Chem. Mater. 2005, 17, 2833-2840
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New Series of Layered Vanadyl Phosphates with Varied Polyamine Templates Ya-Ching Yang, Ling-I Hung, and Sue-Lein Wang* Department of Chemistry, National Tsing Hua UniVersity, Hsinchu, Taiwan 300 ReceiVed January 26, 2005. ReVised Manuscript ReceiVed March 24, 2005
Four two-dimensional vanadyl phosphates, (H3dien)[(VOPO4)2(OH)]‚H2O (dien ) diethylenetriamine) (1), (H2dach)1.5[(VOPO4)2(OH)]‚2H2O (dach ) 1,4-diaminocyclohexane) (2), (H2tmdpp)[V3O4(OH)(PO4)2]‚ 3H2O (tmdpp ) 4,4′-trimethylenedipiperidine) (3), and (H2tmdpp)(H1.5tmdpp)K0.5[V5O7(H2O)2(PO4)4]‚ H2O (4), with clearly distinct but orderly increasing layer separations from 7.75 to 18.07 Å, have been prepared via hydrothermal routes and characterized by single-crystal X-ray diffraction, thermogravimetric analysis, and magnetic susceptibility or ion-exchange studies. The series possesses three unique layer topologies, but all contain VIVO5 square pyramid, PO4 tetrahedron, discrete dimers of V-O polyhedra, and 3-, 4-, 5-, and 8-membered rings. Structures 1 and 2 are VIV species, having the same layer topology but different amine cations. Compounds 3 and 4 are VIV/VV mixed valent, holding the same amine templates in varied inclined angles. Being similar to 1 and 2, the layer of 3 contains extra vanadate groups. In contrast, the layers in 4 are distinct and contain VVO6 and VIVO6 octahedra besides VIVO5 square pyramid. It exhibits an interlayer d-spacing of 18.07 Å, the largest propped up by noncovalent intermediates between VPO layers. With an extremely low density of 1.71 g‚cm-3, compound 4 also demonstrates the lightest layered material ever prepared in the V/P/O system. Structural relationship, template effect, factors controlling layer gaps, ion exchange, thermal stability, and magnetic properties are discussed.
Introduction The system of microporous or layered metal phosphates has been a subject of intense research owing to their interesting structural chemistry,1-5 physical properties, and potential applications in catalysis, adsorption, and ion exchange.5-9 The porosity or gap of layers can be mediated by organic amine molecules, either as templates, counterions, or ligands coordinating to metal centers. For example, by using diethylenetriamine (dien) and 4,4′-trimethylenedipyridine (tmdp), a 24-membered ring channel structure10 and a highly porous zeolitic framework11 were respectively obtained. In the former case, dien acted as a tridentate ligand to Ga while in the latter case tmdp was fully protonated to balance charge. In the search for new microporous materials, we have also investigated the layered metal phosphate systems.12-15 By introducing the same or similar polyamines * To whom correspondence should be addressed. E-mail: slwang@ mx.nthu.edu.tw. Fax: 886-35-711082.
(1) Finn, R. C.; Zubieta, J.; Haushalter, R. C. Prog. Inorg. Chem. 2003, 51, 421. (2) Cheetham, A. K.; Ferey, G.; Loiseau, T. Angew. Chem., Int. Ed. 1999, 38, 3268. (3) Bu, X. H.; Feng, P. Y.; Stucky, G. D. Science 1997, 278, 2080. (4) Lii, K. H.; Huang, Y. F.; Zima, V.; Huang, C. Y.; Lin, H. M.; Cheng, J. C.; Liao, F. L.; Wang, S. L. Chem. Mater. 1998, 10, 2599. (5) Mark. E. D. Nature 2002, 813, 417. (6) Hartmann, M.; Kevan, L. Chem. ReV. 1999, 99, 635 and references therein. (7) Centi, G.; Trifiro. F. Chem. ReV. 1988, 88, 55. (8) Clearfield, A. Chem. ReV. 1988, 88, 125. (9) Yu, J.; Xu, R. Acc. Chem. Res. 2003, 36, 481 and references therein (10) Lin, C. H.; Wang, S. L.; Lii, K. H. J. Am. Chem. Soc. 2001, 123, 4649. (11) Liao, Y. C.; Liao, F. L.; Chang, W. K.; Wang, S. L. J. Am. Chem. Soc. 2004, 126, 1320.
to the 2D system, we obtained a new vanadyl(IV) compound, (H3dien)[(VOPO4)2(OH)]‚H2O (1), in which dien acts not as ligand to metal but is triprotonated to balance charge, and a unique VIV/VV mixed-valence compound, (H2tmdpp)[V3O4(OH)(PO4)2]‚3H2O (3) (tmdpp ) 4,4′-trimethylenedipiperidine), wherein tmdpp acts as cation as tmdp. The layers for 1 and 3 are related (vide infra) but the interlayer spacing changes from 7.75 to 13.05 Å due to varied lengths of amine cations. According to the results from a literature search on layered vanadyl phosphates with protonated amine as a template, 10 structures16-20 fell into this category and their layer separations and densities ranged from 7.32 to 11.65 Å and 2.16 to 2.50 g‚cm-3. In an attempt to adjust the layer gaps we tried to introduce 1,4-diaminocyclohexane (dach) or inorganic ion such as K+ into our reactions. Another two compounds were subsequently prepared, the V(IV)-containing (H2dach)1.5[(VOPO4)2(OH)]‚2H2O (2) and the mixedvalent (H2tmdpp)(H1.5tmdpp)K0.5 [V5O7(H2O)2 (PO4)4]‚H2O (4), with gaps respectively larger than 1 and 3 and the density dropped to 1.71 g‚cm-3 for 4, the lightest ever reported in (12) Chang, W. M.; Wang, S. L. Chem. Mater. 2005, 17, 74. Lin, C. H.; Wang, S. L. Inorg. Chem. 2005, 44, 251. (13) Chang, W. K.; Chiang, R. K.; Jiang, Y. C.; Wang, S. L.; Lee, S. F.; Lii, K. H. Inorg. Chem. 2004, 43, 2564. (14) Lin, C. H.; Wang, S. L. Inorg. Chem. 2001, 40, 2918. (15) Wang, S. L.; Kang, H. Y.; Cheng, C. Y.; Lii, K. H. Inorg. Chem. 1991, 30, 3496. (16) Soghomonian, V.; Chen, Q.; Haushalter, R. C.; Zubieta, J. Inorg. Chem. 1994, 33, 1700. (17) Soghomonian, V.; Chen, Q.; Zhang, Y.; Haushalter, R. C.; O’Connor, C. J.; Tao, C.; Zubieta, J. Inorg. Chem. 1995, 34, 3509. (18) Bircsak. Z.; Harrison, W. T. A. Inorg. Chem. 1998, 37, 3204. (19) Do, J.; Bontchev, R. P.; Jacobson, A. J. J. Solid State Chem. 2000, 154, 514. (20) Zima, V.; Lii, K. H. J. Solid State Chem. 2003, 172, 424.
10.1021/cm050185e CCC: $30.25 © 2005 American Chemical Society Published on Web 04/29/2005
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Table 1. Crystallographic Data for (C4H16N3)[(VOPO4)2(OH)]‚H2O (1), (C6H16N2)1.5[(VOPO4)2(OH)]‚2H2O (2), (C13H28N2)[(V3O4)(OH)(PO4)2]‚3H2O (3), (C26H55.5N4)K0.5[(V5O7)(H2O)2(PO4)4]‚H2O (4) chemical formula fw a/Å b/Å c/Å β/deg V/Å3 Z space group T/C λ(Mo KR)/Å Fcalcd/g cm-3 µ(Mo KR)/cm-1 R1a wR2b
1
2
3
4
C4H19N3O12P2V2 465.04 17.8461(6) 9.9884(4) 18.4530(7) 117.3950(1) 2920.4 (2) 8 P21/c (No. 14) 20 0.71073 2.115 15.7 0.0404 0.0902
C9H29N3O13P2V2 551.17 11.4110(9) 10.1948(8) 17.977(1) 104.019(1) 2029.0(3) 4 P21/n (No. 14) 20 0.71073 1.804 11.5 0.0516 0.0963
C13H35N2O16P2V3 690.19 13.151(2) 10.963(2) 18.312(3) 96.939(4) 2620.7(8) 4 P21/c (No. 14) 20 0.71073 1.749 12.4 0.0659 0.1690
C26H61.5K0.5N4O26P4V5 1244.42 16.3569(3) 36.1381(2) 9668.7(5) 8 P4/ncc (No. 130) 20 0.71073 1.710 11.9 0.0462 0.1092
a R1 ) Σ||F | - |F ||/Σ|F | for F > 4σ(F ). b wR2 ) [Σw(F 2 - F 2)2/Σw(F 2)2]1/2 , w )1/[σ2(F 2) + (aP)2 + bP], P ) [Max(F ) + 2(F )2]/3, where o c o o o o c o o o c a/b ) 0.0453/3.20 for 1, 0.0253/3.72 for 2, 0.0869/10.99 for 3, and 0.0653/0.00 for 4.
the layered V/P/O system. The density could be altered by ion exchange with NH4+. We observed that the layer gaps can be defined by the length, shape, and most importantly, inclined angle of the amine cation with or without hydrogen bonds to the VPO layers. Herein, we report the synthesis, characterization of the structures, and properties of compounds 1-4, which form a new series of layered structures with clearly distinct but orderly increasing layer separations up to 18.07 Å and common building units of VIVO5 square pyramid, PO4 tetrahedron, dimers of V-O polyhedra, and 3-, 4-, 5-, and 8-membered rings. Template effect along with factors controlling layer gaps, thermal stability, ion exchange, and magnetic properties are to be discussed in detail. Experimental Section Syntheses and Initial Characterizations. Chemicals of reagent grade were used as received. Hydrothermal reactions were carried out at 180 °C for 3 d in a Teflon-lined acid digestion bomb (internal volume of 23 mL) followed by slow cooling at 6 °C h-1 to room temperature. Blue tabular crystals of (H3dien)[(VOPO4)2(OH)].H2O (1) were obtained from a mixture of dien, VO2, H3PO4, and H2O in a molar ratio of 3:1:6:660 and a small amount of NH4OH to adjust the reaction mixture to pH ) 6. The product contained 1 in a yield of 64.8% (based on V) and white amorphous powders. By substitution dach for dien in the above reaction, the product was turned into a small amount of lamellar crystals of (H2dach)1.5[(VOPO4)2(OH)]‚2H2O (2) plus a large quantity of unidentified multiphasic gray powders. With further substitution by the larger amine, tmdpp, it would yield no identified product until extra V2O5 was added to increase the molar ratios to amine:V:P ) 3:2:6. Thereupon, pale-blue platelets of (H2tmdpp)[V3O4(OH)(PO4)2]‚ 3H2O (3) were produced in a yield of 20%, with the rest being amorphous powders. For better solubility and crystallization, we replaced all vanadium oxides by VOSO4 and added KNO3 as a mineralizer to the reaction mixture, from which dark green lamellar crystals of (H2tmdpp)(H1.5tmdpp)K0.5[V5O7(H2O)2(PO4)4]‚H2O (4) resulted. Conditions for preparing monophased products of 1, 2, and 3 have not been reached. However, pure single-phase product of 4 could be achieved by reducing the amount of VOSO4 to the final molar ratios K:amine:V:P ) 1:3:0.5:6, an optimum condition for higher yield of 45%. All measurements (vide infra) were performed on samples21 with individual purity preliminarily checked by powder XRD patterns. The presence of K in 4, first determined from single-crystal structure refinements (see next section), was
also evidenced by EDX. The results of elemental analyses (EA) confirmed the stoichiometry of all organic contents: Found/calcd (%) for 1: C, 10.31/10.33; H, 4.27/4.12; N, 8.56/9.04; for 3: C, 23.38/22.60; H, 5.03/5.11; N, 4.23/4.06; and for 4: C, 25.52/25.09; H, 4.84/4.98; N, 4.44/4.50. Single-Crystal X-ray Diffraction Analysis. Crystals of dimensions 0.10 × 0.12 × 0.15 mm for 1, 0.30 × 0.20 × 0.10 mm for 2, 0.10 × 0.10 × 0.15 mm for 3, and 0.15 × 0.10 × 0.01 mm for 4 were selected for indexing and intensity data collection at 295 K. The diffraction measurements were performed on Bruker SMART CCD diffractometer systems equipped with a normal focus, 3 kW sealed-tube X-ray source (λ ) 0.71073 Å). Intensity data were collected in 1271 frames with increasing ω (0.3° per frame). Unit cell dimensions were determined by a least-squares fit of 8052 reflections for 1, 5061 reflections for 2, 6550 reflections for 3, and 4306 reflections for 4. Empirical absorption corrections based on symmetry equivalents were applied (Tmin/Tmax ) 0.89/0.98 for 1, 0.82/0.96 for 2, 0.64/0.97 for 3, and 0.86/0.96 for 4). On the basis of systematic absences and statistics of intensity distribution, the space groups were determined to be P21/c for 1 and 3, P21/n for 2, and P4/ncc for 4. The structures were solved by direct methods with all non-hydrogen atoms located on electron-density maps. Based on the results from bond-valence-sum calculations,22 the atoms, O(17) and O(20) in 1 and O(10) in both 2 and 3, were assigned to hydroxy groups, and O(10) in 4 was assigned to a coordination water molecule. The hydrogen atoms in the abovementioned OH groups and water molecule, plus those on the nitrogen atoms in 2, could be directly located on difference maps. The final cycles of refinement, including the atomic coordinates and anisotropic thermal parameters for all non-H atoms, and fixed atomic coordinates and isotropic thermal parameters for H atoms,23 converged at R1/wR2 ) 0.040/0.086 for 1, 0.052/0.096 for 2, 0.066/ 0.169 for 3, and 0.0462/0.1092 for 4. Neutral-atom scattering factors were used and anomalous dispersion and secondary extinction corrections were applied. All calculations were performed by using the PC version of the SHELXTL program package.24 Crystallographic data are listed in Table 1 and selected bond distances in Table 2. The valence for each vanadium site was determined based on its coordination geometry, bond-valence sum (see Table 2), and (21) Isolation of crystals of 2 for measurements other than single-crystal diffraction has not been successful due to low yield and contaminations. (22) Brown, I. D.; Altermatt, D. Acta Crystallogr. 1985, B41, 244. (23) Hydrogen atoms of the organic groups were calculated by using a riding model. (24) Sheldrick, G. M. SHELXTL Programs, version 5.1; Bruker AXS GmbH: Karlsruhe, Germany, 1998.
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Chem. Mater., Vol. 17, No. 11, 2005 2835
Table 2. Selected Bond Lengths (Å) and Bond Valence Sums (ΣS) for 1-4 V(1)-O(1) V(1)-O(15)a* V(1)-O(18) ΣS[V(1)-O] ) 4.08 V(2)-O(4)a V(2)-O(13) V(2)-O(19) ΣS[V(2)-O] ) 3.98 V(3)-O(6) V(3)-O(11)b V(3)-O(21) ΣS[V(3)-O] ) 4.16 V(4)-O(5) V(4)-O(14) V(4)-O(22) ΣS[V(4)-O] ) 4.15 P(1)-O(1) P(1)-O(3) ΣS[P(1)-O] ) 5.00 P(2)-O(5) P(2)-O(7) ΣS[P(2)-O] ) 5.00 P(3)-O(9) P(3)-O(11) ΣS[P(3)-O] ) 5.00 P(4)-O(13) P(4)-O(15) ΣS[P(4)-O] ) 5.01 V(1)-O(2) V(1)-O(8)e V(1)-O(10) ΣS[V(1)-O] ) 4.10 V(2)-O(1) V(2)-O(5) V(2)-O(10)g ΣS[V(2)-O] ) 4.06 P(1)-O(1) P(1)-O(3) ΣS[P(1)-O] ) 4.99 P(2)-O(5) P(2)-O(7) ΣS[P(2)-O] ) 5.04
1 1.975(2) 1.962(2) 1.599(2)
3 V(1)-O(3)a V(1)-O(17)
1.958(2) 1.972(2)
1.945(2) 2.006(2) 1.605(2)
V(2)-O(10) V(2)-O(17)
1.976(2) 1.990(2)
2.011(2) 1.923(2) 1.589(2)
V(3)-O(8)c V(3)-O(20)
1.971(2) 1.950(2)
1.980(2) 1.973(2) 1.586(2)
V(4)-O(12) V(4)-O(20)d
1.947(2) 1.961(2)
1.549(2) 1.547(2)
P(1)-O(2) P(1)-O(4)
1.509(2) 1.533(2)
1.548(2) 1.518(2)
P(2)-O(6) P(2)-O(8)
1.533(2) 1.538(2)
1.536(2) 1.531(2)
P(3)-O(10) P(3)-O(12)
1.546(2) 1.525(2)
1.545(2) 1.524(2)
P(4)-O(14) P(4)-O(16)
1.548(2) 1.520(2)
2 1.971(3) 1.940(3) 1.970(3)
V(1)-O(6)f V(1)-O(9)
1.999(3) 1.588(3)
2.005(3) 1.960(3) 1.987(3)
V(2)-O(3)g V(1)-O(6)f V(2)-O(11)
1.954(3) 1.999(3) 1.592(3)
1.549(3) 1.538(3)
P(1)-O(2) P(1)-O(4)
1.535(3) 1.518(3)
1.537(3) 1.506(3)
P(2)-O(6) P(2)-O(8)
1.538(3) 1.542(3)
V(1)-O(3)h V(1)-O(7) V(1)-O(10) ΣS[V(1)-O] ) 4.00 V(2)-O(2) V(2)-O(5) V(2)-O(11) ΣS[V(2)-O] ) 4.06 V(3)-O(1) V(3)-O(12) ΣS[V(3)-O] ) 4.98 P(1)-O(1) P(1)-O(3) ΣS[P (1)-O] ) 5.04 P(2)-O(5) P(2)-O(7) ΣS[P(2)-O] ) 4.99 K(1)-O(7) ΣS[K(1)-O] ) 1.23 V(1)-O(2)m V(1)-O(8)m V(1)-O(10) ΣS[V(1)-O] ) 4.24 V(2)-O(1) V(2)-O(6)l V(2)-O(10) ΣS[V(2)-O] ) 4.99 V(3)-O(3) V(3)-O(3)m V(3)-O(13) ΣS[V(3)-O] ) 3.95 V(4)-O(4) V(4)-O(4)n V(4)-O(14) ΣS[V(4)-O] ) 4.19 P(1)-O(1) P(1)-O(3) ΣS[P(1)-O] ) 5.02 P(2)-O(5) P(2)-O(7) ΣS[P(2)-O] ) 5.03
1.977(3) 1.990(3) 1.977(3)
V(1)-O(6)i V(1)-O(9)
1.998(3) 1.592(4)
1.979(4) 1.963(3) 1.594(4)
V(2)-O(4)j V(2)-O(10)
1.993(3) 1.967(3)
1.854(4) 1.605(5)
V(3)-O(8)k V(3)-O(13)
1.875(4) 1.634(4)
1.572(4) 1.508(3)
P(1)-O(2) P(1)-O(4)
1.525(3) 1.528(3)
1.518(3) 1.543(4)
P(2)-O(6) P(2)-O(8)
1.521(3) 1.562(4)
4 2.746(3) (4x)
K(1)-O(11)
2.922(3) (4x)
1.945(3) 1.998(3) 2.464(3)
V(1)-O(7)l V(1)-O(9) V(1)-O(11)
1.999(3) 1.955(3) 1.592(3)
1.944(3) 1.995(3) 2.524(3)
V(2)-O(5) V(2)-O(9) V(2)-O(12)
1.988(3) 1.733(3) 1.594(3)
1.997(3) 1.997(3) 1.586(7)
V(3)-O(3)n V(3)-O(3)
1.997(3) 1.997(3)
1.968(3) 1.968(3) 1.576(6)
V(4)-O(4)m V(4)-O(4)m
1.968(3) 1.968(3)
1.534(3) 1.536(3)
P(1)-O(2) P(1)-O(4)
1.519(3) 1.541(3)
1.530(3) 1.524(3)
P(2)-O(6) P(2)-O(8)
1.546(3) 1.533(3)
a-o Symmetry transformations used to generate equivalent atoms. a-x, y + 1/ , -z + 1/ . bx, y - 1, z. c-x - 1, y - 1/ , -z - 1/ . d-x - 1, y + 1/ , -z 2 2 2 2 2 - 1/2. e-x, -y + 1 , -z. fx, y - 1, z. g-x + 1/2, y + 1/2, -z + 1/2. hx, -y + 3/2, z + 1/2. i-x + 1, y + 1/2, -z + 1/2. j-x + 1, -y + 2, -z. kx, -y + 3/2, z - 1/2. l-x + 1, -y + 2, -z. my - 1, -x + 3/2, z. n-y + 3/2, x + 1, z. o-x + 1/2, -y + 5/2, z.
effective magnetic moment (vide infra). Atomic coordinates and thermal parameters are given in the Supporting Information. Magnetic Susceptibility Measurements. Variable-temperature magnetic susceptibility χ(T) were measured from 2 to 300 K in a magnetic field of 5 kG using a Quantum Design SQUID magnetometer on powder samples of 1 (12.8 mg), 3 (6.5 mg), and 4 (22.0 mg). Corrections for diamagnetic contribution were made according to Selwood.25 All data above 50 K were fitted with the Curie-Weiss law from which the Curie constant (Cm in cm3‚K‚ mol-1) and Weiss temperatures (θ) were respectively obtained: 0.686 and -9.0 K for 1, 0.725 and -12.2 K for 3, and 0.996 and -3.5 K for 4. Thermogravimetric Analysis. Thermal analyses, using a PerkinElmer TGA-7 analyzer, were performed on powder samples 1, 3, and 4 under flowing N2 with a heating rate of 10 °C min-1. The TG curves for 1 and 4 contained unresolved multisteps of weight loss while the curve for 3 revealed a clear stage before 280 °C owing to the weight loss of one of its lattice water molecules (vide infra). The organic components were decomposed right after all lattice water molecules were removed. For all three, the total observed weight losses seemed lower than the calculated values: (25) Selwood, P. W. Magnetochemistry; Interscience: New York, 1956.
32.56% vs 33.79% for 1, 34.19% vs 42.22% for 3, and 35.77% vs 40.69% for 4. The disagreement should be attributed to the incomplete removal of the organic components under measurements up to 900 °C. Ion-Exchange Study. Initially, a 40.4 mg sample of 4 was magnetically stirred with 4 M NH4Cl in water overnight under ambient conditions. The product was filtered, washed, and dried, and powder XRD (PXRD) measurements and EA analysis were then performed. Those results revealed that the original structure was sustained but only 20% of H2tmdpp2+ was replaced by NH4+ ions. When another batch of sample (63.6 mg) was used and solvent was changed to a mixture of water and alcohol in 7:3 ratios, the interchange between H2tmdpp2+ and NH4+ ions could reach 80%. On the measured PXRD patterns, the (002) reflections were observed to shift upward angles and the interlayer d-spacing shrank to 17.92 Å in maximum after the ion exchange.
Results and Discussion Structure Description and Conformity in 1-3. Compounds 1-4 exhibit three unique layer structures (Figure 1) in which 1-3 are closely related to each other. 1 and 2 are both vanadyl(IV) species with similar layer topology in the
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Figure 1. Perspective views of the layered structures 1-4 along the b-axis. In the plots, the VIV-O polyhedra are in green (1-4) or deep green (4), the VV-O polyhedra in cyan (3 and 4), and phosphate tetrahedra in yellow (1-4) or pink (the bridging P(2) in 4, see text). The rectangular part in 4 is the brimmed-hat-like SBU. Amine cations and water molecules are drawn in a ball-and-stick model: C, gray; N, blue; and O, red. H atoms are omitted for clarity.
composition of [(VOPO4)2(OH)]3- and polyhedral connectivity, which is made of VO5 square pyramids and PO4 tetrahedra (Figure 2). Compound 3 is VIV/VV mixed valence and the building unit for [V3O4(OH)(PO4)2]2- layer includes vanadate group, VVO4, in addition to VIVO5 square pyramids and PO4 tetrahedra. In all three structures, the VIVO5 square pyramids form a binuclear V2O8(OH) unit via a shared OH ligand and are further bridged by a bidentate PO4 tetrahedron to form a three-membered ring (3R) which acts as the common secondary building unit (SBU) (see circled part in Figure 2). The 3Rs directly link to each other in a head-totail manner into ribbons along b, which are connected further along c through additional PO4 groups to generate a polyhedral sheet containing 3R, 4R, 5R, and 8R. As to the additional VO4 group in 3, it bridges the two phosphate tetrahedra on the 5R and is pendent to the two-dimensional sheet as shown in Figure 1. Structural Dissimilarity in 1-3. Although having the same composition, layers of 1 and 2 are different in symmetry and stacking sequence (Table 3). The asymmetric unit of 1 includes four V independent sites which form two distinct binuclear sites, V(1)/V(2) with two VdO vertexes aligned parallel and V(3)/V(4) with two VdO vertexes in opposite directions. On the other hand, the asymmetric unit of 2 contains two V independent sites, forming only one binuclear unit with two VdO vertexes pointing oppositely, while that of 3 as well contains one binuclear site; the two
VdO vertexes are in parallel orientation. Regarding each layer along the c-axis, as shown in Figure 4, the orientation of VO5 square pyramids is in UD DD UD ... arrangement for 1, and straight DU DU DU... for 2 and DD DD DD... for 3. Despite the symmetry and conformational difference, the new vanadium phosphate layers look the same for 1 and 2 and they are similar to the phosphite sheet in (HMeNC2H4)2[(VO)4(OH)2(HPO3)4].26 Nonetheless, the vanadate-mediated version makes 3 a unique layer topology in the V/P/O system. The triply charged [(VOPO4)2(OH)]3- layers in 1 and 2 are respectively neutralized by one fully protonated triamine and one-and-half diamine. The [V3O4(OH)(PO4)2]2- of 3, though having different composition and charge, can now be viewed as (VO2)+[(VOPO4)2(OH)]3-. Apparently the vanadate group compensates one charge on the [(VOPO4)2(OH)]3- layer so that only one diprotonated amine is needed for chargebalancing in 3. Structure Description for 4. Compound 4 is also VIV/ V V mixed valence like 3, but with three distinct VIV sites, V(1) in octahedral and V(3) and V(4) in square pyramidal centers, and one VV site, V(2) in octahedral coordination instead of being vanadate centers, and two P tetrahedral sites. As shown in Figure 2, binuclear clusters as well exist in 4 and they are a mixed-valence V2O9(H2O) unit formed of (26) Bonavia, G..; DeBord, J.; Haushalter, R. C.; Rose, D.; Zubieta, J. Chem. Mater. 1995, 7, 1995.
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Figure 2. Section of VPO layers in 1-4 along the c-axis. All four exhibit 3-, 4-, 5-, and 8-membered rings. The circled 3R in 1 is a common SBU for 1-3 and the circled part in 4 is the brimmed-hat-like SBU. Notations for polyhedron colors are the same as those in Figure 2. The vanadate tetrahedra (cyan) are capped on 5Rs in 3. The gray circle in 4 is K+ ion, which is bound tightly within 8R of the layer. Table 3. Layer Symmetry and Stacking Direction and Sequence for 1-4 anionic framework
layer symmetry
stacking direction
stacking sequence
[(VO)2(OH)(PO4)2]3- (1) [(VO)2(OH)(PO4)2]3- (2) [(V3O4)(OH)(PO4)2]2- (3) [(V5O7)(H2O)2(PO4)4]4- (4)
21 2 1, i 2 1, i 4-fold
[-1 0 1] [-1 0 1] [1 0 0] [0 0 1]
ABCD AAAA AAAA ABAB
edge-sharing V(1)/V(2) octahedra, in contrast to the singlevalence V2O8(OH) of corner-sharing square pyramids in 1-3. Despite no direct linkage between the square pyramids of V(3) and V(4), they are paired through four P(1)O4 tetrahedra to form a copper acetate-type core {V2(µ2-PO4)4}27 with two VdO vertexes point to opposite directions, (refer to Figure 3). The core has 4-fold symmetry and connects further to four mixed-valence bioctahedral units via P(1) tetrahedra, constituting the wide-brimmed-hat-like SBUs. The unit exhibits 3R, 4R and 5R windows by itself and link further through P(2)O4 tetrahedra, generating the two-dimensional [V5O7(H2O)2(PO4)4]4- net with 8R windows, in which K+ ions are embraced. The structure of 4 thus exhibits a much different layer topology from those of 1-3. Viewed along the b-axis, the brimmed-hat-like SBUs bind to each other with c-glide symmetry, forming apparent and deep indentations. The result is a beautiful zigzag layer (Figure 4) with three polyhedra in thickness and high symmetry in 4-fold, rarely observed in other layered phosphate materials. (27) Doedens, R. J. Prog. Inorg. Chem. 1976, 21, 209.
Hydrogen Bonding and Ion-Exchange Property. On examining the interaction between various counter species and layers in Table 4, we observed that all amine cations in 1-3 are involved in strong hydrogen bonding (HB), directly or via interleaved water molecules, to the anionic layers. But in 4, no significant HB was observed. The space between the deeply indented layers of 4 is occupied by lattice water and protonated tmdpp molecules, ca. 75% being dicharged and 25% being monocharged. They are rather loosely bound as compared with the other amine cations in 1-3. Therefore, we performed ion exchange on 4 and confirmed that the large protonated tmdpp molecules could be replaced by NH4+ ions to various extents (vide supra). Figure 5 shows the PXRD patterns of ion-exchanged products along with the parent compound. It suggests the layer gap can be reduced by interchanging the larger organic with the smaller cations. No observable exchange of K+ ions has been detected since they are tightly bound by eight oxygen atoms (refer to Table 2) within the thick layers of 4. Magnetic and Thermal Properties. Compounds 1-4 are considered as a series because of some shared structural features: 3-, 4-, 5-, and 8-membered rings within 2D layers formed of PO4 tetrahedron, VIVO5 square pyramid, and binuclear unit of V-O polyhedra. The V2O8(OH) unit for 1 and 3 are in single-valence with two d1 (VIV) centers only 3.56 Å apart, leading to the observed antiferromagnetism below 50 K. Plots of χMT vs T and χM-1 vs T are given in Figure 6. The bioctahedral unit in 4 has only one VIV center,
2838 Chem. Mater., Vol. 17, No. 11, 2005
Yang et al.
Figure 3. The orientation of VO5 square pyramids in (a) 1 (top), 2 (middle), and 3 (bottom) and (b) a copper acetate-type core in 4. Viewed along the c-axis.
Figure 5. Powder XRD patterns of the (002) reflections measured on ionexchanged products (red peak for 20% replacement and green peak for 80% replacement by NH4+) along with the parent 4 (peak in black).
Figure 4. Section of the beautiful and highly symmetric layer of 4. In this representation, blue wires connect between polyhedral centers with intralayer K+ ions drawn in yellow balls and interlayer amine cations drawn in brown lines. Table 4. Hydrogen Bonding in 1-4 com- counter pound species
1
dien
donor-H‚‚‚acceptor
d(H‚‚‚A) d(D‚‚‚A) ∠(D-H‚‚‚A) (Å) (Å) (°)
O(17)-H(1)‚‚‚O(3) O(20)-H(2)‚‚‚O(8) N(1)-H(21)‚‚‚O(7) N(2)-H(24)‚‚‚O(9) N(2)-H(25)‚‚‚O(2) N(4)-H(27)‚‚‚O(9) N(4)-H(28)‚‚‚O(19) N(5)-H(30)‚‚‚O(9) N(5)-H(31)‚‚‚O(16)
1.849 1.989 1.575 1.912 1.858 2.023 1.983 1.832 2.009
2.746 2.878 2.679 2.815 2.654 2.861 2.835 2.670 2.770
161.74 167.24 171.88 165.58 160.32 172.14 171.38 159.87 160.57
1.754 1.770 1.884 1.812 1.892 1.760
2.689 2.735 2.800 2.876 2.776 2.615
167.18 175.83 171.06 175.70 165.53 165.55
1.917 1.864
2.964 2.935
174.82 153.22
2.104
2.811
133.15
2
dach
N(1)-H(10A)‚‚‚O(3) N(1)-H(10B)‚‚‚O(4) N(2)-H(11A)‚‚‚O(12) N(2)-H(11C)‚‚‚O(1) N(3)-H(12A)‚‚‚O(7) O(12)-H(13A)‚‚‚O(4)
3
tmdpp
N(1)-H(2)‚‚‚O(14) O(16)-H(25)‚‚‚O(14)
4
tmdpp N(1)-H(1A)‚‚‚O(2)
which is at least 5.0 Å apart from the other V atoms. However, the two VIV centers of the {V2(µ2-PO4)4} core are only apart by 3.57 Å so that magnetic coupling can occur and 4 becomes antiferromagnetic at low temperatures as 1
Figure 6. Temperature dependence magnetic susceptibility data: χM-1 vs T (2) and χMT vs T (b). Curves for 1 are in black, for 3 in red, and for 4 in green.
and 3. The observed effective magnetic moments (in µB), 2.41 for 1, 2.37 for 3, and 2.78 for 4, can be compared well with the calculated values, 2.45 µB for two d1 centers and 3.00 µB for three d1 centers, confirming the presence of two VIV atoms and three VIV atoms per formula weight of 1, 3, and 4. From TG analysis combined with PXRD measurements, we noticed that upon heating 1, 2, and 3 would immediately lose one lattice water molecule respectively but without collapsing the original structures until 200 °C. At this temperature, however, there are two more lattice water molecules remaining in 3 because of stronger hydrogen
Vanadyl Phosphates with Varied Polyamine Templates
Chem. Mater., Vol. 17, No. 11, 2005 2839
Table 5. Comparison in Interlayer d-Spacing and Density for Layered VPO Structures d-spacing (Å)
density (g‚cm-3)
[H2pip][(VO)4(OH)4(PO4)2] (H2pip)[(VO)(VO2)2(H2O)(PO4)2] [H2dabco]2(VO)8(HPO4)3(PO4)4(OH)2‚2H2O (H2dabco)[(VO)3(OH)2(PO4)2] (H2pip)[(VO)(PO4)]2 (CN3H6)2(VO2)3(PO4)(HPO4) (H2pip)2[(VO)3(HPO4)2(PO4)2] ‚H2O [H2pip]1.5[(VO)2(HPO4)2(PO4)] (H2en)2[V4O6H(HPO4)2(PO4)2] [H4appip][(VO)5(OH)2(PO4)4‚2H2O
10.011 9.928 9.332 9.771 8.198 8.816 7.316 7.646 11.653 8.586
2.497 2.495 2.466 2.397 2.359 2.320 2.280 2.253 2.212 2.159
14 16 14 14 13 15 13 17 17 14
(H3dien)[(VO)2(OH)(PO4)2]‚H2O (1) (H2dach)1.5[(VO)2(OH)(PO4)2]‚2H2O (2) (H2tmdpp)[(V3O4)(OH)(PO4)2]‚3H2O (3) (H2tmdpp)(H1.5tmdpp)K0.5[(V5O7)(H2O)2(PO4)4]‚H2O (4)
7.750 10.581 13.054 18.069
2.115 1.804 1.749 1.710
this work this work this work this work
formula
Figure 7. Plot of density and layer gap for VPO materials with previously reported shown in triangles and current series in blue circles. Refer to Table 5 for corresponding compounds.
bonding. Structure 3 could be sustained up to 300 °C. A common feature to the thermal behavior of 1, 3, and 4 is that their structures would collapse on losing organic amine which decomposed right after all lattice water was evacuated. Densities, Layer Gaps, and Controlling Factors. Inorganic materials with low densities are of practical usage and applications. It is challenging to explore the lowest limit of a system. Among the existing amine templated twodimensional vanadium phosphates, the density (g‚cm-3) ranges from 2.16 to 2.50. As listed in Table 5, compounds
reference no.
1-4 are all lighter than those previously reported and they push the density down to 1.71, 30% lower than the average of those and the lowest ever observed in layered VPOs. It is clearly seen in Figure 7 that a correlation between density and layer gap may be established for 1-4, whereas previously reported structures seem to fall randomly on the plot. The layer gap from 1 to 3 steadily expands from ∼7.75 to 13.06 Å in an average step of ∼2.65 Å as the template amine changes from dien, dach, to tmdpp (Figure 8), whose lengths (head to tail) are ∼6.8, 5.7, and 10.8 Å. The shorter dach gives rise to a larger gap than the longer dien, owing to strong HB and higher incline angles (82-86°) whose differences come from various molecular shapes or amine configurations. The latter effect has been even more prominent in the abovementioned phosphite,26 whose template is a tertiary amine; its layer gap has diminished to ∼6.5 Å despite similar amine length and molecular shape to dach. Furthermore, the gap suddenly jumps by 5.0 Å from 3 to 4 with the same amine. This is due to a drastic change in the incline angle of tmdpp, from 42° in 3 to 90° in 4, by lacking H-bonding and dissimilar layer shape. In conclusion, four new organically templated VPO layered materials including two V(IV) and two mixedvalence V(IV)/V(V) phases have been synthesized and characterized with successful ion exchanges being explored. The new series is highly distinctive for three unique layer
Figure 8. The orderly increasing layer separations from 1 to 4. Refer to text for numerical values.
2840 Chem. Mater., Vol. 17, No. 11, 2005
topologies, common building units and rings, orderly increasing layer separations, and lowest densities with thermal stability up to 200-300 °C. The layer topologies are similar or related for 1, 2, and 3, while 3 and 4 employ the same amine template. They demonstrate that the same type of layers can be propped up to different extents by various amine cations, while the same amine can result in different layer gaps; i.e., the template effect mostly reflects on layer separations. In addition, hydrogen bonding in 1-3 has been a hinge which can either enlarge or shrink the separation according to the molecular configuration and layer topology. Furthermore, the structure of 4, being the first example containing both inorganic and organic counterions in layered VPO,28-31 is the most distinctive for its comparatively loose structure, which is indexed by the largest layer gap, lowest
Yang et al.
density, and trivial hydrogen bonds between organic cations and layers, and hence is suitable for ion exchange. Will any two-dimensional VPO phase with larger layer gap and lower density than 4 exist? Investigation for more porous and lighter materials in the vanadium phosphate system is in progress. Acknowledgment. We are grateful to the National Science Council of Taiwan for support of this work (93-2113-M-007032). Supporting Information Available: X-ray crystallographic information files (CIF), ORTEP drawings for 1, 2, 3, and 4, and TGA curves for 1, 3, and 4. The material is available free of charge via the Internet at http://pubs.acs.org. CM050185E
(28) No layered VPO phases with mixed organic-inorganic counterions were reported before. However, previously there were three 3D framework VPO structures29-31 in which mixed counterions were observed. (29) Soghomonian, V.; Chen, Q.; Zhang, Y.; Haushalter, R. C.; Zubieta, J.; O’Connor, C. J. Science 1993, 259, 1596.
(30) Soghomonian, V.; Chen, Q.; Zhang, Y.; Haushalter, R. C.; Zubieta, J. Chem. Mater. 1993, 5, 1595. (31) Khan, M. I.; Meyer, L. M.; Haushalter, R. C.; Schweitzer, A. L.; Zubieta, J.; Dye, J. L. Chem. Mater. 1996, 8, 43.
