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J O U R N A L O F C H E M I S T R Y Materials Low temperature synthesis, structure and properties of La4BaCu5-xMxO13+d (M=Ni, Co and Fe)† C. Shivakumara,a M. S. Hegde,*a K. Sooryanarayana,a T. N. Guru Rowa and G. N. Subbannab aSolid State and Structural Chemistry Unit, and bMaterial Research Centre, Indian Institute of Science, Bangalore-560 012, India. E-mail: mshegde@sscu.iisc.ernet.in Received 8th June 1998, Accepted 9th September 1998 Oxygen deficient defect perovskite oxides having the general formula La4BaCu5-xMxO13+d (M=Ni or Co, 0x1.0, Fe, x=0.5) have been synthesized from NaOH–KOH fluxes at 450 °C.Structures of these materials have been refined by the Rietveld method and confirmed by electron diVraction studies. Ni3+, Co3+ and Fe3+ ions are shown to occupy the octahedral 1(a) site in the La4BaCu5O13+d structure.While the Ni substituted compound is metallic, composition controlled metal to insulator (M–I ) like behaviour is observed for Co and Fe substituted compounds. While temperature independent magnetic susceptibility in the case of the Ni substituted compound indicated Pauli paramagnetic behaviour, Co and Fe substituted oxides were weakly paramagnetic. 0x1, Fe, x0.5) and here we report their low temperature Introduction synthesis, structure and properties. Among the new families of copper oxides discovered since the outbreak of superconductivity studies in 1986,1 La4BaCu5O13+d2 is unique because it shows metallic behaviour Experimental down to lowest possible temperatures without undergoing a Stoichiometric amounts of high purity La2O3, CuO, NiO, superconducting transition.LaCuO33 is another oxide which Co3O4, Fe(C2O4)·2H2O and an excess of Ba(OH)2·8H2O were shows metallic properties and no superconductivity. Otherground in an agate mortar and added to a preheated 151 melt wise, families of copper oxides such as La2-xSrxCuO4, of NaOH and KOH (AR grade) at 400 °C in a recrystallized YBa2Cu3O7-d , and Bi2Sr2Can-1CunO2n+4+d (n=1, 2, 3) alumina crucible.A typical run contained La2O3 (1.3032 g), etc., show metallic and superconducting behaviour.4–6 CuO (0.7954 g), Ba(OH)2·8H2O (2.52 g), NaOH (10 g) and La4BaCu5O13+d crystallizes in a tetragonal structure in the KOH (10 g) and led to a product La4BaCu5O13.14. The space group P4/m, which is related to cubic perovskite subcell temperature was increased and held at 450 °C for 2–4 days.by a#ap Ó5=8.65 A° and c=ap=3.86 A° . The model structure7 Initially a clear blue solution was observed and gradually dark consists of groups of corner sharing CuO5 pyramids linked crystals precipitated. The melt was furnace cooled to room through CuO6 octahedra in such a way that each octahedron temperature, washed with distilled water followed by acetone shares four corners with four pyramids and two corners with and dried at 120 °C for 4 h.Powder X-ray diVraction patterns two octahedra and each pyramid is connected to four other were recorded on a JEOL JDX-8P diVractometer, with a scan pyramids and one octahedron. While substitution for the La speed of 2° min-1 with a Cu-Ka (l=1.5418 A° ; Ni filter) source site in this system has been performed by Vijayaraghavan to identify the phases.The structural parameters of some of et al.,8 to the best of our knowledge, no substitution for Cu these phases were refined by Rietveld profile analysis with the has been reported in the literature. diVraction data collected on a STOE STADI/P diVractometer. Superconducting oxides having the formula The data were collected using a linear position sensitive La2-xMxCuO4(M=Na, K),9 pyrochlore related oxides detector (PSD) in the range of 5<2h/°<80 in steps of 0.02° A2BB¾O7 (A=La or Nd; BB¾=Pb, Sn or Bi)10 and in the transmission mode.The morphology and composition RBa2Cu3O7-d (R=Nd, Sm, Eu or Gd)11 have been syntheof these crystalline phases were obtained from scanning elec- sized at low temperature by the NaOH–KOH flux method; tron microscopy (SEM) and energy dispersive X-ray (EDX) however, LaBa2Cu3O7-d could not be synthesized by this analysis. Oxygen content was determined by iodometric method.It is known that partial substitution of Ni for Cu in titration and thermogravimetric analysis (TGA) by heating YBa2Cu3O7 occurs with Ni2+ occupying Cu(2) sites.12 the sample under a stream of 15% H2–85% Ar.Electron However, by partial substitution of Ni for Cu in LaBa2Cu3O7, microscopy studies were carried out on as-synthesized samples Ni3+ ions were shown to occupy the Cu(1) sites.13 Also, to confirm the structure using a JEOL 200-CX transmission LaBa2Cu3-xNixO7+d (x0.3) showed metallic behaviour.In electron microscope. The polycrystalline powder was pelletised an attempt to synthesize the LaBa2Cu3O7-d phase by a low and sintered at 900 °C. No detectable change in the structure temperature route employing NaOH–KOH flux, we found was observed in any of the samples. Further, a temperature that a thermodynamically stable La4BaCu5O13+d phase was programmed desorption (TPD) system attached to a VG obtained.In the La4BaCu5O13+d phase, out of five Cu, one QXK-300 quadrupole mass spectrometer showed no evolution Cu has octahedral coordination and since Ni3+, Co3 + and of oxygen up to 750 °C indicating that there is no measurable Fe3+ ions prefer octahedral co-ordination, it was conceivable change in the oxygen content after sintering. Further, oxygen that one Cu can be substituted by these trivalent ions.Indeed estimation of the sample sintered at 750 °C and also at 900 °C we have synthesized La4BaCu5-xMxO13+d (M=Co or Ni, were carried out and no measurable changes in the total oxygen content were observed. Electrical resistivity measurements were carried out on the sintered pellets by a four-probe †Contribution No. 1338 from Solid State and Structural Chemistry Unit.method in the temperature range 300–15 K. dc Magnetic J. Mater. Chem., 1998, 8, 2695–2700 2695susceptibility measurements have been performed in the range 300–20 K employing a Lewis coil force magnetometer (George Associates, Model 2000). Results and discussion Synthesis and structure In an attempt to obtain the LaBa2Cu2NiO7+d phase by a low temperature method, stoichiometric amounts of La2O3, CuO and NiO with an excess of Ba(OH)2·8H2O were melted in an NaOH–KOH flux.The resulting crystalline material on examination by X-ray powder diVraction, electron microscopy and energy dispersive X-ray (EDX) analysis showed the presence of hexagonal BaNiO2+d and CuO, in addition to an unknown phase. Formation of BaNiO2+d in an alkali flux is known.14 Therefore it was clear that almost all of the Ni in the melt formed a BaNiO2+d phase.A composition corresponding to LaBa2Cu3O7 was heated in the flux with the absence of Ni in the melt. The powder XRD data of the resulting product revealed the formation of the same unknown phase and CuO as an impurity. On careful examination of several crystals in spot mode by EDX, compositions of La5Ba5Cu was found to be 45155 in the unknown phase indicating the possibility of La4BaCu5O13+d oxide formation.Then, the composition corresponding to La4BaCu5O13+d was heated in the flux and the powder X-ray diVraction pattern of this compound is shown in Fig. 1(a). All the lines could be indexed to the La4BaCu5O13+d phase. The lattice parameters agreed well with those reported in the literature.7 Mixed oxides La4BaCu5-xNixO13+d (0x1.0) were then synthesized by taking stoichiometric amounts of La2O3, CuO and NiO with an excess of Ba(OH)2·8H2O. An X-ray powder diVraction pattern for x=1.0 is shown in Fig. 1(b). As can Fig. 2 Scanning electron micrographs of (a) La4BaCu5O13.14 and be seen, all the lines could be indexed to the parent phase.In (b) La4BaCu4CoO13.35. an attempt to substitute Ni to >1 atom per formula unit, compounds were prepared for composition La4BaCu4-xNi1+xO13+d. However, the resulting products did not crystallize in the La4BaCu5O13+d structure. Mixed oxides La4BaCu5-xCoxO13+d (0x 1) were also synthesized and the pattern for x=1 is shown in Fig. 1(c). In the case of Fe, a value of x up to 0.5 could be substituted.For x>0.5, LaFeO3 impurity phase was observed in the Xray pattern in addition to Fe substituted La4BaCu5O13+d. DiVraction patterns for x=0.5 and 1.0 are shown in Fig. 1(d) and (e), respectively. Scanning electron micrographs of La4BaCu5O13+d, and the Ni, Co and Fe substituted samples showed a cuboidal morphology. Crystals of size 0.1–0.2 mm were seen in these preparations.Typical scanning electron micrographs of the Fig. 1 Powder X-ray diVraction patterns of (a) La4BaCu5O13.14 (b) Fig. 3 Thermogravimetric analysis curves for (a) La4BaCu5O13.14 and La4BaCu4NiO13.20, (c) La4BaCu4CoO13.35, (d) La4BaCu4.5Fe0.5O13.28 and (e) La4BaCu4FeO13+d (asterisk indicates LaFeO3 impurity phase). (b) La4BaCu4CoO13.35. 2696 J. Mater. Chem., 1998, 8, 2695–2700Table 1 Compounds, lattice parameters and oxygen contents Table 2 Crystallographic and structural refinement data for La4BaCu4NiO13.20 and La4BaCu4CoO13.35 Lattice parameter/A° Oxygen contenta Empirical formula La4BaCu4NiO13.20 La4BaCu4CoO13.35 Crystal system Tetragonal Tetragonal Compound a c Iodometryb TGAc Space group P4/m P4/m Unit cell dimensions/A° a=8.6820(1) a=8.6790(1) La4BaCu5O13+d 8.668(3) 3.862(5) 13.14 13.23 La4BaCu4NiO13+d 8.682(1) 3.869(6) 13.20 — c=3.8699(6) c=3.8731(6) Volume/A° 3 291.69 291.72 La4BaCu4CoO13+d 8.679(1) 3.873(6) 13.35 13.29 La4BaCu4.5Fe0.5O13+d 8.673(3) 3.866(5) 13.28 13.25 Z 1.00 1.00 F(000) 533.8 532.6 aIn atoms per formula unit.bValues accurate to within ±0.02. cValues Dc/g cm-3 6.952 6.983 accurate to within ±0.03.Radiation (l/A° ) Cu-Ka1 (1.540 56) Cu-Ka1 (1.540 56) DiVractometer STOE STADI/P STOE STADI/P DiVraction mode Transmission Transmission Measurement method 2h–v 2h–v parent and the Co substituted samples are shown in Fig. 2(a) 2h° (begin, end, step) 5.0, 79.94, 0.02 5.0, 79.94, 0.02 and (b). EDX analysis in spot mode was performed on each 2h zero point -0.1236 -0.1182 of these samples.Results showed that the metal ions were Absorption correction Empirical Empirical within 3% of the formula corresponding to La4BaCu4MO13+d Refinement method Refinement F2 Refinement F2 (M=Ni, Co) and La4BaCu4.5Fe0.5O13+d. Profile function Pearson VII with Pearson VII with Thermogravimetric analysis curves for La4BaCu5O13+d and exponent 2.00 exponent 2.00 R(1. hkl) 0.130 0.150 for the Co substituted sample are shown in Fig. 3. The TGA Rp 0.085 0.063 products contained La2O3, BaO and Cu as identified by XRwp 0.108 0.080 ray diVraction. For Co and Ni substituted compounds, Cu, Co and Ni metal peaks could be detected in addition to La2O3 and BaO. Oxygen estimation was also determined by iodo- Table 3 Selected bond lengths (A° ) for La4BaCu4NiO13.20 and metric titration.Oxygen content as determined by thermo- La4BaCu4CoO13.35 gravimetric analysis as well as iodometric titration and the lattice parameters are summarized in Table 1. La4BaCu4NiO13.20 La4BaCu4CoO13.35 Having confirmed the compositions of these phases, powder NiMO1×2 1.935(3) CoMO1×2 1.937(3) X-ray diVraction patterns were recorded for Rietveld analysis.NiMO4×4 1.932(33) CoMO4×4 1.973(23) Fig. 4 shows the observed, calculated and diVerence X-ray CuMO2×1 1.721(41) CuMO2×1 1.707(44) diVraction patterns for the La4BaCu4CoO13.35 phase. CuMO3×1 2.156(20) CuMO3×1 2.235(19) Refinements were performed keeping Co in the octahedral site CuMO3¾×1 2.076(10) CuMO3¾×1 1.931(20) fully occupied and also allowing it to mix with the other CuMO4×1 1.833(23) CuMO4×1 1.870(23) CuMO5×2 1.951(25) CuMO5×2 1.944(20) allowed sites of copper.The refinements with Co in the BaMO3×8 2.844(15) BaMO3×8 2.861(15) octahedral site gave the best fit as indicated by the R factors BaMO5×4 2.903(16) BaMO5×4 3.056(20) given in Table 2. For La4BaCu4NiO13.20 also, the structure LaMO1×1 2.670(20) LaMO1×1 2.643(18) was refined with Ni3+ in the 1(a) site similarly to the Co case LaMO2×2 2.905(16) LaMO2×2 2.940(18) and the final R factors are good. Mixing of Ni ions in Cu sites LaMO3×2 2.582(13) LaMO3×2 2.576(13) either fully or partially did not show any significant increase LaMO4×2 2.749(14) LaMO4×2 2.671(18) LaMO4¾×2 2.659(13) LaMO4¾×2 2.717(16) in R factors because of nearly similar scattering factors.LaMO5×1 2.859(17) LaMO5×1 2.758(20) Therefore, occupation of Ni3+ solely in the 1(a) position could LaMO5¾×1 2.565(19) LaMO5¾×1 2.738(20) not be ascertained.However, Ni3+ is known to prefer six co- LaMO5×1 2.808(19) LaMO5×1 2.648(20) ordination in perovskite related oxides such as LaNiO3. It may be noted that La4BaCu4-xNi1+xO13+d does not crystallize in the parent structure. Therefore it is reasonable to expect Table 4 Fractional atomic coordinates and isotropic thermal Ni3+ ions to occupy the 1(a) position with six co-ordination parameters (A° 2) for La4BaCu4NiO13.20 and La4BaCu4CoO13.35 while four Cu ions occupy 4( j) positions with five coordi- La4BaCu4NiO13.20 nation.Details of the refinement with Ni in the 1(a) site are given in Table 2. Selected bond lengths for La4BaCu4NiO13.20 Atom x y z Uiso and La4BaCu4CoO13.35 are given in Table 3 and fractional La 0.1221(22) 0.2823(27) 0.50000 0.020(14) Ba 0.50000 0.50000 0.50000 0.030(1) Ni 0.00000 0.00000 0.00000 0.022(6) Cu 0.3988(50) 0.1705(38) 0.00000 0.022(6) O1 0.00000 0.00000 0.50000 0.05000 O2 0.00000 0.50000 0.00000 0.05000 O3 0.2858(251) 0.3917(205) 0.00000 0.05000 O4 0.2041(279) 0.0888(224) 0.00000 0.05000 O5 0.4268(230) 0.1738(189) 0.50000 0.05000 La4BaCu4CoO13.35 Atom x y z Uiso La 0.1248(25) 0.2778(28) 0.50000 0.018(4) Ba 0.50000 0.50000 0.50000 0.050(2) Cu 0.4073(52) 0.1735(51) 0.00000 0.018(8) Co 0.00000 0.00000 0.00000 0.018(8) O1 0.00000 0.00000 0.50000 0.05000 O2 0.00000 0.50000 0.00000 0.05000 O3 0.2801(242) 0.3974(196) 0.00000 0.05000 O4 0.2111(262) 0.0843(311) 0.00000 0.05000 Fig. 4 Observed, calculated and diVerence powder X-ray patterns for O5 0.4188(236) 0.1574(219) 0.50000 0.05000 La4BaCu4CoO13.35. J. Mater. Chem., 1998, 8, 2695–2700 2697atomic coordinates and isotropic thermal parameters are given correspond to the ‘a’ parameter of the unit cell. The inset shows the corresponding diVraction pattern. Thus, electron in Table 4. Full Crystallographic details, excluding structure factors, microscopic studies confirm the formation of La4BaCu5O13+d, and the Ni and Co substituted phases by our low have been deposited at the Cambridge Crystallographic Data Centre (CCDC).See Information for Authors, J. Mater. temperature route. Synthesis of these oxides using a low temperature Chem., 1998, Issue 1. Any request to the CCDC for this material should quote the full literature citation and the NaOH–KOH flux is important, because, Ni, Co and Fe substituted compounds cannot be synthesized by a solid state reference number 1145/117. Selected area electron diVraction patterns were recorded on route.Substitution of both Co and Ni up to one atom per formula unit has been achieved. several crystallites, to confirm the formation of the La4BaCu5O13.14 phase.Fig. 5(a) and (b) show the electron diVraction patterns of the parent phase recorded along (001) Electrical and magnetic properties and (010) zone axes. Lattice parameters obtained here agree well with the X-ray results and those reported in the literature.7 Fig. 6(a) shows plots of electrical resistivity vs. temperature between 300 and 15 K for La4BaCu5O13.14, La4BaCu4NiO13.20 The electron diVraction pattern of the Ni substituted oxide La4BaCu4NiO13.20 is shown in Fig. 5(c) recorded along the and La4BaCu4CoO13.35. The parent and the Ni substituted phases showed metallic behaviour. La4BaCu5-xNixO13+d (x= (001) zone axis. High resolution images were also recorded on the parent as well as Ni and Co substituted oxides.Fig. 5(d) 0.25, 0.50) were also synthesized and these compounds also showed metallic behaviour, while the La4BaCu4CoO13.35 oxide shows the high resolution image recorded along (010) for the Co substituted oxide. Observed lattice fringes of ca. 8.65 A° showed semiconducting like behaviour. It is important to note Fig. 5 Selected area electron diVraction patterns of La4BaCu5O13.14 in (a) (001) and (b) (010) zone axes; SAED of La4BaCu4NiO13.20 in (c) (001) zone axis and (d) high resolution image of La4BaCu4CoO13.35 showing ca. 8.65 A° periodicity; inset shows corresponding diVraction pattern recorded along the (010) axis. 2698 J. Mater. Chem., 1998, 8, 2695–2700Fig. 8 Resistivity vs. temperature curve for La4BaCu4.5Fe0.5O13.28. In inset susceptibility vs.temperature plot is given. The susceptibility value of the Co containing phase was higher at 300 K and nearly temperature independent and weak paramagnetic like behaviour was observed as the sample is cooled which did not follow the Curie law. As the Co content was increased, the susceptibility at 300 K increased from 3×10-6 to 18×10-6 emu g-1 from x=0 to 1.0. The susceptibility x was fitted to a function (C/T)+a, where a is a temperature independent contribution. For La4BaCu5-xCoxO13+d, magnetic moments were 0.3, 0.8 and 1.0 mB for x=0, 0.5 and 1.0, respectively, per formula unit.The low value of 0.06 mB per Cu is characteristic of delocalized carriers.2 If Co3+ ions in this compound are in high spin state, the expected moment is 4.7 mB, even assuming that the magnetic moment solely arises from Co in La4BaCu4CoO13.35.The low Fig. 6 Resistivity as a function of temperature curves for value of 1.0 mB observed here suggests that the spins on Co (a) La4BaCu5-xMxO13+d and (b) La4BaCu5-xCoxO13+d. are not fully localized. Fig. 8 shows the resistivity vs. temperature plot of that the resistivity of La4BaCu4CoO13.35 at 300 K is of the La4BaCu4.5Fe0.5O13.28. The oxide showed metallic behaviour same order of magnitude as that of the parent as well as from 300 to 100 K and started showing semiconducting like the Ni substituted oxides.Fig. 6(b) shows resistivity vs. tem- behaviour below 100 K. In the inset the susceptibility as a perature plots of La4BaCu5-xCoxO13+d (0x1.0). For x= function of temperature is shown.The results reveal that the 0.5, the compound is still metallic and for x>0.5, semiconduct- Fe doped compound exhibits weakly paramagnetic behaviour. ing like behaviour is observed. Thus, the Co doped oxide Metallic behaviour in La4BaCu5O13.14 is due to complete shows composition controlled metal to insulating like overlap of Cu 3d and O 2p bands. The average oxidation state behaviour as the cobalt content increased from 0 to 1.of Cu in this compound is 2.45. This can be represented by Magnetic susceptibility vs. temperature plots of the equilibrium:15 La4BaCu5O13.14, La4 BaCu4NiO13.20, La4BaCu4.5Co0.5O13+d Cu3++O2-=Cu2++O1- (1) and La4BaCu4CoO13.35 are shown in Fig. 7. Both Cu and Ni phases showed temperature independent susceptibility from This indicates the presence of holes on copper as well as 300 to 20 K.oxygen. The Ni, Co and Fe substituted oxides are made under highly oxidizing conditions and these metal ions should be in the +3 state. This follows from the fact that LaNiO3, LaCoO3 and LaFeO3 can be synthesized from NaOH–KOH flux at 450 °C. Thus, with Ni3+ in La4BaCu4NiO13.2, the average oxidation number of Cu is 2.35.Accordingly, the hole concentration on Cu is high as indicated by equilibrium (1). As in LaNiO3, Ni3+ in this compound is in octahedral coordination. Since LaNiO3 itself is a metallic and Pauli paramagnetic oxide, metallic and Pauli paramagnetic behaviour is expected for La4BaCu4NiO13.2. A similar situation exists in LaBa2Cu3-xNixO7+d (0.1x0.3),13 where Ni occupies the Cu(1) sites in the +3 state and the compounds are metallic down to 15 K.The cobalt substituted compound, La4BaCu4CoO13.35, shows semiconducting behaviour. Assuming Co in the +3 oxidation state, the average oxidation state of Cu is 2.42. Therefore, equilibrium (1) should exist in this compound. Since, oxidation of Co3+ to Co4+ is more facile than Cu2+ to Cu3+, it is possible to consider additional electron exchange Fig. 7 Magnetic susceptibility as a function of temperature curves for via oxygen as follows: (a) La4BaCu5O13.14, (b) La4BaCu4NiO13.20, (c) La4BaCu4.5Co0.5O13+d and (d) La4BaCu4CoO13.35. Cu3++Co3+=Cu2++Co4+ (2) J. Mater. Chem., 1998, 8, 2695–2700 2699A similar situation exists in LaBa2Cu2CoO7.35 which also References shows semiconducting behaviour.16 It should be noted that 1 J.G. Bednorz and K. A. Muller, Z. Phys. B, 1986, 64, 189. LaCoO3 is semiconducting and the presence of Co3+ or excess 2 C. Michel, L. Er-Rakho and B. Raveau, Mater. Res. Bull., 1985, of Cu2+ by equilibrium (2) would lead to a semiconducting 20, 667. behaviour in this compound. A fairly high conductivity at 3 G. Demazeau, C. Parent, M. Pouchard and P. Hagenmuller, 300K in La4 BaCu4CoO13.35 can be attributed to the high Mater. Res.Bull., 1972, 7, 913: J. B.Goodenough, N. F. Mott, oxidation number of Cu (2.42) or equivalently, high M. Pouchard, G. Demazeau and P. Hagenmuller, Mater. Res. Bull., 1973, 8, 647. concentration of holes. 4 R. J. Cava, R. B. Van Dover, B. Batlogg and E. A. Rietman, Phys. For the Fe substituted oxide, even at x=0.5, the compound Rev.Lett., 1987, 58, 408. exhibits semiconducting behaviour below 100 K. Here also, 5 M. K. Wu, J. R. Ashburn, C. J. Torng, P. H. Hor, R. L. Meng, L. Gao, Z. J. Huang, Y. Q. Wang and C. W. Chu, Phys. Rev. Cu3++Fe3+=Cu2++Fe4+ (3) Lett., 1987, 58, 908. 6 M. Maeda, Y. Tanaka, M. Fukutomi and A. Asano, Jpn. J. Appl. equilibrium can occur as is seen in La2-xSrxCu1-yFeyO4.17 Phys., 1988, 27, L209.Unlike in the case of divalent ion doped LaCoO3 (e.g. 7 C.Michel, L. Er-Rakho, M. Herview, J. Pannetier and B. Raveau, La0.67Sr0.33CoO3) which is metallic, La1-xSrxFeO3 phases do J. Solid State Chem., 1987, 68, 143. not show metallic behaviour. Therefore, semiconducting 8 R. Vijayaraghavan, R. A. Mohan Ram and C. N. R. Rao, J. Solid State Chem., 1988, 78, 316.behaviour is expected for the Fe substituted compound even 9 W. K. Ham, G. F. Holland and A. M. Stacy, J. Am. Chem. Soc., for x=0.5. 1988, 110, 5214. 10 S. Uma and J. Gopalakrishnan, J. Solid State Chem., 1993, 105, 595. Conclusions 11 L. N. Marquez, S. W. Keller and A. M. Stacy, Chem. Mater., 1993, 5, 761. La4BaCu5O13.14 and Ni, Co and Fe substituted phases have 12 J. M. Tarascon, P. Barboux, P. F. Miceli, L. H. Greene, been synthesized by a low temperature route employing an G. W. Hull, M. Eibshutz and S. A. Sunshine, Phys. Rev. B, 1998, NaOH–KOH flux. While the parent La4BaCu5O13.14 and the 37, 7458. La4BaCu4NiO13.20 showed metallic and Pauli paramagnetic 13 S. Sundar Manoharan, S. Ramesh, M. S. Hegde and G. N. Subbanna, J. Solid State Chem., 1994, 112, 281. behaviour, Co and Fe substituted oxides show composition 14 J. DiCarlo, I. Yazdi, and A. J. Jacobson, J. Solid State Chem., controlled metal to insulator transitions and they are weakly 1994, 109, 223. paramagnetic. These observations are explained by possible 15 J. B. Goodenough and A. Manthiram, J. Solid State Chem., 1990, charge exchange between Co3+ and Fe3+ with Cu3+ via 88, 115. oxide ion. 16 S. Ramesh, N. Y. Vasanthacharya, M. S. Hegde, G. N. Subbanna, H. Rajagopal, A . Sequiera and S. K. Paranjpe, Physica C, 1995, 253, 243; S. Ramesh and M. S. Hegde, J. Phys. Chem., 1996, We thank Professor J. Gopalakrishnan for useful suggestions 100, 8443. and the Department of Science and Technology for financial 17 K. Ramesha, S. Uma, N. Y. Vasanthacharya and assistance. One of us (KS) thanks the Council of Scientific J. Gopalakrishnan, J. Solid State Chem., 1997, 128, 169. and Industrial Research (CSIR) for a senior research fellowship. Paper 8/04334E 2700 J. Mater. Chem., 1998, 8, 2695–2700

ISSN:0959-9428    

DOI:10.1039/a804334e

出版商:RSC    

年代:1998

数据来源: RSC

摘要:

J O U R N A L O F C H E M I S T R Y Materials Self propagating high-temperature synthesis of chromium substituted magnesium zinc ferrites Mg0.5Zn0.5Fe2-xCrxO4 (0x1.5) Maxim V. Kuznetsov,a Quentin A. Pankhursta and Ivan P. Parkin*b aDepartment of Physics and Astronomy, University College London, Gower Street, London, UK WC1E 6BT bDepartment of Chemistry, University College London, 20 Gordon Street, London, UK WC1H 0AJ.E-mail: i.p.parkin@ucl.ac.uk Received 29th June 1998, Accepted 4th September 1998 Magnesium ferrite MgFe2O4 and chromium substituted magnesium–zinc ferrite Mg0.5Zn0.5Fe2-xCrxO4 (0x1.5) have been made in air by self-propagating high temperature synthesis (SHS), a combustion process involving the reaction of magnesium, zinc, iron(III ) and chromium(III ) oxides with iron or chromium metal powders and sodium perchlorate.This produced an orange–yellow propagation wave of velocity 2–3 mm s-1. Two series of SHS samples were produced: series 1, SHS followed by annealing at 1400 °C for 2 h and series 2, SHS in a magnetic field of 1.1 T followed by annealing at 1400 °C for 2 h. X-Ray data showed that in all cases nearly phase pure cubic spinel ferrites were produced.Changes in the cubic lattice parameter were seen as a function of Zn and Cr content. Room temperature and 80 K Mo� ssbauer data showed a significant change in sublattice occupancy with Cr content. Magnetic hysteresis data for series 1 and 2 showed that the coercive force of doped samples is higher than pure compositions whilst magnetisation is lower.It was also shown that the use of a magnetic field during SHS can influence the microstructure and magnetic properties of the final material. ferrites of formula MgFe2-xCrxO4 are valuable for the long Introduction wave part of the high-frequency range (10–14 cm) as they As part of an on-going research programme aimed at exploring have very low coeYcient losses.5 Pure and Cr-substituted the potentials and problems associated with innovative routes Mg-ferrites also demonstrate catalytic activity.6 to ceramic materials, we are currently interested in synthesising In this paper we present the first SHS preparation of materials by self-propagating high temperature synthesis chromium substituted Mg and Mg–Zn ferrites and investigate (SHS).1 This is a non-conventional method for materials the eVects of the presence of an applied magnetic field during synthesis which makes use of an exothermic chemical reaction.the combustion synthesis. SHS processes rely on a balance between the heat generated and dissipated in a chemical reaction. It involves mixing diVerent reactant powders, such as oxides, metals and non- Experimental metals, which on initiation produce an exothermic chemical reaction that is self-sustaining due to a positive energetic All reagents were obtained from Aldrich Chemical Company balance.2 The reaction produces rapid heating (up to 3000 °C (UK) and used as supplied.Manipulations, weighings and in 1–2 s) and cooling and is propagated by a combustion wave grindings were performed under a nitrogen atmosphere in a (also known as thermal flash, synthesis wave or solid flame) SaVron Scientific glove box.SHS reactions were carried out that moves out from the source of initiation. SHS processes in air on pre-ground powders on a ceramic tile using sodium are fast, do not require external energy such as from a furnace perchlorate as an oxygen source. Initial reaction compositions and can be used to produce complex oxides, intermetallics and are given in Table 1.The reactions were initiated by a heated composite materials. SHS reactions produce materials with filament (ca. 800 °C). Sintering was carried out in a Carbolite unusual often porous microstructure. rapid heating furnace with heating and cooling rates of Single phase magnesium ferrite MgFe2O4 with the spinel 20 °Cmin-1.Samples were ground after the SHS reaction and structure cannot be made from stoichiometric combination of also after sintering, and all measurements were recorded on MgO and Fe2O3. The spinel structure can be made by using powder samples. For the applied field SHS reactions a permaa superstoichiometric amount of MgO (1.092 equivalents) to nent magnet Halbach cylinder purchased from Magnetic help combat oxygen loss from the ferrite.3 Unsubstituted Solutions Ltd was used.This 20 mm bore cylinder, comprising magnesium ferrites have low magnetic penetration and rela- eight NdFeB magnets, provided a field of 1.1 T transverse to tively small specific resistance. They have only limited indus- the cylinder axis. For the applied field SHS reactions a ceramic trial use.In contrast doped magnesium ferrite is known tile, containing the green mixture, was placed inside a quartz commercially as ‘Ferramic-A’ and has comparably good mag- tube which was in turn inserted into the Halbach cylinder netic properties up to 100 MHz (Bs=1400 G; r=4.5 g cm-3).4 prior to initiation of the combustion process. Much better properties are obtained for the series of solid X-Ray diVraction was performed in reflection mode on a solutions of Mg–Zn ferrite.The ferrite Mg0.5Zn0.5Fe2O4 is Philips X-Pert using unfiltered Cu-Ka radiation (l1=1.5405 A° , known commercially as Ferroxcube-2 and has a saturation l2=1.5443 A° ). Vibrating sample magnetometry was carried magnetic induction Bs=3500 G and a coercivity Hc= out on a Aerosonic 3001 magnetometer at room temperature 600 G Oe-1 (r=4.7 g cm-3). These ferrites are used widely, in applied fields up to 7.5 kOe. 57Fe Mo� ssbauer spectra were for example in mobile telephones. Chromium substituted recorded with a Wissel MR-260 constant acceleration specmagnesium and magnesium–zinc ferrites are suitable not only trometer with a triangular drive waveform.Spectra were folded for fundamental studies of structural and magnetic properties to remove baseline curvature and were calibrated relative to a-iron at room temperature. FTIR spectra were obtained as but also for industrial application. Chromium substituted iron J. Mater. Chem., 1998, 8, 2701–2706 2701Table 1 Molar ratio of components used in self-propagating high-temperature synthesis (SHS) of Mg0.5Zn0.5Fe2-xCrxO4, and nominal composition of the end product, using a notation where parentheses denote tetrahedral sites and square brackets denote octahedral sites x Fe2O3 Fe Cr2O3 Nominal composition 0 0.50 1.00 0 (Zn0.5Fe0.5)[Mg0.5Fe1.5]O4 0.3 0.35 1.00 0.15 (Zn0.5Fe0.5)[Mg0.5Fe1.2Cr0.3]O4 0.6 0.20 1.00 0.30 (Zn0.5Fe0.5)[Mg0.5Fe0.9Cr0.6]O4 0.9 0.05 1.00 0.45 (Zn0.5Fe0.5)[Mg0.5Fe0.6Cr0.9]O4 1.2 0.40 1.00 (Cr) 0.10 (Zn0.5Fe0.5)[Mg0.5Fe0.3Cr1.2]O4 1.5 0.25 1.00 (Cr) 0.25 (Zn0.5Fe0.5)[Mg0.5Cr1.5]O4 KBr pellets on a Nicolet 205. SEM/EDAX measurements were Two diVerent series of samples were prepared: series 1, the zero field SHS product subsequently sintered at 1400 °C for performed using a Hitachi S570. 2 h, and series 2, SHS product of an applied field synthesis of 1.1 T followed by sintering at 1400 °C for 2 h.Preparation of Mg0.5Zn0.5Fe2-xCrxO4 (0x1.5) The same reaction scale and procedure was used for all Characterisation reactions illustrated here for Mg0.5Zn0.5Fe1.4Cr0.6O4. Relative molar ratios of the reactants are given in Table 1. X-Ray powder diVraction showed that nearly single phase cubic spinel structures were produced for all the sintered Magnesium oxide (0.200 g, 5.0 mmol), iron oxide (0.638 g, 4 mmol), chromium oxide (0.916 g, 6 mmol), zinc oxide products.Representative diVractograms are shown in Fig. 1, and the deduced lattice parameters are given in the Table 2. A (0.204 g, 2.5 mmol), iron metal (1.116 g, 20 mmol) and sodium perchlorate (0.458 g, 3.75 mmol) were ground together in a pestle and mortar. The resultant solid was placed on a ceramic tile (ca. 1 cm by 7 cm strip) in air and a reaction initiated by means of a heated filament at one end. This produced an orange–yellow propagation wave of velocity ca. 2–3 mm s-1. The resultant black powder was washed with distilled water (2×1l ) filtered through a Buchner funnel and air dried. The powder was reground and sred at 1400 °C for 2 h.Yields in all reactions were essentially quantitative. The resultant powder was analysed by X-ray powder diVraction, Mo�ssbauer spectroscopy, vibrating sample magnetometry, FTIR and SEM/EDAX. Results Sample preparation SHS reactions were performed using various starting mixtures of Fe2O3, Fe, MgO, ZnO, Cr2O3 and NaClO4. The molar ratio of each reagent was chosen to conform with the desired stoichiometry in the product, Table 1.At high degrees of chromium substitution (Mg0.5Zn0.5Fe2-xCrxO4; x=1.2 and 1.5) Cr metal powder was used in the SHS process instead of Fe metal powder. The overall reaction is driven by the Fig. 1 Representative X-ray powder diVraction patterns obtained from exothermic oxidation of Fe or Cr metal by oxygen which was the sintered products of the SHS reactions of: (1) MgO, Fe2O3, Fe evolved by the decomposition of sodium perchlorate at 600 °C.7 and NaClO4 in the ratio 1.0050.5051.0050.375 to produce MgFe2O4; In the case of Mg0.5Zn0.5Fe1.7Cr0.3O4 the reaction scheme was: (2) MgO, ZnO, Fe2O3, Fe and NaClO4 in the ratio 0.5050.5050.5051.0050.375 to produce Mg0.5Zn0.5Fe2O4, and 0.5 MgO+0.5 ZnO+0.35 Fe2O3+0.15 Cr2O3+Fe (3) MgO, ZnO, Fe2O3, Fe, Cr2 O3 and NaClO4 in the ratio 0.5050.5050.5051.0050.4550.375 to produce Mg0.5Zn0.5Fe1.1Cr0.9O4.+0.375 NaClO4�Mg0.5Zn0.5Fe1.7Cr0.3O4+0.375 NaCl Also shown for comparison is a reference stick pattern for MgFe2O4. It should be noted that all reactions were carried out in air using solid oxidisers. Sodium perchlorate acts as the oxidising Table 2 Cubic lattice parameter a for two series of MgFe2O4 and agent.On decomposition it co-produces sodium chloride which Mg0.5Zn0.5Fe2-xCrxO4 samples produced by self-propagating highis easily removed from the product by washing with water. temperature synthesis (SHS): series 1, zero field SHS followed by The SHS preparation of pure and chromium substituted annealing at 1400 °C for 2 h; series 2, SHS conducted in a magnetic field of 1.1 T followed by annealing at 1400 °C for 2 h magnesium and magnesium–zinc ferrites is much quicker than standard conventional methods.8,9 Using SHS instead of a aa/A° furnace enables the first step in ferrite production to be reduced Mg0.5Zn0.5Fe2-xCrxO4 to ca. 30 s. In standard ceramic technology this stage requires x Series 1 Series 2 some hours heating at 1200–1350 °C.The SHS reaction however does not completely alleviate the need to sinter the 0 8.416 8.415 0.3 8.408 8.399 material. After the initial SHS reaction the product contained 0.6 8.398 8.379 about 90% of the required ferrite mixed in with partially 0.9 8.375 8.369 combined starting materials and sodium chloride. Subsequent 1.2 8.373 8.367 washing with water followed by sintering of the powder at 1.5 8.362 8.334 1400 °C for 2 h produces virtually single phase ferrites. The MgFe2O4 8.381 8.377 sintering process is relatively quick as the SHS material has aError limit: ±0.004 A° .good contact between reacting grains. 2702 J. Mater. Chem., 1998, 8, 2701–2706the spectra at 620 cm-1 with increasing chromium substitution.The absorption bands are all characteristic of metal oxygen stretches. 57Fe Mo� ssbauer absorption spectra were recorded for series 1 and 2 samples of MgFe2O4 at room temperature (see Fig. 2), and of Mg0.5Zn0.5Fe2-xCrxO4 at room temperature and at 80 K (see Fig. 3). The spectra were least squares fitted using Lorentzian lineshapes and a first order perturbation approach to the combination of electric quadrupole and magnetic interactions. For the MgFe2O4 samples two subcomponent spectra, attributable to Fe atoms in the octahedral and tetrahedral sites, were fitted.For the Mg0.5Zn0.5Fe2-xCrxO4 spectra broad lines were observed, indicating the occurrence of distributions in the environments of the 57Fe nuclei, with corresponding distributions in the Mo�ssbauer hyperfine parameter.Such distributions are to be expected in the chromium substituted materials where the Cr atoms disrupt the long range magnetic interactions between the Fe atoms. Consequently these spectra were analysed using a 200 box histogram model for the distribution of hyperfine fields experienced by the 57Fe nuclei. For simplicity a single isomer shift parameter was used for all the histogram subspectra, and the quadrupole splitting was set to zero.The linewidths of the histogram subspectra were fixed at an appropriate experimental minimum, namely Fig. 2 Room temperature Mo�ssbauer spectra for samples of MgFe2O4 0.28 mm s-1. Smoothing and endpoint constraints were prepared by SHS in zero field and in a field of 1.1 T, after sintering for 2 h at 1400 °C.Solid lines represent a least squares fit with two applied to the allowed histogram solutions. Further details of subcomponents corresponding to Fe atoms in octahedral and the histogram fitting program are available elsewhere.13 The tetrahedral sites in the spinel structure. fitted spectra are shown as solid lines in Fig. 2 and 3 and selected parameters obtained from these fits are given in general decrease in a parameter with increasing chromium Table 3 and 4.content was noted. This mirrors the same results for conven- Hysteresis loops were recorded on all the samples in fields tionally prepared materials.10,11 This variation in unit cell may up to 7.5 kOe at room temperature. Representative data are be attributed to the smaller ionic radii of six-coordinate Cr3+ shown in Fig. 4. The maximum magnetisation smax, remanent ions compared to those of six-coordinate high spin Fe3+ magnetisation sr and coercive force Hc are listed in Table 5. ions.12 The chromium preferentially replaces iron from octa- For all samples prepared in magnetic field (series 2) the hedral sites because of favourable crystal field eVects (Cr3+ magnetic parameters are greater than those prepared in the 6/5 Do, Fe3+ 0 Do).absence of a magnetic field. A general decrease in smax and sr For series 1 materials the lattice parameters were consistently and an increase in Hc was observed with chromium larger than for series 2, albeit at the limits of experimental substitution. resolution. This eVect is minor, and might be explained by diVerences in the degree of Cr substitution achieved in the two Discussion series.However, from our observations both series of products appear to be almost single phase, with no signs of unreacted Mo�ssbauer measurements chromium oxide. We surmise therefore that this observation may be an eVect of the applied field during synthesis. It is well known that magnesium ferrite MgFe2O4 has an inverse spinel structure with Mg occupying octahedral sites EDAX measurements for Mg0.5Zn0.5Fe2-xCrxO4 showed the presence of magnesium, iron, chromium and zinc only and Fe equally occupying octahedral and tetrahedral sites: Fe[MgFe]O4.In contrast zinc ferrite is a normal spinel with (oxygen was below the machine cut oV ). The elemental ratios were within experimental error (1–2%) identical for the same Zn occupying the tetrahedral positions and Fe occupying the octahedral sites: Zn[Fe2]O4.Mg–Zn ferrite is a solid solution sample across many surface spots indicating that a homogeneous powder was formed. The atom percentages mirrored between these, with Zn2+ ions occupying tetrahedral sites and Mg2+ ions on octahedral sites.Chromium substitution into very closely the expected values, for example the sample of formula Mg0.5Zn0.5Fe0.5Cr1.5O4 gave an average elemental this species occurs preferentially on the octahedral sites. From the current set of Mo�ssbauer spectra these site ratio of Mg0.5Zn0.5Fe0.6Cr1.6. The FTIR spectra of MgFe2O4 and Mg0.5Zn0.5Fe2-xCrxO4 occupancies may be tested for the pure Mg ferrites, as shown in Fig. 2. As can be seen from the data, reasonable quality fits mirrored previous literature measurements, showing three broad overlapping bands: a shoulder at 685 cm-1 and two have been obtained for both the zero field and applied field SHS samples assuming an equal spectral area for the two bands at 520 and 410 cm-1. An additional band grows into Table 3 Room temperature Mo�ssbauer parameters for sintered MgFe2O4 ferrites prepared v performed in zero field and in an applied field of 1.1 T (series 1 and 2): isomer shift d (±0.01 mm s-1); quadrupole shift 2e (±0.01 mm s-1); linewidths C and DC (±0.01 mm s-1) and hyperfine field Bhf (±0.1 T).Two equal area subspectra were fitted, corresponding to Fe atoms at the octahedral and tetrahedral sites.Preferential line broadening due to distributions in local environments was modelled by ascribing linewidths of C+DC, C and C-DC to the outer, middle and inner pairs of lines in the sextets Octahedral sextet Tetrahedral sextet d 2e C DC Bhf d 2e C DC Bhf Series 1 0.43 0.06 0.51 0.16 48.1 0.16 -0.08 0.49 0.14 47.6 Series 2 0.45 0.04 0.54 0.15 48.3 0.17 -0.08 0.49 0.11 47.9 J.Mater. Chem., 1998, 8, 2701–2706 2703Fig. 3 Mo�ssbauer spectra measured at room temperature and at 80 K for samples of Mg0.5Zn0.5Fe2-xCrxO4 (x=0, 0.3 and 0.6) prepared by SHS in zero field and in an applied field of 1.1 T, after sintering for 2 h at 1400 °C. Solid lines represent least squares fits to the data: for the magnetically split spectra a probability distribution of hyperfine fields was used, otherwise a combination of one or two quadrupole split doublets was used.subcomponent sextets. This is consistent with the equal occu- field SHS sample are larger than in the zero field SHS counterpart. pancy of octahedral and tetrahedral sites by the Fe atoms. The parameters obtained from the fits, given in Table 3, are Mo�ssbauer spectra of some selected Mg0.5Zn0.5Fe2-xCrxO4 samples recorded at room temperature and 80 K are shown in also consistent with this assignment.Comparison of the Mo�ssbauer parameters for the two samples shows only minor Fig. 3.We note in passing that further Mo�ssbauer experiments, such as at liquid helium temperatures in the presence of large diVerences, although it may be significant that the hyperfine fields at both the octahedral and tetrahedral sites in the applied external magnetic fields, could be used to garner information Table 4 Mo�ssbauer parameters at room temperature and 80 K for selected examples of sintered Mg0.5Zn0.5Fe2-xCrxO4 ferrites prepared via SHS reactions in zero field and in an applied field of 1.1 T (series 1 and 2): isomer shift d (±0.01 mm s-1) and mean hyperfine field Bhf (±0.5 T).The spectra were modelled with a 200 box histogram probability distribution of subcomponent sextets, each of which had the same isomer shift d, a quadruple shift of zero, and a hyperfine field covering the range from zero to 65.0 T. In some cases the spectra comprised one or two paramagnetic doublets, in which case the parameters given are the isomer shift d (±0.01 mm s-1) and quadrupole splitting D (±0.01 mm s-1) Room temperature spectra Spectra at 80 K Series 1 Series 2 Series 1 Series 2 x d D Bhf d D Bhf d D Bhf d D Bhf 0.0 0.32 — 31.7 0.33 — 31.4 0.43 — 49.9 0.42 — 48.0 0.3 0.33 — 19.7 0.35 — 27.4 0.42 — 46.1 0.42 — 47.2 0.6 0.31 0.90 — 0.38 — 36.5 0.35 0.42 — 1.5 0.33 0.49 — 0.44 0.52 — 2704 J.Mater. Chem., 1998, 8, 2701–2706Magnetic measurements As is evident from the data in Table 5, the introduction of Cr3+ ions into magnesium zinc ferrite strongly aVects the room temperature magnetic parameters of the system. The decrease in both the maximum magnetisation smax and the remanent magnetisation sr mirrors the fall in Mo�ssbauer hyperfine fields, and may be ascribed to the increasing fluctuations in the Fe moments as the increasing Cr concentration disrupts the interatomic exchange interactions. Systematic diVerences in the magnetisation parameters are seen for the series 1 and 2 samples, with the applied field samples having consistently higher smax and sr parameters.This is most probably indicative of a degree of magnetic texturing, generated during the applied field SHS processing, remaining in the sintered powders.This is an interesting result and indicative of possible microstructural eVects which may be related to the Fig. 4 Representative room temperature hysteresis loops of samples lattice parameter changes seen earlier in the X-ray diVraction of Mg0.5Zn0.5Fe2-xCrxO4 prepared by SHS in zero field (ZF) and in experiments.In contrast the coercive force Hc data for both an applied field (AF) of 1.1 T, after sintering at 1400 °C for 2 h. series 1 and series 2 samples are similar. Table 5 Bulk magnetic properties of sintered MgFe2O4 and EVect of magnetic field on the synthesis Mg0.5Zn0.5Fe2-xCrxO4 prepared by SHS performed in zero field and in an applied field of 1.1 T (series 1 and 2): maximum magnetisation The only diVerence between the samples prepared in series 1 smax (±0.1 emu g-1), remanent magnetisation sr (±0.1 emu g-1) and and 2 was the application of an external magnetic field during coercive force Hc (±0.5 Oe).Measurements were made at room the SHS step. Despite this, the two series of samples show temperature in applied fields up to 7.5 kOe some small diVerences in X-ray and Mo�ssbauer parameters, Series 1 Series 2 and major diVerences in magnetic parameters.The changes in Mg0.5Zn0.5Fe2-xCrxO4 unit cell dimension may indicate diVerent levels of crossx ss sr Hc ss sr Hc substitution or defects in the two series. These eVects may have arisen as a consequence of a slightly faster propagation 0 59.8 1.42 9.4 82.6 1.80 9.3 rate, coupled with an increased reaction temperature, in the 0.3 46.8 1.34 9.9 59.1 1.37 9.8 0.6 12.2 0.31 12.5 24.5 1.10 11.8 applied field SHS reactions: visual inspection of the reactions 0.9 2.45 0.19 16.7 10.9 0.56 16.2 indicated that the synthesis wave moved faster and glowed 1.2 0.99 0.14 39.5 2.78 0.26 21.7 with a more yellow coloration in the applied field series.In 1.5 0.61 0.10 82.0 1.17 0.24 77.4 the applied field some pre-organisation of the precursor pow- MgFe2O4 34.6 1.97 19.8 39.6 2.42 18.3 ders was observed prior to initiation of the SHS reaction, most likely due to the alignment of the iron and iron oxide components along the magnetic flux lines.It is reasonable to on the cation distributions in the Cr substituted materials.14 suppose that this pre-organisation leads to better surface However, in the present work we choose to limit our consider- contacts between the reacting powders, hence giving rise to ation to the general features of the Mo�ssbauer spectra of these the hotter and faster reaction conditions.samples, and to a comparison of the data obtained from the series 1 and 2 samples. On inspection of Fig. 3 it is apparent that in the case of Conclusions Mg0.5Zn0.5Fe2O4 there is little diVerence between the series 1 Self propagating high temperature synthesis allows the rapid and 2 samples either at room temperature or at 80 K, while formation of near single phase chromium substituted mag- there are discernible diVerences between the two series for nesium and magnesium zinc ferrite.Despite the short synthesis Mg0.5Zn0.5Fe1.7Cr0.3O4 at room temperature, but less so at time solid solutions of the ferrites were formed. The ferrites 80 K. The fitted parameters in Table 4 bear this out, with the had magnetic orders of merit equal to those prepared by main diVerence being a higher mean hyperfine field in the conventional synthesis. Mo�ssbauer spectroscopy showed that applied field SHS x=0.3 sample at room temperature than in for all samples the chromium metal was substituted on the its zero field counterpart.We tentatively ascribe this to a octahedral sites within the spinel. Use of a magnetic field possibly less disruptive distribution of substituted Cr atoms in during SHS synthesis increases the rate of reaction propa- the series 2 sample, with a commensurate increase in the gation. The materials prepared by SHS in a magnetic field samples Curie temperature. However, such a result needs showed increased saturation magnetisation compared to those further investigation, beyond the scope of the present study, prepared in the absence of a field.It is likely that these before this can be known for certain, especially since a slightly enhanced magnetic eVects are a consequence of chanvel of Cr doping in the two samples might give rise product microstructure rather than in spinel site occupancy.to a similar eVect. Representative data for the higher Cr dopings of x=0.6 and 1.5 are also shown in Fig. 3 for series 1 samples. These References spectra are paramagnetic doublets at room temperature, indicating that in these samples the Cr substitution is suYciently 1 I.P. Parkin, Chem. Soc. Rev., 1996, 199; I. P. Parkin, G. E. Elwin, A. V. Komarov, Q. T. Bui, Q. A. Pankhurst, L. Fernandez high to disrupt the Fe ordering enough that the Curie tempera- Barquin and Y. G. Morozov, J. Mater. Chem., 1998, 8, 573. tures of the samples fall below room temperature. Indeed, for 2 A. G. Merzhanov, Proc. Technol., 1996, 56, 222. the x=1.5 sample the Curie temperature falls below 80 K, so 3 A. E. Padalino, J. Am. Ceram. Soc., 1960, 43, 183; that even at that temperature a doublet is measured. For the Y. D. Tretyakov and N. I. Oleinikov, Inorg. Mater., 1965, 1, 254. x=0.6 sample at 80 K a broad hyperfine split spectrum is 4 Ferrites, ed. L. A. Rabkin, S. A. Soskin and B. S. Epshtein, observed, with parameters that are in line with those seen for Energy, Leningrad, 1968, p. 384. 5 H. Kojima, in Ferromagnetic Materials: A Handbook of the the lower Cr content samples. J. Mater. Chem., 1998, 8, 2701–2706 2705Properties of Magnetically Ordered Substances, ed. 11 F. C. Romeijn, Philips Res. Rep., 1953, 8, 304. 12 R. Shanon, Acta Crystallogr., Sect. A, 1976, 32, 751. E. P. Wohlfarth, North-Holland, Amsterdam, 1982, vol. 3. 6 V. S. Darshane, S. S. Lokegaonkar and S. G. Oak, J. Phys. IV Fr., 13 Q. A. Pankhurst, S. Suharan andM. F. Thomas, J. Phys. Condens. Matter, 1992, 4, 3551. 1997, 7, C1. 7 M. V. Kuznetsov, Y. G. Morozov, M. D. Nersesyan and 14 P. M. A. de Bakker, E. De Grave, D. GryVroy, R. E. Vandenberghe and P. Moens, Mater. Sci. Forum, 1991, T. I. Ignateva, Inorg. Mater., 1995, 31, 1125. 8 L. C. F. Blackman, Trans. Faraday Soc., 1959, 55, 391. 79–82, 777. 9 A. H. Morrish and P. E. Clark, Phys. Rev. B, 1975, 11, 278. 10 E. W. Gorter, Philips Res. Rep., 1954, 9, 295. Paper 8/04942D 2706 J. Mater. Chem., 1998, 8, 2701–2706

ISSN:0959-9428    

DOI:10.1039/a804942d

出版商:RSC    

年代:1998

数据来源: RSC

摘要:

J O U R N A L O F C H E M I S T R Y Materials Influence of the nature of the organic precursor on the textural and chemical properties of silsesquioxane materials Genevie`ve Cerveau, Robert J. P. Corriu,* Ce�dric Lepeytre and P. Hubert Mutin Laboratoire de Chimie Mole�culaire et Organisation du Solide, UMR 5637, Universite� Montpellier II, Case Courrier 007–34095 Montpellier Ce�dex 5, France Received 24th July 1998, Accepted 8th September 1998 The hydrolytic sol–gel polymerization of molecular organosilicon precursors with a rigid geometry C6H4[Si(OMe)3]2-1,4 and C6H3[Si(OMe)3]3-1,3,5 2 was investigated and compared to the results obtained with precursors having a more flexible structure C6H4RR¾-1,4 [R=R¾=CH2Si(OMe)3 3; R=R¾=CH2CH2Si(OMe)3 4].Compounds 1–4 have been studied in the same conditions.They were hydrolyzed under nucleophilic catalysis (TBAF: tetrabutylammonium fluoride) in MeOH and in THF. The structure of the organic group was found to be a determining parameter for both the physical and chemical properties of the resulting silsesquioxane materials. The molecular precursors 1 and 2 containing a ‘rigid’ organic group led to hydrophilic solids with similar degrees of condensation.In all cases, high specific surface area (370–1018 m2 g-1) and poor chemical reactivity towards Cr(CO)6 (11–33%) were observed. By contrast, the precursors containing a ‘flexible’ organic group (3 and 4) led to hydrophobic solids; the texture, the degree of condensation and the reactivity towards Cr(CO)6 of these solids strongly depended on the solvent.For instance the solids prepared in MeOH had no significant specific surface area. The solids derived from the most flexible precursor (4) exhibited the highest chemical reactivity. The short range organization of the solid is a function of the geometry of the precursor and the experimental conditions. tural and chemical properties of diVerent aryl bridged Introduction silsesquioxane xerogels.Organic–inorganic hybrid materials are a wide field of growing interest.1,2 Sol–gel chemistry, which corresponds to an inor- Experimental ganic polymerization, oVers an access to a wide variety of silica-like structures.3 The mild reaction conditions allow the All the syntheses of precursors and reactions of complexation incorporation of organic moieties into inorganic oxide net- with Cr(CO)6 were carried out under argon using a vacuum works.The preparation of monocomponent hybrid materials line and Schlenk tube techniques.15 Solvents were dried and in which organic molecules are covalently bound to silica is distilled before use. IR spectra were recorded using a Perkin opening interesting perspectives for chemists.The incorpor- Elmer 1600 FTIR spectrophotometer using KBr pellets or by ation of an organic unit in the core of an inorganic matrix the DRIFT method. Solid state NMR spectra were obtained with a Bruker FTAM 300 spectrometer: 13C CP MAS NMR can be achieved when at least two covalent bonds are formed at 75.47 MHz, recycling delay 5 s, and contact time 5 ms; 29Si between the organic molecule and the solid.A large variety of CP MAS NMR at 59.62 MHz, recycling delay 10 s, and nanostructured hybrid materials has been reported4–13 and it contact time 2 ms. Chemical shifts are given relative to tetra- has been shown that changing the nature of the organic group methylsilane. To obtain quantitatively reliable 29Si data, single- induces changes in the macroscopic properties of the hybrid pulse MAS NMR experiments (SPE-MAS) have been per- solid.For instance, linear rigid rod structures with p-phenylene formed on a Bruker ASX 200 spectrometer at 39.74 MHz, groups4,5 and flexible structures due to methylene groups6,7 using a pulse angle of 30°, a recycling delay of 60 s and high- influence properties such as the microporosity. Microporous power proton decoupling during the acquisition.These experi- bridged polysilsesquioxanes have been used as a confinement ments have been done for two xerogels derived from precursors matrix for nanosized particles.9 Short range organization in 1 and 4 by hydrolysis in MeOH. The spinning rate was the amorphous solids arising from the molecular structure of 5000 Hz in all cases. the precursor has been detected using the chemical reactivity Specific surface areas, pore volumes and pore size of organic spacers in the case of hybrid materials containing distribution were determined using a Micromeritics Gemini buta-1,3-diyne or thiophene bridging fragments.10,11 III 2375 apparatus. Elemental analyses were carried out by Moreover, the inclusion of charge transfer complexes in gels11a the ‘Service Central de Micro-Analyse du CNRS’.Oxygen illustrates the importance of weak interactions between the percentages were deduced by diVerence. X-Ray powder organic units on the texture of the solid. In a preliminary diVraction measurements were performed using a Seifert MZ4 report, we have shown that the nature of the organic spacer apparatus. appears as a very important parameter in the control of the Compounds 1, 2 and 3 were prepared according to literature properties of the solid14a such as the specific surface area, the procedures4a,12b while 4 was commercial and purified before hydrophilicity and the chemical reactivity.use. In this context, we were interested in investigating to which Gels starting from 1,2 and 3 have been already described extent can the structure of the precursor be a determining under diVerent experimental conditions.4a,5a,13 parameter for the solid state properties of the resulting materials.We therefore examined the gel formation from precursors Preparation of silsesquioxane gels with diVerent structures, under the same experimental conditions. The preparation of the gels was carried out according to the We report here our studies concerning the relationships following general procedure.The preparation of 1M is given as an example. To 2.52 g (7.92×10-3 mol) of 1 in 10 ml of between the structure of the organic groups and the tex- J. Mater. Chem., 1998, 8, 2707–2713 2707Table 1 Experimental conditions and gelation time of xerogels Precursor conc./ Gelation Entry Precursor Solvent Xerogel mol L-1 time/min 1 1 MeOH 1M 0.5 160 2 1 THF 1T 0.5 135 3 2 MeOH 2M 0.5 7 4 2 THF 2T 0.5 4 5 3 MeOH 3M 0.5 45 6 3 THF 3T 0.5 <1 7 4 MeOH 4M 0.5 720 8 4 THF 4T 0.5 <5 methanol was added a solution of 79×10-3 ml of TBAF (solution 1 mol l-1 in THF) and 428×10-3 ml of water (3 mol. equiv.) in 5.33 ml of methanol.After 160 min a monolithic opaque gel formed. After ageing during 5 days at room temperature the solid was collected, then ground and washed with ethanol, acetone and diethyl ether.The resulting solid was dried at 120 °C in vacuo during 3 h yielding 1.23 g of a Scheme 1 Molecular precursors 1–4. white powder 1M. The experimental conditions and the gel times of the xerogels are reported in Table 1.These analyses revealed an excess of carbon and hydrogen indicating the presence of residual hydroxy and methoxy Reaction of complexation with Cr(CO)6 groups. This excess of carbon and hydogen was larger when the reaction was carried out in MeOH (Table 2, entries 1, 3) The reaction of complexation of the xerogel was carried out according to the following general procedure.14a than in THF (Table 2, entries 2, 4) as shown by the experimental formula.This can be attributed to a higher degree of The complexation of 1M is given as an example. The xerogel 1M (0.58 g, 3.22×10-3 mol ) and an excess of Cr(CO)6 (1 g, hydrolysis in THF than in MeOH. The X-ray powder diVraction pattern of the samples showed 4.8×10-3 mol) were introduced in a mixture of 10 ml of THF and 40 ml of Bun2O.The mixture was refluxed during 65 h. absence of crystallinity in all cases. After this, the yellow–green solid was filtered, washed with dichloromethane and diethyl ether, then dried in vacuo at NMR characterization of the xerogels room temperature during 3 h. A pale green solid (0.72 g) was The IR and NMR characteristics of the xerogels prepared obtaih was analysed by IR and NMR spectroscopy.from 1–4 have been determined and are in agreement with the The degree of complexation was determined by chemical and conservation of the organic units bonded to the silica matrix: EDS elemental analysis. The experimental ratio (Cr/Si)exp was 29Si CP MAS NMR (Table 2) clearly established that the Si-C determined from the elemental analysis and compared to the bond was retained within the gel in all cases:17 no 29Si theoritical value (Cr/Si)th assuming a degree of complexation resonances attributable to SiO4/2 units were detected 18 (only of 100%.For xerogel 1M, (Cr/Si)exp=0.09; degree of com- T0, T1, T2, T3 units were observed). Futhermore 13C CPMAS plexation=18%. The results obtained were confirmed by NMR spectra showed that the organic fragments were not elemental EDS analysis. modified.When the hydrolysis–polycondensation reaction was Results and discussion performed in methanol, in the case of gels prepared from 1 and 2, 29Si CP MAS NMR showed a major substructure T2: The molecular precursors 1–4 containing phenylene units with CSiO2(OX) (X=Me or H). Starting from 3 and 4 a major various geometries have been investigated4a,12b (Scheme 1).substructure T2 and signals corresponding to a substructure Compounds 1 and 2 have a ‘rigid’ spacer, whereas 3 and 4 of type T0: CSi(OX)3 (X=Me or H) were observed (Fig. 1). contain more ‘flexible’ organic groups. When the solvent was THF, the 29Si CP MAS NMR characteristics were very similar to those obtained in methanol Preparation and characterization of silsesquioxane gels in the case of 1T and 2T.However the solid 3T appeared more polycondensed (T2 and T3 major substructures). Solid The sol–gel polymerization of monomeric precursors 1–4 was performed in MeOH and in THF, in the presence of (TBAF) 4T showed a major substructure T3: CSiO3 indicative of a higher degree of polycondensation (Fig. 2).tetrabutylammonium fluoride (1 mol%) as a catalyst,16 for a concentration of 0.5 mol l-1 of the precursor at room tempera- Quantitatively reliable 29Si SPE MAS NMR spectra have been collected for two typical silsesquioxane xerogels, 1M and ture (reaction 1). The experimental procedure was strictly controlled, all the reactions were performed three times and 4M, and compared to the CP MAS NMR spectra of the same precursors (Fig. 3). The percentages of the diVerent Tx units, were rigorously reproducible. When the reaction was performed in MeOH, opaque gels obtained by deconvolution of the spectra are reported in Table 3. The SPE MAS and CP MAS percentages found for formed within a short period of time for 1 and 2 whereas white precipitates were obtained for 3 and 4.When the solvent the diVerent Tx units were comparable in both cases. Accordingly, the degrees of condensation derived from the was THF, transparent gels formed in all the cases. Gel times are reported in Table 1. The gels were allowed to stand at 29Si CP MAS spectra were close to those derived from the quantitative SPE MAS NMR spectra. It was not possible to room temperature for 5 days.After washing with ethanol, acetone and ether, the powders were dried in vacuo at 120 °C perform quantitative SPE MAS experiments for all the samples; thus the degrees of condensation reported in Table 4 during 3 h. Elemental analysis showed that in all cases the hybrid gels deviated from the ideal stoechiometry based on have been estimated from CP MAS spectra. All the samples derived from the rigid precursors 1 and 2 totally polycondensed silsesquioxane materials (Table 2). 2708 J. Mater. Chem., 1998, 8, 2707–2713Table 2 Elemental analyses, experimental formulas, and 29Si CP MAS NMR data of xerogels Elemental analysis (found %) 29Si CP MAS NMR (d)e Entry Xerogel C H Si Experimental formula T0 T1 T2 T3 1 1M 38.73 3.77 23.40 C7.76H9.01Si2O5.16 a — -61 -70 -78 2 1T 36.15 3.21 25.40 C6.66H7.06Si2O4.88 a — -61 -70 -78 3 2M 33.36 3.82 26.10 C8.93H12.22Si3O7.38 b — -62 -70 -78 4 2T 30.85 3.20 27.35 C7.89H9.78Si3O7.44 b — -61 -70 -78 5 3M 46.62 5.88 25.45 C8.62H12.94Si2O3.16 c -46 -55 -63 -71 6 3T -47 -55 -63 -70 7 4M -42 -50 -59 -67 8 4T 50.31 5.42 22.75 C10.32H13.24Si2O3.30 d — — -57 -66 Ideal formula: aC6H4Si2O3; bC6H3Si3O4.5; cC8H8Si2O3; dC10H12Si2O3; emajor resonances in bold type.Fig. 1 29Si CP MAS NMR spectra of xerogels; (a) 1M, (b) 2M, (c) 3M, (d) 4M. Fig. 2 29Si CP MAS NMR spectra of xerogels; (a) 1T, (b) 2T, (c) 3T, (d) 4T. had similar degrees of condensation, lying in the range 61–67%, whatever the solvent and concentration. These values are comparable to those reported by Shea and coworkers6 on than in MeOH, in good agreement with the elemental analysis other examples.reported in Table 2. On the other hand, the degree of condensation of the samples derived from the more flexible precursors 3 and 4 Hydrophilic character of the xerogels depended on the nature of both the solvent and the precursor. Thus, the samples prepared in THF showed significantly higher All the solids obtained from 1 and 2 exhibited significant hydrophilic character, whereas the gels derived from 3 and 4 degrees of condensation than those prepared in MeOH; for a given solvent, the samples prepared from precursor 4 showed always showed a low aYnity for water independent of the gelation solvent.Weight increases in a 60% humidity atmos- significantly higher degrees of condensation than those prepared from precursor 3.phere at 25 °C (E0.6%) are reported in Table 4 and are in agreement with the IR data of the xerogels: the n(OH) 13C CP MAS NMR spectra (Fig. 4) showed very weak signals attributable to residual methoxy groups when the absorption band centered at 3370 cm-1 due to the presence of silanol groups was stronger for the xerogels obtained from 1 solvent was THF and more intense signals in the case of methanol indicative of a higher degree of hydrolysis in THF and 2 than from 3 and 4.J. Mater. Chem., 1998, 8, 2707–2713 2709Fig. 3 29Si SPE MAS NMR and 29Si CP MAS NMR spectra of xerogels; (a) 1M, (b) 4M. Table 3 Comparison between SPE MAS and CP MAS 29Si NMR data for samples 1M and 4M %T0 %T1 %T2 %T3 %condensation Xerogel SPE/CP SPE/CP SPE/CP SPE/CP SPE/CP 1M 0/0 17.0/18.7 61.5/63.5 21.5/17.8 68.2/66.4 4M 4.5/6.4 26.0/27.1 46.2/44.3 23.4/22.3 62.9/60.9 Fig. 4 13C CP MAS NMR spectra of xerogels; (a) 4M, (b) 4T. Texture of the solids Nitrogen BET measurements19 gave specific surface areas very high for both samples, which is also indicative of microporosity. which were very diVerent depending on the structure of the precursor and the nature of the solvent.The solids obtained All the xerogels prepared from 2 exhibited isotherms intermediate between type I and IV (characteristics of meso- from 1 and 2 exhibited very high specific surface areas whatever the solvent used: 549–1018 m2 g-1 in MeOH and porous solids) and high specific surface areas (Table 5, entries 3 and 4). No narrow pore size distribution was observed in 370–766 m2 g-1 in THF (Table 4, entries 1–4).By contrast, the solvent employed for the hydrolysis– all cases. Sample 3T (Table 5, entry 5) was mesoporous and showed polycondensation reaction had a drastic influence on the texture of the solids in the case of 3 and 4. The xerogels 3M a substantial specific surface area (277 m2 g-1), whereas 3M presented no significant specific surface area.and 4M prepared in MeOH exhibited no significant surface areas (Table 4, entries 5, 7) while high specific surface areas For xerogels derived fom precursor 4, the nature of the solvent used during the hydrolysis–polycondensation had a were observed for samples 3T and 4T prepared in THF (Table 4, entries 6, 8). drastic influence on the texture of the resulting solids since sample 4T exhibited a high specific surface area (565 m2 g-1) Adsorption–desorption isotherms of 1M, 1T, 2M, 2T, 4T are shown in Fig. 5 and 6. The determination of the porous whereas sample 4M had no significant specific surface area. This diVerence may be correlated to the increase of the rigidity volume by the BJH method 20 and the evaluation of the microporous volume by the analysis of the t-plot diagram of the network of the sample prepared in THF owing to the higher degree of condensation (61% for 4M and 87% for 4T).have been performed in each case. The BET specific surface areas and porous volumes of the xerogels are reported in For 4T the solid was mainly mesoporous, with a low microporous contribution (estimated to be ca. 20% of the total porous Table 5. The xerogels 1M and 1T (Table 5, entries 1 and 2) showed volume). No narrow pore size distribution was observed. Despite its high specific surface area, gel 4T had a low aYnity type I isotherms,21 characteristic of microporous solids. Indeed, the microporous volume represented respectively 60 for water (5–6%) in accord with the low amount of hydroxy groups as shown by IR spectroscopy.and 79% of the total porous volume. The BET constant c was Table 4 Degree of condensation, hydrophilicity, specific surface area and degree of complexation of xerogels Degree of Surface area/ Degree of Entry Xerogel condensation (%)a E0.6 (%) m2 g-1 complexation (%) 1 1M 66 22 549 18 2 1T 67 18–22 370 11 3 2M 61 22–24 1018 27 4 2T 64 30–31 766 33 4 3M 55 2 <10 25 6 3T 72 3 277 42 7 4M 61 2 <10 84 8 4T 87 5–6 565 64 aEstimated from the 29Si CP MAS NMR spectra. 2710 J. Mater. Chem., 1998, 8, 2707–2713Fig. 5 N2 adsorption–desorption isotherms of xerogels; (a) 1M, (b) 2M. The most important feature for the silsesquioxanes reported here is the diVerence of the texture of the solids connected with the geometry of the organic unit: the materials with a ‘rigid’ bridge obtained from 1 and 2 exhibit in all cases a high hydrophilicity (18–31%) and a high surface area (370–1018 m2 g-1).The hydrophilic character (E0.6) is larger in THF than in MeOH for 2 (Table 4, entries 3, 4) although the surface area is lower, which suggests a larger amount of hydroxy groups. This observation is consistent with the IR and 13C NMR data.By contrast, with more ‘flexible’ spacers 3 and 4, the texture is dependent on the nature of the solvent Fig. 6 N2 adsorption–desorption isotherms of xerogels; (a) 1T, (b) used in the hydrolysis–polycondensation reaction. No signifi- 2T, (c) 4T. cant surface areas were observed using MeOH while high surface areas were obtained using THF. at ca. 1970 and 1880 cm-1 due to carbonyl groups, the Chemical reactivity of xerogels intensity of which depended on the degree of complexation with Cr(CO)3. 13C CP MAS NMR spectra clearly revealed We have previously shown that the chemical reactivity of hybrid solids can be used as a tool for studying the solid the presence of both uncomplexed aryl and aryl–Cr(CO)3 units: for example, for 4M, the spectrum showed signals arrangement as a function of molecular structure.10,14 The accessibility of the aromatic groups of the hybrid network has corresponding to carbonyl groups at d 234, complexed aromatic carbons aryl–Cr(CO)3 at d 93 and 117 and uncomplexed been studied, using the reaction of complexation of aryl fragments with Cr(CO)6 according to reaction 2.aromatic groups at d 128 and 145 (Fig. 7). These 13C CP MAS NMR data are reported in Table 6. 29Si CP MAS NMR Complexation reactions occur under heterogeneous conditions. The silsesquioxanes obtained from 1–4 were treated spectra before and after complexation with Cr(CO)6 were unchanged. The degree of complexation was determined by with Cr(CO)6. After 65 h of reflux in a 80/20 mixture of Bun2O–THF a yellow–green powder was isolated.The com- EDS and chemical elemental analysis. The results deduced from elemental analysis (see Experimental section) showed a plexation of arene groups was evidenced by FTIR and 13C CP MAS NMR spectroscopies as described in the case of ‘auth- greater reproducibility and are reported in Table 4. The xerogels obtained from ‘rigid’ precursors 1 and 2 led to entic’ materials.12b FTIR spectra showed new absorption bands J.Mater. Chem., 1998, 8, 2707–2713 2711Table 5 N2 adsorption desorption data of xerogels Entry Xerogel BET surface/m2 g-1 Vpore tot a/cm3 g-1 Vpore ads b/cm3 g-1 Vpore des b/cm3 g-1 Vmicropore c/cm3 g-1 c 1 1M 549 0.27 0.11 0.11 0.16 470 2 1T 370 0.19 0.04 0.03 0.15 814 3 2M 1018 0.80 0.74 0.74 0.10 106 4 2T 766 0.53 0.55 0.49 — 146 5 3T 277 0.20 0.17 — — 83 6 4T 565 0.37 0.29 0.27 0.08 122 aP/P0=0.99.bCumulative pore volume of pores between 17 and 3000 A° diameter. cEstimated by the t-plot method, using Harkins and Jura standard isotherm and thickness range between 4 and 6 A° . attributed to flexibility due to the methylene groups present in the organic moiety. When the gelation solvent was THF a decrease of the degree of complexation (64%) was observed for 4T (Table 4, entry 8).This decrease can be explained by the higher degree of polycondensation of the hybrid material which induces a lower swelling of the solid corresponding to a lower diVusion of Cr(CO)6. However the poor reactivity observed with the gels obtained from 3 appears unexpected, since the solids obtained from 3 and 4 in MeOH exhibited the same specific surface areas (<10 m2 g-1) and the same aYnity for water (2%).This can be explained by a less ‘flexible’ organic spacer for 3 and consequently more diYcult diVusion of Cr(CO)6 in the hybrid network. The precursor 3 appears to be intermediate between 1 and 4. Fig. 7 13C CP MAS NMR spectrum of the solid obtained by reaction of xerogel 4M with Cr(CO)6.Analysis of the surface of solids 1M and 4M by time of flight secondary ion mass spectrometry (TOF SIMS) was in agreement with the results presented above. For 1M, the main Table 6 13C CP MAS NMR data (d) of xerogels after reaction with ion detected is at m/z=45 (SiOH+), in accord with the high Cr(CO)6 hydrophilicity (OH groups at the surface) and poor chemical Complexed reactivity.22 By contrast, for 4M, ions at m/z=77 (phenyl ) Residual Unchanged and m/z=91 (tropylium) are observed23 in accord with an Xerogel CH2Si CH2Ar CH3O Ar Ar CO hydrophobic solid and a high chemical reactivity.For 1M, the OH groups are located at the surface in agreement with the 1M — — 50 134 —a —a high hydrophilicity, while for 4M the presence of ions at m/z= 1T — — 50 134 —a —a 2M — — 50 131, 143 88, 105 232 77 and 91 is in accord with the hydrophobicity observed.This 2T — — 51 130, 143 —a —a means that the arrangement of the organic groups in the two 3M — 21 50 129, 133 96, 109 235 solids is completely diVerent. 3T — 21 50 133, 129 106, 94 234 4M 14 29 51 145, 128 93, 117 234 4T 15 29 50 143, 128 114, 92 233 Conclusion aNot detected.The results presented here show that the kinetic parameters involved in the hydrolysis–polycondensation reactions have an influence on both the physical and chemical properties of poor levels of complexation (11–33%), despite their high specific surface areas (370–1020 m2 g-1). However, the surface the resulting silsesquioxane materials. The structure of the organic precursor appears to be a area and the degree of complexation of the xerogels derived from precursor 2 were about twice as high as those of the determining parameter for the solid state properties of the xerogels containing aromatic groups.Molecular precursors xerogels derived from precursor 1. These results suggest an organization of the solids in which only a few aromatic groups containing a ‘rigid’ organic group always led to hydrophilic solids with similar degrees of condensation.In all cases, these are accessible at the surface. Futhermore the precursors 1 and 2 have diVerent geometries: 1 is linear with six hydrolysable solids had high specific surface areas and no narrow pore size distribution whatever the solvent and the concentrations used groups, while 2 has a planar geometry with nine hydrolysable groups.during the hydrolysis–polycondensation process and poor chemical reactivity towards Cr(CO)6 was observed (11–33%). For xerogels obtained from ‘flexible’ precursors 3 and 4 the degrees of complexation were highly dependent on the nature By contrast when the precursor contained a ‘flexible’ organic spacer, the texture, the degree of condensation and the reactiv- of the organic spacer and the solvent and poor reactivity was observed when 3 was hydrolysed in MeOH (Table 4, entry 5).ity towards Cr(CO)6 of the resulting solids strongly depended on the solvent. The solids prepared in methanol had very low A moderate degree of complexation was observed for 3T which may be attributed to the higher specific surface area significant specific surface area, whereas in THF high specific surface area products were observed.The degree of com- observed in this case (277 m2 g-1). For 4, a high degree of complexation (84%) was obtained plexation with Cr(CO)6 depended on the flexibility of the organic group: when four methylene groups were present (high in the case of 4M (Table 4, entry 7), showing a high accessibility of the organic groups, although the specific surface area flexibility) a high reactivity was observed.By contrast, a low reactivity was observed when the flexibility was decreased (two was very low (<10 m2 g-1). This behaviour can be explained by the facile diVusion of Cr(CO)6 in the network due to methylene groups). In both cases, however, the solids were hydrophobic.swelling of the solid in the presence of solvent. This may be 2712 J. Mater. Chem., 1998, 8, 2707–271310 R. J. P. Corriu, J. J. E. Moreau, P. The�pot and M. Wong Chi The results are rigorously reproducible if the experimental Man, Chem. Mater., 1996, 8, 100. conditions are strictly controlled. 11 (a) R. J. P. Corriu, J. J. E. Moreau, P. The�pot, M.Wong ChiMan, Work is now in progress in order to determine the influence C.Chorro, J. P. Le`re-Porte and J. L. Sauvajol, Chem. Mater., of other kinetic parameters on the properties of the solids 1994, 6, 640; (b) J. L. Sauvajol, C. Chorro, J. P. Le` re-Porte, obtained by this sol–gel process. R. J. P. Corriu, J. J. E. Moreau, P. The�pot and M. Wong Chi Man, Synth. Met., 1994, 62, 233. 12 (a) G. Cerveau, R. J. P. Corriu and N. Costa, J. Non-Cryst. Solids, 1993, 163, 226; (b) G. Cerveau, R. J. P. Corriu and C. Lepeytre, References Chem.Mater., 1997, 9, 2561; (c) R. J. P. Corriu, P. Hesemann and 1 (a) H.K. Schmidt, Mater. Res. Soc. Symp. Proc., 1984, 32, 327; G. Lanneau, J. Chem. Soc. Chem. 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Lorenz, p. 210 and references therein; (c) G.Cerveau, P. Chevalier, Chem. Mater., 1995, 7, 2010; (h) D. A. Loy and K.J. Shea, Chem. R. J. P. Corriu, C. Lepeytre, J. P. Le`re-Porte, J. Moreau, Rev., 1995, 95, 1431; (i) P. Judenstein and C.Sanchez, J. Mater. P. The�pot and M. Wong Chi Man, Tailor-maide Silicon Oxygen Chem., 1996, 6, 511. Compounds. From Molecules to Materials, ed. R. Corriu and 2 (a) R. J. P. Corriu and D. Leclercq, Angew. Chem., Int. Ed. Engl., P. Jutzi, Vieweg Publ., 1996, p. 273 and references therein. 1996, 35, 1420 and references therein; (b) R. J. P. Corriu, C.R. 15 D. F. Schriver, The manipulation of air-sensitive compounds, Acad.Sci. Paris, Se�r. II, 1998, 83 and references therein; MacGraw-Hill, New York, 1969. (c) R. J. P. Corriu, Polyhedron, 1998, 17, 925 and references 16 R. J. P. Corriu, D. Leclercq, A. Vioux, M. Pauthe and therein. J. Phalippou, Ultrastructure Processing of Advanced Ceramics, ed. 3 K. J. Shea, D. A. Loy and O. W. Webster, Polym. Mater.Eng. 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Chem. Soc., 1951, K. J. Shea, Chem. Mater., 1996, 8, 656. 73, 373. 6 H. W. Oviatt Jr, K. J. Shea and J. H. Small, Chem. Mater., 1993, 21 S. Brunauer, L. S. Deming, W. S. Deming and E. Teller, J. Am. 5, 943. Chem. Soc., 1940, 62, 1723. 7 A. Antony, R. J. P. Corriu, J. J. E. Moreau and M. Wong Chi 22 G. Cerveau, R. J. P. Corriu, J. Dabosi, J. L. Aubagnac, Man, unpublished results. R. Combarieu and Y. de Puydt, J. Mater. Chem., 1998, 8,1761. 8 S. T. Hobson and K. J. Shea, Chem. Mater., 1997, 9, 616. 23 G. Cerveau, R. J. P. Corriu, C. Lepeytre and R. Combarieu, to 9 (a) K.M. Choi and K. J. Shea, Chem.Mater., 1993, 5, 1067; (b) K. be published. M. Choi and K. J. Shea, J. Phys. Chem., 1994, 98, 3207; (c) K. M. Choi, J. C. Hemminger and K. J. Shea, J. Phys. Chem., 1995, 99, 4720 and references therein. Paper 8/05794J J. Mater. Chem., 1998, 8,

ISSN:0959-9428    

DOI:10.1039/a805794j

出版商:RSC    

年代:1998

数据来源: RSC

摘要:

J O U R N A L O F C H E M I S T R Y Materials Processing stoichiometric silicon carbide fibers from polymethylsilane. Part 1 Precursor fiber processing Z-F. Zhang, C. S. Scotto and R. M. Laine* Departments of Materials Science and Engineering, Chemistry and the Macromolecular Science and Engineering Center, University of Michigan, Ann Arbor, MI 48109-2136, USA. E-mail: talsdad@umich.edu Received 8th July 1998, Accepted 9th September 1998 A highly branched form of polymethylsilane (PMS), –[MeSiH]x[MeSi]y–, has been synthsesized and successfully processed into infusible precursor fibers ca. 30–100 mm in diameter. These precursor fibers were converted into stoichiometric, nanocrystalline SiC fibers, 20–70 mm in diameter, by pyrolysis in an inert atmosphere at ramp rates up to 20 °Cmin-1 to 1000 °C.Precursor synthesis, fiber processing, fiber curing and pyrolytic processing are described. Bulk materials were characterized using TGA, DTA, chemical analysis, and XRD. (NO2) infusibility can be obtained with the incorporation of Introduction only small amounts of oxygen.7–9 The NO2 treated fibers are In the 1970s, Yajima et al.1–4 developed a polymer precursor then exposed to boron trichloride (BCl3).The incorporation route to thin (10–15 mm diameter) Si–C–O ceramic fibers that of boron permits pyrolytic processing to dense, substantially are basis of the NicalonTM and TyrannoTM fibers now used in crystalline SiC fibers. Thermally stable, substantially polycryshigh performance composite materials. In this process, precur- talline SiC fibers can be formed from PCS with 3–5 wt.% sor fibers are first produced by melt-spinning polycarbosilane boron and some titanium which binds with the excess boron (PCS), –[MeHSiCH2]x–.These precursor fibers are then air to make TiB2. The boron acts as a sintering aid to promote cured and pyrolytically transformed to ceramic fibers at ca. densification at temperatures >1400 °C.It is also required to 1200 °C. Unfortunately, this approach has several draw- retain fiber integrity. The resulting SiC fibers have O contents backs:1–6 (1) PCS is produced from polydimethylsilane, of <0.1 wt.% after heating to >1600 °C. Stoichiometric b-SiC –[Me2Si]x–, via an expensive multistep synthesis; (2) the initial fibers, as well as SiC fibers containing up to 20 wt.% excess 152 Si5C ratio leads to excess C in the final product; (3) air carbon were produced. Fiber densities approach 3.1 g cm-3 curing used to provide polymer fiber infusibility introduces (fully dense SiC#3.2 g cm-3).Average tensile strengths of up undesirably high oxygen contents; (4) the resulting non- to 3 GPa and elastic moduli of >420 GPa were obtained. stoichiometric, amorphous fibers oVer mechanical properties These properties are closer to the properties of bulk SiC than inferior to bulk, polycrystalline, stoichiometric SiC, and (5) any other precursor derived fibers reported so far.These fibers fiber application temperatures are limited to 1200 °C because represent the state-of-the-art in SiC fiber processing but still the retained oxygen reacts with C and Si to form gaseous require expensive, multistep processing.species at high temperatures. The release of gaseous species Clearly, precursor polymers with a Si5C ratio of 151 oVer degrades fiber properties as pores form coincident with exag- the best potential to obtain stoichiometric SiC fibers. gerated grain growth leading to significant decreases in tensile Polymethylsilane (PMS), –[MeSiH]x–, with a 151 Si5C stoichistrengths at >1200 °C.ometry, oVers the opportunity to meet this potential. Spinnable To overcome these problems and achieve SiC literature PMS, –[MeSiH]x[MeSi]1-x, was first synthesized by Seyferth mechanical properties, stoichiometric, dense and polycrystal- et al.,10,11 using dehalocoupling of MeHSiCl2 (Si5C=151) line SiC fibers with diameters of ca. 15 mm must be made, with Na: preferably via a simple, inexpensive route. Recent eVorts have MeHSiCl2+Na � –[MeSiH]x[MeSi]1-x–+NaCl3 (1) targeted lowering oxygen and carbon contents to obtain near stoichiometric SiC fibers, as described below. However, precursor fibers drawn from this polymer (Mn= Toreki et al. have prepared Yajima PCS withMn#5–10 kDa 400–700 Da) gave black powders on pyrolysis in N2, unless (cf. 1–2 kDa in the Yajima process).5 These polymers do not they were air cured prior to pyrolysis. Pyrolysis gave materials melt on heating, but are soluble in organic solvents and form with excess Si (ca. 25 wt.%) and low ceramic yields (<30 wt.%). viscous solutions suitable for dry-spinning. The dry-spun pre- To increase yields and C contents, compounds with vinyl cursor fibers are heated directly in an inert atmosphere to high groups, e.g.[Me(CH2NCH)SiNH]3 or [Me(CH2NCH)- temperature, without air-curing. SiC fibers produced by this SiO]4–6, were combined with this PMS. The improved ceramic method contain <2 wt.% oxygen and therefore have better yields were ca. 70 wt.%. No detailed analyses of fiber mechanithermal stability than Nicalon fibers.However, the initial 152 cal properties were reported. Si5C ratio still gives fibers with excess carbon. The Toreki PMS, –[MeSiH]x–, can also be synthesized via dehydrocoup- fibers exhibit tensile strengths of ca. 1.8 GPa at 1000 °C, and ling of MeSiH3, the Harrod reaction, using titanocene or 1.2 GPa after heating to >1500 °C in Ar.By comparison, zirconocene complexes, Cp2MMe2 (M=Ti, Zr; Cp=C5H5), Nicalon fibers heated to 1500 °C exhibit tensile strengths of as catalysts:12 only 0.3 GPa. Sacks et al. have improved on the original Toreki fibers to produce phase pure, SiC fibers with the xMeSiH3CCCCCCCCA 0.2 mol% Cp2TiMe2 cyclohexene, 45–60 °C –[MeSiH]x–+0.5xH2 appropriate properties, unfortunately the exact chemistry has (2) not been described.6 Kobayashi et al.recently described a similar PMS synthesis An alternative approach designed to minimize oxygen conusing (C5Me5)2NdCH(SiMe3)2 as catalyst.13 The synthesis is tents was developed at Dow Corning. Dow Corning patents indicate that when Yajima PCS is cured in nitrogen dioxide a one-step polymerization of MeSiH3, with ca. 90% conversion J.Mater. Chem., 1998, 8, 2715–2724 2715of monomer to PMS. Like Seyferth PMS, Harrod PMS oVers vacuum and the product purified by sublimation at 100 °C at access to nearly pure SiC upon pyrolysis.14,15 The highly 10-2 Torr. crosslinked, solid polymer does not melt on heating and gives ceramic yields of 70–80 wt.%. On heating to ca. 1000 °C in Preparation of methylsilane (MeSiH3): CAUTION, this N2, PMS provides near stoichiometric SiC (SiC0.9H0.2O0.1), material can burn on contact with air.Commercial MeSiH3 with nanosized b-SiC grains and 5–10 wt.% excess Si. This contains suYcient chlorosilane impurities to deactivate the polymer oVers the type of ceramic product desired for SiC catalyst and further purification before polymerization was fibers.necessary. Consequently, two procedures were developed to In related work, Hengge et al. used Cp2MMe2 to catalyze produce pure MeSiH3: (A) by reacting MeSiCl3 with LiAlH4 dehydropolymerization of disilanes:16 using ethylenediamine (en) as the purification agent, and (B) as a by-product of the catalytic redistribution of polymethyl- MeH2SiSiH2Me (neat) CA Cp2ZrMe2 H[MeSiH0.58]xH (3) hydridosiloxane, –[MeHSiO]x–, as described below.The low Si5H ratio is indicative of a highly crosslinked and intractable material. These polymers were reported to provide Method A. MeSiCl3 (Aldrich) was refluxed over Mg phase pure SiC, although the method of characterization was turnings and distilled under N2 to eliminate impurities. not described. Ethylenediamine was stirred over CaH2 overnight and dis- The target of the work reported here was to use Harrod tilled under N2.All solvents and reagent liquids were PMS precursor to process stoichiometric SiC fibers. The transferred via cannulae under N2. LiAlH4 reduction of aantages of using Harrod PMS are: a one step, high-yield MeSiCl3 was run in a flame dried three-necked, 1 L flask.synthesis; 151 Si5 C ratio and high ceramic yields. Dry THF (500 mL) was added and the flask was then taken Furthermore, the as-produced polymer is spinnable right inside the drybox. LiAlH4 (24 g, 0.6 mol), an addition funnel from the polymerization solution. Unfortunately MeSiH3, and a condenser were added to the flask, the assembly was the polymerization catalysts, and the resulting polymer are removed from the drybox, connected to a Schlenk line and quite pyrophoric.A nonpyrophoric PMS precursor built by pressure equalized with an N2 flush. The condenser was reverse engineering of the precursor developed here will be cooled to -46 °C with a liquid N2–MeCN slush. The outlet described at a later date.15 of the condenser was connected to a 200 mL, thick walled, The studies described below define parameters that must Pyrex trap charged with 30–50 mL of ethylenediamine (en) be considered/controlled in the overall process that leads to and cooled with liquid N2. stoichiometric, dense SiC fibers.The following sections MeSiCl3 (80 mL) was then transferred to the addition discuss: (1) synthesis of a spinnable, modified Harrod PMS; funnel and added dropwise to the reaction flask with magnetic (2) fiber spinning; (3) fiber curing; (4) control of stoichi- stirring.The MeSiH3 gas that evolved and some MeSiHCl2 ometry during pyrolysis, and (5) conversion of PMS fibers to and MeSiH2Cl were collected in the en trap over 1–2 h. After dense ceramic fibers. Studies on the polymer-to-ceramic addition, the reaction was stirred for 30 min as it warmed to transformation process for bulk polymer, using 29Si solid room temperature and was then heated slowly.Vigorous gas state NMR and FTIR, have been described.14 evolution was observed at temperatures as low as -20 °C. By employing a stepwise increase in reaction temperature (10 °C steps from 10 to 50 °C), foaming was controlled and Experimental the chemical yield maximized.During reaction, the condenser was maintained at -46 °C to condense THF and partially 1 General synthetic procedures reacted volatiles, e.g. MeSiHCl2 and MeSiH2Cl. The level of All air and moisture sensitive materials were handled using the trap bath must be high enough to prevent the excape of standard Schlenk techniques or in the argon atmosphere of a MeSiH3 out of the bubbler (w/Firestone valve), but low glove box, Vacuum Atmosphere Model No.MO40-2-Drienough to prevent clogging with frozen silane. Slight positive Lab. All solvents were distilled in Ar–N2 and degassed prior N2 pressure prevents backflow of silanes into the Schlenk to use. line. The reaction was heated at 50 °C for 4 h. During the last 0.5 h, no further gas evolved for the reaction scale Solvent purification.THF was distilled from sodium benzo- described here. Pure MeSiH3 was obtained by trap-to-trap phenone ketyl. Hexane and toluene were distilled using the distillation into an evacuated weighed metal cylinder cooled same procedure as used for THF with 10 g of tetraglyme with liquid N2. The transfer requires ca. 2 h and provides added to improve the solubility of sodium benzophenone 85–95% yields.ketyl. Diethyl ether was distilled from sliced sodium (20 g/2L flask). Acetonitrile was distilled from calcium hydride in Ar (2 g/2 L solvent). Methanol and ethanol were distilled from Method B. Reaction was carried out in a dry 2 L, threeactivated magnesium (5 g Mg, 0.5 g I2/L solvent). Small necked flash using previously published methods.17 Initially, quantities of solvent (70 mL) were added first to initiate 750–900 mL of freshly distilled toluene was added to the flask.reaction. A vigorous reaction occurs and after 15 min, 1 L of A five fold volume of toluene to –[MeHSiO]x– (Mn#2000 solvent can be added. Da, from Hu� ls) is required to avoid gelation as redistribution occurs. Then, 150 ml of –[MeHSiO]x– was placed in a dry 250 mL Schlenk flask and degassed by sparging Ar through Catalyst syntheses. Cp2TiMe2 or Cp2ZrMe2 were prepared the oligomer for 1 h.The degassed –[MeHSiO]x– was trans- by reaction of Cp2TiCl2 or Cp2ZrCl2 with MeLi according to ferred to the 2 L flask and 5–10 mL of hexane containing published methods.12 In general, ca. 100 mg of either Cp2TiCl2 20–40 mg of Cp2TiMe2 was added dropwise under Ar.or Cp2ZrCl2 (Strem Chemicals) were placed in a dry 50 mL Initiation of the redistribution reaction is slow and can require Schlenk flash with a stir bar (in the drybox). Freshly distilled 0.5–2 h depending on adventitious impurities. Reaction com- and deoxygenated hexane was added to this flask using a mences when the solution turns royal blue.17 Redistribution cannula.Approximately 1.5 mL of 1.4M of MeLi (Aldrich) to –[MeSiO1.5]x– occurs concurrent with release of MeSiH3, in either was added dropwise, and the solution was then which can be trapped without using en. The collection time filtered through Celite under Ar to remove the resulting LiCl precipitate. The filtrate was evaporated to dryness under for this reaction is 48–72 h. 2716 J. Mater. Chem., 1998, 8, 2715–27242 Polymer synthesis The amount of Me2S·BH3 added was determined by assuming that: (1) no B loss occurs during further processing, Polymerization of MeSiH3. This reaction was performed in and (2) all the Si combines with all the C to form pure SiC a 400 mL Parr reactor equipped with magnetic stirrer. The after pyrolysis.An example of the synthesis of a successful catalyst [Cp2TiMe2 or Cp2ZrMe2, 327 mg] was dissolved in spinning solution includes: 10 wt.% of TVS (0.8 g, 6 mmol), distilled cyclohexene (80 g) and added to the Parr reactor 3 wt.% Me2S·BH3 (0.24 g, 3.2 mmol), and 87 wt.% reacted under Ar–N2. The reactor was then sealed, cooled with liquid MeSiH3 (7 g, 150 mmol), which gives a molar ratio of N2 and evacuated.MeSiH3 was then transferred under vacuum Si5C5B#151.350.015. Based on the above assumptions, the from the metal container (see above) by condensing into the final B concentration in the SiC product would be 0.4 wt.%. cooled reactor. The resulting solution was warmed to 55±1 °C Note that this amount of boron makes no changes in the in a thermostatted oil bath.behaviour of TVS-PMS on pyrolysis to temperatures of Dehydrocoupling occurs with concurrent production of H2. 1000 °C. Consequently, the various discussions below do not However, the catalyst also promotes rapid hydrogenation of consider its presence or absence during pyrolysis. The eVects cyclohexene to cyclohexane. Thus, the reaction was followed of B addition are only important when fibers are processed by decreases in MeSiH3 pressure with time.The rate of above 1000 °C. This will be the subject of a following paper. pressure decrease exhibits a linear, first order dependence on initial MeSiH3 pressure. Heating was ceased when the rate of 3 Precursor fiber spinning the pressure decrease was <2 psi h-1 [ca. 25 h (1 psi#6.895× 103 Pa)] as rapid gelation occurs beyond this point.Unreac- Attempts made to melt-draw fibers at 80 °C were not successful as melting Harrod PMS rapidly leads to crosslinking and an ted MeSiH3 (with some H2 and N2) was transferred back to the attached metal cylinder cooled with liquid N2. By mass intractable material. Thus, eVorts focused on dry-spinning. diVerence, 25 g of MeSiH3 were found to react, giving a 90% yield of PMS.The PMS concentration was ca. 0.2 g mL-1. Dry-spinning (fiber extrusion). All vinylsilane modified PMS solutions were dry-spinnable when concentrated to 0.6–0.8 g The molecular weight (Mn) was ca. 1200 Da.12,14 This PMS was characterized by NMR, FTIR, TGA and DSC as mL-1 from 0.15–0.25 g mL-1. The resulting solutions were placed in an extruder (Fig. 1) mounted inside an Ar dry box. described below. Typically, 3–5 ml of viscous solution were loaded into the extruder chamber, and fibers were then extruded by applying Increasing PMS molecular weight. The reaction vessel om 100–500 psi Ar pressure to force the polymer through a above, containing ca. 25 g PMS was taken into the dry box 140 mm diameter spinneret. These extruded fibers continuously and the residual gases vented.A sample (ca. 5 ml ) was self-draw at 20–40 cm below the spinneret. Longer fibers could transferred in the dry box to a sealed, 50 ml Schenk flask and not be drawn due to dry box height limitations. Precursor heated under Ar at 60 °C until gelation occurred. Gelation fibers with 70–120 mm diameter collected across a square times were typically 7–12 h.The remaining polymer solution wooden framework with a spacing of ca. 10 cm. The fiber was then transferred into Schlenk flasks in the dry box. The diameters are not uniform because of the crude spinning sealed flasks were removed from the dry box and heated at system. In some cases, thin 30 mm diameter fibers were 60 °C (Ar) to increase the molecular weight (MW).Heating obtained. The extruded fibers were dried for at least 5 h prior was stopped after a period equivalent to 80–90% of the gel to pyrolysis. time and the solutions were stored below 0 °C. 4 Curing Star-branched polymers via vinyl modification. To further Unmodified Harrod PMS fibers melts on heating. To avoid increase the MW to improve spinnability, and to provide melting, eVorts were made to cure precursor fibers.The functionality for self-curing, PMS was modified by reaction methods examined included: (1) low temperature thermal with tetravinylsilane (TVS), Si(CHNCH2)4, 1,3,5-trimethylcures; (2) curing with traces of ammonia; (3) curing with c- 1,3,5-trivinylcyclotrisilazane [SiMe(CHNCH2)NH]3, or irradiation, and (4) curing by incorporating reactive func- dimethyldivinylsilane SiMe2(CHNCH2)2. 5–20 wt.% of these tionality.Only the last method, based on bringing the polymer compounds were added to PMS solutions brought to 80–90% close to its gelation point and then adding thermally reactive of their gelation time. The weight percentage added was based on: (MeSiH3reacted+additive)=100 wt.%. For example, 48.8 g (1.06 mol) MeSiH3 was polymerized to give 214 ml (PMS+solvent) solution.Therefore, a 30 ml portion of this solution consumed 6.84 g (0.15 mol) MeSiH3. Addition of 0.36 g (2.6 mmol), 0.76 g (5.6 mmol), or 1.71 g (12.5 mmol) TVS to a 30 mL portion of PMS solution results in 5, 10 and 20 wt.% vinylsilane-PMS solutions respectively. After adding the vinyl compounds, the PMS solutions were again heated at 60 °C (Ar, 12–24 h) to form branched, vinylmodified PMS (discussed below).After vinylsilane modifi- cation, the resulting PMS solution is stable and can be stored at room temperature for >3 d. Most research focused on TVS modified PMS solutions (TVS-PMS), to avoid incorporating N into the resulting SiC fibers. Boron modified TVS-PMS. Boron was incorporated into PMS by hydroboration of the residual vinyl groups in TVSPMS, resulting in B- and TVS-modified PMS (B-TVS-PMS).Several B additives were tested including Me2S·BH3, THF·BH3, NH3 ·BH3, Me3 N·BH3 and C4H9N2·BH3. Only Me2S·BH3 reacted with TVS-PMS to provide clear, spinnable Fig. 1 Schematic diagram of a pressure extruder made from standard swagelock fittings. solutions. J. Mater. Chem., 1998, 8, 2715–2724 2717vinyl functionality really worked.In this instance, no inter- were 5–80° 2h in 0.01° increments with a 2° 2h min-1 scan speed. Cu-Ka (l=1.54 A° ) radiation was used. mediate curing stages or green fiber pretreatments were necessary as the fibers cured even with heat ramp rates up to 20 °Cmin-1. Scanning electron microscopy (SEM). Micrographs were taken on a HITACHI S-800 microscope.SEM samples were 5 Pyrolysis prepared by breaking fibers into small segments and mounting them on the edge of an aluminum stub using double stick Precursor fibers were pyrolyzed in Ar to transform them into tape. Samples were sputter coated with a layer of Au/Pd to ceramic fibers. All pyrolysis steps below 1400 °C were carried enhance their conductivity.Micrographs of fresh fracture out in a single zone, Lindberg tube furnace (model No. 58114, surfaces were recorded to evaluate fiber microstructure. Watertown, WI) or a Thermolyne high temperature tube furnace (type 54500, Dubuque, IA). Both tube furnaces are Results and discussion equipped with Eurotherm temperature controllers (model No. 818P, Northing, England). The heating rates used were 1 Modification of PMS 5–20 °Cmin-1.Thinner fibers were cured at 20 °Cmin-1 without loss of fiber integrity. Harrod PMS typically has Mn=1000–2000 Da.12 NMR spec- Pyrolyses above 1400 °C were run in an Astro high tempera- tra provide some information on polymer structure.4,14 The ture furnace (Model 1000). All samples pyrolyzed to>1400 °C PMS 1H NMR (Fig. 2) shows only two broad PMS resonances were first pyrolyzed to 1000 °C in a Lindberg furnace, under for Si–H (3.87 ppm) and C–H (0.39 ppm); the remainder result Ar.Samples were transferred to the Astro high temperature from residual cyclohexene, cyclohexane and C6D6. The 13C furnace under ambient conditions. The Astro furnace consists NMR shows one broad Si–CH3 peak at 9.7 ppm. The 29Si of a Eurotherm temperature controller (model No. 818P, MAS spectrum exhibits resonances at -34.0 and -63.0 ppm, Northing, England), a vacuum pump, and an Ar–N2 supply. Two vacuum/Ar fill cycles were applied before starting heattreatment to ensure elimination of O2/moisture in the furnace. Samples were then heated above 1400 °C at 20–30°Cmin-1 under flowing Ar. 6 Materials characterization Thermogravimetric analyses (TGA).TGA studies of PMS precursor were carried out using a Hi-Res TGA 2950 Thermogravimetric TA Instruments Thermal Analyst 2200. Samples of 10–30 mg (chunks) were removed from the drybox and quickly placed in a Pt pan in air. The time required to load the samples was 3–5 min. Samples were then heated (10 °Cmin-1) to 1000 °C in Ar (60 cm3 min-1). DiVerential thermal analyses (DTA). DTA experiments were conducted on a DSC 2910 diVerential scanning calorimeter, with a 1600 °C DTA cell, TA Instruments Thermal Analyst 2200.Samples (10–15 mg) were removed from the drybox and quickly loaded in a Pt pan in air. The loading time was 3–5 min. Samples were heated at 5 °Cmin-1 to 1000 °C in Ar (50 cm3 min-1). Calcined alumina (Aluminum Co.of America) was used as the reference material. NMR characterization. All solution spectra were run in CDCl3 and recorded on a Bruker AM 360 MHz instrument at room temperature unless otherwise noted. Residual CHCl3 was used as an internal reference. 1H, 13C and 29Si NMR spectra were obtained with the spectrometer operating at 360, 90.6 and 71.5 MHz, respectively. Spin rates of 20 and 14 rps were used for 5 mm and 10 mm tubes respectively. 1H NMR spectra were obtained using a 4000 Hz spectral width, an acquisition time of 4.096 s and 32 K data points. 13C NMR spectra were obtained using a 20 000 Hz spectral width, an acquisition time of 0.8192 s and 32 K data points. 29Si NMR spectra were obtained using an inverse gated technique, a 20 000 Hz spectral width, an acquisition time of 0.819 s, a delay between pulses of 5–10 s and 32 K data points.Chemical analyses. Elemental analyses for selected pyrolyzed samples were performed by Galbraith Laboratories of Knoxville, TN. X-Ray diVraction ( XRD). XRD powder patterns were obtained using a Rigaku Rotating Anode Goniometer (Rigaku Denki Co. Ltd., Tokyo, Japan). Powder samples (100–200 mg) Fig. 2 (a) 1H NMR of polymethylsilane polymer synthesized via the were ground in an alumina mortar and pestle, packed in a Harrod procedure. (b) 1H NMR of 20 wt.% TVS-PMS. (c) Vinyl region of (b) expanded. glass specimen holder, and placed in the goniometer. Scans 2718 J. Mater. Chem., 1998, 8, 2715–2724corresponding to –MeSiH– units and –MeSiH2 groups respectively.14 The broad resonances indicate that the magnetic environments around H and C are not unique, suggesting branching.The OSi–CH35Si–H integration ratio in the 1H NMR spectrum is 4.5:1 rather than 351, supporting a branched structure containing cyclics. Assuming Mn=1–1.2 kDa, we can propose Fig. 3 Idealized molecular structure for PMS. an idealized PMS composition as shown in Fig. 3. In related studies that will be described in a following paper,15 we have react.If terminal –MeSiH2 groups are the most reactive Si–H identified (by mass spectral analysis) branched cyclics similar sites12 then TVS most likely reacts with these groups to form to: vinyl-capped PMS. This implies that MeSiH2 groups also cause gelation. Thus, endcapping should reduce or eliminate gelation. Indeed, following reaction with vinylsilanes, the system is stable at ambient for days to weeks without gelation.Because one TVS can react with up to four PMS molecules to form a star-branched polymer, the MW of PMS could increase as much as fourfold as suggested in Fig. 4. Initial eVorts to produce high quality SiC fibers from TVS-PMS were unsuccessful because the desired final microstructure was not obtained, as discussed below.Thus eVorts were made to introduce boron to the precursor synthesis. Small amounts of B are known to aid SiC densification during sintering.20–24 Several B containing organosilicon polymers have been synthesized.25–27 Riccitiello and coworkers25,26 and Riedel et al.27 describe reacting BH3 adducts with vinyl modified poly(diorganosilane)s to form B containing polymers.TVS-PMS is an end-functionalized oligomethylsilane (Fig. 4). However, the vinyl groups in TVS-PMS can also react with BH3 adducts, especially in the presence of catalysts, The composition shown in Fig. 3 is proposed based on the as in the TVS-PMS solution: structure shown above.15 The implication is that dehydrocoupling occurs at both chain terminating –MeSiH2 and backbone –MeSiH– groups.The formation of one tertiary Si for every three silicons suggests that the reactivity of the internal Si–H groups is (Si CH CH2)n (Si CH2 CH2 B )n BH3-adducts Cp2ZrMe2 (5) almost as high as found for the chain ends. However, dehydrocyclization is likely much favored over chain growth because This results in the formation of more complex, hyper-branched it is a unimolecular process whereas the latter is bimolecular.molecules (Fig. 5). The BH3 adduct used is (Me)2S·BH3. The implication is that the chain termini (–MeSiH2 groups) (Me)2S·BH3 and TVS are added simultaneously to a solution are much more reactive than internal Si–H groups as previously of Harrod PMS previously heated to 80–90% of its gel point. suggested by Harrod et al.12,14 One BH3 is potentially capable of reacting with three Si–vinyl The low MW polymer obtained from the Harrod procedure groups and should increase the MW and polymer viscosity as is an obstacle to fiber spinning.It is diYcult to increase MW shown by Riedel et al.27 Indeed, we have reversed engineered by simply extending the dehydropolymerization reaction time B-TVS-PMS (PMS-TVS-B) by first forming TVS-B and then because gelation occurs readily.However, stable PMS soluhydrosilylating this material with PMS to form essentially the tions can be obtained by vinyl modification of Harrod PMS. identical polymer.15 This more air stable version exhibits the Vinylsilanes react with PMS via reaction (4). Hydrosilylation GPC trace shown in Fig. 6 which supports the structure occurs thermally at 150–200 °C;10,18 however, in our system it proposed in Fig. 5; note the expected polymodality of a hyper- occurs at <60 °C most likely aided by a Cp2ZrMe2 derived branched polymer shown in Fig. 6. catalyst. The critical issues are whether or not these modifications impart spinnability, curability and sinterability, as discussed below.The 1H NMR spectrum shows no significant change in the Si–H5Si–CH3 ratio on adding TVS,19 suggesting that only a Fig. 4 Proposed molecular structure of TVS-PMS. small percentage of the Si–H bonds (e.g. –MeSiH2 groups) J. Mater. Chem., 1998, 8, 2715–2724 2719polymer for catalyst. Depolymerization was assumed to play a minor role in the reaction sequence. After venting, the polymer was reheated at 60 °C for 5–10 h under Ar to increase the MW.The solutions were brought to 80–90% of the gel time. The resulting PMS solutions, containing 0.6–0.8 g mL-1 upon partial solvent removal, were suitable for dry-spinning, although the resulting fibers were not infusible. Fig. 7 shows an SEM for a typical precursor fiber with a smooth surface and a dense interior without visible microstructure.The irregular cross-section, typical of dry-spun fibers, is due to uneven drying. Although this procedure provides improved spinnability, the fibers still melt at 100 °C. Further heating led to increased MWs; however, gels formed rapidly with loss of processability. Thus, two diVerent chemical approaches to improving infusibility, without impairing processability, were explored.One was to increase theMWlinearly to increase chain entanglement thereby improving spinnability and raising Tm above the curing point (Tc) to provide polymer infusibility. The other was to introduce reactive functional groups into the polymer structure to provide higher latent reactivity. To achieve these goals, multifunctional vinylsilanes were incorporated into the precursor synthesis.Multifunctional vinylsilanes are capable of linearly linking two or more PMS molecules together, by reaction with terminal –MeSiH2 groups, as discussed above. Linear increases in MW, obtained with divinyldimethylsilane provided better rheological properties as Fig. 5 Proposed B-TVS-PMS molecular structure. evidenced by a reduction in fiber necking during spinning; however, the fibers still melted.In contrast, the addition of tri- and tetra-vinyl functionalized silanes provided improved spinnability, and remaining unreacted vinyl groups provide sites for further branching with BH3 and higher latent reactivity to enhance polymer self-curing. Note that in all cases mentioned here, the increases in MW are assumed to occur as a consequence of the type of chemistry used; however the pyrophoric nature of the polymers produced precluded conducting MW measurements using standard techniques.A future paper will present more details about the development of higherMWPMS using a much less air sensitive derivative.15 The utility of adding vinylsilanes to increase MW is strongly dependent on the length of PMS segments linked.If vinylsilane addition occurs too early, many reactive Si–H sites are elimin- Fig. 6 GPC Trace of reverse engineered PMS and PMS-TVS-B.15 2 Precursor fiber spinning Melt-drawing was initially examined using unmodified PMS. While PMS melts and fibers can be drawn from the melt, the melted polymer crosslinks too rapidly to be considered for long term studies. Extensive eVorts were made to cure these fibers, using a variety of processes, without success. EVorts then focused on the developing stable, spinnable, and infusible polymers for dry-spinning.Toreki et al. find that Yajima PCS with molecular weights (MWs) of 5–10 kDa decomposes before it melts. Although it no longer melts, toluene solutions can be dry-spun.5 Furthermore, because it does not melt, air curing is not necessary and low oxygen content fibers result, although excess C remains a problem.Thus, eVorts were made to increase the PMS Mn to >5000 Da. Initially, eVorts were made to extend the duration of dehydrocoupling to improve PMS MWs. To increase catalyst eYciency for chain extension, residual MeSiH3 and H2 were vented, after completion of the Harrod procedure, to ensure Fig. 7 SEM of an as-spun PMS precursor fiber. that residual monomer (MeSiH3) would not compete with 2720 J. Mater. Chem., 1998, 8, 2715–2724ated at an early stage and only short chain segments are linked principle, vinyl groups that survive the incorporation process [see Fig. 2(b)] provide the requisite latent reactivity such that together. This limits the MW increases possible and impairs the processability/infusibility.For example, the addition of fiber melting no longer occurs (see below). Fig. 2(b) shows that addition of ca. 20 wt.% TVS (ca. TVS to PMS heated to <50% of the gel time did not give spinnable materials even after all the solvent was removed. 26 mol% vinyl groups) to PMS solutions provides access to vinyl-modified PMS.Fibers spun from this modified precursor, The PMS chains, before vinyl modification, were too short. This led us to add vinylsilane only at 80–90% of the gel time. TVS-PMS, were infusible. However, PMS modified with 20 wt.% Me2Si(CHNCH2)2 (ca. 17 mol% vinyl groups) still After a thorough evaluation of di- and tri-functional vinyl compounds (see Experimental section), TVS was selected for melts.One explanation is that precursor infusibility comes not only from amounts of added vinyl groups, but also from further extensive studies. TVS contains the excess carbon needed to oVset the excess silicon produced during pyrolysis macromolecular architecture. Each TVS is potentially capable of linking four PMS chains to form a star branched polymer and no nitrogen.In principle, TVS oVers the opportunity to improve spinnability by increasing the MW (therefore chain whereas Me2Si(CHNCH2)2 can only increase the PMS MW by extending the chain in one dimension to form a new, linear entanglements), and because it oVers latent reactivity which enhances self-curing. Furthermore, because it appears to cap molecular structure. The linear molecular structure may provide insuYcient chain entanglement to achieve infusibility.reactive –MeSiH2 endgroups, it stabilizes the spinning solution. Finally, B-TVS-PMS displays even better spinnability (evi- The importance of molecular architecture on curability is further supported by the fact that addition of 20 wt.% denced by the absence of necking during spinning) than TVSPMS, likely because the higher degree of branching and higher [SiMe(CHNCH2)NH]3 (ca. 11 mol% vinyl groups) also provides infusible precursor fibers. This result may arise because MW provide better chain entanglement leading to better viscoelastic properties. [SiMe(CHNCH2)NH]3, with one more vinyl group than SiMe2(CHNCH2)2, can potentially link three PMS chains to The only drawback that remains is the high degree of air sensitivity as illustrated by Fig. 8 which shows the TGA of B- form a star-branched polymer thereby providing suYcient entanglement to aid in spinning and curing.For the reasons TVS-PMS precursor fibers held at 30 °C for 24 h in dry air. The fibers exhibit a mass gain of ca. 30 wt.%, indicating mentioned above, TVS was found to be the best choice for further processing studies.extensive oxidation. This oxidation sensitivity impairs the opportunity to obtain phase pure SiC fibers unless the fibers As discussed below, pyrolysis of unmodified PMS gives a mixture of SiC and excess Si. Using TVS to modify PMS are processed in an inert atmosphere. compensates for the carbon loss by introducing additional carbon content. However, the correct balance between carbon 3 Curing unmodified PMS fibers loss and introduction must be identified to produce phase pure Before precursor fibers are subjected to high temperature SiC fibers.Fortunately, 5 wt.% TVS provides infusible PMS pyrolytic processing, they must be made infusible (cured/ precursor fibers as eVectively as 20 wt.%. This result permits crosslinked) so they will not melt on heating.Prior to our selection of an optimal quantity of TVS to produce stoichiodiscovery of the utility of vinyl-modified PMS, several curing metric SiC. studies were run on unmodified PMS fibers, including the use of low temperature long term pyrolyses, curing with traces of 5 Pyrolysis ammonia,29–31 c-irradiation32–34 and by using an excess of catalyst.10,35 None of these methods proved particularly useful, After curing, the subsequent step is pyrolytic conversion of the precursor fibers to SiC fibers.In the following section, and eVorts turned to enhancing chemical reactivity using vinyl compounds. studies on bulk pyrolytic processing of precursors using thermogravimetric analyses (TGA), diVerential thermal analyses (DTA) and powder X-ray diVraction (XRD) are discussed. 4 Curing of vinyl-modified PMS fibers Scanning electronic microscopy and chemical analysis data on Schmidt et al.36 showed that on thermolysis, vinylic polysilanes SiC fibers will also be described. heated at low temperatures generate R3Si· free radicals solely by scission of Si–Si bonds. These free radicals promote Si–H Thermogravimetric analyses (TGA) of unmodified PMS and addition across CNC double bonds (hydrosilylation) which TVS-PMS leads to crosslinking.In related work, Seyferth et al. showed that radical initiated hydrosilylative crosslinking gave Fig. 9 shows the TGA curves for PMS with selected amounts of added TVS. Both unmodified PMS and TVS-PMS precur- improved PMS ceramic yields.10,11 These results, coupled with our inability to cure unmodified PMS, led to PMS synthetic sors have higher ceramic yields (79 and 83 wt.% respectively) than typical Yajima PCS (55 wt.%).1–4 strategies that incorporated multifunctional vinyl silanes.In Fig. 9 TGAs of batches of PMS with selected amounts of TVS added. Fig. 8 TGA of TVS-PMS precursor fibers (10 wt.% TVS added) isothermed at 30 °C in dry air for 24 h.Samples were heated at 10 °Cmin-1 to 1000 °C in Ar. J. Mater. Chem., 1998, 8, 2715–2724 2721Unmodified PMS has a 151 Si5C ratio. Ideally, H2 will be the only gaseous species released during pyrolysis and the 151 Si5C stoichiometry will be retained after pyrolysis. The theoretical ceramic yield for linear, unmodified –[MeSiH]x– is 90.9 wt.%. Branched structures, e.g., –[MeSiH]x[MeSi]y–, will have slightly higher ceramic yields.However, TGAs of diVerent batches of unmodified PMS gave ceramic yields ranging from 61 to 79 wt.% (Fig. 9) indicating some loss of C and/or Si occurs concurrent with release of H2. The TGA profiles of PMS and TVS-PMS (Fig. 9) reveal several stages of mass loss. Stage 1: below 200 °C, the mass loss is insignificant (<3 wt.%), indicating good stability to this temperature.The observed mass loss is likely due to volatile low MW species. Stage 2: in the 200–400 °C range unmodified PMS undergoes mass losses in the range 13–30 wt.%, indicating that primary decomposition processes take place in this range and/or low molecular weight cyclics volatilize. Kobayashi et al. observe release of MeSiH3 in this range.13 They suggest that MeSiH3 Fig. 10 DTAs of PMS with selected amounts of TVS added. Samples were heated at 10 °Cmin-1 to 1000 °C in Ar. forms by cleavage of terminal –MeSiH2 groups. Low MW, short chain and/or branched polymers will have more terminal groups than high MW, long chain, linear polymers or species containing cyclic structures. The mass loss ranges for Harrod indicate a multitude of events that are discussed as for the TGA studies.PMS batches vary considerably depending on the reaction conditions, storage time after synthesis and solution concen- Stage 1: below 200 °C, unmodified PMS exhibits a slight endotherm, likely due to volatilization of low MW species, or tration because reaction continues under ambient conditions. TVS-PMS has smaller, quite consistent mass losses residual solvent.The TVS-PMS precursors exhibit an exotherm at low temperatures (50–150 °C) not seen for unmodified (7–10 wt.%), implying that TVS modification provides a more stabile PMS with a well defined MW and architecture. By PMS. This exotherm is ascribed to thermally promoted hydrosilylative crosslinking of remaining vinyl groups. Schmidt heating TBS-PMS to 50–150 °C, retained vinyl groups will react with remaining –MeSiH2 groups, and internal Si–H sites et al.36 and Schilling37 observed similar exotherms at 150–300 °C for such processes.The lower temperature range to crosslink the polymer. This process, seen in the DTA (below), ties up terminal –MeSiH2 groups increasing ceramic observed here is probably due to the presence of active catalyst.Stage 2: between 200 and 400 °C, a broad exotherm appears yield and coincidentally reducing gas evolution related defects in the resulting ceramic fibers. TVA-PMS also appears to in the DTA of the unmodified PMS. This transition could result from a decomposition reaction that involves cleavage of undergo Kumada rearrangement [reaction (6)] as discussed below.terminal –MeSiH2 groups, with simultaneous coupling of the resulting fragments, and evolution of MeSiH3, as proposed Stage 3: in the 400–600 °C range, unmodified PMS undergoes Kumada rearrangement (as seen by FTIR and by Kobayashi et al.13 who report the release of H2 at this stage indicating that dehydrocoupling continues with heating. NMR studies)14,15 and loses 7–8 wt.%. The mass loss in this temperature range is ascribed to release of CH4 and H2 per A similar exotherm is not observed in the DTAs of TVS-PMS precursors.The probable reason is that loss of –MeSiH2 Kobayashi et al.13 groups is minimized by crosslinking as discussed above and as supported by TGA results which show only minor mass losses for TVS-PMS in the 200–300 °C range compared to unmodified PMS.An exotherm for the TVS-PMS precursors is seen in the 300–450 °C region. Similar exotherms are also observed by Schmidt et al.36 and Schilling37 in DTAs of vinyl-substituted polysilane decomposition. The exact source of this exotherm is not clear at this point, but may be associated with the Kumada rearrangement, see below. Stage 3: between 400 and 500 °C, a strong exotherm appears in the DTA for unmodified PMS.IR and 29Si solid state NMR indicate that the Kumada rearrangement occurs in this temperature range.14,15 The Kumada rearrangement also occurs in TVS-PMS, as shown by DRIFTS studies.38 However, the TVS-PMS DTA does not show the same strong, sharp exotherm. It seems that the PMS to PCS transition exotherm shifts to lower temperature, and is partially hidden by an exotherm ascribed to loss of CH4 and H2.If this is in fact the case, then it is possible that the two events occur simul- Stage 4: in the 600–1000 °C range, only minor mass loss taneously. Another possibility is that free radicals generated (<2 wt.%) is observed, likely due to H2 evolution (see during thermally promoted hydrosilylative crosslinking pro- DRIFTS below).mote the PMS to PCS transition. More detailed studies are The TGA profile of 10 wt.% TVS-PMS precursor fibers is required to understand the exact source of these transitions very similar to that of the bulk material. and exotherms. Stage 4: the DTAs for unmodified PMS and TVS-PMS DTAs of unmodified PMS and TVS-PMS precursors show broad exotherms between 600 and 900 °C.These exotherms most likely result from H2 evolution, accord- DTAs (Ar) or PMS precursors with selected amounts of added TVS are shown in Fig. 10. As can be seen, the DTA profiles ing to the studies of Kobayashi et al.13 and hydrogenated SiC 2722 J. Mater. Chem., 1998, 8, 2715–2724results. The relatively sharp peaks at 900 °C result from however, densities increase slightly to 2.5 g cm-3.It is only on processing these fibers to higher temperatures that significant crystallization of SiC, as supported by solid state NMR, DRIFTS and XRD studies.14,18,38 changes occur. These changes and fiber mechanical properties are the subject of the next paper in this series. In future papers, we will describe the synthesis of a more air stable precursor,39 Powder X-ray diVraction ( XRD) of unmodified PMS and TVS– PMS the use of PMS for joining applications40 and for the manufacture of particle and fiber reinforced composites.41,42 In stages 1–4 (pyrolysis 800 °C), the XRD patterns of unmodified PMS and TVS-PMS exhibit amorphous features. No defined diVraction peaks can be observed in XRDs of Conclusions samples heated to <800 °C.Samples heated to 1000 °C (not Extensive eVorts were made to learn to modify polymethylsil- shown) show three broad peaks at 2h#35, 60 and 72° correane (PMS) produced directly by dehydrocoupling of MeSiH3 sponding to the (111), (220) and (311) peaks of b-SiC, and to obtain spinnable polymers. It was determined that careful indicating crystallization occurs at 1000 °C. control of the polymerization reaction conditions provided access to a branched version of PMS that exhibits viscoelastic Chemical analyses of TVS-PMS derived SiC properties that just permit it to be spun.Unfortunately, the Chemical analyses show that pyrolysis of unmodified PMS to spun fibers do not survive pyrolysis to give SiC ceramic fibers. 1000 °C (1 h, Ar) produces a material containing ca. 72.4 wt.% Furthermore, the as-synthesized PMS is highly flammable. Si, 25.4 wt.% C and trace amounts of H, indicating the The addition of chain extending/branching molecular addipresence of excess Si (Si5C=1.2251). Adding TVS permits tives containing tri- and preferably tetra-vinyl functionality, balancing the carbon loss, thus chemical analysis of 10 wt.% prior to the PMS gel point, provides access to higher molecular TVS-PMS produces a material with 68.9 wt.% Si and 31.4 wt.% weight, highly branched materials with improved viscoelastic C (Si5 C=151.06), after pyrolysis to 1000 °C (1 h, Ar).properties such that improvements in spinning are attained Chemical analysis of 1000 °C pyrolyzed fibers derived from with increased resistance to oxidation. The latter appears to this TVS-PMS gives 69.7 wt.% Si and 29.0 wt.% C (Si5C= result from capping of residual Si–H groups that are more 1.0351).Therefore, careful control of the amount of added susceptible to oxidation. Furthermore, the added vinyl com- TVS leads to near-stoichiometric SiC fibers. pounds provide reactive sites that promote thermal crosslinking and decomposition of the spun fibers before they melt.Scanning electron microscopy (SEM) of TVS-PMS/B-TVS- Finally, by controlling the amounts of additives, it is possible PMS derived SiC fibers to adjust the stoichiometry of the resulting ceramic fiber from silicon rich, to exactly stoichiometric SiC, to carbon rich fibers. Fig. 11 shows a SEM micrograph of a 10 wt.% TVS-PMS The results of these studies have suggested a new way to precursor fiber heated to 1000 °C.The fibers exhibit dense prepare related spinnable precursors that are even less air interiors and surfaces; however, at this point the fibers are sensitive and permit processing in air.41,42 nanocrystalline (2–4 nm size crystallites) and have densities (2.3 g cm-3) that are much lower than theory (3.2 g cm-3). Heating to temperatures of up to 1800 °C leads to densification Acknowledgements to ca. 3.1 g cm-3.28 SiC produced from B-TVS-PMS (0.04 wt.% B after pyrol- The authors would like to thank the Army Research ysis) behaves identically to TVS-PMS derived SiC up to Laboratories for generous support of this work through con- 1000 °C. No changes are observed by any of the analytical tract No. DOD-C-DAAL04-91-C-0068.techniques used above. Likewise fibers produced using B-TVSPMS are essentially identical to those produced without B; References 1 (a) S. Yajima, K. Okamura, J. Hayashi and M. Omori, J. Am. Ceram. Soc., 1976, 59, 324; (b) S. Yajima, J. Hayashi, M. Omori and K. Okamura, Nature, 1976, 261, 683; (c) S. Yajima, T. Shishido and H. Kayano, Nature, 1978, 273, 525; (d) S.Yajima, Y. Hasegawa, J. Hayashi and M. Iimura, J. Mater. Sci., 1978, 13, 2569; (e) Y. Hasegawa, M. Iimura and S. Yajima, J. Mater. Sci., 1980, 15, 720; ( f ) Y. Hasegawa and K. Okamura, J. Mater. Sci., 1980, 18, 3633. 2 (a) T. Yamamura, T. Ishikawa, M. Shibuya and T. Hisayuki, J. Mater. Sci., 1988, 23, 2589; (b) C. Y. Song, Y. Hasegawa, S-J. Yang and M. Sato, J. Mater. Sci., 1988, 23, 1911. 3 (a) R. M. Laine and F. Babonneau, Chem. Mater., 1993, 5, 260; (b)M. Birot, J.-P. Pillot and J. Dunogues, Chem. Rev., 1995, 1443; (c) K. J. Wynne and R. W. Rice, Annu. Rev. Mater. Sci., 1984, 14, 297; (d) R. R. Wills, R. A. Markle and S. P. Mukherjee, Ceram. Bull., 1983, 62, 904; (e) R. H. Baney and G. Chandra, in Encyclopaedia of Polymer Science and Engineering, J. Wiley and Sons, New York, 1988, vol. 13, pp. 312–44; (e) J. Bill and F. Aldinger, Adv. Mater., 1995, 7, 775; ( f ) W. Toreki, Polym. News, 1991, 16, 6; (g) G. Pouskouleli, Ceram. Int., 1989, 15, 213. 4 R.M. Laine and A. Sellinger, Si-containing ceramic precursors, in The Chemistry or Organic Silicon Compounds, ed. Z. Rappoport and Y. Apeloig, J. Wiley & Sons, London, 1998, vol. 2, pp. 2245–310. 5 See, for example: (a) W. Toreki, C. D. Batich, M. D. Sacks, M. Saleem, G. Choi and A. A. Morrone, Comput. Sci. Technol., 1994, 51, 145; (b) W. Toreki, G. J. Choi, C. D. Batich, M. D. Sacks and M. Saleem, Ceram. Eng. Sci. Proc. (July–August 1992, Cocoa Fig. 11 SEM micrograph of a TVS-PMS fiber (10 wt.% of TVS added) Beach, FL), 1992, pp. 198–208. 6 See, for example: M. D. Sacks, G.W. ScheiVele, M. Saleem, G. A. heated to 1000 °C for 1 h in Ar. J. Mater. Chem., 1998, 8, 2715–2724 2723Staab, A. A. Morrone and T. J. Williams, Mater. Res. Soc. Symp. 20 S. Prochazka and R. M. Scanlan, J. Am. Ceram. Soc., 1975, 58, 72. 21 S. Prochazka, Ceramics for High-Performance Applications, ed. Proc., 1995, 365, 3. 7 J. A. Rabe, J. Lipowitz and P. P. Lu, US Pat., 5 051 215, Sept.J. J. Burke, A. E. Gorum and R. N. Katz, Book Hill, Chestnut Hill, MA, 1974, p. 239. 1991. 8 D. C. Deleeuw, J. Lipowitz and P. P. Lu, US Pat., 5 071 600, 22 K. M. Friederich and R. L. Coble, J. Am. Ceram. Soc., 1983, 66, C141. Dec. 1991. 9 J. Lipowitz, J. A. Rabe and G. A. Zank, Ceram. Eng. Sci. Proc., 23 C. Greskovich and J. H. Rosolowski, J. Am. Ceram. Soc., 1975, 59, 336. 1991, 12, 1819. 10 (a) D. Seyferth, T. G.Wood, H. J. Tracy and J. L. Robison, J. Am. 24 J. E. Lane, C. H. Carter, Jr. and R. E. Davis, J. Am. Ceram. Soc., 1988, 71, 281. Ceram. Soc., 1992, 75, 1300; (b) D. Seyferth, H. J. Tracy and J. L. Robison, US Pat., 5 204 380, 1993; (c) D. Seyferth and Y-F. Yu, 25 M. T. S. Hsu, S. R. Riccitiello, T. S. Chen and R. Salvatore, J. Appl. Polym.Soc., 1991, 42, 851. Design of New Materials, ed. D. L. Cocke and A. Clearfield, Plenum Press, New York, 1987, p. 79. 26 S. R. Riccitiello, M. T. S. Hsu and T. S. Chen, US Pat., 4 987 201, January 1991. 11 D. Seyferth and H. Lang, Organometallics, 1991, 10, 551. 27 R. Riedel, A. Kienzle, V. Szabo and J. Mayer, J. Mater. Sci., 1993, 12 (a) Y. Mu and J. F. Harrod, in Inorganic and Organometallic 28, 3931.Oligomers and Polymers, IUPAC 33rd Symp. Macromol., ed. J. F. 28 (a) Z-F. Zhang, F. Babonneau and R. M. Laine, manuscript in Harrod and R. M. Laine, Kluwer Publ., Dordrecht, 1991, p. 23; preparation; (b) Z-F. Zhang, S. Scotto and R. M. Laine, in Mater. (b) J. F. Harrod, in Inorganic and Organometallic Polymers with Res. Soc. Symp. Proc. (Covalent Ceramics II: Non-oxides), ed.R. Special Properties, ed. R. M. Laine, NATO ASI Ser. E, vol. 206, Gottschalk, 1994, vol. 327, pp. 207–23. Kluwer Publ., Dordrecht, 1991, p. 87; (c) X. Xin, C. Aitken, J. F. 29 R. J. P. Corriu, D. Leclercq, P. H. Mutin and A. Vioux, Chem. Harrod and Y. Mu, Can. J. Chem., 1990, 68, 471; (d) H. Q. Liu Mater., 1992, 4, 711. and J. F. Harrod, Organometallics, 1992, 11, 822; (e) J. He, Q. Liu, 30 K. Okamura, M. Sato and Y. Hasegawa, Ceram. Int., 1987, 13, 55. J. F. Harrod and R. Hynes, Organometallics, 1994, 13, 336. 31 G. Burns and G. Chandra, J. Am. Ceram. Soc., 1989, 72, 333. 13 T. Kobayashi, T. Sakakura, T. Hayashi, M. Yumura and 32 P-E. Sundell, S. Jonsson and A. Hult, Radiation of curing of poly- M. Tanaka, Chem. Lett., 1992, 1157. meric materials, ACS Symp. Ser. vol. 417, ed. C. E. Hoyle and 14 (a) Z.-F. Zhang, F. Babonneau, R. M. Laine, Y. Mu, J. F. Harrod J. F. Kinstle, Am Chem. Soc.,Washington DC, 1990, pp. 459–73. and J. A. Rahn, J. Am. Ceram. Soc., 1990, 74, 670; (b) Z-F. Zhang, 33 K. Okamura, T. Matsuzawa and Y. Hasegawa, J. Mater. Sci., Y. Mu, R. M. Laine, F. Babonneau, J. F. Harrod and J. A. Rahn, 1990, 4, 55. Inorganic and Organometallic Oligomers and Polymers, IUPAC 34 M. Takamizawa, T. Kobayashi and A. Hayashida, US Pat., 33rd Symp. Macromol., ed. J. F. Harrod, R. M. Laine, Kluwer 4 604 367, August 1986. Publ., Dordrecht, 1991, pp. 127–146. 35 D. Seyferth, C. A. Sobon and J. Borm, New J. Chem., 1990, 15 (a) R. M. Laine, A. Sellinger and K. W. Chew, US Pat. pending; 14, 545. (b) A. Sellinger, Ph.D. dissertation March, 1997; (c) A. Sellinger 36 W. R. Schmidt, L. V. Interrante, R. H. Doremus, T. K. Trout, and R. M. Laine, manuscript in preparation. P. S. Marchetti and G. E. Maciel, Chem.Mater., 1991, 3, 257. 16 (a) E. Hengge, M. Weinberger and Ch. Jammegg, J Organomet. 37 C. L. Schilling Jr., Br. Polym. J., 1986, 18, 355. Chem., 1991, 410, C1; (b) E. Hengge, Organosilicon Chem. II, 38 Z-F. Zhang, Ph.D. Dissertation, Univ. of Michigan, 1995. 1996, 2, 275; (c) E. Hengge and M. Weinberger, J. Organomet. 39 A. Sellinger and R. M. Laine, manuscript in preparation. Chem., 1992, 433, 21. 40 D. R. Treadwell, R. M. Laine and R. Burzynski, to be submitted. 17 R. M. Laine, K. A. Youngdahl, F. Babonneau, J. F. Harrod, 41 K. W. Chew and R. M. Laine, J. Am. Ceram. Soc., in press. M. L. Hoppe and J. A. Rahn, Chem.Mater., 1990, 2, 464. 42 K. W. Chew, M. Nechanicki and R. M. Laine, submitted. 18 B. Boury, R. J. P. Corriu and W. E. Douglas, Chem.Mater., 1991, 3, 487. 19 C. S. Scotto, A. Sellinger and R. M. Laine, unpublished work. Paper 8/05288C 2724 J. Mater. Chem., 1998, 8, 2715–2724

ISSN:0959-9428    

DOI:10.1039/a805288c

出版商:RSC    

年代:1998

数据来源: RSC

摘要:

J O U R N A L O F C H E M I S T R Y Materials Balloon-shaped graphitic-carbon material induced by shockcompression of dehydrochlorinated poly(vinylidene chloride) Tamikuni Komatsu*a and Miho Samejimab aNational Institute of Materials and Chemical Research, High Density Energy Laboratory 1-1 Higashi, Tsukuba-shi, Ibaraki 305, Japan bExplosive Research Laboratory, Asahi Chemical Industry Co., Ltd., 304 Mizushiri, Nobeoka, Miyazaki 882, Japan Received 27th April 1998, Accepted 14th September 1998 Shock-compression of dehydrochlorinated poly(vinylidene chloride) at 15 GPa and 6500 K produced a small portion of balloon-shaped graphitic-carbon material mixed with a large proportion of graphite and diamond.The size and thickness of the various balloon particles were ca. 40–300 nm and 4–6 nm, respectively. The balloonshaped material is presumably a by-product from a carbon source fragmented under shock-compression and would not be related to the high yield of diamond. Carbon forms fundamentally three types of allotropes resulting a trace of a new crystalline carbon mixed with diamond and graphite.16 The new carbon was assigned to the hexagonal from its available three bond modes, sp, sp2 and sp3.In nature, crystal system with cell dimension a0=0.338 nm and was only the sp2-type allotrope (graphite) and sp3-type (diamond) compared with carbyne in terms of the carbon geometry exist. The search for a sp-type has originated from a discovery projected onto the 001 plane. Here, we further investigate of two resonance hybrids, a-carbyne1 (polyyne form) prepared the possibility of producing unknown carbon-based substances by high temperature treatment of oxidative condensates of under a shock pressure of 15 GPa, the medium pressure copper acetylide and b-carbyne2 (polycumulene form) derived required for the shock-induced graphite-to-diamond trans- by coupling of carbon suboxide and sodium acetylide, which formation, using the same starting material as previously.was made by a Russian group between 1961 and 1967. This was followed by the preparation of eight or more polymorphs of carbon from vaporized carbon,3 de(hydro)halogenated polymers having long polyyne segments (carbynoids),4–6 and Experimental a coil form of polyyne by laser vaporization of graphite.7 Sample preparation However, the presence of carbyne as a high temperature material is unusual considering the fragility of conjugated The starting material was prepared by dehydrochlorination of polyyne compounds.8 poly(vinylidene chloride) (Asahi Chemical Industry Co.Ltd., The world of carbon allotropes seemed to have been Saran polymer MW=105) using 1,8-diazabicyclo[5.4.0]undeccompleted with diamond, graphite and carbyne.However, 7-ene (DBU) as a base and N,N-dimethylacetamide as solvent. between 1985 and 1992, an outstanding discovery of carbon Determination of the chemical structure using elemental analyclusters by Kroto et al.,9 Iijima,10 and Ugarte,11 the so-called sis, IR, Raman, UV–VIS, and NMR spectroscopy was carried fullerenes, nanotubes and carbon onions, which form topologi- out in the same way as described previously.16 The material cally closed-shell sp2-carbon networks completely diVerent which was obtained as a fine black powder was an amorphous from planner graphite networks, were synthesized upon high block polymer linked with conjugated polyene and polyyne energy irradiation of graphite such as laser vaporization, arc segments, –(CHLCH)n–(CMC)m–, containing small amounts evaporation, and electron irradiation.This finding along with of carbonyl and nitrogen and trace amounts of chlorine, and the recent prediction of an unexpected variety of carbon this structure was confirmed to be the same as previously. isomers12 like cyclo-C18 and graphyne, etc. has encouraged the A homogeneous mixture of the starting material (2 equiv.) search for other new carbon-based substances. On the other and coarse-grained copper balls (98 equiv.) was filled in a steel hand, the carbon clusters including carbyne were found to sample holder of 30 mm diameter and 15.5 mm depth, and show surprisingly high diamond conversions under much pressed at 28 MPa for 30 min.The product was then dried at milder physical conditions in comparison with the graphite- 80 °C for 20 min under ordinary pressure, and vacuum-dried to-diamond transformation, for example, C60-to-diamond (90 at 120 °C for 2 h.The packing density of the starting material mass%) conversion occurs under a non-hydrostatic pressure in the pressed sample was 0.44 g cm-3 (20% of the theoretical of 20±5 GPa at room temperature,13 and carbyne-to-diamond density of graphite).Shock-compression of this sample was (99 mass%) occurs under a static pressure of 8 GPa at carried out using the plane shock-compression apparatus 1400–1700 °C without catalyst.14 shown in Fig. 1. The apparatus was constructed with a deton- Knowledge of the isomerisation between two carbon ator, an explosive lens composed of a set charge of hydrazine allotropes suggests the possibility of producing hitherto nitrate (63.5 mass%)–hydrazine hydrate (36.5 mass%) and unknown carbon allotropes with or from diamond.Shock- nitromethane, a high melting point explosive (HMX, detoncompression15 used for diamond synthesis owing to the ation speed 9.1 km s-1), a copper flyer, a brass vessel containextremely high dense energy supply by shockwaves and success- ing the sample holder, and a steel momentum trap surrounding ive rapid cooling in microseconds is expected to be a very the brass vessel.The average shock pressure applied to the useful method to search for new metastable carbon-based sample was estimated to be 15 GPa. The recovered sample substances. We studied previously shock-compression of was machined, immersed in 10% HNO3 to remove the copper dehydrochlorinated poly(vinylidene chloride) (a carbynoid) matrix, washed with distilled water, and vacuum-dried at 200 °C.A fine black powder was obtained in a yield of ca. 25%. under several GPa for the preparation of carbyne and found J. Mater. Chem., 1998, 8, 2725–2728 2725Fig. 1 Section of the plane shock-compression apparatus: 1, detonator; 2, explosive lens consisting of (a) hydrazine nitrate–hydrazine hydrate and (b) nitromethane; 3, high melting point explosive; 4, copper-flyer; 5, brass vessel containing the sample; 6, steel momentum trap.Measurements The C, H, N contents of the sample were determined on a Holiba CHN analyzer. Raman spectra were measured at an excitation wavelength of 514.5 nm generated with a 1.0 mW argon laser using a MST foundation Ga-505 spectrometer.The crystal structures were investigated using a Rigaku RINTFig. 2 Raman spectra of the starting material and the shock- 2500 X-ray powder diVractometer equipped with a position- compacted sample: (a) the starting material; (b) the shocksensitive proportional counter and a graphite monochromator compacted sample.on the detector. Ni-filtered Cu-Ka radiation generated at 50 kV and 200 mA was used as the X-ray source. The micro- X-Ray diVraction scopic morphologies were observed using a JEOL JEMFig. 3 shows the X-ray powder diVraction of the 4000FX high-resolution transmission electron microscope shock-compacted sample. The diVraction consisted of two (HRTEM) equipped with an energy-dispersive X-ray analyzer patterns.The observed d-values, intensities, and lattice con- (EDX), an electron energy-loss spectrometer (EELS) and an stants of the patterns are given in Table 1 in addition to the electron diVractometer (ED). The nanoscaled observation was data of the known carbon materials. Pattern 1, a cubic complemented using a Hitachi HF-2000 instrument for field structure with a=0.35597 nm, agreed with that of diamond emission transmission electron microscopy (FETEM) (JCPDS 06-0676) except for a broad FWHM (2h=1.664° for equipped with an ED, a parallel electron energy-loss specthe 111 peak).Pattern 2, a hexagonal structure with the trometer (PEELS) and an EDX. The sample powder was diVused supersonically in a methanol–distilled water (151) solution for 5 min, a drop of the solution was then placed on a microgrid coated with a carbon–collodion membrane, air-dried, and measured at 400 kV accelerating voltage.Results and discussion Elemental analysis and Raman spectrum The C/H/N content of the shock compacted sample was 98.1% C, 0.3% H and 0.3% N. The elements of the same sample detected by EDX were almost entirely carbon except for oxygen and silicone impurities due to the carbon–collodion membrane and copper due to the microgrid used for the TEM measurement.Fig. 2 shows the Raman spectra of the starting material and the shock-compacted sample. The spectra indicate that the starting material was entirely transformed into diVerent materials. The bands at 1592 and 1352 cm-1 of the shockcompacted sample were similar to those of glassy carbon17 in terms of the peak position, and were assigned to G- and Dbands of the graphite structure, respectively.A broad line Fig. 3 X-Ray powder diVraction of the shock-compacted sample. width and a relatively comparable intensity of the peaks For comparison, the standard patterns of graphite (JCPDS 25-0284) indicate the material is coagulated with poorly crystalline and diamond (JCPDS 06-0676) are shown together with their superposition (syn).fine grains. 2726 J. Mater. Chem., 1998, 8, 2725–2728Table 1 X-Ray diVraction pattern of the shock-compacted sample and assignment of the structures by comparison with patterns of standard references Pattern 1 Cubic Diamond (JCPDS 06-0676) a=0.35597 nm a=0.35667 nm 2h/degrees dobs/nm dcalc/nm 100 I/I0 hkl d/nm 100 I/I0 hkl 44.022 0.20553 0.20552 100 111 0.20600 100 111 75.479 0.12585 0.12585 24 220 0.12610 26 220 91.734 0.10733 0.10733 13 311 0.10754 16 311 120.416 0.08876 0.08899 4 400 0.08916 8 400 141.221 0.08166 0.08166 8 331 0.08182 16 331 Pattern 2 Graphite (JCPDS 25-0284) Hexagonal c=0.6683 nm a=0.2458 nm, c=0.6696 nm 2h/degrees dobs/nm dcalc/nm 100 I/I0 hkl d/nm 100 I/I0 hkl 26.657 0.33413 0.33413 100 002 0.33480 100 002 0.21270 3 100 0.20270 15 101 0.17950 3 102 53.953 0.16981 0.16707 5 004 0.16740 6 004 lattice constant c=0.6683 nm, fitted well with that of graphite (JCPDS 25-0284).The 100 peak of pattern 2 was apparently absent because of overlapping with the 111 peak of pattern 1. As a guide to indexing, the standard patterns of the graphite and diamond are included in Fig. 3.The average size of diamond crystallites estimated from the FWHM is ca. 5 nm, and the formation of such nanosized diamond particles is also a characteristic of the shock-compression synthesis. The existence of diamond was confirmed by XRD, however, it could not be detected by Raman spectroscopy, probably because of its very small size.The mass ratio of diamond to graphite contained in the shock-compacted sample, which was estimated by calibration with the relative intensity of known composition, was ca. 70%. As already stated, diamond conversion of the carbon clusters exceeds 90% under even much lower pressures. A characteristic common feature of these starting materials is an abundance of active unsaturated bonds.The bonds would be easily fragmented even under mild conditions, which may be related to such a high diamond conversion. TEM observation Fig. 4 shows the HRTEM image of the shock-compacted sample. This reveals a large portion of graphitic domains and microdiVused fine crystalline particles showing a lattice image. Fig. 4 High resolution TEM image of the shock-compacted sample.The FETEM-ED patterns of the graphitic domains and crystal- The areas enclosed within squares indicate microdiVused fine line particles showed a diVuse ring pattern and a spot pattern, crystalline particles having a lattice image. respectively. The interplanar spacings determined from the spot pattern were 0.208 nm 111 , 0.127 nm 220 and spectrum showed both 1s�p* and 1s�s* transitions at the 0.0826 nm 331 .The values are in accord with those of carbon K-edge similar to those of graphite, which indicates diamond within an experimental error of 2% using the silicon the material is composed of graphitic sp2 carbon. The size and pattern. Therefore, the crystalline material was assigned to thickness of the various balloon particles estimated from the diamond. The graphitic domains were assigned to graphite TEM observation were ca. 40–300 nm and ca. 4–6 nm, from the similarity to the ED pattern of low crystalline respectively. This form of carbon material is probably new. graphite. These assignments were also supported by the Raman The shock pressure, P, applied to the sample and the particle and XRD results described above.In addition to these mate- velocity, Up, estimated from the Hugoniot data by Marsh,18 rials, balloon-shaped particles as shown in Fig. 5 were are 15 GPa and 5.2 km s-1 respectively. The internal energy occasionally seen. In this figure, the various balloon particles increase, DE, and a temperature increase, DT , of the sample cluster together locally near the graphite domains.The outside under shock-compression are derived from the well known of the particles is covered with a dense wall as a round closed Rankin–Hugoniot equations:19 shell in contrast to the inside which suggests a bright non- DE=Up2/2 (1) structured space. The shell structure is seen as laminated with graphitic thin layers oriented along the walls.The EELS DT=E/3R (2) J. Mater. Chem., 1998, 8, 2725–2728 2727Conclusions Creation of a new type of carbon-based substance was attempted by shock-compression of dehydrochlorinated poly (vinylidene chloride). Codeposition of a small quantity of balloon-shaped graphitic-carbon material and a large quantity of graphite and of diamond was confirmed by TEM analysis. The size and thickness of the various balloon particles were 40–300 nm and 4–6 nm, respectively. The pressure and temperature applied to the sample by shock-compression were estimated to be 15 GPa and 6500 K, respectively.The balloonshaped material was presumably deposited as a by-product from a carbon source fragmented under shock-compression and would not be related to the high yield of diamond. References 1 V.V. Korshak, V. I. Kasatochikin, A. M. Sladkov, Yu. P. Kudryavtsev and K. Usenbaev, Dokl. Akad. Nauk SSSR, 1961, 136, 1342. 2 V. I. Kasatochkin, T. M. Babchinitsev, Yu. P. Kudryavtsev and A. M. Sladkov, Dokl. Akad. Nauk SSSR, 1967, 177, 358. 3 A. G. Whittacker, Science, 1978, 200, 763. 4 K. Akagi, M. Nishiguchi, H. Shirakawa, Y. Fulukawa and I. Harada, Synth. Met., 1987, 17, 557. 5 Yu. P. Kudryavtsev, S. E. Evsyukov, V. G. Babaev, M. B. Guseva, V. V. Khvostov and L. M. Krechko, Carbon, 1992, 30, 213. 6 J. Kastner, H. Kuzmany, L. Kavan, F. P. Dousek, and J. Kurti, Macromolecules, 1995, 28, 344. Fig. 5 High resolution TEM image of balloon-shaped particles 7 R. J. Lagow, J. J. Kampa, H. C. Wei, S. L. Battle, J. W. Genge, contained in the shock-compacted sample.D. A. Laude, C. J. Harper, R. Bau, R. C. Stevens, J. F. Haw and E. Munson, Science, 1995, 267, 20. 8 R. Eastmond, T. R. Johnson and D. R. M. Walton, Tetrahedron, where R is the gas constant. From these, DE=13.5 MJ kg-1 1972, 28, 4601. and DT=6500 K are obtained. This temperature is suYciently 9 H. W. Kroto, J. R. Heath, S. C. O’Brien, R. F. Curl and high to make the sample fragment, therefore the composition R.E. Smalley, Nature (London), 1985, 318, 162. of the shock-compacted sample would originate from carbon- 10 S. Iijima, Nature (London), 1991, 354, 56. aceous fragments, that is, the carbonaceous fragments are 11 D. Ugarte, Nature (London), 1992, 359, 707. presumably transformed into diamond as a high pressure 12 F. Diederich and Y. Rubin, Angew.Chem., Int. Ed. Engl., 1992, 31, 1101. phase, graphite as the thermodynamically the most stable 13 M. N. Regueiro, P. Monceau and J. L. Hodeau, Nature (London), phase, and the balloon-shaped graphitic carbon possibly as a 1992, 355, 237. high temperature phase. However, the previous crystalline 14 V. V. Korshak, Yu. V. Korshak, Yu. P. Kudryavtsev, carbon16 was not observed in this work in spite of the same M.B. Guseva, V. G. Babaev, V. V. Khvostov, S. E. Evsyukov, starting material. This is probably due to the diVerence in the a. D. Varfolomeeva, USSR SU, 1,533,221, 1993; Chem. shock conditions. The pressure and temperature in this work Abstr., 1994, 120, 110831a. 15 E. I. du Pont de Nemours, USP., 3401019, 1968; G. R. Cowan, were much higher than those (several GPa, 600–800 K) in the B.W. Dunnington and A. H. Holtman, Chem. Abstr., 1969, 70, previous study. The high pressure increased the yield of 699. diamond, while the high temperature (6500 K) would com- 16 T. Komatsu, M. Nomura, Y. Kakudate, S. Fujiwara and pletely decompose the previously observed crystalline material R. B. Heimann, Macromol. Chem. Phys., 1995, 196, 3031. even if it were formed. Also, codeposition of known carbon 17 H. Hiura, T. W. Ebbessen and K. Tanigaki, Chem. Phys. Lett., clusters such as fullerenes, nanotubes and carbon onions is 1993, 202, 509. 18 S. P. Marsh, in LASL Shock Hugoniot Data, Univ. California, unknown. This exclusive tendency among carbon allotropes Berkeley, 1980, p. 43. other than graphite and diamond (we do not know any 19 R. G. McQueen, S. P. Marsh, J. W. Taylor, J. N. Fritz and examples of codeposition for the carbon clusters) suggests W. J. Carter, in High-Velocity Impact Phenomena, ed. R. Kinslow, that the balloon-shaped material would be a kinetically con- Academic Press, New York, 1970, p. 244. trolled by-product but not a thermodynamically controlled intermediate leading to diamond. Paper 8/03131B 2728 J. Mater. Chem., 1998, 8, 2725–2728

ISSN:0959-9428    

DOI:10.1039/a803131b

出版商:RSC    

年代:1998

数据来源: RSC

摘要:

J O U R N A L O F C H E M I S T R Y Materials Influence of pressure on the crystal structure of Nd2CuO4 Heribert Wilhelm,*a C. Cros,b E. Reny,b G. Demazeaub and M. Hanflandc aDe�partement de Physique de la Matie`re Condense�e, Universite� de Gene`ve, 24, Quai Ernest- Ansermet, CH-1211 Geneva 4, Switzerland. E-mail: Heribert.Wilhelm@physics.unige.ch; Tel. (+41)22 702 62 61. Fax. (+41)22 702 68 69.bInstitut de Chimie de la Matie`re Condense�e de Bordeaux, UPR-CNRS 9048, 87, Avenue Dr. Albert Schweitzer, F-33608 Pessac, France cEuropean Synchrotron Radiation Facility, B.P. 220, F-38043 Grenoble, France Received 28th July 1998, Accepted 7th October 1998 The pressure evolution of the crystal structure of Nd2CuO4 (tetragonal T¾-type) was studied at room temperature up to 36 GPa using synchrotron radiation.At PT=21.5 GPa a structural transformation into the T-structure (tetragonal K2NiF4-type) occurred. Upon releasing pressure a gradual distortion of the T-structure into the orthorhombic O-phase (Cmca) was found in the pressure range 10<P<18 GPa, and at lower pressure the starting T¾-phase was restored. The pressure evolution of the unit-cell parameters and the interatomic distances were determined by Rietveld refinement of the diVraction pattern.pressure O-phase [distorted K2NiF4-type, Fig. 1(b)] or T- 1 Introduction phase [K2NiF4-type, Fig. 1(c)] the Ln3+ and the Cu2+ ions In a recent study1 the structural evolution of the solid-solution have now a nine- and a six-fold (elongated octahedron) oxygen La2-xNdxCuO4 (T¾-structure, I4/mmm) under pressure was coordination, respectively.Owing to the poor resolution of investigated for 0.6x1.5. At a pressure PT new lines in the the observed lines in the energy-dispersive X-ray study of energy-dispersive diVraction pattern appeared, indicating a La2-xNdxCuO41 it was not possible to determine whether the structural phase transition. The transition pressure PT increases high pressure phase was distorted or not.It was assumed that with the Nd content x. The PT(x) dependence was related to the same phase sequence (T¾AOAT) is followed as was found compressive stress in the Ln–O2 linkages of the fluorite-type for the tolerance factor.4,5 In the O-phase the CuO6 octahedra LnO2-layers in the T¾-structure. The compressive stress rotate cooperatively about the [110] axis and the crystal decreases when the average lanthanide ion size is reduced, i.e.structure is orthorhombic. This structure is found for La2CuO4 xA2. The pressure eVects were also described in terms of a at low pressure (P<3.4 GPa) and ambient temperature6 or at pressure dependent tolerance factor t, defined by Goldschmidt2 low temperature (T<573 K) and ambient pressure.7 to describe the stability of the related perovskite structure.For For Nd2CuO4 itself first indications of a pressure induced the solid solution La2-xNdxCuO4 it was found that the structural change were found around 20 GPa1 which was at transition pressure PT increases as t decreases.1 the limit of the pressure device used. The experiments presented In the T¾-structure of Nd2CuO4 the Cu-ions at the origin here were performed at the European Synchrotron Radiation (2a-site) are surrounded by four oxygen ions, labeled O(1) in Facility (ESRF) in Grenoble.The accessible pressure range Fig. 1(a), which occupy the 4c-site.3 The lanthanides at the was much higher and the high flux of the synchrotron radiation 4e-site have eight nearest oxygen-ion neighbours [O(2) at 4d- should give diVraction patterns which reveal a better insight site] in a pseudo-cubic symmetry.As pressure is applied to into the structural changes and should allow one to determine this structure, the O(2) ions are forced to the 4e-position the symmetry of the high pressure phase. whereas the other ions remain at their sites. In the high 2 Experimental The polycrystalline sample of Nd2CuO4 was synthesised by high temperature reaction of stoichiometric amounts of the oxides CuO and Nd2O3 in air at 950 °C during 24 h, followed by a second treatment at the same conditions after intermediate grinding.The resulting product was identified by X-ray diVraction, using a conventional powder diVractometer (Cu-Ka and h<70°).The high pressure experiments were performed at ambient temperature using a membrane-type diamond anvil cell (DAC). A well powdered specimen was filled into a 0.125 mm bore, which was drilled in a stainless steel gasket. The gasket was placed between the two diamonds of the DAC. Nitrogen served as pressure transmitting medium. This ensured quasi-hydrostatic pressure conditions up to the highest pressure.The pressure was determined with the ruby luminescence technique8 using the non-linear ruby pressure scale.9,10 Under these circumstances the experimental error in Fig. 1 Schematic view of the structure of (a) the T¾-phase (tetragonal, determining the pressure was <0.2 GPa. The X-ray powder Nd2CuO4-type), (b) the O-phase (orthorhombic, distorted K2NiF4- diVraction spectra were recorded using synchrotron radiation type) and (c) the T-phase (tetragonal, K2NiF4-type) of the Ln2CuO4 at the beamline ID09 at the ESRF.The high X-ray flux of the oxides (Ln=lanthanide). The oxygen atoms O(2) are distinguished from the O(1) ones by a central point. synchrotron combined with the image plate (size A3) provides J. Mater. Chem., 1998, 8, 2729–2732 2729a much better resolution than the technique used in the recent investigation.1 The diVraction images were collected at a wavelength of l=0.4558 A° (E#25 keV) during 60 s exposure time.The images were integrated with the program fit2d.11 The structural parameters and interatomic distances were obtained by Rietveld refinement12 of the diVraction pattern in the range (3°<2h<23°). Isotropic temperature factors were used for all atoms.In each pattern the temperature factors of the Nd and Cu atoms and those of the oxygen atoms were kept the same and these two parameters were refined independently. The N2 diVraction lines, originating from the pressure transmitting medium, were also refined. 3 Results and discussion Fig. 2 shows diVraction patterns of Nd2CuO4 at ambient pressure and P=30.5 GPa.At pressures up to P=20 GPa the tetragonal T¾-phase is stable. In the pressure range 21.5<P<31 GPa a structural phase transformation into the tetragonal T-phase takes place gradually, which is clearly seen from the relative positions of some lines in the pattern recorded at 30.5 GPa in comparison to those in the pattern at ambient Fig. 3 Relative unit-cell volume V/V0 of Nd2CuO4 versus pressure.At pressure [for example, (103) and (110), (114) and (200), (213) PT=21.5 GPa the T¾-phase (bold squares) starts to transform into the high pressure T-structure (bold circles). The T-phase fraction increases and (107)] [see Fig. 2(b)]. The pressure where first signs of with pressure as is depicted in the inset.Upon releasing pressure (open the high pressure phase were observed is chosen as transition symbols) the orthorhombic O-phase (diamonds) appears and at low pressure, and therefore PT=21.5 GPa. Upon releasing pressure the T¾-phase (squares) is restored again. pressure, the T-phase exists down to #18 GPa. The gradual splitting of some characteristic lines [(110), (114), (213), ...] in the pressure range 18>P>10 GPa, indicates a distortion The refinement of the diVraction pattern gave Rwp values of the tetragonal T-phase into the orthorhombic (O) one.This between 3 and 6% and x2<5 (Table 1). is shown explicitly in the inset of Fig. 2 with a pattern obtained The V(P) diagram of Nd2CuO4 is shown in Fig. 3. For the at 12.0 GPa and indexed according to the space group Cmca.T¾-phase the Murnaghan equation of state (EOS)13 Below 8 GPa the low pressure T¾-phase was recovered again. V(P)=V0 AB0¾ B0 P+1B-1/B0¾ (1) was adjusted to the data and a bulk modulus B0=145(1) GPa and its pressure derivative B0¾=4.1(1), with V0= 189.252(1) A° 3 (solid line) and for the high pressure T-phase B0=69(1) GPa and B0¾=8.7(1) were obtained,ively.Using the Birch EOS14 P(V)= 3 2 B0 {x7/3-x5/3} C1- 3 4 (4-B0¾) (x2/3-1)D (2) with x=V0/V(P), gives B0=146(1) GPa and B0¾=4.0(2) for the T¾-phase. Rather diVerent values were obtained for the T-phase [B0=56(5) GPa and B0¾=14(2)]. The deviation of the extrapolated EOS (dotted line in Fig. 3) from the data points above PT is interpreted as a sign of structural changes starting in this pressure range.Up to #30 GPa both the T¾- and T-phase were used to refine the diVraction pattern. As shown in the inset of Fig. 3, the fraction of the T-phase, i.e. the high pressure form, increases in the transition region. It was also possible to use the orthorhombic structure to refine the pattern in this transition region. However, neither the R-values were improved nor the splitting of e.g.the (110) line was obvious. Therefore, the higher symmetry phase is used to describe the diVraction pattern. Above 30 GPa the pattern are well described using the Tphase only. The pattern recorded during pressure release showed a gradual and clear splitting [see inset of Fig. 2(a)] and the orthorhombic O-structure was used to refine the pattern.The corresponding V(P)-data are included in Fig. 3 (open diamonds). Below 10 GPa the same structural parameters were obtained as upon increasing pressure, indicating Fig. 2 Powder diVraction pattern, refined and diVerence pattern as the reversibility of the structural changes. For each phase the well as the peak positions of (a) the low pressure T¾-phase (P=1 bar) lattice parameters, the unit-cell volume, the fractional coordi- and (b) the high pressure T-phase (P=30.5 GPa) of Nd2CuO4.In the nates, and the temperature factors are given in Table 1. The inset the diVraction pattern of the orthorhombic O-phase, clearly entries are chosen for the lowest (highest) pressure at which indicated by the splitting of several lines, obtained on pressure release, is shown. the T-structure (O-structure) were observed. 2730 J. Mater. Chem., 1998, 8, 2729–2732Table 1 Symmetry, structural parameters, site symmetry, fractional coordinates, temperature factors (multiplied by 100), Rwp and x2 values of the ambient (T¾) and high pressure phases (T and O) of Nd2CuO4. The orthorhombic O-phase was obtained upon releasing pressure T¾ (I4/mmm) Z=2 T (I4/mmm) Z=2 O(Cmca) Z=4 P=1 bar P=21.5 GPa P=17.3 GPa a/A° 3.943(1) 3.629(3) 5.1374(4) b/A° 3.943(1) 3.629(3) 12.450(1) c/A° 12.1704(5) 12.40(2) 5.1815(4) V/A° 3 189.252(1) 163.3(3) 331.32(3) atom x/a y/b z/c U/A° 2 x/a y/b z/c U/A° 2 x/a y/b z/c U/A° 2 Nd 4e 0 0 0.352(1) 0.9(1) 4e 0 0 0.387(3) 1.6(1) 8f 0 0.13(1) 0.49(1) 1.6(1) Cu 2a 0 0 0 0.9(1) 2a 0 0 0 1.6(1) 4a 0 0.5 0.5 1.6(1) O(1) 4c 0 0.5 0 1.5(4) 4c 0 0.5 0 2.6(1) 8f 0 0.43(1) 0.51(2) 0.3(2) O(2) 4d 0 0.5 0.25 1.5(4) 4e 0 0 0.16(2) 1.5(4) 8e 0.25 0.48(1) 0.25 0.3(2) Rwp(%) 4.8 5.4 5.7 x2 3.6 4.4 4.4 The transition pressure PT=21.5 GPa found for Nd2CuO4 and B0¾=7.0(5), respectively.The relative lattice parameter change at the transition is #-3% and #+7% for the a- and is in good agreement with the pressure where in a recent work1 first signs of a structural transition were observed.c-axis, respectively. In the crystal structure of the T¾-phase the only free Furthermore, this value gives additional support for the relation between PT and the tolerance factor t to describe the parameter is the z-value of the Nd ion (zNd). It is almost pressure independent up to PT and jumps from z=0.352 to stability of the La2-xNdxCuO4 solid solution.1 For Nd2CuO4 the tolerance factor is t=0.8509 and a transition pressure of zNd=0.387 (Fig. 5). It strongly decreases down to zNd=0.362 at P=27 GPa and is then almost pressure independent up to about 20 GPa can be deduced from the PT–t relation given in Fig. 4 of ref. 1. As the tolerance factor increases (tA1) the the highest pressures.For the T-phase also the position of the oxygen ion O(2) is a free parameter (zO(2)). Its value increases phase sequence T¾AOAT was obtained at normal conditions, 4,5 suggesting that under pressure the O-structure monotonically with pressure from zO(2)#0.155 at PT= 21.5 GPa to #0.195 at P=36.6 GPa (see inset Fig. 5). should occur before the T-phase. However, the refinement of the synchrotron data gave no evidence that the intermediate For the pressure evolution of the crystal structure of Nd2CuO4 a few interatomic distances are important.In the O-structure is attained upon increasing pressure. The T¾-structure transforms in a relatively wide pressure range into T¾-phase the CuKO(1) distance, i.e. dCu–O(1)=a/2=1.9717(5) A° at ambient pressure decreases to dCu–O(1)=1.9146(6) A°at the T-structure. During pressure release however, the O-structure is found at intermediate pressures before the 20.2 GPa.Its pressure dependence is given by that of the aaxis. The pressure dependence of the NdKO(2) distance as T¾-phase is finally formed at low pressure. The T¾-structure is more compressible along the c-axis than well as that of NdKO(1) are well described by the c-axis compressibility. As far as interatomic distances in the high along the a-axis.This is seen from the c/a-ratio (Fig. 4) which decreases from 3.09 to #3.01 at the transition pressure. The pressure phase are concerned, the NdKO(2) and CuKO(2) distances are of particular interest because they determine the pressure dependence of the lattice parameters (inset in Fig. 4) is described by the Murnaghan EOS and gives for the a- and height of the CuO6-octahedron. As is shown in Fig. 5, the c-axis B0=527(3) GPa and B0=326(4) GPa with B0¾=16.7(4) Fig. 5 The fractional coordinate zNd in Nd2CuO4 as function of Fig. 4 The c/a-ratio of Nd2CuO4 versus pressure up to 36 GPa. In the pressure. Above 25 GPa the Nd-position in the T-phase is pressure independent.The inset shows the fractional coordinate zO(2). It inset the pressure variation of the a and c lattice parameter is shown for the T¾- and T-phase. Open symbols represent data obtained during increases with pressure, i.e. the CuO(2)-octahedron is enlarged along the c-axis. pressure release. J. Mater. Chem., 1998, 8, 2729–2732 2731fractional z-coordinate of Nd is rather pressure independent References above 30 GPa and therefore the NdKO(2) distance is deter- 1 H.Wilhelm, C.Cros, F. Arrouy and G. Demanzeau, J. Solid State mined through the pressure variation of zO(2). Above 30 GPa Chem., 1996, 126, 88. the NdKO(2) distance decreases rather strongly (#.7%) and 2 V.M. Goldschmidt, Akad. Oslo I. Mater. Natur., 1926, 2, 7. as a consequence the CuKO(2) distance increases by the same 3 H.Mu¡§ ller-Buschbaum and W. Wollschla¡§ger, J. Anorg. Allg. amount. This means that the CuO6 octahedron is elongated Chem., 1975, 414, 76. with increasing pressure. 4 A. Manthiram and J. B. Goodenough, J. Solid State Chem., 1990, 87, 402. 5 J. F. Bringley, S. S. Trail and B. A. Scott, J. Solid State Chem., 4 Conclusion 1990, 86, 310. 6 J.Shu, J. Akella, J. Z. Liu, H. K. Mao and L. Finger, Physica C, A structural phase transition from the low pressure T�ú- to the 1991, 176, 503. high pressure T-phase was observed for Nd2CuO4 at PT= 7 B. Grande, H. Mu¡§ ller-Buschbaum and M. Schweitzer, Z. Anorg. 21.5 GPa at room temperature using synchrotron radiation. Allg. Chem., 1977, 428, 120. Above PT the T-phase fraction increases and the transition is 8 G. J. Piermarini, S. Block, J. D. Barnett and R. A. Forman, completed at 30 GPa. The transition pressure is in good J. Appl. Phys., 1975, 46, 2774. agreement with the value predicted from the relation between 9 H. K. Mao, P. M. Bell, J. W. Shanner and D. J. Steinberg, Appl. PT and the tolerance factor t of this system. An orthorhombic Phys., 1978, 49, 3276. distorted O-phase was observed during pressure release in the 10 H. K. Mao, J. Xu and P. M. Bell, J. Geophys. Res., 1986, 91, range 10<P<18 GPa. This phase is not observed in the 4673. 11 A. P. Hammersly, ESRF Internal Report EXP/AH/95-01, 1995. pattern upon increasing pressure due to hysteresis in th12 A. C. Larson, GSAS manual, LAUR 86-748, 1986. transition. At low pressure the initial T�ú-phase was found again. 13 F. D. Murnaghan, Proc. Natl. Acad. Sci. USA, 1944, 430, 244. 14 F. Birch, Phys. Rev., 1947, 47, 809. 5 Acknowledgements We would like to acknowledge helpful discussions with Dr. R. C¢� erny about the Rietveld refinement. Paper 8/05886E 2732 J. Mater. Chem., 1998, 8, 2729.

ISSN:0959-9428    

DOI:10.1039/a805886e

出版商:RSC    

年代:1998

数据来源: RSC

摘要:

J O U R N A L O F C H E M I S T R Y Materials Hybrid open frameworks (MIL-n). Part 3† Crystal structures of the HT and LT forms of MIL-7: a new vanadium propylenediphosphonate with an open-framework. Influence of the synthesis temperature on the oxidation state of vanadium within the same structural type D. Riou* and G. Fe� rey Institut Lavoisier UMR CNRS C173, Universite� de Versailles St-Quentin-en-Yvelines, 45 Avenue des Etats-Unis, 78035 Versailles cedex, France Received 9th April 1998, Accepted 17th September 1998 The hydrothermal synthesis and structure determinations of two vanadium propylenediphosphonate compounds are presented.MIL-7, formulated as [(VO)2(OH) (H2O){O3P(CH2)3PO3}](H2O)2(NH4), is synthesized at 200 °C. Its structure is monoclinic [space group C2/c (no. 15)] with lattice parameters a=14.2928(2) A° , b=10.2440(2) A° , c=18.9901(1) A° , b=96.658(1)°, V=2761.69(7) A° 3, Z=8. The three-dimensional framework is built up from inorganic VIV–P–O layers strongly related by the alkyl chains. Upon heating hydrothermally the same initial mixture but at 170 °C one obtains a diVerent phase, formulated as [V2O3(H2O){O3P(CH2)3PO3}](H2O)2(NH4), the structure of which is closely related to MIL-7.Its symmetry is monoclinic [space group C2/c (no. 15)] with lattice parameters a=14.8998(8) A° , b=10.2903(6) A° , c=18.515(1) A° , b=101.079(1)°, V=2785.9(3) A° 3, Z=8. The topology of the inorganic layers is almost identical, but presents a mixed valence VIV–VV state in a 151 ratio. water in the molar ratio 150.65500. The mixture was heated Introduction at 473 K during four days.The initial pH was approxi- Numerous organically templated metallophosphates with matively 3 and increased up to 6 at the end of the reaction. open-framework structures have been evidenced since the work After filtering, MIL-7 is obtained as isolated parallelepipedic of Flanigen and coworkers1 devoted to the AlPO family.This blue crystals. The IR spectrum, recorded on a Nicolet large class of materials has been extended (i) to mixed Co- Magna-IR 550 in the range 2000–300 cm-1, presents a strong GaPO by Chippindale et al.,2 (ii) to 3d transition metal band around 1410 cm-1 corresponding to the NH4+ cationic phosphates, principally vanadium and cobalt by the groups of vibrations. The bands located around 1190, 1035 and Haushalter3 and Stucky4 respectively and (iii) to oxyfluorin- 770 cm-1 are attributable to PO3, n(VLOterminal) and ated phosphates by Kessler with Cloverite5 and our team with n(V–Obridging) respectively.TG analysis performed with a TA the ULM-n compounds.6 In this last series (n19),7 we have Instruments TGA 2050 apparatus under nitrogen flow shows shown that it is possible to obtain some magnetic compounds, (i) up to 150 °C a first weight loss (#11.5%) corresponding synthesizing for the first time some oxyfluorinated iron phos- to the dehydration and the partial departure of the phates with open frameworks.8 ammonium cations, this transformation does not aVect the One common feature to all these phases is the diYculty of crystallinity of the product, (ii) up to 600 °C a continuous removing the organic template; only a small number retain a weight loss (#9.4%) corresponding both to the departure of good crystallinity after the thermal degradation of the template.the remaining NH4+ and the beginning of the degradation of To avoid this problem, we have recently initiated a new approach the propyl chains. The resulting product is rather amorphous for hybrid open-framework compounds using alkyldiphosphonic but shows the strongest peaks of a-VOPO4.acids. Indeed, we have published MIL-2, MIL-39 and MIL-510 By heating the mixture previously described at 170 rather (forMaterials of Institut Lavoisier), some vanadodiphosphonates than 200 °C, a sheath of dark green crystals is obtained. with three-dimensional open-frameworks.In these phases, the Their XRD pattern and IR spectra are very similar to those alkyl chains participate in building the three-dimensional struc- of MIL-7. Note that the crystal used for the crystallographic ture by strong covalent P–C and C–C linkages. The cavities of study presented here, was obtained in a more concentrated the frameworks contain some ammonium cations and water mixture (molar ratio 150.65150). molecules.In the case of MIL-5, the framework is neutral and inserts solely some water molecules. Structure determinations This paper deals with the synthesis and the structure determination of [(VIVO)2(OH)(H2O){O3P(CH2)3PO3}](H2O)2(NH4), Single crystals of both phases were optically selected and their denoted MIL-7, a new vanadodiphosphonate with a 3D-strucquality tested by Laue photography.The data were collected ture synthesized with propylenediphosphonic acid. The strucup to 2h=60 ° on a three-circle Siemens SMART ture of the compound obtained at lower temperatures is also diVractometer equipped with a CCD bidimensional detector. determined and discussed. The monochromatized wavelength was l(Mo-Ka)= 0.710 73 A° .Both phases show monoclinic symmetry [space Experimental group C2/c (no. 15)] with lattice parameters a=14.2928(2), b=10.2440(2), c=18.9901(1) A° , b=96.658(1)°, V= Chemical investigations 2761.69(7) A° 3 and a=14.8998(8), b=10.2903(6), c= 18.515(1) A° , b=101.079(1)°, V=2785.9(3) A° 3 for MIL-7 and MIL-7 was synthesized hydrothermally from NH4VO3 (99%, its low-temperature (LT) form, respectively.The data were Prolabo), propylenediphosphonic acid (Alfa) and desionized corrected for absorption eVects with the SADABS11 program, and the structures were solved using the SHELX-TL structure †Part 2: see ref. 10 of this paper. J. Mater. Chem., 1998, 8, 2733–2735 2733Table 2 Atomic coordinates (×104) and equivalent isotropic displacement parameters (103 A° 2) for [V2O3(H2O){O3P(CH2)3PO3}]- (H2O)2(NH4), MIL-7(LT) Atom x y z Ueq a V(1) 1674(1) 6176(1) 929(1) 29(1) V(2a)b 2423(1) 4462(1) -2167(1) 26(1) V(2b)c 1923(8) 4181(6) -2195(3) 22(2) P(1) 2158(1) 6208(1) -747(1) 22(1) P(2) 3377(1) 1659(1) -1667(1) 22(1) O(1) 2096(2) 5751(3) 29(1) 32(1) O(2) 3029(2) 7000(2) -734(2) 29(1) O(3) 3338(2) 928(3) -2386(1) 31(1) O(4) 3285(2) 742(3) -1029(1) 31(1) O(5) 2148(2) 4989(2) -1211(1) 30(1) O(6) 2651(2) 2710(3) -1715(2) 32(1) O(7) 3432(2) 5022(4) -2120(2) 58(1) O(8) 612(3) 6379(3) 864(3) 70(1) O(9) 2223(4) 3700(4) -3147(2) 79(2) C(1) 1188(3) 7208(3) -1103(2) 27(1) C(2) 4478(3) 2422(4) -1444(2) 29(1) C(3) 283(2) 6482(2) -1242(2) 33(1) Ow1 937(2) 3530(2) -2264(2) 99(2) Ow2 3450(2) 2066(2) 376(2) 119(2) Ow3 107(2) 9123(2) 566(2) 132(3) N 4249(2) 5877(2) -3274(2) 199(7) H(1a) 1156(3) 7907(3) -757(2) 33 H(1b) 1278(3) 7598(3) -1561(2) 33 H(2a) 4569(3) 2938(4) -1863(2) 35 H(2b) 4480(3) 3010(4) -1035(2) 35 H(3a) 222(2) 6000(2) -804(2) 39 H(3b) 274(2) 5865(2) -1639(2) 39 aUeq is defined as one third of the trace of the orthogonalized Uij tensor.bOccupancy=88%. cOccupancy=12%.Fig. 1 Vicinities of the vanadium atoms in MIL-7 (top) and its lowtemperature form (bottom). In MIL-7LT, the V–O distances (A° ) are given for V(2a). Table 1 Atomic coordinates (×104) and equivalent isotropic displacement parameters (103 A° 2) for [(VO)2(OH) (H2O){O3P(CH2)3PO3}]- (H2O)2(NH4), MIL-7 Atom x y z Ueq a V(1) 1554(1) 6147(1) 894(1) 16(1) V(2) 2276(1) 4439(1) -2192(1) 19(1) P(1) 2149(1) 6251(1) -749(1) 15(1) P(2) 3338(1) 1675(1) -1694(1) 15(1) O(1) 2036(1) 5746(2) -6(1) 24(1) O(2) 3078(1) 6997(2) -759(1) 22(1) O(3) 3445(1) 973(2) -2388(1) 22(1) O(4) 3171(1) 712(2) -1098(1) 22(1) O(5) 2111(1) 5064(2) -1232(1) 23(1) O(6) 2529(1) 2665(2) -1759(1) 22(1) O(7) 3324(2) 4909(2) -2280(1) 40(1) O(8) 433(1) 6243(2) 755(1) 32(1) O(9) 1909(2) 3487(2) -3095(1) 31(1) C(1) 1194(2) 7339(2) -1046(1) 21(1) C(2) 4421(2) 2535(2) -1433(1) 23(1) C(3) 255(2) 6628(2) -1209(2) 26(1) Ow1 700(2) 3625(2) -1977(1) 42(1) Fig. 2 Projection along [010] of MIL-7. A ball-and-stick model was Ow2 3372(2) 2095(3) 345(2) 63(1) choosen for the diphosphonic groups. Large circles: black=C, gray= Ow3 9(2) 9037(3) 492(2) 81(1) watsmall circles: black=P, gray=NH4+. N 4473(5) 5943(4) -3176(3) 118(2) H(1a) 1136(2) 7991(2) -683(1) 26 H(1b) 1339(2) 7789(2) -1470(1) 26 For the latter structure, a strong peak of electronic residual H(2a) 4570(2) 3071(2) -1826(1) 27 density (>8 eA° -3) was observed in the vicinity of V(2) and H(2b) 4332(2) 3112(2) -1041(1) 27 the reliability factor remained around 9%.The reliability was H(3a) 127(2) 6146(2) -791(2) 32 improved by splitting this crystallographic site into two diVer- H(3b) 309(2) 6001(2) -1585(2) 32 ent positions whose the occupancy factors were refined to 0.88 aUeq is defined as one third of the trace of the orthogonalized Uij tensor.and 0.12. That leads to the situation drawn in Fig. 1. In MIL- 7, Ow1 corresponds to a water molecule whereas in MIL- 7(LT) O1 corresponds to a terminal oxygen atom for 88% determination package.Geometrical constraints were applied to locate the hydrogen atoms of the alkyl chains. The refine- and a water molecule for 12% (and vice versa for O7). Atomic coordinates are given in Tables 1 and 2 for MIL-7 ment converged to R1(Fo)=0.0335, wR2(Fo2)=0.0966 and R1(Fo)=0.0483, wR2(Fo2)=0.1315 with 3886 and 4137 unique and MIL-7(LT) respectively.Principal bond distances appear in Fig. 1. Full crystallographic details, excluding structure reflections [Iµ2s(I )] for MIL-7 and MIL-7(LT) respectively. 2734 J. Mater. Chem., 1998, 8, 2733–2735plated monophosphonate [(C2H5)2NH2][(CH3)2NH2][V4- O4(OH)2(C6H5PO3)4].13 It is of note that the same layers have been observed by Beltran-Porter in [H3N(CH2)2- NH3]2[H3N(CH2)2NH2][FeIII(H2O)2(VIVO)8(OH)4(HPO4)4- (PO4)4]·4H2O,14 where the connections between the V–P–O layers are ensured via FeIIIO4(H2O)2 octahedra. To our knowledge, this is the first time that such an analogy between the pillared role of an organic chain and an inorganic fragment is observed in a structure. This example confirms the possibility of obtaining three-dimensional frameworks free of template since the ethylenediamine molecules are substituted by water molecules and ammonium cations (Fig. 4). The low-temperature form of MIL-7 presents a structure that is almost identical. The more important diVerences are (i) the disorder around the V(2) site already described, (ii) Fig. 3 Projection along [100] of MIL-7 showing the V–P–O inorthe mixed valency VIV–VV observed in the inorganic layers ganic layers.and explaining the change of color: blue for MIL-7 and dark green for MIL-7(LT). The change of oxidation state concerns solely the V(1) site (Fig. 1). An increase of the V(1)–O(9) distance is observed [from 1.753(3) to 1.965(2) A° ]; consequently, the bridging atom of the vanadium dimers is transformed from a hydroxyl group in MIL-7 to an oxygen atom in its low-temperature form.This structure provides a nice example of a structural type which can accept diVerent oxidation states of vanadium, whilst retaining the initial topology. In MIL-7, all the vanadium are +IV whereas MIL-7LT is a mixed valence compound VIV–VV. The change of valence state is a consequence of the oxygen atom bridging the two polyhedra of the dimer being O2- (at 170 °C) or OH- (at 200 °C).As yet, we have no explanation for this phenomenon. Perhaps the reducing character of the phosphonate increases with temperature and leads to the formation of one V4+ which leads to protonation of O(9) with Fig. 4 Projection of MIL-7 along [001] showing the tunnels occupied H+ coming from the solution, to preserve electroneutrality. by the water molecules (large circles) and ammonium cations (small circles).References 1 S. T. Wilson, B. M. Lok, C. A. Messina, T. R. Cannan and E. M. factors, have been deposited at the Cambridge Flanigen, J. Am. Chem. Soc., 1982, 104, 1146. Crystallographic Data Centre (CCDC). See Information for 2 A. M. Chippindale and R. I. Walton, J. Chem. Soc., Chem. Authors, J. Mater. Chem., 1998, Issue 1.Any request to the Commun., 1994, 2453; A. M. Chippindale and A. R. Cowley, CCDC for this material should quote the full literature citation Chem. Commun., 1996, 673; A. M. Chippindale and A. R. Cowley, and the reference number 1145/119. Zeolites, 1997, 18, 176. 3 M. I. Khan, L. M. Meyer, R. C. Haushalter, A. L. Schweitzer, J. Zubieta and J. L. Dye, Chem.Mater., 1996, 8, 43.Description 4 P. Feng, X. Bu and G. D. Stucky, Nature, 1997, 388, 735. 5 M. Estermann, L. B. McCusker, C. Baerlocher, A. Merrouche and [(VO)2(OH)(H2O){O3P(CH2)3PO3}](H2O)2(NH4) (MIL-7) H. Kessler, Nature, 1991, 352, 320. presents a pillared structure (Fig. 2) constituted by the stacking 6 Th. Loiseau and G. Fe�rey, J. Solid State Chem., 1994, 111, 403; along [100] of inorganic layers connected by the organic J.Mater. Chem., 1996, 6, 1073. propyl chains. Water molecules and ammonium ions are 7 G.Fe� rey, J. Fluorine Chem., 1995, 72, 187; C. R. Acad. Sci. Paris, Ser. II, 1998, 1, 1. inserted between the V–P–O layers. In the inorganic layers, 8 M. Cavellec, D. Riou, C. Ninclaus, J. M. Grene`che and G. Fe� rey, the two vanadium sites adopt square pyramidal coordination Zeolites, 1996, 17, 250; M.Cavellec, J. M. Grene`che, D. Riou and with four V–O distances in the basal plane in the range G. Fe� rey, Microporous Mater., 1997, 8, 103; M. Cavellec, D. Riou, 1.960(2)–2.011(2) A° and a fifth shorter bond corresponding J. M. Grene`che and G. Fe� rey, J. Magn. Magn. Mater., 1996, 163, to a vanadyl VLO linkage [1.597(2) and 1.600(2) A° ]. 173; M. Cavellec, C. Egger, J. Linares, M. Nogues, F. Varret and Furthermore, trans to the vanadyl bond, V(2) presents a very G. Fe� rey, J. Solid State Chem., 1997, 134, 349. 9 D. Riou, O. Roubeau and G. Fe� rey, Microporous and Mesoporous long distance to a water molecule (Fig. 1). The inorganic Materials, 1998, 23, 23. layers (Fig. 3) are built up from dimers of V(1)O5 and V(2)O5 10 D.Riou, C. Serre and G. Fe� rey, J. Solid State Chem., in press. square pyramids bridged by the O(9) oxygen atom, these 11 G. M. Sheldrick, SADABS program: Siemens area detector dimers being related by the PO3C phosphonate groups. absorption corrections, G. Sheldrick, unpublished work. According to the data of Brese and O’KeeVe,12 both V(1) and 12 N. E. Brese and M. O’KeeVe, Acta Crystallogr., Sect. B, 1991, V(2) are in oxidation state V4+, and the valency of O(9) is 47, 192. 13 M. I. Khan, Y. S. Lee, C. J. O’Connor, R. C. Haushalter and 1.2 showing unambiguously that O(9) corresponds to a J. Zubieta, J. Am. Chem. Soc., 1994, 116, 4525. hydroxyl group. In the phosphonates, as is usually observed, 14 M. Roca, M. D. Marcos, P. Amoros, A. Beltran-Porter, the P–O distances are in the range 1.520(2)–1.541(2) A° , A. J. Edwards and D. Beltran-Porter, Inorg. Chem., 1996, 35, shorter than the P–C distances [1.802(2) and 1.799(2) A° ]. The 5613. connections between the dimers of square pyramids and the tetrahedral phosphonate units lead to the formation of layers Paper 8/02711K characterized by the simultaneous presence of five- and eight-membered rings. Such V–P–O layers have already been described by Zubieta and coworkers in the organically tem- J. Mater. Chem., 1998, 8, 2733

ISSN:0959-9428    

DOI:10.1039/a802711k

出版商:RSC    

年代:1998

数据来源: RSC

摘要:

J O U R N A L O F C H E M I S T R Y Materials Hybrid open frameworks (MIL-n). Part 4† Synthesis and crystal structure of MIL-8, a series of lanthanide glutarates with an open framework, [Ln(H2O)]2[O2C(CH2)3CO2]3·4H2O F. Serpaggi and G. Fe� rey* Institut Lavoisier,UMR CNRS 173, Universite� de Versailles Saint-Quentin-en-Yvelines, 45, avenue des Etats-Unis, 78035 Versailles Cedex, France. E-mail: ferey@chimie.uvsq.fr Received 9th April 1998, Accepted 17th September 1998 The first series of rare-earth carboxylates with an open framework has been prepared hydrothermally (180 °C, 3 days) by the action of glutaric acid on the metal chlorides in the presence of base.The crystal structure of the neodymium compound [NdIII(H2O)]2[O2C(CH2)3CO2]3·4H2O has been determined by single-crystal X-ray diVraction.The composite material crystallizes in the monoclinic space group C2/c (no. 15) with a=8.1174(1) A° , b=15.1841(3) A° , c=19.8803(3) A° , b=93.762(1)° (final agreement factors R1=0.0279, wR2=0.0693). The organic– inorganic network is three-dimensional and consists of chains of edge-sharing rare-earth polyedra NdO8(H2O) along the [100] direction, linked together by the carbon chains along two directions.The connection involves the formation of channels parallel to the rare-earth chains in which weakly bonded water molecules are incorporated. The analogous compounds were obtained with Pr, Sm, Eu, Gd, Dy, Ho and Y. species react with inorganic compounds.4 While most of the Introduction papers cited in the literature concern non-functionalized mono- Since 1992, the ULM-n (n19) series of fluorinated micropo- phosphonates, with the aim of synthesizing layered comrous gallophosphates that our group discovered and charac- pounds,5 some attempts with diphosphonates6 and terized structurally led us to propose a hypothesis for the monophosphonates functionalized with –CO2H or –NH2 mechanism of their formation1 from solution during their groups7 led to a few three-dimensional compounds.The chelattemplated synthesis. Indeed, the structural studies showed that ing power of the diphosphonate group generally leads to a the inorganic skeleton of the porous solids was built up from pillaring between inorganic layers or chains. This property can a small number of well defined oligomers with a formal charge be utilised as a general method for obtaining composite solids of -2 (mainly gallophosphate tetramers Ga2P2 and hexamers in which the skeleton is built up simultaneously by organic Ga3P3).The hypothesis therefore claimed that the same oligo- and inorganic species. This approach can present three advanmers existed in the solution and that the charge density of the tages: (i) owing to the large number of commercial phosphonprotonated amine was the driving force of the synthesis.In ates and the possibility to prepare some of them by the the solution, we assumed that it controlled (i) the extent of Arbuzov reaction, a large modulation of the open framework the oligomeric condensation of monophosphate complexes of character of the corresponding materials may be expected, (ii) the gallium species up to the equalization of the charge it can allow non-templated syntheses of microporous samples, densities of the amine and the oligomer and (ii) the formation and (iii) this strategy can be extended to other chelating agents of a neutral ion pair which allows the infinite condensation and diVerent from phosphonates such as sulfonates and carbtherefore the formation of the solid. The structure of the latter, oxylates.Complexation of the lanthanide elements by carbwhich depends on the volume and the plasticity of the pair, is oxylates has already been studied and usually leads to the obtained using criteria of minimization of the lattice energy. formation of clusters, some of which have been structurally This hypothesis has just received a few weeks ago its first characterized.8 To our knowledge, only two-dimensional rareexperimental proof by Taulelle and coworkers2 by in situ earth oxalates have been mentioned previously,9 and no three- NMR experiments under hydrothermal conditions.dimensional lanthanide carboxylates with longer carbon chains Before this result, and considering that this hypothesis was have been reported.We report here the hydrothermal preptrue, we found for the first time some hitherto unknown aration and the crystal structure determination of the first magnetic microporous iron and vanadium phosphates,3 in three-dimensional lanthanide glutarates. which the total substitution of Ga by Fe or V induces new structural types. Supplementary work is currently in progress Experimental in this field with the use of other 3d transition metals.The extension of this idea to microporous rare earth phosphates Reagents unfortunately failed owing to the strong aYnity of phosphate LnCl3·xH2O (x=6 or 7) (Aldrich, 99.9%), glutaric acid and fluoride anions towards lanthanide elements which, what- (HO2C(CH2)3CO2H, Aldrich, 99%), and 1,3-diaminopropane ever the chemical conditions, leads to the formation of monaz- [H2N(CH2)3NH2, Aldrich, 99%] were used as received with ite type phosphates LnPO4 and fluorides LnF3.no further purification. In order to obtain lanthanide compounds with an open framework, it was then necessary to change our strategy and Preparation of lanthanide glutarates substitute phosphate anions by other chelating agents which prevent the formation of dense, insoluble inorganic species.Neodymium glutarate, [Nd(H2O)]2[O2C(CH2)3CO2]3·4H2O, This is the case for phosphonates and since the work of was hydrothermally synthesized in a 23 ml Teflon-lined Parr Alberti, Dines and Clearfield, it is well known that these bomb under autogeneous pressure (180 °C, 3 days). The starting reagents were neodymium(III) chloride hexahydrate (NdCl3·6H2O, Aldrich, 99.9%), glutaric acid [HO2C- †Part 3: preceding paper.J. Mater. Chem., 1998, 8, 2737–2741 2737Table 1 Crystal data and structure refinement for [Nd(H2O)]2- (CH2)3CO2H, Aldrich, 99%; pKa(1)=4.31 and pKa(2)= [O2C(CH2)3CO2]3·4H2O 5.4110], 1,3-diaminopropane [H2N(CH2)3NH2, Aldrich, 99%] and distilled water.The molar ratio was 1 NdCl3·6H2O51 Empirical formula C15H30Nd2O18 HO2C(CH2)3CO2H51.3 H2N(CH2)3NH25100 H2O. Neo- Formula weight 786.86 dymium chloride and glutaric acid were first dissolved sepa- Temperature/K 293(2) Wavelength/A° 0.71073 rately in 2 ml H2O. The amine was added to the glutaric acid Crystal system Monoclinic solution which was then mixed with the neodymium chloride Space group C2/c (no. 15) solution.The initial pH was 6 (this pH value was reached by Unit cell dimensions the addition of the amine and was selected in order to a/A° 8.1174(1) deprotonate both acid groups of the diacid) and the resulting b/A° 15.1841(3) pH was 5–6. The replacement of 1,3-diaminopropane by c/A° 19.8803(3) b/degrees 93.762(1) diVerent bases (NaOH, NH3, ethylenediamine, tetramethylam- Volume/A° 3, Z 2445.07(7), 4 monium hydroxide) led to the same product.The crystalline Dc/g cm-3 2.138 product obtained was filtered oV, washed with distilled water Absorption coeYcient/mm-1 4.282 and dried at room temperature. Similar procedures were used F (000) 1536 to obtain the analogous compounds with Pr, Sm, Eu, Gd, Dy, Crystal size/mm 0.3×0.2×0.16 Ho and Y.h range for data collection/ 3.38–32.24 degrees Limiting indices -11h11, -15k22, X-Ray data collection -29l21 X-Ray powder diVraction (XRD) data were collected on a Reflections collected 9823 Independent reflections 4095 (Rint=0.0294) Siemens D5000 diVractometer with Cu-Ka radiation, in the Refinement method Full-matrix least-squares on F2 range 5<2h<60°, with step size 0.04° (2h) and acquisition Data/restraints/parameters 4095/0/160 with steps of 1 s (Fig. 1). Goodness-of-fit on F2 1.152 Final R indices [I>2s(I )] R1=0.0279, wR2=0.0681 Thermogravimetry R indices (all data) R1=0.0307, wR2=0.0693 Extinction coeYcient 0.0011(1) TG analysis was carried out on a TA Instrument type 2050 Largest diV. peak and 1.435 and -1.251 theralyzer under O2 gas flow with a heating rate of hole/e A° -3 5 °Cmin-1, from 30 to 900 °C.IR spectroscopy The final reliability factors converged to R1=0.0279 and wR2=0.0693. Final positional parameters and intramolecular FTIR spectra were obtained on a Nicolet Magna-IRTM 550 distances and angles are given in Tables 2 and 3. The cell spectrometer with the usual KBr pellet technique.parameters for the isotypic Pr, Nd, Sm, Eu, Gd, Dy, Ho and Y compounds are summarized in Table 4. Structure determination Full crystallographic details, excluding structure factors, A suitable single-crystal for X-ray analysis was mounted with have been deposited at the Cambridge Crystallographic Data Araldite on a glass fiber. The intensity data were collected on a Siemens SMART three-circle diVractometer equipped with Table 2 Atomic coordinates and equivalent isotropic displacement a CCD bidimensional detector.The crystal-to-detector disparameters (A° 2) for [Nd(H2O)]2[O2C(CH2)3CO2]3·4H2O tance was 45 mm allowing for data collection up to 65° (2h). Slightly more than one hemisphere of data were recorded. Atom x y z Ueq a Crystal data and details of the data collection for [Nd(H2O)]2[O2C(CH2)3CO2]3·4H2O are given in Table 1.An Nd 0.2456(1) 0.0377(1) 0.4881(1) 0.016(1) O1 0.5142(3) 0.0448(1) 0.4384(1) 0.024(1) empirical absorption correction was applied using the O2 0.2319(3) -0.0496(2) 0.5943(1) 0.034(1) SADABS program11 based on the method of Blessing.12 The O3 -0.0150(2) 0.0797(1) 0.5344(1) 0.024(1) cell was found to be monoclinic, space group C2/c (no. 15), O4 0.2661(2) -0.1158(1) 0.4401(1) 0.029(1) a=8.1174(1) A° , b=15.1841(3) A° , c=19.8803(3) A° , b= O5 0.1534(3) 0.0551(2) 0.3665(1) 0.029(1) 93.762(1)°. The structure was solved using direct methods of O6 0.1679(3) 0.1778(1) 0.4258(1) 0.026(1) the SHELXTL package.13 Nd and O atoms were first located Ow1 0.3882(3) 0.1483(2) 0.5619(1) 0.032(1) Ow2 0.607(1) -0.4081(4) 0.6992(3) 0.181(4) and C atoms were found from diVerence-Fourier maps.Ow3 0.875(1) -0.4304(7) 0.7825(6) 0.223(5) Hydrogen atoms were refined with geometrical constraints. C1 0.3798(3) -0.0742(2) 0.6015(1) 0.018(1) C2 0.4283(4) -0.1410(2) 0.6554(2) 0.022(1) C3 0.3594(5) -0.2332(2) 0.6356(2) 0.029(1) C4 -0.0518(4) 0.2256(2) 0.5782(2) 0.030(1) C5 -0.1157(3) 0.1359(2) 0.5568(2) 0.020(1) C6 0.1334(3) 0.1379(2) 0.3701(2) 0.020(1) C7 0.0746(4) 0.1903(2) 0.3080(2) 0.024(1) C8 0 0.1340(3) b 0.027(1) H2A 0.3856(4) -0.1228(2) 0.6977(2) 0.026 H2B 0.5476(4) -0.1438(2) 0.6618(2) 0.026 H3A 0.3705(5) -0.2716(2) 0.6746(2) 0.035 H3B 0.2427(5) -0.2281(2) 0.6221(2) 0.035 H4A -0.0620(4) 0.2647(2) 0.5396(2) 0.036 H4B 0.0647(4) 0.2206(2) 0.5920(2) 0.036 H7A 0.1672(4) 0.2231(2) 0.2923(2) 0.029 H7B -0.0074(4) 0.2326(2) 0.3206(2) 0.029 H8A 0.0851(4) 0.0964(3) 0.2335(2) 0.033 H8B -0.0851(4) 0.0964(3) 0.2665(2) 0.033 aUeq is defined as one third of the trace of the orthogonalized Uij tensor.) Fig. 1 X-Ray pattern for [Nd(H2O)]2[O2C(CH2)3CO2]3·4H2O. 2738 J. Mater. Chem., 1998, 8, 2737–2741Table 3 Bond lengths (A° ) and angles (degrees) for [Nd(H2O)]2[O2C- (CH2)3CO2]3·4H2Oa Nd–O3 2.445(2) C1–C2 1.508(4) Nd–O1 2.455(2) C2–C3 1.549(4) Nd–Ow1 2.467(2) C3–C4c 1.524(4) Nd–O5 2.498(2) C4c–C5c 1.509(4) Nd–O2 2.500(2) C5c–O3c 1.282(3) Nd–O6 2.521(2) C5c–O4d 1.264(3) Nd–O4 2.529(2) C6–O5 1.270(3) Nd–O3a 2.602(2) C6–O6 1.278(3) Nd–O1b 2.671(2) C6–C7 1.518(4) C1–O1b 1.288(3) C7–C8 1.528(4) C1–O2 1.257(3) O3–Nd–O1 162.32(7) Ow1–Nd–O1b 72.37(7) Fig. 2 Schematic of the open framework of [Nd(H2O)]2- O3–Nd–Ow1 89.02(8) O5–Nd–O1b 137.79(7) [O2C(CH2)3CO2]3·4H2O showing neodymium chains linked along O1–Nd–Ow1 79.32(8) O2–Nd–O1b 50.29(7) two directions by two types of carboxylates, in order to form tunnels O3–Nd–O5 97.17(8) O6–Nd–O1b 144.57(7) along the metal chains. O1–Nd–O5 79.78(8) O4–Nd–O1b 73.15(7) Ow1–Nd–O5 126.99(8) O3a–Nd–O1b 105.31(7) O3–Nd–O2 74.55(8) C1b–O1–Nd 155.6(2) O1–Nd–O2 116.96(7) C1b–O1–Ndb 90.3(2) Ow1–Nd–O2 84.53(9) Nd–O1–Ndb 113.25(8) O5–Nd–O2 147.80(9) C1–O2–Nd 99.2(2) O3–Nd–O6 76.70(7) C5–O3–Nd 153.1(2) O1–Nd–O6 87.98(7) C5a–O3a–Nd 92.7(2) Ow1–Nd–O6 79.04(8) Nd–O3–Nda 112.75(8) O5–Nd–O6 52.07(7) C5a–O4–Nd 96.6(2) O2–Nd–O6 146.97(8) C6–O5–Nd 94.7(2) O3–Nd–O4 117.55(7) C6–O6–Nd 93.5(2) O1–Nd–O4 78.83(7) O2–C1–O1b 119.9(3) Ow1–Nd–O4 144.28(7) O2–C1–C2 118.9(2) O5–Nd–O4 75.83(8) O1b–C1–C2 121.1(2) O2–Nd–O4 80.66(9) C1–C2–C3 110.7(3) O6–Nd–O4 127.80(8) C2–C3–C4c 112.4(3) O3–Nd–O3a 67.25(8) C3–C4c–C5c 114.3(3) O1–Nd–O3a 127.50(7) O4d–C5c–O3c 119.8(3) Ow1–Nd–O3a 150.79(8) O4d–C5c–C4c 121.3(2) O5–Nd–O3a 74.92(8) O3c–C5c–C4c 118.9(2) O2–Nd–O3a 73.20(8) O5–C6–O6 119.7(3) O6–Nd–O3a 109.84(7) O5–C6–C7 120.5(3) O4–Nd–O3a 50.81(6) O6–C6–C7 119.8(3) O3–Nd–O1b 122.37(7) C6–C7–C8 114.1(3) O1–Nd–O1b 66.75(8) C7–C8–C7e 111.9(4) aSymmetry transformations used to generate equivalent atoms: a -x, -y, -z+1; b-x+1, -y, -z+1; cx+1/2, y-1/2, z; d-x+1/2, -y-1/2, -z+1; e-x, y, -z+1/2.Centre (CCDC). See Information for Authors, J. Mater. Chem., 1998, Issue 1. Any request to the CCDC for this Fig. 3 Projection of the structure of [Nd(H2O)]2[O2C(CH2)3- material should quote the full literature citation and the CO2]3·4H2O along the [011] direction showing the linkage of the reference number 1145/120. chains of neodymium polyhedra by the carbon chains (in black) along the [101] direction (other carbon atoms, free water molecules and hydrogen atoms have been omitted for more clarity). Results Structure of [Nd(H2O)]2[O2C(CH2)3CO2]3·4H2O formation of small channels along the [100] direction (with free aperture 3.3 A° and parallel to the neodymium polyhedra The structure of [Nd(H2O)]2[O2C(CH2)3CO2]3·4H2O is threedimensional, consisting of chains of edge-sharing NdO8(H2O) chains), in which weakly bonded water molecules are incorporated.polyhedra, along the [100] direction, linked together by the carbon chains along the [010] and roughly [101] directions. As highlighted in Fig. 2, there are two types of carboxylates, in the ratio 152. The first type (carboxylate I, black in the The complex connection, schematized in Fig. 2, involves the Table 4 Cell parameters, unit cell volume, and calculated densities for [M(H2O)]2[O2C(CH2)3CO2]3·4H2O (M=Pr, Nd, Sm, Eu, Gd, Dy, Ho or Y) M a/A° b/A° c/A° b/degrees V/A° 3 Dc/g cm-3 Pr 8.1319(1) 15.1855(2) 19.8758(2) 93.732(0) 2449.2(1) 2.12 Nd 8.1174(1) 15.1841(3) 19.8803(3) 93.762(1) 2445.1(1) 2.14 Sm 8.0160(2) 15.0592(1) 19.7063(4) 93.940(1) 2373.2(1) 2.24 Eu 8.0161(3) 15.0740(5) 19.7237(6) 93.978(1) 2377.6(1) 2.24 Gd 7.9767(1) 15.0043(2) 19.6852(1) 94.326(1) 2349.3(1) 2.30 Dy 7.9516(1) 14.9801(2) 19.7034(3) 94.668(1) 2339.2(1) 2.34 Ho 7.9355(1) 14.9338(1) 19.6973(1) 94.808(1) 2327.6(1) 2.36 Y 7.9355(3) 14.9438(6) 19.6973(8) 94.808(1) 2327.6(3) 1.93 J.Mater. Chem., 1998, 8, 2737–2741 2739Fig. 6 Space filling representation of the structure of [Nd- (H2O)]2[O2C(CH2)3CO2]3·4H2O showing the open framework with small channels along the [100] direction.Fig. 4 Projection of the structure of [Nd(H2O)]2[O2C(CH2)3- coordinated O1b and O3a oxygen atoms, bonded to two CO2]3·4H2O along the [001] direction showing the linkage of the neodymium atoms and carbon; in the chelating –C6O5O6- chains of neodymium polyhedra by the carbon chains (in white) carboxylic group (carboxylate I ), the C6–O5 and C6–O6 along the [010] direction (other carbon atoms, free water molecules distances are equivalent [1.270(3) and 1.278(3) A° , respect- and hydrogen atoms have been omitted for more clarity).ively]. The chelating and bridging eVects of the carboxylic groups can also be evidenced by FTIR analysis. Indeed, the bands observed in the range 1600–1400 cm-1 (1536 cm-1, 1445 and 1411 cm-1) can be assigned to nCLO and nCKO vibrations for bridging and chelating carboxylic groups, as Deacon and Phillips showed for metal acetates and trifluoroacetates. 14 The whole arrangement leads to the formation of an open framework, as shown in Fig. 5 and 6. The channels are elliptical with free aperture dmin#3 A° (between two H atoms, RH=1.1 A° ) by dmax#5 A° (between two O atoms, RO= 1.5 A° ). Such dimensions do not allow any porosity.Two Nd–Nd distances, 4.20(1) and 4.28(1) A° occur in the chains. The neodymium atoms are nine-coordinated by one water molecule (Ow1) and eight oxygen atoms from five carboxylic groups, as shown in Fig. 7. Three carboxylate groups chelate the metal atom while two other carboxylate Fig. 5 Projection of the structure of [Nd(H2O)]2[O2C(CH2)3- CO2]3·4H2O along the [100] direction showing the channels and water molecules within them (for a better distinction between the carbon chains, both types of chains are represented in white and black, according to Fig. 3 and 4). figures), which connect the chains along the [101] direction, simply chelates one neodymium atom at each end, as shown in Fig. 3. The second type (carboxylate II, white in the figures) which ensures the linkage of the chains along the [010] direction chelates a metal atom but one of the chelating oxygen atoms is also shared with an adjacent metal atom, as shown in Fig. 4. Examination of the C–O distances shows two types of –CO2- carboxylate groups: both –C1O1bO2- and –C5aO3aO4-, which belong to carboxylate II, exhibit one Fig. 7 Representation of the coordination about the neodymium atom short [C1–O2 1.257(3), C5a–O4 1.264(3) A° ] and one longer in [Nd(H2O)]2[O2C(CH2)3CO2]3·4H2O including the numberings scheme used in the Tables.distance [C1–O1b 1.288(3), C5a–O3a 1.282(3) A° ], due to three- 2740 J. Mater. Chem., 1998, 8, 2737–2741P. Zappelli, Angew. Chem., Int. Ed. Engl., 1993, 32, 1357; groups share only one bridging oxygen atom.The angles G. Alberti, F. Marmottini, S. Murcia-Mascaro� s and R. Vivani, formed at the neodymium atom by the chelate rings are quite Angew. Chem., Int. Ed. Engl., 1994, 33, 1594; L. A. Vermeulen and small [O5–Nd–O6 52.1(1), O2–Nd–O1b 50.3(1), O4–Nd–O3a M. E. Thompson, Chem. Mater., 1994, 6, 77; V. Soghomonian, 50.8(1)°], leading to a highly distorted polyhedron around the Q.Chen, R. C. Haushalter and J. Zubieta, Angew. Chem., Int. Ed. neodymium. Moreover, each chelate ring has one short and Engl., 1995, 34, 223; V. Soghomonian, R. Diaz, R. C. Haushalter, C. J. O’Connor and J. Zubieta, Inorg. Chem., 1995, 34, 4460; one longer Nd–O bond [Nd–O2 2.50(1) and Nd–O1b H. Byrd, A. Clearfield, D. Poojary, K. P. Reis and M. E. 2.67(1) A° , Nd–O4, 2.53(1) and Nd–O3a 2.60(1) A° ].The pres- Thompson, Chem. Mater., 1996, 8, 2239; D. M. Poojary, ence of water molecules seen by the X-ray analysis and B. Zhang, P. Bellinghausen and A. Clearfield, Inorg. Chem., 1996, indicated by bond valence calculations15 is confirmed by TG 35, 4942; 5254; G. Bonavia, R. C. Haushalter, C. J. O’Connor and analysis, the curve indicating two successive weight losses of J.Zubieta, Inorg. Chem., 1996, 35, 5603; P. J. Zapf, D. J. Rose, 7.4 and 4.6 wt.% in the ranges 30–100 and 100–200 °C, which R. C. Haushalter and J. Zubieta, J. Solid State Chem., 1996, 125, 182; D. L. Lohse and S. C. Sevov, Angew. Chem., Int. Ed. Engl., can be attributed to the loss of free water molecules Ow2 and 1997, 36, 1619. Ow3 (9.2 wt.%) and coordinating water molecule Ow1 7 S.Drumel, P. Janvier, P. Barboux, M. Bujoli-DoeuV and (4.6 wt.%), respectively. The final residue at 900 °C is the B. Bujoli, Inorg. Chem., 1995, 34, 148; S. Drumel, P. Janvier, D. neodymium oxide Nd2O3. The compound is able to reversibly Deniaud and B. Bujoli, J. Chem. Soc., Chem. Commun., 1995, adsorb and desorb free water molecules in the temperature 1051. range 25–100 °C; the study of this behaviour will be reported 8 J.W. Bats, R. Kalus and H. Fuess, Acta Crystallogr., Sect. B, 1979, 35, 1225; M. C. Favas, D. L. Kepert, B. W. Skelton and elsewhere.16 A. H. White, J. Chem. Soc., Dalton Trans., 1980, 54; M. S. Khiyalov, I. R. Amiraslanov, F. N. Musaev and Kh. S. Mamedov, Koord. Khim., 1982, 8, 548; H. Gries and H. Miklautz, Physiol. Acknowledgements Chem.Phys. Med. NMR, 1984, 16, 105; M. S. Konings, W. C. Dow, D. B. Love, K. N. Raymond, S. C. Quay and S. M. We are grateful to Dr. T. Loiseau for the X-ray data collection Rocklage, Inorg. Chem., 1990, 29, 1448; M. A. J. Moss and and Rhodia for financial support. C. J. Jones, J. Chem. Soc., Dalton Trans., 1990, 581; D. Zhi-Bang, J. Zhing-Sheng, W. Ge-Cheng and N.Jia-Zan, J. Struct. Chem., 1990, 9, 64; L. Ehnebom and B. F. Pedersen, Acta Chem. Scand., References 1992, 46, 126; S. J. Franklin and K. N. Raymond, Inorg. Chem., 1994, 33, 5794; C. Daiguebonne, Y. Gerault, O. Guillou, 1 G.Fe� rey, J. Fluorine Chem., 1995, 72, 187 and references therein; A. Lecerf, K. Boubekeur, P. Batail, M. Khan and O. Khan, C. R. Acad. Sci. Se�r. C, 1998, 2, 1 and references therein.International Conference on f Elements 3, Paris, France, 1997. 2 M. Haouas, C. In-Ge�rardin, F. Taulelle, C. Estournes, T. Loiseau 9 S. Romero, A. Mosset and J. C. Trombe, Eur. J. Solid State Inorg. and G. Fe� rey, J. Phys. Chem., 1998, 95, 320. Chem., 1997, 34, 209 and references therein. 3 D. Riou and G. Fe� rey, J. Solid State Chem., 1994, 111, 422; 10 Handbook of Chemistry and Physics, Boca Raton, FL, 77th edn., D.Riou, F. Taulelle and G. Fe� rey, Inorg. Chem., 1996, 35, 6392; 1996. M. Cavellec, D. Riou, C. Ninclaus, J.-M. Grene`che and G. Fe� rey, 11 G. M. Sheldrick, SADABS, a program for the Siemens Area Zeolites, 1996, 17, 250; M. Cavellec, D. Riou, J.-M. Grene`che and Detector ABSorption correction, 1994. G. Fe� rey, J. Magn. Magn. Mater., 1996, 163, 173; M. Cavellec, 12 R. Blessing, Acta Crystallogr., Sect. A, 1995, 51, 33. J.-M. Grene`che, D. Riou and G. Fe� rey, Microporous Mater., 1997, 13 G. M. Sheldrick, SHELXTL version 5.03, software package for 8, 103; M. Cavellec, J.-M. Grene`che and G. Fe� rey, Microporous the Crystal Structure Determination, 1994. Mater., 1998, 20, 45; M. Cavellec, C. Egger, J. Linares, 14 G. B. Deacon and R. J. Phillips, Coord. Chem. Rev., 1980, 33, 227. M. Nogues, F. Varret and G. Fe� rey, J. Solid State Chem., 1997, 15 N. E. Brese and M. O’KeeVe, Acta Crystallogr., Sect. B, 1991, 134, 349. 47, 192. 4 A. Clearfield, Curr. Opin. Solid State Mater. Sci., 1996, 1, 268 and 16 F. Serpaggi, T. Luxbacher, A. K. Cheetham and G. Fe� rey, J. Solid references therein. State Chem., submitted. 5 M. E. Thompson, Chem. Mater., 1994, 6, 1168 and references therein. 6 G. Alberti, U. Costantino, F. Marmottini, R. Vivani and Paper 8/02713G J. Mater. Chem., 199

ISSN:0959-9428    

DOI:10.1039/a802713g

出版商:RSC    

年代:1998

数据来源: RSC

摘要:

J O U R N A L O F C H E M I S T R Y Materials Hybrid open frameworks (MIL-n). Part 5† Synthesis and crystal structure of MIL-9: a new three-dimensional ferrimagnetic cobalt(II ) carboxylate with a two-dimensional array of edge-sharing Co octahedra with 12-membered rings Carine Livage,a Chrystelle Egger,a Marc Noguesb and Ge�rard Fe� rey*a aInstitut Lavoisier, Universite� de Versailles St-Quentin, 45 av.des Etats-Unis, 78035 Versailles, France. E-mail: ferey@chimie.uvsq.fr; livage@chimie.uvsq.fr bLaboratoire de Magne�tisme et d’Optique, Universite� de Versailles St-Quentin, 45 av. des Etats- Unis, 78035 Versailles, France Received 9th April 1998, Accepted 17th September 1998 Co5(OH)2(C4H4O4)4, a new cobalt(II ) succinate with an open framework, was prepared hydrothermally (180 °C, 72 h, autogenous pressure) from a 253585120 mixture of Co(II) chloride, succinic acid, potassium hydroxide and water.Its monoclinic structure was solved by single crystal X-ray diVraction [space group P21/c (no. 14) with a=9.5631(2) A° , b=9.4538(2) A° , c=12.5554(2) A° , b=96.968(1)°, V=1126.72(4) A° 3, Z=4] from 3077 unique reflections [I2s(I )], R1=0.020 and wR2=0.054. The three-dimensional structure is built up from layers of edge sharing octahedra pillared by succinate ions.Within the layers, cobalt octahedra form 12-membered ring windows. Below 10 K, Co5(OH)2(C4H4O4)4, exhibits ferrimagnetic behavior. to the molar composition of 2 CoCl2·6H2053 CO2 H- Introduction (CH2)2CO2H58 KOH5120 H2O, was homogenized for 10 min The preparation of three-dimensional open frameworks based in an ultrasonic bath and the resulting solution was heated on transition metals is one of the most important aims of for three days at 180 °C under autogenous pressure (pH research due to their practical application as catalysts, hosts around 6).The resulting solid phase was collected by filin intercalation compounds and their potential electronic tration, washed with distilled water and dried at room temperaproperties. 1–3 Among the 3d metal zeolite analogues, some of ture. The solid product was a single phase with large hexagonal the most promising and studied materials are those based on dark red crystals of the title compound and was obtained in cobalt.4–7 With the utilization of the hydrothermal technique, a yield based on cobalt of around 70%.The X-ray powder considerable progress has been reported on the development diVraction pattern is in agreement with that calculated after of open framework compounds based on cobalt, and the resolution of the structure. A single crystal of suitable size was literature already contains numerous examples of cobalt phos- used for structure determination by X-ray diVraction.IR phates and phosphonates with a large structural variety.8–14 spectra exhibited the following relevant features (KBr pellet): We recently introduced a new way for obtaining microporous a narrow band due to the hydroxyl group, n(CoO–H) materials in which both organic (dicarboxylates) and inorganic 3330 cm-1; n(C–H) stretching bands characteristic of CH2 species build the open framework.3,15,16 We present here the groups between 2910 and 3000 cm-1; a very broad band, synthesis and characterization of Co5(OH)2(C4H4O4)4, a new composed of four peaks between 1510 and 1610 cm-1, associcobalt carboxylate with a two dimensional array of edge- ated with the deprotonated carboxylic groups, and the followsharing Co2+ octahedra pillared by succinate ions.ing relevant bands; 1460, 1440, 1420, 1410, 1325, 1305, 1275, Co5(OH)2(C4H4O4)4 is denoted MIL-9 for Materials of 1240, 1225, 1180, 1165, 1035, 865, 810, 680, 660, 565, 510 and Institut Lavoisier. 380 cm-1. TG measurements under oxygen gas flow showed a unique and abrupt weight loss around 320 °C characteristic Experimental of the combustion of the organic moiety (theoretical weight loss 53%, observed 56%).The resulting product at 350 °C is Materials and methods CoO. Satisfactory elemental analysis was obtained. Hydrothermal reactions were carried out in 23 ml Teflonwalled Parr acid digestion bombs. X-Ray powder diVraction Single crystal structure determination data were collected on a Siemens D5000 diVractometer (Cu- Ka radiation). FTIR spectra were obtained on a Nicolet One of the dark red hexagonal crystals of Co5(OH)2(C4H4O4)4 Magna-IR 550 spectrometer.TG measurements were done (0.5×0.3×0.15 mm) was glued to a glass fiber and mounted using a TA-instrument 2050 thermo-analyser (oxygen gas flow, on a Siemens SMART CCD diVractometer using monochro- 5 °Cmin-1). Susceptibility measurements were carried out matic molybdenum radiation [l(MoKa)=0.7107 A° ].Intensity using a SQUID magnetometer; data were not corrected for data were collected on a one half sphere in 1271 frames with diamagnetism. v scans (width of 0.30° and exposure time 30 s per frame). A summary of crystal data is presented in Table 1. The data Hydrothermal synthesis and characterization of collected (7953 total reflections, 3077 unique) were corrected Co5(OH)2(C4H4O4)4 for Lorentz and polarization eVects. Absorption corrections were applied using the SADABS program.17 The structure A hydrothermal synthesis has been set up using CoCl2·6H2O as the cobalt source.The starting mixture, corresponding was solved by direct methods and standard diVerence Fourier techniques (SHELXL-93).18 Cobalt and oxygen atoms were first located and all the remaining atoms, including hydrogen †Part 4: preceding paper.J. Mater. Chem., 1998, 8, 2743–2747 2743Table 1 Summary of crystal data and structure refinement tivity of the three Co2+ ions is given in Fig. 2. Co(1)O6 and Co(2)O6 octahedra are strongly distorted, with three short Formula weight 396.5 Co–O bond distances (2.02–2.09 A° ), two medium Space group P21/c (2.17–2.22 A° ) and one long [2.368(1) and 2.314(1) A° ].By Unit cell dimensions contrast, Co(3), which lies on an inversion center, has a a/A° 9.5631(2) b/A° 9.4538(2) regular octahedral geometry with Co–O bonds of ca. c/A° 12.5554(2) 2.11±0.05 A° . The hydroxide oxygen atom, O(9), is shared b/degrees 96.9680(10) between the three distinct cobalt atoms with Co–m3-O(H) Volume/A° 3, Z 1126.72(4), 2 bonds between 2.02 and 2.11 A° .Only one noticeable hydrogen Dc/Mg m3 2.337 bond linkage exists in the solid, a bond between the hydrogen Absorption coeYcient/mm-1 3.697 atom of the hydroxide group and an oxygen atom of a F(000) 786 Crystal size/mm 0.5×0.3×0.15 neighboring octahedron [(O(9)–H(9),O(3) 2.073 A° ]. The h range for data collection/degrees 2.70–30.24 metallic oxide framework can be described as an infinite square Limiting indices -12h12, -12k13, net of edge-sharing cobalt octahedra.Co(3) octahedra occupy -17l11 the vertices of this square net. The topology creates lozenge- Goodness-of-fit on F2 1.044 shaped cavities made from 12 edge-sharing octahedra in which Final R indices [I>2s(I )] R1=0.0202, wR2=0.0540 one of the two alkyl chain [carbons C(1)–C(4)] is located R indices (all data) R1=0.0236, wR2=0.0551 Largest diV.peak and hole/e A° -3 0.535 and -0.395 (Fig. 3). Each dicarboxylate anions has covalent bonds with the three diVerent cobalt atoms: with one carboxylic group bridging two pairs of cobalt octahedra (Co–m2-O, bond lengths atoms, were found by diVerence Fourier maps.Refinements between 2.06 and 2.31 A° ) and the other linking two cobalt (206 parameters) were performed by full-matrix least-squares octahedra (Co–m1-O, bond lengths between 2.02 and 2.09 A° ). analysis, with anisotropic thermal parameters for all non- The first succinate is in the layers [carbons C(1)–C(4)] while hydrogen atoms. The reliability factors converged to R1(FO)= the second one [carbons C(5)–C(8)], in which the same type 0.020 and wR2(FO2)=0.054.Fractional atomic coordinates of linkage occurs, acts as a pillar leading to a three-dimensional are given in Table 2 and selected bonds distances and angles structure (Fig structure can be estimated as a class in Table 3. IV solid for cobalt compounds in the classification of Stucky.10 Full crystallographic details, excluding structure factors, have been deposited at the Cambridge Crystallographic Data Magnetic properties Centre (CCDC).See Information for Authors, J. Mater. The presence of the infinite array of edge sharing Co2+ Chem., 1998, Issue 1. Any request to the CCDC for this octahedra has, of course, an important eVect on the magnetic material should quote the full literature citation and the properties of the compound, with the predicable existence of reference number 1145/121.strong magnetic couplings between the d7 centers. The temperature dependence of x-1, measured with a SQUID suscep- Results tometer (100 G), is shown in Fig. 5 with the magnetization vs. the applied magnetic field at 2 K. The linear fit of x-1(T) data Structure of Co5(OH)2(C4H4O4)4 above 50 K indicates a Curie–Weiss law (C=18.73 emu mol-1 The three-dimensional framework consists of an infinite and hP=-72.5 K) as well as the room temperature eVective two-dimensional array of edge-sharing cobalt octahedra (b, c moment of 5.5 mB per atom which is slightly larger than the plane) covalently linked by two diVerent succinate anions commonly observed magnetic moments for independent (Fig. 1). The layers are stacked along the a axis, the length of Co2+octahedra.19 Around 25 K a marked change in the x-1(T) which is the interlayer spacing (9.56 A° ). Cobalt atoms occupy curve, characterized by an important increase of susceptibility, three diVerent crystallographic sites with an octahedral coordi- indicates a ferrimagnetic behavior confirmed by the M(H) nation of oxygen atoms arising from the two succinate ions curve below the critical temperature (TC#10 K).The ferrimagand one hydroxyl group. A representation of the local connec- netism of the title compound can be easily understood from structural considerations and superexchange analysis.20 Indeed, another way of describing the layers starts from the Table 2 Atomic coordinates (×104) and equivalent isotropic fact that the diVerent cobalt sites of the structure have diVerent displacement parameters (10-3 A° 2) for non-hydrogen atoms Atom x y z Ueq a Co(1) 8853(1) 2072(1) 1645(1) 14(1) Co(2) 11659(1) 3195(1) 3457(1) 14(1) Co(3) 10000 0 0 12(1) O(1) 8741(1) 1902(1) -127(1) 17(1) O(2) 9520(1) 2268(1) 3356(1) 18(1) O(3) 8519(1) 4230(1) 1632(1) 22(1) O(4) 12546(1) 1280(1) 3921(1) 29(1) O(5) 11299(1) 2546(1) 1767(1) 17(1) O(6) 11696(1) 3642(1) 5272(1) 18(1) O(7) 13551(1) 4184(1) 3464(1) 23(1) O(8) 6708(1) 1577(1) 1592(1) 22(1) O(9) 9497(1) 41(1) 1591(1) 13(1) C(1) 8734(2) 2819(2) -877(1) 16(1) C(2) 7740(3) 4072(3) -913(2) 45(1) C(3) 6832(2) 4237(2) 12(1) 21(1) C(4) 12342(2) -33(2) 4015(1) 17(1) C(5) 12138(2) 2996(2) 6153(1) 15(1) C(6) 13747(2) 2938(2) 6425(2) 22(1) Fig. 1 Representation of the structure parallel to the crystallographic C(7) 15642(2) 5552(2) 3533(2) 26(1) C(8) 14024(2) 5442(2) 3467(1) 17(1) a axis. Black spheres are carbon atoms C(1)KC(4) which connect the octahedra in the cobalt layer. Gray spheres [C(5)KC(8)] correspond aUeq is defined as one third of the trace of the orthogonalized Uij tensor.to the second succinate ion linking two successive layers. 2744 J. Mater. Chem., 1998, 8, 2743–2747Table 3 Selected bond lengths (A° ) and angles (degrees) for Co5(OH)2(C4H4O4)4 a Co(1)KO(9) 2.0199(10) Co(3)KO(1) 2.1587(10 Co(1)KO(3) 2.0649(12) Co(3)KO(1)d 2.1587(10) Co(1)KO(8) 2.0973(12) O(1)KC(1) 1.279(2) Co(1)KO(2) 2.1730(11) O(2)KC(1)e 1.294(2) Co(1)KO(1) 2.2211(11) O(3)KC(4)a 1.289(2) Co(1)KO(5) 2.3682(11) O(4)KC(4) 1.264(2) Co(2)KO(7) 2.0357(11) O(5)KC(5)b 1.284(2) Co(2)KO(4) 2.0536(12) O(6)KC(5) 1.289(2) Co(2)KO(9)a 2.0634(10) O(7)KC(8) 1.272(2) Co(2)KO(5) 2.1960(11) O(8)KC(8)c 1.278(2) Co(2)KO(2) 2.2149(11) C(1)KC(2) 1.516(2) Co(2)KO(6) 2.3138(11) C(2)KC(3) 1.540(3) Co(3)KO(6)b 2.0644(11) C(3)KC(4)a 1.535(2) Co(3)KO(6)e 2.0644(11) C(5)KC(6) 1.536(2) Co(3)KO(9) 2.1111(11) C(6)KC(7)f 1.541(2) Co(3)KO(9)d 2.1112(11) C(7)KC(8) 1.543(2) O(9)KCo(1)KO(3) 170.53(5) O(9)aKCo(2)KO(2) 81.08(4) O(9)KCo(1)KO(8) 95.07(4) O(5)KCo(2)KO(2) 78.37(4) O(3)KCo(1)KO(8) 94.02(5) O(7)KCo(2)KO(6) 90.25(5) O(9)KCo(1)KO(2) 93.45(4) O(4)KCo(2)KO(6) 85.70(5) O(3)KCo(1)KO(2) 87.16(4) O(9)aKCo(2)KO(6) 79.55(4) O(8)KCo(1)KO(2) 102.67(5) O(5)KCo(2)KO(6) 169.99(4) O(9)KCo(1)KO(1) 82.84(4) O(2)KCo(2)KO(6) 91.85(4) O(3)KCo(1)KO(1) 94.28(4) O(6)bKCo(3)KO(6)c 180.0 O(8)KCo(1)KO(1) 91.37(5) O(6)bKCo(3)KO(9) 95.53(4) O(2)KCo(1)KO(1) 165.77(4) O(6)cKCo(3)KO(9) 84.47(4) O(9)KCo(1)KO(5) 83.05(4) O(6)bKCo(3)KO(9)d 84.47(4) O(3)KCo(1)KO(5) 87.96(4) O(6)cKCo(3)KO(9)d 95.53(4) O(8)KCo(1)KO(5) 177.31(4) O(9)KCo(3)KO(9)d 180.0 O(2)KCo(1)KO(5) 75.58(4) O(6)bKCo(3)KO(1) 85.07(4) O(1)KCo(1)KO(5) 90.31(4) O(6)cKCo(3)KO(1) 94.93(4) O(7)KCo(2)KO(4) 93.89(5) O(9)KCo(3)KO(1) 82.29(4) O(7)KCo(2)KO(9)a 94.83(4) O(9)dKCo(3)KO(1) 97.71(4) O(4)KCo(2)KO(9)a 162.87(5) O(6)bKCo(3)KO(1)d 94.93(4) O(7)KCo(2)KO(5) 99.67(5) O(6)cKCo(3)KO(1)d 85.07(4) O(4)KCo(2)KO(5) 92.23(5) O(9)KCo(3)KO(1)d 97.71(4) O(9)aKCo(2)KO(5) 100.79(4) O(9)dKCo(3)KO(1)d 82.29(4) O(7)KCo(2)KO(2) 174.98(5) O(1)KCo(3)KO(1)d 180.0 O(4)KCo(2)KO(2) 90.81(5) Magnetic couplings Within the pentamer Between pentamers Co(1)KO(1)KCo(3) 91.5 Co(1)KO(5)KCo(2) 98.8 Co(1)KO(9)KCo(3) 98.9 Co(1)KO(2)KCo(2) 104.4 Co(1)KO(9)KCo(2) 129.8 Co(2)KO(9)KCo(3) 97.9 Co(2)KO(6)KCo(3) 91.9 Symmetry transformations used to generate equivalent atoms: a-x+2, y+1/2, -z+1/2; b-x+2, y-1/2, -z+1/2; cx, -y+1/2, z-1/2; d-x+2, -y, -z; ex, -y+1/2, z+1/2; f-x+3, -y+1, -z+1.Fig. 2 Local connectivity for the three Co2+. {CoO6 } octahedra are represented by a polyhedral representation and organic alkyl chains Fig. 3 Polyhedral representation of the twelve-membered rings cavity by a ball and stick representation [black spheres C(1)KC(4) and gray spheres C(5)KC(8)].The small black sphere corresponds to the defined by the 2-D array of CoKOKCo. The organic moieties, covalently bond to cobalt atoms, have been omitted for clarity. hydroxyl group O(9)KH. J. Mater. Chem., 1998, 8, 2743–2747 2745Fig. 4 Representation of one layer of the structure of Co5(OH)2- (C4H4O4)4. {CoO6} octahedra are represented by a polyhedral repre- Fig. 6 Representation showing the connectivity between cobalt sentation and organic alkyl chains by a ball-and-stick representaoctahedra within the pentamers. The organic chains have been omitted tion. for clarity. Therefore, the observed ferrimagnetic behavior can be justified assuming (i) antiferromagnetic couplings within the pentamer, which leads, owing to the diVerent multiplicities of the Co sites, to a resulting moment of 3mCo2+; (ii) a ferromagnetic coupling between the pentamers to avoid the compensation of the moments, which implies a Co(1)RO(2)S SO(5)R Co(2) ferromagnetic interaction in agreement with the largest superexchange angles of the structure, and (iii) a ferromagnetic coupling between the layers.Such a proposal is currently being studied by neutron diVraction.Conclusion Owing to the diYculties in synthesizing pure metal oxides with an open framework, synthetic strategies using organic agents are of interest for the self-assembly of infinite solids.3,6 Dicarboxylic acids have long been known to act as chelating ligands, generating isolated metal complexes. With the synthesis of Co5(OH)2(C4H4O4)4 we have demonstrated that, using a hydrothermal technique, dicarboxylic acids can participate in the skeleton with inorganic species and lead to non templated open framework solids, in which they act both as part of the oxide sheet and as pillars between the latter.This type of building leads also to magnetic solids. Study of the Fig. 5 Temperature dependence of x-1 (a) and M(H) at 2K (b). magnetic structure of the title compound is currently in progress.Complementary studies are on the way for tailoring the structure by changing the length of the dicarboxylate multiplicities, the WyckoV positions being 4e, 4e and 2a for Co(1), Co(2) and Co(3) respectively. Therefore, Co(3) is chains. surrounded by two Co(1) and two Co(2), and generates a pentameric unit in which Co(1) and Co(2) octahedra are References linked by corners [O(9) atoms] and share edges with Co(3) (Fig. 6). The layer is generated by the connection of these 1 R. C. Haushalter and L. A. Mundi, Chem. Mater., 1992, 4, 31. 2 S. Drumel, P. Janvier, M. Bujoli-DoeuV and B. Bujoli, Inorg. pentamers by edges. In terms of superexchange magnetic Chem., 1996, 35, 5786. couplings, this structure exhibits, according to Goodenough,20 3 G.Ferey, C.R. Acad. Sci. Ser. C1, 1998, 1. 180° [Co(1)–Co(2)] and 90° interactions [Co(1)–Co(3), 4 A. M. Chippindale and A. R. Cowley, Zeolites, 1997, 18, 176. Co(2)–Co(3), Co(1)–Co(2) (between pentamers)]. Table 3 5 A. M. Chippindale, A. R. Cowley and R. I. Walton, J. Mater. gives the values of the diVerent superexchange angles. If the Chem., 1996, 6, 611. 6 P.Feng, X. Bu and G. D. Stucky, Nature, 1997, 388, 735. d7–d7 superexchange 180° interactions are always antiferro- 7 X. Bu, P. Feng and G. D. Stucky, Science, 1997, 278, 2080. magnetic, the 90° ones can be either antiferromagnetic 8 Q. M. Gao, A. M. Chippindale, A. R. Cowley and J. S. Chen, (eg–p–t2g) or ferromagnetic (eg–ps–ps–eg), the latter case being J. Phys. Chem. B, 1997, V101, 48, 9940.illustrated for instance by Co2PO4F.21 In our case, the value 9 P. Feng, X. Bu, S. H. Tolbert and G. D. Stucky, J. Am. Chem. of hP (-72 K) indicates moderate antiferromagnetic inter- Soc., 1997, 119, 2497. actions. If all the interactions, whatever the superexchange 10 P. Feng, X. Bu and G. D. Stucky, J. Solid State Chem., 1997, 131, 160 and 387. angle, were AF, a larger value of hP would be expected. 2746 J. Mater. Chem., 1998, 8, 2743–274711 D. L. Lohse and S. C. Sevov, Angew. Chem., Int. Ed. Engl., 1997, 17 G. M. Sheldrick, SADABS, a program for the Siemens Area Detector ABSorption correction, 1994. 36, 1619. 12 J. R. Debord, R. C. Haushalter and J. Zubieta, J. Solid State 18 G. M. Sheldrick, SHELXTL version 5.03, software package for the Crystal Structure Determination, 1994. Chem., 1996, 125, 270. 13 F. Sanz, C. Parada, U. Amador and Mongema, J. Solid State 19 R. L. Carlin, Magnetochemistry, Springer-Verlag, Berlin, New York, 1986. Chem., 1996, 123, 129. 14 R. LaDuca, D. Rose, J. R. D. DeBord, R. C. Haushalter, 20 J. B. Goodenough, Magnetism and chemical bonds, Wiley-Interscience, New York, 1963. C. J. O. Connor and J. Zubieta, J. Solid State Chem., 1996, 123, 408. 21 M. Leblanc, T. Collin Fe` vre and G. Fe� rey, J. Magn. Magn. Mater., 1997, 167, 71. 15 S. O. H. Gutschke, M. Molinier, A. K. Powell and P. T. Wood, Angew. Chem., Int. Ed. Engl., 1997, 36, 991. 16 F. Serpaggi and G. Fe� rey, J. Mater. Chem., preceding paper. Paper 8/02714E J. Mater. Chem., 1998, 8, 2743–2747

ISSN:0959-9428    

DOI:10.1039/a802714e

出版商:RSC    

年代:1998

数据来源: RSC

摘要:

J O U R N A L O F C H E M I S T R Y Materials Hybrid open frameworks (MIL-n). Part 6† Hydrothermal synthesis and X-ray powder ab initio structure determination of MIL-11, a series of lanthanide organodiphosphonates with three-dimensional networks, LnIIIH[O3P(CH2)nPO3] (n=1–3) F. Serpaggi and G. Fe� rey* Institut Lavoisier,UMR CNRS 173, Universite� de Versailles Saint-Quentin-en-Yvelines, 45, avenue des Etats-Unis, 78035 Versailles Cedex, France.E-mail: ferey@chimie.uvsq.fr Received 9th April 1998, Accepted 17th September 1998 A series of lanthanide and yttrium propylenediphosphonates has been prepared hydrothermally (210 °C, 4 days) by action of propylenediphosphonic acid on the metal chlorides. The crystal structure of the gadolinium compound GdIIIH[O3P(CH2)3PO3] has been determined ab initio from X-ray powder diVraction data and refined by the Rietveld method.The compound crystallizes in the monoclinic space group C2/m (no. 12) with a=8.2141(3) A° , b=18.9644(8) A° , c=5.2622(2) A° , b=111.999(2)° and Z=4. The final agreement factors are Rp=0.113, Rwp=0.142, Bragg R=0.050, RF=0.034 and x2=1.91. In the three-dimensional structure, the gadolinium atoms are eight-coordinated.The framework consists of inorganic Gd–P–O sheets joined by organic groups with an interlayer spacing of 9.58 A° . The entire series of the lanthanide elements and yttrium give isotypic structures. Attempts with ethylenediphosphonic acid and gadolinium led to the analogous compound GdIIIH[O3P(CH2)2PO3] which crystallizes in the monoclinic space group P21/c (no. 14) with cell parameters a=5.2918(9), b=15.975(3), c=8.338(1) A° , b=111.491(6)°, Z=4 (final agreement factors Rp=0.078, Rwp=0.105, Bragg R=0.034, RF=0.026 and x2=1.50), and with an interlamellar distance of d=7.99 A° .Moreover, the action of methylenediphosphonic acid on La, Ce, Pr and Nd chloride led to a similar structure with a shorter interlamellar distance, d=7.03 A° for PrIIIH[O3P(CH2)PO3] (space group C2/m, with a=8.3271(4), b=14.0645(7), c=5.3489(3) A° , b=111.433(2)°, Z=4, and final agreement factors Rp=0.092, Rwp=0.121, Bragg R=0.059, RF=0.035 and x2=1.98).ethylene- and methylene-diphosphonates, which all present a Introduction pillared layered structure. The discovery and the structural determination of the ULM-n (n19) series of oxyfluorinated microporous gallium phos- Experimental phates by our group six years ago led us to propose a hypothesis for the mechanism of their formation1 from solution Reagents during their templated synthesis.The hypothesis claimed that LnCl3·xH2O (x=6 or 7) (Aldrich 99.9%), propylenediphos- the oligomers depicted in the solid also exist in the solution phonic acid (Alfa), ethylene- and methylene-diphosphonic and that the charge density of the protonated amine is the acids (Aldrich) were used, as received, with no further driving force of the synthesis, as described in the paper purification.concerning MIL-8 in this issue. (Part 4 in this series.) We evidenced for the first time some hitherto unknown magnetic microporous iron and vanadium phosphates,2 in Preparation of lanthanide and yttrium diphosphonates which the total substitution of Ga by Fe or V induces new The starting mixture, of molar ratio 1 LnCl3·xH2O51 structural types.Supplementary work is currently in progress H2O3P(CH2)nPO3H2 (n=1–3)5100 H2O, was placed in a in this field with the use of other 3d transition metals. The Teflon-lined stainless-steel autoclave and heated at 210 °C for extension of this idea to microporous rare earth phosphates 4 days (pHi=1 and pHf=1).Powders of the product com- unfortunately failed owing to the strong aYnity of phosphate pounds were collected by filtration, washed with distilled water and fluoride anions towards lanthanide elements which, whatand air dried. The propylenediphosphonates of the whole ever the chemical conditions, leads to the formation of lanthanide series and Y were prepared and X-ray powder monazite type phosphates LnPO4 and fluorides LnF3.patterns indicate these solids are isotypic with the gadolinium In order to obtain microporous lanthanide compounds, it compound. Ethylenediphosphonates of La, Ce, Pr, Nd, Eu, was then necessary to change our strategy and substitute Gd and Yb were prepared; X-ray powder patterns indicate phosphate anions by other chelating agents which prevent the one type of material. Green and white powders were obtained formation of dense, insoluble inorganic species.This is the for the Pr and Gd methylenediphosphonates, respectively. case of phosphonates: since the pioneering works of Alberti, X-Ray powder patterns indicate two types of solid: one for Dines and Clearfield, it is well known that these species react La, Ce, Pr and Nd, a second for Eu, Gd and Yb.with inorganic compounds.3 Most of the papers concern nonfunctionalized monophosphonates with the aim of synthesizing X-Ray data collection layered compounds,4 but several attempts with diphosphonates led to three-dimensional compounds.5 We used this idea and Owing to the pseudo-lamellar character of the compounds, we report here the hydrothermal preparation and ab initio the powders were first milled using a McCrone Micronising structural determination of lanthanide and yttrium propylene-, Mill in order to reduce the size of the particles and to prevent preferred orientation.Step-scanned X-ray powder data for the sample (side-loaded into a flat Mc-Murdie type aluminium †Part 5: preceding paper.J. Mater. Chem., 1998, 8, 2749–2755 2749sample holder) were collected on the finely ground sample by means of a Siemens-D5000 computer-automated diffractometer (Cu-Ka, 40 kV, 30 mA). Data were collected between 5 and 60° in 2h with a step size of 0.02° and a count time of 18 s step-1.The powder patterns were indexed using DICVOL916 on the basis of the first 20 observed lines. For the gadolinium propylenediphosphonate, the best solution which indexed all the lines (figure of merit FOM= 30) indicated a monoclinic unit cell with parameters a= 8.21(1) A° , b=18.96(1) A° , c=5.26(1) A° and b=112.0(1)°. The systematic absences (hkl5h+k=2n) were consistent with the space group C2/m (no. 12).For the gadolinium ethylenediphosphonate, the best solution (FOM=15) led to unit-cell parameters similar to those for the propylenediphosphonate, with reversed a and c parameters and a shorter b parameter: a=5.30(1) A° , b=16.01(1) A° , c= Fig. 2 Observed (+) and calculated (–––) profiles for the Rietveld 8.34(1) A° , b=111.6(1)°. The systematic absences (h0l5l=2n; refinement of gadolinium ethylenediphosphonate. 0k05k=2n) were consistent with the space group P21/c (no. 14). eters, the structures were refined with the original coordinates For the praseodymium methylenediphosphonate, the best found for GdH[O3P(CH2)3PO3]. solution (FOM=30) corresponded to a similar unit-cell with shorter b parameter: a=8.33(1) A° , b=14.06(1) A° , c= Structure solution and refinement of GdH[O3P(CH2)2PO3] 5.35(1) A° , b=111.4(1)° (space group C2/m).For the gadolin- The procedure is strictly similar to that used for the ab initio ium methylenediphosphonate, the best solution (FOM=37) structure determination of GdH[O3P(CH2)3PO3]. A final indicated cell parameters: a=15.75(1) A° , b=6.61(1) A° , Rietveld refinement plot is given in Fig. 2. c=7.03(1) A° , b=121.3(1)°. Structure solution and refinement of PrH[O3P(CH2)PO3] Structure solution and refinement of GdH[O3P(CH2)3PO3] Considering the similarity of the unit cell to that of For better precision concerning the positions and the intensities GdH[O3P(CH2)3PO3], the structure was readily solved using of the peaks, new data were collected between 7 and 60° and FULLPROF with X-ray data collected between 7 and 60° and between 60.02 and 100° in 2h with a step size of 0.02° and a between 60.02 and 100° in 2h with a step size of 0.02° and a count time of 26 and 52 s step-1, respectively.Initially, the count time of 26 and 52 s step-1, respectively. Background, individreflection intensities were extracted from the powder profile and cell parameters were first refined.The structure pattern using the PROFILE program in the DIFFRACTplus was then refined with the positional parameters of package.7 Then, background, profile and unit cell parameters GdH[O3P(CH2)3PO3] (except one C atom). A final Rietveld were refined using the Rietveld method in the FULLPROF refinement plot is given in Fig. 3. program package.8 Gadolinium was first located using the Full crystallographic details, excluding structure factors, direct methods option of the SHELXS program.9 Phosphorus, have been deposited at the Cambridge Crystallographic Data oxygen and carbon atoms were then revealed by using Centre (CCDC).See Information for Authors, J. Mater. FULLPROF and SHELXL together. The structure was refined Chem., 1998, Issue 1.Any request to the CCDC for this without any constraints and with an overall isotropic temperamaterial should quote the full literature citation and the ture factor. A correction was made for preferred orientation reference number 1145/122. using the usual Rietveld function, with a diVraction vector along the b*-axis. A final Rietveld refinement plot is given in Fig. 1. Results The structure for each lanthanide propylenediphosphonate TG analysis under O2 (heating rate=5 °Cmin-1) was carried was refined by FULLPROF with X-ray data collected between out for all products.The TG curves indicate the compounds 5 and 60° in 2h (step size=0.02°, count time=18 s step-1). are anhydrous and begin to decompose at 200 °C with a single After initial refinement of background, profile and cell paramweight loss.Nevertheless, thermodiVractometry (in air, heating rate+5 °Cmin-1) showed that the structure of the compounds is conserved until ca. 400 °C. For GdH[O3P(CH2)3PO3], the Fig. 1 Observed (+) and calculated (–––) profiles for the Rietveld Fig. 3 Observed (+) and calculated (–––) profiles for the Rietveld refinement of praseodymium methylenediphosphonate. refinement of gadolinium propylenediphosphonate. 2750 J. Mater. Chem., 1998, 8, 2749–2755Table 1 Crystallographic data for GdH[O3P(CH2)3PO3], GdH[O3P(CH2)2PO3] and PrH[O3P(CH2)PO3] GdH[O3P(CH2)3PO3] GdH[O3 P(CH2)2PO3] PrH[O3P(CH2)PO3] Formula weight 358.28 344.26 313.89 Crystal system Monoclinic Monoclinic Monoclinic Space group C2/m (no. 12) P21/c (no. 14) C2/m (no. 12) a/A° 8.2141(3) 5.2918(9) 8.3271(4) b/A° 18.9644(8) 15.975(3) 14.0645(7) c/A° 5.2622(2) 8.338(1) 5.3489(3) b/degrees 111.999(2) 111.491(6) 111.433(2) V/A° 3 760.04(1) 655.91(1) 583.12(1) Z 4 4 4 Dc/g cm-3 3.13 3.49 3.57 l(CuKa1, Ka2)/A° 1.5406, 1.5444 1.5406, 1.5444 1.5406, 1.5444 T/°C 20(1) 20(1) 20(1) No.of reflections 822 379 635 No. of fitted parameters 38 51 35 Rp a 0.113 0.078 0.092 Rwp a 0.142 0.105 0.121 Bragg Ra 0.050 0.034 0.059 RF a 0.034 0.026 0.035 x2 a 1.91 1.50 1.98 aSee ref. 8 for definitions. Table 3 Intramolecular distances (A° ) and angles (degrees) involving weight loss is 6.0%. According to X-ray data, the residue the non-hydrogen atoms of GdH[O3P(CH2)3PO3]a (900 °C) is well crystallized monazite type GdPO4, which requires a weight loss of 29.6%. The diVerence between the GdKO1 2.54(1) GdKO3e 2.29(1) observed and calculated weight losses is due to (i) a heavy GdKO1a 2.54(1) PKO1 1.52(2) carbon deposit on the residue and (ii) a too low temperature GdKO1b 2.39(2) PKO2 1.53(2) GdKO1c 2.39(2) PKO3 1.47(2) to allow the volatilization of P2O5 and the conversion to GdKO2 2.50(1) PKC2 1.83(2) GdPO4, as already noted by Clearfield and coworkers for GdKO2a 2.50(1) C1KC2 1.49(3) LaH[O3PC6H5]2.10 GdKO3d 2.29(1) O1KGdKO1a 128(1) Structure of GdH[O3P(CH2)3PO3] O1KGdKO1b 125(1) O1KGdKO1c 64.9(7) Crystallographic data are given in Table 1, final positional O1KGdKO2 57.3(7) parameters in Table 2, and bond lengths and angles in Table 3.O1KGdKO2a 82.1(7) The structure is a pillared layered one, as seen in Fig. 4(a) and O1KGdKO3d 141(1) (b). The gadolinium atoms are dodecahedrally coordinated O1KGdKO3e 77.8(8) O1aKGdKO1b 64.9(7) by eight oxygens of the phosphonate groups, as seen in O1aKGdKO1c 125(1) Fig. 5(a) and (b). Each phosphonate group chelates one O1aKGdKO2 82.1(7) gadolinium atom and half the chelating oxygen atoms (O1) O1aKGdKO2a 57.3(7) then bridge to another adjacent gadolinium atom in order to O1aKGdKO3d 77.8(8) create chains of gadolinium polyhedra along the [100] direc- O1aKGdKO3e 141(1) tion.The third oxygen (O3) bonds to a unique gadolinium O1bKGdKO1c 160(1) O1bKGdKO2 78.1(8) atom of an adjacent row and ensures the connection of the O1bKGdKO2a 118.9(9) chains in order to form inorganic Gd–P–O layers in the (010) O1bKGdKO3d 89.7(9) plane. The angles formed at the gadolinium atoms by the O1bKGdKO3e 76.8(9) chelate rings are quite small [O1–Gd–O2, 57.3(7)°] leading to O1cKGdKO2 118.9(9) O1cKGdKO2a 78.1(7) O1cKGdKO3d 76.8(9) O1cKGdKO3e 89.7(9) O2KGdKO2a 76.3(7) O2KGdKO3d 159(1) O2KGdKO3e 95.8(8) O2aKGdKO3d 95.8(8) O2aKGdKO3e 159(1) O3dKGdKO3e 97(1) O1KPKO2 105(2) O1KPKO3 111(2) O1KPKC2 112(2) O2KPKO3 111(2) O2KPKC2 105(2) O3KPKC2 112(2) PKC2KC1 118(1) C2KC1KC2f 109(2) aSymmetry transformations used to generate equivalent atoms: a-x, a highly distorted dodecahedron around the gadolinium atom.y, -z; bx-1.2, -y+1/2, z; c-x+1/2, -y+1/2, -z; dx-1/2, The P–C bonds point out of the sheets and allow the cross- -y+1/2, z-1; e-x+1/2, -y+1/2, -z+1; fx, -y, z. linking of the inorganic sheets into a three-dimensional structure via the organic groups.The unit-cell parameters and volume for each lanthanide (and yttrium) propylenediphosphonate are reported in Table 4. When compared to the of the polyhedra vs. the lanthanide atom. Finally, owing to the similarity of their ionic radii, yttrium leads to a structure lanthanum compound unit cell parameters and volume, the normalized unit-cell parameters and volumes, a/aLa, b/bLa, with cell parameters very close to those for HoH[O3P(CH2)3PO3].c/cLa and V/VLa, are found to increase with the ionic radii11 of the lanthanide cation, as shown in Fig. 6. The slight decrease of b with the cation may occur because of slight distortions Structure of GdH[O3P(CH2)2PO3] Crystallographic data are given in Table 1. Final positional Table 2 Positional parameters for GdH[O3P(CH2)3PO3] parameters and bond lengths and angles are given in Tables 5 and 6, respectively.Symmetry and unit-cell parameters are Atom x y z Site occupation factor closely related to those for GdH[O3P(CH2)3PO3]. The structure can be simply deduced from that of GdH[O3P(CH2)3PO3] Gd 0 0.2677(1) 0 0.5 by replacing the C3 chain by the C2 chain, as shown in P 0.246(1) 0.1506(4) 0.370(2) O1 0.299(2) 0.2100(7) 0.222(3) Fig. 7(a) and (b). Except for a slight distortion, the inorganic O2 0.052(2) 0.1641(6) 0.314(3) layers remain unchanged [Fig. 8(a) and (b)]. Thus, the main O3 0.352(2) 0.1526(7) 0.666(3) diVerences between the two structures are (i) that the interla- C1 0.220(4) 0 0.359(6) 0.5 mellar space (along the b axis) is shortened to 7.99 A° , cf.C2 0.253(3) 0.064(1) 0.220(5) 9.56 A° and (ii) that the evenness of the number of carbons in J. Mater. Chem., 1998, 8, 2749–2755 2751Fig. 5 (a) Layer arrangement in the structure of gadolinium propylenediphosphonate showing the eight-coordinated gadolinium atoms; the acid proton is evidenced within the circle. (b) Polyhedral representation of the inorganic layer in propylenediphosphonate showing the arrangement of Gd and P atoms polyhedra.Table 4 Evolution of the cell parameters and volume of LnH- [O3P(CH2)3PO3] vs. the lanthanide element, and cell parameters and volume for YH[O3P(CH2)3PO3] Fig. 4 (a) Projection of the structure of gadolinium propylenediphos- Element a/A° b/A° c/A° b/degrees V/A° 3 phonate down the c axis showing a pillared layered structure.(b) Polyhedral drawing of the projected structure of gadolinium La 8.435(1) 19.216(2) 5.358(1) 111.53(1) 807.9(1) propylenediphosphonate down the c axis as in (a). Ce 8.389(1) 19.153(2) 5.334(1) 111.63(1) 796.6(1) Pr 8.348(1) 19.112(2) 5.321(1) 111.72(1) 788.7(1) Nd 8.312(1) 19.075(1) 5.308(1) 111.80(1) 781.3(1) Sm 8.258(1) 19.014(1) 5.284(1) 111.91(1) 769.7(1) the chain is responsible for a symmetry change (P21/c instead Eu 8.232(1) 18.982(1) 5.270(1) 111.95(1) 763.9(1) of C2/m) and a shift of the layers as shown in Fig. 9. Gd 8.214(1) 18.964(1) 5.262(1) 112.00(1) 754.6(1) Tb 8.190(1) 18.928(1) 5.244(1) 112.03(1) 753.7(1) Dy 8.171(1) 18.899(1) 5.231(1) 112.03(1) 748.7(1) Structure of PrH[O3P(CH2)PO3] Ho 8.153(1) 18.873(1) 5.221(1) 112.09(1) 744.4(1) Crystallographic data are given in Table 1.Final positional Er 8.138(1) 18.848(2) 5.209(1) 112.10(1) 740.3(1) Tm 8.120(1) 18.826(1) 5.201(1) 112.10(1) 736.6(1) parameters and bond lengths and angles are given in Tables 7 Yb 8.102(1) 18.798(1) 5.183(1) 112.11(1) 731.4(1) and 8, respectively. The symmetry and unit-cell parameters Lu 8.095(1) 18.787(2) 5.176(1) 112.17(1) 729.0(1) are closely related to those for PrH[O3P(CH2)3PO3].The Y 8.156(1) 18.867(1) 5.221(1) 112.04(1) 744.8(1) structure can be simply deduced from that of PrH- [O3P(CH2)3PO3] by replacing the C3 chain by C1, as shown in Fig. 10(a) and (b). Thus, the main diVerence between the Discussion two structures is that the interlamellar space (along the b axis) is shortened to 7.03 A° , cf.of 9.56 A°. Because of their poor Prior to this study, only two layered lanthanide phosphonates were structurally characterized. Indeed, five years ago, while crystallinity, the structures of the heavier lanthanide compounds still remain unsolved. studying a series of phenyl- and benzyl-phosphonates of the 2752 J. Mater. Chem., 1998, 8, 2749–2755Fig. 6 Curves showing the evolution of the normalized unit-cell parameters and volume of LnH[O3P(CH2)3PO3] vs.the ionic radii of the lanthanide elements Ln (normalized parameter=parameter for Ln/parameter for La). Table 5 Positional parameters for GdH[O3P(CH2)2PO3] Atom x y z Gd 0.7816(9) 0.2255(2) 0.2152(6) P1 0.415(4) 0.1411(8) 0.477(2) P2 0.139(3) 0.375(1) 0.455(2) O1 0.114(6) 0.340(2) 0.279(4) O2 -0.044(7) 0.315(2) 0.495(4) O3 0.136(6) 0.128(2) 0.391(4) O4 0.572(5) 0.212(2) 0.404(2) O5 0.461(7) 0.348(2) 0.155(4) O6 0.456(6) 0.377(2) 0.571(4) C1 0.428(6) -0.039(1) 0.489(7) C2 0.06(1) 0.484(2) 0.440(5) Table 6 Intramolecular distances (A° ) and angles (degrees) involving the non-hydrogen atoms of GdH[O3P(CH2)2PO3]a GdKO1a 2.45(3) P1KO4 1.64(3) GdKO2a 2.60(3) P1KO5d 1.43(3) GdKO2b 2.42(3) P1KC1e 1.81(3) GdKO3a 2.46(3) P2KO1 1.53(4) GdKO4 2.25(3) P2KO2 1.48(4) GdKO4c 2.62(2) P2KO6 1.60(4) GdKO5 2.51(3) P2KC2 1.79(3) GdKO6c 2.37(3) C1KC1e 1.43(3) P1KO3 1.40(4) C2KC2f 1.45(7) O1aKGdKO2a 54(1) O3aKGdKO6c 97(2) Fig. 7 (a) Projection of the structure of gadolinium ethylenediphos- O1aKGdKO2b 85(2) O4KGdKO4c 126(1) phonate down the a axis showing a pillared layered structure closely O1aKGdKO3a 91(2) O4KGdKO5 75(2) related to that of gadolinium propylenediphosphonate.(b) Polyhedral O1aKGdKO4 115(2) O4KGdKO6c 80(2) drawing of the projected structure of gadolinium ethylenediphosphon- O1aKGdKO4c 87(2) O4cKGdKO5 60(1) ate down the a axis as in (a). O1aKGdKO5 81(2) O4cKGdKO6c 78(2) O1aKGdKO6c 163(2) O5KGdKO6c 97(2) the new pillared layered LnH[O3P(CH2)nPO3] 1 is closely O2aKGdKO2b 136(2) O3KP1KO4 12(4) O2aKGdKO3a 83(2) O3KP1KO5d 107(4) related to that of the layered La[O3PC6H5][HO3PC6H5] 2.As O2aKGdKO4 62(1) O3KP1KC1e 106(3) shown in Table 9, except for the diVerent b parameter and O2aKGdKO4c 124(2) O4KP1KO5d 112(3) symmetry (due to the diVerent organic groups), the unit-cell O2aKGdKO5 75(2) O4KP1KC1e 115(2) parameters are almost the same.Vectors of the unit cell for 2 O2aKGdKO6c 142(2) O5dKP1KC1e 93(3) can be deduced from those for 1 by roughly applying the O2bKGdKO3a 82(2) O1KP2KO2 98(3) transformation matrix. O2bKGdKO4 158(2) O1KP2KO6 107(3) O2bKGdKO4c 60(1) O1KP2KC2 111(3) O2bKGdKO5 118(2) O2KP2KO6 120(4) O2bKGdKO6c 81(2) O2KP2KC2 120(3) A-1 0 -1 0 -1 0 0 0 1B O3aKGdKO4 89(2) O6KP2KC2 101(3) O3aKGdKO4c 142(2) P1KC1KC1e 125(2) O3aKGdKO5 157(2) P2KC2KC2f 116(4) aSymmetry transformations used to generate equivalent atoms: ax+1, When correctly re-oriented, the structures look the same and y, z; bx+1, -y+1/2, z-1/2; cx, -y+1/2, z-1/2; dx, -y+1/2, in both case the inorganic layers are strictly similar.The whole z+1/2; e-x+1, -y, -z+1; f-x, -y+1, -z+1. arrangement of the Ln, P and O atoms within the layer is the same and bond lengths and angles in LnH[O3P(CH2)3PO3] are consistent with those observed in La[O3PC6H5]- lanthanide elements, Clearfield and coworkers obtained crystals of the lanthanum compounds, La[O3PC6H5][HO3PC6H5] [HO3 PC6H5].Clearfield and coworkers prepared La[O3PC6H5]- [HO3PC6H5] at low pH (#2), and thus they obtained an and La[O3PCH2C6H5][HO3PCH2C6H5]·2H2O, and solved their crystal structures.10 acidic phosphonate (La[O3PC6H5][HO3PC6H5] which can be rewritten LaH[O3PC6H5]2).10 Nevertheless, they could not After Clearfield sent us the correct coordinates for La[O3PC6H5][HO3PC6H5], it appeared that the structure of locate the proton in the Fourier diVerence maps.But after J. Mater. Chem., 1998, 8, 2749–2755 2753Table 8 Intramolecular distances (A° ) and angles (degrees) involving the non-hydrogen atoms of PrH[O3P(CH2)PO3]a PrKO1 2.42(1) PrKO3d 2.39(1) PrKO1a 2.42(1) PrKO3e 2.39(1) PrKO1b 2.38(2) PKO1 1.63(1) PrKO1c 2.38(2) PKO2 1.52(1) PrKO2 2.62(1) PKO3 1.54(1) PrKO2a 2.62(1) PKC 1.77(9) O1KPrKO1a 129.4(7) O1cKPrKO2 114.9(6) O1KPrKO1b 132.5(8) O1cKPrKO2a 79.3(5) O1KPrKO1c 56.9(5) O1cKPrKO3d 80.5(6) O1KPrKO2 59.6(5) O1cKPrKO3e 87.9(6) O1KPrKO2a 80.9(5) O2KPrKO2a 78.3(4) O1KPrKO3d 137.3(7) O2KPrKO3d 161.0(6) O1KPrKO3e 80.4(5) O2KPrKO3e 94.8(5) O1aKPrKO1b 56.9(5) O2aKPrKO3d 94.8(5) O1aKPrKO1c 132.5(8) O2aKPrKO3e 161.0(6) O1aKPrKO2 80.9(5) O3dKPrKO3e 96.9(6) O1aKPrKO2a 59.6(5) O1KPKO2 105(1) O1aKPrKO3d 80.4(5) O1KPKO3 116(1) O1aKPrKO3e 137.3(7) O1KPKC 113.1(7) O1bKPrKO1c 162.5(8) O2KPKO3 108(1) O1bKPrKO2 79.3(5) O2KPKC 107(1) O1bKPrKO2a 114.9(6) O3KPKC 107(1) O1bKPrKO3d 87.9(6) PKCKPf 131.0(6) O1bKPrKO3e 80.5(6) aSymmetry transformations used to generate equivalent atoms: a-x, y, -z; bx-1/2, -y+1/2, z; c-x+1/2, -y+1/2, -z; dx-1/2, -y+1/2, z-1; e-x+1/2, -y+1/2, -z+1; fx, -y, z.examination of the P–O lengths [two two-coordinated oxygen atoms, O*, form slighty longer P–O* bonds and are separated by a distance of 2.41(1) A° ] and 31P MAS NMR analysis, they found the proton to be either randomly distributed between the O* oxygen atoms or equidistant between them.As no single crystals of LnH[O3P(CH2)3PO3] could be obtained, the structure was determined ab initio and no hydrogen atom could be located in the Fourier diVerence maps.However, since the LnH[O3P(CH2)nPO3] compounds were prepared at low pH (=1) and are analoguous to LaH[O3PC6H5]2, they should also be acidic. In GdH[O3P(CH2)3PO3], two-coordinated O2 atoms form P–O2 bonds of 1.53(2) A° and are Fig. 8 (a) Layer arrangement in the structure of gadolinium ethylenediseparated by a distance of 2.41(2) A° . Thus, one can easily phosphonate similar to the arrangement in the gadolinium propylenediphosphonate shown in Fig. 5(a). (b) Polyhedral representation of imagine one acid proton either randomly distributed between the inorganic layer in ethylenediphosphonate showing the arrangement the O2 oxygen atoms or equidistant between them [Fig. 5(a)], of Gd and P atoms polyhedra. as in LaH[O3PC6H5]2. Moreover, this added proton satisfies the electroneutrality of the structure.Conclusion In order to obtain microporous lanthanide compounds, we investigated the system rare-earth/diphosphonic acid. Until now, the only lanthanide phosphonates to be reported were layered due to the use of a non-functionalized monophosphonic acid as a precursor.10,12 By using diphosphonic acids, we were able to prepare and characterize pillared layered Table 9 Comparison between crystallographic data for La[O3PC6H5]- [HO3PC6H5] and LaH[O3P(CH2)3PO3] Fig. 9 EVect of the parity of the number of carbon atoms in the chain on the layout of the inorganic sheets. La[O3PC6H5][HO3PC6H5] (small cell11) LaH[O3 P(CH2)3PO3] Table 7 Positional parameters for PrH[O3P(CH2)PO3] Formula weight 452.07 339.94 Crystal system Triclinic Monoclinic Atom x y z Site occupation factor Space group P1 (no. 2) C2/m (no. 12) a/A° 8.410(3) 8.4348(7) Pr 0 0.2739(1) 0 0.5 b/A° 15.696(7) 19.216(2) P 0.241(1) 0.1148(3) 0.356(1) c/A° 5.636(1) 5.3584(5) O1 0.282(1) 0.2003(7) 0.181(2) a/degrees 90.24(3) 90.0 O2 0.055(1) 0.1294(5) 0.330(2) b/degrees 108.99(1) 111.530(5) O3 0.355(1) 0.1134(6) 0.657(2) c/degrees 85.59(4) 90.0 C 0.253(3) 0 0.226(4) 0.5 V/A° 3 701.3(4) 807.9(1) 2754 J.Mater. Chem., 1998, 8, 2749–2755does not give rise to any porosity. In order to generate porosity, attempts are currently in progress using the coprecipitation of phosphate (or phosphite) and phosphonate groups described by Alberti et al.5a,b In this way, the phosphate groups may act as spacers between the pillared phosphonates and generate the desired porosity. Acknowledgments The authors are grateful to Rho�ne-Poulenc for financial support and to Professor Abraham Clearfield for providing us the correct coordinates of the structure of La[O3PC6H5][HO3PC6H5].References 1 G.Fe� rey, J. Fluorine Chem., 1995, 72, 187; C. R. Acad. Sci. Se�r. C, 1998, 2, and references therein. 2 D. Riou and G. Fe� rey, J.Solid State Chem., 1994, 111, 422; D. Riou, F. Taulelle, and G. Fe� rey, Inorg. Chem., 1996, 35, 6392; M. Cavellec, D. Riou, C. Ninclaus, J.-M. Grene`che and G. Fe� rey, Zeolites, 1996, 17, 250; M. Cavellec, D. Riou, J.-M. Grene`che and G. Fe� rey, J. Magn. Magn. Mater., 1996, 163, 173; M. Cavellec, J.-M. Grene`che, D. Riou and G. Fe� rey, Microporous Mater., 1997, 8, 103; M.Cavellec, J.-M. Grene`che and G. Fe� rey, Microporous Mater., 1998, 20, 45; M. Cavellec, C. Egger, J. Linares, M. Nogues, F. Varret and G. Fe� rey, J. Solid State Chem., 1997, 134, 349. 3 A. Clearfield, Curr. Opin. Solid State Mater. Sci., 1996, 1, 268 and references therein. 4 M. E. Thompson, Chem. Mater., 1994, 6, 1168 and references therein. 5 (a) G. Alberti, U. Costantino, F.Marmottini, R. Vivani and P. Zappelli, Angew. Chem., Int. Ed. Engl., 1993, 32, 1357; (b) G. Alberti, F. Marmottini, S. Murcia-Mascaro� s and R. Vivani, Angew. Chem., Int. Ed. Engl., 1994, 33, 1594; (c) L. A. Vermeulen and M. E. Thompson, Chem. Mater., 1994, 6, 77; (d) V. Soghomonian, Q. Chen, R. C. Haushalter and J. Zubieta, Angew. Chem., Int. Ed. Engl., 1995, 34, 223; (e) V.Soghomonian, R. Diaz, R. C. Haushalter, C. J. O’Connor and J. Zubieta, Inorg. Chem., 1995, 34, 4460; ( f ) H. Byrd, A. Clearfield, D. Poojary, K. P. Reis and M. E. Thompson, Chem. Mater., 1996, 8, 2239; ( g) D. M. Poojary, B. Zhang, P. Bellinghausen and A. Clearfield, Inorg. Chem., 1996, 35, 4942; (h) D. M. Poojary, B. Zhang, P. Bellinghausen and A. Clearfield, Inorg. Chem., 1996, 35, 5254; (i) G. Bonavia, R. C. Haushalter, C. J. O’Connor and J. Zubieta, Inorg. Chem., 1996, 35, 5603; ( j ) P. J. Zapf, D. J. Rose, R. C. Haushalter and J. Zubieta, J. Solid State Chem., 1996, 125, 182; (k) D. L. Lohse and S. C. Sevov, Angew. Chem., Int. Ed. Fig. 10 (a) Projection of the structure of praseodymium methylenedi- Engl., 1997, 36, 1619. phosphonate down the c axis showing a pillared layered structure 6 A. Boultif and D. Lou� er, J. Appl. Crystallogr., 1991, 24, 987. closely related to that of gadolinium propylenediphosphonate. 7 Siemens AG, DIFFRACTplus, Karlsruhe, Germany, 1996. (b) Polyhedral drawing of the projected structure of praseodymium 8 J. Rodriguez-Carjaval, in Collected Abstracts of Powder Difmethylenediphosphonate down the c axis as in (a). fraction Meeting, Toulouse, France, 1990, p. 127. 9 G. M. Sheldrick, Siemens Analytical X-ray Instruments, 1994. 10 R.-C. Wang, Y. Zhang, H. Hu, R. R. Frausto and A. Clearfield, Chem. Mater., 1992, 4, 864. lanthanide diphosphonates. The inorganic layers are the same 11 R. D. Shannon, Acta Crystallogr., Sect. A, 1974, 32, 751. in all the layered compounds, as discussed above, but the 12 G. Cao, V. M. Lynch, J. S. Swinnea and T. E. Mallouk, Inorg. diphosphonate replaces the dangling organic groups in order Chem., 1990, 29, 2112. to cross-link the sheets. Unfortunately, in this series, the short distance between adjacent lanthanide atoms in the inorganic Paper 8/02715C layer (ca. 4.2 A° ), and therefore between the carbon chains, J. Mater. Chem., 1998,

ISSN:0959-9428    

DOI:10.1039/a802715c

出版商:RSC    

年代:1998

数据来源: RSC