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