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