Mg(OH)2, as reported by Holt et ~1.'~The transformation of the sample in Fig. 9 is in its initial state. Only a small amount of MgO at the external edge of the pellet has been transformed. Small platelets of Mg(OH)2 with a thickness of ca. 1000 8, grow perpendicular to the MgO surface. Mg(OH)2, therefore, does not form a protective layer on the MgO surface that would prevent further transformation. On the contrary, as long as the sample is exposed to steam at the proper temperatures and pressures, the front at which the transformation proceeds will gradually move to the centre of the pellet.Finally, the MgO will have been entirely transformed to Mg(OH)2. The transformation to Mg(OH)2 thus causes a substantial change of the morphology and an increase of the B.E.T. surface area. At the same time, the average pore radius decreases from ca. 300 to 40 A and perhaps to even smaller values. The pore-size distribution after treatment in static steam is shown in Fig. 10. Also some wide pores appear in the range 10 000-60 000 A. The T-4403 support material (Sud-Chemie) shows similar behaviour to that of the Mg-0601 magnesium oxide support. The B.E.T. surface area increases from 0.18 to 6 m2 g-' upon static steam treatment. Addition-Fig. 9 Scanning electron micrograph of the edge of the fracture surface of a Mg-0601 magnesium oxide pellet after a partial transformation of periclase into brucite (bar indicates 10 pm) radius/B( Fig.10 Pore-size distribution of Mg-0601 magnesium oxide after treatment in static steam at 423 K, obtained with mercury intrusion. The dotted line indicates the lower limit of the detection range J. MATER. CHEM., 1991, VOL. I ally, the mechanically very strong T-4403 preshaped mag- nesium oxide bodies disintegrate entirely owing to the transformation into Mg(OH)2, which is not the case with the Mg-0601 magnesium oxide support. So far, the magnesium oxides have been treated in an autoclave with a fixed volume of water. The magnesium oxides have also been treated at 973 K in a steam flow of 1 bar, since this approaches more closely the common practice of ethylbenzene dehydrogenation. The Mg-060 1 support shows a decrease in B.E.T.surface area from 14.7 to 11.9 m2 g-'. This decrease can be completely attributed to a temperature effect and not to the effect of steam. Thermal treatment at 973 K without steam brings about an equal drop of the surface area, as shown in Fig. 2. Steam itself, therefore, does not affect the MgO at all at 973 K. For the T-4403 magnesium oxide, on the other hand, the B.E.T. surface area slightly increases from 0.18 to 0.28 m2 g-' upon treatment in a steam flow at 973 K. Since the temperature treatment does not affect the texture of the T-4403 magnesium oxide, as was shown earlier, this increase is solely caused by the steam.With scanning electron microscopy some fine granular mater- ial is observed on the large MgO crystallites of T-4403 magnesium oxide. Thermodynamically, the formation of bru- cite, Mg(OH)2, at 973 K and at steam pressures lower than 1 bar is unfavourable, as can be seen in Fig. 8. Therefore, the presence of these fine granules can be explained by the formation of some Mg(OH)2 during heating or cooling of the reactor in the presence of steam. Alternatively, the presence of Si impurities reacting with steam might be responsible for the higher surface area. Conclusions The texture of the magnesium oxide obtained from Engelhard, Mg-0601, shows a strong dependence on the pretreatment temperature. At pretreatment temperatures above 773 K the B.E.T.surface area decreases and the pore size distribution shifts to higher values. This distribution is narrow and remains remarkably narrow after treatment at high temperatures in air. The surface area can be varied between 16 and 0.3 m2 g-' and the average pore radius between 300 and 10 000 A. The texture of the support can thus be well controlled by a simple thermal treatment. The Siid-Chemie T-4403 magnesium oxide, however, does not show any temperature dependence up to 1473 K. As the initial texture resembles the Engelhard magnesium oxide after calcination in air at 1473 K, it must be concluded that the T-4403 magnesium oxide has already undergone a sinter treatment above 1473 K in the manufacturing process. The texture is characterized by a very low surface area of 0.18 m2 g-and an average pore radius of 30 000 A.More-over, the material is very thermostable. This magnesium oxide, on the other hand, contains considerable amounts of impurit- ies such as Fe, Si and Ca. With both magnesium oxides, when used in atmospheres that contain steam, extreme care should be taken to avoid low temperatures. At temperatures lower than ca. 673 K, depending on the applied partial steam pressure, the mag- nesium oxide is transformed into small platelets of magnesium hydroxide. The magnesium oxide will completely react to magnesium hydroxide, if sufficient water vapour is present within the proper range of temperatures and vapour pressures. The transformation also leads to an increase of the surface area and a shift of the average pore radius to a very low value. Additionally, the mechanical strength decreases.For the T-4403 magnesium oxide the periclase-brucite transform- ation even leads to a complete disintegration of the preshaped support bodies. Because of its controllable texture, the Mg-060 1 magnesium oxide (Engelhard) will be used in future work as a preshaped support for the application of iron and potassium. The preparation and characterization of magnesia-supported dehydrogenation catalysts will be described in subsequent publi~ations.'~-'~ References 1 E. H. Lee, Catal. Rev., 1973, 8(2), 285. 2 P. Courty and J. F. Le Page, in Preparation ofcatalysts, ed. B. Delmon, P. Grange, P.Jacobs and G. Poncelet, Studies in Surface Science and Catalysis, vol. 3, Elsevier, Amsterdam, 1979, VOI. 11, pp. 293-305. 3 B. D. Herzog and H. F. Rase, Ind. Eng. Chem. Proc. Res. Dev., 1984, 23, 187. 4 W. D. Mross, Catal. Rev. Sci. Eng., 1983, 25, 591. 5 D. E. Stobbe, Ph.D. Thesis, Utrecht, 1990. 6 A. Krause, Sci. Pharm., 1970, 38, 266. 7 V. Perrichon and M. C. Durupty, Appl. Catal., 1988, 42, 217. 8 S. Colluchia, A. J. Tench and R. L. Segall, Trans. Faraday Soc., 1979, 75, 1769. 9 J. Green, J. Muter. Sci., 1983, 18, 637. 10 M. G. Kim, U. Dahmen and A. W. Searcy, J. Am. Ceram. Soc., 1987, 70, 146. 11 D. Beruto and R. Botter, J. Am. Ceram. Soc., 1987,70, 155. 12 T. E. Holt, A. D. Logan, S. Chakraborti and A. K. Datye, Appl. Catal. 1987, 34, 199. 13 J. W. Geus, in Preparation of Catalysts, ed. G. Poncelet, P. Grange and P. A. Jacobs, Studies in Surface Science and Cataly- sis, vol. 16, Elsevier, Amsterdam, 1983, vol. 111, pp. 1-33. 14 Handbook of Chemistry and Physics, ed. R. C. Weast, CRC Press, Boca Raton, 62nd edn., 1981, D-169. 15 I. Barin, 0. Knacke and 0. Kubaschewski, Thermochemical Properties of Inorganic Substances (Supplement), Springer-Verlag, Berlin, 1977. 16 D. E. Stobbe, F. R. van Buren, A. W. Stobbe-Kreemers, J. J. Schokker, A. J. van Dillen and J. W. Geus, J. Chem. SOC.,Faraday Trans., 1991, 87, 1623. 17 D. E. Stobbe, F. R. van Buren, A. W. Stobbe-Kreemers, A. J. van Dillen and J. W. Geus, J. Chem. SOC. Faraday Trans., 1991, 87, 1631. 18 D. E. Stobbe, F. R. van Buren, M. S. Hoogenraad, A. J. van Dillen and J. W. Geus, J. Chem. Soc., Faraday Trans., 1991, 87, 1639. 19 D. E. Stobbe, F. R. van Buren, A. J. Orbons, A. J. van Dillen and J. W. Geus, J. Muter. Sci., in the press. Paper 1/01111A; Received 28th December, 1990

ISSN:0959-9428    

DOI:10.1039/JM9910100539

出版商:RSC    

年代:1991

数据来源: RSC

摘要:

J. MATER. CHEM., 1991, 1(4), 545-549 Phase Relations in the System BiO,.,-SrO-CuO at 1123 K K. Thomas Jacob and Tom Mathews Department of Metallurgy, Indian Institute of Science, Bangalore 560 012, India Phase relations in the system Bi-Sr-Cu-0 at 1123 K have been investigated using optical microscopy, electron- probe microanalysis (EPMA) and powder X-ray diffraction (XRD) of equilibrated samples. Differential thermal analysis (DTA) was used to confirm liquid formation for compositions rich in BiO,,,. Compositions along the three pseudo-binary sections and inside the pseudo-ternary triangle have been examined. The attainment of equilibrium was facilitated by the use of freshly prepared SrO as the starting material. The loss of Bi,O, from the sample was minimized by double encapsulation.A complete phase diagram at 1123 K is presented. It differs significantly from versions of the phase diagram published recently. Keywords: Phase equilibria; Coexistence domain; Bi-Sr-Cu-0 system; Oxide superconductor; Bismuth Oxide Superconductor. Three superconducting phases have been found in the Bi-Sr- Ca-Cu-0 system.1-3 A clear understanding of phase relations in the system is useful for optimizing conditions for the synthesis of the superconducting compounds. For most practi- cal purposes the system can be represented as a pseudo-quaternary BiO .,-SrO-CaO-CuO. A prerequisite for under- standing phase equilibria in the four-component system is an adequate definition of phase relations in the bounding binary and ternary systems.As a part of a larger programme of research, this paper discusses equilibrium compatibilities between phases in the system Bi01.5-Sr0-Cu0 at 1123 K. Prior to the discovery of high-T, superconducting oxides there were no systematic studies of phase relations in the Bi-Sr-Cu-0 system. Earlier studies were confined to the bounding pseudo-binary sections of the BiO,+,-SrO-CuO system. Sillen and Aurivillius4 have deduced the structure of rhombohedra1 Bil -xSrxOl~,~o~sx for 0.14<x<0.25. Phase relations in the bismuth-rich region of the Bi01.5-Sr0 system were determined by Levin and Roth' using high-temperature X-ray diffraction. More information on phase relations was provided by Guillermo et aL6 They identified four additional phases, Bi2Sr04, Bi2Sr205, Bi2Sr306 stable above 1090 K and a solid solution containing ca.45 mol% SrO stable above 1043 K. Phase diagrams for the system BiO1.,-SrO are given in ref. 7. In the SrO-CuO binary system, three compounds, Sr,Cu03, SrCuO, and SrCu203, were identified by Teske and Muller-Buschbaum.8-11 Cassedanne and Campelo' determined the phase diagram for the BiO1.,-CuO system by analysing quenched samples. They identified the compound Bi4Cu07. More recent studies by Kakhan et ~1.'~using thermogravimetric, thermal and X-ray diffraction analysis indicate that the only compound in this pseudo-binary system is Bi2Cu04 with space group P4/rncc. Available information on the BiO,,,-CuO system is reviewed in ref.7. The powder diffraction pattern for Bi4Cu0712 is surprisingly similar to that of Bi,Cu04,13 for which two crystal structure refinements have been rep~rted.'~~'~ During the course of the present study partial phase relations in the ternary BiO, .,-SrO-CuO system have been published by Saggio et all6 at 1073 K and Ikeda et ~1.'~at 1173 K. Both groups did not study phase relations in the vicinity of BiO,,,-CuO binary. Saggio et ~1.'~added 0.5 wt.% of Li2C03 as a mineralizer to their samples to accelerate the attainment of equilibrium. They16 reported four pseudo-ternary phases, Bi4Sr9CuO16 (491), Bi2Sr,Cu2012 (272), Bi,Sr2Cu06 (221) and a solid solution close to the compound 221. The solid-solution phase was found to be superconducting at the high-strontium-content limit of solubility, with a transition temperature of ca.9 K. The solid solubility range is characterised by the Bi:Sr:Cu ratio of (1 1 -x):(9+x):5, 0 <x c0.4. The compounds 491 and 272 were probably stabil- ized by the presence of Li2C03. Ikeda et all7 identified four ternary phases using transmission electron microscopy (TEM) and XRD techniques, Bi4Sr8Cu50z (485), Bi2Sr3Cu2OZ (232), Bil,Sr16Cu70, (17 16 7) and the solid solution Bi, +$r2 -xCul (0.1<x <0.6; 0 <y <x/2). Superconduc- tivity with T,zlO K was found at the strontium-rich end of the solid solution, in agreement with Saggio et all6 Recently, a more comprehensive study of phase relations in the ternary BiO .,-SrO-CuO system including the binary systems Bi01.5-Sr0 and SrO-CuO has been presented by Roth et a2.l' in the temperature range 1148-1198 K.In agreement with Ikeda et al.17 these authors also report the presence of compounds 485, 232, 221 and a solid-solution region close to the 221 compound. The phase designated as Sr,Cu,O, was found to have the more complex stoichiometry Sr14Cu24041.18-20 Surprisingly, the phase diagram suggested by Roth et shows the presence of the compound Bi,CuO, and absence of the liquid phase along the BiO,.,-CuO binary. This is in conflict with the binary phase diagrams given in ref. 7. Both Ikeda et ~1.'~and Roth et a1." did not delineate phase relations with certainty in some regions of the ternary system. In earlier ~tudies'~,'~ the samples were held in open containers. The possible change in composition or the presence of gradients in composition caused by preferential vaporiz- ation of Bi203 was not considered. Roth et a1." fired their samples either as small pellets or in small 3 mm diameter gold tubes, either sealed or unsealed.They observed that repeated heat treatments in the gold tube resulted in noticeable loss of copper to the gold tube. This would also result in a change in the composition of the sample. In all earlier studies16-'* the samples were synthesized from SrCO, at atmospheric pressure. Since the decomposition temperature of SrC0, is 1455K,,l C02 may have been an important constituent of some of the final phases obtained. Evidence for C0,-stabilized phases in the Y,O,-BaO-CuO system has recently been d~cumented.~~.~~ In view of the uncertainties in the reported phase relations, especially in the vicinity of the BiO,.,-CuO binary, results of our investigations are presented in full.Experimental Starting materials used in the preparation of pseudo-binary and pseudo-ternary compositions were powders of Bi203, SrC03 and CuO, each of 99.99% purity. SrC03, contained in a stabilized-zirconia crucible, was decomposed in vucuo (1 Pa) at 1000 K to SrO. The SrO formed by decomposition under vacuum was found to be highly reactive. When SrO was used as a starting material rather than SrC03, the time required to reach equilibrium was significantly reduced. The oxides were weighed and then mixed, either dry or with acetone, using an agate mortar and pestle.The intimate mixture was pressed into pellets using a steel die. The pellets were placed inside a small zirconia crucible and covered with a zirconia lid. The main pellet was placed on top of a thin platform of identical composition. The crucible was placed inside a larger zirconia crucible. The space between the two zirconia crucibles was packed with loose powder of the same composition as the pellet. The larger zirconia crucible was also covered with a lid and sealed with a zirconia-based cement. A schematic diagram of the arrangement is shown in Fig. 1. The closed system was used to minimize the volatiliz- ation of Bi203. Values for the vapour pressure of Bi203 are not available in the literature.From the mass loss of Bi203 in flowing oxygen at 1123 K, an apparent vapour pressure of 150 Pa was obtained in preliminary experiments. The joint between the lid and crucible was not air-tight; therefore, a small loss of Bi203 was still encountered from the closed crucibles. The double-crucible assembly was effective in pre- venting vaporization loss. The loss of material by vaporization from the outer crucible occurred preferentially from the pow- der packed around the inner crucible. The composition of the pellet inside the inner crucible remained virtually unaltered. The pellet was heat treated several times at 1123 K with grinding and repelletizing between each heat treatment. Each treatment lasted ca.24 h. Generally, the phase composition of the pellet became invariant with time after three heat treatments. For a few compositions, however, up to five heat treatments were found to be necessary to reach equilibrium. The crucible assembly was suspended in the even-tempera- ture zone of a vertical furnace as shown in Fig. 2. Pure oxygen was allowed to flow around the crucible. The temperature of the furnace was controlled to within +1 K and measured by a calibrated Pt/Pt-l3%Rh thermocouple. After each heat treatment the crucible assembly was quenched by dropping it into liquid nitrogen. The quenched pellet was examined by optical microscopy, XRD and EPMA. In XRD Cu-Ka radi-ation and Ni filters were used. Because of the large difference in the X-ray scattering factor between Bi and other elements, detection of Bi-free phases, especially at low concentrations, in the presence of Bi-containing phases, was found to be difficult.In such cases, EPMA was very useful in identifying Bi-free phases. A beam size of 1 ym was used. Synthetic samples of CuO, SrCuO, and Sr,Bi209 were used as stan- dards. However, to obtain good reproducibility by EPMA the grain size had to be larger than 40 ym. When powders of this size were used for the preparation of the samples, the packing powder zirconia crucible with lid ' sample pellet sample platform Fig. 1 Schematic diagram of the double encapsulation system for containing the samples J. MATER. CHEM., 1991. VOL. 1 ?--brass cap furnace alumina tube sample water-cooled joint I =t-02 inlet cellophane paper -~t--=~+-z:=-l _-----Fig.2 Schematic diagram of the apparatus for equilibration and quenching time required for reaching equilibrium was increased consider- ably. When phase identification could be established solely by XRD, fine powders of starting oxides were used to minimize the equilibration period. The samples were polished with a diamond paste prior to optical microscopy and EPMA. Complete melting of the samples was easily identified by visual inspection. However, detection of partial melting in some samples was difficult because the small amount of liquid formed was held between solid grains by surface-tension forces, and the external appearance of the pellet remained unaltered.The liquid phase was found to crystallize despite rapid quenching. DTA was used as a supplementary tool in such cases. The sample was placed in a gold crucible under pure oxygen. In a few experiments equilibrium was approached from different directions by using different syn- thetic compounds as starting materials. The samples were stored in a desiccator, although they were not as sensitive to moisture as compositions from the Y203-Ba0-Cu0 system. Results The overall chemical compositions of samples examined in this study are shown in Fig. 3. Note that the entire compo- sition space of the ternary system is covered. Phase identifi- cation in equilibrated samples was based on comparison with published diffraction patterns and those calculated from pub- lished structural data.l6-I8 The crystal structures, lattice parameters and the sources of diffraction patterns for the compounds are listed in Table 1.Although there are differences J. MATER. CHEM., 1991. VOL. I CUO / . .0.. .\Y4 / . \ SrO/ v -v -u u-u-v -&-\/0.8 -A/ -0.2 0.4 0.6 -'BiO, XBlO, 5 Fig. 3 Overall chemical compositions of the different samples exam- ined in this study in the structure descriptions of the phases reported in the literature, the diffractograms are similar. For the purpose of phase identification, differences in the reported crystal struc- tures listed in Table 1 are not important. Optical microscopy and EPMA provided additional information. The compo- sitions of non-stoichiometric phases were obtained primarily from EPMA.No phase other than those already reported in the literature has been identified in this study. The isothermal section of the phase diagram for the BiO,.,-SrO-CuO system at 1123 K produced from the results of this study is shown in Fig. 4. Along the pseudo-binary BiO, ,,-SrO, four compounds, SrBi204, Sr2Bi,0S, Sr3Bi206 and Sr,Bi,09, and two solid solutions, /? and y,were identified. The composition of the /? phase varied from 12.3 to 26.5 mol% SrO. The y phase ranges from 43.4 to 45.3 mol% SrO. There is a small liquid-phase Table 1 Crystal structure and lattice parameters of phases in the system BiO,,,-SrO-CuO lattice parameter/A compound a b 22 1 23.73 13.242 24.493 5.4223 232 24.804 5.396 24.937 5.395 33.907 23.966 34.035 24.05 33.991 24.095 6" 26.856 5.380 5.389 5.385 26.889 5.384 SrBi,04 19.301 4.3563 Sr, Bi,O , 14.293 7.651 14.307 6.1713 Sr,Bi,06 12.526 Sr,Bi,O, 6.009 Sr,CuO, 12.68 3.9 1 12.684 3.9064 SrCuO, 16.33 13 3.9136 Sr14cu2404 1 13.0 11.3 13.399 11.483 B 3.979 Y 13.239 region near pure Bi01.5.These results are identical with the data for the pseudo-binary reported by Roth et ~l.,'~but differ from the phase diagram suggested by Guillermo et aL6 Along the SrO-CuO pseudo-binary, three compounds, Sr2Cu03, SrCu02 and were detected at 1123 K, in agreement with Saggio et ~1.'~and Roth et a1." Along the BiOl .,-CuO pseudo-binary no compounds were detected at 1123 K.A liquid phase was found to be present from 66 to 100mol% BiO1.s. A two-phase region exists between CuO and the liquid phase. Phase relations along this pseudo-binary are in agreement with the diagram proposed by Kakhan et ~1.'~The phase diagram suggested by Cassedanne and Cam- pelo12 shows a much more restricted liquid-phase field ranging from 80 to 100 mol% BiO,.,. The phase diagram suggested by Roth et a1.18 does not show the formation of a liquid phase but instead indicates the presence of solid phases including Bi,Cu04 in the temperature range 1148-1 198 K. Four pseudo-ternary solid phases were detected, Bi,Sr8Cu5019+x (485), Bi2Sr3Cu,08 (232), Bi,Sr2Cu06 (221) and a solid solution 6 which can be approximately charac- terized as Bi2.44-xSrl.,6+xCul +,,Oz,where 0 <x <0.24 and -0.05 <y <0.1 1.The compounds 221 and 232 were found to be stoichiometric. The X-ray diffraction patterns and EPMA of these phases were almost identical in the different three- phase regions. Compound 221 is deficient in CuO by ca. 1 mol% and exhibits a small variation in the Sr:Bi ratio. The fifth single-phase region in the Gibbs' triangle is an extension of the liquid phase present along the BiO,.,-SrO and BiO ,-CuO binaries. Compounds 491 and 272 identified by Saggio et ~1.'~have not been detected in this study. Their occurrence is probably caused by the addition of a small amount of Li2C03 as a mineralizer. These authors did not observe the compounds 485 and 232 detected in this study, but these were identified by Ikeda et a1.17 and Roth et all8 The presence of compound 221 and solid solution 6 has been established by all investi- gators,16-" although there are some differences in the exact compositions reported for these phases.The ternary diagram shown in Fig. 4 differs significantly from that suggested by Saggio et ~1.'~They show only three c PI" 4.08 1 2 1.959 105.40 4.888 19.094 96.97 5.373 5.389 5.3677 26.908 113.55 24.64 24.630 26.933 1 13.67 6.1049 94.85 6.172 3.8262 18.331 58.663 3.48 3.4957 3.5730 3.94 3.9356 28.5 1 4.257 structure ref. orthorhombic 16 monoclinic, C2/m 27 orthorhombic 17 monoclinic, C2/m 18 orthorhombic 24 orthorhombic, Fmmm 17 orthorhombic, Fmmm 18 monoclinic, C2 25 pseudotetragonal 16 pseudotetragonal 17 monoclinic, C2 18 monoclinic, C2/m 18 orthorhombic, Pcmm 6 orthorhombic, Cmcm 18 rhombohedral, R3m 18 rhombohedral 18 orthorhombic, Immm 8 orthorhombic, Immm 18 orthorhombic, Cmcm 26 orthorhombic 20 orthorhombic, Fmmm 18 rhombohedral 6 tetragonal, 14/m 6 J.MATER. CHEM., 1991. VOL. 1 CUO Sr Bi01.5 Fig. 4 Isothermal section (1123 K) of the phase diagram for the system BiO,.,-SrO-CuO: 1, Bi,Sr,Cu,O,,+,; 2, Bi,Sr,Cu,O,; 3, Bi,Sr,CuO,; 4, 6; 5, liquid strontium bismuthates. About one quarter of the Gibbs' triangle adjacent to the pseudo-binary BiO 1,,-CuO where the liquid phase is present has not been explored at all by Saggio et ~1.'~or in detail by Ikeda et all7 The possible presence of solid phases including Bi2Cu04 in this region of the diagram has been suggested, however, Ikeda et ~1.'~have not reported the presence of SrBi204.The phase relations in the region of the ternary phase diagram bounded by the compounds Sr3Cu50z, SrCu02 and the pseudo-ternary phases 485 and 232, have not been well characterized by Ikeda et ~1.'~There are also some differences in the exact compositions of the 221 and 6 phases. In other respects, the major phase fields identified by them are in agreement with the results of this study. The phase diagram suggested by Roth et all8 in the temperature range 1148-1198 K is in good agreement with the results obtained in this study except for the region near the BiO1.,-CuO binary.Results of this study indicate an extensive liquid-phase region which does not appear in the phase diagram suggested by Roth et a1.,18 instead they show the presence of solid phases including Bi2Cu04. Conclusion The isothermal section of the phase diagram at 1123 K for the system BiOl .,-SrO-CuO has been completely charac- terized by analysis of equilibrated and quenched samples using optical microscopy, XRD and EPMA. A limited number of DTA experiments have been conducted to delineate the liquid region. By minimizing C02 contamination of the sample, reproducible and consistent results were obtained for phase relations in the pseudo-ternary system.The loss of Bi203 from the sample was minimized by double containment. Four compounds, SrBi204, Sr2Bi205, Sr,Bi206, Sr6Bi20,, and two solid-solution series, /? and y, were detected along the BiOl .,-SrO binary. Three compounds, Sr2Cu03, SrCuO, and Sr14Cu24041, were found to be stable in the system SrO- CuO. There is an extensive liquid-phase region near BiO 1., in the Gibbs triangle. Four pseudo-ternary solid phases were detected: Bi4Sr8Cu5019+,, Bi2Sr3Cu208, Bi2Sr2Cu06 and a solid solution, 6, which can be approximately characterized as Bi2.44-,Sr .56 + ,Cu +,,OZ where 0 <x <0.24 and -0.05 <y <0.11. The compound Bi2Sr2Cu06 has a small homogeneity range and is deficient in CuO by ca. 1 mol%. The authors are grateful to Mr.A. V. Narayana for assistance in the preparation of the manuscript. References C. Michel, M. Hervieu, M. M. Bore], A. Grandin, F. Deslandes, J. Provost and B. Raveau, 2.Phys. B, 1987, 68,421. J. Akimitsu, A. Yamazaki, H. Sawa and H. Fujiki, Jpn. J. Appl. Phys., 1987, 26, L2080. H. Maeda, Y. Tanaka, M. Fukutomi and T. Asano, Jpn. J. Appl. Phys., 1988, 27, L209. L. G. Sillen and B. Aurivillius, Z. Kristallogr., 1939, 101, 483. E. M. Levin and R. S. Roth, J. Res. Nut. Bur. Stand., Sect. A, 1964,68, 197. R. Guillermo, P. Conflant, J. C. Boivin and D. Thomas, Rev. Chim. Mineral., 1978, 15, 153. R. S. Roth, J. R. Dennis and H. F. McMurdie, Phase Diagrams for Ceramicists, American Ceramic Society, Westerville, OH, 1987. C.L. Teske and H. Muller-Buschbaum, Z. Anorg. Allg. Chem., 1969, 371, 325. J. MATER. CHEM., 1991. VOL. 1 549 9 10 11 12 13 14 15 C. L. Teske and H. Muller-Buschbaum, Z. Anorg. Allg. Chem., 1970, 379, 234. C. L. Teske and H. Muller-Buschbaum, Z. Anorg. Allg. Chem., 1970, 379, 113. H. Muller-Buschbaum, Ang. Chem. Int. Ed. Engl., 1977, 16, 674. J. Cassedanne and C. P. Campelo, Ann. Acad. Bras. Cienc., 1966, 38, 35. B. G. Kakhan, V. B. Lazarev and I. S. Shaplygin, Russ. J. Inorg. Chem., 1979, 24, 922. V. R. Arpe and H. Muller-Buschbaum, Z. Anorg. Allg. Chem., 1976, 426, 1. J. C. Boivin, J. Trehoux and D. Thomas, Bull. Mineral., 1976, 99, 193. 19 20 21 22 23 24 25 E. M. McCarron 111, M. A. Subramanian, J. C. Calabrese and R. L. Harlow, Mater. Res. Bull., 1988, 23, 1355.T. Siegrist, L. F. Schneemeyer, S. A. Sunshine, J. V. Waszczak and R. S. Roth, Mater. Res. Bull., 1988, 23, 1429. Y. A. Chang and N. Ahmad, Thermodynamic Data on Metal Carbonates and Related Oxides, The Metallurgical Society of AIME, Warrendale, Pennsylvania 15086, 1982. D. M. DeLeeuw, C. A. H. A. Mutsaers, C. Langereis, H. C. A. Smoorenburg and P. J. Rommers, Phys. C, 1988, 152, 39. G. M. Kale and K. T. Jacob, Chem. Mater., 1989, 1, 515. A. Fuertes, C. Miravitlles, J. Gonzalez-Calbet, M. Vallet-Regi, X. Obradors and J. Rodriguez-Carvajal, Phys. C, 1989, 157, 525. M. Onada and M. Sato, Solid State Commun., 1988, 67, 799. 16 17 18 J. A. Saggio, K. Sujata, J. Hahn, S. J. Hwu, K. R. Poeppelmeier and T. 0. Mason, J. Am. Ceram. SOC., 1989, 72, 849. Y. Ikeda, H. Ito, S. Shimomura, Y. Oue, K. Inaba, Z. Hiroi and M. Takano, Phys. C, 1989, 159, 93. R. S. Roth, C. J. Rawn, B. P. Burton and F. Beech, J. Res. Nat. 26 27 W. K. Wong-Ng, H. F. McMurdie, B. Paretzkin, C. R. Hubbard and A, L. Dragoo, Powd. Difl., 1988, 3, 117. R. S. Roth, C. J. Rawn and L. A. Bendersky, J. Mater. Res., 1990, 5, 46. Inst. Stand. Technol., 1990, 95, 291. Paper 1/00034I; Received 3rd January, 1991

ISSN:0959-9428    

DOI:10.1039/JM9910100545

出版商:RSC    

年代:1991

数据来源: RSC

摘要:

J. MATER. CHEM., 1991, 1(4), 551-554 55I Low-temperature Vapour Deposition of High-purity Iridium Coatings from Cyclooctadiene Complexes of Iridium Synthesis of a Novel Liquid Iridium Chemical Vapour Deposition Precursor Jeffrey B. Hoke,* Eric W. Stern and H. H. Murray Engelhard Corporation, Menlo Park, CN 40, Edison, NJ 08818, USA High-purity, crystalline iridium coatings have been prepared by low-temperature chemical vapour deposition (CVD) from three volatile cyclooctadiene (COD) iridium precursors. One of these, (MeCp)lr(COD) (MeCp = methylcyclopentadienyl), is a novel complex which melts at low temperature (40 "C) and therefore can be used as a liquid iridium source for CVD. When hydrogen is used as a carrier gas, iridium coatings containing < 1 atm.% carbon are generated at ca.120 "C using (MeCp)lr(COD) and Cplr(C0D) (Cp =cyclopentadienyl). Likewise, deposition under low oxygen pressure in partial vacuum also generates coatings free of carbon and oxygen. However, when the deposition is carried out in vacuo (no carrier gas), ca. 80% carbon is incorporated into the films. When [(COD)lr(p-OAc)], (OAc =acetate) is used as the metal-organic CVD (MOCVD) precursor, films containing c1% carbon and oxygen are obtained at ca. 250 "C in vacuo without the need for a carrier gas. Keywords: Metal-organic chemical vapour deposition; Iridium; Thin film In recent years there has been growing interest in the develop- ment of volatile organometallic precursors to low temperature (<300 "C) vapour-deposited metal and metal oxide coat-ings.'.2 This interest has resulted largely from the demand for new thin-film materials in the electronics industry and from the benefits of the chemical vapour deposition process itself which allows for the deposition of dense, high-purity coatings onto complex shapes at high growth rates.The availability of suitable precursors which have sufficient volatility and which can be cleanly decomposed to the desired metal or oxide, however, has been a common hindrance to further development. In this paper we describe the preparation of pure iridium coatings at low temperature (5250 "C) from one novel and two known cyclooctadiene (COD) complexes of iridium. Iridium is of current interest as a high-temperature (>1600 "C) oxidation barrier for carbon-carbon composite^,^ and it also has potential applications in the microelectronics and optics ind~stries.~ Excluding the iridium halide^,^"-^*' only four CVD precur- sors to metallic iridium have been reported in the literature.These include Ir(acac), (acac =acetylacetonate),6 [(COD)Ir (p-OMe)I2 (OMe =meth~xide),~Ir(acac) (COD),7 and Ir(a1- lyl),.' While all reportedly produce metallic iridium coatings, these sources have their drawbacks. They require high (>500 "C) deposition temperatures (Ir(acac),, Ir(acac)(COD), [(COD)Ir(p-OMe)],, halides}, or they yield coatings contain- ing measurable impurity levels ([(COD)Ir(p-OMe)],, Ir(acac),, Ir(all~l)~}.None of these compounds combines the beneficial features of low deposition temperature and clean decompo- sition in addition to air stability and high volatility.However, not only do the complexes described in this paper extend the number of available iridium precursors, they also satisfy these basic requirements. Experimental (MeCp)Ir(COD), a novel compound, was prepared using an improvement to published procedures for (Cp)Ir(COD). (Reac- tion of NaCp with [(COD)Ir(p-Cl)], at -78 "C increased product yield by 50% over the reported reactions of NaCp with [(COD)IrHCl(p-Cl)], or [(COD)Ir(p-C1)I2 at room tem- perature.)* To [(COD)Ir(p-C1)],9 (0.89 g, 1.32 mmol) dissolved under argon in THF (30 cm3) at -78 "C was added sodium methylcyclopentadienide (1.30 cm3, 2.8 mmol; 2.1 5 mol dm-, in THF) by syringe. An immediate reaction ensued with the formation of a clear yellow solution. After it had been stirred at -78 "C for 10 min, the reaction mixture was warmed to room temperature and stirred an additional 15 min.Removal of the solvent in U~CUOleft a yellow oil. Extraction with hexane (3 x 10 cm3), filtration under argon, and removal of solvent in U~CUOleft a pale-brown solid. Sublimation at 95-100 "C and 0.05 mmHg gave (MeCp)Ir(COD) as a white, air-stable solid, yield 0.82 g, 2.16 mmol, 8l%, m.p. 38.5-40.0 "C. (Found: C, 44.51; H, 5.06. Calc. for CI4Hl9Ir C, 44.31; H, 5.05%) dH (solvent CD2C12; 200 MHz) 1.80 (m, 4 H, CH2), 1.89 (s, 3 H, CH3), 2.00 (m, 4 H, CH2), 3.53 (br s, 4 H, cyclooctadiene CH), 4.95 (t, 2 H, cyclopentadienyl CH, J=1.9 Hz), 5.16 (br s, 2 H, cyclopentadienyl CH).hC (solvent CD,Cl,; 50.4 MHz) 12.1 1 [q, CH3, J(C-H)= 127 Hz], 34.26 [t, CH2, J(C-H)= 125 Hz], 47.49 [d, cyclooctadiene CH, J(C-H) = 153 Hz], 80.44 [d, cyclo- pentadienyl CH, J(C-H) = 176 Hz], 83.24 [d, cyclopentadienyl CH, J(C-H)= 175 Hz]. CpIr(C0D) was prepared similarly from [(COD)Ir(p-Cl)], and NaCp at -78 "C in 65% sublimed yield (1 10 "C ca. 0.01 Torrl.) and identified by comparison of NMR and melting- point data with literature values.8 Depositions onto readily available fused silica substrates were accomplished using a 1 in$ 0.d. externally thermostatted hot-walled quartz reactor. The iridium precursor was sublimed into the hot zone of the reactor under a stream of hydrogen (1.6 cfh), under vacuum with a low-pressure oxygen bleed [p(02)1.3 Torr], or under full vacuum with no carrier gas.A typical run lasted 4 h. Thermogravimetric and mass spectrometric data were obtained using an Omnitherm high-temperature TG-DTA 1500 and a Dycor quadrapole mass spectrometer operating in the electron impact (EX) mode. Freshly sublimed samples of (Cp)Ir(COD) and (MeCp)Ir(COD) were heated under flowing hydrogen to 120 "C at 10 "C min-' and then held at 120 "C. [(COD)Ir(p-OAc)], was heated under flowing helium t 1 Torr z133.322 Pa. $ 1 in=2.54 cm. to 250°C at lO"Cmin-' and then held at 250 "C. Mass spectral analysis of volatile by-products was accomplished in real time. Film composition and thickness data were obtained by X-ray photoelectron spectroscopy using an SSI model 206 electron spectrometer with a monochromatized A1 X-ray source.The instrument was operated with a 600 p X-ray spot and a pass energy of 150 eV. Depth profiling was accomplished with a Leybold-Hereaus IQ 12/38 argon ion gun operating at 5 kV with a current density of ca. 100 pA cm-2. Film thicknesses were based on the etching rate for SO2. The pressure during data collection was 2 x 10-Torr; data were collected using the Ir 4f line (binding energy =60.6 eV). Quantification was accomplished using linear background subtraction and Scofield sensitivity factors. lo Results and Discussion The three cyclooctadiene iridium precursors chosen for this study were (MeCp)Ir(COD) (MeCp =methylcyclopen-tadienyl), CpIr(C0D) (Cp=cyclopentadienyl),8 and [(COD)Ir(p-OAc)], (OAc =acetate)." R Ir \\ACOzMe Of these, (MeCp)Ir(COD) is a novel compound and was prepared from [(COD)Ir(p-Cl)]2 and sodium methylcyclopen- tadienide as described above.All are air stable and sufficiently volatile for CVD (Table 1). All produce impurity-free coatings of iridium at low temperature [120 "C for both CpIr(C0D) and (MeCp)Ir(COD)] and are thus superior to other iridium precursors described in the literature. (MeCp)Ir(COD) is par- ticularly attractive since its low melting point (38.5-40 "C) permits its use as a liquid source of iridium near room temperature. This is a significant advantage as many commer- cial CVD systems are designed for the use of liquid precursors.Reduction of (MeCp)Ir(COD) and CpIr(C0D) vapours (sublimation temperature 95 "C)in flowing hydrogen (1.6 cfht) at ca. 120 "C and ambient pressure resulted in the deposition of pure, crystalline coatings of iridium (Table 2). Scanning electron microscopy photographs of coated and uncoated fused silica substrates are shown in Fig. 1. ESCA depth-profile analysis detected <1 atom% carbon within the bulk of the coatings, which were up to 5300 A thick (Fig. 2). Thin-film X-ray analysis (Cu-Ka radiation) confirmed film crystallinity (Fig. 3). The line-broadening evident in the diffraction peaks is consistent with the presence of microcrystalline iridium particles of ca. 50 8, diameter." In contrast to hydrogen reduction, decomposition of (MeCp)Ir(COD) and CpIr(C0D) vapours in uucuo at ca.590 and 680 "C, respectively, generated black films which incorporated ca. 80 atom% carbon as 1 cfhz2.83 xlOP2m3 h-', Table 1 Melting-point and sublimation data for iridium CVD precursors precursor m.p./ "C Tub/ "C (MeCp)Ir(COD) CpIr(C0D) C(COD)Ir(CL-OAc)l, 38.5-40.0 125.5-128.5 135" 95 (0.05 Torr) 110 (0.01 Torr) 125 (0.07 Torr) "Decomposed. J. MATER. CHEM., 1991, VOL. 1 determined by ESCA (Table 2). [X-Ray analysis of the coating derived from (MeCp)Ir(COD) showed the iridium to be mic- rocrystalline.] Clearly, hydrogen is required to cleave the organic ligands from iridium and concurrently reduce the metal to the zero oxidation state.'H NMR and TG-MS were utilized to deduce a possible mechanism for the reduction of (MeCp)Ir(COD) and (Cp)Ir(COD) at 120 "C. For both complexes, 'H NMR anal- ysis of the volatiles collected during vapour deposition showed only the presence of saturated hydrocarbon. No alkene species (methylcyclopentadiene, cyclopentadiene, methylcyclopentene, cyclopentene, cyclooctadiene, or cyclooctene) were detected. Likewise, TG-MS analysis of the decomposition of both complexes in flowing hydrogen at 120 "C confirmed the formation of cyclooctane but no cyclooctadiene, cyclooctene, cyclopentadiene, or methylcyclopentadiene. These results would indicate that the primary reduction mechanism pro- ceeds via a multistep process involving oxidative additions of H2 to Ir' with subsequent reductive eliminations back to Ir' and formation of uncomplexed hydr~carbon.'~ The 1r'-H species which would remain from such a process may then undergo homolytic bond cleavage (Ir-H+Ir +H.) or a bimolecular process (2Ir-H-Ir +H2) to yield metallic iridium. Owing to the gradual decomposition of the source materials under hydrogen during sublimation, the observed deposition rates were slow.However, this problem can be alleviated by directing the organometallic vapours onto the substrate prior to hydrogen exposure.2a Consequently, the precursor will not see hydrogen until the point of deposition, and a subsequent increase in sublimation temperature should significantly improve the rate.Oxidation of (MeCp)Ir(COD) and CpIr(C0D) vapours (sublimation temperature 80 "C) in partial vacuum [p(O,)1.3 Torr] at ca. 270 "C also yielded pure, crystalline iridium coatings. In each case, ESCA depth-profile analysis detected <1 atom% carbon and oxygen through the bulk, and thin- film X-ray analysis confirmed film crystallinity. In agreement with the low oxophilicity of iridium, the presence of oxygen during CVD was not a problem. Since iridium does not form an oxide below 550 "C,14 oxygen is free to consume the organic ligands leaving behind only pure iridium. Unlike the cyclopentadienyl complexes of iridium, the acet- ate bridged dimer, [(COD)Ir(p-OAc)],, does not require a reactive gas (either hydrogen or oxygen) to produce clean coatings of iridium.Deposition at ca. 250 "C in uucuo (subli-mation temperature 130 "C) produced a thin (400 A) coating containing <1 atom% carbon or oxygen within the bulk as determined by ESCA depth-profile analysis. (In this instance, deposition was hampered by the simultaneous decomposition of the precursor at the sublimation temperature.) Thin-film X-ray analysis confirmed the presence of crystalline iridium. 'H NMR analysis of volatiles trapped during the CVD experiment showed the presence of cyclooctadiene, cyclooctene, and cyclooctane in roughly equal amounts. TG mass spectral analysis during the decomposition of [(COD)Ir(p-OAc)], in flowing helium at 250 "Cgave molecu- lar ions corresponding to carbon dioxide, cyclooctadiene, cyclooctene, cyclooctane and possibly ethane.These data suggest that the primary decomposition pathway involves the simultaneous liberation of carbon dioxide from the acetate bridge and cyclooctadiene from iridium. Formation of cyclo- octene and cyclooctane may result from further reaction of the resulting acetate derived methyl radicals with either bound or liberated cyclooctadiene. Dimerization of the methyl rad- icals would also produce ethane. Pure Iro is thus obtained. Although the sublimation temperature of [(COD)Ir(p-OAc)], is somewhat high, its greatest advantage for CVD is its ability J. MATER. CHEM., 1991, VOL. I Fig. 1 (a)SEM of an iridium coating on fused silica produced from the hydrogen reduction of (MeCp)Ir(COD);(b)SEM of an uncoated fused silica substrate Table 2 Data summary for CVD iridium coatings precursor co-reactant &ec/ "C 120 120 285 270 680 590 250 100 1 Ir f 60 1 C ._:40 20 0 25 50 75 100 sputter time/min Fig.2 ESCA depth profile of an iridium coating produced from the hydrogen reduction of (MeCp)Ir(COD); sputter rate 70 A min-' to produce iridium coatings free from contamination without the need for a reactive carrier gas. Such a result is remarkable since most chemical vapour depositions require reactive gases (e.g.hydrogen) to produce coatings completely free of carbon or oxygen. The authors express their gratitude to the following individ- uals: A. Amundsen for supplying [(COD)Ir(p-OAc)] 2; N.Brungard and D. Anderson for providing the ESCA analyses; Professor K. Unruh (University of Delaware) for providing the thin-film X-ray analyses; Earl Waterman for conducting depth/A composition deposition rate/A h- 5300 <1% c 900 460 <I% c 100 500 950 <1O/O c, 0 <1% c,0 150 250 47000 82% C, 18% Ir 9000 1400 80% C, 20% Ir 350 400 <1% c,0 80 10 Fig. 3 Thin-film X-ray scan of an iridium coating produced from the hydrogen reduction of (MeCp)Ir(COD); peaks at ca. 40, 47 and 70" correspond to those in JCPD file for iridium (Ir6-598) the TG-MS experiments; and M. Gashasb for helpful dis- cussions on CVD processing. References 1 (a)J. E. Gozum, D. M. Pollina, J. A. Jensen and G. S. Girolami, J.Am. Chem. Soc., 1988, 110, 2688; (b)Y. Chen, H. D. Kaesz, H. Thridandam and R. F. Hicks, Appl. Phys. Lett., 1988, 53, 1591; (c) Z. Xue, M. J. Strouse, D. K. Shuh, C. B. Knobler, H. D. Kaesz, R. F. Hicks and R. S. Williams, J. Am. Chem. SOC., 1989, 111, 8779; (d) E. Feuer, S. Kraus and H. Suhr, J. Vac. Sci. Technol. A, 1989, 7,2799; (e) M. J. Rand, J. Electrochem. SOC., 1973, 120, 686; (f)P. M. Jeffries and G. S. Girolami, Chem. Muter., 1989, 1, 8; (g) C. G. Dupuy, D. B. Beach, J. E. Hurst and J. M. Jasinski, Chem. Muter., 1989, 1, 16; (h) D. B. Beach, F. K. LeGoues and C-K. Hu, Chem. Mater., 1990, 2, 216; (i) R. 554 J. MATER. CHEM., 1991, VOL. 1 2 3 L. van Hemert, L. B. Spendlove and R. E. Sievers, J. Electrochem. SOC.,1965, 112, 1123; (j) F.A. Houle, C. R. Jones, T. Baum, C. Pic0 and C. A. Kovac, Appl. Phys. Lett., 1985, 46, 204; (k) C. Larson, T. H. Baum and R. L. Jackson, J. Electrochem. SOC., 1987, 134, 266; (I) T. H. Baum, J. Electrochem. SOC., 1987, 134, 2616; (m) C. L. Czekaj and G. L. Geoffroy, Inorg. Chem., 1988, 27, 8; (n) W. L. Gladfelter, D. C. Boyd and K. J. Jensen, Chem. Muter., 1989, 1, 339. (a)H. D. Kaesz, R. S. Williams, R. F. Hicks, Y. A. Chen, Z. Xue, D. Xu, D. Shuh and H. Thridandam, Muter. Res. SOC. Symp. Proc., 1989, 131, 395; (b) D. C. Smith, C. J. Burns, A. P. Sattelberger, S. G. Pattillo, D. W. Carroll and J. R. Laia, Mater. Res. SOC.Symp. Proc., 1990, 168, 369. (a)J. R. Strife and J. E. Sheehan, Ceram. Bull., 1988, 67, 369; (b) J. E. Sheehan, Proc. Fourth Ann.Con5 Muter. Tech.-Recent 7 8 9 10 11 12 V. R. Fry, Prec. Met., Proc. Int. Prec. Met. Inst. ConJ, loth, International Precious Metals Institute, Allentown, PA, 1986, 431. J. A. Papke, R. D. Stevenson, Proc. Con$ Chem. Vapor Dep. Refract. Metals, Alloys, Comp., 1967, 193. (a) S. D. Robinson and B. L. Shaw, J. Chem. SOC., 1965, 4997; (b)G. Pannetier, D. Tabrizi and R. Bonnaire, J. Less Common Metals, 1971, 24, 470. J. L. Herde, J. C. Lambert and C. V. Senoff, Znorg. Synth., 1974, 15, 18. J. H. Scofield, J. Electron. Spectrosc. Relat. Phenom., 1976, 8, 129. R. N. Haszeldine, R. J. Lunt and R. V. Parish, J. Chem. SOC. (A), 1971, 3696. Elements of X-Ray Digraction, ed. B. D. Cullity, Addison-Wesley, 4 5 6 Res. Carbon-Carbon Composites, Southern Illinois University, 1987, 56; (c)J. M. Criscione, R. A. Mercuri, E. P. Schram, A. W. Smith and H. F. Volk, ML-TDR-64-173, Part 11, 1974; (d) Nut. Acad. Sci. Eng. Pub. no. ISBM 0-309-01769-6, 1970, 112. (a)M. L. Green and R. A. Levy, J. Metal., 1985, 63; (b)G. Haas, J. Opt. SOC. Am., 1982, 72, 27. B. A. Macklin and J. C. Withers, Proc. ConJ Chem. Vapor Dep. Refract. Metals, Alloys, Comp., American Nuclear Society, Gatlin- berg, 1967, 161. (a) J. T. Harding, V. R. Fry, R. H. Tuffias and R. B. Kaplan, AFRPL TR-86-099, 1987; (b) J. T. Harding, R. H. Tuffias and R. B. Kaplan, AFRPL TR-84-035, 1984; (c) J. T. Harding and 13 14 Reading, MA, 1978, 284. (a) Advanced Inorganic chemistry, ed. F. A. Cotton and G. Wilkinson, Wiley, New York, 4th edn., 1980, 1237; (b)Principles and Applications of Organotransition Metal Chemistry, ed. J. P. Collman and L. S. Hegedus, University Science Books, Mill Valley, CA, 1980, 176. W. P. Griffith, C. J. Raub and E. Raub, Gmelin Handbook of Inorganic Chemistry; Iridium- Band 2, ed. K. Swars, Springer- Verlag, New York, 1978, pp. 2-4. Paper 1/OO 1 59K; Received 14th January, 1991

ISSN:0959-9428    

DOI:10.1039/JM9910100551

出版商:RSC    

年代:1991

数据来源: RSC

摘要:

J. MATER. CHEM., 1991, 1(4), 555-558 Synthesis and Crystal Structures of the Layered I-Ill4 Zintl Phases, K,ln,X,, where X=As, Sb Teresa L. T. Birdwhistell," Cheryl L. Klein," Tammy Jeffries/' Edwin D. Stevensb and Charles J. O'Connor*b a Department of Chemistry, Xa vier University of Louisiana, New Orleans, Louisiana 70125,USA Department of Chemistry, University of New Orleans, New Orleans, Louisiana 70148, USA Ternary Zintl phase materials of the formula K,ln,X,, where X=As or Sb, have been prepared following a high- temperature procedure. The crystal structure of K,In,As, has been determined at low temperature and consists of [In,As:-], sheets of ca. 5 A thickness insulated by a layer of potassium ions of ca. 3 A thickness. The crystal structure of K41n,Sbs has been determined at room temperature and is isomorphous with the K,ln,Sb, compound.~=4,For K,I~,As,, a= 14.323(3) A, 6=7.106(2) A, c= 15.795(3) A, p=90.30(2)", space group P~,/c, p,=4.44 g cm-3 at T= lOO(5) K, R= 0.035 for 2688 unique observed reflections. For K,ln,Sb,, a= 15.282(5)A, b= 7.544(1) A, c= 16.788(3) A, /?=90.52(2)", space group P2,/c, Z=4, p,=4.62 g cmP3 at T=299 K, R=0.042 for 3001 unique observed reflections. Keywords: Zinti phase; Crystal structure; indium; Antimony; Arsenic; Layered structure Zintl materials are 'valence' compounds: the metals and metalloids that comprise the material will transfer or share electrons in order to achieve an octet in the outermost electron shell.' This often results in the formation of covalently bonded polyatomic anionic units, referred to as Zintl anions.The valence character of Zintl materials is often expressed as the 8-N rule (i.e., N covalent bonds are formed to complete an octet of electrons in the valence shell).' The octet valence shell of the Zintl phase arises when the more electropositive metals (ie. alkali and alkaline-earth metals) are allowed to react with the less electropositive metals and metalloids (i.e. the post-transition main-group metals). Binary Zintl alloys are usually prepared by heating a direct combination of the elements. For example, the Zintl material KSn may be prepared by mixing molten potassium with molten tin to give the KSn powder.2 Similar synthetic tech- niques produce KPb,3 K51n8,4 KSb,' K3Bi,6 KTl,7 K5Ga8,8 and others.These binary Zintl phases may be isolated and identified by powder diffraction prior to subsequent reaction. In recent years there has been a rebirth of interest in Zintl- phase materials with numerous reports of ternary materials from Corbett and co-worker~,~ von Schnering and co-work- ers," Schafer and co-workers," Cordier and co-workers,'2 Eisenmann and co-workers,13 Nespar and co-workers,14 Hau- shalter and co-~orkers,'~ among others. We have undertaken the synthesis of a I-III-V ternary Zintl phase material as a preliminary step in the investigation of new synthetic routes to the preparation of III-V-type semiconductors and semiconducting devices. The reactivity of Zintl phase materials affords the possibility of solution-phase deposition of semiconducting films and perhaps the layering of metal-semiconductor deposition.16 Several I-III-V Zintl phase materials have already appeared in the literature including KGaSb2,17 K3A12As3,18 Na7A12Sb5,19 Na2A12Sb3,20 K2A12Sb3,20 and K3Ga3A~4.2' We report here on the preparation and structural charac- terization of two additional Zintl-phase materials that have layered structures composed of In :X layers alternating with K layers.Experimental Synthesis. The same synthetic procedure was used for the preparation of K41n4As, and K41n4Sb6. Therefore, only the synthesis of K4In4AS6 is described. K41n4As6 was prepared by adding K (1.00 g, 25.6 mmol), In (0.97 g, 8.5 mmol), and As (1.27 g, 17.0 mmol) to a quartz tube that was then sealed under a vacuum.The sample was heated at 750 "C in a tube furnace for 10 h, then cooled to ambient temperature over a 40 h period. A metallic-grey crystalline product was obtained and could be isolated in ca. 80% yield. Crystal Data.? K41n4As6, M = 1065.2, monoclinic, a = 14.323(3) A, b=7.106(2)A, c= 15.795A, p =90.30(2)", U = 1607.6(7)A3 at lOO(5) K (by least-squares refinement on diffractometer setting angles for 25 automatically centred reflections in the range 54<28/" <67, A =0.71073 A), space group P2Jc (No. 14), Z=4, p,=4.44 g ~m-~. Extremely air- sensitive metallic-grey crystal of irregular shape and approxi- mate dimensions 0.15 mm x 0.25 mm x 0.50 mm was separated from melt and mounted under dodecane oil, then rapidly transferred to the diffractometer and cooled to 100 K in a stream of N2 gas [p(MoKa)= 188.2 cm-'1.K4In4Sb6, M = 1346.2, monoclinic, a = 15.288(5)A, b= 7.544( 1) A, c = 16.790(3)A, p =90.54(2)", at 296 K (by least- squares refinement on diffractometer setting angles for 25 automatically centred reflectipns in the range 28 <20/" d37, 1=0.71073 A), space group P2Jc (No. 14), Z=4, pc= 4.62 g cm- '. Air-sensitive metallic-grey crystal of irregular shape and approximate dimensions 0.22 mm x 0.34 mm x 0.1 1 mm was separated from melt in an inert atmosphere and sealed in a glass capillary tube [p(Mo-Ka)= 137.3 cm-'1. Data Collection and Processing. K41n4AS6, CAD4 diffractometer, 0-28 scan mode with scan width = 1.00" +0.35" tan 8, scan speed 0.95-6.8" min-', graphite-monochromated Mo-Ka radiation; temperature maintained to within +lo as measured by a thermocouple in N2 gas stream, 8709 reflections measured (2 <28/"<50, fh, fk, & E), 30 16 unique [merging R =0.032 after corrections for decay (linear, 1 S%) and absorption (empirical, max., min.relative transmission factors =1 .O, 0.24)], giving 2688 reflections with I>341). K41n4Sb6, CAD4 diffractometer, 0-28 scan mode with scan t Supplementary data available from the University of Bonn: see Information for Authors, J. Muter. Chem, 1991, Issue 1. K41n4Sb6,CAD4 diffractometer, 0-28 scan mode with scan width =0.90" + 0.35" tan 8, scan speed 1.4-6.8" min- ', graph-ite-monochromated Mo-Kcr radiation; 7624 reflections meas- ured (2 < 20/" < 50, h, & k, l), 3679 unique [merging R = 0.014 after corrections for decay (linear, 0.8%) and absorption (empirical, max., min.relative transmission factors = 1.O, 0.21)], giving 300 1 reflections with I > 341). Structure Analysis and Refinement. K41n4As6, direct methods yielded positions of all In, As, and K atoms. Full-matrix least- squares refinement on F magnitudes with anisotropic thermal parameters. The weighting scheme used w = l/a2(Fo)where a(F2)= [azs+ (0.02F2)2]'12,with ocsfrom counting statistics. Final R and R' values are 0.035, 0.047. All programs from the CAD4-SDP system22 and scattering factor data from ref. 23. K4In4Sb6, starting coordinates taken from the structure of K41n4As,.Full-matrix least-squares refinement of F magni-tudes with anisotropic thermal parameters and an isotropic extinction parameter. The weighting scheme used w = l/02(Fo) where a(F2)= [ozS+ (0.04F2)2]'I2. Final R and R' values are 0.042 and 0.063. Resistivity Measurements. The linear four-probe methodz4 was used on pressed pellets of the material. The current was supplied by a Keithley Model 224 programmable source and the voltage drop across sample measured with a Keithley model 18 1 digital nanovoltmeter. Results and Discussion The crystal structures of K41n4As6 and K41n4Sb, are found to be isomorphous with the previously reported structures of Na4A1,Sb620 and K4A14Sb6.20 The structure is described in terms of the K41n,&6 compound. The structure of K41n4AS6 consists of potassium ions and [In4As614- alternating in the c direction.The structure of the [In4As614- layer is quite different from that of the well known semiconductor InAs The latter has the zinc blende structure, with the In and As atoms alternating in six-membered rings in an infinite three-dimensional array. When n J. MATER. CHEM., 1991, VOL. 1 the structure is truncated and restricted to two dimensions, smaller, more highly strained ring systems are formed. The asymmetric unit of K41n4AS6 contains a polyhedron com-posed of edge-sharing four-, five-, and six-membered rings (see Fig. 1). In InAs all of the atoms are tetrahedrally coordi- nated.In K41n4AS6, each of the In atoms is four-co-ordinate, but the As atoms are only three-co-ordinate. In addition, two of the six As atoms in the asymmetric unit are bonded to each other in what may formally be viewed as an As$-fragment. The average In-As bond distance of 2.67(4)A is only slightly longer than the 2.62 8, distance observed in InAs. The As- As bond distance of 2.492( 1) A is only slightly longer than the sum of the covalent radii for As, 2.44 A. The [In4As614- fragments are linked together to form two- dimensional, covalently bonded sheets which run perpendicu- lar to c. These are insulated from one another by layers of K+ ions. The InAs sheets are not planar but 'rippled', and the K+ ions sit in the channels created by this rippling effect Fig.1 ORTEP diagram of the asymmetric unit of K,In,As, n Fig. 2 Structural diagram showing the layered nature of the indium-arsenide sheets insulated by potassium sheets J. MATER. CHEM., 1991, VOL. 1 (see Fig. 2). The thickness of the InAs layers is ca. 5 A and they are separated by ca. 3 A. In K4In4Sb6, the average In-Sb bond distance is 2.86(4) 8, compared with the distance of 2.81 8, in the structure of InSb. The Sb-Sb bond distance is 2.866(1)& compared with 2.892( 1) A in Na4A14Sb620 and 2.877( 1) A in K4A14$b6.20 The reactivity of K4In4AS6 requires handling of the sub- stance in an argon atmosphere. Attempts to dissolve the material in polar solvents without decomposition have been unsuccessful. The material decomposes in H20 and is insol- uble in ethylenediamine, liquid ammonia, and organic sol- vents.Preliminary data indicate that K4In4AS6 will dissolve in molten salt solution (e.g. NaCl at 750 "C) and we are investigating the reactivity of K4In4AS6 in this solvent system. The room-temperature resistivity measurements of both materials were unsuccessful because the specific resistivity was beyond our detection limits (p>lo7 Q cm) and both materials would therefore be classified as insulators. Substitution of other Group 13 or Group 15 atoms for the In and As has Table 1 Positional parameters atom X Y Z B/A2 0.31768(4) 0.091 80(4) 0.58959(4) -0.183 7 l(4) -0.02929(6) 0.23019(7) 0.2 1490( 7) 0.24642( 7) 0.24875( 7) 0.04 18(I) 0.1679 l(4) 0.23024(4) 0.32393(4) 0.25827(4) 0.32857(5) 0.503(9) 0.505(9) 0.523(9) 0.544(9) 0.54(1) 0.47828(6) 0.24871(6) 0.33 3 54( 6) 0.163 19(6) 0.74634(6) 0.1418( 1) 0.0834(1) 0.3440(1) 0.5624(1) 0.0448(1) 0.2054(1) 0.57 10( 1) 0.0606( 1) 0.3550(1) 0.5470(3) 0.5636(2) 0.5826(3) 0.4596(2) -0.1 5804( 5) 0.32289(5) 0.10800(5) 0.09 104( 5) 0.17277(5) 0.3940( 1) 0.4767(I) 0.0896(I) .0.0084(1) 0.54( 1) 0.57(1) 0.55( 1) 0.53(1) 0.54(1) 0.83(3) 1.07(3) 0.94(3) 1.32(3) Anisotropically refined atoms are given in the form of the isotropic equivalent thermal parameter.Table 2 K,In,As, interatomic distances and angles ~~~~ ~ atoms dis tance/A atoms distance/A AS(AS AS(6) 2.492(1) In(4)-As(2) 2.669( 1) In(1)-As(2) 2.657(1) In(4)-As(4) 2.692( 1) In(1)-As( 3) 2.650(1) In( 4)- As( 6) 2.733(I) In( 1)-As(4) 2.61 I( 1) In(4)-As( 2) 2.67 1( 1) In( 1)-As(5) 2.793(1) In(3)-As( 1) 2.648(1) In(2)-As( 1) 2.639(1) In( 3)-As(4) 2.7 1q1) In(2)-As(1) 2.656(1) In(3)-As(5) 2.621(1) In(2)-As( 3) 2.677( 1) In(3)-As(6) 2.697(1) In(2)-As(5) 2.666( 1) atoms angle/" atoms angle/" As(2)-In( 1)-As(3) 110.39(3) As( l)-In(3)-As(4) 113.58(3) As(2)-In( 1)-As(4) 1 1 1.2q3) As( 1)-In(3)-As(5) 11 1.22(3) As(2)-In( 1)-As(5) 116.45(2) As( I)-In(3)-As(6) 119.21(3) As(3)-In( l)-As(4) 115.48(3) As(4)-In(3)-As( 5) 105.99( 3) As(3)-In( l)-As(5) 94.26(3) As(4)-In(3)-As(6) 10 1.03( 3) As(4)-In( 1)-As(5) 108.24( 3) As( 5)-In(3)-As(6) 104.48(3) As( I)-In(2)-As( 1) 113.08(2) As(2)-In(4)-As(2) 120.22(2) As( l)-In(2)-As( 3) 102.67( 3) As(2)-In(4)-As(4) 116.84(3) As( l)-In(2)-As(5) 123.37( 3) As(2)-In(4)-As( 6) 110.30(3) As( 1)-In(2)-As(3) 119.61(3) As(2)-In(4)-As(4) 97.46(3) As( l)-In(2)-As( 5) 101.62(3) As( 2)-In(4)-As(6) 109.23(3) As( 3)-In(2)- As( 5) 96.64(3) As(4)-In(4)-As( 6) 100.57( 3) In(1)-As( 3)-As( 6) 94.66(3) In(4)-As(6)-As( 3) 106.60(3) In(2)-As(3)-As(6) 93.67(3) In(3)-As(6)-As(3) 104.54(3) Numbers in parentheses following values of distance or angle are estimated standard deviations in the least significant digits.Table 3 K41n4Sb6 positional parameters atom X Y Z B/A2 0.31683(5) 0.09279(5) 0.59240(5) 0.47880(5) 0.25040(5) 0.3 3262( 5) 0.16193(5) 0.74944(5) 0.8585(2) 0.6543(2) 0.0778(2) 0.5582(2) -0.18225(5) -0.02488(5) 0.2207(1) 0.21 30( 1) 0.2375( 1) 0.2360( 1) 0.0365(1) 0.0337(1) 0.2 I63( 1) 0.5638(1) 0.0550(I) 0.3 366( 1 ) 0.5336(4) 0.4492(4) 0.5352(4) 0.5562(5) 0.16490(5) 0.22865(5) 0.32674(5) 0.25969(5) 0.33 134(5) 0.15869(5) 0.32216(5) 0.10330(5) 0.08857(5) 0.173 17(5) O.OOSS(2) 0.5226(2) 0.3887( 2) 0.101 l(2) I .42(2) 1.37(1) 1.41( 1) 1.48(2) 1.34(1) 1.41(1) 1.45( 1) 1.32(1) 1.34(I) 1.44(1) 2.43(6) 2.48(6) 2.79(6) 3.41(7) Anisotropically refined atoms are given in the form of the isotropic equivalent thermal parameter.Table 4 K,In,Sb, interatomic distances and angles atoms dist ance/A atoms distance/A Sb( 3)-Sb( 6) 2.866(1) In(4)-Sb(2) 2.852(1) In( 1 )-Sb( 2) 2.853(1) In(4)-Sb(4) 2.871(1) In( 1)-Sb( 3) 2.838(1) In( 4)- 5b( 6) 2.9 18( 1) In( 1)-Sb(4) 2.798(1) In(4)-Sb(2) 2.858(1) In( 1)-Sb(5) 2.959(1) In(3)-Sb( I) 2.844(1) In(2)-Sb( 1) 2.836(1) In(3)-Sb(4) 2.904(1) In(2)-Sb( 1) 2.833(1) In( 3)-Sb( 5) 2.801( 1) In(2)-Sb(3) 2.864(1) In( 3)-Sb(6) 2.872(1) In(2)-Sb( 5) 2.849( 1) atoms angle/" atoms angle/" Sb(2)-In( 1)-Sb(3) 1 10.28(2) Sb( 1)-In(3)-Sb(4) 114.90(2) Sb(2)-In( 1)-Sb(4) 1I 1.47(2) Sb( 1)-In(3)-Sb(5) 110.63(2) Sb(2)-In( 1)-Sb( 5) 117.81(2) 5b( )-In( 3)-Sb( ) 117.61(2)16 Sb(3)-In( 1)- Sb( 4) 112.81(2) Sb(4)-In(3)-Sb(5) 105.36(2) Sb(3)-In( 1)-Sb(5) 96.08(2) 5b( 4)-In( 3)-Sb( ) 101.42(2)6 Sb(4)-In( 1)-Sb( 5) 107.5 9( 2) Sb( 5)-In( 3)-Sb( 6) 105.7 l(2) Sb( l)-In(2)-Sb( 1) 1 12.84(2) 5b( 2)-In( 4)-5b( 2) 118.24(2) Sb( 1)-In(2)-Sb(3) 101.89(2) Sb(2)-In(4)-Sb(4) 118.00(2) Sb( l)-In(2)-Sb(5) 123.22(2) 5b( 2)-In(4)-S b( ) 109.98(2)6 Sb( 1)-In(2)-Sb(3) 119.41(2) Sb(2)-In(4)-Sb(4) 97.054 2) Sb( 1)-In(2)-Sb(5) 10 1.8q2) 5b( 2)-In(4)-S b( ) 110.73(2)6 Sb( 3)-In( 2)-Sb( 5) 98.O 1(2) Sb(4)-In(4)-Sb(6) 101.09(2) In( 1)-Sb(3)-Sb(6) 92.12(2) In(4)-5b(6)-5b( 3) 104.29(2) In( 2)-S b( 3)-Sb( 6) 90.39( 2) In(3)-5b(6)-5b( 3) 103.62(2) Numbers in parentheses following values of distance or angle are estimated standard deviations in the least significant digits.produced related layered2'g2' and p~lymeric'~ structures. The related ternary I-111-V Zintl-phase material composed of K, Ga, and As (K3Ga3As4) has also been synthesized in our lab, and its structure and electrical properties have recently been reported.22 K3Ga,As4 shows a layered structure similar to the K41n4X6 materials, but K3Ga,As4 does not contain any catenated bonds.The analogue with K, Ga, and Sb (K2Ga2Sb4) has a polymeric structure with (Ga2Sb3) rings bridged by Sb atoms. K2Ga,Sb4 has also been shown to be an intrinsic semicond~ctor.~~ C.J.O. wishes to acknowledge support from a grant from the Louisiana Education Quality Support Fund administered by the Board of Regents of the state of Louisiana and the donors of the Petroleum Research Fund administered by the Amer- ican Chemical Society. 558 J. MATER. CHEM., 1991, VOL. 1 References H.Ochmann and H. Schafer, Rev. Chim. Min., 1985, 22, 58; G. Cordier, H. Ochmann and H. Schafer, Rev. Chim. Min., 1984, 1 H. Schafer, Ann. Rev. Muter.Sci., 1985, 15, 1; H. Schafer, 21, 282; G. Cordier, H. Schaeffer and M. Stelter, J. Naturforsch., B. Eisenmann and W Muller, Angew. Chem., Znt. Ed. Eng., 1973, 12, 694, and references therein; H. G. von Schnering, Bol. SOC. Quim., 1988, 33, 41; J. D. Corbett, Chem. Rev., 1985, 85, 383; B, 1987, 42, 1258; G. Cordier and H. Ochmann, J. Naturforsch., B, 1988 43, 1538; G. Codier and M. Stelter, 2. Naturforsch., B, 1988,43, 463; W. Blase and G. Cordier, 2. Naturforsch., B, 1988, S. Kauzlaricn, Comm. Znorg. Chem., 1990, 10, 75; E. Zintl, A. Horder and B. Danth, 2. Electrochem., 1934, 40,588; E. Zintl and G. Brauer, 2. Electrochem., 1935, 41, 297. 13 43, 1017. J. Klein and B. Eisenmann, Muter. Res. Bull., 1988, 23, 587; B. Eisenmann and J. Klein, 2. Naturforsch., B, 1988, 43, 69; 2 3 4 5 I.F. Hewaidy, E. Busmann and W. Klemm, 2. Anorg. Allg. Chem., 1964, 328, 283; M. Hansen, Constitution of Binary Alloys, McGraw-Hill, New York, 2nd edn., 1958. B. F. Alblas, C. van der Marel, W. Geertsma, J. A. Meijer, A. B. van Oosten, J. Dijkstra, P. C. Stein and W. van der Lugt, J. Non-Cryst. Solids, 1984, 61-62(1), 201. R. Thummel and W. Klemm, 2. Anorg. Allg. Chem., 1970, 376, 44; G. Bruzzone, Acta Crystallogr., Sect. B, 1969, 25, 1206. E. Busmann and S. Lohmeyer, 2.Anorg. Allg. Chem., 1961,312, 14 15 B. Eisenmann and R. Zagler, 2. Naturforsch., B, 1987, 42, 1079; B. Eisenmann and J. Klein, J. Naturforsch., B, 1988, 43, 1156; B. Eisenmann, J. Klein and M. Somer, Angew. Chem., Znt. Ed. Engl., 1990, 29, 87. R. Nespar and J.Curda, 2. Naturforsch., B, 1987, 42, 557; R. Nespar and J. Curda, 2. Naturforsch., B, 1987, 42, 557; R. Nespar, Angew. Chem., 1989, 101, 99; R. Nesper and H. G. von Schnering, J. Solid State Chem., 1987, 70, 48. R. C. Haushalter, J. Chem. SOC., Chem. Commun., 1987, 196; 6 53. G. Brauer, Handbook of Preparative Znorganic Chemistry, New York, 2nd edn., 1963, vol. 1; G. Braueer and E. Zintl, 2. Phys. Chem., 1937, B37, 323. M. M. J. Tracy, R. C. Haushalter and S. B. Rice, Ultramicroscopy, 1987, 23; J. C. Huffman, J. P. Haushalter, A. M. Umarji, G. K. Shenoy and R. C. Haushalter, Inorg. Chem., 1984, 23, 2312; K.-H. Lii and R. C. Haushalter, J. Solid State Chem., 1987, 67, 374; 7 8 9 10 11 12 M. Hansen, Constitution of Binary Alloys, McGraw-Hill, New York, 2nd edn., 1958; R.Thummel and W. Klemm, 2. Anorg. Allg. Chem., 1970, 376, 44. E.Rinch and P.Feschote, C.R. Acad Sci., 1961, 252, 3592, S. Yatsenho, Kristallograjya, 1983, 28(4), 809. W. M. Hurng, J. D. Corbett, G. L. Wang and R. Jacobson, Inorg. Chem., 1987, 26, 2393; W. M. Hurng, E. S. Petersom and J. D. Corbett, Znorg. Chem., 1989, 28, 4177; W. M. Hurng and J. D. Corbett, Chem. Muter., 1989, 1, 311; J. D. Corbett, Chem. Rev., 1985, 85, 383. R. Nesper and H. G. von Schnering, J. Solid State Chem., 1987, 70, 48; H.G. von Schnering, M.Somer, M.Hartweg and K. Peters, Angew. Chem., Znt. Ed. Engl., 1990, 29, 65; H. G. von Schnering, Bol. SOC. Quim., 1988, 33, 41. H. Schafer, Ann. Rev. Muter. Sci., 1985, 15, 1; H. Schafer, B. Eisenmann and W. Muller, Angew. Chem., Znt.Ed. Engl., 1973, 12,694; G. Cordier, H. Ochmann and H. Schafer, J. Less-Common Met., 1986, 119, 291; G. Cordier, H. Ochmann and H. Schafer, 2. Anorg. Chem., 1984, 517, 118; B. Cordier, H. Schaefer and M. Stelter, 2. Naturforsch., B, 1987, 42, 1268; G. Cordier, H.Ochmann and H.Schafer, Rev. Chim. Min., 1985, 22, 58; G. Cordier, H. Ochmann and H. Schafer, Rev. Chim. Min., 1984, 21, 282; G. Cordier, H. Schafer and M. Stelter, 2. Naturforsch., B, 1987, 42, 1258. G. Cordier, H. Ochmann and H. Schafer, J. Less-Common Met., 1986, 119, 291; G.Cordier, H.Ochmann and H.Schafer, 2. Anorg. Chem., 1984, 517, 118; B. Cordier, H. Schaefer and M. Stelter, 2. Naturforsch., B, 1987, 42, 1268; G. Cordier, 16 17 18 19 20 21 22 23 24 25 R. C Haushalter, B. W. Eichhorn, A. L. Rheingold and S. J. Geib, J. Chem. SOC. Chem. Commun., 1988, 1027; R. C. Haushalter, C.J. O’Connor, J. P. Haushalter, A. M. Umarji and G. K. Shenoy, Angew. Chem., 1984, 97, 147; R. C. Haushalter, C. J. OConnor, A. M. Umarji, G. K. Shenoy and C. K. Saw, Solid State Commun., 1984, 49, 929. R. C. Haushalter, Thin Solid Films, 1983, 102, 2312. G. Cordier, H. Ochman and H. Schafer, J. Less-Common Met., 1986, 119, 291. G. Cordier, H. Ochman and H. Schafer, Rev. Chim. Mineral., 1985, 22, 58. G. Cordier, H. Ochman and H. Schafer, 2. Anorg. Allg. Chem., 1984, 517, 118. G. Cordier, H. Ochman and H. Schafer, Rev. Chim. Mineral., 1984, 12, 282. T. L. T. Birdwhistell, E. D. Stevens and C. J. O’Connor, Znorg. Chem, 1990, 29, 3892. B. A. Frenz, in Computing in Crystallography, ed. H. Schenk, R. Olthof-Hazenkamp, H. van Koningsveld and G. C. Bassi, Delft University Press, Delft, 1982. Zntenational Tables for X-ray Crystallography, Vol. Z V, Kynoch Press, Birmingham, 1974. Standard F374-84, in ASTM Annual Book of Standards, Vol. 10.05, 1986. L. T. Birdwhistell, B. Wu, M.-J. Jun and C. J. OConnor, Bull. Korean Chem. SOC., 1990, 11,464. Paper 1/00204J; Received 15th January, 199 1

ISSN:0959-9428    

DOI:10.1039/JM9910100555

出版商:RSC    

年代:1991

数据来源: RSC

摘要:

J. MATER. CHEM., 1991, 1(4), 559-562 Preparation of Novel Intercalation Compounds of Silver and Copper in Layered Perovskites, ALaNb,O, Tsuneo Matsuda, Tetsuya Fujita and Masahiko Kojima Department of Applied Chemistry, Faculty of Engineering, Saitama University, 338, Shimo-ohkubo, Urawa, Japan Novel intercalation compounds with silver and copper ions in the interlayers of layered perovskite-like parent materials, ALaNb,O,, have been prepared. Silver ions were readily intercalated by exchange between isovalent ions. Copper was intercalated by the reaction of copper(r1) nitrate aqueous solution with rrC8H,,NH,LaNb,0,. The attempted direct preparation of the sodium compound NaLaNb,O, by the ceramic method was not successful, but it could be easily synthesized using a simple ion-exchange method.The lattice parameters of the intercalated compounds were estimated, and these indicated that the crystal structure of the parent materials had been retained. The intercalated state of copper was also examined. The silver intercalation compound was stable on heating to ca. 750 "C in air without oxidation of silver, but decomposed at 760 "C. On the other hand, the copper and sodium intercalated compounds decomposed at ca. 700 and 670 "C, respectively. Keywords: Intercalation; Lan than urn niobium oxide ; Per0 vskite Recently, a new series of layered perovskite oxides, ALaNb,O, (A=alkali metal, H, NH4 and amines) has been reported,' one of a series of layered niobium corn pound^.^-^ These oxides have a layered perovskite structure consisting of LaNb,07 layers of two octahedra interleaved by A atoms and having ion-exchange properties.However, the syntheses of the new compounds by ion exchange with ions other than those cited above have not been reported. Consequently, we attempted to prepare the ion-exchanged or intercalated com- pounds of silver and copper and to examine the lattice parameters and the intercalated state of the ions of these new compounds. Furthermore, the thermal stability of the newly synthesized compounds was also examined. Since direct synthesis of the sodium-exchanged compound NaLaNb,O, (abbreviated as 'Na salt') failed, another prepara- tive method is reported in this paper. Experimental Synthesis of the Parent Oxides The parent oxides with A=K, Rb and Cs were prepared by heating mixtures of AzC03, Laz03 and Nb205 at 1100 "C for 1 day and for another day after grinding.However, the preparation procedure of KLaNb,07 (K salt), was partly modified as follows. Aqueous K2C03 solution containing ca. 25 mol% excess over the stoichiometric ratio and appropri- ate amounts of La203 (99.9% purity) and Nbz05 (the last two purchased from Wako Junyaku, analytical grade) were mixed and stirred for 1 day and then evaporated to dryness. The subsequent procedures were the same as described in the literature.' HLaNb,07 (H salt) was prepared by the reaction of ALaNb,07 with 6 mol dm-3 nitric acid at 60 "C. Prepared ALaNb,O, samples were confirmed to be in agreement with the X-ray powder diffractometry (XRD) result reported in the literature.' Intercalation of Silver The introduction of silver ions into the interlayer was carried out by reaction of the H salt with silver nitrate solution (5.71xlO-, mol dm-3) at 60 "C for 24 h with a molar ratio of silver to the H salt of 2.5: 1.The K salt was also used in the presence and absence of 2 mol dmP3 HN03. During the treatment, the reaction vessel was protected from light. The amounts of Ag taken up were determined by X-ray fluor- escence spectrometry. Intercalation of Copper The intercalation of copper was achieved by the reaction of copper nitrate solution (0.5 mol dm- 3, with intercalated com- pounds containing n-octylamine and n-C8H17NH3LaNb207 (oct-LaNbO) (molar ratio =2 : 1).The reaction was performed at 60 "C or refluxing temperature for 65 h. The amount of copper taken up was determined by analysing the quantity of copper released into solution by refluxing the intercalated compound with 3rnoldmp3 HN03 for 6h, followed by washing with a small quantity of HN03 of the same concen- tration and then with deionized water until no copper was detected in the washing. Analysis was carried out with a Shimadzu 670 atomic absorption spectrophotometer. Characterization of the Intercalated Products The properties of the solid products were examined by XRD, employing Ni-filtered Cu-Ka radiation (Rigaku Denki Rad C), X-ray fluorescence spectrometry (Rigaku Denki DS), IR spectroscopy (JASCO Model 8 10) and X-ray photoelectron spectroscopy (XPS) (Ulvac Phi, Model 558 UPESCA).The XRD measurements were carried out using Si as a standard reference, and values of diffraction angles >70 "C were used to determine the lattice parameters by a least-squares method. A thin disc (10 mm diameter) of the sample for IR measure- ment was prepared by pressing a mixture of the intercalated product with KBr (IR analytical grade). The XPS was recorded with Mg-Ka radiation; the C 1s level of a trace of contaminant carbon, 285.0 eV, was taken as a reference. Results and Discussion Intercalation of Silver The exchange reaction of A in ALaNbz07 (A=H and K) with Ag, especially in the case of A=K, proceeded well in the presence of nitric acid, indicating that acid would promote the exchange reaction.In the absence of acid a mixture of Ag and HLaNb,O, was obtained. The reaction of the K salt J. MATER. CHEM., 1991, VOL. 1 Table 1 X-Ray diffraction data of AgLaNb,O, essentially the same. The X-ray powder diffraction data of AgLaNb,O, (Ag salt) are shown in Table 1. The crystal hkl structure appears to be tetragonal and values of the a=b and 15.80 5.604 002 5.605 35 c parameters could be estimated as shown in the table. These 22.80 3.897 010 3.897 16 values are typical of the silver-intercalated compound. The 23.79 3.737 003 3.737 67 value of c is larger than that of the H salt, indicating an 24.16 3.680 01 1 3.681 10 expansion of the interlayer spacing. The IR spectra of the 27.85 3.200 012 3.200 100 products are shown in Fig.1. The broad peak at ca.3450-3 1.90 2.803 004 2.803 66 3550 cm-' can be attributed to water in the interlayers of the 32.47 2.755 110 2.756 25 33.19 2.697 013 2.697 50 Ag salt. The exchange of Ag in the reaction with the H salt 33.45 2.676 111 2.676 41 was 98.6%. 39.61 2.273 014 2.275 11 40.18 2.242 005 2.242 31 40.65 2.217 113 2.2 18 14 Intercalation of Copper 46.14 1.965 114 1.965 10 By the intercalation of a large molecule such as octylamine 46.57 1.948 020 1.949 39 48.67 1.869 006 1.868 9 into the interlayer spacing of the materials, the H salt can be 52.55 1.740 115 1.739 32 enlarged from 12.213 to 30.38A.I It is known that such 55.1 I 1.665 122 1.664 20 enlargement makes some compounds easy to inter~alate.~ 57.54 1.600 007 1.601 11 The reaction products of oct-LaNbO with Cu(N03), turned 024 1.600 brown from the white of oct-LaNbO.The amount of copper 58.36 1.579 123 1.579 18 incorporated at 60 "C and at reflux temperature was 0.955 62.64 1.481 017 1.48I 17 124 I .480 and 1.02 mol, respectively, per unit mol of oct-LaNbO, i.e. an 63.13 1.471 025 1.47I 10 exchange of ca.100%. The intercalation of copper could be 67.94 1.378 220 1.378 10 inferred, because the XRD peaks derived from oct-LaNbO 125 1.376 (denoted with a star in Fig. 2) disappeared. However, the 69.63 1.349 026 1.349 10 pattern was broadened especially in the high-diffraction-angle a=b=3.897 A, c=11.21 A.region so that it was difficult to determine the lattice param- eters precisely. This is probably because, even after the inter- calation of copper, the distortion caused by the enlargement of the basal spacing will remain. However, two characteristic peaks in the low-diffraction-angle region were detected, one at 28=7.1" (basal spacingzl2.1 .$) and another at 285~7.9" (11.2 A) as a shoulder indicated with the arrow symbol in Fig. 2. These characteristic peaks are due to the intercalated copper compounds. From the XPS results described later, 28=7.1" can be ascribed to (CuN03)+, which is the main intercalated ion, and 28 =7.9" to (CuOH)+. When the intercal- ation procedure was performed at reflux temperature, the peak at 28=7.1" disappeared and the peak at 28=7.9" was 1 I I I I enlarged to become the main peak, implying a slight shrinkage 4000 3000 2000 1500 1000 400 of the basal spacing.wavenumberkm-' The IR spectra of the reaction product together with oct- LaNbO are shown in Fig. 3(a) and (b).No peaks due to CH2 Fig. 1 IR spectrum of the ion-exchanged product with silver stretching (291 5-2940 cm- I) and deformation vibrations (1440-1480 cm- derived from octylamine could be detected with nitric acid to form the H salt proceeded well in times as [see Fig. 3(c)]. On the other hand, a peak assigned to NO3 short as 3 h. Presumably, the presence of nitric acid produces could be detected at ca. 1360 cm-' in the reaction product at the H salt at first and then the intercalated product with 60°C.Under refluxing cpnditions the peak due to NO3 silver. The XRD results for the products obtained by both decreased markedly [see Fig. 3(b)]. The broad peak at methods (AgN03-H salt and AgN03-K salt-HN03) were ca.3400-3550 cm-' assigned to water and/or OH [probably I 6 7 8 9 20 30 40 50 60 70 281" Fig. 2 XRD pattern of the reaction product of CU(NO~)~+~-C~H,~NH,L~N~,O~at 60 "C (*of n-C8Hl7NH3LaNb2O7).Note only the peak in the low-diffraction-angle region is shown in the figure; (1)see text J. MATER. CHEM., 1991, VOL. I 4000 3500 3000 25002000 1 500 1000 400 wavenumberkm -' Fig. 3 IR spectra of the reaction product of Cu(NO,),+n-C,H,,NH,LaNb,O, (a) at 60 "C, (b) at reflux temperature. (c) IR spectrum of n-C,H,,NH,LaNb,O, from the (CuOH)' ion] increased under reflux.As both NO3 and/or OH radicals could be detected in the intercalated product, the state of the copper in the interlayer was assumed to be (CuNO,)' and/or (CuOH)'. The XP spectra of Cu 2p in the product are shown in Fig. 4, together with those of CU(NO~)~. There is a complex set of peaks of Cu 2p,,,, referred to as satellites, between binding energies of 932.2 and 953.6 eV. These are characteristic of the Cu2+ valence ~tate,~,~ not appearing with Cu' and metallic copper. However, the peak at 932.2eV is very close to the binding energy of Cu2p3,, in CU~O,~.~ that is it may be attributable to univalent copper. Although the state of the univalent copper is still unclear, it may be formed by the reduction of CU(NO~)~ by octylamine intercalated in the interlayer.The peak at 934.4 eV, appearing in Fig. 4(a), can be assigned to Cu of (CuN03)+ in the interlayer, because it is in good agreement with the peak in the spectrum of CU(NO~)~.Another peak at 937.1 eV may be attributed to Cu 2p3,, in (CuOH)', since the binding energy of Cu 2p3,z is in good agreement with the corresponding value in CU(OH)~.~'This was confirmed by the fact that each linewidth between the peak at 937.1 eV and s1 (ca. 7.6 eV, see Fig. 4), is in good agreement with the values in the literature." From the above results two kinds of the intercalated compounds can be inferred; one is CuN03LaNb207 (1) and the other is 953.6 934.4 561 CuOHLaNb207(2).The formation of (2) is considered likely since the reaction of copper nitrate and octylamine in aqueous solution under reflux produced the dicopper trihydroxide nitrate, CU~NO~(OH)~.Thus, it can be concluded that the complicated nature of the copper-incorporated product is due to the presence of both Cu2' and Cu' ions. Ion-exchange reactions with ALaNb207 (A =K, Cs and H) using various copper salts Ccopper(r1) nitrate, chloride and acetate] in aqueous solution were attempted, but no interca- lated product with copper could be obtained, although the solid after such treatment was pale-blue. The reason why divalent copper ions cannot easily exchange with ions such as silver may be due to the difficulty in forming the 0 YllN0 binding structure in the interlayer.Since the bond length between two oxygen atoms situated at the top of two octa- hedral structures of an LaNb207 layer can be estimated to be ca. 3.8 A' on average and the bond length of Cu-0 is 1.72481,'' it is impossible to construct the 0,cu,O binding structure, hence the failure to intercalate the divalent copper ion. Only when Cu2' combines with anions such as NO, or OH-, is it possible to intercalate copper as a univalent ion. Ion Exchange with Sodium The direct preparation of the Na salt was attempted from the calcination of (a) a mixture of Na2C03, La203 and Nb205, (b) the precipitate obtained by adding lanthanum acetate aqueous solution to a mixture of C,H50Na and Nb(C2H50)5 in alcohol solution, and (c) a mixture as in (a) but adding a small amount of CaO as a sintering promoter.None of the methods described above led to the formation of the pure Na salt. The difficulty of the direct preparation of the Na salt by the ceramic method is probably due to its thermal instability, as suggested by Bhat. '* Accordingly, the ion-exchange reac- tion between an excess of NaOH aqueous solution and the H salt was tried at 60 "C for 48 h. The XRD pattern of the product obtained is shown in Fig. 5, from which the crystal parameters of the a=b and c axes could be estimated to be 3.896 and 25.69 A,respectively. These values are in almost exact agreement with those of NaLaNb207 -xH20, which was prepared by the molten-salt method.' Therefore, the easy formation of the Na salt may also be due to the easy exchange of univalent ions.Thermal Stability The silver-intercalated compound was stable up to 500 "C in air, although some extent of shrinkage of the c axis was observed due to the removal of water from the interlayer as shown in Fig. 6. The decomposition of the layered structure of the Ag salt was detected at 760 "C and in the decomposed products as shown in Fig. 7, the oxidized silver was not observed. From the thermogravimetric analysis (TG)the water content in the Ag salt was estimated to be 0.7 H20. In the case of the copper-intercalated compounds the I I I I I 955 950 945 940 935 930 925 binding energ yIeV 281' Fig.4 XP spectrum of (a)the reaction product in Fig. 2, (b)Cu(NO,), Fig. 5 XRD pattern of NaLaNb,O, .2Hz0 J. MATER. CHEM., 1991, VOL. I TG mg1'' 100 200 300 400 500 600 700 800 TI "C Fig. 6 DTA and TG of AgLaNb,O, .0.7H,O 0 O------l 10 20 30 40 60 70 281" Fig. 7 XRD pattern of AgLaNb,O, heat-treated at 800 "C in air: 0,AgNbO,; A, La20,; 0,NbzO,; A,LaNbO,; 0,Ag 7 8 9 20 30 LO 50 60 70 201" Fig. 8 XRD pattern of the reaction product in Fig. 2 heat-treated at 500 "C for 3 h in air products obtained both at 60°C and at reflux temperature were heated at 500 "C in air for 3 h. As seen in Fig. 8 only one peak at 28=8.32" (basal spacing= 10.6 A) by XRD measurement, could be observed, still maintaining the layered structure.However, by heat treatment at 700 "C for 10 h, decomposition of the compounds occurred, although the differential thermal analysis (DTA) and TG data (see Fig. 9) showed decomposition at ca. 730 "C. The DTA behaviour was not simple, probably owing to the complicated nature of the product. The broad exothermic peaks between 200 and 500 "C, accompanying the weight loss of ca. 0.48%, probably indicate a change in the intercalated copper ions or a reaction with water in the interlayer. The thermal behaviour of the Na salt was examined as shown in Fig. 10. The removal of water in two stages at ca. 100 and 160 "C was observed, with accompanying weight losses of 3.4 and 3.6%, respectively. The total content of water TG I 0 100 200 300 400 500 600 700 800 900 1000 TI "C Fig.9 DTA and TG of the reaction product in Fig. 2 I I 0 100 200 300 400 500 600 700 800 900 TI"C Fig. 10 DTA and TG of NaLaNb,07.2H,0 corresponded to NaLaNb207-2H20. This value is rather small compared with the result (3.4 mol) in the literature. At ca. 660-670 "C an exothermic peak was detected (see Fig. lo), indicating the decomposition of the Na salt, which was also confirmed by XRD measurements. The thermal behaviour of the intercalated compounds with copper, together with XPS measurements will be examined in further detail elsewhere. Partial support for this work from Nissan Science Foundation is acknowledged. We wish to thank Mr. Makoto Tokunaga for carrying out the XRD measurements and also Mr.Masaaki Ohsima for drawing the figures. References 1 J. Gopalakrishnan and V. Bhat, Muter. Res. Bull., 1987, 22, 413. 2 M. Dion, M. Ganne and M. Tournoux, Muter. Res. Bull., 1981, 16, 1429. 3 M. A. Subramanian, J. Gopalakrishnan and A. W. Sleight, Muter. Res. Bull., 1988, 23, 837. 4 M. Dion, M. Ganne and M. Tournoux, Rev. Chim. Mineral., 1986, 23, 61. 5 R. M. Barrer and D. M. MacLeod, Trans. Faraday SOC.,1970, 51, 1290. 6 A. D. Cross, An Introduction to Practical Infrared Spectroscopy,Butterworths, London, 1980, p. 80. 7 J. Haber, T. Machej, L. Ungier and J. Ziolkowski, J. Solid State Chem., 1978,25, 207. 8 S. Evans, E. L. Evans, D. E. Parry, M. J. Tricker, M. J. Walters and J. M. Thomas, Faraday Discuss. Chem. SOC.,1975, 58, 97. 9 T. Robert, M. Bortel and G. Offergeld, Surf: Sci., 1972, 33, 123. 10 D. C. Frost, A. Ishitani and C. A. McDowell, Mol. Phys., 1972, 24, 861. 11 Kagaku Binran (Handbook of Chemistry), ed. Chemical Society of Japan, Maruzen, Tokyo, 1984, p. 714. 12 V. Bhat, personal communication, 1988. Paper 1/00294E;Received 21st January, 1991

ISSN:0959-9428    

DOI:10.1039/JM9910100559

出版商:RSC    

年代:1991

数据来源: RSC

摘要:

J. MATER. CHEM., 1991, 1(4), 563-568 27AINuclear Magnetic Resonance Spectroscopy Investigation of Thermal Transformation Sequences of Alumina Hydrates Part 1.-Gibbsite, y-AI(OH), Robert C. T. Slade,*" Jennifer C. Southernb and Ian M. Thompsonb a Department of Chemistry, University of Exeter, Exeter EX4 4QD, UK Alcan Chemicals Ltd, Chalfont Park, Gerrards Cross, Buckinghamshire SL9 OQB, UK High-resolution 27AI magic-angle spinning nuclear magnetic resonance spectroscopy (MAS NMR) (78.15 MHz) spectra are reported for commercial and natural gibbsites and materials occurring in the thermal transformation sequences of gibbsite (boehmite; x, a and p-aluminas; calcines produced at 400, 700, 900 and 1000 "C). Separate peaks assignable to aluminiums in near-regular six- and four-co-ordination in oxygen are observed for the materials in which use of such sites is believed to occur.For p-alumina a third peak (at 27 ppm) is seen due to the presence of Al in five-co-ordination. Ic-Alumina may retain approximately hexagonal-close-packed oxygens (with a defect structure leading to a grossly asymmetric contributory line from four-co-ordinate Al) or may contain some five-co-ordinate Al (AIO,) in addition to AIO, and AIO, environments (and hence have oxygen packing deviating from h.c.p.). Distortions/disorders (when present) result in broader underlying signals and manifest themselves instrumentally for the most disordered systems as wings extending to either side of the central spectrum . Keywords: Gib bsite ; Ca lcina tion ; Deh ydroxyla tion; Alumina hydrate ; Nuclear magnetic resonance spectroscopy Alumina (Al,O,) and its 'hydrates' [the hydroxide y-Al(OH), and the oxy-hydroxide y-AlOOH] are commercially import- ant materials marketed both as dried hydrate and as calcined aluminas produced by heating.Gibbsite [y-Al(OH),, some- times known as hydrargillite] is the product of the Bayer process, and is itself used as a flame retardant/smoke sup- pressant in polymers, as a toothpaste filler, as a paper additive, in the manufacture of synthetic marble, in stabilisation of titania and as feedstock for the manufacture of other alu- minium chemicals including ceramic powders. Dehydroxyl- ation (during calcination) of gibbsite leads first to one or more transition aluminas with partially disordered structures (all based on close-packed oxygen layers with varying interstitial aluminium configurations) and varying residual hydrogen contents.These have their own particular applications, e.g. as high-surface-area sorbents or glass additives. As the calci- nation temperature increases, the structures become more ordered until the final transformation to the extremely stable corundum (a-Al,O,) form, which is itself used in abrasives, refractories, polishing, aluminous porcelain, technical and engineering ceramics and catalyst supports. The crystal structures of gibbsite [y-Al(OH),], boehmite (y-A100H) and corundum (a-Al,O,) are well known. Gibbsite is monoclinic (space group P2Jb :a =8.64 A, b= 5.07 A, c= 9.72 A, fl= 85"26').' The structure contains double layers of have examined the dehydration (strictly dehydroxylation) sequences of aluminium hydroxides during calcination e.g.ref. 4-13. There is still disagreement on the sequence of tran- sition alumina phases, the mechanism of dehydration and the structures of the transitional phases. It is generally accepted14 that in vucuogibbsite transforms via p-alumina (100-400 "C), q-alumina (270-500 "C), and &alumina (870-1 150 "C) In air it follows two paths: (i) via boehmite (60-300 "C), y-alumina (500-850 "C), &alumina (850-1050 "C) and &alumina (1050-1150 "C); (ii) via x-alumina (300-500 "C) and Ic-alumina (800-1150 "C). The relative proportions following these two paths depend on a number of factors (including gibbsite particle size, moisture, alkalinity, pressure, bed depth and heating rate).The various transformation sequences for gibbsite are illustrated in Fig. 1. Characteristic structures of transition aluminas are believed to be as follows: p-Alumina is considerably amorphous, with only a few diffuse lines in its X-ray powder diffraction pattern. in vacuo in air hydroxyl ions (each layer in hexagonal close packing) with aluminiums in octahedral co-ordination inside the layers in a pattern of hexagonal rings. The double layers stack to give an AB BA anion sequence. Boehmite is orthorhombic (space group Cmcm:a=2.87 A, b= 12.20 A, c= 3.69 A).2The struc- ture is isomorphous with lepidocrocite and contains octa- hedrally co-ordinated aluminiums, with the octahedral units linking to form complex layers and with hydrogens present ->+boehmite Y 6 --+ 8 as interlayer hydroxyl groups (i.e.attached to oxygens at top and bottom of the layers). The oxygens are approximately cubic-close-packed. Corundum is rhombohedra1 (space group R3c:a=4.76 A, c= 12.99 A).3 The structure contains oxygen in approximate hexagonal close packing with aluminiums in two-thirds of the octahedral sites. A number of studies utilising a wide variety of techniques I I I I II I 0 200 400 600 800 lo00 1200 TIT Fig. 1 Thermal transformation sequences for gibbsite. Temperature increases from left to right. Transition aluminas are denoted by the appropriate Greek symbol q-Alumina has cubic close packing (c.c.P.) of oxygens and is a defect spinel structure with A1 atoms in both tetrahedral and octahedral site^.'^,'^ &Alumina is monoclinic with approximately cubic close packing of oxygens and may also be related to the spinel structure.Aluminiums are in both octahedral and tetrahedral sites, but the ratio of tetrahedral A1 to octahedral A1 is higher than for q-alumina. y-and 6-aluminas are both spinel-related, with cubic-close-packed oxygens. y may be ordered or disordered with respect to the aluminium arrangement depending on the production con- ditions. The proportion of tetrahedral aluminiums increases through the sequence y, 6, 8 (as the calcination temperature is increased).x and IC aluminas both have hexagonal close packing (h.c.p.) of oxygens. x has a fairly diffuse X-ray powder diffraction pattern and contains a large number of stacking faults. Aluminiums are disordered over octahedral and tetra- hedral sites, with progressive filling of octahedral sites as temperature is increased. The advent of more routine multinuclear high-resolution NMR spectroscopy of solids is well known to have provided a powerful probe of the chemical environments of probe nuclei in condensed matter. We now present a systematic examination of A1 environments in gibbsite and its calcines (both single phase and polyphasic materials) via variations in the high-res~lution~~ A1 NMR absorption spectrum. Experimenta1 Materials A variety of gibbsites and gibbsite calcines were taken for examination using high-resolution NMR techniques.Some materials were commercial products, while others were pro- duced for this study. X-Ray powder diffraction patterns (Ni- filtered Cu-Ka radiation) for all materials were recorded using a computer-controlled Philips PW 1050 goniometer incorpor- ating accumulation of a variable number of scans. Gibbsites from three different origins were examined: two Bayer process gibbsites (BACO SF 7 and BACO UF 35 E) and a natural (Greek) gibbsite. The Bayer process products are highly crystalline, while the natural gibbsite is less crystal- line (with broader X-ray peaks). SF 7 has a medium particle size of ca.0.7 pm, with that for UF 35 E being ca.0.5 pm.UF 35 E has a lower soda content (0.14% Na20) than SF 7 (0.35% Na,O). Other single-phase materials used were as follows: commer- cial samples (BA Chemicals) of boehmite (BACO Cera Hydrate), a-alumina (BACO LS 2, mean particle size 7.5 pm) and X-alumina (BACO AA 101, median particle size 9 pm); p-alumina prepared from gibbsite UF 35 E by calcination in vacua at 200 "C. X-Ray powder diffraction patterns for single- phase materials are given in Fig. 2. Gibbsite SF 7 was calcined in air in a thin static bed to various temperatures with 2 h soak times at temperature and 5 K min-heating and cooling rates. X-Ray powder diffrac- tion patterns (Fig. 3) showed the presence of the following phases (categorised according to soak temperature): 400 "C, boehmite and palumina; 700 "C, y-and X-aluminas; 900 "C, 6-, 8-and Ic-aluminas (predominantly IC);1000 "C, 8-, IC-and a-aluminas.NMR Spectroscopy High-resolution MAS NMR spectra for 27Al (78.15 MHz) were recorded at ambient temperature using a Varian VXR300 spectrometer. A high spin-rate (Doty) probe was used with spin rates of ca.12 kHz. The use of high spin rates is essential in this work: use of a lower spin rate (such as the more usual J. MATER. CHEM., 1991 VOL. 1 I I I I I I (e ) 10 20 30 40 50 60 70 80 2ep Fig. 2 X-Ray powder diffraction patterns for single-phase materials (see text). (a) Gibbsite; (b) boehmite; (c) alpha; (d) chi; (e) rho ca. 3 kHz at the Larmor frequency in this study) would result in spinning sidebands within the shift range discussed below, and consequent difficulty in discussing the form of some of the spectra. A small signal due to A1 in the probe was subtracted from recorded spectra. Relaxation delays (0.5- 2.0 s) were more than sufficient to avoid saturation. Spectra are referenced to Al(H,O):+(aq.) and 46 r.f.pulses (liquid sample) were employed. Results and Discussion The magic-angle spinning removes the featureless internuclear dipolar broadenings characteristic of 'static' spectra. Each J. MATER. CHEM., 1991 VOL. I k---l-----L---’ I I I I I I I 10 20 30 40 50 60 70 80 2elo Fig. 3 X-Ray powder diffraction patterns for materials produced on calcination of gibbsite BACO SF 7 in air to various soak temperatures (see text).T/ “C:(a)400;(b)700; (c) 900; (d) 1000 27Al nucleus (I = 5/2) possesses a quadrupole moment, eQ, which will interact with non-zero electric-field gradients, eq, (determined by the charge distribution around the nucleus); that interaction is characterised by the asymmetry q of the electric-field gradient tensor and by the quadrupole coupling constant e2qQ/h [or the quadrupole frequency vQ : vQ = (3/20)x (eZqQ/h)for the 1/2+3/2 transition if q=O]. Usually, only the central +1/2+ -1/2 transition is observed by NMR spectroscopy. That transition is usually free of quadrupole effects to first order, but is subject to smaller second-order effects (including quadrupole shifts oQS)and the lineshape can be asymmetric in consequence.In this study, the linewidths for resonances in the spectra of calcines assignable to A106 are considerably greater than those of the more ordered materials (gibbsite, boehmite, corundum). This is consequent on the defect structures of the calcines, which lead to electric- field gradient (EFG) distributions at A1 sites. Discussions of 27Al spectra commonly neglect line-broadenings and oQs(the true field-independent chemical shift acs=uCG-uQs, where gCGis the centre of gravity of the observed lineshape). Ranges of chemical shift (acs)for A1 in various co-ordinations to oxygens in aluminosilicates have been given:I7 A104 (‘tetra- hedral’) 50-80, A105 (‘trigonal bipyramidal’) 30-40, A106 (‘octahedral’) -10 to + 20 ppm. Detailed consideration of second-order effects for the systems in this study would be problematic and further discussion of shifts is restricted to the position of observed peaks.The spectra in this study show clear similarities to those obtained from aluminosilicates and will be discussed in a manner entirely analogous to that used in discussion of those ~pectra.’~ Intensities of different lines in 27Al spectra cannot usually be simply related to relative populations in different environ- ments: A1 in near-regular geometries leads to the observation of distinct peaks at characteristic shifts but some lines (arising from A1 in low-symmetry environments) can be broadened (perhaps beyond observation) giving no distinct peak.Further- more, observed intensities can be affected by possible exci- tation of satellite transitions by the r.f. pulse and in the case of overlapping complex absorptions there is no non-arbitrary method for deconvolution of the unknown contributory line- shapes. It follows that information concerning the number and identity of distinct and observable A1 environments of near-regular geometry can be obtained (from the positions of observed peaks), but that in the general case (unknown lineshapes, etc.)relative populations in different environments cannot usually be deduced. It follows from the discussion above that peak positions will be slightly field dependent. Gibbsite Spectra for the two Bayer process products and for the natural sample are given in Fig.4. In order to present the data in the form leading to the maximum amount of derived information each spectrum is presented twice: the right-hand spectrum in each case is an expansion of the central features of the left hand spectrum. In each case the central absorption is asym- metric. Observed shifts of the peaks are 6.0 (SF 7), 4.7 (UF 35 E) and 4.4ppm (natural). These peak positions are fully consistent with six-co-ordinate (‘octahedral’) Al, as known from diffraction studies.’ Examination of the expanded (right-hand) spectra alone could suggest little difference between the two Bayer process products. Examination of the wider-shift-range spectra reveals an extensive side-band pattern in both cases, indicative of the breadth of the static (non-MAS) spectra in each case.In the case of UF 35 E a residual underlying broad (unnarrowed) component is evident, indicative of a proportion of A1 present being in low-symmetry environments (i.e. not in sites in 400 0 -400 100 0 -100 6 (PPW Fig. 4 27Al MAS NMR spectra (78.15 MHz) for commercial gibbsites (BA Chemicals) (a) BACO SF 7 and (b) BACO UF 35 E and (c) a natural (Greek) gibbsite 100 0 -100 I: Fig. 5 "A1 MAS NMR spectra (78.15 MHz) for (a)commercial (BA Chemicals) boehmite (BACO Cera Hydrate) and (b)or-alumina (BACO LS 2) crystalline gibbsite). This is likely to be a consequence of UF 35 E being a milled product, unlike SF 7. The lower crystallinity and lower purity of natural gibbsite manifests itself in considerable smoothing of the shoulder 400 0 -400 J.MATER. CHEM., 1991 VOL. 1 evident to high field (at ca. -13 ppm) of the peak in the Bayer process products. Boehmite The spectrum for synthetic boehmite is presented in Fig. 5. Side-bands extend to higher and lower fields. No underlying broad component is seen (i.e. all A1 are in the same environ- ment). The peak in the nearly symmetrical absorption occurs at 3.4 ppm, fully consistent with near-regular octahedral co- ordination of A1 as known from crystallographic studies.2 a-Alumina The spectrum for a-alumina (corundum) is also presented in Fig. 5. Side-bands extend to higher and lower fields. No underlying broad component is seen (i.e. all A1 are in the same environment).The peak occurs at 11.2 ppm, fully consist- ent with octahedral co-ordination of Al, as known from crystallographic ~tudies.~ The observation of a nearly sym- metrical line again corresponds to a more regular octahedral co-ordination of A1 than in gibbsite. X-Alumina The spectrum of X-alumina is shown in Fig. 6 in wide-shift- range and expanded forms. Peaks observed at 5.7 and 63.8 ppm are simply assigned to six-co-ordinate A1 and four- co-ordinate Al, consistent with the description of this material given in the introduction. There is a low-intensity broader component underlying the side-band structure, this being a result of the stacking faults (and lower local site symmetries) in this material. This component is, however, contained within the wide shift-window shown. This is not the case for the considerably broader underlying components (indicative of massively disordered regions) characteristic of Bayer gibbsite UF 35 E (see above) and of p-alumina and the gibbsite calcines in this study (see below).100 0 -100 l""1""I""I""I"' "1""1""1""1""1""1' 1000 0 -1000 100 0 -100 6 (PPm) Fig. 6 27Al MAS NMR spectra (78.15 MHz) for (a)x (BACO AA-101) and (b)p (200 "Cin uucuocalcination of gibbsite BACO UF 35 E) aluminas J. MATER. CHEM., 1991 VOL. 1 p-Alumina The spectrum of p-alumina is also shown in Fig. 6 in wide- shift-range and expanded forms. The massive disorder charac- teristic of this material is evident in the 'amorphous' X-ray pattern (Fig.1) and also in the high-intensity wings (unnar- rowed signal) in the absorption spectrum, those A1 in very distorted geometries giving rise to very broad spectral contributions. Examination of the expanded (right-hand) spectrum clearly shows three distinct peaks corresponding to A1 sites of near regular geometry. The peaks at 1.9, 27.2 and 54.4 ppm are easily assigned to six-co-ordinate, five-co-ordinate and four- co-ordinate Al, respectively. The slight upfield shift of the peak assigned to A105 relative to the chemical shift (acs) range cited above is a consequence of (a) the material not being an aluminosilicate, (b)the superposition of three absorp- tions (each broad) and (c) a positive (field-dependent) second- order quadrupole shift (aas).Assignment of a peak at ca. 30 ppm to A105 is unambiguous in the case of andalusiteI8 and has also been made in the case of a variety of thermally/ hydrothermally treated alumino~ilicates.~~ The presence of five-co-ordinate aluminium in an alumina has previously been reported for anodically formed amorphous alumina films (peak at 27-29 ppm, very similar to the value in this study)." It should be re-emphasised that the use of high spin rates is essential in this work. Use of a lower spin rate (ca. 3 kHz is more usual at the Larmor frequency in this study) would result in a spinning sideband close to the location of the peak assigned to five-co-ordinate Al, and consequent difficulty in deriving any conclusion as to the origin of that feature.Calcines of Gibbsite SF 7 The spectra for the calcines at 400, 700, 900 and 1000 "C are shown in Fig. 7 in both wide-shift-range and expanded forms. The wide rising wings (unnarrowed signal) evident in the wide-range spectra show that in each calcine some A1 is present in sites of highly irregular geometry. These underlying absorptions are, however, considerably less intense than in the case of p-alumina (above). None of the calcines analysed (X-ray diffraction, see above) as a single-phase material. The spectra therefore have to be discussed in terms of superposition of spectra for the various chemical components present. The spectrum for the 400°C calcine (contained boehmite and X-alumina) has peaks at 5.9 and 62.3 ppm, assigned to six- and four-co-ordinate Al, respectively.The spectra for boehmite and palumina themselves are discussed above. The absorptions for six-co-ordinate A1 in the different materials overlap in the mixture (calcine). The absorption assigned to four-co-ordinate A1 will arise solely from the X-alumina pre- sent. That the calcine differs from a simple admixture is evident on comparison of the wide-shift-range spectrum of the calcine with those of boehmite and X-alumina. The un- narrowed (underlying) component for the calcine is consider- ably broader than for either material, indicative of some A1 being present in more highly distorted environments than characteristic of either material on its own. The spectrum of the 700 "C calcine (containing x-and y-aluminas) has peaks at 6.8 and 62.7 ppm, assignable to six and four-co-ordinate Al, respectively.Both aluminas present are believed to have A1 present in both four- and six-co- ordination (see introduction) and the appropriate resonances for equivalent co-ordination numbers will overlap in the spectrum of the calcine. The spectrum for the 900°C calcine (predominantly IC-alumina) has peaks at 4.0 and 64.6 ppm (assigned to six- and four-co-ordinate Al, respectively) consistent with use of octa- jlI n --m"l--p ,.(..,.,.... ,,.. ,.,. .,,, , 400 h0 -400 100 0 ' -100 /I'I i\ i; L 400 -4 00 100 0 -100 Fig. 7 27Al MAS NMR spectra (78.15 MHz) for calcines of gibbsite BACO SF 7 produced with soak temperatures of (a)400, (b)700,(c) 900 and (d) 1000"C(see text) hedral and terahedral sites in an h.c.p. array of oxygens, as discussed in the introduction.In the area 30-70ppm the spectrum has an asymmetry evident in a shoulder at ca. 45 ppm. This could arise from the defect structure and the associated range of environments and consequent EFG distri- bution for Al0,-type sites, with a consequent marked asym- metry in the contributory lineshape. An alternative explanation is that some A1 in ic-alumina are in A105 environ- ments, leading to overlapping resonances arising from near- regular A106, A105 and A104. No spectral feature unambigu- ously assignable to A105 environments (which could result only from deviation of the oxygen packing from h.c.p.) is evident in the spectrum however.Overlapping is a major interpretational problem due to the widths of the two (reten- tion of h.c.p.) or three (deviation from h.c.p.) contributory lines; these will be broad and complex owing to the EFG distribution at each occupied A1 site type, and there is no realistic basis on which the contributory lineshapes can be modelled. Resolution of this problem is not possible with the instrumentation available in this study; spectra at a much higher field would improve the resolution of contributory lines, with further information also being available from spectra recorded using instruments enabling variable or dynamic angle spinning or double rotation. The spectrum for the 1000 "C calcine (containing 8-,ic-and a-aluminas) has a peak at 6.2ppm that is assigned to six-co- ordinate aluminium.In the shift region 30-70ppm some structure is apparent, with a peak 64.9ppm and another apparent maximum at 45.6 ppm. As discussed in the introduc- tion, 0 (c.c.P. oxygens) and IC (h.c.p. oxygens) are both believed to have A1 in both four- and six-co-ordination, while a has A1 only in six-co-ordination. The contributions from six-co- ordinate A1 in the various phases overlap. The peak at 64.9 pprn is assigned to overlapping contributions from four- co-ordinate A1 in the components of the calcine. The feature at 45.6 ppm is in the region associated with a shoulder in the contributory spectrum of the Ic-alumina component present (see above).The contributory spectrum of 0-alumina is not available. Conclusions High-resolution 27Al MAS NMR spectra reveal information about the sites occupied by A1 atoms in gibbsite and its derived calcines. A peak assigned to six-co-ordinate A1 is always observed. A second peak, assigned to four-co-ordinate Al, is also seen for those materials in which such sites are commonly believed to be used. In the case of the massively disordered and poorly understood p-alumina, a third peak is observed. That peak arises from the presence of some five- co-ordinate Al, as previously reported for anodically formed amorphous alumina. For calcines containing Ic-alumina, a shoulder or maximum at ca.45 ppm (upfield of the region usually associated with A104) may arise from a highly defective structure (and consequent changes in the shape and position of resonances arising from tetrahedral Al), but could indicate that the oxygen packing in that material deviates from h.c.p.by the introduction of five-co-ordinate A105 sites. Disorders resulting in A1 sites of much reduced symmetry manifest themselves in broad (incompletely narrowed) under- lying components in the spectra. For the most massively disordered/distorted systems the broad components manifest themselves instrumentally as wings extending well above and well below the central (narrowed) spectrum. Only those A1 in near-regular geometries give rise to the peaks in the preceding discussion. No information concerning the distorted geo-metries is available from the spectra.These are likely to be grossly distorted four- and six-co-ordinated aluminiums, but J. MATER. CHEM., 1991 VOL. 1 the possibility of similarly distorted five-co-ordinate alu-miniums cannot be ruled out for any of the materials whose spectra feature a broad background. R.C.T.S. thanks SERC for supporting the study of thermal transformation sequences under grant GR/E 8 1999 and for access to the national solid-state NMR service (University of Durham). We thank the staff of that service for recording high-resolution spectra. We thank the Laboratoire des Agre- gats Moleculaires et Materiaux Inorganiques (URA CNRS 79, Montpellier) for access to X-ray equipment. We thank BA Chemicals Ltd, and Alcan Chemicals Ltd, for supplying commerical-grade aluminas and hydrates. References H.D. Megaw, 2. Krist., 1934, A87, 185. P. P. Reichertz and W. J. Yost, J. Chem. Phys., 1946, 14, 495. R. E. Newnham and Y. M. de Haan, Z. Krist., 1962, 117, 235. R. Tertian and D. Papee, J. Chim. Phys., 1958, 55, 341. H. Saalfeld, N. Jb. Miner. Abh., 1960, 95, 1. G. W. Brindley and J. 0.Choe, Am. Mineral., 1961, 46, 771. B. C. Lippens and J. H. de Boer, Acta Crystallogr., 1964, 17, 1312. 8 J. Beretka and M. J. Ridge, J. Chem. SOC.(A), 1967, 2106. 9 S. J. Wilson, Proc. Br. Ceram. SOC., 1979, 28, 281. 10 H. Dexpert, J. F. Larne, I. Mutin, B. Moraweck, Y.Bertaud and A. Renouprez, J. Metal., 1985, 37, 17. 11 T. Sato, J. Thermal Anal., 1987, 32, 61. 12 G. D. Chunkin and Yu. L. Seleznev, Inorg. Muter., 1987,23, 374. 13 V. Jayaram and C. G. Levi, Acta Metal., 1989, 37, 569. 14 W. H. Gitzen, Alumina as a Ceramic Material, American Ceramic Society, Columbus, 1970. 15 E. J. W. Verwey, Z. Krist., 1935, 91, 65. 16 A. J. Leonard, P. N. Semaille and J. J. Fritpiat, Proc. Br. Ceram. SOC., 1969, 13, 103. 17 G. Engelhardt and D. Michel, High Resolution Solid-State NMR of Silicates and Zeolites, Wiley, Chichester, 1987. 18 E. Lipmaa, A. Samoson and M. Magi, J. Am. Chem. SOC., 1986, 108, 1730. 19 J. Gilson, G. C. Edwards, A. W. Peters, K. Rajagopalan, R. F. Wormsbecher, T. G. Roberie and M. P. Shattock. J. Chem. SOC., Chem. Commun., 1987, 91. 20 R. Dupree, I. Farnan, A. J. Forty, S. El-Mashri and L. Bottyan, J. Phys. (Paris), 1985, 46, C8-113. Paper 1/00304F; Received 22nd January, 199 1

ISSN:0959-9428    

DOI:10.1039/JM9910100563

出版商:RSC    

年代:1991

数据来源: RSC

摘要:

J. MATER. CHEM., 1991, 1(4), 569-576 Reinvestigation of the Nickel Phosphine Catalysed Electrochemical Synthesis of Poly(2,5=pyridine) X-Ray Crystal Structures of [Ni2Br2(p-5-BrC,H3N-C2,EI)2(PPh3)2]and [PtBr(5-BrC5H3N- C2)(PPh3)2] Nathaniel W. Alcock," Philip N. Bartlett," Vanessa M. Eastwick-Field," Graham A. Pike" and Paul G. Pringleb" Department of Chemistry, University of Warwick, Coventry, CV4 7AL, UK School of Chemistry, University of Bristol, Cantock's Close, Bristol BS8 1TS, UK Poly(2,5-pyridine) films have been deposited on glassy carbon, platinum and gold electrodes by the electroreduc- tion of a novel binuclear nickel complex, trans(PlN)-bis[bromo(~-5-bromopyridyl-C2,N)(triphenylphosphine) nickel(11)1. The synthesis, characterisation and electropolymerisation of this complex are described.The results from analytical and electrochemical investigations of poly(2,5-pyridine) are presented. The resultant poly(2,5- pyridine)-modified electrodes display electroactivity in their reduced state and co-ordinate nickel ions. The synthesis and electrochemistry of the analogous platinum and palladium complexes are also discussed. The X-ray crystal structures of the Ni and Pt complexes have been determined. The binuclear Ni complex contains Ni-(C,H,N)-Ni bridges, and the Ni atoms are also co-ordinated by one Br and one PPh,. The platinum complex is mononuclear with the Pt bound to the C, of the pyridyl ring, to Br and to two trans PPh, groups. Keywords: Conducting polymer; Oxidative addition; Poly(2,5-pyridine); Electroreductive polymerisation; Nickel complex It is well known that nickel@) complexes catalyse the chemi- or ele~tr~~hemi~al~-" coupling of aryl halides to give biaryls.The accepted mechanism for these reactions is sum- marised in Scheme 1. The nickel(o) complex undergoes oxidat- ive addition of the aryl halide to produce an aryl nickel@) species, which then undergoes ligand exchange to give two symmetrical species. In the presence of a reducing agent or excess aryl halide the product is the biaryl and the nickel(o) complex is regenerated. It is noteworthy that detailed mechanistic pathways pro- posed for this kind of coupling are varied and often inconsist- ent.3,7,12-16 This probably implies that there are several different mechanisms operating; the precise mechanism depending on the ligands on the nickel(o), the aryl halide, the solvent, and the presence or absence of excess ligand.It is likely that further complications arise because different reac- tion pathways will not be mutually exclusive. The judicious choice of an aryl dihalide can lead to the formation of a polymer. For example polyarenes have been made by electroreductive polymerisation (in the presence of a Ni(o) complex) of 1,4-dibromoben~ene,'~-~~2,Sdibrorno-reported to elucidate the reaction pathways. We are interested in understanding the electrochemical synthesis of polyarenes and believe that the synthesis and isolation of the polymeris- ation intermediates is an important step in achieving this aim.In particular, we have chosen to investigate the synthesis of poly(2,5-pyridine) based on the reductive electropolymeris- ation of 2,5-dibromopyridine in the presence of [Ni(PPh3)4].20 Poly(2,5-pyridine) is an interesting material for several reasons. First, the work of Schiavon et d2'has shown that the polymer is an electronic conductor in its reduced state. Although many examples of polymers which are conducting in their oxidised state are now known, reduced-state con-ducting polymers are much less numerous.28 Secondly, the material has the possibility of forming metal complexes by co-ordination of metals ions directly to the polymer backbone. Thirdly, the polymer has recently been shown to have interest- ing non-linear optical proper tie^.^' The first reported electrochemical synthesis of poly(2,5- pyridine)20 involved the preparation of a stock solution of anhydrous [Ni(CH,CN),] [C104]2 from a sacrificial nickel electrode in the presence of 0.1 mol dm-, tetrabutylam-pyridine,20q2' 2,6-dibr0mopyridine,~' 2,7-dibrornofl~orene,~~ 4,4'-dibromoben~ophenone,~~ 2,5-2,7-dibromofl~orenone,~~ 2,6-dibromona~thalene~~dibr~mothiophene,~~.~~ and 2,5-dibr~mofuran.~~However, little conclusive evidence has been 2X -Nil'-Ni"R, +Ni"X,R -monium perchlorate in acetonitrile.Reductive electrolysis of the stock solution after the addition of 10 equiv. of PPh, produced a solution of [Ni(PPh,),]. It was suggested that addition of 1 equiv. of 2,5-dibromopyridine to the [Ni(PPh,),] solution gave either or both of the organometallic intermedi- ates 1 and 2 although these were not characterised.Br\N/PPh3 R -X/eNi"R, -NiO+R -R Deposition of poly(2,5-pyridine) onto the working electrode Scheme 1 was achieved by a reductive potential step or by repetitive cyclic voltammetry in solutions containing 1 and/or 2 in the presence of an excess of PPh,. In this paper we report our reinvestigation of the mechanism of this polymerisation and show that stable, binuclear organo- nickel intermediates are involved. Bisaryl metal complexes increase in stability towards reductive elimination as the transition-metal triad Ni, Pd and Pt is de~cended.~',~~ Consequently, it was of interest to investigate whether the palladium and platinum analogues of the nickel complexes would produce polymers of type 3, and this work is also reported.Experimental Syntheses. All the solvents were reagent-grade quality and were further purified by distillation over calcium hydride (acetonitrile, dichloromethane) or sodium benzophenone (ben- zene, toluene, diethyl ether) under a nitrogen atmosphere. 2,5- Dibromopyridine (Aldrich Chemicals) was purified by subli- mation under a reduced pressure at 60 "C. Triphenylphosphine (Aldrich Chemicals) was used as received. Bis(cyc1oocta- 13-diene)nickel(o), [Ni( 1,5-~od),],~~ tetrakis(tripheny1phosphine)-palladium(o), [Pd(PPh,)4]33 and tetrakis(tripheny1phosphine)-platinum(o), [Pt(PPh,),] 34 were prepared as reported in the literature.All reactions were carried out with the exclusion of oxygen. J. MATER. CHEM., 1991, VOL. I to reflux (1 10 "C) for 4 h. The solid [Pd(PPh,),] dissolved and a cream-coloured product began to precipitate within 30min. After filtration, CH2C12 (15 cm3) was added to the solid product to give a dark suspension which was then treated with Florosil (0.5 g). After filtration, CH30H (10 cm3) was added to the clear-yellow solution and the CH2C12 evaporated off until crystals formed. The crystals were filtered and dried in uucuo over P205. The original filtrate was taken to dryness under reduced pressure to yield a yellow solid. The solid was dissolved in a minimum volume of CH2C12 (10 cm3) and precipitated by the dropwise addition of Et20 (20 cm3).This solid was worked up as described above to give a combined yield of 64% (1.16 g). Elemental analysis found: C, 45.33; H, 3.04; N, 2.12; Br, 24.34. Cak. for C46H36Br4N2P2Pd2: c, 45.62; H, 3.00; N, 2.31; Br, 26.39%. 31P-{1H) NMR 6, (162 MHz, solvent CDCl,, to high frequency of 85% H3PO4) 22.7 and 22.0 (ratio 1 : 10). 'H NMR 6, (220 MHz, solvent CDCl,, standard Me4Si) 8.71 (s, 2 H, H6), 6.60 [d, 2 H, J(HH)= 11 Hz, H3], 6.45 [dd, 2 H, J(HH)= 11 Hz, H4] 7.20-7.95 (PPh, signals). Preparation of trans-Bromo(5-bromopyridyl-C2)bis(triphenyl-phosphine)platinum(rI).A suspension of [Pt(PPh,),] (0.800 g, 0.643 mmol) in benzene (20 cm3) was treated with 2,5-dibromopyridine (0.165 g, 0.695 mmol). The mixture was heated to reflux (80 "C) for 24 h to give a yellow solution and a cream-coloured precipitate.After filtration, the solid product was redissolved in a mixture of C6H6-CH2C12 (1 : 1 v/v)(7 cm3), treated with charcoal and filtered. Et20-n-hexane Preparation of trans(P,N)-Bis[bromo(p-5-bromopyridyl-C2,N) (triphenylphosphine)nickel(~~)]. [Ni( 1,5-c0d)~] (1.02 g, 3.71 mmol) in acetonitrile (80 cm3) was added to a stirred solution of PPh, (9.91 g, 37.1 mmol) in acetonitrile (80cm3). Immediately an orange solution and a red precipitate formed. 2,5-Dibromopyridine (0.95 g, 4.01 mmol) in acetonitrile (5cm3) was added slowly to the mixture which was then stirred for 3 h at room temperature. The crude solid product was filtered off and then redissolved in CH2C12 (40 cm3).The resulting solution was filtered and reduced to ca. 7cm3. A dark-orange solid was precipitated by dropwise addition of CH30H. The solid was filtered off, washed with Et20 (40 cm3) and dried in uacuo over P205. The original filtrate was reduced to a minimum volume and more crude product was precipitated by the dropwise addition of CH30H. This solid was then recrystallised as before to give a combined yield of 21% (0.87 g). Elemental analysis found: C, 49.32; H, 2.51; N, 2.58; Br, 25.54. Calc. for C46H36Br4N2P2Ni2: c, 49.52; H, 3.25; N, 2.51; Br, 28.65%. 31P-{1H) NMR 6, (162 MHz, CDCl,, to high frequency of 85% H3PO4) 27.8 and 26.6 (ratio 20: 1). 'H NMR 6, (220 MHz, CDCl,, from Me4%) 8.85 (m, 2 H, H6), 6.54 [d, 2 H, J(HH)= 11 Hz, H3], 6.30 [dd, 2 H, J(HH)= 11 Hz, J(HP)=4 Hz, H4] 7.19-7.92 (PPh3 signals).Signals for the minor isomer were not observed either because of acciden- tal equivalence or because they were lost in the noise. Preparation of trans(P,N)-Bis[bromo(p-5-brornopyridyl-C2,N) (triphenylphosphine)palladiurn(~~].A suspension of [Pd(PPh,),] (1.745 g, 1.5 mmol) in toluene (25 cm3) was treated with 2,5- dibromopyridine (0.51 1 g, 2.1 1 mmol). The mixture was heated (3: 1 v/v) (4 cm3) was added to the clear pale-yellow solution causing the product to precipitate. After filtration, the product was washed with Et20 (2x5cm3) and dried in uucuo over P205. The original filtrate was evaporated to minimum volume under reduced pressure. Addition of Et20-n-hexane (3: 1 v/v) (4 cm3) caused precipitation of the crude complex, which was purified by recrystallisation from CH2C12-Et20 to give a combined yield of 34% (0.21 8).Elemental analysis found: C, 51.37; H, 3.58; N, 1.32; Br, 15.83. Calc. for C41H33Br2NP2Pt: C, 51.48; H, 3.48; N, 1.46; Br, 16.71%. 31P-{1H) NMR 6, (162 MHz, solvent CDCl,, to high frequency of 85% H3PO4) 21.9 ['JJPtP)=3133 Hz]. 'H NMR (220 MHz, solvent CDCl,, standard Me4%) 6.59 [d, J(HH)=6 Hz, H3], 6.44 [d, 1 H, J(HH)=6 Hz, H4) 7.25-7.88 (PPh, signals and H6). Electrochemistry. Cyclic voltammetry and chronoamperome- try were performed using a Thompson Electrochem potentio- stat (Ministat 251 28 V/1 A) and triangular-wave generator (Miniscan MSl) connected to a Gould XY/t recorder (series 60000).The electrochemical cells were of two types: the larger (25 cm3 working volume) was a jacketed cell with two com- partments separated by a glass sinter, the smaller (2 cm3) was an unjacketed single-compartment cell. Either a Teflon-shrouded glassy carbon (GC; area=0.200 cm2) or a Kel-F- shrouded platinum (area =0.387 cm2) disc (Oxford Electrodes) was used as the working electrode, with a platinum gauze counter electrode and a homemade Ag/Ag (AgC104,+ 0.01 mol dm-, in acetonitrile, E,,,=80 mV us. Fc/Fcf) refer- ence electrode. Bulk electrolyses were carried out using a large platinum gauze as the working electrode. Specular reflectance spectra of polymer-modified Pt disc electrodes were recorded at 21" to the surface normal (Perkin-Elmer A20X FT-IR spectrometer and specular reflectance accessory).All solvents for electrochemistry were analytical grade and were further purified either by distillation over calcium hydride under nitrogen (acetonitrile, dichloromethane) or by standing over powdered barium oxide for 3 days followed by distillation over alumina powder under nitrogen (dimethylformamide). J. MATER. CHEM., 1991, VOL. 1 Supporting electrolytes (tetraethylammonium perchlorate, TEAP, Fluka; tetrabutylammonium perchlorate, TBAP, Fluka; tetraethylammonium tetrafluoroborate, TEATFB, Ald- rich) were purified by reported procedure^.^^ Hexakis(dimethy1 sulphoxide)nickel(rI) perchlorate [Ni(DMSO),](C10,), was prepared by a literature method.36 Electrochemical polymerisation was attempted either by repetitively cycling the potential between preset limits or by stepping to a suitable reducing potential at both stationary and rotating-disc electrodes in a millimolar solution of the organometallic complex.A second approach, based on a modification of the procedure reported by Schiavon et uZ.,~' was adopted for the synthesis of poly(2,5-pyridine) in the presence of nickel. [Ni(PPh,),] was prepared in situ by reductive electrolysis of millimolar solutions of [Ni(DMSO),]-(C104)2 in acetonitrile containing 10 equiv. of PPh3 and 0.1 mol dmP3 TEAP. Addition of 1 equiv. of 2,5-dibromopyri- dine gave an orange solution which was used for subsequent electrochemical studies.Crystal Data (4a). C46H36Br4N2P2Ni2+2CHC13, M = 1115.8+238.7, triclinic, a= 12.743(8) A, b= 13.414(10)A, c= 16.758( 14) A, a =90.40(6)", p = 102.43(6)", y = 105.73(6)", U= 2686(2)A3 (by least-squares refinement on diffractometer angles for 15 automatically centred reflections, A= 0.710 69 A), space group Pi,2=2, pc= 1.67 g cm-3. Dark-orange tablets. Crystal dimensions 0.10 mm x 0.34 mm x 0.60 mm, ~(Mo-Ka)=40.5 cm-'. Crystal Data (7). C4,H3,Br2NP2Pt, M =956.6, triclinic, a= 12.167(6)A, b= 12.746(8)A, C= 13.280(8)A, a=90.538", p= 1 15.46", y = 107.24", U = 1753(2)A3 (by linear-squares refine- ment on diffractometer angles for 15 automatically centred reflections, i=0.710 73 A), space group Pi, Z=2, pc= 1.82g cm -'. Clear, well formed blocks.Crystal dimensions 0.19 mm x 0.18 mm x 0.23 mm, p(Mo-Ka) =64.2 cm- '. Data Collection and Processing. Siemens P2, four-circle diffractometer, 0-28 mode to 28 (max) of 50" with scan width +1.1 (28) around Kal-Ka, angles, scan speed 2-29" min-', graphite-monochromated Mo-Ka radiation; 4a: 5857 unique reflections [merging R =0.072 after absorption correction (max., min. transmission factors =0.44, 0.71)], giving 3352 with I >2a(I);7: 5953 unique reflections [merging R =0.038 after absorption correction (max., min. transmission factors = 0.78, 0.48)], giving 4878 with I >241). Structure Analysis and Refinement. The data for 7are in brackets. For both structures Pi was assumed and confirmed by successful refinement.Heavy atoms were located by the Patterson interpretation section of SHELXTL Plus37 and the light atoms were found on successive Fourier syntheses. Two chloroform solvate molecules were located in 4a. Anisotropic temperature factors were used for all non-H atoms. Hydrogen atoms were given fixed isotropic temperature factors, U = 0.08 A2. Those defined by molecular geometry were inserted at calculated positions and not refined. Final refinement was on F by cascaded least-squares methods refining 577 (424) parameters. Largest positive and negative peaks on a final difference Fourier synthesis were of height 0.76 and -0.64eA-3 C1.11 and -1.02eA-3 (near Pt)]. A weighting scheme of the form w= 1/[02(F)+gF2] [g=0.0012 (4a); g= 0.00086 (7)] was used and shown to be satisfactory by a weighting analysis.Final R and R, values were 0.0776 and 0.076 (0.038 and 0.039). Maximum shift/error in final cycle 1.38 (0.01). Computing was with SHELXTL Plus37 on a DEC MicroVax 11. Scattering factors are in the analytical form and anomalous dispersion factors were taken from ref. 38. Final 57 1 atomic coordinates are given in Table 1 and selected bond lengths and angles in Table 2. Results and Discussion Synthesis Treatment of [Ni( 1,5-c0d)~] with PPh3 in acetonitrile gener- ated a suspension of [Ni(PPh,),] to which was added 2,5- dibromopyridine. The red solid product that formed was shown by 31P-{'H} NMR spectroscopy to contain two compo- nents (6, 27.8 and 26.6) in the ratio ca. 20: 1.The main product was recrystallised from acetonitrile and its structure (as determined by X-ray crystallography, Fig. 1) was found to be binuclear with the trans arrangement shown in 4a. The ratio of the two products formed was not affected by adding up to 10 equiv. of PPh3, indicating that no equilibrium between mononuclear (1) and binuclear (4a) complexes is present. Most likely the other product is the other trans isomer, 4b. Br Br \ \ Br 4a Br Br Hence, we conclude that the reaction between 2,5-dibromo- pyridine and [Ni(PPh,),] yields the two binuclear complexes 4a and 4b rather than the two mononuclear complexes 1 and 2 postulated by Schiavon et aL2' The structure of 4a closely resembles that reported for a similar palladium complex.39 It contains square-planar Ni bound to Br, C2 of the pyridyl ring, PPh3, and N of the other pyridyl ring.The Ni2C2N2 ring is in boat form. Most dimensions are standard, but it is t Supplementary data available from the Cambridge Crystallo- graphic Data Centre: set Information for Authors, J. Muter. Chem., 1991, Issue 1. Fig. 1 Structure of 4a as established by X-ray crystallography (Hatoms omitted for clarity) J. MATER. CHEM., 1991, VOL. 1 Table 1 Atomic coordinates and equivalent isotropic displacement parameters atom 104 104 lo4 z lo3 U(eqY/A* atom 104 104 104 z lo3 U(eqY/A2 (a) For 4a Br(l) Br(2) Br(3) W4)Ni( 1) Ni(2) C1( 1 1) C1( 12) C1( 13) Cl(21) Cl(22) Cl(23) P(1) P(2) NU) N(2) C(1) C(2) C(3) C(4) C(5) C(6) C(7) C(8) (29) C(10)C(101) C( 102) C(103) C( 104) C( 105) C( 106) C(111) C(112) C(113) C(114) C(115) C(116) C(121) C( 122) C( 123) C( 124) C(125) C( 126) C(201) C(202) C(203) C(204) C(205) C(206) C(2 11) C(212) C(2 13) C(2 14) C(215) C(216) C(22 1) C(222) C(223) C(224) C(225) C(226) C(1A) C(W 22 14(2) 38 16(2) 535(2) 19332) 2270(2) 8 892(9) 92 12( 13) 10596(8) 801 7( 10) 58 15( 14) 6393( 12) 3242(4) 2904(4) 780(11) 1681(10) 949( 14) 83(14) -2343(2) -876( 16) -1034( 15) -183( 16) 15 1 I( 13) 988( 13) 698( 14) 888(16) 1389( 15) 3460( 14) 321 8( 14) 3213(16) 3497(20) 3786( 17) 3739( 14) 2848( 16) 1779( 16) 1453( 16) 219 l(23) 3278(2 1) 3617( 15) 4665( 14) 5570( 1 9) 6636(20) 68 10( 18) 5928(20) 484( 17) 3116(16) 2506(17) 2595(2 3) 3 190(28) 38 52( 2 1) 3827( 18) 41 94( 14) 4555(1 6) 5494(25) 6096( 24) 5748(20) 4805( 19) 2026( 14) 1 841 (1 5) 1088( 19) 472(2 1) 620( 19) 1402( 1 7) 936 l(24) 6627(29) 3422( 1) 2310(2) 2798(2) 2046(2) 2636(2) 7420(9) 5678(9) 7765( 10) 9377( 11) 8382( 10) 10357( 1 1) 1422( 3) 4300(3) 2497(9) 1 193(9) 2804(11) 3075( 1 1) 3090( 13) 2762( 13) 2523( 12) 920( 12) -1498(2) -110(13) -840( 12) -537( 14) 494( 13) 299( 12) -675( 15) -1527( 14) -1395(19) -4 19( 19) 424( 13) 947( 12) 794( 14) 370( 17) 130( 1 6) 319(14) 7 1 O(14) 2288( 12) 2 107( 15) 271 7( 19) 3533( 19) 3 742( 14) 3 1 30( 1 4) 4553( 14) 3819( 15) 397 3(24) 48 52(26) 5618(22) 5M6( 16) 4943( 13) 6046( 1 5) 65 15( 18) 5904(27) 4924(24) 4370( 15) 5075( 12) 5189( 1 4) 5626( 16) 6039( 17) 5969( 15) 5486( 12) 693 l(23) 9217(26) 4285(1) 1204( 1) 262 1 (2) 337(1) 3319(1) 1622(1) 3 19 l(6) 4051(11) 4582(8) I175(7) I236(8) 4058(2) 1490( 3) 2597(9) 1774(8) 1842(9) 13 19(9) 1555( 1I) 2306(11) 2821(10) 254 1(10) 2634( 10) 1974(11) 1239( 10) 1144(10) 3564(11) 3841(11) 33954 14) 2660( 15) 2352( 1 1) 2819(11) 5002(10) 5057( 1 1) 5742( 13) 6385( 13) 6353( 10) 5667( 12) 4423(9) 4228( 12) 4528( 13) 5047( 13) 5239(1 1) 4946(11) 454(10) 897( 1 1) -163(11) -962( 16) -1 123( 14) -551(20) 268( 13) 2228( 10) 2335( 13) 2899( 17) 3362(16) 3267( 14) 2705( 1 1) 1670( 10) 2436(11) 2602( 13) 2000( 19) 12 19( 15) 1035(11) 4 178(20) 785( 18) 66(I ) 75U)llO(1) 39U) 41(1) 103( 1) 216(7) 353( 1 4) 260(8) 245(9) 325( 12) 341(13) 39P) W2) 48(7) 42(6) 40(8) 36(7) 53(9) 55(9) 49(9) 40(8) 47(8) 56(8) 63(9) 54(9) 47(8) 59(9)71(10) 95(14) 76(11) 5l(9) 45(8)61(10) 82(11) 86( 12) 67(1 1) 64(9) 40(8)67( 10) 79( 12) 82( 12) 79( 10) 72( 10) 53(8)70( 10) 109( 16) 108(18) 115(17) 90(11) 5003)81(10) 112(15) 112(16) 96( 14) 75(10) 48(8) 55(9)78( 1 1) 102( 1 5) 85(12) 59(9)165(21) 158(21) (b) For 7 Pt( 1 ) Br( 1) Br(2) P(1) P(2) NU) C(1) C(2) C(3) C(4) C(5)C(111) C(112) C(113) C(114) C(115) C(116) C(121) C( 122) C( 123) C( 124) C(125) C( 126) C(131) C( 132) C(133) C( 134) C(135) C( 136) C(211) C(212) C(2 13) C(214) C( 2 15) C(2 16) C(221) C(222) C(223) C(224) C(225) C(226) C(23 1) C(232) C(233) C(234) C(235) C(236) 1266.8(3) 948.3(8) 1312.4(11) 32804 17) 1 168(7) 1439(6) 1166(8) 1445(8) 1747(8) 1764(7) -772(2) -2090( 7) -1897(8) -2923(9) -4 152(9) -4358(7) -1267(7) -1574(7) -1937(9) -1980(9) -1664(9) -1296(8) -962(7) -198 l(8) -2 103( 10) -1 2 56( I 2) -240( 1 1) -70(8) -3349(7) 3 179(7) 4 186(7) 4135(8) 3084(8) 2102(8) 2141(7) 43 7 5(7) 4138(8) 4966( 10) 6033( 10) 6241 (9) 5425(7) 4276(7) 5299(7) 6075(8) 58 60( 9) 4857( 1 0) 405 l(8) 2833.9(2) 774.1(6) 8014.5(8) 2427(2) 323 1.9( 14) 4936(6) 4457(6) 60 1 O(7) 65 74( 6) 6074(7) 5014(5) 1681(6) 1106(7) 51 l(7) 526(8) 1088(7) 1675(7) 3602(6) 4243(7) 5136(7) 5407(8) 4794(8) 3 893(7) 1592(6) 613(7) 40(8) 443(9)1406(9) 1962(7) 2954(6) 3521(6) 3239(7) 2410(7) 1845(7) 2 12 l(6) 4660( 6) 549 l(6) 6582(7) 68 16(7) 601 5(7) 4936( 6) 2443(5) 2349(7) 18 17(7) 1371(7) 1479(8) 1998(6) 2258.8(3) 2 1 65.0(9) 2536.7( 10) 2 140(2) 23 1 8.1 (1 6) 1415(6) 2354(6) 1487(7) 2480(7) 3415(7) 3359(6) 799(6) 25(7) -968(8) -125 l(9) -505(8) 493(7) 2370(6) 1530(7) 1660(8) 2634(9) 3471(8) 3379(7) 3188(6) 2906(8) 3759(11) 4867( 10) 5156(9) 4312(8) 922(6) 673(7) -351(7) -1146(7) -898(7) 120(7) 2850(6) 2199(8) 2632(9) 3694(8) 43 15(8) 3919(7) 3 1 7 1 (6) 3023(7) 371 l(9) 4567(8) 4750( 8) 4028(7) Equivalent isotropic U defined as one third of the trace of the orthogonalised Uijtensor.notable that the mean Ni-C distance [1.870(10)A] is shorter mers containing these metals could be made. 2,5-Dibromopy- than the overall mean (1.917 A) obtained by Orpen et ~1.~' ridine was added to [Pd(PPh,),] in toluene to give a product for 18 nickel-(aryl) bonds. that contained two components in the ratio 10: 1; addition of We have investigated the analogous palladium and platinum 10 equiv. of PPh3 to the mixture had no effect as detectable chemistry in order to determine whether precursors to poly- by 31P-{1H} NMR spectroscopy.The binuclear structures 5a J. MATER. CHEM., 1991, VOL. 1 Table 2 Bond lengths and angles (a)for 4a bond length/8i bond length/8i Br( 1)-Ni( 1) Ni(1)-P(1) Ni( 1)-C( 6) Ni(2)-N(2) 2.348(3) 2.212(5) 1.870(16) 1.918(11) Br(2)-Ni(2) Ni( 1)-N( 1) Ni(2)-P(2) Ni(2)-C(I) 2.371(4) 1.930( 14) 2.198(5) 1.869(20) bond angle/" bond angle/" ~ ~ ~~ Br( I)-Ni( I)-P( 1) P(1)-Ni(1)-N(1) P(1)-Ni(1)-C(6) Br(2)-Ni( 2) -P(2) P(2)-Ni(2)-N(2) P(2)- Ni( 2) -C(1) Ni( I)-N( I)-C( 1) Ni(2)-N(2)-C(6) 94.2(1) 174.9(4) 9 1.1 (5) 9 1.1(2) 177.45) 9 1.7( 5) 118.2( 12) 118.0(10) Br( I)-Ni( I)-N( 1) Br( I)-Ni( 1)-C(6) N( 1)-Ni( 1)-C(6) Br(2)- Ni(2) -N( 2) Br( 2)- Ni( 2)- C( I) N( 2)- Ni(2)- C(1) Ni(I)-N(1)-C(5) Ni(2)-C( 1)-N( 1) 90.9(4) 172.4(5) 83.9( 6) 9 1.2( 5) 173.44) 86.2(6) 121.8(11) 113.8(12) Ni(l)-C(6)-N(2) 113.9(10) (b)for 7 bond length/A bond length/8i Pt(1)-Br(1) Pt( 1)-P(2) 2.53 l(2) 2.3 16(3) Pt(I)-P( 1) Pt( 1)-C( 1) 2.3 I2(3) 2.0 13( 8) bond angle/" bond angle/" Br(1)-Pt(1)-P(1) P( 1)-Pt(1)-P(2) P(1)-Pt(1)-C(1) 88.1(1) 178.2(1) 88.9(2) Br(l)-Pt(l)-P(2) Br( 1)-Pt(1)-C(1) P(2)-Pt(l)-C(I) 91.8(1) 176.9(2) 9 1.3(2) and 5b, analogous to the nickel compounds 4a and 4b above, are assigned to the products.Br Br \ \ Br Br This is further supported by elemental analysis and 'H NMR spectroscopy (see Experimental). The crystal structure of a similar dipalladium complex 6 has been rep~rted.~' Addition of 2,5-dibromopyridine to [Pt(PPh,),] in benzene gave the mononuclear complex 7 as the sole product with no detectable amounts of binuclear complexes formed.The structure of 7 is unambiguously determined as the trans isomer with Pt bound to C2 of the pyridyl ring from 31P-{'HI, and 'H NMR spectroscopy, elemental analysis and X-ray crystallography, Fig. 2. As with 4a the Pt-C bond is somewhat short [2.013(8) A], compared to the mean for 35 distances (2.049 A) for platinum-(aryl) bonds.,' Electrochemistry of Ni System We begin by comparing the electrochemistry of the binuclear Ni complexes (4a, b) with the behaviour found for a mixture of electrochemically generated [Ni(PPh,),] and 2,5-dibromo- pyridine (see Experimental).Fig. 3(a) and (b)show repetitive cyclic voltammograms recorded at a platinum electrode for the two systems. In both cases we observe an increase in charge passed with each successive cycle consistent with the progressive deposition of an electroactive material on the electrode surface. Film growth is observed at potentials below -1.2 V. After 28 cycles a film is easily visible on the electrode surface and integration of the charge under the oxidation peak at -1.2 V in the cyclic voltammogram shows that more than 50 equiv. monolayers of material have been deposited. The similarity in the behaviour observed for the electrochemis- try of the binuclear Ni complexes 4a, b and for the reactive intermediate generated in situ in our experiments and in those of Schiavon et al.strongly suggests that 4a, b is the common intermediate in all three polymerisations. On extension of the cathodic switching potential to -2.35 V a second redox wave is observed which also increases with each successive cycle. At potentials more cathodic than -1.6 V the polymeric films are orange or orange-brown depending on the film thickness. At potentials positive of -1.2 V the polymer films change colour to yellow; a similar change is observed on exposure to oxygen. Films can also be grown by stepping the potential of the electrode from -0.5 V to potentials between -1.2 and -2.4 V. The most smooth and reproducible films are prepared by potential steps to -1.8 V at a stationary electrode in a millimolar solution of 4a, b and these growth conditions were preferred for subsequent studies.In background electrolyte, n Fig. 2 Structure of 7as established by X-ray crystallography (H atoms omitted for clarity) J. MATER. CHEM., 1991, VOL. 1 I -2 -1 0 EN 50 0 f a-50 -1 00 -1 50 I I I -1.5 -1 .o -0.5 0 EIV Fig. 3 Cyclic voltammograms for the nickel system recorded at 100 mV s-l at a platinum disc electrode in acetonitrile containing 0.1 mol dm-, TEAP: (a) 10 mmol dm-, binuclear nickel complexes 4a, b and 100 mmol dm-3 PPh,; (b) 1 mmol dmP3 Ni(o) generated in situ from [Ni(DMSO),](CIO,), in the presence of 10 mmol dm-, PPh3 followed by addition of 1 mmol dm- 2,Sdibromopyridine Fig.4, the coated electrodes show two broad cathodic peaks, (i) and (ii), which merge for the thicker films (~0.50C cmP2). The peak currents for both processes increase linearly with sweep rate, as expected for a surface-confined redox species.41 The corresponding anodic peaks (iii) and (iv) are less well resolved but are distinct for thin films (~0.15C cmP2). At potentials < -2.7 V the films dissolve and orange material can be seen streaming away from the electrode. At potentials >1.7 V the films come away from the electrode in flakes. Exhaustive electrolysis (until the current dropped to 5% of its original value) of the dinuclear nickel complexes 4a, b to form a polymeric deposit at a large-area platinum gauze held at -1.8 V in a stirred solution showed that 1 mol electrons was required per mole of nickel.This is consistent with the following stoichiometry for the overall reaction 4a, b +2e- +poly(2,5-pyridine) +2 Ni' +4Br -Addition of a five-fold excess of 2,5-dibromopyridine did not alter the stoichiometry of the polymerisation showing that the nickel@) is unable to undergo oxidative addition with the excess 2,5-dibromopyridine; this may be because the nickel is bound to, or trapped within, the polymer. Our results are not 2PPh3+4a+2e -f t!:7q+2Br-PPh3 1 f -@)-+ Ni1Br(PPh3)3 -2 -1 EN Fig. 4 Cyclic voltammogram of the as-grown polymer film recorded at 200 mV s-l on a platinum electrode in acetonitrile containing 0.1 mol dm-, TEAP consistent with the suggestion of Schiavon et aL2' that the reduction involves two electrons per nickel centre to generate Ni(o).A mechanism for the formation of polymer, consistent with our results, is shown in Scheme2 where we postulate the involvement of an organonickel(u1) intermediate which undergoes reductive elimination of poly(2,5-pyridine). This elimination may occur after the polymer has formed, as shown in the scheme, or during the formation of the polymer. Organonickel(II1) intermediates are common in phosphine- nickel(o) catalysed coupling of aryl bromides." Assuming that the reduction of the binuclear nickel complex is a two-electron process, we calculate its diffusion coefficient from cyclic voltammetry to be 3.2 x cm2 s-'.Nickel and PPh3 were extracted from the films by soaking in EDTA (0.01 mol dm-3 aqueous solution buffered to pH 9.2) for 30 min, followed by washing in water, ethanol and finally acetonitrile. The treated films show significantly differ- ent cyclic voltammetry in the background electrolyte (Fig. 5). Comparison with Fig. 4 shows that peaks (i) and (iv) are no longer present and that peaks (ii) and (iii) are much sharper (EPII1= -2.29 V; AEp=0.36 V; ip/v constant). The original form of the cyclic voltammetry can be restored by soaking the film in a solution of 1 mmol dm-3 [Ni(DMSO),][ClO,], containing 10mmol dm-3 PPh3 in acetonitrile for 30min. Typically, removal and subsequent replacement of the Ni leads to ca. 50% reduction in the redox capacity of the film, I I I0.5---Oe5-1.0 t v.-I I I I -2 -1 EIV Fig.5 Cyclic voltammogram of the polymer film after treatment with aqueous EDTA recorded at 200 mV s-l on a platinum electrode in Scheme 2 acetonitrile containing 0.1 mol dm-, TEAP J. MATER. CHEM., 1991, VOL. 1 probably as the result of dissolution of the polymer. Based on these observations we conclude that the redox activity at ca. -1.35 V [peaks (i) and (iv)] is associated with Ni bound within the polymer film and that this Ni can be removed and replaced within the film. The redox activity at ca. -2.29 V [peaks (ii) and (iii)] is associated with oxidation and reduction of the polymer itself and occurs in the presence and absence of bound Ni.Specular reflectance FTIR spectra of the film-coated Pt electrodes, Fig. 6, show bands corresponding to the presence of aromatic rings at 1468, 1439 and 837 cm-', the latter being consistent with 1,4-disubstitution of the pyridine ring.42 The presence of PPh, in the as-grown films is also confirmed by absorptions at 1098, 738 and 697 cm- ' which are noticeably absent for the EDTA-treated films. The intensity of the bands attributable to TEA+ and ClO, from the background electro- lyte varies with the oxidation state of the film. For the reduced film (removed from solution at -1.8 V) there are strong bands due to TEA' (1098 cm-I); for the oxidized film (removed from solution at -0.5 V) there are strong bands due ClO, (620 and 1098cm-').In both cases residual absorption due to the other counterion is also observed. The absorption band centred at 1098cm-' is broad because PPh,, TEA' and ClO, all absorb in this region. Electrochemistry of Pd and Pt Systems The Pd and Pt complexes are only slightly soluble in acetonit- rile and so dirnethylformamide was used as the solvent for the electrochemistry. Fig. 7 shows a cyclic voltammogram for the binuclear Pd complexes 5a, b. On the first anodic cycle starting from 0.0 V there are two irreversible oxidations at 0.44 and 1.08 V. On the cathodic cycle there are four irrevers- ible reductions. The first of these at -1.66 V is associated with a solution product of the oxidation at 0.44V. The remaining three reductions at -2.04, -2.40 and -2.68 V are associated with the Pd complexes 5a, b and are present on an initial cathodic sweep from 0.0 V (not shown).Associated with the irreversible reduction of 5a, b at -2.04 V there are two oxidation processes of solution products in the subsequent anodic scan at -0.46 and 0.72 V. The oxidations at 0.44 and 1.08 V appear to be associated with the oxidation of the Br- and are not present in the electrochemistry of the analogous I I I 1 I 1 1 1 -2 -1 0 1 EIV Fig. 7 Cyclic voltammogram of the dinuclear palladium complexes 5a, b, 5 mmol dm-3, recorded at 50 mV s-' on a glassy carbon electrode in DMF containing 0.1 mol dm-3 TEAP chloro compound. Analysis of the variation of peak height with square root of the sweep rate for the main reduction peak at -2.04V gives a diffusion coefficient of 3.2 x lo-' cm2 s-' assuming n=2.This agrees with our result for the corresponding nickel compound. On repetitive cycling through the reduction peak at -2.04V, with and without a 10-fold excess of PPh,, the current slowly decays and a thin visible film is deposited at the electrode. However, there is no evidence for any electrochemical activity of this film in back- ground electrolyte. Fig. 8 shows the cyclic voltammogram for the mononuclear platinum complex 7. There are two irreversible reductions at -2.58 and -3.00 V. On the subsequent anodic scan there are two oxidations at -0.48 and 0.40V associated with the oxidation of solution products formed from the reduction of 7.Analysis of the variation of the peak height with the square root of the sweep rate for the main reduction peak at -2.58 V gives a diffusion coefficient of 2.1 x lop7 cm2 s-' assuming n =2. Repetitive cycling through the reduction peak, with and without an added 10-fold excess of PPh,, provided no evidence for the formation of a film at the electrode surface. Conclusions Oxidative addition of 2,5-dibromopyridine to Ni(o) in the presence of excess PPh, gives a mixture of two species in the ratio 20 : 1 as shown by ,'P NMR. The major species is shown by X-ray crystallography to be the binuclear nickel(I1) complex I I I 'I II d I & L 1800 1600 1400 1200 1000 800 600 F/cm-' Fig.8 Cyclic voltammogram of the platinum complex 7, 5mmol Fig.6 Specular reflectance FTIR spectrum of the as-grown film on dmP3, recorded at 50 mV s-' on a glassy carbon electrode in DMF a platinum electrode removed from the growth solution at -1.8 V containing 0.1 mol dm-3 TEAP 576 4a; the minor species is probably the other trans isomer, 4b.Using this mixture we have shown that these intermediates can be reduced electrochemically at -1.8 V vs. Ag/Ag+ to give a polymeric film on the electrode which is indistinguish- able by infrared spectroscopy and electrochemistry from the film formed by the in situ generation of Ni(o) in the presence of PPh3 and 2,5-dibromopyridine. Exhaustive electrolysis of the mixture shows that the polymerisation requires one elec- tron per nickel atom.We have isolated the corresponding mixture of binuclear palladium complexes (5a, b) and investigated its electrochemis- try. In this case there is no evidence for the formation of conducting polymer films. Finally we have investigated the corresponding platinum chemistry and isolated and character- ised by X-ray crystallography and NMR the mononuclear platinum complex 7. Again there is no evidence for the production of a conducting polymer film on electrochemical reduction of this complex. We thank SERC (21st century materials initiative) for a studentship for V. E-F. and Johnson Matthey for the loan of precious-metal salts. References 1 K. Takagi, N. Hayama and K. Sasaki, Bull. Chem. SOC. Jpn., 1984, 57, 1887. 2 M. Tiecco, L. Testaferri, M.Tingoli, D. Chianelli and M. Montanucci, Synthesis, 1984, 736. 3 T. Tsou and J. Kochi, J. Am. Chem. SOC., 1979, 101, 6319. 4 M. 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Allen, 0.Kennard, D. G. Watson and R. Taylor, J. Chem. SOC., Dalton Trans., 1989, S1. 41 A. J. Bard and L. R. Faulkner, Electrochemical Methods, Wiley, New York, 1980, p. 521. 42 R. Silverstein, G. Bassler and T. Morrill, Spectrometric Ident$- cation of Organic Compounds, Wiley, New York, 4th edn., 1981. Paper 1/00398D; Received 29th January, 1991

ISSN:0959-9428    

DOI:10.1039/JM9910100569

出版商:RSC    

年代:1991

数据来源: RSC

摘要:

J. MATER. CHEM., 1991, 1(4), 577-582 Zirconium Compounds as Coatings on Polystyrene Latex and as Hollow Spheres Nobuo KawahashiJ Christina PerssonS and Egon Matijevic* Department of Chemistry, Clarkson University, Potsdam, NY 13699, USA Cationic and anionic polystyrene latices have been coated with uniform layers of zirconium compounds by ageing, at elevated temperatures, dispersions of the polymer colloid in the presence of aqueous solutions of zirconium sulphate, formamide, urea, and poly(vinylpyrro1idone). The thickness of the deposited layers could be altered by suitable adjustment of the reactant concentrations. It is suggested that the mechanism fob the formation of the coating shell is based on heterocoagulation between the latex and in situ precipitated inorganic particles.Hollow colloidal spheres of zirconium compounds were obtained by calcination of the so-coated polystyrene latices at elevated temperatures in air. Keywords: Coated particle ; Colloid; Latex; Zirconium In recent years, several papers have been published on the preparation of composite particles consisting of cores covered with shells of different chemical composition. Since the active surface sites can be altered by appropriate coatings, the properties of these dispersions (magnetic, optical, electric, adsorptive etc.) may be adjusted to meet specific requirements for a given application. Previous studies have shown that inorganic cores can be enveloped with shells of either inorganic'-5 or organic mater- iak6 Moreover, procedures have been described to coat polystyrene particles with inorganic compounds,' which makes it possible to extend the use of these colloids in different areas of high technology.Because of their lower density and optical properties, hollow particles have been of interest as fillers, coatings, capsule agents etc. Several techniques for the preparation of such polymer spheres have been In contrast, only few reports have dealt with the processes for the generation of hollow inorganic particles, which include dehydration and decomposition of copper sulphate pentahydratel29 l3 and the diffusion of solvents from cores of alumina and titania par- Inticle~.~~a novel approach, it was shown that hollow inorganic colloidal spheres of a narrow size distribution could be obtained by decomposition of the polymer core of poly- styrene particles coated with basic yttrium ~arbonate.'~ This study demonstrates that the described process can be applied to other systems. Thus, under certain conditions zirconium compounds can be deposited uniformly on poly- styrene latices by precipitation, using the corresponding salt solutions in the presence of formamide and/or urea.Hollow zirconium oxide particles of a narrow size distribution can then be obtained by calcining such coated particles at elevated temperatures in air. Experimental Materials Zirconium sulphate [99.9% reagent grade ZT(SO~)~ *4Hz0, Aldrich], 2,2'-azobis(2-methylpropionitrile)(AIBN, Aldrich), potassium persulphate (Aldrich), urea (Fisher), formamide (990/,,EM Science), poly(vinylpyrro1idone) (PVP, average mol.wt. =360 000, Aldrich), styrene (Aldrich) and commercial t On leave from the Japan Synthetic Rubber Company, Tsukuba, Japan. $ Participant of the CHUST Program, Stockholm, Sweden. grade Triton X-100 (Rohm and Haas) were used without further purification. Preparation of Particles Polystyrene Latices A cationic (PS-C) and an anionic (PS-A) polystyrene latex, used as core particles, were prepared by batch polymerization using conditions described previ~usly.~ Fig. l(a) shows the electron micrograph of the so-obtained PS-C colloid polymer. Colloidal Zirconium Compounds As the first step in the preparation of coated particles, the nature of the precipitates found in solutions of zirconium salts, in the absence of latex, was investigated employing a procedure developed ea~-lier.~,~ Basic zirconium sulphate par- ticles of reasonably uniform size and nearly spherical shape were obtained by ageing, at 70 "C for 5 h, a solution 5 x 10-mol dm -in Zr(SO& and 1 .O mol dm -in formam- ide, containing 0.9 wt.% PVP.The electron micrograph of Zrz(OH)6S04 particles, prepared by this procedure, is given in Fig. 1(b). Basic zirconium carbonate dispersions were obtained by ageing, at 70°C for 8 h, a solution 1 x 10-mol dm -in ZT(SO~)~, 1.5 mol dm -in formamide, and 0.72 mol dmP3 in urea, containing 0.9 wt.% PVP. Since the pH of solutions after ageing was >6, the sulphate group co-ordinated by the zirconium ion was completely replaced Fig.1 Transmission electron micrographs (TEM) of (a) polystyrene latex (PS-C) particles used as cores, and (b) basic zirconium sulphate particles prepared by ageing at 70 "C for 5 h a solution 5 x mol dm-3 in Zr(SO,), and 1.0mol dm-3 in formamide, containing 0.9 wt.% PVP by the carbonate ion.'6-18 Properties of these solid zirconium compounds are described later. Coated Particles It was demonstrated that haematite particles could be coated with zirconium compo~nds,~ by dispersing preformed col- loidal cr-Fe203 in zirconium salt solutions and treating the system in a manner similar to that described in the previous section. To produce analogous coatings on latex, the reaction was carried out in Pyrex test tubes tightly closed with Teflon- lined caps and heated in a forced-convection oven.It was found that the order of adding reagents was important in preventing aggregation of core particles. First, doubly distilled water, urea, and formamide were mixed in a test tube, followed J. MATER. CHEM., 1991, VOL. 1 was lowered to ca. 2 by adding 5 x mol dm-, HNO,, but this treatment caused PS-C particles to aggregate. Formamide System. In a second series of experiments urea was replaced by formamide, while the other parameters were kept essentially the same. Fig. 2 summarizes the results obtained in terms of ZT(SO~)~ and formamide concentrations at constant amounts of the PS-C latex (0.25 g drn-,) and PVP (0.9 wt.%).The dashed boundary delineates conditions yield- ing spheres with smooth coatings. Outside this region, mixed dispersions consisting of coated latex and separate particles of zirconium compounds are found. It is evident that successful coating was strongly dependent on the concentration of by PVP and polystyrene latex. After sonication, ZT(SO~)~ solution was gradually (ca. 1-2 min) added to this dispersion. In a typical experiment, the volume ratio of the premixed dispersion to the zirconium salt solution was 9: 1. After ageing for different times (2, 5, 8, 15, and 21 h) and at different temperatures (50, 70, or 90 "C),the system was quenched in cold water to discontinue the reaction. The resulting disper- sions were centrifuged at 3000 rpm for 30 min, the supernatant solutions discarded, and the particles resuspended in doubly distilled water in an ultrasonic bath.This process was repeated five times and the so-purified precipitates were dried in a desiccator. Hollow Particles Recently, hollow spherical particles of yttrium compounds were obtained by coating a polystyrene latex with basic yttrium carbonate layers and subsequent calcination at elev- ated temperatures in air." The same procedure was used in this study. To produce hollow 'zirconia' particles, the polymer coated with the zirconium compound was calcined for 3 h in air in a furnace either at 500 or 800 "C at the rate of 10 "C min-'. Analyses The average size of the dispersions was determined by trans- mission electron microscopy.The coated and hollow particles were examined by infrared (IR) spectroscopy, X-ray diffraction (XRD), differential thermal analysis (DTA) and thermogravi- metric analysis (TG). The weight loss of all solids was also determined by heating for 3 h samples of known weight in a furnace at different fixed temperatures (up to 800 "C). The powders were removed, weighed again, and returned to the furnace for additional temperature treatment, until no further change took place. Electrokinetic measurements, using the DELSA 440 instru-ment (Coulter Electronics), were carried out with all disper- sions as a function of the pH at a constant ionic strength (O.Olmo1 dmP3 NaNO,). Results Preparation of Coated Particle Cationic Polystyrene Latex Cores Urea System. To investigate the effect of urea on coating cationic polystyrene (PS-C) latex with zirconium compounds, a suspension of 0.1-0.4 g dm-3 of PS-C particles in a solution of 5 x 10-4-1 x mol dmP3 ZT(SO~)~, containing 0.5-3.0 mol dm-3 urea and 0.9 wt.% PVP, was aged for 2-21 h at temperatures varying from 50 to 90 "C.In all samples, mixed dispersions consisting of coated solids and separate zirconium compounds were found. In order to delay the onset of precipitation of the latter, the pH of the original solution Zr(S04)2. When the latter was sufficiently high, the precipi- tation of zirconium compounds was too fast for the generated solids to be consumed in the deposition process alone.The domain given in Fig. 2 also depends on the amount of the preformed core material used in a given system. For example, with more latex, a somewhat higher concentration of zir- conium sulphate will produce only coated particles. It is also to be expected that the thickness of the shell will depend on the ratio of the concentrations of the cores to the coating reactants. Temperature was another important factor in obtaining a good coating of the PS-C latex. Temperatures 290 "C enhanced the decomposition of formamide, which accelerated the hydrolysis, resulting in mixed dispersion; thus, the opti- mum ageing temperature was 70 "C. Combination System (Formamide and Urea). In order to alter the chemical composition of the inorganic shell, coatings were carried out in solutions containing large amounts of both formamide and urea (1.45 mol dm-, total).Fig. 3 displays the results obtained in terms of the ZT(SO~)~ concentration and the ratio of concentrations of the two additives in the presence of 0.25gdrn-, of PS-C latex and 0.9 wt.% of PVP. The dashed boundary delineates conditions yielding spheres with smooth coatings, which depend on the concentration of the MIs sI I S! M M I I I I Mt'3: M ME MM I I I I I I I 0 0.001 0.002 0.003 [Zr(SO,),]/mol dm-3 Fig. 2 Precipitation domain for systems containing varying amounts of Zr(S04)2 and formamide in the presence of 250 mg dm-3 PS-C latex and 0.9 wt.% PVP, aged at 70 "C for 5 h.S=smooth-coated latex; M =mixed systems J. MATER. CHEM., 1991, VOL. 1 I I s: (6.6) I I I I I M M 0 0.001 0.002 0.003 [Zr(SO,),] /mol dm-3 Fig. 3 Precipitation domain for systems containing varying amounts of Zr(SO,),, and different formamide to urea ratios in the presence of 250 mg dm-3 PS-C latex and 0.9 wt.% PVP, aged at 70 "C for 5 h. S =smooth-coated latex; M =mixed systems. Data in parentheses represent pH values after ageing Zr(SO& as well as on the content in formamide. Since on ageing the pH increased above 4 (as shown in Fig. 3), the shell layers of coated particles were partially altered from Zr,(OH),SO, to Zr202(0H)2C03,53'5-'7 while at pH >6 only Zr202(0H)2C03 formed on the PS-C latex. Table 1 summarizes the results obtained under several sets of experimental conditions, and the transmission electron micrographs in Fig.4(a)-(c) illustrate these samples. Anionic Polystyrene Latex Cores In order to coat PS-A particles with zirconium compounds, the latter needed to bear a positive charge, a condition which required careful control of reactant concentrations. Since the isoelectric point (i.e.p.) of the zirconium compounds of interest was at pH 4.5 and 3.3, respectively (Fig. 9, later), only small amounts of formamide or urea could be used in order to maintain the systems sufficiently acidic. ahen a broader range of reactant concentrations was investigated, successful coating resulted with 0.1-0.4 g dm-3 PS-A particles suspended in solutions containing 1 x 5 x 10-mol dm- Zr(SO&, 0.25-0.50 mol dm-3 formamide, and 0.9 wt.% PVP, aged at 70 "C for 5 h.In all cases, in addition to the coated latex, a very small amount of tiny Fig. 4 TEM of particles obtained by ageing at 70 "C for 5 h a dis- persion consisting of: (a)400 mg dm-3 PS-C latex, 5 x lo-, mol dm-3 Zr(SOJ2, 1.0 mol dm-3 formamide, 0.72 mol dm-3 urea, and 0.9 wt.% PVP (sample 1, Table 1); (b) 250 mg dm-3 PS-C latex, 1 x mol dm-3 Zr(SO,),, 1.0 mol dm-3 formamide, 0.45 mol dm-j urea, and 0.9 wt.% PVP (sample 2, Table 1); (c) 100 mg dm-3 PS-C latex, 1 x rnol dm-3 ZT(SO,)~, 0.5 mol dm-3 formamide, 0.18 mol dm-3 urea, and 0.9 wt.% PVP (sample 3, Table 1); (d) 100 mg dm-3 PS-A latex, 1 x mol dm-3 Zr(SO,),, 0.25 rnol dmW3 formamide, and 0.9 wt.% PVP (sample 4,Table I) independent inorganic particles were noted, which could be separated readily by filtration.Fig. 4(d) displays the anionic polymer colloid covered with basic zirconium sulphate shell, prepared under the conditions given in Table 1. Preparation of Hollow Particles In order to obtain hollow spheres of zirconium compounds, coated particles (samples 1 and 3, Table 1) were calcined at 500 and 800 "C, respectively, for 3 h in air. It should be noted that polystyrene latex completely decomposes at 430 "C in air. The results are summarized in Table 2 and Fig. 5 illustrates the particles obtained at different temperatures. The compo- sition of the shell material depends on calcination conditions as discussed later. Table 1 Properties of spherical coated particles obtained by ageing, at 70 "C for 5 h, dispersions containing 0.9 wt.% PVP, in the presence of different amounts of Zr(SO,),, formamide, urea, and PS-latex coated ratio of particle inner :outer shell sample PS/mg dm-3 Zr(SO,),/mol dm-3 diameter/pm diameters composition fig.1" 400 (PS-C) 5 x lo-, 0.19 0.89 Zr202(0H)2C03 qa)2b 250 (PS-C) I x10-3 0.2 1 0.81 Zr202(0H)2C03 4(b)3' 100 (PS-C) 1 XIO-3 0.25 0.68 Zr 2(0H)6S04 4(c)4d 100 (PS-A) 1 x10-3 0.26 0.54 Zr,(OH), 4(d) "1.0 mol dm-3 in formamide, 0.72 mol dmP3 in urea; bl.O mol dm-3 in formamide, 0.45 rnol dm-3 in urea; '0.5 mol dm-3 in formamide, 0.18 mol dm-' in urea: d0.25mol dm-3 in formamide. J.MATER. CHEM., 1991, VOL. 1 Table 2 Properties of hollow particles obtained by calcination at different temperatures (heating rate 10 "C min-' and cooling rate 20 "C min-') original particle diameter/pm sample calcination sample (Table 1) temperature/ "C outer inner core A 3 500 0.22 0.12 Void B 3 800 0.20 0.10 Void C 1 800 0.17 0.13 Void "Mixture of crystalline tetragonal and monoclinic ZrO,; bcrystalline tetragonal ZrO,. composition shell fig. Zr,O,SO, 5M ZrO," 5(b) ZrOzb - I I I 1500 1000 500 ' I I SI 4000 3000 2000 e__ 0.1 ym 0.1 pm Fig. 5 TEM of hollow particles obtained by calcining sample 3: (a) at 500 "C for 3 h (sample A, Table 2) and (b)at 800 "C for 3 h (sample B, Table 2) Characterization Coated Particles Fig.6 shows the infrared (IR) data for the polystyrene latex (PS-C) and coated particles [samples 1 and 3, Fig. 4(a) and 4(c)]. The IR spectrum of this latex reveals well defined bands (700, 750, 1050 and 3020cm-') of the phenyl group and a peak at 2920 cm-' due to the CH2 group. Curve 1 obtained with sample 1 (Table 1) shows bands characteristic of poly- styrene, in addition to the OH stretching vibrations (3000- 3500 cm-I), as well as bands of water of hydration (1650 cm-') and carbonate (1350-1600 and 8600-880 cm-'), which were earlier shown to correspond to Zr202(0H)2C03*2H20.5The spectrum of sample 3 has additional bands of sulphate (1070-1200, 570-670 cm- '). Again, it was demonstrated that this compound is consistent with Zr2(OH),$o4 -2H20.' Consequently, samples 1 and 3 consisted of coated particles, but the composition of their surface layers was different.Additional information is obtained from the weight loss, DTA, and electrokinetic measurements. Fig. 7 compares the weight loss of coated particles (samples 1 and 3) and corre- sponding zirconium compounds when they are heated to 800 "C. Curves (b) and (d), which refer to coated particles, show two inflection regions: the first at 300-400 "C and the second at 530-700 "C, signifying the weight loss due to the decomposition of polystyrene and dehydration of the inor- ganic shells to Zr02, respectively. The DTA curve for sample 1 (Fig. 8) exhibits two broad endothermic peaks at ca.170 and 400 "C, and one exothermic peak at ca. 640°C. The first endothermic peak and the exothermic peak indicate the decomposition of Zr202(OH)2C03-2H20,5while the second one is due to the volatilization of polystyrene. Sample 3 exhibits a somewhat different behaviour, which is due to a different shell compound [Zr2(OH)6S04 * 2H20)]. Fig. 9 displays the mobilities of the two kinds of zirconium compounds as well as those of the coated polymer latices (samples 1 and 3) as a function of the pH. The isoelectric points (i.e.p.) of samples 1 and 3 (at pH ca. 3.3 and ca. 4.5, wavenumberlcm-Fig. 6 IR spectra of polystyrene latex (PS-C) (a),of original coated particles (sample 1 and sample 3, Table I), and of sample 3 calcined at 500 "C (A), and 800 "C (B) (Table 2) respectively) are the same as reported earlier for aqueous dispersions of Zr202(OH)2C03 and Zr2(0H)6S04.5 Hollow Particles Fig.6 shows the IR spectra of the powders of coated particles calcined at 500 and 800 "C. Curve A, which represents original sample 3 (A, Table 2) reveals, on heating, no spectral character- istics of polystyrene, confirming that the polymer core was decomposed by calcination >475 "C, while sulphate bands are still recognizable. The same solids calcined at 800 "C (B, Table2) exhibit essentially the same IR spectrum as Zr02, which leads to the conclusion that this powder consists of hollow zirconium oxide particles. Additional support for the consistency of the results is offered by the mobility data, which show ZrO, particles produced by calcining Zr2(0H)6S04 at 800 "C and hollow particles (sample B) to have the same dependence on the pH (Fig.10). Table 3 displays XRD data for ZI-~(OH)~SO~and J. MATER. CHEM., 1991, VOL. 1 -90 80 -70 -60-Y In 50-E .-0)P 40-30-9+-12ol10 0 200 400 600 800 temperature1 "C Fig. 7 The change in the weight as a function of temperature for (a) PS-C latex, (b)sample 1, (c) Zr,0,(OH)2C0,~2H,0, (d) sample 3, and (e)Zr,(OH),S04.2H,0 1 I 1 I I I I 200 400 600 800 1000 TI "C Fig. 8 DTA curves for PS-C latex (a), sample 1 (b),and sample 3 (c) Zr202(OH)2C03 powders, and samples 1 and 3 calcined at 800 "C for 3 h in air. These results indicate that hollow particles C (Table 2) consist of crystalline tetragonal Zr02, while sample B underwent partial transformation to mono- clinic Zr02. Discussion Recently, it was shown that cationic polystyrene particles can be covered with a smooth inorganic layer by heterocoagul- ation with in situ formed basic yttrium carbonate.' It was of interest to apply this procedure to another inorganic com- pound in order to establish if the concept is more generally applicable.This work has demonstrated that both positively (PS-C) and negatively (PS-A) charged polystyrene latices could be 58 1 \ -1 .o I I I I I I 1 I I I 1 3 5 7 9 11 PH Fig. 9 Electrokinetic mobilities of dispersions consisting of Zr,O,(OH),CO, (n),Zr2(OH),SO4 (D), and of sample 1 (O),and sample 3 (A) as a function of pH in 0.01 mol dm-, NaNO, 1 3 5 7 9 11 PH Fig.10 Electrokinetic mobilities of dispersions consisting of zir-conium oxide particles (A), and hollow zirconium oxide particles (0)(sample B, Table 2), as a function of pH in 0.01 mol dm-3 NaNO, Table 3 X-Ray diffraction data for powders obtained by calcination at 800 "C for 3 h of original Zr,(OH),SO, and Zr,O,(OH),CO, particles and of coated particles (samples 1 and 3) original powder original powder Zr2(0H)6S04calcined at 800 "C sample B (Table 2) Zr,O,(OH),CO,calcined at 800 "C sample C (Table 2) dIA III, dlA III, dlA 111, djA Ill, 3.16 100 3.17 100 2.93 100 2.95 100 2.85 68 2.85 78 2.57 18 2.59 25 2.61 45 2.62 41 2.52 21 2.52 24 2.54 33 2.54 32 1.80 49 1.81 55 1.84 35 1.85 35 1.53 34 1.52 32 1.81 43 1.81 45 1.54 27 1.53 30 2.96 55 coated with zirconium compounds, although under more restrictive conditions than the previously described case. Fig.11 shows the change in the pH as a function of the ageing time for the cationic latex in the presence of Zr(S0J2 and the organic additives, which suggests that the mechanism of formation of the coated particles is indeed based on I I I I I I I I 0 1 2 3 4 5 6 7 8 9 ageing time/h Fig. 11 The change in the pH as a function of ageing time of a dispersion containing 250 mg dm-3 PS-C latex, 1 x mol dmP3 ZT(SO~)~,1 mol dmP3 formamide, 0.2 mol dm-3 urea, and 0.9 wt.% PVP at 70 "C.Arrow indicates i.e.p.of Zr, (OH), SO4. S =smooth-coated particles; R =rough-coated particles heterocoagulation. The actual sequence of events is deter- mined by the hydrolysis (and complexation) of the zirconium ion due to the change in the pH, which also determines the charge of the resulting particles. The coating process on the cationic latex is initiated once the pH rises sufficiently high to exceed the i.e.p. of the precipitated solids, thus yielding negatively charged inorganic particles. At first, a small amount of the latter adheres to the latex producing a rough surface, which on additional deposition results in a thicker and smoother shell.In view of the strong hydrolysis and complexation tendency of the zirconium ion, rapid precipitation readily occurs, lead- ing to mixed dispersions of coated particles and solid zir- conium compounds. Furthermore, the incomplete interaction between the latex and the inorganic particles is caused by the weak charge on the latter over the pH range 4.5-6.0 (Fig. 9). These reasons explain the relatively narrow range of con- ditions that result in uniformly coated particles. When working with anionic polystyrene latex, it is required that the pH during the ageing period be kept below the i.e.p. (at pH 4.5) of Zr2(OH),S04, in order to maintain positively charged particles of the latter. Consequently, urea or formam- ide in concentrations <0.25 mol dm-3 must be used in this system.Obviously, the surface-charge characteristics of the core and coating particles, which form the shell, are essential for the formation of a good coverage. This work has also demonstrated that hollow particles of J. MATER. CHEM., 1991, VOL. 1 zirconium compounds can be obtained by using an analogous process as previously de~cribed.'~ During the calcination process, which produces the 'hollow spheres, a change in the composition of the shell takes place. This phase transformation may proceed through the following sequence of reactions: shell layer 100-200 "CZr, (OH), S04-2H2 0-Zr, (OH), so4 ca.400 "C ca 700 "C -Zr203S04---------) 2Z1-0, core >430 "Cpolystyrene-C02 and H20 The results using different samples (1 and 3) also indicate that the hollow spheres may vary in chemical composition and crystal structure, depending on the nature of the original coated particles.References 1 S. Kratohvil and E. Matijevik, Adu. Ceram. Muter., 1987, 2, 798. 2 A. Garg and E. Matijevik, Langmuir, 1988, 4, 38. 3 A. Garg and E. Matijevik, J. Colloid Interface Sci., 1988, 126, 243. 4 B. Aiken and E. MatijeviC, J. Colloid Interface Sci., 1988, 126, 645. 5 B. Aiken, W. P. Hsu and E. MatijeviC, J. Muter. Sci., 1990, 25, 1886. 6 F. C. Mayville, R. E. Partch and E. MatijeviC, J. Colloid Interface Sci., 1987, 120, 135. 7 N. Kawahashi and E. Matijevik, J. Colloid Interface Sci., 1990, 138, 534. 8 M. Okubo, M. Ando, A. Yamada, Y. Katsuta and T. Matsumoto, J. Polym. Sci., Polym. Lett. Ed., 1981, 19, 143. 9 A. Kowalski, M. Vogel and R. M. Blankenship, Rohm and Haas Co., US. Pat., 4 427 836, 1984. 10 M. Hattori, K. Kasai, N. Sakai and H. Takeuchi, Japan Synthetic Rubber, US. Pat., 4 798 691, 1989. 11 K. Kasai, M. Hattori, H. Takeuchi and N. Sakai, Japan Synthetic Rubber, Jpn., Kokai Tokkyo Koho, J.P. Kokai, 62-127336, 1987. 12 M. Ramamuri and K. H. Leong, J. Aerosol. Sci., 1987, 18, 175. 13 C. Roth and R. Kobrich, J. Aerosol Sci., 1988, 19, 939. 14 L. Durand-Keklikian and R. E. Partch, J. Aerosol Sci., 1988, 19, 511. 15 N. Kawahashi and E. Matijevik, J. Colloid Interface Sci., 1991, 143, 103. 16 F. C. Baes and E. R. Mesmer, The Hydrolysis of Cations, Wiley, New York, 1976. 17 H. H. Willard and C. H. Fogg, J. Am. Chem. SOC., 1937, 59, 1 197. 18 H. H. Willard and K. N. Tang, J. Am. Chem. SOC., 1937, 59, 1 190. Paper 1/00413A; Received 29th January, 199 1

ISSN:0959-9428    

DOI:10.1039/JM9910100577

出版商:RSC    

年代:1991

数据来源: RSC

摘要:

J. MATER. CHEM., 1991,1(4), 583-589 Second-harmonic Generation Properties of some Co-ordination Compounds based on Pentanedionato Ligands Royston C. B. Copley, Curt Lamberth, Jonathan Machell, 0. Michael P. Mingos,* Don M. Murphy and Harry Powell Inorganic Chemistry Laboratory, University of Oxford, South Parks Road, Oxford OX13QR, UK The synthesis and non-linear optical properties of pentanedionato ligands and their complexes with BF;, rhodium(1) and palladium(I1) are described. 4-Nitrobenzoylacetone 1, 3-(2,4-dinitrophenyl)pentane-2,4-dione 3, and the BF; adduct difluoro(4-methoxyben+oylacetonato)boron 2, were used to synthesize a range of palladium(1r) and rhodium(1) complexes. The single-crystal X-ray structures of bis(triphenylphosphine)(4-nitrobenzoylacetona-to) pal Iadiu m (11) te t r af Iuorobor ate 4, and b is( t r ip h en y Ip hosp h ine)[3-( 2,4-d init rop hen y I)-pen tane-2,4-d ionato] pa IIadi-um(I1) tetrafluoroborate 5, were determined.4 and 5 crystallize in the triclinic space group fi,with two molecular units per unit cell with dimensions of a= 10.995(1) A, b= 13.692(3) A, c= 14.964(4)A, a=102.933(20)", B= 92.286(16)", y=98.466(14)" for 4, and a= 12.066(2) A, b= 12.112(2)A, c= 15.681(2) A, a= 103.840(12)", B= 91.227(12)", y=99.596(14)" for 5. Both 4 and 5 have the pentanedionato oxygens directly bonded to the square- planar Pd" atom, with Pd-0 bond lengths of 2.034(5) and 2.046(5) A for 4 and 2.019(2) and 2.033(2) A for 5. The phenyl ring in 4 is planar with the pentanedionato ring, but in 5 the phenyl group is perpendicular to the pentanedionato ring.The second-harmonic generation (SHG) properties of the compounds were measured and compared with those for urea. Keywords: Second-harmonic generation; Non-linear optical material; Crystal structure In recent years considerable success has been achieved in designing organic materials that display non-linear optical properties. The molecular requirements for maximizing the non-linear properties of organic molecules are well defined and the introduction of appropriate donor and acceptor functional groups can be achieved using conventional syn- thetic procedures. There are additional crystallographic requirements. First, the molecules must pack in a non-centro- symmetric space group and, secondly, they must satisfy phase- matching criteria by packing close to a particular inclination to the principal axis.These requirements are difficult to achieve in practice.2 Recently, some attempts have been made to transfer these molecular design concepts to co-ordination and organometallic corn pound^.^*^ The results that have been achieved with substituted ferrocenes have been particularly promising in this regard.' In this paper we describe the synthesis and characterization of substituted metal pentanedionato complexes, which rep- resented reasonable target molecules for non-linear optical properties. These complexes were chosen for the following reasons: (a) thermally stable pentanedionato complexes have been reported for the majority of metals; (b) the pseudo- aromatic nature of the metal pentanedionato ring can provide a range of derivatives via electrophilic substitution reactions; (c) a wide range of conjugated pentanedionato ligands can be ~ynthesized.~-~Such complexes have been prepared and characterized by conventional analytical, spectroscopic and, in some cases, X-ray crystallographic techniques. Their non- linear optical properties have been probed directly on pow- dered samples using a modification of the Kurtz powder second-harmonic generation experiment." Results Pentanedionato complexes with substituents at the 3 and 4 positions were made directly from the free ligands, which were formed either in their enol forms or as BF2 derivatives.For example, the 4-nitrophenyl derivative 1 was synthesized in 29% yield from 4-nitroacetophenone and acetic anhydride, using BF,*Et,O as catalyst, according to the following equation: l19 l2 The product is a yellow crystalline compound soluble in the majority of organic solvents and was characterized by elemen- tal analyses as well as infrared and NMR spectral measure- ments. A characteristic of enolates in solution is that the enolised proton has a 'H NMR signal at ca. 15 ppm; for example compound 1 shows a single proton resonance at 15.92 ppm, in CDCl,. The synthesis of the 4-methoxyphenyl derivative 2, shown in Scheme 1, was similar to that developed for 1, but required the addition of a copper@) ethanoate solution during the reaction quenching stage. If the reaction was carried out without the copper salt, a dark-orange solid resulted, which was found to contain multiple 4-methoxy- phenyl rings and methyl groups, and was presumed to be the result of the alternative base-catalysed condensation of the starting materials.Compound 2 was a dark-green crystalline solid, highly soluble in most organic solvents, forming fluor- escent green solutions. Reaction of 2 with ethanolic NaOH, followed by re-acidification to isolate the free acid, formed an orange compound identical with the by-product. The crystal structure of difluoro(benzoy1acetonato)boron has been reported previou~ly,'~ and similar structure is assumed for 2. The 'H NMR of 2 has a single proton resonance at 6.48 ppm, due to the enol proton, and this is similar to the signal of the enol proton in compound 1, which is at 6.25 ppm.The 2,4-dinitrophenyl derivative 3 was synthesized, by a literature method', based on the reaction between 2,4-dinitro- fluorobenzene and sodium pentane-2,4-dionate in 85% yield. It is a pale-cream crystalline solid and shows the characteristic enolised proton signal at 16.61 ppm. Attempts at growing good single crystals of 3 for X-ray crystallographic analysis failed. 584 2 NO2 OMe + BFA Me 3 + BF4-1 5 6 7 OMe 8 NO, 10 11 Scheme 1 Palladium Compounds 4 and 5 The palladium(I1) compounds 4 and 5 were synthesized from cis-Pd(PPh,)Cl, and the pentane-2,4-dionato ligand. AgBF4 was added to these reactions as a halide-abstracting reagent.Both are air-stable yellow crystalline compounds, with the cis geometry retained. They were synthesized in 47 and 65% yields, respectively. The 'H NMR spectra were consistent with the proposed structures, with the enol proton signal of 4 occurring at 6.18 ppm. Single crystals of 4 and 5 suitable for X-ray crystallography were grown from the slow diffusion of a 1: 1 mixture of tetrahydrofuran and diethyl ether into dichloromethane solutions of the palladium compounds. The synthesis of the 4-methoxyphenyl analogue of 4 was attempted using the same conditions, but no palladium complex was identified. Discussion of the Crystal Structures of 4 and 5 The details of the crystal-structure determinations of 4 and 5 are summarized in Table 1, and the relevant atomic coordi- nates in Tables 2 and 33..The important structural features of the basic molecular skeletons are illustrated in Fig. 1 and 2, with selected bond lengths and angles listed in Table 4. The t Supplementary data available from the Cambridge Crystallo- graphic Data Centre: see Information for Authors, J. Muter. Chem., 1991, Issue 1. J. MATER. CHEM., 1991, VOL. 1 Fig. 1 Inner co-ordination geometry of the cation in compound 4. For reasons of clarity the phenyl rings on the phosphine ligands have been omitted Fig.2. Inner co-ordination geometry of the cation in compound 5. For reasons of clarity the phenyl rings on the phosphine ligands have been omitted structures confirm the formulations proposed for the com- pounds on the basis of spectroscopic data.For both 4 and 5 the palladium atom retains the square- planar geometry common to Pd" compounds, with the pen- tane-2,4-dionato ligands bonded to the oxygen atoms.I4 The Pd-0 bond lengths for 4 and 5 are 2.034(5), 2.046(5), 2.019(2) and 2.033(2)& respectively, which fall into the range of Pd" square-planar molecules with Pd-0 bonds. The Pd-0 bond lengths have been reported to be 1.96(1) A for bis(pen- tane-2,4-dionato)palladium(11).'~The degree of electronic delocalisation can be measured by the length of the C-C bonds in the pentane-2,4-dionato ring. In bis(pentane-2,4- dionato)palladium(Ir), the C-C delocalised bonds have lengths of 1.44(2)-1.40(2) A, shorter than the normal C-C bond length of 1.52(3)A.In 4 the C(38)-C(39) distance is 1.40( 1) A, and in 5 the corresponding bond is 1.405(5) A; thus, both pentane-2,4-dionato rings are delocalised. The C-C bond lengths between the pentane-2,4-dionato ring and the phenyl groups are 1.51( 1) and 1.502(5) A, respectively, showing that the bond order is nearer to one than to two, and that the conjugation between the pentadionato ring and the phenyl ring is not extensive. The C-0 bond lengths compare well to those reported in the 1iterat~re.l~ The major difference between 4 and 5 is that in 4 the benzene ring, containing the electron-accepting nitro group, is planar with the pentane- 2,4-dionato ring, and therefore maintains some conjugation J.MATER. CHEM., 1991, VOL. 1 Table 1 Structural details for 4 and 5 compound formula formula weight crystal system :7rgroupblA CIA ffl" PI" Yl" UjA3 Z DJg cm-3 linear absorption coefficient data collection crystal dimensions/mm radiation scan mode omin, 6maxi" w-scan width parameters A, B/" in width =A +B tan 8 horizontal aperturelmm min, max h; k; 1 total data total unique data total observed data (1>301) Sheldrick merging R factors (YO) absorption correction tY Pe minimax correction in 6 refinement: no. of parameters ratio of data :parameters weighting scheme method of solution final R, R, with it, whereas in 5the conjugation is broken between the substituted 2,4-dinitrophenyl ring and the pentane-2,4-dionato ring.All nitro groups remain almost planar to the benzene rings to which they are attached; however, the ortho-nitro group of 5 has the greatest deviation from planarity, this effect being common in compounds containing dinitrophenyl groups.' Rhodium Compounds 6 and 7 The rhodium(1) compounds 6 and 7, were synthesized by a modification of the method outlined by Varshavskii et ~1.'~ The ligands were reacted directly with RhC13-3H20, in dimethylformamide. The dimethylformamide acts both as the solvent and as the source of CO ligands. The 4-methoxyphenyl derivative (7) is a bright-orange solid, whereas the 2,4-dinitro- phenyl derivative (6)is a darker orange. The 'H NMR spectra of both compounds correspond to the proposed structures, and the enol proton signal of 7 occurs at 6.26 ppm.Attempts at the synthesis of 8 produced a complex brown and yellow mixture of compounds which could not be separated effec- tively. Second-harmonic Measurements The second-harmonic generation properties of the pentane- dionato compounds described in this paper were measured by a modification of the Kurtz powder method." Samples were ground, but not sieved, and exposed to incident light of 1064nm. The source was a low-power Nd:YAG laser (<7.4mJ per pulse), attenuated by a series of calibrated neutral optical density filters, which irradiated a silica cell containing the sample. The cell faces were at right angles to C46H38B1F4N104P2Pdl C47H39B1F4N206P2Pd1 923.962 982.985 triclinic triclinic Pf Pi 10.9954( 14) 13.6922(28) 14.9637(42) 102.933(20) 92.286( 16) 98.466( 14) 2165.5 12.0657( 19) 15.6807(20) 103.840( 12) 9 1.227( 12) 99.596( 14) 2185.4 12.1 121(21) 2 2 I .4 I7(exp.1.4 13) 1.491 5.5286 5.550 0.35 x 0.35 x 0.35 0.30 x 0.28 x 0.28 Mo-Ka Mo-Ka w-2e 0-26 1.5, 22.0 1.0, 25.0 0.9, 0.35 0.7, 0.35 3.5 3.5 -11, 11; -14, 14; -15, 15 -8, 14; -14, 14; -18, 18 9353 8649 5306 7705 4032 5928 1.75 1.77 DIFABS NIA @-scan profile 1.00, 1.06 632 568 6.40 10.44 unit weights Patterson unit weights Patterson 4.26, 4.58 3.16, 3.41 the incident beam, and the cell was located at the centre of a concave mirror, which collected all reflected light.The reflected light was then passed through an interference filter centred at 532nm (bandwidth 2nm). The intensity of the second-harmonic frequency was detected by a photomultiplier tube. The amplified anode signal was measured with a sum- ming oscilloscope. Each measurement was the average of 64 pulses, and this ensured that the pulse to pulse variation was removed. The sample signals were compared with those from graded (100 pm) reference samples. To avoid any ambiguity, the test was repeated with a different incident laser power, and a new measurement taken. If the relationship between the two measurements was second order with respect to the incident power, then the signal was presumed to be a second harmonic. The measured SHG properties of the ligands and complexes 1-10 relative to urea are summarized in Table 5.The ligands 1 and 2 both show some SHG effect (0.6xurea) whereas 3 has an effectively zero value. These observations may relate more to the centrosymmetric or non-centrosymmetric nature of the space groups in which the molecules choose to crys- tallize, rather than any molecular properties associated with the donor and acceptor functions on the pentanedionato ligand. Unfortunately, the crystal structures of these ligands have not been reported. The crystal structures of the palladium complexes 4 and 5 have been described in this paper and unfortunately they both crystallize in centrosymmetric space groups.The SHG proper- ties of these complexes should be zero for symmetry reasons, but nonetheless significant SH signals were observed for both compounds (see Table 5). The observation of this signal was reproduced both for samples from the same batch and for different syntheses. We conclude that these observations must 586 J. MATER. CHEM., 1991, VOL. 1 Table 2 Positional (x 104) and thermal parameters for 4 with estimated Table 3 Positional (x lo4) and thermal parameters for 5 with estimated standard deviations in parentheses standard deviations in parentheses atom X Y z u:q 4138.9(5) 2990.3(4) 2840.2(4) 314 Pd( 1) 3293(7) 2528.6(8) 2812.2(5) 314 2092(2) 2439(1) 2482(I) 347 P(1) 3248.5( 7) 2363.6(8) 1 3 3 1.3( 6) 33 1 4498(2) 1806( 1) 3644( 1) 344 P(2) 5 15734) 2 530.7( 4) 3048.4( 3) 345 5969(4) 3514(4) 3 160(3) 420 B(1) 573(3) 1697(3) 7630(2) 552 40 19(4) 4048(4) 2081(3) 399 C(1) 2255(3) 261 5(3) 4517(2) 365 2702( 7) 7053(5) -792(5) 805 C(2) 902(3) 2470( 3) 3266(2) 367 4454(7) 80 1 O(6) -370(6) 90 3 C(3) 1153(3) 2474(3) 4 147(2) 359 1 134(7) 2478(6) 3438(5) 386 C(4) 190( 3) 2212(3) 4700(2) 362 -138(8) 2227(7) 3309(6) 557 C(5) -163(3) 2961(3) 5432(2) 40 1 -870(1) 2340(8) 4037(8) 689 C(6) -990(3) 2601(3) 5952(3) 447 -330( 1) 2718(8) 4909(7) 666 C(7) -15 18(3) 1468(3) 57 19( 3) 455 920( 1) 2989(8) 5074(7) 680 C(8) -1257(3) 707(3) 498 5(2) 49 1 1654(8) 2871(6) 4333( 6) 505 C(9) -410(3) 1084(4) 4487(2) 436 1865(7) 1198(6) 17 12(5) 403 C( 12) 2486(3) 2659(4) 5474(2) 459 2800(8) 969(7) 1 152(6) 52 1 C(22) -289(3) 2422(3) 2932(2) 461 2700( 1) 21(8) 553(7) 702 C(111) 249 l(4) 3488(4) 11 57(3) 389 168q 1) -693(8) 504(7) 68 1 C(112) 2606(5) 4514(4) 1781(3) 558 740( 1) -475(7) 1038(7) 694 C(113) 2037(4) 5383(4) 1683(4) 650 830(8) 461(7) 1658(7) 571 C(114) 1 349( 5) 5220(5) 953(4) 686 1403(6) 3254(6) 1874(5) 382 C(115) 1244(4) 42 12(4) 3 lO(3) 797 1243(8) 4205(7) 2373(6) 488 C(116) 1811(3) 334 1 (3) 407(2) 604 687(9) 484 l(7) 1953(7) 589 C(121) 2435(3) 988(3) 717(2) 362 257(9) 4520(8) 1046( 7) 623 C( 122) 2398(4) 7 I2(4) -209( 3) 462 420( 1) 360 l(9) 542(7) 66 1 C(123) 17 I4(4) -282(4) -683(3) 543 1OOO(9) 2953(7) 951(6) 569 C( 124) 1088(4) -10 16(4) -261(3) 577 5475(7) 966(5) 3029(5) 362 C(125) 1145(3) -774( 3) 645(2) 557 5575(8) 36(6) 3230(6) 497 C( 126) 18 12(3) 238(3) 1 135(2) 45 1 6350(1) -568(7) 2768(7) 639 C(131) 452I(3) 2528(3) 744(3) 358 7052(9) -266(8) 21 18(7) 623 C( 132) 4950(4) 3559( 4) 529(3) 489 6969(9) 643(8) 1905(6) 592 C( 133) 5940(3) 3654(4) 93(3) 56 1 6 182(8) 1267(7) 2350(6) 484 C( 134) 6496( 3) 2732(3) -131(3) 554 3273(7) 944(6) 397 1 (5) 394 C(135) 6079(3) 171O(3) 85(2) 517 2905(8) 11 lO(7) 4870(6) 534 C( 136) 5 109(3) 1607(3) 523(2) 419 1939(9) 453(9) 5075(8) 67 1 C(211) 5560(3) 1121(3) 2700(3) 389 1334(9) -343(9) 44 12(9) 66 1 C(212) 4783(4) 163(4) 2291(3) 48 3 1685(9) -519(8) 3536(8) 653 C(213) 5084(4) -923(4) 21 18(3) 622 2660(8) 122( 6) 3309(7) 509 C(214) 6157(4) -1044(4) 2333(3) 619 5340(6) 2477(5) 4726(5) 345 C(215) 6930( 3) -92(4) 2764(3) 626 5257(8) 348 l(7) 5100(6) 497 C(216) 6640(3) 978(3) 2954(2) 523 5830( 1) 3987( 7) 5942(6) 583 C(221) 5557( 3) 2888(3) 4224(2) 384 6501(9) 349 I(8) 6439( 6) 585 C(222) 5217(4) 2048(4) 4684(3) 470 6613(9) 2503(8) 6081(6) 597 C(223) 5503(4) 2269(4) 5577(3) 529 6039(8) 1994(6) 5227(6) 469 C(224) 6 133(5) 3324(4) 6003(3) 600 7952(7) 44 13(7) 3154( 7) 629 C(225) 64 7 7( 4) 4143(4) 5562(3) 679 6601(7) 42 15(6) 2865(5) 417 C(226) 6 190(3) 3944(3) 4668(2) 552 61 37(7) 4775(6) 2292(6) 470 C(231) 6084(4) 3592(4) 2623( 3) 43 1 4932(7) 4684(5) 1953(5) 366 C(232) 5776( 6) 4677(4) 27 50( 3) 574 4608( 7) 5377(5) 1357(5) 385 C(233) 6475(6) 5549(5) 2489(3) 720 3 566( 8) 5090(6) 759(6) 475 C(234) 7454(4) 5343(6) 2105(4) 770 3255(8) 571 l(7) 199( 6) 550 C(235) 7746(3) 4284(4) 1976(3) 777 40 13(8) 66 15(6) 255(6) 480 C(236) 7065(3) 3 3 89( 4) 2226( 2) 579 5037(9) 6924(7) 839(7) 579 F(1) 1335(3) 1808(3) 8298(2) 1063 5343(9) 631l(7) 1404( 6) 563 F(2) 1 lOO(3) 1773(3) 6886(3) 898 3693(7) 7279(6) -350(5) 609 F(3) -39(4) 2529(3) 7892(2) 1093 151q1) 3709(8) 8363(8) 1200( 2) F(4) -90( 3) 654(3) 746 1( 2) 1106 2 1 OO( 1) 2675(8) 7 150(7) 1200( 2) N5) 353(3) 4 198(3) 57 19(3) 568 150( 1) 2807(8) 72 15(8) 1200( 2) N(7) -2346(2) 1057(2) 6299(1) 615 1 170( 1) 2038(8) 8220(8) 1200( 2) O(11) 3155(2) 2738(2) 4 120( 1) 389 -170( 1) 2660( 1) 8040( 1) 1200( 2) O(2 1 ) 16 13(3) 2529(3) 2682(3) 406 1180(2) 1860( 1) 7110(1) 1200( 2) O(51) 11 14(4) 4591(3) 5350( 3) 799 1770(2) 2580( 1) 8630( 1) 1200(2) O(52) -44(3) 4790(3) 6324(2) 962 1540(2) 359q 1) 7620( 1) I200(2) O(71) -2571(4) 1743(3) 6941(3) 697 1077(9) 2671(8) 7851(8) 1125(5) O(72) -2774(4) 42(3) 6097(3) 908 Experimental result from either the co-crystallization of more than one Reactions were routinely carried out using Schlenk line tech- polymorph, or from the large surface effects associated with niques under pure, dry nitrogen, with dry, oxygen-free sol- fine powders.Other workers have reported similar residual vents. Microanalyses (C, H, N, Rh and Pd) were carried out SHG effects for organometallic ferrocenes l7 and organic poly- by Mr. M. Gascoyne and his staff at this laboratory. Infrared mers.I8 The remaining complexes 6-10 did not show signifi- spectra were recorded on a Perkin-Elmer FT17 10 spec-cant SHG effects.trometer, as Nujol mulls between KBr discs. ‘H NMR spectra J. MATER. CHEM., 1991, VOL. I Table 4 Important bond lengths and angles for 4 and 5" 4 atoms ~ ~~~~~~ distance Pd(1)-O( 1) Pd(1)-O(2) Pd(1)-P(l) Pd(1)-P(2) O(1)-C( 38) O(2)-C(40) C( 37)- C( 38) C( 3 8)-C( 39) C(39)-C(40) C(40)-C(41) C(44)-N( 1) "1)-0(3) N(1)-0(4) 2.034(5) 2.046(5) 2.268(2) 2.293(2) 1.271(8) 1.279(8) 1.498( 10) 1.400(11) 1.377(11) 1.509(10) 1.485( 10) 1.2 14(9) 1.213(9) 4 atoms angle O(1)-Pd( 1)-0(2) P(1)-Pd( 1)- P(2) c(40)-C(41)-c(42) C(44)-N(1)-0(3) 90.88( 19) 97.49(7) 119.75(66) 117.09(81) 5 atom distance Pd( 1)-O(11) Pd(1)-O(2 1) Pd(1)-P(1) Pd( 1) -P(2) O(1 1)-C( 1) O(21) -C(2) C(l)-C(12) C(2)-C( 22) C(3)-C(2) C(3)- C( 1) C(3)-C(4) C(5)--N(5) (77) -N7)N(5)-O( 5 1) N(7)-O(7I) 2.0 I9(2) 2.033(2) 2.28 1( 1) 2.272( 1) 1.269(4) 1.274(4) 1.507(4) 1.507(5) 1.407(5) 1.405(5) 1.502(5) 1.479(5) 1.47 1 (5) 1.189(4) 1.201(4) 5 atom angle 0(1 l)--Pd(1)-0(21) P(1)-Pd( 1)-P(2) C(2)-C(3)-C(4) C(5)- N( 5)-O( 5 1) C(7)- N(7) -O(7 1) 88.55(9) 98.6(3) 118.07(29) 120.83(34) 118.74(36) a Standard errors in parentheses.Table 5 Measured second-harmonic signals at 1064 nm fundamental laser wavelength; all relative to urea compound efficiency" comments 1 0.56 2 0.67 3 0.01 4 0.22 5 0.73 luminescent 6 0.08 luminescent 7 0 luminescent 8 0 luminescent 9 0 luminescent 10 0 11 not tested " All measured with respect to urea, and as a sum of 64pulses. were run using a Bruker A.M.300 spectrometer, deuterium locked. Electronic spectra were obtained using a Perkin-Elmer 552 UV-VIS spectrophotometer with 10 mm silica cells, in solvents, where possible, which were transparent at the fre- quencies used. Compounds 9-11 (Scheme 1) were synthesized by literature method^.'^*'^*^^ Crystal-structure Determination of 4 and 5 Data Collection Suitable crystals of 4 and 5 were mounted in 0.5 mm Lindem- ann capillary tubes. Crystal data were collected at room temperature on an Enraf-Nonius CAD4-F automatic diffractometer using molybdenum radiation (Mo-Ka, 2 = 0.71069 A). The unit-cell dimensions were calculated from the setting angles of 25 accurately centred reflections in each case.Data were collected using the 0-28 scan method. Three standard reflections were measured after every 3600 s of X-ray exposure time as intensity standards and after every 250 reflections as orientation controls. Data Reduction The intensity data were corrected for Lorentz and polarization effects. An empirical absorption correction was applied to 5, and equivalent reflections were averaged. Structure Solution and Rejinement The structures were solved and refined within the CRYSTALS package. Bis(triphenylphosphine)(4-nitrobenzoylacetonato)palladium(~~ tetrajuoroborate 4.The coordinates of the Pd atom in 4 were determined from interpretation of a Patterson synthesis. Four- ier syntheses were used to ascertain the positions of the remaining non-hydrogen atoms. Following full-matrix least- squares refinement of atomic coordinates and isotropic ther- mal parameters, DIFABS was applied to unmerged data, which were then remerged.A difference Fourier synthesis gave the positions of all the hydrogens except those of the methyl group, which were included in geometrically idealized positions. The difference map also showed residual electron density in the region of the anion, indicating disorder. This was modelled as a minor and rigid idealized tetrahedral BF, ion. In the final stages of least-squares refinement, the matrix used consisted of three blocks. The first block contained the scale factor and a 'dummy overall isotropic temperature factor'. The second contained the atomic coordinates of all the atoms.There were eight fluorine positions, four in each of the major and minor components of the anion. The third block contained the thermal parameters: anisotropic for the non-hydrogen atoms in the cation, isotropic for the boron atom, a single isotropic parameter for all the hydrogens and another for the fluorine atoms. The bond angles among the generated hydrogens and among the fluorines of the minor component were restrained to idealized values. The bond lengths in the minor component were restrained to their mean value. Unit weights were maintained throughout the solution. Bis(triphenylphosphine)[3-(2,4-dinitrophenyI)pentane-2,4-dionato]palladium(z~)tetrajuoroborate 5.A Patterson synthesis gave the coordinates of the Pd atom in 5 and the remaining non-hydrogen atoms were easily located by further Fourier syntheses. The hydrogen atoms were positioned geometrically.The matrix used for the final cycle of refinement consisted of two blocks. In the first were the coordinates of the non-hyrogen atoms. In the second were the anisotropic thermal parameters for these atoms plus one isotropic thermal param- eter for all the hydrogens. Unit weights were employed. Details of the two structures and their solution are summarized in Table 1. Synthesis of 4-Nitrobenzoylacetone 1 A mixture of 4-nitroacetophenone (1.65 g, 0.01 mol), acetic anhydride (2.04 g, 0.02 mol) and toluenesulphonic acid monohydrate (0.076 g, 0.4 mmol) was stirred for 30 min.Boron trifluoride etherate (2.1 1 cm3, 2.44 g, 0.172 mol) was added slowly to the mixture which released heat, and the solution became amber. The reaction mixture was stirred for a further 16-20 h at room temperature. The reaction mixture was then quenched with aqueous sodium acetate (5.52 g, 0.04 mol, in 10 cm3 of water). The reaction vessel was fitted with a reflux condenser and the reaction mixture was refluxed for 3 h. The solution was cooled, and extracted with three aliquots of 30-60 "C light petroleum and diethyl ether (10 cm3 each). The combined extracts were washed with 5% sodium hydrogencarbonate solution, and finally with water. The combined organic extracts were dried over anhydrous sodium sulphate, which left a clear yellow solution.The dried ether solution was reduced in volume, and yellow crystals formed; crude yield of 4-nitrobenzoylacetone 1 was 0.64 g (29%). The crude product was purified by sublimation or by conversion into its water-soluble sodium salt, and final re- acidification followed by recrystallization from hot hexane. Elemental analysis of a sublimed sample was carried out (Found: C, 57.9; H, 4.2; N, 7.1. CloH9N04 requires C, 58.0; H, 4.4; N, 6.7%). IR (Nujol mull), v,,,/cm-': 1694w (C=O), 1519s (NO,), 1346s (NO,). 'H NMR data: aH (solvent CDCl,) 15.92 (s, 1 H, remaining enol proton), 8.17 [d of d, 4 h, Ph, 3J(H-H)=7.18 Hz, 3J(H-H)=8.21 Hz], 6.25 (s, 1 H, enolised proton), 2.28 (s, 3 H, CH3). Electronic spectrum: (ethanol solution), A,,,/nm 320 (log E 4.1 I), 250 (4.02), 201 (3.94); (n-hexane solution) 3 10 (4.16), 242 (4.1 l), 197 (3.82).m/z at 207 f1 mass units (m.u.). Synthesis of Difluoro(4-methoxybenzoylacetonato)boron 2 4-Methoxyacetophenone (1.5 g, 0.01 mol), was added to dried, fused and degassed toluene-4-sulphonic acid (0.20 g), under nitrogen. The mixture became reddish-amber, and was dis- solved in acetic anhydride (50 crn3, dried and degassed) when cool. The solution was re-heated to help dissolution, and cooled to room temperature. Boron trifluoride etherate (2.2cm3) was added slowly, and the reaction mixture was stirred for 2 days during which the solution became black, with a white suspension. The mixture was then quenched with both a sodium acetate solution (5 g in 10 cm3 water) and a copper(1r) ethanoate solution (2 g in the minimum amount of water); a green precipitate was formed, which was filtered off, washed with water, and the residue redissolved in 1: 1: 1 mixture of light petroleum (80-100 "C), acetone and chloro- form. The dark solution was dried over sodium sulphate, reduced in volume, and crystallized three times from the above solvent mixture.Dark-green crystals of difluoro(4- methoxybenzoy1acetonato)boron2 formed, yield 0.53 g (22%) (Found: C, 55.8; H, 4.7 Na, tO.l; C1, 0.4; Cu, 0.1. CllHllBF303 requires C, 55.05; H, 4.62%. The compound also had a positive flame test for copper, indicating BF,). IR (Nujol mull), v,,,/cm-': 1606 m (CO), 1567s (CO), 151 Is (CO), 1267s (BF), 1190s (BF), 1130s (BF), 1092s.'H NMR data: 6, (solvent CDC13) 8.06 [d, 2 H, Ph, 3J(H-H)= 8.45 Hz], 7.00 [d of d, 2 H, Ph, 'J(H-H)=9.63 Hz, 4J(H-H)=2.00 Hz], 6.48 (s, 1 H, C-H enol proton), 3.93 (s, 3 H, OMe), 2.38 (s, 3 H, CH3). Electronic spectrum: (ethanol solution) A,,,/nm 349 (log& 4.23), 275 (3.36), 239 (3.67), 204 (3.64); (CH,Cl, solution) 349, 280, and 242 nm. J. MATER. CHEM., 1991, VOL. 1 Synthesis of 3-(2,4-Dinitrophenyl)pentane-2,4-dione 3 Freshly prepared sodium pentane-2,4-dianato (0.67 g, 5.49 mmol) was dissolved at room temperature in dry, degassed acetone (50 cm3). 2,4-Dinitrophenylfluorobenzene (1.00 g, 0.67 cm3, 5.37 mmol) was added to the acetone solu- tion, and the mixture refluxed for 5 h. On adding the fluoro- benzene, the solution went violet, but quickly turned brown.At the end of the reflux, the reaction mixture was diluted with dichloromethane (50 cm3), filtered, and the filtrate was reduced to dryness, forming an amber resin. This was extracted with warm 1 mol dm-3 sodium hydroxide solution (10 cm3), and the extract filtered carefully. The red filtrate was then neu- tralized with 1 mol dmP3 hydrochloric acid, and at the end point a cream solid separated out. The solid was filtered off, washed well with water, then cold ethanol, and the crude 3-(2,4-dinitrophenyl)pentane-2,4-dione3 was dissolved in chloroform, dried over anhydrous sodium sulphate, filtered, reduced to dryness, and recrystallized from ethanol forming very pale-yellow crystals, yield 0.69 g (47%) (Found: C, 49.3; H, 3.8; N, 10.4.CllH10N206 requires C, 49.6; H, 3.8; N, 10.5%). IR (Nujol mull), v,,,/cm-': 1614s (CO), 1712s (CO), 1536vs (NO,), 1348vs (NO,). 'H NMR data: 6, (solvent CDC1,) 16.61 (s, 1 H, enolised proton), 8.81 [d, 1 H, Ph, 4J(H-H)=2.4 Hz], 8.52 [d of d, 1 H, Ph, 3J(H-H)= 7.89 Hz, 4J(H-H)=2.35 Hz], 7.64 [d, 1 H, Ph, 3J(H-H)= 8.52 Hz], 1.87 (s, 6 H, 2Me). Electronic spectrum: (ethanol solution) Amax/nm 270 (log E 4.09), 235 (4.07), 203 (4.06); (CH2C12 solution) 268 (4.15), 230 (4.10). Synthesis of Bis(triphenylphosphine)(4-nitrobenzoylacetonato) palladium(1r) Tetrafluoroborate 4 cis-Pd(PPh3)C1, (0.24 g, 0.342 rnmol), AgBF4 (0.13 16 g, 0.676 mmol), and p-nitrobenzoylacetone (0.070 g, 0.338 mmol), were mixed dry under nitrogen, and CH2Cl2 (10cm3) was added to initiate the reaction.The reaction mixture was stirred overnight at room temperature, and formed a heavy white solid (AgCl), suspended in a clear yellow solution. The mixture was filtered, and the residue was washed with CH2C12, and the filtrate and washings were combined, reduced to dryness, to leave a spongey yellow solid. The solid was extracted with hot hexane, and diethyl ether, to remove unreacted starting materials, and the residue was dissolved in tetrahydrofuran, filtered, and the yellow solution layered with diethyl ether. After 12 h, yellow-green crystals had been deposited, these were isolated, and recrystallized from dichlor- omethane solution, by slow diffusion of a 1: 1 mixture of tetrahydrofuran and diethyl ether into the dichloromethane layer.Yellow crystals of bis(triphenylphosphine)(4-nitroben-zoylacetonato)palladium(u) tetrafluoroborate formed 4, yield 47% (Found: C, 60.2; H, 4.2; N, 1.6; Pd, 11.1. C46H38BF4N04P2Pd requires C, 59.8; H, 4.2; N, 1.5; Pd, 11S%). IR (Nujol mull) v,,,/cm -':1560s (NO,), 1520s (NO,). 'H NMR data: 6, (solvent CD,Cl,) 7.89 [d, 2 H, '(H-H)= 9.1 Hz], 7.4 (m, 30 H, Ph), 6.97 [d, 2 H, Ph, 3J(H-H)= 9.08 Hz], 6.18 (s, 1 H, enol proton), 1.70 (s, 3 H, CH3). Electronic spectrum: (CH2C12 solution) A,,,/nm 238,260,290, 350; (acetone solution) 324, 350 (extinction coefficients not accurate for these solvents). Synthesis of Bis(triphenylphosphine)[3-(2,4-dinitrophenyl) pentane-2,Cdionato]palladium(rr) Tetrafluoroborate 5 AgBF, (0.3583 g, 1.84 mmol), cis-Pd(PPh,)Cl, (0.649g, 0.925 mmol) and 3-(2,4-dinitrophenyl)pentane-2,4-dione (0.229 g, 0.863 mmol) were mixed dry, under nitrogen.Dry, degassed CH2Cl, (10cm3) was added, forming an amber- J. MATER. CHEM., 1991, VOL. 1 yellow solution with the silver tetrafluoroborate in suspension. The mixture was stirred at room temperature, and darkened quickly. After 12 h a heavy grey precipitate had formed (AgCl), with an amber supernatant liquid. The mixture was filtered, and the residue washed with CH2C12, the filtrate and washings were combined, reduced to dryness at 50 "C, forming a sponge- like yellow solid. This yellow solid was carefully broken up, extracted with hexane and ether to remove excess starting materials, and the residue was then dissolved in tetrahydrofu- ran, and layered with diethyl ether.Yellow-orange crystals of bis(triphenylphosphine)[3-(2,4-dinitrophenyl)pentane-2,4-dionato]palladium(~~)tetrafluoroborate formed 5, yield 0.59 g (65%) (Found: C, 57.4; H, 4.1; N, 2.8; Pd, 10.7. C47H39BF4N206P2Pdrequires C, 57.4; H, 4.0; N, 2.9; Pd, 10.8%). IR (Nujol mull) v,,,/cm-': 1558s, 1540s. 'H NMR data: dH (solvent CD2Cl, solution); 8.62 [d, 1 H, Ar, 4J(H-H)=2.04Hz], 8.54 [d of d, 1 H, Ar, 3J(H-H)= 8.548 Hz, 4J(H-H)=2.04 Hz], 8.13 [d, 1 H, Ar, 3J(H-H)= 8.47 Hz], 7.4 (m, 30 H, Ph), 1.19 (s, 6 H, 2Me). Electronic spectrum: (acetone) A,,,/nm 325; (dichloromethane) 255, 235.Synthesis of Dicarbonyl[3-(2,4-dinitrophenyl)pentane-2,4-dionato]rhodium(~)6 RhC13-3H20 (0.2 g, 0.76 mmol) was dissolved in degassed dimethylformamide (15 cm3) to yield a deep-red solution. Solid 3-(2,4-dinitrophenyl)pentane-2,4-dione (0.2 g, 0.76 mmol) was added, and the solution refluxed under N2 for 45 min, during which time the solution acquired a slightly yellow tinge. The solution was allowed to cool to room temperature and water (30cm3) was added; a yellow solid was precipitated, filtered off and dried in uucuo. The yellow solid was extracted with benzene, to give a yellow solution, which, on removal of solvent, deposited a brown crystalline solid. Recrystallization from toluene yielded orange-brown crystals of dicarbonyl[3-(2,4-dinitrophenyl)pentane-2,4-diona-to]rhodium(r) 6, yield 0.15 g (25%) (Found: C, 36.0; H, 2.4; N, 6.4; Rh, 21.1. Cl3H9N2O8Rhl requires C, 36.5; H, 2.6; N, 6.6; Rh, 24.2%).IR (Nujol mull) v,,,/cm-': 2080s (CO), 2006s (CO), 1580m (NO,), 1538m (NO,), 1580 (Ph), 1523 (Ph). 'H NMR data: 6, (solvent CD2C12, 8.73 [d, 1 H, 4J(H-H)= 2.1 Hz], 8.477 [d of d, 1 H, 3J(H-H)=85.5 Hz, 4J(H-H)= 2.4 Hz], 7.60 [d, 1 H, 3J(H-H)=85.5 Hz], 1.81 (s, 6 H, 2CH3). Electronic spectra: (ethanol solution) A,,,/nm 257, 212; (CH2CI2 solution) 321, 258. Synthesis of Dicarbonyl[4-(p-methoxyphenyl)butane-2,4-dionato]rhodium(~)7 The method is identical to that of the synthesis of 6. RhC13*3H20 (0.1 g, 3.8 mmol) was reacted with difluoro(4- methoxyphenylbenzoy1acetonato)boron(0.1 g, 0.42 mmol), the extracted product was recrystallized from hexane and then CH2Cl,, to give dicarbonyl[4-(p-methoxyphenyl)butane-2,4-dionato]rhodium(~)7 as an orange crystalline powder, yield 0.083 g (62%) (Found: C, 44.1; H, 3.3.C1lH1lOSRhl requires C, 44.6; H, 3.1%). IR (Nujol mull) v,,,/cm-l: 2080 (CO), 2067 (CO), 2010 (CO), 1614 (C=C), 1584 (C=C), 1533 (C=C), 1503 (C=C), 1171 (C-0-C) and 1108 (C-0-C). 'H NMR data: 6, (solvent CD,Cl,) 7.86 [d, 2 H, Ph, 3J(H-H)= 8.85 Hz], 6.92 [d, 2 H, Ph, 3J(H-H)=8.55 Hz], 6.26 (s, 1 H, enol proton), 3.84 (s, 3 H, OCH3), 2.18 (s, 3 H, CH3). Electronic spectra: (CH2C12 solution) Amax/nm 226, (hexane solution) 206. We wish to thank ICI and SERC for financial support and generous co-operation (C.L.) and also to the A.F.O.S.R.for their financial support (D.M.M.). We thank Dr R. G. Denning for the use of the laser facility and Ian Morrison for many useful discussions when setting up the Kurtz powder apparatus. References 1 D. S. Chemla and J. Zyss, Nonlinear Optical Properties of Organic Molecules and Crystals, Academic Press, Orlando, 1987, vol. 1 and 2, and references therein. 2 W. C. Egbert, Proc. SPIE-Int. SOC. Opt. Eng., 1987, 824, 107. 3 W. Tam and J. C. Calabrese, Chem. Phys. Lett., 1988, 144(1), 79. 4 D. F. Eaton, A. G. Anderson, W. Tam and Ying Wang, J. Am. Chem. SOC., 1987, 109, 1886. 5 M. L. H. Green, S. R. Marder, M. E. Thompson, J. A. Bandy, D. Bloor, P. V. Kolinsky and R. J. Jones, Nature (London), 1987, 330, 360.6 J. P. Collman, R. A. Moss, S. D. Goldby and W. S. Trahanovsky, Chem. Znd. (London), 1960, 1213. 7 J. P. Collman, R. L. Marshall and W. L. Young (III), Chem. Znd. (London), 1962, 1380. 8 A. I. Rubailo, V. P. Selina and Yu. S. Varshavskii, Koord. Khim., 1984, 10(9), 1231. 9 A. Werner, Chem. Ber., 1901,34, 2584. 10 S. K. Kurtz and T. T. Perry, J. Appl. Phys., 1968, 39, 3798. 11 C. Mao and C. R. Hauser, Organic Syntheses, Wiley, New York, 1962, 51, 90. 12 Y. Nakano and S. Sato, Inorg. Chem, 1980, 19, 3391. 13 A. W. Hanson and E. W. Macaulay, Acta Crystallogr., Sect. B, 1972, 28, 1961. 14 A. N. Knyazeva, E. A. Shugam and L M. Shkol'nikova, J. Struct. Chem., 1970, 11(5), 875. Engl. Transl. Zh. Strukt. Khim., 1970, 11(5), 1938. 15 S. A. Singham, Part I1 Thesis, University of Oxford, 1990. 16 Yu. S. Varshavskii and T. G. Cherkasova, Russ. J. Inorg. Chem., 1967, 12.1(6), 899. 17 J. A. Bandy, H. E. Bunting, M. H. Garcia, M. L. H. Green, S. R. Marder, M. E. Thompson, D. Bloor, P.V. Kolinsky and R. J. Jones, Spec. Publ. R. SOC. Chem., 1989, 69, 225. 18 T. Watanabe and Seizo Miyata, Proc. SPZE Znt. SOC.Opt. Eng., 1990, 1147, 101. 19 F. Bonati and G. Wilkinson, J. Chem. SOC., 1964, 3156. 20 F. Bonati and R. Ugo, J. Organomet. Chem., 1968, 11, 341. 21 D. J. Watkin, J. R. Carruthers and P. W. Retteridge, 1985 CRYS-TALS User Manual, Chemical Crystallography Laboratory, Uni- versity of Oxford. Paper 1/011885; Received 1st February, 1991

ISSN:0959-9428    

DOI:10.1039/JM9910100583

出版商:RSC    

年代:1991

数据来源: RSC