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. 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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,