摘要:

J. MATER. CHEM., 1994, 4(8), 1309-1311 Inelastic Neutron Scattering Study of Hydrogen Embrittlement in Titanium Alloys Peter J. Branton,a Gary Burnell: Peter G. Hall*" and John Tomkinson" a Department of Chemistry, Exeter University, Exeter, Devon UK EX4 4QD Atomic Weapons Establishment, Aldermaston, Reading, Berkshire, UK " Rutherford Appleton Laboratory, Chilton, Didcot, Oxfordshire, UK OX17 OQX Inelastic neutron scattering studies have been carried out on the mixed CI and p phase of the titanium alloy IMI T318 for hydrogen loadings ranging from 400 to 15 500 ppm (a hydrogen loading of 80 ppm gave a spectrum too weak for interpretation). For a hydrogen content of 15 500 ppm, metal subsurface tetrahedral interstitial sites were occupied. As the hydrogen content was decreased, it became evident that an additional site was occupied, this was assigned to hydrogen in surface threefold symmetry binding sites. Titanium metal is of great industrial importance because of its simultaneous properties of low density (less dense than iron), high strength (stronger than aluminium), toughness and corrosion resistance.' These mechanical and chemical proper- ties can be enhanced by addition of alloying metals, such as aluminium, molybdenum, manganese and iron to name but a few.The IMI T318 alloy used in the present work comprises 90% Ti, 6% A1 and 4% V by weight.2 The mechanical properties of titanium (and also zirconium and hafnium in the same group) are greatly affected by traces of impurities such as 0,N, C and H, which have an embrittling effect on the metals making them difficult to fabricate.The embrittle- ment (significant reductions in strength, strain to failure and toughness) caused by hydrogen can be ascribed to the forma- tion of intergranular hydride. At lower hydrogen concen-trations, the materials are embrittled but there is no conclusive evidence of hydride f~rmation.~ As a result, this work aims to identify the site of the hydrogen in the metal lattice using inelastic neutron scattering (INS) spectroscopy. This tech- nique is ideal for the study of the atomic and molecular vibrations of hydrogenous materials where a good resolution is required. The IMI T318 alloy is a two-phase structure containing an hcp IXphase and a bcc fi phase in approximately equal volume fractions.The phase distribution consists of primary SI islands surrounded by a necklace of b. Experimental Hydrogen charged titanium alloy specimens were prepared by the Atomic Weapons Establishment, as plates with dimen- sions 1200 mmx27 mmx 1 mm using a thermal charging technique based on the Sieverts principle. This involved heating the specimen to 630°C and introducing hydrogen at reduced pressure. A thickness of 1mm was chosen so as to minimize the amount of multiple ~cattering.~ The nominal hydrogen contents of the specimens used were 80, 400, 1800 and 15 500 ppm. (A specimen free of hydrogen was analysed and the results showed a weight percentage of C, 0.01; N, 0.013; Fe, 0.2; Al, 6.2; V, 3.8; Y, 50ppm and 0, 0.120, Y (0.005; Ti, balance).The INS spectra were obtained at 30 f5 K using the time- focused crystal analyser (TFXA) spectrometer at the spallation neutron source, ISIS, Rutherford Appleton lab~ratory.~ This is an inverted geometry spectrometer with a fixed analyser neutron energy of approximately 4meV. The energy range covered is typically the molecular vibrational range from ca. 2 to 500meV with a good resolution, at some 2% in AEIE. The specimen containing no hydrogen was used as a back- ground and subtracted from the data, which were tranlsformed by standard programs to S(Q,o) against neutron energy transfer over the range 2-500 meV. Before the experiments, the specimens were quenched from room temperature to 77 K, but it is considered unlikely that this would have any signifi- cant effect in relation to the location of the hydrogen Results and Discussion INS Spectrum of 15 500 ppm Hydrogen-loaded Alloy The spectrum with a hydrogen loading of 15 500 ppm (where 1ppm= 1x lop4wt.%) is shown in Fig.1 and is dorninated by an intense peak at 148meV with a full-width at half maximum (fwhm) of 40meV. This has been assigned to hydrogen vibrations in the interstitial tetrahedral sites of the metal lattice. The frequencies of protons on tetrahedral sites are typically around 150meV, whereas for octahedral sites values around 60 meV are common. Kolesnikov et a1 made this assignment to a peak at 160meV for TiH0.74 in the 6 phase and Hempelmann et aL7 observed only one vibrational mode at 150.5meV due to hydrogen in tetrahedral sites for the a and b mixed phase of TiHo.07.The site chosen by hydrogen is highly dependent on the phase. For example, Kolesnikov et aL8 revealed that in the E phase of rfiH0.71, hydrogen principally occupied the octahedral interstices. Khoda-Bakhsh and Ross' have measured the INS spectra for the cc and b phase of TiHo.05 and TiH0,14, respectively, and concluded that the hydrogen occupied the tetrahedral sites in r neutron energy transferlmev Fig. 1 INS spectrum of 15 500 ppm hydrogen-loaded alloy the titanium hcp a phase and the distorted tetrahedral site in the titanium bcc fi phase. Broadening overtones at 297 and 445 meV indicate that there is no anharmonicity present; fwhm values were 60 and 120meV, respectively.The less intense sharp features at low energy transfer can be attributed to the lattice vibrations of titanium. There are characteristic peaks at 12.2 and 21 meV before the spectrum cuts off at about 40 meV. Similar to the 6 phase: these have been assigned to transverse acoustic modes near the edge of the Brillouin zone. INS Spectra of 1800 ppm Hydrogen-loaded Alloy The spectrum of titanium alloy with hydrogen content 1800 ppm is far more complex as can be seen in Fig. 2. Two peaks at 117 and 154 meV now dominate the spectrum and it appears that the hydrogen occupies two different sites. There is a very broad feature, which peaks at 297 meV, that can be attributed to the first overtone of hydrogen in tetra- hedral sites (the second overtone is too weak to be observed).The new site has been assigned to hydrogen in threefold symmetry binding sites on the surface. Binding in a threefold symmetric site predicts an intensity ratio of 2: 1 for the observed spectral features. Three Gaussian curves were suc- cessfully fitted to the spectrum using the interactive least- squares fitting package, FR1LLS.l' A peak fitted at 151 meV (fwhm =40 meV) was assumed to be from hydrogen in tetra- hedral sites and two peaks with intensities of 2: 1 were fitted giving energy transfer values of 105 (fwhm=25 meV) and 124 meV (fwhm =25 meV) respectively, due to the hydrogen in threefold sites on titanium. The location of hydrogen in threefold sites is not uncommon, for example, using spectro- scopic measurements for Ti(0001)-H( 1x 1), it was calculated that for a monolayer of hydrogen on titanium, the hydrogens were found to be in threefold sites, 0.8 au outside the outer titanium layer, under the site where the next titanium atoms would be if the crystal continued." It is known that adsorption in adjacent threefold sites is less stable than in separated sites sharing only one surface atom and no two hydrogen atoms form a tightly bound molecule in titanium.12 This is consistent with the fact that titanium is known for its strong surface catalytic reaction in dissociating a H, molecule into two adjacent hydrogen atoms.Hydrogen has also been shown to occupy threefold sites on other metals, e.g.raney nickel13 and pa1ladi~m.l~ INS Spectra of 400 and 80 ppm Hydrogen-loaded Alloys The spectrum with 400ppm hydrogen, together with fitted Gaussian curves are shown in Fig. 3 over the energy transfer range 50-200 meV. It is very weak, making interpretation 0.16r I 1 0 100 200 300 400 500 neutron energy transfedme\/ Fig. 2 INS spectrum of 1800ppm hydrogen-loaded alloy J. MATER. CHEM., 1994, VOL. 4 I I II50 100 150 200 neutron energy transferlmev Fig. 3 INS spectrum of 400 ppm hydrogen-loaded alloy difficult (hydrogen found in impurity sites could contribute significantly to the spectrum). Error bars are shown to give an estimate of the accuracy involved. The spectrum reaches a maximum at 119 meV, which slowly tails off.A peak at about 150meV is still present but now it is not the dominant peak in the spectrum, i.e. it 'appears' as if the hydrogen occupies the surface threefold sites in preference to the subsurface tetrahedral sites. Gaussian curves were fitted to the spectrum using the following assumptions; hydrogen occupies surface threefold sites and subsurface tetrahedral sites only; the pos- ition and fwhm of the peak due to hydrogen in tetrahedral sites is 148 and 40 meV, respectively (from the spectrum with 15 500 ppm H); and the two spectral features for hydrogen in surface threefold sites have an intensity ratio of 2 : 1 and the same fwhm values. A best fit of this data gave values of 105 (fwhm=26 meV) and 124 meV (fwhm =26 meV) for hydrogen in surface threefold sites and 148 meV (fwhm=40 meV) for hydrogen in subsurface tetrahedral sites.By calculating the areas under the Gaussian curves, it appears as if the two sites are populated in roughly equal proportions, due to the broadness of the peak from hydrogen in tetrahedral sites compared with that in surface threefold sites. The spectrum with 80ppm hydrogen was too weak for interpretation although one peak at 48.4 meV was clearly visible. This peak was also visible on the spectra with 400 and 1800ppm H although it was less intense relative to the rest of the spectrum. This has been interpreted as being due to bending and stretching vibrations of -OH groups bound to near-surface titanium atoms (0.12 wt.% of oxygen was present in our alloys).Comparison of this work with that of Renouprez et ~21.~'on the characteristic frequencies of the -OH vibrations of water chemisorbed on nickel, and that by Albers et all6 on oxygen impurity in TiMn,.,H,, suggests that the particular vibration being observed is probably due to a Ti-0-H stretch. Conclusions The INS spectra of the titanium alloy IMI T318 were meas- ured as a function of hydrogen content. At very low hydrogen loadings, the hydrogen was shown to occupy surface threefold symmetry sites and subsurface tetrahedral sites in roughly equal proportions. As the hydrogen concentration was increased, the spectra became dominated by hydrogen vibrations in the subsurface tetrahedral sites and for the highest hydrogen loading used (15 500 ppm), no surface scat- tering was visible.However, owing to the scattering from the surface structures being very much weaker than that from the bulk hydrogen, it cannot be ruled out that underlying the big peak at 148 meV in Fig. 1 there is also surface scattering as J. MATER. CHEM., 1994, VOL. 4 1311 revealed by Fig.2 when the bulk hydrogen was very much reduced. 7 Malyshev and E. G. Ponyatovskii, J. Phys: Condens. Mlrtter, 1991, 3, 5927. R. Hempelmann, D. Richter and B. Stritzker, J. Phy.5. F, 1982, 12, 79. We thank the SERC for the provision of neutron beam time, the AWE for the preparation of our hydrogen-loaded alloys and Professor D. K. Ross (Salford University) for helpful discussions. 8 9 10 11 A.I. Kolesnikov, V. K. Fedotov, I. Natkanets, S. Khabrylo, I. 0.Bashkin and E. G. Ponyatovskii, JEPT Lett., 1986,44, 509. R. Khoda-Bakhsh and D. K. Ross, J.Phys. F, 1982,12,15. R. Osborn, internal Report No. RAL91-01 I, Rutherford Appleton Laboratory, 1991. P. J. Feibelman and D. R. Hamann, Phys. Rev: B Condetrs. Matter. 1980,21, 1385. References 12 Myung-Ho Kang and J. W. Wilkins, Phys. Rev: B Condens. Matter, 1990,41, 10182. A. D. McQuillan and M. K. McQuillan, Titanium, Butterworth Scientific, London, 1956. IMI Titanium Ltd., P.O. Box 704, Witton, Birmingham, B6 7UR. 13 14 R. R. Cavanagh, R. D. Kelley and J. J. Rush, J. Chem. Phys., 1982, 77, 1540. J. M. Nicol, T. J. Udovic, J. J. Rush and R. D. Kelley, d,ungmuir, 1988, 4,294. N. S. Clarke, AWE, Aldermaston, Personal Communication. 15 A. J. Renouprez, B. Fouilloux and J. P. Candy, Surf. Sci., 1979, C. G. Windsor, Pulsed Neutron Scattering, Taylor and Francis, London, 1981. 16 83, 285. P. W. Albers, G. H. Sicking and D. K. Ross, J. Phys. Condens. J. Penfold and J. Tomkinson, Internal Report No. RAL86-019, Matter, 1989, 1,6025. Rutherford Appleton Laboratory, 1986. A. 1. Kolesnikov, M. Prager, J. Tomkinson, I. 0.Bashkin, V. Yu. Paper 3/07321A; Received 12th December, 1993

ISSN:0959-9428    

DOI:10.1039/JM9940401309

出版商:RSC    

年代:1994

数据来源: RSC

摘要:

J. MATER. CHEM., 1994, 4(8), 1313-1317 Examination of the Orientation Dependence of the Quasielastic Scattering of Neutrons by Pellicular Zirconium Phosphate Filmt Robert C. T. Slade,*" Helen A. Pressman: Antonella Peraioavb and Mario CasciolaC a Department of Chemistry, University of Exeter, Stocker Road, Exeter, UK EX4 400 lstituto Superiore di Ricera e Formazione sui Materiali Speciale per le Technologie Avanzate (ISRIM), Loc. Pentima Bassa 21, 05700 Terni, ltaly Dipartimento di Chimica, Laboratorio di Chimica lnorganica, Universita di Perugia, Via Elce di Sotto 8, 06100 Perugia, Italy Variable-temperature quasielastic neutron scattering (QNS) measurements on a time-of-flight spectrometer have been used in investigation of the orientation dependence of quasielastic scattering by a film of pellicular zirconium phosphate [p-ZrP, Zr(HP0,)2.1.3H,0].The partially oriented film, in the plane of which the lamellae of the ZrP structure lie, was produced by intercalation and deintercalation reactions of n-propylamine with microcrystalline a-zirconium phosphate. QNS spectra were recorded with the plane of the film inclined at 135" ('transmission') and 45" ('reflection') to the incident neutron beam. Quasielastic broadenings consistent with hydrogenic species undergoing motions with a timescale s in p-ZrP were observed at T>318 K, and the scattering law was also found to be dependent on sample orientation. The dependence on scattering vector magnitude, Qe,, of the scattering law with the sample in 'transmission' geometry [in which scattering was dominated by motion in the plane of the film (parallel to ZrP lamellae)] indicated detection of both reorientational and translational (diffusion in the plane of the film) motions.Quasielastic scattering with the sample in 'reflection' geometry was less intense and could not be modelled with a simple scattering law. Zirconium phosphates [Zr( HPO,),.nH,O, ZrP] are of con- temporary interest as inorganic ion-exchangers, acid catalysts and proton-conducting solid electrolytes. The structure of crystalline a-Zr(HP04),-H20 (aZrP) is well known. Single- crystal X-ray diffraction was first reported by Clearfield and Smith,' and showed a monoclinic unit cell of space group P2,lc. The structure was shown to consist of zirconium phosphate layers of pseudo-hexagonal symmetry (Fig.1)hE1d together by van der Waals forces (interlayer distance z 7.54 A), with quasi-zeolitic interlayer cavities in which the water molecules reside. The 0-H bonds in the acid phosphate groups point into the interlayer region. Various preparative routes to a-ZrPs of differing crystallinities are kn~wn.~-~ 7 Neutron scattering experiments were carried out at the Institut Laue-Langevin, Grenoble. Fig. 1 The ab layer of the a-ZrP structure, showing the approximate position of the monoclinic unit cell. The hydrogen atoms of the acid phosphate groups are attached to terminal oxygens, the OH bond pointing into the interlayer region. Colloidal suspensions of ZrP lamellae can be obtained by intercalation-deintercalation reactions of n-propylamine and a-ZrP; after re-acidification large thin films (pellicles) are obtained on filtration of, or deposition from, such suspen- sions.8 These films are termed pellicular zirconium phosphate (p-ZrP).In p-ZrP films the lamellae are believed to lie in the plane of the pellicle, this resulting in a marked anisotropy in protonic cond~ctivity~*~~ and the observation of only broad OOn reflections in the X-ray powder diffraction profile (p-ZrP is turbostratic, in common with clays). The water content of p-ZrP varies with relative humidity (RH)," with a maximum of 1.3H20 per formula unit being accommodated, This vari- ability of composition is associated with&ructural defects resulting from some hydrolytic attack during the intercal- ation-deintercalation reactions, the imperfect stacking of ZrP lamellae, and a large extension of the interparticle liquid phase.For the 'H nucleus the cross-section, oinc,for incoherent scattering of neutrons is very high and, as a consequence, the incoherent quasielastic scattering of neutrons (QNS) offers a powerful method for examination of reorientational and trans- lational motions of hydrogenic species," provided that the quasielastic broadening of the elastically scattered peak is observable with an available instrumental resolution (this criterion corresponds to a motional timescale 10-''-1 0-l2 s). The low symmetry of the unit cell for a-ZrP would cause severe experimental difficulties in recording neutron scattering spectra free of coherent Bragg scattering (diffraction) in the elastic component, and consequently would lead to intractable problems in data analysis (modelling both the elastic and the quasielastic components of the scattering).The diffraction profile of p-ZrP is much simpler (eliminating the problems due to Bragg scattering), and p-ZrP is also a suitable novel material for investigation of QNS by a partially ordered sample, for which the scattering law is predicted to depend on the relative orientations of the sample and the incident neutron beam." We have previously reported an orientation dependence of the inelastic neutron scattering vibrational spectrum of p-ZrP J.MATER. CHEM., 1994, VOL. 4 film (in the intensities in the region 720-1120 cm-' associated with acid phosphate groups).12 In the same study, quasi- elastic broadening at 343 K was observed on a triple-axis spectrometer, and a fuller investigation using a time-of-flight spectrometer was suggested. We now present the results of that investigation. Experimental Sample Preparation Microcrystals (2-10 pm) of a-ZrP were prepared by refluxing an amorphous ZrP in aqueous phosphoric acid (10 mol dmP3) for ca. 300 h. These was then intercalated with n-propylamine by mixing (using a DK Mettler Automatic Titrimeter operating by the equilibrium-point method) a dispersion of the microcrystals suspended in water with a standard aqueous solution of n-propylamine (0.1 mol dme3).A dispersion of the intercalate was slowly acidified to pH 2 with vigorous stirring and highly hydrated lamellae of ZrP settled out. On removing the electrolyte (by repeated washing with distilled water) a dense suspension of lamellae was obtained. Slow filtration (using a Millipore RAWPOl plastic filter), followed by air-drying, resulted in a compact, nacreous and fairly flexible film (thickness ~0.1-0.2 mm) of p-ZrP, which was easily removable from the filter.8 The X-ray powder diffraction profile (Philip diffractometer, Ni-filtered Cu-Ka radiation, A =1.541 78 A) was in full agreement with previous studies;8 a broad peak occurred at 26 = 12.5" with a second, low-intensity peak at 28 =48.2". Isothermal thermogravimetric dehydration (at 150 "C) of the sample gave a total water loss of 1.3H20 per ZrP formula unit [i.e.in this study p-ZrP =Zr(HPO4),.1.3H,O]. QNS Measurements QNS spectra were collected on the time-of-flight instrument IN6 at the Institut Laue-Langevin (ILL, Grenoble). The p-ZrP film was contained in a sealed slab-shaped aluminium can of circular cross-section. An incident neutron beam with io=5.9 A was used; the resolution function for IN6 is known to be a close wproximation to a gaussian. Any quasi- elastic broadenings would be consequent on motions with a characteristic time of ca. s. Data acquisition times were typically 2 h. Spectra were recorded across an energy range of -2 <E/meV <214 Fnd a range of elastic scattering vector magnitude 0.25 <Qel/A-' <1.75 (at scattering angle 6, Qel= 47r sin 6/10).QNS spectra were recorded for slab orientations of 135" and 45" to the incident beam (corresponding to 'transmission' and 'reflection' of neutrons respectively), and at temperatures T/K=363, 348, 333, 318, 303, 288, 273, 258 (controlled by a standard ILL cryostat with a heated centre- stick). For both orientations the experimental Qel-dependent resolution function (scattering from a similarly mounted vanadium sheet sample) and empty-can scattering were determined at T =300 K. After subtraction of background and empty-can scattering, scattering spectra were corrected for absorption and slab geometry, and converted to the symmetrised scattering law S(Q,o)form (all steps using standard ILL procedures), where Q is the scattering vector.Spectra at Qel values contaminated by Bragg scattering (as determined from the raw dada by using the ILL program CSUM) were ignored, uiz. Qel/A-'= 1.35, 1.46 for the sample in transmissiqn geometry (135" to the incident neutron beam) and Qel/A-' =0.55, 0.66, 1.75 for the sample in reflection geometry (45" to the incident neutron beam). Results QNS spectra recorded for T>318 K showed appreciable quasielastic broadening for both orientations of the sample. Spectra below this temperature were indistinguishable from the instrumental resolution function (at all values of Qel and for both orientations of the sample) and were therefore not used in data analysis.The further discussion of QNS results will consider spectra at 363 K (at which the largest quasielastic broadenings were observed), but the same general features were observed at lower temperatures. Fig. 2 and 3 show the Qel dependence of the scattering law S(Q, o)at 363 K for the sample in transmission (135") and reflection (45") geometries, respectively. Spectra were initially fitted individually to the empirical Qel-dependent resolution function [i.e. assuming no quasielastic broadening; A,( Q)= 1 in eqn. (1) below]. For IN6 that function is known to be approximately gaussian in form; dashed lines in Fig. 2 and 3 correspond to gaussian fits to the eel-dependent resolution function (no broadening), with the corresponding instrumental resolutions being given in Table 1.Quasielastic broadenings are clearly evident at high Qel values. The form of the scattering law will depend on the detail of the dynamic processes that the hydrogenic species present in a given population undergo. If different populations of 'H are involved in different motions, the observed spectra will result from summation of the various contributions. For a popu- lation 'static' on the instrumental timescale the scattering law (before convolution with the instrumental resolution function) is a 6 function, for a reorienting population it is the sum of a 6 function and one or more Lorentzian terms (with one Lorentzian being dominant), and for a diffusing population it is Lorentzian in form." p-ZrP film offers a complicated set of proton environments, the resulting total scattering law then corresponding to the population-weighted sum of the laws for the individual environments.Thus, Hs in acid phosphate groups would contribute a 6 function, interlamellar H20s could contribute a 6 function and a Lorentzian of Qe,-independent width, and Hs involved in diffusion (either as H+ or on a carrier) could contribute a Lorentzian of Qel-dependent width. Further, the defective nature of the film leads to incorporation of non-ideal H20 environments, and possibly also H30+.Full interpretation of the experimental scattering laws is, consequently, not possible, but a qualitative discussion is possible. Transmission Geometry Spectra obtained in this geometry could be fitted individually and fully satisfactorily [with no systematic deviation of the model S(Q,co) from the experimental data] to a simple analytical form, consisting of a simple scattering law S(Q, ~)=Bo(Q>6(~)+F(Q,0) (1) convoluted with the instrumental resolution function.The quasielastic component F(Q, co) was taken to be adequately represented by a single Lorentzian, L (see above). The empiri- cal elastic incoherent structure factor [EISF, Ao(Q)] is the ratio of the elastic to the total (elastic +quasielastic) intensity in the incoherent scattering spectrum. Ao(Q>=Bo (Q)/CBo(Q)+ SF(Q, a)dml =Bo(Q) for normalised S(Q,co) (2) The empirical EISF as a function of Qel is shown in Fig. 4. The variation of the halfwidth, r, of the Lorentzian compo- nent, L, with Qel is shown in Fig.5. In the presence of a single reorientational motion of a hydrogenic species r would be essentially independent of Qel;" this not the case in this study. J. MATER. CHEM., 1994, VOL. 4 '.+it, I ArA-CC+i .ti" +i cc* . i 4 *I Fig. 2 The scattering law S(Q, w)obtained on IN6 in transmission geometry (slab inclined a! 135"to the incident neutron beam) for pellicular zirconium phosphate film at 363 K and (left-to right) Qel=0.252, 0.748, 1.159 and 1.558A-I. Dashed lines correspond to fits to the Qe,-dependent gaussian instrumental resolution function (i.e.assuming no broadening). #,I 1 1 1 0,:-0.4 4.2 0 0.2 0.4 0.6 I, Fig. 3 The scattering law S(Q, w) obtained on IN6 in reflection geometry (slab inclined at- 45" to the incident neutron beam) for pcllicular zirconium phosphate film at 363 K and (left-to right) Qe1=0.252, 0.748, 1.159 and 1.558 A-I.Dashed lines correspond to fits to the Qel-dependent gaussian instrumental resolution function (i.e.assuming no broadening). In the presence of only diffusive motion of hydrogenic species Table 1 Empirical resolutions (FWHM) obtained by fitting the exper- it is common to assume that rmQ:l;" this law also is not imental resolution function to a gaussian form obeyed in this study. The observed variation in r with Qel (Fig. 5) could be interpreted as observation of a combination -QA resolution/peV R of these motional types for different populations of hydrogenic transmission geometry species.The individual contributions to the scattering law 0.252 43.2 0.997 could not be resolved. 0.748 45.8 0.967 1.250 54.2 0.980 1.558 66.3 0.995 Reflection Geometry 40.60.252 reflection geometry 0.982 Spectra obtained in this geometry could be fitte< adequately 0.758 38.5 0.970 to a law of the form of eqn (1) only at Q,,< 1.0 A-'. Adding 1.250 48.4 0.992 a second Lorentzian component to eqn. (1) failed to bring 1.558 51.1 0.943 the model law and the empirical data into coincidence at high Qe, values, suggesting either that several components were J. MATER. CHEM., 1994, VOL. 4 It I Fig. 4 Variation of the elastic incoherent structure factor, EISF, with scattering vector magnitude, Qel, for a p-ZrP film at 363 K in ‘transmission’ geometry.Vertical lines indicate associated error bars. 100) 1 + 4 pure diffusion pure rotation V.0.0 1.o 2:o 3.0 Q,,~A-~ Fig. 5Variation with scattering vector magnitude, Qel, of the half- width, r,of the Lorentzian component in the scattering law [eqn (l)] for a p-ZrP film at 363 K in ‘transmission’ geometry. Vertical lines indicate associated error bars. Dashed lines illustrate the forms of the variations anticipated for pure rotation (horizontal) and pure trans- lation (sloping); the height of the horizontal line and the gradient of the sloping line have been given arbitrary values for the purpose of illustration. present adding to the quasielastic intensity at higher Qel or that the quasielastic broadening (<10% of the total intensity) is insufficient for reliable modelling with the available data.In view of these difficulties in fitting, a meaningful presentation of variations in EISF and I? with Q,, could not be given for this geometry. It is, however, evident in Fig. 2 and 3 that the quaisielastic broadening at high Qel does not extend to such high and low energies as in transmission geometry. Influence of Sample Orientation The observations above indicate that the form of Qel-depen- dent QNS spectra is a function of the orientation of the p-ZrP film with respect to the incident beam. As already suggested for conductivity this anisotropy can be related to the partial ordering of the ZrP lamellae in p-ZrP, which results in lamellae tending to lie in the plane qf the film.Two special cases exist at Qel= 1.51 A-l (8=45”): in trans- mission geometry Q then lies parallel in the plane of the film (parallel to the ZrP lamellae if stacking were perfect, Q= Q,,), while in reflection geometry Q is perpendicular to the film (normal to the ZrP lamellae if stacking were perfect, Q= el).The QNS spectrum in transmission geometry thus depends on motion parallel to the plane of the film, while that in reflection geometry depends on motion perpendicular to the film. It follows that the observed quasielastic broadenings at high Qel values (Fig. 2 and 3) in transmission (Q=Q,,)and reflection (QzQl)geometries result primarily (stacking of lamellae will not be perfect) from components of motions in and perpendicular to the plane of the film, respectively.In Fig.2 and 3 it can be seen that the broadened component (observed at high Q,,) is more intense in transmission geometry; at Qel= 1.558 A-l, for instance, the fit to the resolution function accounts for ca. 90% of the total intensity in reflection geometry but for only ca. 65% in transmission geometry (using model-independent intensities estimated using the trapezium rule). This anisotropy may be related to more facile diffusion between lamellae and across particle surfaces than perpendicular to them. The latter process would rely on convoluted pathways and accessing a range of defect types, and this could account for the difficulty in fitting the scattering law at high Qel (the widths of quasielastic contributions arising from diffusion are proportional QZ, 11) in reflection geometry.The greater overall width of quasielastic broadening at high Qel in transmission geometry may indicate that diffusion is predominantly in the plane of the film. Contributions to quasielastic broadening arising from reorientation of interlamellar water can also be expected to differ in the two geometries. p-ZrP film is a deceptively attractive system for investi- gation of the orientation dependence of quasielastic scattering. The system is indeed partially oriented but is, in fact, massively defective (as exemplified by the variable water content) with imperfect stacking of ZrP lamellae.The observation of a diffusive motion [of water, or H+ (by a Grotthus mechanism of hopping between H,O carriers), or H30+, or all three species] in this study, and of enhanced protonic conductivity in low-crystallinity ZrPs in general,13 is consequent on this non-ideality. In contrast, NMR relaxation studies of highly crystalline a-ZrP detect only reorientation of interlamellar water molecules.14 Conclusions Quasielastic broadening consistent with hydrogenic species undergoing motions with a timescale of ca. s in p-ZrP was observed at T>318 K in this work. The form of the scattering law was found to be dependent on the relative orientation of the sample film and the incident neutron beam. The Qel dependence of the scattering law with the sample in ‘transmission’ geometry [in which the origin of scattering is predominantly components of motion in the plane of the film (parallel to ZrP lamellae)] is consistent with detection of both reorientational and translational (diffusion parallel to the plane of the film) motions.QNS spectra with the sample in ‘reflection’ geometry could not be modelled with a simple scattering law, but quasielastic scattering was less intense overall than in ‘transmission’ geometry. We thank the Institut Laue-Langevin for access to the neutron spectrometer IN6. We thank SERC for supporting the Exeter neutron scattering programme and for a studentship for H.A.P. This work was supported in part under the Science programme of the Commission of the European Communities.A.P. thanks the Istituto Superiore Ricerca Materiali (Terni) for a Fellowship. References 1 A. Clearfield and G. D. Smith, Inorg. Chem., 1969,8,431. 2 A. Clearfield and J. A. Stynes, Inorg. Chem., 1964,26, 117. J. MATER. CHEM., 1994, VOL. 4 1317 3 4 5 6 7 8 9 G. Alberti and E. Torracca, J. Inorg. Nucl. Chem., 1968,30,317. G. Alberti, U. Constantino, S. Allulli and M. Massucci, J. Inorg. Nucl. Chem., 1975,37, 1779. G. Alberti, U. Costantino and R. Giulielli, J. Inorg. Nucl. Chem., 1980,42,1062. T. Mitsumoto, Y. Horri, H. Narai and I. Motooka, Nippon Kagaku Kaishi, 1987,8, 1541. H. Benhamza, P. Barboux, A. Bouhaouss, F. Josien and J. Livage, J. Muter. Chem., 1991, 1, 681. G. Alberti, M. Casciola and U. Costantino, J. Colloid Interface Sci., 1986,107,256. G. Alberti, M. Casciola, U. Costantino and M. Leonardi, Solid State Ionics, 1984, 14,289. 10 11 12 13 14 M. Casciola and U. Costantino, Solid State Ionics, 1986,20,69. M. Bee, Quasielastic Neutron Scattering: Principles and Applications in Solid State Chemistry, Biology and Materials Science, Adam Hilger, Bristol, 1988. R. C. T. Slade, C. R. M. Forano, H. A. Pressman, J. M. Nicol, A. Peraio and G. Alberti, J. Muter. Chem., 1992,2, 583. G. Alberti, M. Casciola, U. Costantino, G. Levi and G. Ricciardi, J. Inorg. Nucl. Chem., 1978,40, 533. R. C. T. Slade, C. R. M. Forano, A. Peraio and G. Alherti, Solid State Ionics, 1993,61,23. Paper 4/02386B; Received 22nd April, 1994

ISSN:0959-9428    

DOI:10.1039/JM9940401313

出版商:RSC    

年代:1994

数据来源: RSC

摘要:

J. MATER. CHEM., 1994,4(8), 1319-1323 Novel Structural Arrangement for Divalent Metal Phosphonates: Synthesis of tert-Butylphosphonates and Structure of CO[(CH~)~CPOJ*H,O Jean Le Bideau," Alain Jouanneaux; Christophe Payena and Bruno Bujoli*" a IMN, UMR CNRS 170, Faculte des Sciences et des Techniques, 2 rue de la Houssiniere, 44072 Nantes Cedex 03, France Laborafoire de Resonance Magnetique, Faculfe des Sciences, Universite du Maine, 7201 7 Le Mans Cedex, France Laboratoire de Synthese Organique, URA CNRS 475, Faculte des Sciences et des Techniques, 2 rue de la Houssiniere, 44072 Nantes Cedex 03, France The synthesis and characterization of new divalent metal tert-butylphosphonates are described: M"[(CH3),CP03].xH20 [MI' =Co, Mn (x =1); M"=Zn (x =2/3)] and Cu,,,0,,,[(CH3),CPO&H,0.Co[(CH3),CPO3]~H,O crystallizes in the monoclinic space group P2,/c with a =12.256(1)A, b =17.939(1)A, c =10.769(1)A, p= 93.57(1)", V= 2363.1(4) A3, Z=12, with R = 0.064 and R,=0.075 for 1805 observed reflections, according to the criterion />30(/). The layer arrangement of this new phase is different from that observed in the case of the n-alkyl M"(RP03).H20 analogues owing to the steric effect of the bulky tert-butyl group. The structural relationship between the cobalt, manganese and zinc compounds is discussed. The observed magnetic moments are consistent with the presence of high-spin Mn" or Co" and with the existence of both octahedral and tetrahedral environments about these metals. Since the first example of the lamellar phosphonate Zr(C6H5P03)2, described in 1978 by Alberti et al,' many studies have been devoted to tetravalent metal phosphon- ates M'V(RP03)2[M'V=Sn, Ti, Th, U, Ce, Zr]2,3 with the same layer arrangement as the well known a-ZrP [Zr( HOP03)2-H20]4 in which the hydroxy groups pointing towards the interlayer space are replaced by organic radicals, R.All these materials were prepared by the reaction of phosphonic acids with metallic salts. More recently, the use of phosphonic acids as precursors to lamellar metal phosphon- ates has been extended, leading to new structures depending on the nature and oxidation state of the metal centre, including vanadium(1v) phosphonates,' divalent"' and trivalentl03" metal phosphonates.Since 1988, we have intensively studied the chemistry of divalent metal phosphonates (Mn, Fe, Co, Ni, Cu, Zn), reporting the structure and the original magnetic properties observed for some of these corn pound^.^,^*'^ At the same time, it seemed very attractive to investigate the possibility of anchoring catalytic complexes (ie. porphyrins) on a phosphon- ate matrix, to perform supported homogeneous catalysis. This required the functionalization of the desired catalytic species with phosphonic acid ends that would then allow the construc- tion of a metal phosphonate net~ork.'~ Until now, however, the chemistry of divalent metal phosphonates has been limited to phenyl or linear alkyl groups and, before using our sophisticated and bulky catalytic phosphonic complexes, pre- liminary studies were performed using tert-butylphosphonic acid, in order to determine whether the reactivity of the P03H2function was affected by the size of the organic radical bound to the phosphorus centre. In the n-alkyl series, two different layered structural arrangements have been described for the divalent M(RPO,).H,O: the first is observed for Mg, Mn, Fe, Co, Ni, Zn and Cd6*7 while the second is specific to copper.8 Consequently, manganese, cobalt and zinc on the one hand, and copper on the other hand, were selected to carry out this study.We describe the synthesis and characteriz- ation of four new tert-butylphosphonates and discuss the effect of the tert-butyl group on the nature of the resulting compounds.Experimental Synthesis and Characterization The chemicals used were of reagent-grade quality from Aldrich and were used without further purification. Compounds 1-4 (Table 1) were prepared by mixing 1 mmol of the desired metal nitrate (Co, Mn, Zn, Cu) and 1mmol of tert-butylphos-phonic acid in the PTFE cell (20 ml capacity) of an autoclave. Then 2.7 ml of 0.75 mol I-' NaOH (2 mequiv.) was added and the volume was made up with distilled water. The autoclave was sealed and placed in a drying oven at 150°C for 7 days. The product obtained was filtered off under suction, washed with water and dried at room temperature. The average yield for the four compounds was 80%. Metal, phosphorus, carbon and hydrogen analyses of pure samples of compounds 1-4 were performed by the CNRS Analysis Laboratory, Vernaison.Thermogravimetric (TG) data were collected on a Setaram TG-DTA92. A heating rate of 5°C min-' was used and runs were carried out under flowing air. The IR absorption spectra (4000-400 cm-were obtained by using an FTIR Nicolet 20SX spectrometer with the usual KBr pellet technique. The X-ray powder diffraction patterns were collected at room temperature in Debye-Scherrer geometry using an INEL CPS 120 detector. Monochromatic Cu-Ka, radiation was used. To obtain a better signal-to-noise ratio, a homogeneous thin layer of powder was placed on the outside of a 0.1 mm diameter capillary with modelling clay as sticking agent. The first 20 reflection positions were determined with the program PROLIX, specially designed for analysing INEL data,I4 and subsequently processed by the auto-indexing program TRE0R.l' The cell constants were finally refined using the U-FIT program.16 Magnetic susceptibility measurements were performed on a Quantum Design SQUID magnetometer.Powder samples of 1, 2 and 3 were initially zero-field cooled down to 5 K and then warmed to 300K in a static iipplied field of 5 kOe. Data were first corrected for the contribution of the sample holder. As expected, the Zn phase was found to be diamagnetic with Xdia close to the value calculated from Pascal's constants. Data for 1 and 2 were then corrected for diamagnetism using Pascal's constants. J. MATER. CHEM., 1994, VOL.4 Table 1 Composition and TG data for tert-butylphosphonates compound 1 Co [(CH,),CPO,] *H,O 2 Mn[(CH,),CPO,] -H,O 3 Zn [(CH,),CPO,] -2/3H,O 4 CUi ,7500.75[(CH3 )3Cpo31*HzO dehydration temperaturerc; metal (YO)” P (Yo)” c (Yo)” H (%)” weight loss (YO)” 27.68 14.56 22.50 5.17 35 to 250 (27.90) 26.52 (14.57) 15.00 (22.31) 22.86 (5.13) 5.22 8.5 (8.5) 35 to 170 (26.30) 30.66 (14.84) 14.53 (22.97) 22.50 (5.26) 4.84 8.5 (8.6) 35 to 250 (30.41)40.1 1 (14.67)11.18 (22.45) 17.32 (4.83) 3.97 5.5 (5.6) 265 (40.10) (11.11) (17.24) (4.00) b “Experimental values in brackets. ’Dehydration concomitant with P-C bond scission. Structure Determination of Co [(CH,),CPO,]*H,O A blue platelet of Co [(CH3),CPO3].H,O having approximate dimensions 0.025 x 0.15 x 0.15 mm3 was mounted on a glass fibre.All measurements were made on an Enraf-Nonius CAD-4 diffractometer yith graphite-monochromated Mo-Ka radiation (A=0.710 73 A). Cell constants and an orientation matrix for data collection were obtained from least-squares refinement, with use of the setting angles of 25 randomly oriented reflections in the range 10”<28 <35”, corresponding to a monoclinic cell. To check the crystal and instrument stability, three representative reflections were measured every 60 min and no decay was observed. An empirical absorption correction based on $-scan measurements was applied and the data were corrected for Lorentz and polarization effects. The data were collected out to 60” in 28 scan technique.On the basis of the systematic absences (OkO, k= 2n+ 1; h01; 1=2n+ 1) and the successful refinement of the structure, the space group was found to be P2,lc. The atomic scattering factors were taken from ref. 17 and anomalous dispersion corrections were taken from ref. 18. For the data reduction, structure solution and refinement, the MOLEN program (1990 version), written by Kay Fair, was implemented on a micro VAX 3900 computer. Unique reflections (1805) corre-sponding to the condition I> 341) were used. The positions of the cobalt and phosphorus atoms were determined from a three-dimensional Patterson map, with the oxygen and carbon atoms being found from successive differ- ence Fourier maps.The non-hydrogen atoms were refined anisotropically, except for the carbon atoms that were refined isotropically due to the limited number of reflections. The final cycle of full-matrix least-squares refinement for 2 12 variables converged (largest parameter shift was 0.03 times its esd) with unweighted and weighted agreement factors of R = C (IF,[ -~Fc~)/Z~Fo~=0.064 and R, =[Cw(lFoI-IFc1)2/Zw(F,”)]1/2 =0.075, where w =4F,2/[0(F02)]2. Crystallographic data and refinement conditions are listed in Table 2.t Results and Discussion The tert-butylphosphonates resulting from the reaction of tert-butylphosphonic acid with cobalt, manganese, zinc and copper nitrate are denoted 1, 2, 3 and 4, respectively, and are described in Table 1.Positional and thermal parameters of the atoms of 1 are given in Table 3, and selected bond distances and angles are listed in Table4. Fig. 1 shows the coordination environment of the three types of Co positions and the numbering scheme used in the tables. This structure f Supplementary crystallographic data are available from the Cambridge Crystallographic Data Centre; see Information for Authors, J. Mater. Chem., 1994, issue 1. Table 2 Crystallographic parameters for Co[(CH,),CPO,] H,O empirical formula mol wt. habit crystal sizelmm crystal system a14 bl+ CIA PldFgrees V/A3z space group Pcalclg cm -T/”CA( Mo-Kct)/A p/cm -observed data refined parameters RV,) RW(F0) CoPO,C,H,, 213.04 deep blue platelet 0.025 x 0.15 x 0.15 monoclinic 12.256( 1) 17.939( 1) 10.769( 1) 93.57( 1) 2363.1 (4) 12 P2,/c (no.14) 1.769 25(1)0.7 1073 22.95 1805 212 0.064 0.075 is layered and made of corrugated sheets in the (b, c) plane. There are three different sites of cobalt atoms. Only one of them, Co( l),has an octahedral environment made from three phosphonate oxygens [0(2)”, 0(2)’, 0(5)d] and three water molecules [0(6), 0(9), 0(11)”] yith Co-0 distances ranging between 2.04( 1) and 2.20( 1)A. These Co( 1)06 octa- hedra form pairs with a common edge resulting in Co( 1)-0(2)-Co[ 1)-0(2) parallelograms [@termetallic dis- tance: 3.!74(3)A] with a long [2.20(1)A] and a short [2.08( 1)A] Co( 1)-0(2) bond. Alternatively, a tetrahedral environment is observed for the two other cobalt positions, only bonded to phosphonate :xygens with Co-0 distances between 1.89(1) and 2.01(1)A: Co(2) [O(l), 0(4), 0(7)”, O(lO)dand co(3) [0(3)”, 0(3)f, O(8)c0(12)b.The Co(3)04 tetrahedra are arranged in edge-sharing pairs, with again Co( 3)-O( 3)-C00(3)-0( 3) parallelograms [intermetallic dis-tance: 2.996(3) A].Each oxygen of the three types of PO3 groups is bonded to metal atoms, ensuring the connection of the C0(l)06, C0(2)04 and c0(3)04 polyhedra within the layer, according to a sequence of C0(2)04 chains (parallel to c) intercalated by chains based on alternating Co( 1)06pairs and c0(3)04 pairs (parallel to c)(Fig. 2). The (CH,),C groups extend into the interlamellar space, roughly perpendicular to the corrugated layers (Fig.3). Although 1 has the same formulation as its n-alkylphos- phonate analogue^,^,^ a different structural arrangement is observed, probably due to the bulkiness of the tert-butyl group. Only one of the three sites of cobalt, Co( 1)is hydrated with three water molecules in its coordination sphere. This is consistent with the continuous weight loss (35-250 “C) recorded in TG data and with the two minima on the DTG J. MATER. CHEM., 1994, VOL. 4 Table 3 Atomic positional and thermal parameters for CO [(CH3),CP03] -H20 atom X Y z Beqn 0.0557( 2) 0.1 342( 2) 0.10 14( 2) 0.1873 (3) 0.2090( 3) 0.903 1 (3) 0.1937(9) 0.9038( 7) 0.9401(8) 0.2162( 9) 0.8850(8) 0.1968( 9 0.9900( 9 0.8466( 9 0.010(1) 0.1450(9 0.981 (1) 0.170( 1) 0.688( 1) 0.355( 1) 0.776( 1) 0.414( 2) 0.653( 1) 0.742( 2) 0.372( 2) 0.597( 1) 0.71 3( 2) 0.401(1) 0.686( 2) 0.793 (2) 0.0521 (1) 0.1814( 1) 0.0360( 1) 0.0144( 2) 0.1976( 2) 0.0861 (2) 0.2286( 6) 0.0021(5) 0.0416( 6) 0.0982( 6) 0.0378( 6) 0.1170(6) 0.1449(6) 0.0126(5) 0.1 171 (7) 0.2433( 6) 0.1428( 6) 0.1 176(6) 0.0369( 9) 0.1994( 9) 0.132 1 (9) 0.148(1) 0.018( 1) 0.184( 1) 0.169( 1) 0.015( 1) 0.219( 1) 0.072( 1) 0.179( 1) 0.122( 1) 0.4030( 2) 0.7505( 2) 0.9573( 2) 0.6850( 3) 0.0343 (4) 0.8OO9( 4) 0.9035( 9) 0.4166( 9) 0.9193( 9) 0.687( 1) 0.6881(9) 0.422( 1) 0.786( 1) 0.1870( 9) 0.243( 1) 0.121( 1) 0.504( 1) 0.040( 1 ) 0.345( 1) 0.077( I) 0.835( 1) 0.988(2) 0.478 (2) 0.721 (2) 0.215( 2) 0.246( 2) 0.335 (2) 0.571(2) 0.847( 2) 0.953( 2) 1.44(4) 1.57(4) 1.83(4) 1.28( 7) 1.47(7) 1.37(7) 2.0(2) 1.4(2) 2.1(2) 2.3(2) 2.1(2) 2.4(2) 2.7(3) 1.8(2) 2.7(2) 2.5(2) 3.0( 3) 1.8(3)* 2.0(3)* 1.8(3)* 3.1 (3)* 3.6(4)* 3.2(4)* 3.6(4)* 2.8(3)* 3.7(4)* 3.5(4)* 3.4(3) 3.3(4)* 3.3(4)* "The cobalt, phosphorus and oxygen atoms were refined aniso- tropically and are given in the form of equivalent displacement parameter defined as Be, =4/3CiCj/Ii&4,. Values with asterisks denote atoms that were refined isotropically. Table 4 Selected bond lengths (,/A)and angles (/degrees) for the non-hydrogen atoms of Co[( CH,),CPO,] *H,O Co( 1)-O(2)" 2.08(1) C0(3)-0(12)~ 1.89(1) Co( 1)-0(2)f 2.20( 1) P(1)-0(2)a 1.54(1) Co( 1)-O( 5)d 2.04( 1) P( 1)-0(4) 1.54( 1) Co(1)-0(6) 2.08( 1) P(1)-O(8)" 1.54( 1) Co( 1)-O(9) 2.13(1) P(l)-C(l)" 1.83( 1) Co( 1)-0(11)" 2.19( 1) P(2)-O( 1)' 1.51(1) Co(2)-O( 1) 1.95( 1) P(2)-O( 10) 1.50( 1) Co( 2)- O(4) 1.95( 1) P(2)-O( 12) 1.51(1) Co(2)-O( 7)" 1.94( 1) P(2)-C(2) 1.82(1) co (2) -0( 10)d 1.95( 1) P(3)-0(3) 1.55(1) CO( 3)- o(3)" 1.99(1) P(3)-0(5) 1.50( 1) CO( 3)-0( 3)f 2.01(1) P(3)-0(7) 1.51(1) CO (3)- 0(8y 1.92( 1) P(3)-C(3) 1.82( 1) 0(2)"-C0( 1)-0(2)c 84.3(3) 0(5)c-C0( 1)-0(9) 97.3(4) 0(2)"-C0( 1)-0(5)c 92.3(4) 0(5)'-C0(1)-0(11)" 175.5(4) 0(2)"-Co( 1)-O(6) 167.0(4) 0(6)-Co( 1)-o(9) 87.2(4) 0(2)"-C0( 1)-0(9) 95.8(4) 0(6)-C0(1)-0(ll)" 84.4(4) 0(2)"-C0( 1)-O( 11)" 83.3(4) 0(9)-Co( 1)-O( 11)" 84.2(4) 0(2)"-C0( 1)-0(5)c 90.4(4) 0-CO(2)-0 109.6(5)g 0(2)'-C0(1)-0(6) 91.1(4) 0-CO (3)- 0 109.4( 5)g 0(2)'-C0( 1)-0(9) 172.2(4) 0-P(1)-0 110.9(5)g 0(2)'-C0( 1)-O( 11)" 88.1(4) 0-P(2)-0 109.9(5)g 0(2)'-C0(1)-0(6) 99.8(4) 0-P(3)-0 110.6(5)g "Atom related by x-1, y, z; *x, y, 1+z; '1 -x, -y, 1-z; -x, 1/2 +y, 1/2-z; y, z-1; f 1-x, -y, 2 -z; gtetrahedral average.curve: the first (150°C) corresponds to the loss of two water molecules, probably 0(9) and O(11)" taking into account the comparative water-cobalt distanfes [Co(1)-O( 11)"= 2.19(1)A; C0(1)-0(9)=2.13(1) A; c0(1)-0(6)= 2.08( 1)A]. The last water molecule is lost at a higher tempera- Fig. 1 Schematic representation of the coordination about the three types of cobalt atoms in Co [(CH3),CPO3].H2O, and the numbering scheme used in the tables Fig. 2 Schematic representation of a Co [(CH,),CP0,].H20 layer viewed down the a axis.The carbon atoms have been omitted for clarity. Fig. 3 Layer arrangement in Co[(CH3),CP03].H20 as viewed down the c-axis. The carbon atoms are in black. ture (240 "C). This dehydration phenomenon is not reversible, and would lead to a three-coordinate cobalt atom; conse- quently it is evident that a structural rearrangement takes place after dehydration, for example through a shift of one of the phosphonate oxygens to complete the coordination sphere of Co(1). Such a rearrangement has previously been described for copper n-alkyl phosph~nates.~ This rearrange- ment is apparent in the IR spectrum of the dehydrated Co(ButPO,) compound. A drastic change in the v(P02) region is observed after dehydration of the sample, which may be explained by major modifications of the metal-PO3 linkage within the layer.An amorphization of the product occurs after the removal of the three water molecules, and the powder XRD spectrum shows only three hOO lines, inditating a decrease of the interlayer spacing, from 12.2 to 11.4 A. In order to demonstrate whether the layer arrangement for 1,2 and 3 was similar, we have compared their IR and X-ray data. In the case of Co and Mn, the IR spectra are nearly identical, particularly in the v( PO,) region, which is character- istic of the metal-PO3 linkageoh the slabs. Moreover, the c%ll parameters of 2 [a = 12.30( 1) A; b =18.OO(1)A; c = 10.75(1)A; fl=91.0(1)"] are also closely related to those of 1.On the other hand, the water content per formula unit in compound 3 is only two-thirds of the value in compound 1 or 2. We can, however, reasonably assume that the Zn compound adopts a layer arrangement similar to that seen in 1 and 2, differing only in the coordination of the hydrated metal site noted Co( 1) in the structural description of 1. While Co( 1)has an octahedral environment with three coordinated water mol- ecules, in 3 the zinc atom would be in a five-coordinate geometry (probably square pyramidal) with only two water molecules bound to the metal centre. This assumed difference between 1 and 3 should not induce significant changes in the IR spectrum of 3 compared with that of 1, and that is effectively the case as the two spectra are very similar.An indirect confirmation for this hypothesis is the strong simi- larity between the IR spectra of Co( ButP03) and Zn( Bu'PO,) prepared by thermal treatment of the corresponding hydrates (Fig. 4). In the v(P02)region, characteristic of the arrange- ment within the inorganic layer, comparisons of the frequency and intensity of the main bands for Co(Bu'P0,) (1154, 1061, 944 cm- ') and Zn(Bu'P0,) (1 165, 1065, 962 cm-') imply that the corresponding hydrates probably undergo the same type of rearrangement upon dehydration and that their respective structures are closely related.oIn addition, the Fefined cell paraometers of 3 [a = 12.30(1)A; b =17.92(1)A; c= 10.33(1)A; orthorhombic] are similar to those of 1 and 2, with, only a deviation concerning the c parameter that is ca.0.4A shorter than it is in 1 or 2, probably because of the difference in the coordination number of site 1 in the Zn compound. From the magnetic data, the Mn and Co compounds are found to be paramagnetic over the entire 5-300 K temperature range. This can be seen in Fig. 5, which shows a plot of the inverse molar susceptibilities. For the Mn compound, the Curie-Weiss law is obeyed in the 20-300 K region. The Curie constant C=4.5 emu K-' mol-' corresponds to an effective moment peff=6.0~~which is very close to the expected value for high-spin Mn" in either an octahedral or tetrahedral coordination (5.92,~~). This does not contradict the possible similarity of the structures of the manganese and cobalt tert- butylphosphonates.Antiferromagnetic coupling between Mn" ions are indicated by a negative Weiss constant, 0,z -40 K, and a slight departure (lower susceptibilities) from the Curie- Weiss law below 20 K. Both phenomena could correspond to magnetic coupling within Mn20, and/or Mn2010 entities similar to that found in 1. For the Co compound, the Curie law is approximately obeyed over the whole 5-300K range. J. MATER. CHEM., 1994, VOL. 4 c a20" 0.160 a 0.108 0.056 li, I' 0.004 ' '4( 10 3200 2400 ' 1600 ' 800 ' waven um berkm-' Fig. 4 Absorption IR spectra of (a) Co[(CH,),CPO,] and (b) Zn C(CH3)$Po3 1 120r n I U U 0 0 0 100 200 300 TIK Fig. 5 Temperature dependence of the inverse molar susceptibility for Co [(CH,)3CP03].H,0 (0)and Mn [(CH3),CP03].H,0 (0) The room-temperature moment 4.8~~is consistent with the presence of both octahedral and tetrahedral high-spin Co" in the observed 1/3, 2/3 ratio. Finally, on the basis of empirical formula and IR data, the structure of copper tert-butylphosphonate 4 is different from the structure of compounds 1, 2 and 3, as was the case in the n-alkylphosphonate series.Despite all our efforts, no single crystal could be obtained for a structural determination. We note that the Cu :P ratio is higher than in the Cu( RPO,).H,O copper n-alkylphosphonates.' This is likely to be a conse- quence of the steric hindrance caused by the tert-butyl group that cannot be accommodated by this latter structure, leading to the cU1.7500.75 [(CH,),CPO,].H,O formulation in order J.MATER. CHEM., 1994, VOL. 4 1323 to decrease the number of bulky organic groups per surface unit in the layer. In conclusion, the chemistry of phosphonates appears to be very rich because the bulkiness of the phosphonic acid precursor does not seem to impede the formation of layered 7 8 9 A. Clearfield, Inorg. Chim. Acta, 1989,155,7; G. Cao, V. M. Lynch and L. N. Yacullo, Chem. Muter., 1993,5, 1000. B. Bujoli, 0. Pena, P. Palvadeau, J. Le Bideau, C. Payen and J. Rouxel, Chem. Mater., 1993,5, 583. Y. Zhang and A. Clearfield, Inorg. Chem., 1992,31,2821. J. Le Bideau, B. Bujoli, A. Jouanneaux, C. Payen, P. Palvadeau phosphonates. Instead, these systems adopt new structural models to adapt to the size of the organic group bound to phosphorus, by combining different geometries of sites for the metal atoms.10 and J. Rouxel, Inorg. Chem., 1993, 32, 4617; J. Le Bideau, C. Payen, P. Palvadeau and B. Bujoli, Inorg. Chem., submitted. P. Palvadeau, M. Queignec, J. P. Venien, B. Bujoli and J. Villieras, Mater. Res. Bull., 1988, 23, 1561; B. Bujoli, P. Palvadeau and J. Rouxel, Chem. Muter., 1990,2, 582; B. Bujoli, P. Palvadeau and J. Rouxel, C. R. Acad. Sci. Paris, Ser. 2, 1990,310, 1213. References 11 G. Cao, V. M. Lynch, J. S. Swinnea and T. E. Mallouk, Inorg. Chem., 1990,29,2112; R. C. Wang, Y. Zhang, H. Hu, R. K.Frausto and A. Clearfield, Chem. Mater., 1992,4, 864. G. Alberti, U. Constantino, S.Alluli and N. Tomassini, J. Inorg. Nucl. Chem., 1978,40, 1113. M. B. Dines and P. M. DiGiacomo, Inorg. Chem., 1981,20,92. D. A. Burwell and M. E. Thompson, Chem. Mater., 1991, 3, 14, and references therein. A. Clearfield and G. D. Smith, Inorg. Chem., 1969, 8, 431; A. Clearfield and J. M. Troup, Inorg. Chem., 1977,16,3311. 12 13 14 15 16 J. Le Bideau, Ph.D. Thesis, Nantes, 1994. B. Bujoli and P. Battioni, unpublished work. P. Deniard, M. Evain, J. M. Barbet and and R. Brec, Muter. Sci. Forum, 1991,79-82,363. P. E. Werner, L. Erikson and M. J. Westdahl, J.Appl. Criistallogr., 1985, 18,367. M. Evain, U-FIT: a Cell Parameter Refinement Program, IMN, Nantes, France, 1992. J. W. Johnson, A. J. Jacobson, J. F. Brody and J. T. Lewandowski, Inorg. Chem., 1984, 23, 3842; G. Huan, A. J. Jacobson, 17 D. T. Cromer, J. T. Waber, International Tables for X-Ray Crystallography, Kynoch Press, Birmingham, 1974. vol. IV, J. W. Johnson and E. W. Corcoran, Chem. Mater., 1990, 2, 91; Table 2.2B. G. Huan, A. J. Jacobson, J. W. Johnson and D. P. Goshorn, Chem. Muter., 1992,4,661. 18 D. T. Cromer, J. A. Ibers, International Tables for X-Ray Crystallography, K ynoch Press, Birmingham, 1974, vol. IV, G. Cao, H. Lee, V. M. Lynch and T. E. Mallouk, Inorg. Chem., Table 2.3.1. 1988, 27, 2781; G. Cao, V. M. Lynch and T. E. Mallouk, Solid State Ionics, 1988, 26, 63; K. J. Martin, P. J. Squattrito and Paper 4/007 15H;Received 7th February, 1994

ISSN:0959-9428    

DOI:10.1039/JM9940401319

出版商:RSC    

年代:1994

数据来源: RSC

摘要:

J. MATER. CHEM., 1994, 4(8), 1325-1329 1325 Intercalation of Polymerized 3-Methyl- and 3,4=Dimethyl=pyrrole in the VOP04 lnterlayer Space Hiroshi Nakajima and Gen-etsu Matsubayashi* Institute of Chemistry, College of General Education, Osaka University, Toyonaka, Osaka 560, Japan 3-Methylpyrrole (3-Mepyrr) and 3,4-dimethylpyrrole (3,4-Me2pyrr) react with powdered VOP0,.2H20 suspended in ethanol to yield intercalation compounds consisting of the reduced VOPO, lattice and poly-3-Mepyrr or poly-3,4-Me2pyrr chains; VOP04~(H20),.4-(EtOH)o~2~(MeC4HNH)o.65 Poly-3-Mepyrr and poly-3,4-Me2pyrr and VOP0,~(H20),~8~(EtOH)0.2~(Me2C4NH)0.6. moieties in the VOPO, interlayer space afford single interlayer spacings of 8.2 and 9.7 A, respectively. Pyrrole (Pyrr) also reacts with VOP04.2H20 solids suspended in ethanol to yield an oxidatively polymerized compound formed on the surface of the VOPO, grains.Factors causing the polymerization of 3-Mepyrr and 3,4-Me2pyrr in the VOP04 interlayer space and electronic interactions of the reduced VOPO, host lattice with the intercalated poly-3-Mepyrr and poly-3,4-Me2pyrr moieties are described based on powder X-ray diffraction patterns, infrared and X-ray photoelectron spectra together with theoretical calculations of molecular geometries and electron spin densities. Various intercalation compounds having alternating organic and inorganic layers have been extensively studied.'9, In particular, the intercalation of organic polymers into inorganic layered lattices has recently attracted much attention and some examples have been rep~rted.~-~ Electrically conducting poly-pyrrole, -thiophene, and -aniline have been thoroughly studied for application,' but their microstructural properties, such as overall chain conformation, packing and degrees of crosslinking, have not been adequately clarified.Laminated composites of alternating conducting polymer/inorganic layers seem to be useful for elucidating the low-dimensional struc- tures of the polymers. Only a few examples of intercalative polymerizations of pyrrole, aniline, and bithiophene using layered Fe0Cl3q4 and V,05*nH,05'6 have been reported, where factors necessary for the polymerizations in the layered space remain unclarified. Vanadyl phosphates, VOP0410-12 and a-VOP04.2H20,11,13-15 known as layered compounds behave as oxidants and undergo intercalation reactions with ~rganic'~-~' compounds.The VOP04 and organ~metallic~~-~~ moieties can be reduced by organoammonium iodides25 and ferrocenyl corn pound^^^-^^ to include the cation molecules in the layered lattices. Thus, oxidative polymerization of pyrrole and its methyl-substituted derivatives is expected to occur in the VOP04 interlayer space. However, polymerization in the layered lattices is difficult, since polymers are often formed oxidatively on the surface of the layered solids to cover them. We have tried to polymerize them in an ethanol solution suspended with powdered VOP04-2H20 and found successful intercalation/polymerization of 3-methylpyrrole (3-Mepyrr) and 3,4-dimethylpyrrole (3,4-Me2pyrr) in the VOP04 lattice. This paper demonstrates an important role of 3-and 3,4-methyl substituents on the pyrrole ring for the intercalative polymerization process and describes characteristic inter-actions between the reduced VOP04 lattice and the interca- lated poly-3-Mepyrr and poly-3,4-Me2pyrr moieties.A preliminary report of the present work has already appeared.26 Experimental Materials VOP0,.2H20 was prepared according to the literature." 3-Mepyrr and 3,4-Me2pyrr were also prepared according to the literat~re.,~ Pyrrole (Pyrr) was commercially available. They were purified by distillation under reduced pressure prior to use. Intercalation/Polymerizationof Pyrr, 3-MePyrr and 3,4-Me2Pyrr in the VOP04 Lattice Finely powdered VOP04-2H20 (33 mg, 1.5 mmol) was suspended in ethanol (10 ml) solution containing Pyrr (300 mg, 4.5 mmol) and the solution stirred for 48 h at 30°C in darkness.The resulting solid was collected by centrifugation, washed with ethanol and acetone several times and dried in vucuo to afford VOPO,(H,O),.,( EtOH)o~2(C4H2NH)o~6 (1). Found: (2, 13.72; H, 3.00; N, 3.44%. CdC. for C,.,H~.~NO~~O~PV: c', 13.86; H, 2.72; N, 3.46%. By a similar procedure, reactions of 3-MePyrr or 3,4-Me2Pyrr with powdered VOP04-2H20 suspended in etha- nol gave VOPO4( H20)1,4(EtOH)o~,(MeC4HNH)o,65(2) and VOPO,(H,O),.,( EtOH)0.2(MezC4NH)0.6 (3), respectively. For 2 found: C, 17.96; H, 3.03; N, 3.61%.Calc. for C3,7H7~lNo~6506~,PV:C, 17.70; H, 2.84; N, 3.68%. For 3 found: C, 19.06; H, 3.82; N, 3.45%. Calc. for C4,0H9~oN,~,07~oPV: C, 18.52; H, 3.50; N, 3.24%. Oxidative Polymerization of 3,4-Me2Pyrr Electrochemical oxidation of 3,4-Me2pyrr was performed in an ethanol solution containing [NBu",][BF,] as an electro- lyte, using a glass cell constructed with a glassy carbon working electrode, platinum file counter-electrode and a satu- rated calomel reference electrode (SCE) according to the literature.28 Poly-3,4-Me2pyrr was grown on the working electrode by oxidation of the monomer under a constant potential (800 mV us. SCE). The content of the BF4 ion in the obtained polymer (0.2-0.3 per 3,4-Me2pyrr unit) was determined by X-ray photoelectron spectra.Poly-3,4-Me2pyrr was also prepared by a reaction of a 10% 3,4-Me2pyrr toluene solution with a 30% FeCl, aqueous solution by using the previously described pr~cedure.~' Physical Measurements Infrared (IR) spectra were recorded on a Hitachi 215 spectro-photometer for the region 4000-650 cm-' in KBr pellets. Powder X-ray diffraction patterns were measured for com- pressed pellet samples with a Shimadzu XD-3A diffractometer employing Cu-Ka irradiation at 30 kV and 20 mA. X-Ray photoelectron spectra (XPS) were measured for compressed pellet samples by Mg-Ka irradiation at 30 kV and 8 mA using a Shimadzu ESCA 750 spectrometer equipped with a Shimadzu ESCA PAC 760 computer analyser. All the spectra were referenced to the gold 4f,,, signal (83.80 eV) for correc- tion of the charge effect.The error of the binding energy determination was estimated to be 0.1eV. Differential thermal analysis (DTA) was carried out on a Seiko I & E TG/DTA instrument under nitrogen atmosphere. Theoretical Calculations Theoretical studies of molecular geometries, electron spin densities and energies for pyrrole and its derivatives were performed using the PM3 molecular-orbital meth~d.~',~~ The MOPAC program, which was revised as SXOS version-6.02 for the use on an NEC SX-2N supercomp~ter,~~ was used for the calculation. Final molecular geometries and energies were obtained by optimizing total molecular energies with respect to all structural variables.Electron spin densities of the radical cations and their heats of formation were optimized using a half-electron (HE) method with restricted Hartree-Fock (RHF) formalism. Results and Discussion Intercalation and Polymerization of Pyrr, 3-Mepyrr and 3,CMe,pyrr in the VOP04 Lattice Compounds 1, 2 and 3, obtained by reaction of Pyrr, 3-Me- pyrr or 3,4-Me2pyrr with powdered VOPO4.2H,O suspended in ethanol, include 0.6-0.65 monomer units per VOPO, moiety. IR spectra of these compounds clearly show the presence of poly-Pyrr, poly-3-Mepyrr or poly-3,4-Me2pyrr without any evidence of free monomers, as illustrated in Fig. 1 which also shows the spectrum of poly-3,4-Me2pyrr prepared chemically. Intercalated poly-3-Mepyrr and poly-3,4-Me,pyrr have been isolated from 2 and 3 by dissolving the VOPO, framework in an NaOH aqueous solution, followed by the J.MATER. CHEM., 1994, VOL. 4 treatment of the solids by an excess HC1 aqueous solution. XPS of these compounds have exhibited bands of vanadium 2pSi2 electrons at 516.8 eV, which indicates the reduction of the Vv sites of the VOPO, host lattice to the VIv state. In accordance with these findings, these compounds show intense, broad electron paramagnetic resonance (EPR) signals due to the VIv state, as described below. X-Ray powder diffraction patterns of these compounds exhibit clear (001) and (200) reflections, revealing that the layered structures of the VOPO, lattice are preserved for them (Fig. 2), as reported for other VOPO, intercalation corn pound^.^^ The interlayer djstances for 2 and 3 can be determined to be 12.8 and 13.8 A, respectively.The net expansions of the interlayero space for these compounds are estimated to be 8.7 and 9.7 A based on the interlayer distance of 4.1 A for anhydrous VOP0,.12 These findings suggest that poly-3- Mepyrr and poly-3,4-Me2pyrr moieties are located in the interlayer space, their molecular planes being ordered approxi- mately perpendicular to the VOPO, sheet. These arrange- ments are compatible with that of the poly-Pyrr moiety in the FeOC1-poly-Pyrr intercalation c~mpound.~ On the other ha@, the interlayer distance of 1 has been determined to ke 6.5 A; the net expansion of the interlayer space is only 2.4 A. This suggests that no poly-Pyrr moieties are intercalated into the VOPO, interlayer space, the Pyrr molecule being poly- merized on the surface of the VOPO, grains.This seems to be consistent with the presence of only water molecules in the VOPO, interlayer space of 1, as deduced from the thermal analysis.26 The DTA curve for VOPO4.2H,O shows two endothermal bands corresponding to the release of two kinds of water molecule with the rise in temperature; the endother- mal band observed around 120°C corresponds to the release of the water molecule coordinated to the vanadium site and the band around 60°C is ascribed to the release of the water molecule held in the VOPO, interlayer space through the hydrogen bonding to the coordinated water molecule (Scheme l).16934 Compound 3 has exhibited a broad DTA band around 60°C due to the release of water and ethanol molecules.This comes from some destruction of the layered VOPO, structure assisted by the coordinated and hydrogen- bonded water and ethanol molecules16 caused by the intercal- ation of poly-3,4-Me2pyrr moieties. A similar broad DTA band has also been observed for 2. On the other hand, 1 exhibits two bands around 70 and 130°C, which indicate clearly the release of two kinds of water molecule, as observed for VOP04-2H20, although the endothermal band at lower temperature is somewhat broad.26 This supports the fact that no Pyrr moiety is intercalated in the VOPO, lattice but I I 1 A 10 I$OO 1400 1200 1000 800 650 I I I I I I wavenurnber/crn-' 5 10 15 20 25 30 20/degrees Fig.1 IR spectra of: (a) 1; (b) 2; (c) 3; and (d) poly-3,4-Me2pyrr prepared chemically according to the literature2' Fig. 2 X-Ray powder diffraction patterns of (a) 1; (h)2; and (c) 3 J. MATER. CHEM., 1994, VOL. 4 0 II 0 0 II II -V--V-I I H2O H20 Scheme 1 pyrrole is polymerized only on the surface of the VOP04 grains. Structures of the Polymers formed in the VOPO, Interlayer Space 3,4-Me2pyrr can be polymerized oxidatively by coupling only through 2,Scarbons to yield a polymer with a straight chain. Although Pyrr is also polymerized through the oxidative coupling at 2,5-carbons predominantly, couplings at 2,3-, 2,4- and 3,4-carbons can partially occur to form a polymer having a crosslinked or shortly terminated chain str~cture.~,~~ Fig.3 shows XPS bands of carbon lsl,z electrons for 1-3. Compound 1 exhibits an asymmetric band with shoulders at higher energies. These broad structural bands are ascribed to carbons of crosslinked, shortly terminated chain structures or non- coupled 2,Scarbons as well as carbons of partially saturated pyrrole rings.34 On the other hand, 3 exhibits a rather symmetric band with narrower halfwidth (1.8 eV) than that of 1 (2.2eV). The overall linewidth and asymmetry of the band having a peak at 285 eV ascribed to methyl carbons for 3 are appreciably decreased. Thus, the poly-3,4-Me2pyrr moi- eties seem to have less varied kinds of carbon, which is ascribed to the 2,5-coupling owing to 3,4-substituted methyl groups.Compound 2 shows a band-shape intermediate between those of 1 and 3. Considering the occurrence of polymerization of 3-Mepyrr in the VOP04 interlayer space, the poly-3-Mepyrr moiety is also likely to have an essentially 1 1 I I 290 285 280 binding energylev Fig. 3 XPS bands of carbon electrons of the polymers included in the VOPO, solids: 1 (-); 2 (-.-); and 3 (---) straight-chain structure, although the polymer skeletons may have somewhat disordered carbons compared with the poly-3,4-Me2pyrr moieties. Since poly-3-Mepyrr is insoluble in organic solvents, it is difficult to anticipate the chain structure chemically or spectro-scopically. In order to estimate chain structures of‘ poly-3-Mepyrr, semi-empirical PM3 calculations have been per- formed on electron spin densities and heats of formation (AfH)of radical cations of the monomer, dimers and trimers as intermediate compounds to poly-3-Mepyrr, as wits calcu- lated for p01y-Pyrr.~~ In the monomer and dimer radical cations [Fig.4(u)-(d)], the spin density on 2 (or 5)-carbon is significantly larger than that on unsubstituted 3 (or 4 )-carbon atoms. These findings may predict essentially selective coup- lings of the radical cations with the 3-Mepyrr monomer through 2,5-carbons. And species (b)or (c) seems to be formed preferentially as a dimer based on calculated AfH values. Trimers (e)-(h)can be formed by reactions of the dimer radical cation (b) or (c) with the monomer.The difference of spin densities on 2,5-carbons and on unsubstituted 3 (or 4)-carbons of the trimer radical cations is rather smaller than those of the monomer and dimer radical cations. However, the coup- ling at the unsubstituted 3 (or 4)-carbons seems to be difficult because of some steric hindrance of neighbouring methyl groups and/or pyrrole rings. Thus, trimer radical cations are also likely to couple with the monomer at terminal 5-carbons predominantly, which leads to an enlargement of the straight chain. These calculations indicate that methyl groups substi- tuted on 3 (or 4)-carbons cause significant effects both steri- cally and electronically on the 2,5-coupling, as supported by the calculation on pyrrole 01igomers.~~ As discussed above, poly-Pyrr generated on the surface of the VOP04 grain may have a more or less branched-chain structure caused by the crosslinking and 2,3-, 2.4-and 3,4-couplings.Thus, a poly-Pyrr moiety formed at the interface 0.200iY0.20N H 0.03+ 0.19 0.17 \I H 4H= 213.1 kcal mor’ AfH= 212.7 kcal md-I (e1 (f1 H AfH= 212.3 k-1 md-l 4H= 212.5 kcal moT’ (91 (h1 Fig. 4 Spin densities and heats of formation (A,H) of radical cations calculated by the PM3 method J. MATER. CHEM., 1994, VOL. 4 VOPO, VOPO4 IJ;*13.8A 9.7 A I I I I 405 400 395 1 I VOPO, I Fig.5 Schematic diagram of the intercalation of (a) poly-Pyrr and (b)poly-Me,pyrr moieties into the VOP04 interlayer space of the VOPO, lattice is prevented from intercalation into the VOP04 interlayer space, as illustrated in Fig.5(u). On the other hand, the poly-3,4-Me2pyrr moiety having a straight- chain structure generated through coupling at 2,5-carbons is suitable for insertion into the restricted VOPO, interlayer space [Fig. 5(b)].The poly-3-Mepyrr moiety having an essen- tially straight-chain structure, as described above, can also intercalate into the VOPO, lattice. Fig. 6 shows XPS bands of nitrogen lsl,? electrons of 2 and 3 as well as that of poly-3,4-Me2pyrr obtained by the electro- chemical polymerization. Poly-3,4-Me2pyrr from electro-chemical polymerization exhibits an asymmetric band having shoulders at higher binding energies. The resolution fitting indicates the dominant peak at 399.4 eV and shoulders at 400.7 and 402.5 eV suggesting varying electronic states of the nitrogen atoms.In this polymer the BF4- anion is located in the proximity of the positively charged nitrogens of the polymer chain, giving effective electric fields at the proximal nitrogen atoms. The main band is due to the nitrogen atoms which are less affected by the BF4-ion and positively charged nitrogens countered by the BF4-ion (0.2-0.3 per monomer unit) give shoulder bands at higher energies.38 On the other hand, 2 and 3 show rather symmetric bands at 399.7 and 400.0 eV with halfwidths of 1.9 and 2.4 eV, respectively. For both the compounds the reduced VOPO, host lattice works as the counter-anion, in which negative charges are delocalized to form an average field of negative charges against the nitrogen atoms of the intercalated polymers.Thus, the positive charges are distributed homogeneously through the nitrogen atoms. Conclusions Methyl-substituted pyrrole derivatives (3-Mepyrr and 3,4-Me2pyrr) can be oxidatively polymerized in the VOPO, interlayer space, whereas pyrrole is polymerized only on the surface of the VOP04-2H20 grains without intercalation. Intercalation of these polymer fragments into the VOPO, interlayer space depends on the regularity of their chain structures: poly-3-Mepyrr and po1y-3,4-Me2pyrr form a binding energyIeV Fig. 6 XPS bands of nitrogen lsl,2 electrons of 2 (---); 3 (-.-); and electrochemically prepared poly-Me,pyrr (-) containing the BF4- ion straight-chain structure suitable for the intercalation and partially branched chains of poly-Pyrr cannot be inserted.Poly-3-Mepyrr and poly-3,4-Me2pyrr fragments in the inter- layer space are affected characteristic average electronic inter- actions by the host lattice. We are greatly indebted to Professor H. Yoneyama, Faculty of Engineering, Osaka University, for the use of the X-ray powder diffractometer and Mr I. Kawafune, Osaka Municipal Technical Research Institute, for the measurement of XPS. References 1 Intercalation Chemistry, ed. M. S. Whittingham and A. J. Jacobson, Academic Press, New York, 1982. 2 Inclusion Compounds, ed. J. J. Atwood, J. E. D. Davis and D. D. MacNicol, Oxford University Press, Oxford, 1991, vol.5. 3 M. G. Kanatzidis, L. M. Tonge, T. J. Marks, H. 0. Marcy and C. R. Kannewurf, J. Am. Chem. SOC., 1987,109,3797. 4 M. G. Kanatzidis, M. Hubbard, L. M. Tonge and T. J. Marks, Synth. Met., 1989,28, C89. 5 M. G. Kanatzidis, C.-G.Wu, H. 0.Marcy and C. R. Kannewurf, J. Am. Chem. SOC., 1989,111,4139. 6 M. G. Kanatzidis, C-G. Wu, H. 0. Marcy, D. C. Degroot and C. R. Kannewurf, Chem. Muter., 1990,2,222. 7 I. Lagadic, A. Leaustic and R. Clement, J. Chem. Soc., Chem. Commun., 1992, 1396 and references therein. 8 L. F. Nazar, Z. Zhang and D. Zinkweg, J. Am. Chem. Soc., 1992, 114,6239. 9 Handbook of Conducting Polymers, Marcel Dekker, New York, ed. T. A. Skotheim, 1986,vol. 1 and 2. 10 R. Gopal and C. Calvo, J. Solid State Chem., 1972,5,432. 11 B.Jordan and C. Calvo, Can. J. Chem., 1973,51.2621. 12 E. Bodes, P. Courtine and G. Pannetier, Ann. Chim. (Paris), 1973, 8, 105. 13 G. Ladwig, 2.Anorg. Allg. Chem., 1965,338,266. 14 B. Jordan and C.Calvo, Acta Crystallogr., Sect. B, 1976,23,2899. 15 H. R. Tietze, Aust. J. Chem., 1981,34, 2035. 16 J. W. Johnson, A. J. Jacobson, J. F. Brody and S. M. Rich, Inorg. Chem., 1982,21,3820. 17 K. Bemeke, and G.Lagaly, Inorg. Chem., 1983,22,1503. 18 L. Benes, J. Votinsky, J. Kalousova and J. Klikorka, J. Innorg. Chim. Acta, 1986, 114,47. 19 L. Benes, R. Hyklova, J. Kolousova and J. Votinsky, Inorg. Chim. Acta, 1990,177, 71. J. MATER. CHEM., 1994, VOL. 4 20 E. Rodoriquez-Castellon, A. Jimez-Lopez, M. Martinez-Lara and L.Moreno-Real, J. Incl. Phenom., 1987,5, 335. 21 G. Matsubayashi and S. Ohta, Chem. Lett., 1990,787. 22 G. Matsubayashi, S. Ohta and S. Okuno, Inorg. Chim. Actn, 1991, 184,47. 23 S. Okuno and G. Matsubayashi, J. Chem. SOC. Dalton Trans., 1992,2441. 24 S. Okuno and G. Matsubayashi, Chem. Lett., 1993,799. 25 M. Martinez-Lara, A. Jimez-Lopez, L. Moreno-Real, S. Bruque, B. Case1 and E. Ruiz-Hitzky, Mater. Res. Bull., 1985,20, 549. 26 G. Matsubayashi and H. Nakajima, Chem. Lett., 1993, 31. 27 K. Ichikawa, S. Ichikawa and K. Imamura, Bull. Chem. SOC.Jpn., 1976,49,1157. 28 A. F. Diaz, J. I. Castillo, J. A. Logan and W-Y. Lee, J. Electroannb Chem., 1981,129,115. 29 U. Bocchi and G. P. Gardini, J. Chem. SOC., Chem. Commun., 1986,148. 30 J. J. P. Stewart, J. Comput. Chem., 1989, 10,209. 31 M. J. S. Dewar and W. Thiel, J. Am. Chem. SOC.,1977, 99, 4899 and 4907. 32 T. Takagi, K. Matsumura, A. Noda, N. Onozawa and H. Fujiwara, Bull. Computation Center, Osaka Uniu., 1992,22, 1. 33 S. Okuno and G. Matsubayashi, Bull. Chem. SOC.Jpn , 1994, 67, 398. 34 M. R. Antonio, R. L. Barbour and R. Blum, Inorg. Chem., 1987, 26, 1235. 35 P. Pflunger and G. B. Street, J. Chem. Phys., 1984,80,544. 36 G. Wegner, Angew. Chem., Int. Ed. Engl., 1981,20,361. 37 R. J. Waltman and J. Bargon, Tetrahedron, 1984,40,3963. 38 P. Pflunger, M. Krounbi, G. B. Street and G. Weiser. J. Chem. Phys., 1983,78, 3212. Paper 4/00600C; Received 31st Januury, 1994

ISSN:0959-9428    

DOI:10.1039/JM9940401325

出版商:RSC    

年代:1994

数据来源: RSC

摘要:

J. MATER. CHEM., 1994,4(8), 1331-1336 Zirconia Formation by Reaction of Zirconium Sulfate in Molten Alkali-metal Nitrates or Nitrites Huda Al Raihani," Bernard Durand,bVc9* F. Chassagneux,b David H. Kerridged and Douglas lnmana a Department of Materials, Imperial College of Science Technology and Medicine, Prince Consort Road, London, UK SW72BP Laboratoire de Chimie Minerale 3, URA CNRS no. 7 76, ISIDT, Universite Claude Bernard Lyon 7, 43 Boulevard du 17 Novembre 7978, 69622 Villeurbanne Cedex, France Laboratoire de Materiaux Mineraux, URA CNRS no. 428, Ecole Nationale Superieure de Chimie de Mulhouse, 3 rue A. Werner, 68093 Mulhouse Cedex, France Department of Chemistry, University of Southampton, High field, Southampton, UK SO9 5NH Thermogravimetry up to 500 "C reveals several multi-stage reactions between Zr(SO,), and molten alkali-metal nitrates which form poorly crystallised mixtures of tetragonal and monoclinic zirconia.The use of NaNO, gives incomplete transformations. The addition of NaCl as well as the use of LiN0,-KNO,, leads the reaction to completion; the increase of basicity by the addition of Na,CO, also has the same effect, if it is assumed that Na,ZrO, is formed together with ZrO,. Pure and finely divided tetragonal zirconia is produced by a single-stage reaction at a temperature lower than 300 "C, when the basicity of the medium is increased by replacing LiN0,-KNO, by NaN0,-KNO,. Finely divided zirconia powder is of interest as a potentially useful or catalyst ~arrier,~ as well as a precursor of ceramics.Historically, a great deal of effort has been spent on the synthesis of small particle size ceramic powder^.^-^ The ideal powder should be chemically homogeneous at the atomic level and of high purity; it should consist of fine particles without hard aggregates. Reactions in molten salts are likely to lead to such oxide powder^.^,^ For zirconia particularly, Jebrouni et al. showed that the reaction of zirconyl chloride, ZrOC12.8H20, with molten alkali-metal nitrates in the range 400-500 "C leads either to pure' or yttrium-stabilised zirconia powders'' characterised by a satisfactory purity, a very homo- geneous distribution of the elements and nano-sized crystal- lites. Because they have specific surface areas > 100 m2 g-', which are stable to annealing at 6OO0C, these powders are very useful in catalysis as carrier^.^." Moreover, high densities are achieved by natural sintering at 1500 OC.I2 The reaction of zirconium sulfate towards a molten LiN03-KN03 eutectic was first investigated by Kerridge and Can~ela-Rey,'~who showed that the formation of insoluble ZrO, proceeded in two stages. The increase in the basicity of the molten medium brought about by the addition of Na202, Na20 or NaOH shifted the transformations towards low temperatures but favoured the formation of alkaline zircon- ates.The characteristics of the zirconia obtained were not determined. The reactions taking place in molten alkali-metal nitrate baths are based on the Lux-Flood principle. NO3-ions are considered as bases as they give rise to oxide ions 0,-;Zr4+ ions, resulting from the dissolution of the zirconium starting salt, are considered as acids because they accept oxide ion^.'^-'^ The mechanism of the whole reaction can be written as follows: dissolution of Zr(SO,),: Zr(S0,),+Zr4+ +2S042-dissociation of nitrates: NO3- +NO,+ +02-recombination of NO,': NO,' +NO3--+[N2O5]+ 2N02++02 precipitation of zirconia: Zr4++20,--+Zr02 Thus it is easily understood that a change in the acid-base properties or of the complexing efficiency of the molten medium may have a strong influence on the development of reactions of transiton-metal salts and on the properties of the powders obtained.Nitrite ions, NO,-, are more basic than nitrate ions, their dissociation constant to oxide anions being some lo1' larger than that of nitrate ions under equivalent conditions.This paper is concerned with a study of the reaction of zirconium sulfate, either hydrated or anhydrous, with various molten nitrate and nitrite media in order to determine the best conditions for obtaining finely divided zirconia powders. Experimental Materials Zirconium sulfate: zirconium sulfate tetrahydrate, Zr(S04),-4H20 (BDH AnalaR), was used dehydrated or as received. The dehydration was performed with sulfuric acid followed by ignition at 350-400°C according to Bear's method.17 lithium nitrate-potassium nitrate eutectic (mp 132 OC): lithium nitrate trihydrate and potassium nitrate (BDH AnalaR) were dehydrated separately in an oven at 180°C for 24 h.After they had been cooled at room temperature in a desiccator, the nitrates were weighed to give a mixture of 43 mol% lithium nitrate which then melted at 180 "C over a few hours with occasional stirring. The melt was then filtered and cooled in a desiccator. Finally the solidified melt was broken into convenient lumps in a dry box and stored in a desiccator. Sodium nitrite-potassium nitrite eutectic (mp 220 ' C): the eutectic (35 mol% potassium nitrite) was prepared in the same way as for nitrates, from sodium nitrite and potassium nitrite (BDH) and the mixture melted at 240°C. Other materials: sodium nitrate, sodium chloride and sodium carbonate (BDH AnalaR) were used as received.Procedure Most of the reactions were performed in the crucible of a Setaram G70 thermobalance to investigate the weight loss produced by gas release. Depending on the final temperature, either a Pyrex or a silica crucible were used. Zirconium sulfate and alkali-metal nitrates or nitrites were quickly hand-mixed in a mortar; a few hundredmg were introduced into the crucible. From the expected weight loss, blank runs indicated that buoyancy corrections were not necessary. No mass losses J. M.4TER. CHEM., 1994, VOL. 4 were observed below 550 "C when the molten salts (nitrates or nitrites) were heated alone. The derivative of the mass us. temperature relationship (thermogram) was used to increase the resolution of overlapping mass losses.Experiments were generally performed with a heating rate of 5 "C min-'. Some experiments were carried out, on a larger scale, inside a vertical cylindrical Pyrex reactor closed at its upper end with a drying tube filled with silica gel. The reactor was heated in a regulated vertical muffle furnace, the temperature being checked by means of a chromel-alumel thermocouple inserted between the reactor and the furnace walls. The reaction products were identified by X-ray diffractome-try (XRD), either on the ground solidified reaction mixture or on the insoluble solids after the solidified melt had been washed with water. A Siemens D500 diffractometer working with Cu-Kcr radiation (A=0.154 nm) and coupled with a Digital PDP 11 computer was employed.Identification was performed by comparison of experimental values with JCPDS files (Table 1).The size of crystallites in the tetragonal zirconia powders was determined from the line-broadening of the ( 111) XRD peak by means of the Warren-Scherrer formula. The extraction of zirconia powders was performed by dissolving the quenched melt in water, filtering of the insoluble oxide and then washing it with 50ml aliquots of water until qualitative tests showed no sulfate or nitrate in the washings. After the powder had been washed, the remaining liquid was removed by vacuum filtration and the zirconia powder dried in a desiccator. The morphology of some powders was characterised by transmission electron microscopy (TEM) on a JEOL 200CX apparatus.The TEM samples were prepared from alcoholic suspensions dispersed in an ultrasound bath. A drop was carefully evaporated on a carbon film predeposited on a copper grid. Results and Discussion Reaction of Anhydrous Zirconium Sulfate with Sodium Nitrate Reactions were performed, using a stoichiometric excess of NaNO, C0.2 mol Zr(S04)2 per mol NaNO,]. Anhydrous ZT(SO~)~seemed soluble in the molten sodium salt (mp 308°C) and began to react visibly just below the melting point at ca. 260"C, evolving a mixture of nitrogen dioxide (easily recognisable by its brown-red colour) and oxygen (confirmed with pyrogallol). Thermogravimetry (TG) (Fig. 1) showed this first reaction together with a second one com-mencing at ca.370 "C and evolving the same gaseous mixture. The maximum rates were observed at 320 and 400 "C, respect-ively. The investigation of a reaction mixture quenched at 350 "C indicated that the first reaction leads to a water-soluble product. The addition of a small quantity of sodium hydroxide, or heating the aqueous solutions, produced a gelatinous precipitate which was amorphous when analysed by XRD. The solidified melt gave two diffraction lines [d=3.89 (70) and 3.23 (100)A] which could not be attributed to zirconium dioxide. Kerridge and Can~ela-Rey'~previously observed Table 1 XRD identification of monoclinic, tetragonal and cubic-zirconia in the range 27.5-32" [L Cu-Kcr, = 1.5405 A] monoclinic tetragonal cubic JCPDS 37-1484 JCPDS 17-923 JCPDS 27-997 d/A 2O/degrees d/A 281degrees d/A 2O/degrees ~~ 3.165 23.17 2.96 30.17 2.93 30.48 2.841 31.46 91 .G 30E .-1 560 6006 0 100 200 300 400 500 TI'C Fig. 1 TG of the reaction of anhydrous zirconium sulfate in molten sodium nitrate. Influence of the addition of sodium chloride and sodium carbonate: 0, NaNO, alone; A, NaNO,+NaCI; a, NaNO, +Na,CO,.identical behaviour and the same peaks for the reaction of zirconium sulfate with a molten LiN03-KN03 eutectic. The product first formed is probably a basic nitrate. The overall mass loss measured at 650°C corresponds to 68.0% of the total Zr(SOJ2 added. This is lower than the calculated value, 76.3%, if the reaction is assumed to occur according to: Zr(S04)2+4N03--+Zr02+2S0,2-+4NO2+o2 (1) The difference indicates incomplete transformation.XRD on the extracted insoluble solid identified a mixture of tetragonal and monoclinic zirconia [Fig. 2(a), Table 11. When sodium chloride was added to sodium nitrate (0.2 mol NaCl per mol NaN0,) the first transformation was not changed, the maximum rate still occurring near 320"C, but the second one was shifted slightly towards low temperatures, with the highest rate near 370°C (Fig. 1). The overall mass loss, measured at 600"C, 73.7% of the total Zr(S04)2added, is in agreement with eqn. (1). It seems that chloride ions are not involved in the reaction. However, remembering that, as explained above, reactions in molten nitrates proceed accord-ing to a dissolution-precipitation mechanism, the fact that the reaction goes to completion in the presence of chloride ions could be interpreted as an effect of the complexing efficiency of Cl-ions promoting the dissolution of Zr(S04)2.As in pure sodium nitrate, XRD indicated the formation of a mixture of tetragonal and monoclinic zirconia [Fig. 2(b), Table 11. The increase in the basicity of the molten medium, by addition of sodium carbonate to sodium nitrate (0.2 mol I' I 28 29 30 31 26ldegrees Fig. 2 X-Ray diffractogram of zirconia obtained from reactions of anhydrous zirconium sulfate in (a)NaNO,; (b)NaNO, +NaCl; and (c) NaNO, +Na,CO, J. MATER. CHEM., 1994, VOL. 4 Na2C03 per mol NaNO,) brought a similar modification to the differential thermal analysis curve as the addition of sodium chloride (Fig.I). XRD of the extracted powder showed the formation of tetragonal zirconia [Fig. 2(c) Table 11,which could be explained by the following reaction: Zr( SO,), +2N0, -+CO,,--+ ZrO, +2S04,-+2N0, +CO, +40, (2) although the calculated mass loss, 50.8% of the total Zr(S04), added, is in total disagreement with the observed loss, 89.3%. Such a significant loss can be understood if it is assumed that the high basicity of carbonate ions involves the simultaneous formation of zirconia and zirconate ions, Zr03,-, according to the following reaction, giving a calculated value, 84.0%, closer to the experimental value: 2Zr(SO,), +8N03-+CO,'--+ ZrO, +z1-0,~-+4So,,-+8N02+CO, +20, (3) Poorly crystallised Na,ZrO, was identified by XRD (Fig. 3).When sodium chloride or sodium carbonate were added to sodium nitrate, a small mass loss was noticed when the temperature rose above 600°C (Fig. 1). Such a loss was previously observed by Kerridge and Cancela-Rey13 in reac- tions of zirconium sulfate with an LiN03-KN03 eutectic and was attributed to the formation of anionic zirconate. These small losses were not taken into account in the values pre- viously given for the reactions (73.7 and 89.3%). In the same way, the small mass losses at ca. 100"C,due to the elimination of water absorbed during the mixing of reactants, were not considered. Reaction of Zirconium Sulfate, Anhydrous or Hydrated, with an LiN03-KN03 Eutectic Anhydrous Sulfate TG of the reaction of anhydrous zirconium sulfate (0.2 mol kg- ') with LiN0,-KNO, eutectic (mp 132 "C)corrobor-ated Kerridge's and Cancela-Rey's previous re~u1ts.l~It showed a reaction taking place in several stages, beginning above the melting point and finishing at ca.500 "C (Fig. 4). The experimental mass loss, 75.2% of the total Zr(SO,),! added, is in good agreement with that calculated for eqn. (l), 76.3%. The XRD pattern of the extracted insoluble solid showed a mixture of monoclinic and tetragonal zirconia [Fig. 5(a)]. Larger-scale experiments (20 g eutectic heated in a furnace) with the same concentration of zirconium sulfate (0.2 rnol kg-I) showed similar reactions.Analysis of the extracted insoluble reaction products indicated the presence of detectable nitrate, though potassium and lithium were absent. This suggested that complete reaction to zirconia had not always occurred and this was supported by the somewhat !-l----r-~-T~ ' ' ' I.. .-1.7 ' 7 1 -' ' TI ' T' ' I ' ' ' J 25 30 35 40 45 50 55 60 2Bldegrees Fig. 3 X-Ray diffraction pattern of zirconia obtained from reaction of anhydrous zirconium sulfate in NaN03 +Na,CO,: *, Na,ZrO, TPC Fig.4 TG of the reactions of the zirconium sulfate in lithium nitrate-potassium nitrate eutectic. Influence of hydration: ( I,anhy-drous zirconium sulfate; A,tetrahydrated zirconium sulfate. I. 1 28 29 30 31 28ldegrees Fig. 5 X-Ray diffractogram of zirconia obtained from reactions of anhydrous zirconium sulfate in: (a) LiN0,-KNO,; and (b) in NaN02-KN0, gelatinous nature of the precipitate, which diminished as the eutectic melt was heated to higher temperatures and/or for longer times.It was also supported by the mass of dry precipitate, which was greater than that calculated for the mass of pure zirconia. The percentage excess also decreased with temperature/time (Fig. 6), while X-ray powder diffraction timelh Fig. 6 Temperature-time profiles for reactions of anhydrcus zir-conium sulfate in LiN03-KN03 and weight percentages of rec overed precipitate. (a) LiN0,-KN03+0.20 mol kg-I Zr(SO,),, -I 10.8%; (b) LiN0,-KN03+ 0.25 rnol kg-' Zr(SO,),, -108.9%; md (c) LiNO,-KNO, +0.20 mol kg-' Zr(S04)2,-98.9%.showed the presence of both monoclinic and tetragonal zir- conia together with amorphous material in all the samples. Tetrahydrated Sulfate When the tetrahydrate was heated in the nitrate eutectic, white fumes containing nitric acid were evolved and a white suspension was produced. TG (Fig. 4) showed the mass loss to begin from the lower temperature of llO"C, as expected for a hydrolysis reaction. The first stage of mass loss, over the temperature range 110-330 "C was due to overlapping reac- tions. The second stage was similar to that of anhydrous zirconium sulfate. The overall loss, 88.4% of the total Zr(S04),.4H,0 added, was rather higher than the calculated value, 81.1%, for the reaction: Zr(S04)2~4H20+4N03--+ ZrO, +2S042-+4H,O +4N02+o2 (4) The difference is undoubtedly due to the loss of some nitrate as nitric acid.Larger-scale experiments led to results similar to those for anhydrous zirconium sulfate. Reaction of Anhydrous Zirconium Sulfate in Molten Nitrates in the Presence of Nitrite and in a Molten Nitrite Eutectic Addition ofKN02 to the Eutectic LiN0,-KNO, Since longer reaction times or higher temperatures are undesir- able industrially, a change was made to more basic and hence more reactive melts, initially by introducing potassium nitrite in the LiN0,-KNO, eutectic. The nitrite has a dissociation constant, to form oxide anions, some 10" larger than that of nitrate under equivalent conditions. TG (Fig. 7) showed a two-stage process with the major mass loss occurring during the first stage in the temperature range 150-270°C.The second stage, which gave a small mass loss, ended at ca. 370 "C.The overall experimental mass loss, 53.3% of the total Zr(S04)2 added, was close to the calculated value, 53.7%0, for the equation: Zr(S04),+4N0,- +ZrO, +2S04,-+2N0, +2N0 (5) The washed precipitates, from furnace reactions performed at 450 or 5OO0C, again contained some nitrate and possibly lithium and also exhibited a dry mass slightly above that for pure zirconia [Fig. 8 (a)-(c)].XRD patterns gave maxima at the positions for monoclinic and tetragonal zirconia. In fur- nace reactions carried out at 200 "C [Fig. 8(d),(e)], longer durations failed to compensate for the low temperature and low masses of precipitate were recovered; this supports the idea that in the two-stage process only the first stage is involved at low temperature.200 300 400 500 TI'C Fig. 7 TG of the reactions of the anhydrous zirconium sulfate in: A, nitrate/nitrite and 0,pure nitrite melts J. MATER. CHEM., 1994, VOL. 4 0 2468 time/h Fig. 8 Temperature-time profiles for reactions of anhydrous Zr( SO,), in LiN0,-KNO, in the presence of KN02 and weight percentages of recovered precipitate. (a) 0.19 mol kg-' Zr(S04),+0.15 mol kg-' KN02-106.1%; (b)0.14 rnol kg-I Zr(S04),+0.98 rnol kg-' KNO,, -103.8%; (c) 0.19 rnol kg-' Zr(S04),+0.99 mol kg-I KNO,, -104.8%; (d) 0.20 rnol kg- ' Zr(SO,), +0.99 mol kg- KNO,, -62.8%; and (e) 0.20 mol kg-' Zr(SO,),$ 1.00 rnol kg-'KNO,, -67.2%.Reaction in Molten NaN02-KN02 eutectic To increase the basicity of the melt further the LiN0,-KNO, eutectic (mp 132 "C) was replaced by NaN02-KN02 eutectic (mp 220°C). TG (Fig. 7) showed a one-stage reaction with a mass loss maximum almost at the melting point and no loss above 270°C. The measured overall loss was 42.2% of the total Zr(S04), added. In order to match this observed value to a possible stoichiometric equation, it was necessary to dissociate nitrite ions into N203 and 02-according to eqn. (6) and to take account of the known reaction" of N203 to produce nitrogen dioxide and nitrogen monoxide according to eqn. (7), with further reaction of nitrogen dioxide with nitrite ions according to eqn.(8). 2N02- +N203 +0'-(6) N203+N02+N0 (7) NO2+NO2-+NO,-+NO (8) Thus the stoichiometric eqn. (9) was obtained, giving a calculated weight loss of 42.4% Zr(SO,), +6N02- +Zr02 +2S04'-+2NO,-+4NO (9) The XRD pattern of the extracted powder identified tetragonal zirconia [Fig. 5 (b)]. Some Characteristics of Zirconia Powders obtained from Reactions of Anhydrous Zirconium Sulfate with Molten Nitrate and Nitrite Eutectics Some of the zirconia powders were more intensely studied, particularly four samples prepared from anhydrous zirconium sulfate in furnace reactions at 450 or 300°C; the reaction temperature was reached at a rate of 150°C h-' and main- tained for 90 min. The nature of the molten salt and the reaction temperature are indicated together with the results of chemical analysis in Table 2.For samples A and B, prepared in the nitrate medium, the presence of a significant amount of remaining sulfate indicates that reaction is not complete. This is corroborated by XRD patterns exhibiting lines of tetragonal and monoclinic zirconia and also the strongest line of zirconium hydroxysulfate, ZI-~.~~(SO~)(OH),at ca. 7.5" 28 (JCPDS file no. 41 0694) (Fig. 9). For sample A prepared in LiN03-KN03 the forma- tion of tetragonal zirconia predominates, whereas for sample J. MATER. CHEM., 1994, VOL. 4 Table 2 Chemical analysis of zirconia obtained from anhydrous zirconium sulfate by reaction in nitrate and nitrate molten media reaction chemical analysis (wt.%)temperature/ sample molten medium "C Zr so4 N03/NO," LilNa" K ~~ A LiNO3-KNO3 450 57.8 4.10 0.29 0.03 0.05 B NaN0,-KNO, 450 60.7 5.50 0.16 0.57 0.16 C NaN0,-KNO, 450 61.9 0.01 0.17 0.82 0.05 D NaN0,-KNO, 300 53.1 0.01 1.67 0.13 0.13 "NO, for samples A and B, NO, for samples C and D."Li for sample A, Na for samples B, C and D. R ' ic, I-II 10 20 30 40 50 60 70 2O/degrees Fig. 9 X-Ray patterns of zirconia samples A@), B(b), C(c) and D(d) (see Table 2) B prepared in NaN0,-KNO, the formation of monoclinic zirconia is mainly observed, For samples C and D prepared in the nitrite media, the transformation of zirconium sulfate into zirconia is complete. The XRD patterns (Fig. 9) reveal the formation of pure tetragonal zirconia at 450°C and the formation of a mixture of amorphous and poorly crystallised zirconia at 300 "C. When annealed at 500 "C, the latter powder crystallises as tetragonal zirconia and a quantity of nitrates greater than for sample C is simultaneously eliminated.An electron micrograph of tetragonal zirconia obtained at 450°C in the nitrite medium [Fig. lO(u)] shows that the powder is made of soft agglomerates containing nearly spheri- cal elementary grains with diameters close to 6 nm. From the size of crystallites determined by X-ray broadening, 5 nm, it is concluded that the elementary grains are monocrystalline. This powder exhibits a specific surface area >150 m2 g-'. An electron micrograph of sample D [Fig. lo@)] reveals the presence of agglomerates formed of smaller elementary grains Fig.10 Transmission electron micrographs of zirconia powders prepared from reactions of zirconium anhydrous sulphate with molten alkali nitrites. (a) Sample C prepared at 450°C (30nm= 1.05cm). (h) Sample D prepared at 300 "C (30 nm =1.45 cm). with diameters close to 3 nm. The amorphous and tetragonal phases cannot be distinguished. The specific surface area is close to 250m2 g-'. Conclusion Differential thermal analysis investigation of the reaction of zirconium sulfate, either hydrated or anhydrous, with molten alkali-metal nitrates showed that the reactions occurred in at least two stages, each indicated by the release of red -brown nitrogen dioxide. The first step leads probably to a soluble zirconium nitrate or oxynitrate, the second to insoluble zir- conia.In pure sodium nitrate (mp 308"C), the reaction remained incomplete even at temperatures approaching 500 "C. The addition of sodium chloride to the molten medium gave a complete reaction at ca. 440"C. The increase of hasicity by the addition of sodium carbonate also favours the reactions, but sodium zirconate is formed simultaneously with zirconia. The decrease of the melting point of the molten salt, by replacing sodium nitrate by the LiN0,-KNO, eutectic (mp 132 "C), allowed complete transformation to occur as low as 500 "C. When zirconium sulfate tetrahydrate is used. white fumes of nitric acid are evolved at the beginning of the reaction. An increase in basicity by addition of potassium nitrite to the nitrate eutectic or by performing the reaction in the eutectic NaN0,-KN02, shifted the reactions towards lower temperatures.In the latter case, thermal analysis shows only one stage occurring under 300 "C. Reactions of zirconium sulfate with the molten medium led either to monoclinic or tetragonal zirconia. When this latter phase is obtained, it irreversibly transforms into monoclinic by annealing. However, it is much more interesting to synthe- size the tetragonal variety directly. Accordingly, among the molten media studied, the eutectic NaN0,-KN02 appears to be the most suitable for obtaining fine zirconia powders of a satisfactory purity and with large specific surface arcas, as shown by the characterisation of powders prepared at 450 "C for 90 min with anhydrous zirconium sulfate.Such pc )wders are likely to find applications as catalyst supports in hcterog- enous catalysis and as ceramic precursors on the condition that the method may be extended to the preparation of stabilised zirconia. These results were obtained in the frame of a twinning contract between Imperial College and the University of Lyon. The authors are indebted to the Commission of European Communities for financial support. References 1 B. Y. Lee, Y. home and I. Yasumori, Bull. Chem. SOC.Jpn., 1981, 54, 13. 2 T. Lizuka, Y. Tanaka and K. Tanabe, J. Card., 1981,76,1. 3 D. Hamon, M. Vrinat, M. Breysse, M. Jebrouni, B. Durand, M. Roubin and P.Magnoux, Catal. Today, 1991,10,613. 4 K. S. Mazdiyasni, Ceram.Int., 1982,8 (I),42. 1336 J. MATER. CHEM., 1994, VOL. 4 5 J. L. Burke, N. L. Reed and V. Weiss, Ultra-jine-Grain Ceramics, 13 D. H. Kerridge and J. Cancela-Rey, J. Inorg. Nucl. Chem., 1977, Syracuse University Press, Syracuse, 1970. 39,405. 6 M. J. Bannister and W. G. Garrett, Ceram Int., 1975, 1 (3), 127. 14 H. Lux, 2.Elektrochem., 1939,45,303. 7 B. Durand, Ceramic Powders: Preparation, Consolidation and 15 G. Charlot and B. Tremillon, Les Riactions Chimiques dans les Sintering, ed. P. Vincenzini, Elsevier, Amsterdam, 1983, p. 413. Solvants et les Sels Fondus, ed. Gauthier-Villars, 1963, ch. XV, 8 B. Durand and M. Roubin, Mater. Sci. Forum, 1991,73-75,663. p. 486. 9 M. Jebrouni, B. Durand and M. Roubin, Ann. Chim.-Sci. Muter., 16 F. R. Duke and S. Yamamoto, J. Am. Ceram. So(., 1959,81,6378.1991, 16, 569. 17 I. J. Bear, Aust. J. Chem., 1966, 19, 357. 10 M. Jebrouni, B. Durand and M. Roubin, Ann. Chim.-Sci. Muter., 18 N. N. Greenwood and A. Earnshaw, in Chemistr,vof the Elements, 1992, 17, 143. Pergamon Press, Oxford, 1984, p. 521. 11 B. Durand, D. de Mareuil, M. Vrinat and T. des Courieres, Brevet Elf Aquitaine no. 900549. 12 M. Descemond, M. Jebrouni, B. Durand, M. Roubin, C. Brodhag Paper 3/07391B; Received 15th December, 1993and F. Thevenot, J. Muter. Sci., 1993,28, 2283.

ISSN:0959-9428    

DOI:10.1039/JM9940401331

出版商:RSC    

年代:1994

数据来源: RSC

摘要:

J. MATER. CHEM., 1994, 4(8), 1337-1341 1337 Ion Exchange of Ruthenium Cationic Complexes by a-Tin@) Bismonohydrogenphosphate Michael J. Hudsonfaand Andrew D. Workmanb a Department of Chemistry, University of Reading, Box 224, Whiteknights, Reading, Berkshire, UK RG6 2AD Department of Chemistry, University of Leicester, University Road, Leicester, Leicestershire, UK L€2 7RH The ion exchange from aqueous solution of some cationic ruthenium species by a-tin(rv) bismonohydrogenphosphate (SnP) has been investigated. There is a marked difference in behaviour according to the cationic species which are used. Thus the stable [Ru(NH,)~]~+ is only exchanged on the surface; ruthenium red [Ru,O,(NH,),,]~+ and ruthenium nitrosyl species were ion exchanged onto the surface from dilute solutions but, at higher concentrations, the host SnP, and its butylamine intercalation compound SnP-BuA, were delaminated to give disordered non-crystalline materials.In contrast, the reactive [Ru(NH,),]*' was rapidly extracted in an autocatalytic, topotactic reaction to give a polyphasic but microcrystalline intercalation compound, the layered structure of which was retained on heating. At high loadings there appears to be an interlamellar electron transfer resulting in the oxidation of ruthenium(i1) to ruthenium(iii) probably with tran~-[Ru(H,O),(NH,),1~+ as the dominant guest cation. There is much current interest in the ion exchange of metal- containing cationic species into layered hosts. The interest derives from the extraction of radionuclides and the prep- aration of microcrystalline pillared layered solids.One suitable host is the inorganic ion exchanger a-tin(1v) bismonohydrog- enphosphate monohydrate [Sn( HPO,),-H,O] (SnP), which is a layered (hydrogen) phosphate with a basal spacing of 0.78nm, an area of 21.4A2 per phosphate group, and a maximum cation exchange capacity (CEC) of 6.08 mmol 8-l for a monovalent ion.' Despite this high CEC, SnP is regarded as a poor ion exchanger because the free diffusion of counter- ions is limited by the strong Layer-layer interactions and the small passageways (ca. 2.6 A) that connect the interlayer cavities. Normally, only surface ion exchange will occur.' Cationic metal complexes are not known to intercalate directly into SnP or other phosphates and, consequently, alternatives to the direct intercalation have been investigated.For example, amine intercalation compounds have been prepared in order to separate the layers and to reduce the interlayer charge den~ity.~'~In certain cases delamination processes are used to encourage the ion exchange of cationic metal complexes in layered phosphates.' Highly dispersed and hydrated powders of layered phosphates obtained by the sonication of some amine intercalated phosphates may be used to extract large cations such as aqueous Ba2f.6 Unfortunately, both the delamination and sonication methods lead to ill-defined, amorphous products. In this study, the extraction of ruthenium-containing cations has been investigated and the reactivity of the ruthenium@) cation [Ru( NH3)6]2+ has been exploited to produce microcrystalline layered intercalation compounds.A new autocatalytic mechanism has been pro- posed in which labile ammonia ligands extract protons from the host, rendering SnP a stronger acid and a more effective ion exchanger. Experimental Synthesis SnP was synthesized according to the published pr~cedure.~ Its X-ray powder diffraction (XRD) pattern (Spectrolab series 3000 CPS-120 instrument, Ni-filtered Cu-Kcc =0.154051 nm) indicated a basal spacing of 0.78 nm and the absence of any impurity peaks. Hexaamminoruthenium(r1) chloride was prepared by the method of Fergusson and Love.8 The hexa- amminoruthenium(II1) chloride was prepared by the dropwise addition of chlorine water into a stirred solution of the ruthenium(I1) compound at 50 "C.The non-radioactive ruthenium nitrosyl compounds were prepared by the dilution of aqueous ruthenium nitrosyl nitrate (Johnson Matthey Materials) with nitric acid (4 mol drnp3) and alloming the solutions to age at least one month before use. Extraction Experiments All extractions were done in duplicate as batch experiments using degassed, doubly deionised water. The CEC was taken as 6.08 mmol H+ g-' of dry ion exchanger. The solutions were diluted for atomic absorption analysis using hydrochloric acid ( lo%, v/v) and lanthanum(Ir1) chloride penta hydrate (0.5%, w/v) so that the range of ruthenium concentration was 0-100mg dm-3.The mass balances between the amounts extracted from the solution into the solid phases were correct. Since the compounds were polyphasic, the analytical results were not used to calculate the composition of the conipound. Extraction studies for trace quantities of ruthenium nitrosyls were carried out by the Novel Absorbers Club of AEA Harwell Laboratory. The previously aged cocktail of radio-nuclides was at pH 6.4 and contained sodium nitrate (0.05 mol dmV3). The activity of the Io6Ru was 1.23 x lo', Bq g -I. Pyrolysis of SnP-[Ru( NH3)6]2'3+ The pyrolysed form of SnP intercalated with hexaammino- ruthenium@) dichloride SnP-[ RU(NH,)~]~/~ + was prepared as follows. SnP was shaken for 2 h with an [Ru(NH~)~]~+ solution containing 300% of the CEC of SnP.The rcsultant solid was then filtered through a number 4 sintered glass crucible and the exchange process repeated. The filtered sample was washed with doubly distilled water, ethanol and propanone. The air-dried product was heated in dry (sulfuric acid), oxygen-free nitrogen to 1000°C at a ramp rate of 10"C min-' and held at this temperature for 3 h. Scanning electron microscopy was carried out on a JEOL JXA 840 Scanning Microanalyser. Electron paramagnetic resonance (EPR) studies were carried out with a Bruker ESP-300 instrument. All spectra were recorded in the Y-band at 77 K. Results and Discussion Ion-exchange Studies Hexaamminoruthenium(rI1) Cation The direct extraction of [Ru(NH~)~]~+ proceeded only slowly to 14% of the maximum CEC even when 150% of the CEC was present in the initial solution.There was no change in the XRD pattern and clearly only surface ion exchange took place. If ammonia ligands are involved in the exchange, the relative inertness of the cation towards substitution and strong retention of the ammonia ligands may account for its lack of intercalation. The acidity (pK, 12.4)' does not provide an alternative mechanism for the reaction with SnP, which is also a weak acid. Ruthenium Red [RU~O~(NH~)~~]~+ In contrast to the hexaamminoruthenium(II1) cation, the ruthenium red cation was rapidly exchanged by SnP. However, in none of the samples was there any XRD evidence for the formation of microcrystalline intercalation compounds.There appeared to be two well defined stages in the extraction process, Fig. 1. In the first region AB' there was surface exchange possibly followed by delamination (B'C') and an additional stage (C'D') during which the ruthenium red exchanged on the newly formed surfaces. It is known that layered compounds with intercalated monoamines delaminate but those with diamines do not. Therefore, in order to enhance the rate of extraction, the butylamine intercalation (SnP-BuA) compound was used." This has a bilayer of amines with weak van der Waal bonds between the hydrophobic groups of the hydrocarbon chains. This weak intralayer bonding enables the compounds to delaminate. Interestingly, there was less extraction in the region AB than was the case for SnP and it appears that the protonated amine, which is on the surface, is less readily exchanged than the protons in the P-0-H groups.The initial extraction was also much slower with the SnP-BuA compound because the surface BuA groups are less readily exchanged than the protons of the surface PO-H groups." The decrease in the amount of ruthenium red exchanged from B to C or from B' to C' results from the loss of the exchanged ruthenium cations as the compound delaminates. Delamination is necessary for further exchange because the ruthenium red is able to bridge the layers, as do the diamines. As judged by the enhanced extraction, the delamination of SnP-BuA is greater than that of the SnP itself. The products were polyphasic with a microcrystalline unreacted SnP phase and an additional amorphous phase resulting from the delamination and exchange. It was con- sidered that one possible reason why ruthenium red was involved in delamination was that the cation contains exchangeable labile ammonia ligands.Thus the exchange could involve ammonia molecules, which were previously 1.6r , 1 I I 0 400 800 1200 1600 extraction Deriod/min Fig. 1 Extraction of the ruthenium red cation by SnP (a) and SnP-BuA (b) J. MATER. CHEM., 1994, VOL. 4 ligands, and thus enhance extraction compared with the hexaammino rut henium (111) cation. Nitrosyl-containing Cations Ruthenium nitrosyl complexes are formed in nitric acid media during the reprocessing of spent nuclear fuels.The ruthenium nitrosyl solution contained neutral species and cations of charges 1-3 of the general formula [Ru(NO)(H20)x(N03),-x]3-x.."In addition to the nitrosyl ligands, there were also nitrato and water ligands to maintain the overall octahedral ge~metry.'~,'~ The kinetic curve was of a similar shape to that of the ruthenium red, with point A corresponding to 0.15 mmol g-' and 25 min. The extraction under equilibrium conditions, Fig. 2, was a function of the concentration of the original solution. The region from the origin to A and B corresponds to surface extraction and the region beyond B to extraction and delamination. The reason for the increase from B to C is probably connected with the separation of the layer edges in the presence of the excess of cationic species followed by delamination and exchange.The decrease over the region CD may be associated with hydrolysis and loss of phosphate groups. As discussed more fully later, for the compounds with intercalated cationic ammineruthen- ium, when the products were heated ruthenium was retained and a tin(1v) pyrophosphate phase was obtained in which the ruthenium appeared to be covalently bound. Since radioactive (lo6Ru) ruthenium nitrosyl species are present in some aqueous effluents from nuclear industries, there was interest in establishing whether Sn P could extract them from solutions which contain trace quantities such that the concentrations are of the order of 10-12 times lower than those used above.The ruthenium nitrosyl species were indeed extracted by SnP. For example, an initial feed activity for Io6Ru of 73 Bq cmP3 was reduced to 20 within 1 h. Such extraction no doubt involves the surface phosphate groups rather than those in the interlamellar regions. Consequently, if these layered phosphates are to be used for the recovery of pollutants then attention should be given to preparing mate- rials with high surface areas. Hexaamminoruthenium(11) Cation The extraction of [Ru(NH,),I2+ and the resulting materials are quite different from those described above. The extraction curve for hexaamminoruthenium(11) chloride from a degassed, doubly deionised solution (with an initial concentration of ruthenium of 1.5xCEC) onto SnP is shown in Fig.3. Degassed water was used to restrict the conversion of ruthenium(11) to ruthenium(II1). The rate of extraction appears to be quite rapid with t, [the time for half of the ruthenium(11) to be extracted] of <5 min to a capacity of 1.66 mmol g-', 1.8r 7 'm 1.4 --E Eg 1.0-c02 c -$ 0.6 *' 0 100 200 300 CEC (divalent ion) in original soln. (%) Fig. 2 Extraction of some ruthenium nitrosyl cations 3. MATER. CHEM., 1994, VOL. 4 I -cn 1.5 E E ag 1.0 9 c W 1 1 1 50 100 150 200 tlmin Fig. 3 Extraction of the hexaamminoruthenium(r~) [Ru(NH,),]'+ cation (A) by SnP as a function of time which is 55% of the theoretical exchange capacity of 3.04 mmol g-' for a divalent ion.The differences between the extraction of the hexaamminoruthenium(11) and the other cations together with the materials that are formed may be rationalised on the basis of the lability of the ammonia ligands in the hexaamminoruthenium(i~) cation. The rate constant for the exchange of ammonia ligands with water in hexaammino- ruthenium(I1) cation has been measured', as 1.24 x dm3 mol-' s-' whereas the calculated half-life of the ligand- exchange process for the ruthenium(II1)-ammine complex, for example, is 3 years. Thus the ruthenium@) cation has readily exchangeable ammonia ligands which could extract protons from the host. This proton extraction could lead to a local expansion of the layer edges and intercalation of the complex cation.The fate of the ammonium ion is uncertain, but there was little observed change in pH. From the EPR evidence discussed below, it appears that the most likely guest cation is one in which one or more of the ammonia groups have been replaced by a water molecule. It has been suggested previously that trace amounts of sodium can act as catalysts for the intercalation of molecule^.^^ However, the two cata- lysed mechanisms are different because, in the second case, the sodium increases the interlayer distance only and not the effective acidity of the host. Thus the overall reversible mech- anism is: PO-H,,,p, +H,O +[RU(NH3)6J2' =[PO -NH4+](snp)+[Ru( NH3)5H20I2+ This exchange may be repeated to give trans-[Ru(NH,),)(H,O),]~+.It is also possible that the ionised phosphate group could act as a ligand or there could be extensive hydrogen bonding between the ionised phosphate groups and the bound ammonia or water ligands. The separate addition of ammonia to the solution containing the hexaammi- noruthenium(i1) cation did not accelerate the intercalation because SnP is hydrolysed by ammoniacal solutions to give tin@) oxide and phosphate groups. The loss of the phosphate groups reduces the CEC of SnP. In addition, [Ru(NH3)J2+ decomposes in ammoniacal solution, particularly under aero- bic conditions, to produce dark decomposition products.16-" Interlamellar Electron Transfer There are clear indications that there are secondary electron transfer reactions inside the interlamellar regions for the compounds with high loadings of the ruthenium@).The initial evidence comes from the XRD patterns of the intercalation compounds, which changed according to the initial concentrations of the solutions, Fig. 4. Compounds 2-4were biphasic materials in which the unreacted host do02 I I 20 15 10 5 28Idegrees Fig. 4 X-Ray powder diffraction data for the host (1) and the intercalation compounds: 1, SnP; 2, 5% CEC of A in original solution; 3, 10%; 4, 25%; 5, 50%; 6, 75%; 7, 100%; 8, 3Oo"'o (dOo2=0.78nm at 11.3" 20) and the intercalation compound (do,, =1.06 nm) coexist. At higher loadings there is a re-arrangement of the host and guest (sample 4) and a single new microcrystalline phase is formed for which do,, = 0.99 nm.The reasons for the differences in the intensities md pos- itions of the peaks may be related to changes in oxidation state as indicated by the EPR spectra. The first five samples (including the host) up to initial concentrations of 50% CEC were inactive, but from 70 to 300% CEC there were clear EPR signals with g, =3.066, gy=1.115, g, =2.057. The inac- tivity of the first set of samples with the lower initial concen- trations of ruthenium in solution indicate that ruthenium(i1) (spin-paired 4d6) is present. The EPR for the other higher loaded samples indicates that a distorted ruthenium(1ri) octahedral species of C,, symmetry is present (spin-paired 4d5)19320(cf. trans-[RuC1,(NH3), 1' 3.33, 1.54, 1.13; trans-[Ru(en),(NCS), JNCS 3.07, 1.11 and 2.25).The question that must be answered is: why does the electron transfer occur at high loadings and not at low loadings? The oxidation of ruthenium(r1) to ruthenium(rrr) is sensitive to pH with ruthenium@) favoured at low pH.21 The electron transfer involves the ruthenium(I1) cation and either the host or the interlamellar water. It appears, therefore, that although SnP is essentially a weak acid,22 the low pH in the interlamellar regions favours ruthenium(i1) for the lower amounts of exchange (up to 50% CEC and 0.6 mmol Ru g-'). Sample 5 in Fig. 4 corresponds to the half-exchanged material in which the ruthenium(r1) and ruthenium(iI1) species are able to coexist in the interlamellar regions. For a tervalent ion 8Ooh of the CEC is utilised.The reason why not all of the CEC is used is that the ruthenium species cover sites which are not used for ion exchange. The cross-sectional area for the ruthenium(rI1) ion is approximately 0.24 nm2 whereas the free area per phosphate is 0.21 (4) nm2. The estimated cross-sectional area of trans-[ Ru(H,O),(NH,),]~+ is 0.243 nm2 compared with 0.214 nm2 for each phosphate group. Thus some phosphate groups are covered by the guest cation. Thermal Properties The S~P-[RU(NH,),]~'~ compounds were evaluated by+ thermogravimetry (TG) and differential thermochemistry 1340 because it is essential for the nuclear industry that no ruthenium is lost, as lo6Ru04 for example, on heating the compounds. No evidence of loss of ruthenium was found.There are two endotherms (see Fig. 5): the first, at 85"C, is associated with loss of interlamellar water (9.4%, 2.8H20per formula mass); the second, at 430 "C,is related to the decompo- sition of the ruthenium complex and therefore involves loss of water and ammonia, the conversion of phosphate to pyrophosphate is also probably contained in this endo-therm.23,24 The exotherm at 560°C does not involve a mass loss and is associated with the binding of the ruthenium species with the tin pyrophosphate and recrystallisation of the phases so formed. The XRD pattern for this material contains comparatively sharp peaks and the material is more crystalline than SnP, SnP-BuA and the SnP-[ Ru( NH3)6]2'3+ intercalation compound, Fig.6. The peak assignments are shown in Table 1;essentially the material Fig. 5 Thermogravimetry (a) and differential thermal analysis (b) of the S~P-[RU(NH,),]~+ intercalation compound 100 80 h 60 40--20 &lddu0, 2Bldegrees Fig. 6 X-Ray powder diffraction pattern of the SnP-[Ru(NH,),J2+ intercalation compound which had been heated to 1000°C Table 1 X-Ray powder diffractogram of pyrolysed SnP-Ru( NH,), SnP,O, RuO, SnR" [hkr] d/nm I/Z, (%) d/nm I/I, (YO) d/nm 111 0.460 40 0.2217 4 0.458 0.435 110 0.317 100 101 0.2550 50 200 0.399 100 0.2243 10 0.397 210 0.357 30 0.2005 1 0.356 0.343 0.335 21 1 0.326 25 0.1685 30 0.321 220 0.282 30 0.1586 9 0.282 22 1 0.266 2 0.265 002 0.1552 4 "Pyrolysed SnP-Ru"'(NH,),.J. MATER. CHEhl., 1994, VOL. 4 is based on the tin pyr~phosphate~~ with bound ruthenium. There was no evidence for ruthenium(1v) oxide as a separate p hase.26 Morphology The scanning electron micrograph of the SnP-[ Ru(NH3),I3+, Fig. 7, shows that the layered structure is retained but that some of the flakes were curled up. Slow heating of the compound gave a similar morphology but rapid heating, Fig. 8, resulted in holes being formed in the layers by the molecules which had insufficient time to diffuse along the layers. In the synthesis of microcrystalline solids, slow heating rates are considered to be important. Conclusions The extraction appears to involve an ammonia ligand from the reactive ruthenium(11) complex and may be regarded as an autocatalytic, topotactic reaction.The peaks in the XRD patterns are not, however, sharp and there may be some amorphous material in the resultant compound. The reaction of the free ammonia group and the extraction of protons renders the SnP to be a strong acid and an effective ion exchanger. The reactive [Ru(NH3),I2+ was rapidly exchanged in an autocatalytic, topotactic reaction to give a polyphasic, microc- rystalline intercalation compound, the layered structure of which was retained on heating. At high loadings there appears Fig. 7 Scanning electron micrograph of the pyrolysed compound showing the flakey appearance Fig. 8 Scanning electron micrograph of the pyrolysed compound showing the hole caused by the rupturing of the layers of the host when the heating rate was too great J.MATER. CHEM., 1994, VOL. 4 1341 to be an electron transfer involving oxidation of ruthenium@) to ruthenium(m), with truns-[Ru(H2O),(NH,),13f as the resultant dominant guest cation. 9 10 11 D. Waysbort and G. Navon, J. Chem. SOC.D, 1971,1410, M. J. Hudson, E. Rodriguez-Castellon, P. Sylvester, A. Jimenez- Lopez and P. Olivera-Pastor, Hydrometallurgy, 1990,24, 77. C. G. J. Boswell and S. Soentono, J. Inorg. Nucf. Chom., 1981, This work was supported by the Department of the Environment as part of their Radioactive Waste Management 12 13 43, 1625. M. Nowak, Radiochem. Radioanal. Lett., 1971,8, 165. V. G. Shumkov, Jad. Energ., 1974,20,315. Programme.The results may be used in the formulation of Government policy but at this stage do not neces-sarily represent Government policy. Professor B. C. Gilbert, University of York is thanked for use of the EPR equipment. 14 15 16 P. C. Ford, J. R. Kuempel and H. Taube, Innorg. Chtpm., 1968, 7, 1976. G. Alberti, U. Costantino and G. P. Gupta, J. Inorg. Nud. Chem., 1978,40,87. F. M. Lever, Platinum Met. Rev., 1969, 13, 151. 17 F. M. Lever and A. R. Powell, Chem. SOC., Spec. Puhl., 1959, References 18 13, 135. F. M. Lever and A. R. Powell, J. Chem. SOC.A, 1969, 1477. 1 M. J. Hudson, E. Rodriguez-Castellon, P. Sylvester, A. Jimenez-Lopez and P. Olivera-Pastor, Hydrometallurgy, 1990,24, 77. 2 G. Alberti, U. Costantino, S. Alluli and M. A. Massucci, J. Inorg.Nucl. Chem., 1975,37, 1779. 3 M. J. Hudson, E. Rodriguez-Castellon, P. Olivera-Pastor, A. Jimenez-Lopez, P. Maireles-Torres and P. Sylvester, Can, J. Chem., 1989,67,2095. 4 M. J. Hudson, E. Rodriguez-Castellon, P. Olivera-Pastor, A. Jimenez-Lopez, P. Maireles-Torres and P. Sylvester, Can. J. Chem., 1989,67,2095. 5 G. Alberti, M. Casciola and U. Costantino, J. Colloid Interface Sci.,1985, 107, 256. 6 G. Alberti, U. Costantino, F. Marmottini, R. Vivani and C. Valentini, in Recent Developments in Ion Exchange 2, ed. M. J. Hudson and P. A. Williams, Elsevier, London, 1990. 19 20 21 22 23 24 25 26 J. B. Raynor, B. G. Jeliazkowa, J. Chem. Soc., Dalton Trans., 1982,1185. B. Z. Wan and J. H. Lunsford, Inorg. Chim. Actcr., 1982,65, L29. J. R. Pladziewicz, T. J. Meyer, J. A. Broomhead and El. Taube, Inorg. Chem., 1973,12,639. D. J. Jones, J. Penfold, J. Tomkinson and J. Roziere, J. Mol. Struct., 1989, 197, 113. C. H. Huang, 0.Knop, D. A. Othen, F. W. D. Woodhams and R. A. Howe, J. Can. Chem., 1975,53,79. E. Tillmans, W. Gilbert and W. H. Baur, J. Solid Staie Chem., 1973,7, 69. G. G. J. Boswell and S. Soetono, J. Inorg. Nucl. Chem., 1981, 43, 1625. Joint Committee on Powder Diffraction Standards, Card Number 21-1172,1971. U. Costantino and A. Gasparoni, J. Chromatogr., 1970,51,289. J. E. Fergusson and J. L. Love, Inorg. Synth., 1972,13,208. 7 8 Paper 31068 18H; Received 15th November, 1993

ISSN:0959-9428    

DOI:10.1039/JM9940401337

出版商:RSC    

年代:1994

数据来源: RSC

摘要:

J. MATER. CHEM., 1994, 4(8), 1343-1348 Novel Preparation of Highly Dispersed Tungsten Oxide on Silica Sophia Colque," Edmond Payen*b and Paul Grangea a Universite Catholique de Louvain, Groupe de Physico-Chimie Minerale et de Catalyse, 1348 Louvain-la-Neuve, Belgium Laboratoire de Catalyse Heterogene et Homogene & LASIR Universite des Sciences et Techniques de Lille, 59655 Villeneuve d 'Ascq Cedex, France W03/Si0, samples prepared by three different methods and calcined at two temperatures (450 and 900 "C) are studied by different physicochemical techniques [X-ray diffraction (XRD), specific surface area, X-ray photoelectron spec- troscopy (XPS), laser Raman spectroscopy (LRS), electron microscopy and temperature-programmed reduction (TPR)]. When the solids were prepared by mixing two gels (tungsten and silica gel) a good WO, dispersion was achieved and calcination at high temperature gave an amorphous phase.The impregnation of silica gel by ammonium paratungstate allows the interaction of tungsten with silica as dispersed oxoanions and, upon calcination, smaller WO, particles and amorphous glassy particles were formed. In contrast, when the solid was prepared by the wet impregnation method using a silica carrier the interaction of the oxotungsten species with the support was weak. When the sample was calcined the silica and the oxides were segregated. Supported oxides and sulfides of molybdenum and tungsten are well known for catalysing a large variety of reactions. Consequently many studies have been devoted to the prep- aration, characterization and activity of these solids.Most attention has been paid to the alumina-supported catalysts whereas silica-supported catalysts were less studied. Most studies of the latter catalysts deal with MOO,-based solids. These showed that a high dispersion of the molybdenum oxide is never achieved. The formation of crystalline MOO, is observed in Mo03/Si02 catalysts at low Mo loadings,'-3 Fewer studies have been devoted to W03/Si02 catalyst^,^-^ and it has been shown that tungstate is even less well dispersed than molybdate on the same silica ~arrier.~ For a WO, concentration as low as 5 wt.% a crystalline WO, phase is formed.5,7 These solids were generally prepared by impreg- nation of the oxide silica carrier followed by drying and calcination.This classical method is limited for providing good dispersions of the tungsten oxide species owing to the low level of interaction between the oxotungstate species and the silica carrier. The tungsten species tend to agglomerate even at low loadings. The final aim of our work is to prepare dispersed carbide phases using tungsten oxide as a precursor. One of the most important aims for catalytic purposes is to obtain finely divided carbides. In addition to the experimental conditions of the carburization process, the precursor plays an important role in the final properties of the carbide. In order to achieve our purpose, a novel preparation of tungsten oxide supported on silica has therefore been carried out by a sol-gel method which allows simultaneously the preparation of the carrier and the introduction of the oxotungstate species.We recently applied this method of preparation to the syn- thesis of Mo/A1203 oxides and showed that it improves the dispersion limit of oxomolybdate entities." This paper deals with the synthesis of samples obtained by using two new preparation methods, including their solid-state characteriz- ation by different physicochemical techniques. These solids will be compared to those obtained by the traditional impreg- nation method. Tungsten is introduced either as a gel or as an ammonium tungstate salt. The silica is either a high-surface-area Si02 or gel of silica. Experimental Preparation Three different methods of preparation have been used.Mechanical Mixture of Tungsten Gel with Silica Gel Gels of tungsten and silica were prepared separately and then mixed. The silica gel was prepared by adding slowly 95 ml of Si(OEt), to 450 ml of water. After 14 h at 60 "C under stirring, this solution became jelly-like. Ethanol was then removed under reduced pressure in a rotary evaporator. The gel obtained was washed with water and centrifuged several times. The tungsten gel was prepared as follows. Hydrochloric acid solution (3.8 mol 1-l) was dropwise added to an ammonium paratungstate ~(NH,)l,H2W,,0,2~H20J solution (6.5 lop3 mol 1-') at room temperature. The pH of the solution was monitored up to 1-1.5. A clear, yellow solution was obtained.After stirring the solution, it progressively became turbid and turned to a gel after some hours. This gel was aged for 48 h and then separated from the mother solution by centrifugation at 2000 rpm for 10 min. The pH of the silica gel was decreased to 1-1.5 with the hydrochloric acid solution. Then the two gels were rnechan- ically mixed and left together for 12 h before freeze-drying them. Two samples containing 7 and 10.9 wt.% WO, were pre- pared and are referred to hereafter as A7 and A10, respectively, whereas the pure tungsten oxide and silica oxide is denoted as W and silica A. Mixture of Silica Gel and Ammonium Puratungstute Salt The method of preparation of the silica gel was the same as described above.Before the gel was mixed with the ammonium paratungstate solution (8.1 x lo-, mol 1-'), its pH was increased to 9.5-10 with an ammonia solution (6.6 rnol 1-'). This sample is referred to as silica B. The gel and the tungsten solution were then stirred and kept for 24 h. After centrifugation (1000 rpm for 10min) the gel was freeze-dried. This sample is referred to as X6. Impregnation of Si02with Tungsten Salt Commercial SiO, (Degussa FK 700) was impregnated with an aqueous solution of ammonium paratungstate (9.6 x lop3 mol 1-l). The impregnation was carried out using 4.2 ml of solution per gram of SO2. Water was evaporated at 40°C in a rotary evaporator and the sample was dried at 100°C for 2 h. This sample is referred to as 18.All the samples were calcined at 450 and 900°C for 4.5 h and 1.5 h, respectively, and the W03 content of the solids was evaluated by atomic absorption (AA) after dissolution of the samples in hydrofluoric acid at 200°C. The samples are denoted by the method of incorporation of the tungsten, i.e. the content of WO, and the temperature of calcination (for example 18-900 represents the impregnated sample with 8 wt.% WO,, calcined at 9OOOC). Physico-chemical Characterization Powder XRD measurements were carried out with a Siemens D 500 diffractometer using Cu-Ka radiation. The specific surface area was measured gravimetrically by nitrogen adsorption using the BET method. The measurements were made in a vacuum microbalance Setaram MTB x,the fresh and calcined samples first being outgassed to constant weight at 100 and 200 "C, respectively.XPS measurements were carried out with an SSX-100 spectrometer (Surface Science Instruments 206) equipped with an A1 X-ray source working at 200 W. The powdered samples in their original form were pressed into small inox-holders and the C Is, 0 Is, Si 2p and W 4f photoemission lines were recorded for each sample. Binding energies (Eb)were deter- mined with reference to the C 1s line at 284.8 eV. The cali- bration of the spectrometer energy scale was performed using Au 4f,,, (E,=84 eV). A flood gun, with an energy of 6 eV, was used to eliminate differential charging of the samples. XPS atomic ratios were determined by using the total inte- grated areas of the W 4f5/2,7/2 (spin doublet) and the Si 2p photoelectron lines.These ratios were estimated using the formula: NdNsi =(lw/Isi (Ssi/Sw ) (ESi/Ew where Ni,Eiand Siare, respectively, the number of atoms of the element i, the kinetic energy corresponding to a given line and the Scoffield photoelectric cross-sections. LRS measurements were performed using a Raman micro- probe (Mole from Jobin-Yvon). The exciting light source was an Ar' laser emitting the 488 nm line with the power at the sample kept as low as possible, at ca. 1mW, to avoid transformation of metastable phases. TPR experiments were carried out in a home-made dynamic apparatus. A mixture consisting of 5% hydrogen in argon was used as the reducing gas (25 ml min-').The temperature was raised to 840°C at a rate of 10°C min-'. The weight of the sample (20-40 mg) was adjusted in order to have the same content of tungsten in the reactor. The hydrogen con- sumption was measured with a thermal conductivity detector. The electron microscopy studies were performed on a JEOL Temscan lOOCX microscope equipped with a Kevex 5100C energy-dispersive spectrometer for X-ray microanalysis. The samples were dispersed in water using an ultrasonic device and then deposited on carbon films supported on copper grids. These were studied in the conventional transmission mode (CTEM) and by analytical electron probe micro-analysis (EPMA). Results Table 1 shows the surface areas of the catalysts before and after calcination at 450 and 900°C.Heating the catalysts at 450°C has practically no influence on the surface area, while a sharp decrease in surface area is found upon calcination of the catalyst at 900 "C. J. MATER. CHEM., 1994, VOL. 4 Table 1 WO, content and specific surface area of the samples BET surface area/m2 g-calcination temperature/"C WO,sample (wt.%) N,/N,,x lo2 fresh 450 900 ~~ A1 7 1.92 797 702 213 A10 10.9 3.08 705 690 77 X6 6.5 1.77 427 482 277 I8 8.3 2.33 349 352 4 silica A 0 - 803 - 311 silica I 0 - 584 - 11 XRD All the X-ray diffractograms of the samples are shown in Fig. 1 and 2. The XRD pattern of W-25 (Fig. 1 ) is character- 0: 1O( 220 021 c I. I I 9 25 41 57 2gdegrees Fig.1 X-Ray diffraction pattern of the pure tungsten oxides (indexing according to the orthorombic WO, cristallographic data): (a) W-25, (b)w-900 A1 0-900 A10-450 n I, ----4-..----18-450 =X6-450 18-900/ 41 81 1 41 81 2Hdegrees Fig. 2 X-Ray diffraction pattern of the WO,/SiO, samples calcined at 450 "C and 900 "C.The XRD peaks of orthorombic WO, and of silica are referred to in (a) and (d),respectively. 0,Christobalite. J. MATER. CHEM., 1994, VOL. 4 istic of an amorphous sample, and the XRD features of the calcined sample at 900 "C characterize the orthorombic WO, phase (Fig. 1)according to JCPDS data (no. 20-1324). The diffractograms of uncalcined or calcined silica-based samples show a broad band at ca.28=22', which is due to amorphous silica (Fig. 2). The X-ray diffractograms of the A7 and A10 catalysts calcined at 450 'C and 900 "C are shown in Fig. 2[(a) and (b)]. The main characteristic peaks of WO, could be detected in the pattern of A7 calcined at 450°C on the underlying peak of silica. These peaks are more evident with increasing tungsten loading. However, they are not observed in the pattern of A7-900. This is probably due to a modification in the sample of this oxide upon calcination, as will be shown by LRS. After calcination the X6 samples did not exhibit any lines of a crystalline phase. By comparison, the XRD pattern of sample 18-450 [Fig. 2(4] indicated the presence of WO,, whilst after calcination at 900°C these features are present with the diffraction peaks of cristobalite (21.92", 36.18', 31.46').XPS The binding energies of the 0 1s and Si 2p levels for all the catalysts agreed with the values obtained for silica (0Is= 532.9 eV and Si 2p= 103.6 eV). Fig. 3 shows, for all the cata- lysts, the W 4f XPS doublet characteristic of the presence of W6+ species in an oxygen environment. For the uncalcined A7 and A10 catalysts the peaks are narrow and the position is similar to that observed for the tungsten gel W-25 (36.1 and 38.1 eV). Well defined lines at 35.7 and 37.8 eV, character- istic of tungsten trioxide, are observed for the solid W-900, whereas a broadening of this doublet occurs for the calcined A7 and A10 samples. This broadening is even more important for X6, whilst the well resolved lines of bulk WO, are observed in the solid I calcined at 900 "C.The effect of the temperature of calcination on the superficial tungsten concentration is illustrated in Fig. 4 where the XPS atomic ratios (W 4f/Si 2p) are plotted against the temperature. 42 38 34 42 38 34 EdeV Fig. 3 XPS spectra of the W 4f levels for fresh and calcined samples 0 500 10000 500 1000 TIT Fig. 4 (lw/Isi)XPS atomic ratio for fresh and calcined samples: (a) A7, (b)A10, (c) X6, (d) I8 LRS The Raman spectra of the dried silica powder (Fig. 5) show only a broad line at around 1100 cm-'. Thermal treatment of these silica gels at 900°C causes the system to evolve towards vitreous silica, as indicated by the Raman features at 500 and 1100 cm-', in agreement with literature data."*'2 LRS is as a very useful technique for characterizing tungsten oxides or oxotungstate species.Under our experimental con- ditions, using a very low laser beam power to avoid phase transformations, the spectrum of the tungsten gel shows a line at 960 cm-I and a broad band at around 600-720 err-'. This could be assigned by reference to literature data" to the existence of the hydrate WO3.2H,O, of which the particle size and/or the non-ordered nature are likely to produce the spectral distortion and line broadening. In spite of the low pH of preparation, the existence of silicon heteropolyt unsgtate 720 8r 640 A-900 1100 IIIIIIIIII 200 400 600 700 1000 Aijlcm-Fig.5 Raman spectra of reference samples: (a): silica, (h): tungsten oxide. The plasma lines of the laser are indicated by P. J. MATER. CHEM., 1994, VOL. 4 should be pre~1uded.l~ After calcination of the catalysts, intense lines at 810 and 720 cm-', corresponding to bulk WO,, are 0b~erved.l~ The main features of the tungsten oxide gel, identified as WO3.2H,O are also observed on the uncal- cined samples, whereas the Raman features of WO, are mainly seen after calcination at 450°C (Fig. 6) with the broad band of vitreous silica (490 and 11OOcm-I). Although the SiO, support may exhibit a line at 980 cm-', significant intensity variations between the lines are noted on the Raman spectrum of the A7-450 sample and confirm that this line is the W-0, stretching mode of a polytungstate species, where the subscript t denotes a terminal W-0 bond.I5 The relatively poor quality of the Raman spectra is probably due to the poor crystallinity of the supported samples, as shown by XRD measurements.The other vibrational modes are always weaker and are hardly detectable above the background. After calcination of the catalyst at 900 "C the tungsten oxide is the only detectable species (Fig. 6); however a close comparison with the Raman spectrum of bulk oxide indicates that there are some major differences. These occur mainly in the shift and broadening of the main high-frequency lines at 800 and 687 cm-' and in the lattice lines region (100-400 cm-') which reflects the crystal- linity of the sample.These differences suggest that this WO, species shows little crystallinity and/or interacts with the support. Similar LRS features were previously obtained by Pham Thi and Velasco on W03 thin films sputtered on various supports.16 Raman results for samples X and I are reported in Fig. 7. With the Raman features of the vitreous silica, the X6-25 sample exhibits a Raman line at 960 cm-' with a broad band on its low-wavenumber side as well as very broad bands at 560cm-1 and in the 200-400cm-' spectral range. These features are consistent with the presence of a polymeric oxotungstate entity interacting with the silica gel, similar to those previously described for W/Al,O, system^.'^ After calci- nation of the catalyst the features of WO, appear at 810 and 710 cm-'; however, the main Raman line of the precursor at I 810 I P A7-25 200 400 600 800 1000 1200 AVcm-' Fig.6 Raman spectra of fresh and calcined A7 and A10 samples. The plasma lines of the laser are indicated by P 18-9004 720118081X6-900 200 400 600 800 1000 1200 A,/cm-' Fig. 7 Raman spectra of fresh and calcined X6 and I8 samples. The plasma lines of the laser are indicated by P 960 cm-', is still observed. In view of the very high diffusion cross-section of WO, compared to the supported oxoanions, the band of WO, present after calcination at 450°C should not be interpreted as being due to the presence of large amount of WO, resulting from the transformation of the oxotungsten entity.In contrast, the Raman spectrum of the 18-25 sample shows well defined lines at 972 and 891 cm-' as well as bands in the low spectral range which could be assigned to a well defined but weakly interacting polytungstate entity. However, it is not possible to ascertain the exact nature of this oxide species. After calcination of the catalyst at 450 "C the crystal- line oxide is the only species detectable by LRS, in agreement with the XRD results. As the Raman microprobe allows analysis of selected particles, heterogeneity is detected. Thus, after calcination of the sample at 900 "C, the Raman spectrum of some particles shows evidence of the presence of well crystallized WO, (not reported here) whereas the Raman spectrum of other particles shows a broad asymmetric line of vitreous silica beyond 500cm-', as well as the WO, lines.However, the Raman spectrum of cristoballite12 was not observed. As this silica form was evidenced by XRD, this implies that segregation has occurred during calcination at 900°C and, owing to the spatial resolution of the analysis, cristobalite was not detected by Raman spectroscopy. TPR The TPR profiles of the bulk WO, prepared by the gel method are shown in Fig. 8. When the gel was not calcined (W-25), the TPR profile showed two reduction peaks, at 622 and 710 "C. However, when the sample was calcined at 900 "C, the reduction occurred in one step at a higher temperature. The same results were found when mechanical mixtures of bulk oxide and silica were reduced.The TPR profiles of samples A7 and A10 (Fig. 9) show that reduction becomes J. MATER. CHEM., 1994, VOL. 4 440 840 TPC Fig. 8 TPR profiles of the tungsten oxides: (a) fresh gel (W-25) and (b)gel calcined at 900 "C (W-900) Imb2X6-25 11111 11III 440 840 440 84(TI'C Fig. 9 TPR profiles of fresh and calcined samples prepared by mixing tungsten gel and silica gel (A7 and A10); impregnation of silica gel with a solution of tungsten salt (X6)and by impregnation of commer-cial Si02 with tungsten salt (18) more difficult after calcination and that sample A7-900 is practically unreduced. Fig. 9 also shows the reducibility of the X6 samples. For these, it is evident that the hydrogen con- sumption is much lower than for the other samples.In order to correlate the amount of reduction with the different oxidation states of tungsten, some XRD analyses were performed after reduction of the samples at 840°C. The presence of tungsten metal (Wo) is always observed, but the corresponding peaks are weakly detectable on sample A7-900. In the case of bulk tungsten oxide gel (W-25), the XRD spectra taken after stopping the reduction at 650 "C indicates the prcsence of both W02 and W metal. The analysis of the samples A7-900 and X6-900 by CTEM and EPMA indicates the presence of some glassy particles consisting of silica and tungsten, which are smaller in the X6-900 sam2le. Discussion The influence of the method of preparation and the calcination temperature will be discussed separately.Influence of the Method of Preparation The tungsten gel is identified as an amorphous hydrate of tungsten oxide, and this hydrate is clearly identify in the A7 sample. The TPR pattern of the A samples, similar to the fresh unsupported gel, is slightly shifted (by 30 "C) to a higher reduction temperature. This should probably be attributed to the fact that this oxide is trapped in the silica particles. This suggests that, in this preparation, the oxide particles are very small and retain their chemical identity, as would be the case in a mechanical mixture of very fine particles. This explanation is supported by the XPS atomic ratio, which is almost the same as the W: Si atomic ratio. Sample A10 shows the same behaviour.The W 4f XPS doublet of sample X6 is weakly resolved; such broadening has been previously reported for silica- or alumina-supported oxides and assigned to a strong interaction between the oxide and the ~arrier.',~,'~ In agreement with this interpretation, the Raman spectrum indicates that a well dispersed polymeric oxotungstate species is interacting with the silica gel. In contrast, the lowering of the (W/Si)xps intensity ratio of sample I8 may be explained by an inhomogeneous dispersion of a polytungstate species on top of the silica, due to the low level of interaction between the oxotungstate ions and the hydroxy groups of the silica surface. Therefore, this isopoly- tungstate ion transforms easily when the sample is heated into bulk WO,, as will be seen below by LRS. The TPR reduction show two peaks, the higher of which corresponds to the reduction of larger particles of WO,.Effect of Calcination Temperature The presence of tungsten trioxide was ascertained by LRS and XRD in sample A7-450. The TPR behaviour is intermedi- ate between that of a gel and well crystallized WO,. This difference in reducibility may be explained by the incomplete transformation of the interacting gel into WO, and the existence of a new phase characterized in LRS bj a broad line at 980cm-'. Even after calcination of the cxtalyst at 900 "C the tungsten remains homogeneously dispersed in the silica, as shown by XPS. But some modifications of tlie Raman spectrum of the A7-900 sample, with respect to biilk WO,, have been reported in the above paragraph.No crystalline tungsten trioxide is observed by XRD, implying that it is amorphous, microcrystalline or present in undetectable amounts. So in relation with the method of prcparation starting from gel, it is possible to assume that the loss of reducibility should be due to the very small size of the oxide particles which are embedded in the support and intcract with it. It has been demonstrated that small oxide particles are reduced less easily than larger ones." However, the rate of reduction obviously decreased for larger particles. The structure of the solid A10 is similar to A7 described above. Upon calcination of the sample at 450"C, d shift to higher temperature of the TPR peak and a shift and broaden- ing of the XPS lines show that, as in the case of AT-450, the W is distributed in two different species, one interacting with the support, whereas the other, which tends to agglomerate, is identified as crystalline particles of WO,.After c;ilcination of the catalyst at 900"C, due to the higher tungsten content, the heterogeneity increases and some WO, particles should be bigger than those in sample A7-900, in agreement with the decrease in the XPS intensity ratio. Their distribution in the matrix becomes irregular and the surface area decreases drastically. In all these observations, it is striking that the reducibility of these samples calcined at 450°C is controlled by the effect of dispersion in the support and interaction with it.In contrast, the reducibility of the sample calcined at 900 "C is controlled by the crystallite size of the W03 particles. In relation to the X6 samples, calcination increases the surface concentration of tungsten as well as its irr teraction J. MATER. CHEM., 1994, VOL. 4 with the silica, as shown by the broadening of the W 4f lines. These results and the weak reducibility of the samples both before and after calcination could be explained if we assume that the method of preparation had allowed the incorporation of tungsten as isolated oxoanions, giving a higher dispersion and interaction with the silica gel. This preparation allowed the formation in sample X6-900 of small particles of silica and tungsten oxide which seem to have the characteristics of a glass, the nature of which is not defined.Calcination at 450 "C of the impregnated sample allowed the formation of crystalline W03, but the broad XPS W 4f line of sample 18-450 also suggests the existence of oxotungsten species interacting with the carrier. A similar observation was reported by Kerkhof et a1.* On the other hand, cristobalite formation at 9OO0C, with the corresponding decrease in specific surface area, is due to a segregation of the tungsten and silica. In relation to the heterogeneity detected by LRS, these results may explain the increase of the XPS intensity ratio and the narrowing of the W 4f XPS lines.Conclusions The three different methods of introduction of W03 on an SiOz support, and the two different calcination temperatures influence the structure, texture and behaviour of the solids. Mixing two separate gels (tungsten and silica gel) gives well dispersed small WO, particles which, upon calcination at high temperature, give an amorphous phase. Impregnation of ammonium paratungstate on silica gel improves the chemical interaction of isolated tungsten oxoanions with the silica. Upon calcination of the sample, small bulk W03 particles are formed but dispersed oxotungsten species remain on the surface of the support. The interaction of the oxotungstate species with the surface of the support is weak when the solid has been prepared by impregnation of silica with ammonium paratungstate.Upon calcination, both phases seem almost independent. References 1 L. Rodrigo, K. Marcinkowska, A. Adno, P. C. Roberge, S. Kaliaguine, J. M. Stencel, L. E. Makowsky and J. R. Diehl, J. Phys. Chem., 1986,90,2690. 2 Y. Okamoto, T. Imanaka and S. Teranishi, J. Phys. Chem., 1981, 85, 3798. 3 0.Takehiko, A. Masakazu and K. Yutaka, J. Ph.vs. Chem., 1986, 90,4780. 4 P. Biloen and G. T. Pott, J. Catal., 1973,30, 169. 5 L. L. Murrel, D. C. Grenoble, R. T. K. Baker, E. B. Prestidge, S. C. Fung, R. Chianelli and S. P. Cramer, J. CatLil., 1983,79,203. 6 Y. V. Plyuto, J. Stoch, I. V. Babytch and A. A. Chuyko, J. Non Cryst. Solids, 1990, 124,41. 7 F. P. Kerkhof, J. A. Moulijn and A. Heeres, J.Elcctron Spectrosc. Relat. Phenom., 1978, 14,453. 8 F. P. J. M. Kerkhof, J. A. Moulijn, R. Thomas and J. C. Oudejans, in Preparation of Catalysts II. Scient$c Basis for the Preparation of Heterogeneous Catalysts, ed. B. Delmon, P. Grange, P. Jacobs and G. Poncelet, Elsevier, Amsterdam, 1978,p. 77. 9 B. M. Reddy, K. S. Prasad Rao and V. M. Mastikhin, J. Cutul., 1988,113,556. 10 E. Etienne, E. Ponthieu, E. Payen and J. Grimblot, J. Non Cryst. Solids, 1992,147 & 148, 764. 11 A. Bertoluzza, C. Fagnano, M. M. Morelli. M. Gugliemi, G. Scarini and L. Maliavski, J. Raman Spectrosc.. 1988,19,297. 12 J. Etchepare, M. Merian and P. Kaplan, J. Cht)m. Phys., 1978, 68, 1531. 13 M. F. Daniel, B. Desbat, J. C. Lassegues, B. Gerand and M. Figlarz, J. Solid State Chem., 1987,67,235. 14 R. Thouvenot, M. Fournier, R. Franck and C. Rocchiccioli-Deltcheff, Inorg. Chem., 1984, 23, 598. 15 D. Ouafi, F. Mauge, J. C. Lavalley, E. Payen, S. Kasztelan, M. Houari, J. Grimblot and J. P. Bonnelle, Card. Today, 1988, 4, 23. 16 M. Pham Thi and G. Velasco, Solid State Ionics, 1984, 14, 217. 17 J. A. Horsley, I. E. Wachs, J. M. Brown, C;. H. Via and F. D. Hardcastle, J. Phys. Chem., 1987,91,4014. 18 Y. Barbaux, A. R. Elamrani, E. Payen, L. Gengembre, J. P. Bonnelle and B. Grzybowska, Appl. Catal., 1988,44, 117. 19 J. L. Lemaitre, in Characterization of Heterogeneous Catalysts, ed. F. Delannay, Marcel Dekker, New York, 1984, ch. 2. Paper 3/06366F; Received 25th October, 1993

ISSN:0959-9428    

DOI:10.1039/JM9940401343

出版商:RSC    

年代:1994

数据来源: RSC

摘要:

J. MATER. CHEM., 1994, 4(8), 1349-1350 MATERIALS CHEMISTRY COMMUNICATIONS Red Bismuth Emission in Alkaline-earth-metal Sulfates Mariska A. Hamstra, Hilda F. Folkerts and George Blasse Debye Institute, Utrecht University, Postbox 80.000, 3508 TA Utrechf, The Netherlands The red luminescence of bismuth-doped alkaline-earth-metal sulfates is ascribed to the presence of divalent bismuth. The optical transitions are due to transitions within the 6p shell. The Bi3+ ion is known to show an ultraviolet, blue or sometimes even green luminescence.' In 1886 Lecoq de Boisbaudran reported a red luminescence for bismuth in the alkaline-earth-metal sulfates,, which was confirmed later by Kroger et aL3 The latter authors suggested that this lumi- nescence may be due to trivalent or pentavalent bismuth.Here we propose a very different explanation. We were led to this via two ways. First, our research on the luminescence of (s), ions in sulfates led us to a reinvestig- ation of the red emission mentioned above. Secondly, an orange emission for bismuth-doped SrB,O, was reported recently from this laboratory, and shown to be due to divalent bismuth with electron configuration (6s),( 7s)'. Our present results show that the red emission in the sulfates has the same origin. MSO, :Bi (M =Ca, Sr, Ba) samples were prepared by conventional solid-state techniques with firing up to 900 "C. The bismuth concentration was ca. 0.1 mol%. The samples were shown to be single phase by X-ray powder diffraction using Cu-Kcr radiation.The optical measurements were per- formed as described before., The alkaline-earth-metal sulfates show a red photolumin- escence of medium intensity for Ba and Sr, whereas for Ca it is very weak and disappears with time. Fig. 1 shows as an example the emission and excitation spectra of BaSO, :Bi. The decay time of this emission is practically temperature independent and amounts to 4 ps. The data for CaSO,: Bi were very hard to measure and are considered to be inaccurate. The emission spectra agree with those reported (half) a century ag0.~3~ Table 1 summarizes our results. Some samples also showed a bluish emission that could only be excited in the shorter-wavelength UV region, the presence of which depends on the preparation conditions and on the bismuth concentration.At room temperature this 300 400 500 600 hlnm Fig. 1 Emission (---) and excitation (-j spectra of the luminescence of BaSO, : Bi2+ at 4.2 K. Excitation wavelength 455 nm, monitored emission wavelength 625 nm. 0gives the radiant power per constant wavelength interval, and qr the relative quantum output, both in arbitrary units. emission is usually quenched. Kroger et aL3 reported similar results. There is a striking analogy between the results for MSO, :Bi M=Sr, Ba and SrB,O,:Bi (Table 1). This relates also to the values of the decay times of the emissions involved. This analogy is even more pronounced if one considers the fact that the Stokes shift in the SrB,O, host lattice is a1 ways very small., For this reason we assume that the red emission of bismuth in the alkaline-earth-metal sulfates is due to divalent bismuth.Its electron configuration is (SS)~(6p)', vielding a 6P1/2ground state and a crystal-field-split 6P3/2excited state. In Table 1 the two crystal-field levels are denoted (I) and (2) in order of increasing energy. Since the emission is a 6p intraconfigurational transition C2P3I2(l)-+2Pl/2],it is formally parity forbidden. Tht. observed decay time (4ps) points indeed to a partly forbidden rransition. Since the uneven crystal-field terms mix with the (6~)~(7s)', ,SI1, and the 2P3/2and 2Pljzstates,, the parity selection rule becomes partly lifted. The emission and the lowest excitaticbn band [2P1/2-2P3/2(1)]show a side band at ca.1050 cm-' lower and higher energy, respectively (see Fig. 1). This can bc. ascribed to a vibronic transition involving the asymmetric a1 sulfate stretching vibration which is at ca. 1100 cm-' in the infrared spe~trum.~This transition has also been observed in SrB,07: Bi2+ where it is at 1200 cm-' lower or higher energy, corresponding to the borate stretching vibrations. In CaSO, :Bi the divalent state of bismuth is obviously less stable. The reason for this can be the smaller size available, or the hydration of CaSO, yielding oxidation of Bi2+. Although the data for CaSO, :Bi are intriguing in comparison with the others in Table 1, we do not discuss these further in view of their inaccuracy. The much larger Stokes shift is not unusual if one compares with data observed for isoelectronic Pb+.In CaF,: Pb+ a Stokes shift of ca. 5000 cm-' has been reported.6 The observed blue emissions are ascribed to Bi", which may be present in the host lattice or in a second phase. Unfortunately the corresponding absorption band is situated in the shorter-wavelength UV region where it is expected to overlap with the allowed (6s),( 6p)l+( 6s),( 7s)' transition on the Bi2+ ion. As in SrB,07:Bi2+, we observed the red Bi2+ emission also upon excitation of the sulfates in this region: see, e.g., the excitation band at 260 nm in Fig. 1. This shows that the (6s),(6p)' --+(SS)~(~S)' transition is in fact situated in this region (ca. 40000 cm-'). Finally, we note that Kroger et aL3 reported a similar red luminescence for bismuth-activated CaP,O,, Ca2P207, Sr,P,07, SrP206 and Ca3(P04)2.The emission maxima vary from 650 to 700 nm. We assume that this emission is also due to divalent bismuth, This shows that Bi2+ is less rare than suggested by inorganic chemistry textbooks. Kroger et aL3 J. MATER. CHEM., 1994, VOL. 4 Table 1 Positions of some optical transitions of Biz+ in several host lattices (all values in lo3 cm-') composition absorption 2p1,2+zp3,2(11 zpl/2 +2p3/2 SrB,O, :Biz+ 17.4 21.2 BaSO, :Biz+ 17.0 22.0 SrSO, :Biz+ 17.4 21.7 CaS04:Bi2+ 20.0 23.6 This work; this work; uncertain values. obtained efficient cathodoluminescence for the red-emitting sulfates and phosphates.No doubt the Bi2+ ion can very efficiently capture a hole. If an electron recombines with this captured hole, the red bismuth emission occurs. In conclusion, there is ample evidence that Bi2+ can be substituted up to amounts of ca. 0.1 mol% in several alkaline- earth-metal compounds. References 1 G. Blasse, Prog. Solid State Chem., 1988,18, 79. 2 Locoq de Boisbaudran, C.R. Acad. Sci. Paris, 1886,103,629. emission Stokes ref. shift (2) 17.1 0.3 16.0 1.o 16.4 1.o 16.2 3.8 3 F. A. Kroger, J. Th. G. Overbeek, J. Goorissen and J. van den Boomgaard, Trans. Electrochem. Soc., 1949,96, 132. 4 G. Blasse, A. Meijerink, M. Nomes and J. Zuidema, J. Phys. Chem. Solids, 1994,55, 171. 5 L. H. Brixner, M. K. Crawford and G.Blasse, J.Solid State Chem., 1990, 85, 1. 6 M. Fockele, F. Lohse, J. M. Spaeth and R. H. Bartram, J. Phys. Condens. Matter, 1989, 1, 13; M. Fockele, F. J. Ahlers, F. Lohse, J. M. Spaeth and R. H. Bartram, J. Phys. C, 1985,18,1963. Communication 4/03131H; Received 25th May, 1994

ISSN:0959-9428    

DOI:10.1039/JM9940401349

出版商:RSC    

年代:1994

数据来源: RSC

摘要:

J. MATER. CHEM., 1994, 4(8), 1351-1352 First Ferrocene-containing Side-chain Liquid-crystalline Polymers Robert Deschenaux,*a Isabelle Kosztics: Ulrich Scholten," Daniel Guillonb and Mohammed Ibn-Elhajb a Universite de Neuchitel, lnstitut de Chimie, Av. de Bellevaux 57,2000 Neuchitel, Switzerland lnstitut de Physique et Chimie des Materiaux de Strasbourg, Groupe des Materiaux Organiques, 23 Rue du Loess, B.P.20 CR, 67037 Strasbourg Cedex, France The synthesis and mesomorphic properties of the first ferrocene-containing side-chain liquid-crystalline polymers, obtained by grafting either a 1,l'-or 1,3-disubstituted ferrocene derivative functionalized by a vinyl group onto a polysiloxane, are reported; these polymers showed enantiotropic smectic C and/or smectic A phases.Increasing interest is currently devoted to metal-containing latter materials showed only limited properties: ;I nematic thermotropic liquid-crystalline polymers. The incorporation melt was observed at elevated temperatures (isotropization of a metal centre into mesomorphic materials capable of temperatures were not reported); furthermore, these com-forming films or fibres could lead to a source of processable pounds were found to be insoluble in most solvents. materials exhibiting new magnetic, optical and electronic Obviously, new structures are required to rationalize the properties.' structure-mesomorphic property relationship for metal-Main-chain and side-chain coordination liquid-crystalline containing liquid-crystalline polymers. polymers have attracted most attention so far.2 Interesting We report herein the synthesis and mesomorphic behaviour magnetic studies were made with a copper-containing nematic of ferrocene-containing monomers 1 and 2 and of side-chain polyester.2" A series of main-chain polyesters incorporating polysiloxanes 3 and 4.Ferrocene-containing side-chain liquid- These crystalline polymers have not been described previously. The the ferrocene unit in their backbone was also rep~rted.~ 1 CH3I (CH3)3Si-(SiO),-Si(CH3)3I H 5 e 2 6 CH3 (CH&3iO-I Si(CH& c 0 2 0 c o Z e OC 1eH37 I(CH,), ,o~ C O ~ ~ O ~ C ~ 3 4 mesomorphic properties of 1-4 were investigated by differen- tial scanning calorimetry (DSC), polarized optical microscopy and X-ray diffraction studies.1 and 2 were prepared from either ferrocene-1,l'-diacid chloride4 or ferrocene-1,3-diacid chloride5 and the appropriate phenol derivatives6 following a stepwise procedure we recently developed for synthesizing unsymmetrically 1,l'- and chiral 1,3-disubstituted ferrocene-containing thermotropic liquid cry~tals.~The structures of 1 and 2 were confirmed by 'H NMR spectroscopy and elemental analysis. The 1,l'-disubstituted ferrocene derivative 1 exhibited enantiotropic smectic C and smectic A phases (c'124's,'13l.sA'141.I).On heating, the 1,3-disubstituted ferrocene derivative 2 showed an enantiotropic smectic A phase (C.168.SA.201*I). On cooling from the isotropic melt, a monotropic smectic C phase also formed at 160 "C after the smectic A one.Ferrocene derivative 2 melted at a higher temperature than its 1,l'-isomeric ana- logue l. This result can be explained from the X-ray crystal structure obtained for a 1,3-disubstituted ferrocene derivative which revealed that such a substitution leads to highly aniso- metric structures' as compared to the 'step' structure of ferrocene derivatives substituted in l,l'-positi~ns.~ Polymers 3 and 4 were synthesized by grafting of monomer 1 or 2 onto polysiloxane 5 (Huls America Inc., no. PS 120; M =2270) or 6 (Huls America Inc., no. PS 123.5; m= 15-18%, n =82-85%; M =2000-2500), respectively, following a litera- ture procedure" [toluene, 70 "C, 24 h; PtC12( 1,5-C,Hl2); 1.1 equiv.of monomer]. The ratio of substitution is not yet known; however, the strong decrease of the Si-H bond peaks in the reaction as followed by 'H NMR spectroscopy (4.7 ppm, CDC1,) and IR spectroscopy (2160 cm-', KBr), revealed that a high content of monomeric unit was anchored onto the polysiloxane. The bulkiness of the ferrocene unit may have prevented the reaction from going to completion. Polysiloxanes 3 and 4 showed good solubility in common organic solvents (CH,Cl,, CHCl,, THF, toluene). Purification was accomplished by addition of methanol into a CH,Cl, solution followed by centrifugation to recover the precipitated polymer. After several purification cycles, the polymer was obtained in ca. 40% yield. Absence of unreacted monomer was confirmed by gel permeation chromatography (Ultrastyragel, THF).Molecular weight determination of the synthesized polymers is currently under investigation (unsatis- factory results have been obtained so far using GPC with polystyrene standards to calibrate the columns). Polymeric structures 3 and 4 presented interesting meso- morphic behaviour. On heating, both compounds gave rise to a birefringent melt between the crystal state and the isotropic liquid. No decomposition was detected. As is often the case with polymers, the mesophases could not be identified by polarized optical microscopy: owing to the high viscosity of these materials, typical textures cannot develop." However, an unambigous characterization of the liquid-crystalline phases was provided by means of X-ray diffraction analyses which revealed that polymer 3 exhibited enantiotropic smectic C and smectic A phases (c.13o.sc.148.sA.171.I) and polymer 4 presented an enantiotropic smectic A phase (C-146.SA.2O2-I).Therefore, the polymeric structures retained the mesophases J. MATER. CHEM.. 1994, VOL. 4 shown by their corresponding low-molar-mass ferrocene derivative. Note that the polymers exhibited a broader aniso- tropic domain than the monomers (41 "C for 3 and 17 "C for 1; 56 "C for 4 and 33 "C for 2). In the smectic A phase, the d-layer spacine calculated from X-rax diffraction data was found to be 54.5 A (at 160°C) and 64.8 A (at 170"C) for 3 and 4, resptctively. Since CPK models gave a molecular length L of 68.5 A for 1 and 2 (in their fully extended conformation), a d/L ratio of 0.80 and 0.95 was obtained for 3 and 4, respectively.These data suggest a monolayer organization of the monomeric units with a pro- nounced disorganized molecular arrangement in the case of 1. In conclusion, polymers 3 and 4 showed pronounced liquid- crystal character, high thermal stability and good solubility in organic solvents. This combination of properties makes ferrocene-containing side-chain liquid-crystalline polysilox- anes interesting materials for the development of electroactive liquid-crystalline polymers. Finally, owing to the planar chiral- ity of monomeric unit 2, due to the substitution of the 1,3-positions by two different sub~tituents,~~ polymer 4 is also chiral.To our knowledge, this is the first example of a chiral metal-containing liquid-crystalline polymer. R.D. acknowledges the Doktoranden-Stipendien der Chemischen Industrie Base1 for a fellowship to I.K. and the Swiss National Science Foundation for financial support (grant 20-3948 5.93). References 1 D. W. Bruce, J. Chem. Soc., Dalton Trans., 1993,2983. 2 (a) P. J. Alonso, J. A. Puertolas, P. Davidson, B. Martinez, J. I. Martinez, L. Oriol and J. L. Serrano, Macromolecules, 1993, 26, 4304 and references therein; (b)J. S. Moore and S. I. Stupp, Polym. Bull., 1988, 19, 251; (c) U. Caruso, A Roviello and A. Sirigu, Macromolecules, 1991,24,2606 (d)F. Wu, R. Zhang and Y. Jiang, Chinese J. Polym. Sci., 1991,9,71. 3 P.Singh, M. D. Rausch and R. W. Lenz, Polim. Bull., 1989, 22, 247. 4 F. W. Knoblock and W. H. Rauscher, J. Polym. Sc I., 1961,54,651. 5 M. Hisatome, 0. Tachikawa, M. Sasho and K. Yamakawa, J. Organomet. Chem., 1981, 217, C17; A. Kasahara, T. Izumi, Y. Yoshida and I. Shimizu, Bull. Chem. Soc. Jpn., 1982,55, 1901. 6 R. Deschenaux, J-L. Marendaz and J. Santiago, Helv. Chim. Acta, 1993,76,865; M. Dumon, H. T. Nguyen, M. MauTac, C. Destrade and H. Gasparoux, Liq. Cryst., 1991,10,475. 7 (a)R. Deschenaux, M. Rama and J. Santiago, Tetrahedron Lett., 1993, 34, 3293; (h)R. Deschenaux and J. Santiago, Tetrahedron Lett., 1994,352169. 8 R. Deschenaux, I. Kosztics, J-L. Marendaz and H. Stoeckli-Evans, Chimia, 1993,47,206. 9 M. A. Khan, J. C. Bhatt, B. M. Fung, K. M Nicholas and E. Wachtel, Liq. Cryst., 1989, 5, 285; A. P. Polishchuk, T. V. Timofeeva, M. Yu. Antipin, Yu. T. Struchkov, Yu. G. Galyametdinov and I. V. Ovchinnikov, Kristallograjiya, 1992, 37, 705. 10 G. W. Gray, D. Lacey, G. Nestor and M. S. White, Makromol. Chem., Rapid Commun., 1986,7,71. 11 Side Chain Liquid Crystal Polymers, ed. C. B. McArdle, Blackie, London, 1989. Communication 4/03411 B; Received 7th June, 1994

ISSN:0959-9428    

DOI:10.1039/JM9940401351

出版商:RSC    

年代:1994

数据来源: RSC

摘要:

J. MATER. CHEM., 1994, 4(8), 1353-1355 Superconductivity up to 95 K in Mercury-substituted 121 2 Thallium Cuprates (TI,Hg)lSr2+yNdl $u207 F. Letouze, S. Peluau, C. Michel, A. Maignan, C. Martin, M. Hervieu and B. Raveau Laboratoire CRISMAT, CNRS URA 1318-ISMRA, Universite de Caen, Boulevard du Marechal Juin, 14050 Caen Cedex, France The solid solution TI, -xHgxSr,+yNd, -yCu,O,-d has been characterized; the homogeneity range extends up to x =0.2 and y=0.5. Electron diffraction and XRD studies confirm the statistical distribution of the cations in the different sites of the 121 2-type structure. The best properties are observed for x =0.1 and y =0.5, with a T, of 95 K and a diamagnetic volume fraction of 70%. The influence of mercury substitution for thallium in the phase is discussed.Numerous superconducting thallium cuprates have been isolated to date, besides the classical superconductors TlBa,CaC~,0,l,~ and TlSr,CaCu,O, which are rarely pre- pared as a pure pha~e.~,~ In these compounds, whose structure (Fig. 1) consists of pyramidal copper layers intergrown with distorted rock-salt-type layers, thallium can be associated with different cations such as bismuth5 and lead6 without changing dramatically the critical temperature of these phases. In contrast, the nature of the cations interleaved between the pyramidal copper layers plays a determining role in supercon- ductivity. In most of these compounds, the presence of calcium is necessary for the existence of superconductivity; its partial replacement by a trivalent lanthanide may enhance the super- conducting properties, but beyond 20% substitution T, is affected; the superconductivity disappears completely for a total substitution, e.g.for TlBa,NdCu,O, .7,8 In this respect, the cuprate TlSr, _,L~,CU~O~~-~~ is very interesting since it is the only 1212 superconductor without calcium, with a T, onset of 95 K. Divalent mercury, owing to its 5d1' electronic configuration similar to that of Tl"', is a good candidate for partial replacement of this cation. The stabilization of mixed layers [Tll-,Hg,O], was indeed proved in the 2223 cuprate T1, ~,Hg,Ba,Ca,Cu3010'2 for a substitution rate x limited to 0.4. Such a substitution did not modify the critical temperature of this phase, which remained close to 130K.The present study is devoted to the substitution of mercury for thallium in calcium-free 1212 cuprates belonging to the system T1Sr,NdCu20, -,-T1Sr3Cu,07 -Fig. 1 Idealized 1212 structure Mixtures of the oxides T1203, HgO, SrO,, Nd203 and CuO according to the nominal compositions Tll -xHg,Sr2+yNdl -yC~Z09-xx/2+y/2 were heated in cvacuated silica tubes. The temperature was raised slowly o~er 8 h to 900 "C, maintained for 8 h and then slowly decreased to room temperature. The nominal oxygen content is much higher than that required for the ideal composition '0,' of the 1212 oxides, so that an oxygen pressure of several bar exists in the tube in order to favour a partial oxidization of Cu" into Cu"' and to avoid dissociation of mercury oxide into metallic mercury.Different thermal treatments were performed in order to improve the superconducting properties via the optimization of the oxygen content: at 350 "C under an oxygen pressure of 100 bar or at 280 "C under an Ar-H2 (90 : 10) flow. The samples were systematically analysed by X-ray diffrac- tion (XRD), electron diffraction (ED) and energy-ciispersive microanalysis (EDS). The XRD patterns were recorded with a Seifert vertical diffractometer equipped with a primary monochromator (Cu-Ka, radiation). Data were collected by step scanning in the range 10<28/degrees<110 with an increment of 0.02" (28). Lattice constants were determined using the Rietveld method (computer program DBW 3.213).Electron diffraction was performed with a JEO I, 200CX electron microscope, operating at 200 kV and equipped with a eucentric goniometer (k60").Electrical resistivity measure- ments are carried out by the four-probe technique. 'Magnetic measurements were performed with a DC SQUID magnet- ometer; the samples are first zero-field-cooled to 5 K and a magnetic field of 10 G was then applied to register the temperature dependence of the magnetization. No deinagnetiz-ation corrections were performed, owing to the porous charac- ter of the bars. For the above thermal treatments, the formation of a 1212-type phase was observed over a large part of the 'pseudo quaternary' diagram T1, -,Hg,Sr, +,,Nd, -yCu207 -& (Fig. 2). The EDS analysis shows that in many crystals the substitution can be achieved up to x=0.5, i.e.'Hgo,5Tlo,5' and to y=O.8, i.e. 'sr2.8Ndo.i (the two discontinuous lines in Fig. 2). However, the XRD study shows that, in the selected experimental conditions, the monophasic domain i$ smaller and is limited by two lines x=O.2 and y=O.5, corre-sponding to the oxides Tl,~,Hg,~,Sr, +yNd, -,Cu,C), and T1, -xHgxSr2.5Nd0.5C~207 (continuous lines in Fig. 2). All the corresponding data are reported in Table 1. In this table, T,s correspond to the as-synthesized and optimized samples. An improvement in T, is observed only for two samples after oxygen pressure annealing. The reconstruction of the reciprocal space from the ED patterns (Fig. 3) shows a tetragonal cell with axap(up~3.8A, cell parameter of the ideal cubic perovskite), cz J 2 A and Fig.2 Pseudo quaternary diagram TISr,CuzO, -d-HgSr,Cu,O, -HgSr,NdCu,O, -,-TISr,NdCu,O, Table 1 Cell parameters and onset of T, of the as-synthesized samples and after optimization onset cation composition x, I’ (EDS analysis) a/A CIA as-synthesized optimized 0, 0 0, 0.5 3.8503( 1) 12.0724(5) 3.8403( 1 j 12.2073(4) ns 90 ns 95 0.1, 0 3.8506(2) 12.059(1) ns ns 0.1, 0.2 3.8421(2) 12.137(1) 80 85 0.1,0.35 3.8415(5) 12.191(2) 90 90 0.1, 0.5 3.8357(3) 12.208(1) 95 95 0.2, 0 3.8507(2) 12.058( 1) ns ns 0.2, 0.5 3.8339(5) 12.210(2) 95 95 ns, not superconducting. P-type symmetry, whatever x and y. No superstructure or streaks were observed, attesting to the statistical distribution of the various cations over their own sites. From the XRD data refinements, the cell parameters (Table 1) show that the substitution of mercury for thallium J.MATER. CHEM.. 1994, VOL. 4 does not influence the cell size, as observed for the 2223 cuprate.12 The evolution of these parameters us. y, and especi- ally the increase of c with y is consistent with Sr being larger than Nd. In order to understand the changes in superconduction induced by Sr/Nd substitution, the line x=O.1 (Fig. 2) has been especially studied (part 2 of Table 1). This corresponds to the formula Tlo,9Hgo,lSr2+,Nd, -,Cu207 y =0-0.5. As soon as trivalent Nd is replaced by divalent Sr the supercon- ductivity is induced.For the y =0.2 as-synthesized sample, the superconducting transition is broad (Fig. 4);such behaviour can be explained considering the EDS analysis performed on numerous microcrystals of the samples which shows a rather large dispersion of the y values with regard to the mean y= 0.2 value. The T, onset is close to 80 K, with a diamagnetic volume fraction of 25% at 5 K. The critical temperature increases with y (Table 1); the best properties are observed for the limiting composition x =0.1, y =0.5 (as-synthesized sample) with a T, onset of 95 K, a superconducting volume fraction of 70% [Fig. 5 (a)]and a rather sharp transition. Note that the EDS analysis performed on this sample attests to the good homogeneity of the sample with a very small dispersion of y values. Resistivity measurements confirm the T, onset value and the metallic behaviour of the material for r>T, in the normal state.For the annealings performed on this y=OS sample, a decrease in T, was observed [Fig. 5 (m, O)]indicating that the optimal carrier density is achieved in the as-synthesized sample. This latter T, value of 95 K is indeed the same as that of the pure T1-optimized sample T1Sr2.5Ndo.5Cu207 the limit and of T1,-,,Hgo~2Sr,,,Ndo~,C~~207, compound (Table 1). In conclusion: A new solid solution has been characterized, Tl1-,Hg,Sr2+,Nd, -,,CU~O~-~.For the selected thermal pro- cess, the homogeneity range extends up to x=O.2 and y=O.5. Coupled EDS and XRD analyses suggest that these limits can be increased provided the conditions of synthesis (time- temperature-partial pressure) are adapted to each composi- tion.The EDS investigation and XRD refinements confirm the statistical distribution of the cations in the different sites of the 1212 structure. This study confirms the previous observations made for Fig. 3 [0101 ED pattern, x =0.2 and y =0.5 J. MATER. CHEM., 1994, VOL. 4 0.00 v, --0.05 -0.10 -f' c. x -0.15 --0.20--0.250 20 40 60 80 100 TIK Fig. 4 Temperature dependence of the susceptibility for the TI,,,HE,,~S~,,,N~,,,CU,O~-as-synthesized sample 0.0 -0.1 -0.2 4.3h Y? x -0.4 -0.5 -0.6 -0.7 0 20 40 60 80 100 TIK Fig. 5 Temperature dependence of the susceptibility for Tl,,,Hg,,,Sr,,,Nd,.,Cu,O,_, as synthesized (O), 280 "C, 40 min, Ar-H, annealed (D)and 350 "C -7 h -100 bar 0, annealed (0) the 2223 oxidel, concerning Hg for T1 substitution: a similar T, value of 95 K, after optimization, can be reached for the doped and undoped samples, i.e.T1,-,Hg,Sr,,,NdO~,Cu,O7 with x=O, 0.1, 0.2. It can also be compared to the oxides Tlo.8Pbo,2Sr,+,Nd, -,,CU,O-~ of ref. 10: for similar y values close to 0.5, the T,s are comparable, showing that the composition of the thallium layers, which may act as a reservoir of holes, is not of prime importance in the expected maximum T,; the optimal hole carrier density is the only important factor. Such an assertion was also made concerning the T1-deficient 2212 s~perconductor.'~ The role of the layer interleaved between the [CuO,], layers is very different.This fact was observed in numerous 2212 and 1212 oxides and is once more confirmed; a small variataon of the (Sr,Ca)/Ln ratio involves a dramatic change in the critical temperature. References 1 M. Hervieu, A. Maignan, C. Martin, C. Michel, J. Provost and B. Raveau, J. Solid State Chem., 1988,75,212. 2 B. Morosin, D. S. Ginley, P. F. Hlava, M. J. Carr, R. J. Haughman, J. E. Schirber, E. L. Venturini and J. F. Kwak, Physicsa C, 1988, 152,413. 3 W. L. Lechter, M. S. Osofsky, R. J. Soulen, V. M. Le Tourneau, E. F. Skelton, S. B. Qadri, W. T. Elam, H. A. Hoff, K.A. Hein, L. Humphreys, C. Skowronek, A.K. Singh, J. F. Gilfrich, L. E. Toth and S. A. Wolf, Solid State Commun., 1988,h8, 519. 4 F. Izumi, T. Kondo, Y. Shimakawa, T. Manako, Y. Kudo, H. Igarashi and H. Asano, Physica C, 1991,185-189,615. 5 S. Li and M. Greenblatt, Physica C, 1989, 157, 365. 6 M. A. Subramanian, C. C. Torardi, J. Gopalakrishnan, P. L. Gai, J. C. Calabrese, T. R. Askew, R. B. Flippen and A. W. Sleight, Science, 1988,242, 249. C. Martin, D. Bourgault, C. Michel, M. Hervieu and B. Raveau, Mod. Phys. Lett. B, 1989,3,93. C. Michel, E. Suard, V. Caignaert, C. Martin, A. Maignan, M. Hervieu and B. Raveau, Physica C, 1991,178,29. A. K. Ganguli, V. Manivannan, A. K. Sood and C. N. R. Rao, Appl. Phys. Lett., 1989,55,2664. V. Manivannan, N. Rangavittal, J. Gopalakrishnan and C. N. R. Rao, Physica C, 1993,208,253. Y. Xin, Y. F. Li, D. Ford, D. 0.Pederson and Z. Z. Sheng,J.J.A.P., 1991,30,1549. F. Goutenoire, A. Maignan, G. Van Tendeloo, <'. Martin, C. Michel, M. Hervieu and B. Raveau, Solid State Commun., 1994, 90,47. 13 D. B. Wiles and R. A. Young, J. Appl. Crystallogr., 198 1, 14, 149. 14 C. Michel, C. Martin, M. Hervieu, A. Maignan, J. Provost, M. Huve and B. Raveau, J. Solid State Chem., 1992,96,271. Communication 4/03564J; Received 13th June, 1994

ISSN:0959-9428    

DOI:10.1039/JM9940401353

出版商:RSC    

年代:1994

数据来源: RSC