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Hydrothermal Synthesis, Structure Determination, and Solid-State NMR Study of the First Organically Templated Scandium Phosphate D. Riou,*,† F. Fayon,‡ and D. Massiot‡ Institut Lavoisier UMR 8637, Universite´ de Versailles-St. Quentin en Yvelines, 45 Avenue des Etats-Unis, 78035 Versailles Cedex, France, and Centre de Recherche sur les Mate´ riaux a` Haute Tempe´ rature CNRS, 1d Avenue de la recherche scientifique, 45071 Orle´ ans Cedex 2, France Received January 16, 2002. Revised Manuscript Received February 21, 2002
Using the well-known chemical analogy 2SiIVO2 T MIIIPO4, the first organically templated scandium phosphate was hydrothermally synthesized. Sc(HPO4)2‚0.5(N2C2H10) crystallizes in the monoclinic P2/n (no. 13) space group with lattice parameters a ) 9.4088(2) Å, b ) 9.0924(1) Å, c ) 9.6884(2) Å, β ) 117.252(1)°, V ) 736.83(2) Å3, Z ) 4. Its structure was solved by single-crystal X-ray diffraction and was already encountered with indium in place of scandium. It is composed of corner-sharing ScO6 octahedra and HPO4 tetrahedra whose connections ensure a three-dimensional framework exhibiting cages delimited by eightmembered windows where the ethylendiammonium cations are encapsulated. The local structure of the framework was characterized by 31P MAS, 45Sc MAS, and 3QMAS NMR spectroscopies. The interaction between the inorganic network and the template is probed using 1H-31P heteronuclear correlation NMR spectroscopy, which provided evidence for strong hydrogen bonds between the amino protons and the oxygen atoms of the inorganic network.
Introduction From the structural comparison of the similarities between the two families of silicon oxide and aluminophosphate compounds, using the chemical analogy 2SiIVO2 T AlIIIPVO4, Flanigen and co-workers showed in the 1980s the possibility of synthesizing a large series of aluminophosphates with open frameworks.1 Furthermore, they revealed a path toward microporous compounds with nonpurely tetrahedral structures but different zeolite topologies. Twenty years later, the number of compounds with open frameworks has dramatically expanded, and up to 25 elements of the main and transition metal blocks are available to give such compounds.2 The first examples are provided by the GaPO series discovered by Parise3 or the metalloaluminophosphates MeAPO-n where Me is a tetrahedrally coordinated divalent metal.4 However, the breakthrough was illustrated by the vanadophosphate ULM-7,5 which represents the first organically templated 3D metallophosphate whose metal sites are exclusively filled by a 3d transition metal. The vanadophosphate family was * To whom correspondence should be addressed. E-mail: riou@ chimie.uvsq.fr. † Universite ´ de Versailles-St. Quentin en Yvelines. ‡ Centre de Recherche sur les Mate ´ riaux a` Haute Tempe´rature CNRS. (1) Wilson, S. T.; Lok, B. M.; Messina, C. A.; Cannan, T. R.; Flanigen, E. M. J. Am. Chem. Soc. 1982, 104, 1146. (2) Cheetham, A. K.; Fe´rey, G.; Loiseau, Th. Angew. Chem., Int. Ed. 1999, 38, 3268. (3) Parise, J. B. J. Chem. Soc., Chem. Commun. 1985, 606. (4) Flanigen, E. M.; Lok, B. M.; Patton, R. L.; Wilson, S. T. Stud. Surf. Sci. Catal. 1986, 28, 103. (5) Riou, D.; Fe´rey, G. J. Solid State Chem. 1994, 111, 422.
then especially enhanced with the works of Haushalter and Zubieta, which characterized two compounds with giant pores (>13 Å) including either organic or mineral cations.6 The first magnetic microporous compounds characterized as containing iron,7 but the more fascinating example in this family remains the mineral cacoxenite,8 whose large channels are occupied by water molecules. It is worth noting that this last compound, formulated AlFe24(OH)12(PO4)17(H2O)24‚51H2O, can be considered as an inverse example of a 3d transition metal phosphate doped with a small number of diamagnetic Al3+ cations. In the course of the investigation of new microporous compounds, this paper deals for the first time with an organically templated scandium phosphate: Sc(HPO4)2‚ 0.5(N2C2H10) could appear as the first member of a new series of compounds with open frameworks. Its threedimensional structure was previously described in the indium phosphate family.9 In this work, the local structure of Sc(HPO4)2‚0.5(N2C2H10) is characterized by 31P and 45Sc magic-angle spinning (MAS), 45Sc triplequantum magic-angle spinning (3QMAS), and highresolution 1H NMR spectroscopies. The interactions between the inorganic framework and the template are probed using 1H-31P heteronuclear correlation MAS spectra with 1H homonuclear decoupling. (6) Khan, M. I.; Meyer, L. M.; Haushalter, R. C.; Schweitzer, A. L.; Zubieta, J.; Dye, J. L. Chem. Mater. 1996, 8, 43. (7) Riou-Cavellec, M.; Riou, D.; Fe´rey, G. Inorg. Chim. Acta 1999, 291, 317. (8) Moore, P.; Shen, J. Nature 1983, 306, 356. (9) Dhingra, S. S.; Haushalter, R. C. J. Chem. Soc., Chem. Commun. 1993, 1665.
10.1021/cm021116s CCC: $22.00 © 2002 American Chemical Society Published on Web 04/17/2002
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Table 1. Crystallochemical Data for Sc(HPO4)2‚0.5(N2C2H10) Sc(HPO4)2‚0.5(N2C2H10) 268 monoclinic, P2/n (no. 13)
chemical formula formula weight (g mol-1) symmetry, space group a ) 9.4088(2) Å b ) 9.0924(1) Å c ) 9.6884(2) Å volume (Å3), Z crystal size (µm), color dcalc, dmeas (g cm-3) collected intensities unique I g 2σ(I), Rint R1(Fo), wR2(Fo2)
β ) 117.252(1) ° 736.82(2), 4 100 × 30 × 20, colorless 2.416, 2.48(3) 4964 1920, 0.0356 0.0409, 0.0965
Table 2. Atomic Coordinates (×104) and Isotropic Displacement Parameters (Å2 × 103) for Sc(HPO4)2‚0.5(N2C2H10) atoms
x
y
z
Ueqa
Sc(1) Sc(2) P(1) P(2) O(1) O(2) O(3) O(4) O(5) O(6) O(7) O(8) N C H(7) H(8) H(a) H(b) H(c) H(d) H(e)
2500 7500 3322(1) -1432(1) 2485(3) 2351(3) -2493(3) -2431(3) 5039(3) 51(3) 3412(3) -875(3) 577(3) 3322(4) 2494(69) -143(73) -143(20) 81(24) 1137(5) 3791(4) 3204(4)
8943(1) 6173(1) 6021(1) 8427(1) 5596(2) 7231(3) 9488(3) 7663(3) 6449(3) 9129(3) 4640(3) 7217(3) 7961(3) 9067(4) 4333(62) 7116(73) 7684(22) 8358(10) 7182(13) 38(4) 8860(4)
2500 2500 644(1) 279(1) -1070(2) 916(3) -963(3) 921(3) 1175(3) 1526(3) 1657(3) -557(3) -3068(4) -1798(4) 1331(63) -311(74) -4012(4) -2566(27) -2545(27) -1680(4) -873(4)
11(1) 11(1) 12(1) 12(1) 15(1) 17(1) 18(1) 17(1) 18(1) 16(1) 21(1) 23(1) 22(1) 20(1) 61(18) 66(23) 33 33 33 24 24
Figure 1. Projection along [100] of one perforated layer of Sc(HPO4)‚0.5(N2C2H10). (For the sake of clarity, just the H atoms of the hydroxyl functions are drawn as hollow circles, with black and gray circles for C and N, respectively.)
a U eq is defined as one-third of the trace of the orthogonalized Uij tensor.
Table 3. Hydrogen Bonds for Sc(HPO4)2‚0.5(N2C2H10) (Å and °) D-H‚‚‚Aa
d(D-H) (Å)
d(H‚‚‚A) (Å)
d(D‚‚‚A) (Å)
∠(DHA) (°)
O(8)-H(8)‚‚‚O(2) N-H(c)‚‚‚O(1) O(7)-H(7)‚‚‚O(8) #10 N-H(a)‚‚‚O(4) #11 N-H(a)‚‚‚O(5) #9 N-H(b)‚‚‚O(3) #11 N-H(b)‚‚‚O(6) #3
0.62(6) 0.89 0.82(6) 0.89 0.89 0.89 0.89
2.09(6) 2.02 1.95(6) 2.18 2.42 2.42 2.52
2.699(4) 2.900(4) 2.711(4) 2.997(4) 3.113(4) 2.955(4) 3.223(4)
165(8) 171.4 153(5) 151.9 135.1 119.3 136.0
a Symmetry transformations used to generate equivalent atoms: #3, -x, -y + 2, -z; #9, -x + 1/2, y, -z - 1/2; #10, -x, -y + 1, -z; #11, -x - 1/2, y, -z - 1/2.
Experimental Section Synthesis and Chemical Analysis. Sc(HPO4)2‚0.5(N2C2H10) was hydrothermally synthesized from a mixture of Sc2O3 (Alfa Aesar, 99.9%), H3PO4 (Prolabo, 85%), fluorhydric acid (Prolabo, 48%), ethylenediamine (Aldrich, 97%), and deionized water in the molar ratio 1:2:1:1:200. The initial mixture was sealed in a 23-mL Teflon-lined steel autoclave (Parr type) for 2 days at 463 K. The rate filling was approximately 25%. The pH increased from 2 to 7 through the synthesis. The final product was first filtered, washed with water, and then dried in air. It consists of a fine microcrystalline white powder (yield ∼55% based on H3PO4). Attempts to synthesize the title product without HF were unsuccessful. It seems that fluorine anions act here as a mineralizer as they do not participate in the framework of the synthesized compound. Thermogravimetric analysis was performed under O2 flow using a TGA2050 TA Instruments apparatus (heating rate of
Figure 2. Projection along [010] of the 3D structure of Sc(HPO4)‚0.5(N2C2H10) showing the connections between adjacent layers. 5°/min). The TG curve shows a wide signal (experimental, 13.4%) occurring between 150 and 450 °C. It is understood as the combustion of the organic part (theoretical, 11.6%). The calcined product is a mixture of Sc2O3 and an amorphous phase. The density was measured with a Micromeritics multipycnometer operating under He flow. Structure Determination. A small crystal was attached to a glass fiber mounted on a goniometer head. The data were collected with a three-circle Smart Siemens diffractometer working with monochromatized Mo KR radiation (λ ) 0.71073 Å) and equipped with a CCD detector. The lattice parameters were first determined from three sets of 15 frames and then refined during the data collection with all intensities I > 10σ(I). The 4.5-cm distance between the crystal and the detector allowed for data collection up to 2θ ) 60°. The frames covering one hemisphere were registered with a scan width of 0.3° (ω) and an exposure time of 60 s. The unique condition h0l, h + l ) 2n, was consistent both with the P2/n (no. 13) and Pn (no. 7) monoclinic space groups. However, only the centrosymmetric space group was considered and led to an acceptable solution
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Figure 3. 31P MAS NMR experimental spectrum (10-kHz spinning rate) and its simulation.
Figure 4. 45Sc MAS NMR experimental and simulated spectra (30-kHz spinning rate). upon application of the direct methods of SHELX-TL program. The Sc, P, and O atoms were located first, and then the remaining atoms were deduced from subsequent Fourier difference syntheses. The H atoms were located using geometrical constraints. A semiempirical absorption correction specific to the CCD detector was applied using the SADABS program (G. Sheldrick, unpublished). In the last stage of calculation, all atoms (except H) were anisotropically refined, and the reliability factors converged to R1(Fo) ) 0.0409 and wR2(Fo2) ) 0.0965 for 1920 unique reflections with I g 2σ(I). The principal crystallochemical data and conditions for intensity collection are summarized in Table 1. The atomic coordinates as well as the scheme of the hydrogen-bond network are given in Tables 2 and 3, respectively. Solid-State NMR Spectroscopy. All solid-state NMR experiments were carried out on powdered samples at room temperature using a Bruker DSX400 spectrometer (B0 ) 9.4 T) with 2.5- and 4-mm double-bearing MAS Bruker probe heads. The 31P MAS and CP-MAS spectra were acquired at different spinning rates (3-12 kHz) with 1H continuous wave decoupling. The 31P chemical shift anisotropy (CSA) was determined from the spinning sideband intensities in the MAS spectra.10 The 45Sc MAS spectrum (30-kHz spinning rate) was acquired using a single pulse sequence with small pulse angle (π/12) to obtain quantitative spectra.11 The two-dimensional 45Sc 3QMAS spectra12 were obtained using a three-pulse Z-filter sequence13 with spinning at 30 kHz. To avoid spinning sidebands in the ω1 dimension, the t1 time increment was synchronized with the rotor period.14 The two-dimensional 1H31P and 1H-13C heteronuclear correlation spectra (HETCOR) were acquired at a 12-kHz spinning rate using ramped (10) Herzfeld, J.; Berger, A. E. J. Chem. Phys. 1980, 73, 6021. (11) Samoson, A.; Lippmaa, E. Phys. Rev. 1983, B28, 6567. (12) Frydman, L.; Harwood: J. S. J. Am. Chem. Soc. 1995, 117, 5367. (13) Amoureux, J. P.; Fernandez, C.; Steuernagel, S. J. Magn. Reson. 1996, A123, 116. (14) Massiot, D. J. Magn. Reson. 1996, A122, 240.
Figure 5. (a) 45Sc 3Q-MAS NMR spectrum (30-kHz spinning rate) and (b) its simulation.
Figure 6. (a) 1H MAS spectrum and (b) 1H homonuclear decoupled MAS spectrum at a spinning frequency of 12 kHz. The spectrum in b was obtained from the projection, in the ω1 indirectly detected 1H dimension, of the 1H-31P HETCOR spectrum with a contact time of 2.0 ms (not shown). polarization transfer and contact times varying from 200 µs to 2 ms. The phase-modulated Lee-Goldburg (PMLG) homonuclear decoupling sequence15 was used during the incremented t1 time evolution to obtained a high-resolution 1H spectrum in the ω1 dimension. The 31P, 45Sc, and 1H chemical shifts were referenced relative to 75% H3PO4 solution, ScCl3 solution, and Si(CH3)4, respectively.
Discussion Sc(HPO4)2‚0.5(N2C2H10) presents a three-dimensional mixed framework formed by the corner sharing of ScO6 octahedra and HPO4 tetrahedra. The interatomic dis(15) Vinogradov, E.; Madhu, P. K.; Vega, S. Chem. Phys. Lett. 1999, 314, 443.
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Figure 7. Experimental 1H-31P MAS HETCOR NMR spectra recorded for a contact time of 0.2 ms.
tances are very close to those encountered in the isostructural indium compound.9 The Sc-O distances in the range 2.059-2.145 Å are slightly shorter than the In-O distances (2.099-2.166 Å), as expected from the ionic radii of Sc3+ and In3+, which are equal to 0.745 and 0.80 Å, respectively.16 On the other hand, the distributions of P-O distances in the tetrahedra are exactly the same: each PO4 tetrahedron exhibits three distances of around 1.51 Å and one longer P-O distance (
