Inorg. Chem. 2006, 45, 5529−5537
Directed Synthesis of Noncentrosymmetric Molybdates Using Composition Space Analysis Thomas R. Veltman,† Adam K. Stover,† Amy Narducci Sarjeant,‡ Kang Min Ok,§ P. Shiv Halasyamani,§ and Alexander J. Norquist*,† Department of Chemistry, HaVerford College, HaVerford, PennsylVania 19041, Department of Chemistry, UniVersity of Houston, Houston, Texas 77204-5003, and Department of Chemistry, Johns Hopkins UniVersity, Baltimore, Maryland 21218 Received April 3, 2006
A systematic investigation of the factors governing the reaction product composition, hydrogen bonding, and symmetry was conducted in the MoO3/3-aminoquinuclidine/H2O system. Composition space analysis was performed through 36 individual reactions under mild hydrothermal conditions using racemic 3-aminoquinuclidine. Single crystals of three new compounds, [C7H16N2][Mo3O10]‚H2O, [C7H16N2]2[Mo8O26]‚H2O, and [C7H16N2]2[Mo8O26]‚4H2O, were grown. The relative phase stabilities for these products are dependent upon the reactant mole fractions in the initial reaction gel. This phase stability information was used to direct the synthesis of two new noncentrosymmetric compounds, using either (S)−(−)-3-aminoquinuclidine dihydrochloride or (R)-(+)-3-aminoquinuclidine dihydrochloride. [(R)-C7H16N2]2[Mo8O26] and [(S)-C7H16N2]2[Mo8O26] both crystallize in the noncentrosymmetric space group P21 (No. 4), which has the polar crystal class 2 (C2). The second-harmonic generation activities were measured on sieved powders. The structure-directing properties of the molybdate components in each compound were determined using bond valence sums. The structures of all five compounds were determined using single-crystal X-ray diffraction.
Introduction Conducting reactions under hydrothermal conditions is a well-established method for the preparation of inorganic structures templated by organic cations.1-9 Despite the vast amount of effort expended upon such studies, true control over the product composition and structure often remains elusive. Composition space analysis10-13 is known to be a viable technique for the elucidation of the factors governing the * To whom correspondence should be addressed. E-mail: anorquis@ haverford.edu. † Haverford College. ‡ Johns Hopkins University. § University of Houston. (1) Cheetham, A. K.; Fe´rey, G.; Loiseau, T. Angew. Chem., Int. Ed. 1999, 38, 3268. (2) Fernandez, S. J.; Mesa, L.; Pizarro, J. L.; Lezama, L.; Arriortura, M. I.; Rojo, T. Chem. Mater. 2002, 14, 2300. (3) Walker, S. M.; Halasyamani, P. S.; O’Hare, D. J. Am. Chem. Soc. 1999, 121, 7415. (4) Reisner, B. A.; Tripathi, A.; Parise, J. B. J. Mater. Chem. 2001, 11, 887. (5) Bu, X.; Feng, P.; Gier, T. E.; Zhao, D.; Stucky, G. D. J. Am. Chem. Soc. 1998, 120, 13389. (6) Ekambarem, S.; Sevov, S. Inorg. Chem. 2000, 39, 2405. (7) Vaidhyanathan, R.; Natarajan, S.; Rao, C. N. R. Inorg. Chem. 2002, 17, 4496. (8) Choudhury, A.; Kumar, U.; Rao, C. N. R. Angew. Chem., Int. Ed. 2002, 41, 158. (9) Harrison, W. T. A.; Phillips, M. L. F.; Stanchfield, J.; Nenoff, T. M. Angew. Chem., Int. Ed. 2000, 39, 3808.
10.1021/ic060558t CCC: $33.50 Published on Web 06/10/2006
© 2006 American Chemical Society
reaction product composition. Composition space analysis involves the introduction of subtle variations in the reactant concentrations over a series of analogous experiments. All other reaction variables, such as temperature and reaction time, are held constant, enabling direct observation of the effects that result from these composition differences. Bond valence sums14 can be used to educe the structure-directing properties of inorganic architectures, through quantification of the relative nucleophilicities of each potential hydrogenbond acceptor. The ubiquitous hydrogen-bonding networks in such compounds are largely dependent upon the structuredirecting properties of the anions. Product symmetry is of special interest to researchers owing to several symmetrydependent15 physical properties:16 enantiomorphism, optical activity (circular dichroism), piezoelectricity, pyroelectricity, (10) Halasyamani, P. S.; Willis, M. J.; Stern, C. L.; Lundquist, P. M.; Wong, G. K.; Poeppelmeier, K. R. Inorg. Chem. 1996, 35, 1367. (11) Harrison, W. T. A.; Dussack, L. L.; Jacobson, A. J. J. Solid State Chem. 1996, 125, 234. (12) Norquist, A. J.; Heier, K. R.; Stern, C. L.; Poeppelmeier, K. R. Inorg. Chem. 1998, 37, 6495. (13) Doran, M. B.; Norquist, A. J.; O’Hare, D. Inorg. Chem. 2003, 42, 6989. (14) Brown, I. D.; Altermatt, D. Acta Crystallogr., Sect. B 1985, 41, 244. (15) Chen, C.; Liu, G. Annu. ReV. Mater. Sci. 1986, 16, 203. (16) Halasyamani, P. S.; Poeppelmeier, K. R. Chem. Mater. 1998, 10, 2753.
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Veltman et al. Table 1. Crystallographic Data for Compounds 1-5 compd formula fw space group a/Å b/Å c/Å β/deg V/Å3 Z Fcalcd/g cm-3 λ/Å T/K µ/mm-1 total reflns independent reflns obsd reflns param Flack param R1a wR2b a
[C7H16N2][Mo3O10]‚ H2O (1) C7H16Mo3N2O11 591.90 P21/m (No. 10) 8.890(2) 7.6605(8) 10.6695(13) 103.541(15) 706.4(2) 2 2.782 0.71073 110(2) 2.683 5412 1913 1296 [I > 3σ] 148
[C7H16N2]2[Mo8O26]‚ H2O (2) C14H34Mo8N4O27 1457.95 Pbcn (No. 60) 12.7611(8) 16.2554(12) 15.6322(11) 90 3242.7(4) 4 2.986 0.71073 110(2) 3.101 54098 4896 3153 [I > 3σ] 243
[C7H16N2]2[Mo8O26]‚ 4H2O (3) C14H40Mo8N4O30 1512.00 P21/n (No. 14) 7.9547(3) 11.0404(5) 20.6373(7) 94.684(3) 1806.38(12) 2 2.780 0.71073 110(2) 2.794 32095 7288 5181 [I > 3σ] 254
0.0326 0.0743
0.0210 0.0426
0.0208 0.0440
[(R)-C7H16N2]2[Mo8O26] (4) C14H32Mo8N4O26 1439.94 P21 (No. 4) 7.2672(3) 11.6360(5) 19.6965(8) 99.852(4) 1641.00(12) 2 2.914 0.71073 110(2) 3.060 26377 8344 6144 [I > 3σ] 471 -0.07(4) 0.0211 0.0382
[(S)-C7H16N2]2[Mo8O26] (5) C14H32Mo8N4O26 1439.94 P21 (No. 4) 7.2685(3) 11.6423(5) 19.6887(9) 99.948(4) 1641.05(13) 2 2.914 0.71073 110(2) 3.060 25828 8087 5977 [I > 3σ] 471 -0.08(5) 0.0225 0.0438
R1 ) ∑|Fo| - Fc|/∑|Fo|. b wR2 ) [∑w(Fo2 - Fc2)2/[∑w(Fo2)2]1/2.
and second-order nonlinear-optical activity [second-harmonic generation (SHG)]. Several strategies17-20 are currently employed to direct noncentrosymmetry in new crystalline compounds, including the use of chiral organic amines.21,22 A systematic investigation of the MoO3/3-aminoquinuclidine/H2O system was conducted to probe the factors dictating product composition, the structure-directing properties of the inorganic component (and related hydrogen-bonding networks), and the product symmetry. The synthesis, structure, and characterization of five novel organically templated molybdates, two of which are noncentrosymmetric, are reported. Experimental Section Materials. MoO3 (99.5%, Aldrich), H2SO4 (98%, Aldrich), 3-aminoquinuclidine dihydrochloride (aqn; 98%, Aldrich), (S)-(-)3-aminoquinuclidine dihydrochloride (S-aqn; 98%, Aldrich), and (R)-(+)-3-aminoquinuclidine dihydrochloride (R-aqn; 98%, Aldrich) were used as received. Deionized water was used in these syntheses. Synthesis. All reactions were conducted in 23-mL poly(fluoroethylenepropylene)-lined pressure vessels. Reactions were heated to 180 °C over 30 min and allowed to soak for 24 h. The reactions were then cooled to room temperature at a rate of 6 °C h-1. Autoclaves were opened in air, and products were recovered through filtration. Reaction yields ranged between 30 and 60%, based upon molybdenum. No additional reaction products other than those described below, crystalline or amorphous, were observed. [C7H16N2][Mo3O10]‚H2O (1) was synthesized through the reaction of 0.1415 g (9.83 × 10-4 mol) of MoO3, 0.8138 g (4.092 × 10-3 mol) of aqn, 0.1993 g (2.034 × 10-3 mol) of H2SO4, and 1.9998 g (1.111 × 10-1 mol) of deionized water. Colorless needles were recovered. Elem microanal. Obsd for 1 (calcd): C, 14.39 (14.19); H, 2.66 (2.70); N, 4.79 (4.73). IR data (cm-1): ν(N-H) 3113, 1589, ν(C-H) 1466, ν(MdO) 921. [C7H16N2]2[Mo8O26]‚H2O (2) was synthesized through the reaction of 0.5868 g (4.077 × 10-3 mol) of MoO3, 0.2164 g (1.088 × 10-3 mol) of aqn, 0.2164 g (2.208 × 10-3 mol) of H2SO4, and (17) Halasyamani, P. S. Chem. Mater. 2004, 16, 3586. (18) Kwon, Y. U.; Lee, K. S.; Kim, Y. H. Inorg. Chem. 1996, 35, 1161.
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1.0015 g (5.5564 × 10-2 mol) of deionized water. Colorless blocks were recovered. Elem microanal. Obsd for 2 (calcd): C, 11.81 (11.52); H, 2.16 (2.33); N, 3.91 (3.84). IR data (cm-1): ν(N-H) 3136, 1621, ν(C-H) 1491, ν(MdO) 967. [C7H16N2]2[Mo8O26]‚4H2O (3) was synthesized through the reaction of 0.4603 g (3.198 × 10-3 mol) of MoO3, 0.4041 g (2.032 × 10-3 mol) of aqn, 0.2099 g (2.142 × 10-3 mol) of H2SO4, and 1.0358 g (5.754 × 10-2 mol) of deionized water. Light-green blocks were recovered. Elem microanal. Obsd for 3 (calcd): C, 11.14 (11.11); H, 2.48 (2.64); N, 3.71 (3.70). IR data (cm-1): ν(N-H) 3105, 1618, ν(C-H) 1473, ν(MdO) 957. [(R)-C7H16N2]2[Mo8O26] (4) was synthesized through the reaction of 0.3897 g (2.70 × 10-3 mol) of MoO3, 0.03520 g (1.77 × 10-3 mol) of R-aqn, 0.1428 g (1.457 × 10-3 mol) of H2SO4, and 1.0107 g (5.615 × 10-2 mol) of deionized water. Colorless blocks were recovered. Elem microanal. Obsd for 4 (calcd): C, 11.66 (11.66); H, 2.10 (2.22); N, 3.92 (3.88). IR data (cm-1): ν(N-H) 3120, 1607, ν(C-H) 1487, ν(MdO) 975. [(S)-C7H16N2]2[Mo8O26] (5) was synthesized through the reaction of 0.4102 g (2.85 × 10-3 mol) of MoO3, 0.2411 g (1.212 × 10-3 mol) of S-aqn, 0.1603 g (1.636 × 10-3 mol) of H2SO4, and 1.0050 g (5.583 × 10-2 mol) of deionized water. Colorless blocks were recovered. Elem microanal. Obsd for 5 (calcd): C, 11.63 (11.66); H, 2.14 (2.22); N, 3.91 (3.88). IR data (cm-1): ν(N-H) 3121, 1607, ν(C-H) 1460, ν(MdO) 972. Powder X-ray diffraction patterns of each bulk sample match the pattern generated from the respective single-crystal X-ray structure data. Single-Crystal X-ray Diffraction. Data were collected using an Oxford Diffraction Xcalibur3 CCD diffractometer with Enhance Mo KR radiation (λ ) 0.710 73 Å). A single crystal was mounted on a glass fiber using N-paratone oil and cooled in situ to 110(2) K for data collection. Frames were collected, indexed, and processed and the files scaled using CrysAlis RED.23 The heavy-atom positions were determined using SIR92.24 All other non-hydrogen sites were located from Fourier difference maps. All non-hydrogen sites were refined using anisotropic thermal parameters using full-matrix leastsquares procedures on Fo2 with I > 3σ(I). Hydrogen atoms were placed in geometrically idealized positions. All calculations were performed using Crystals.25 Relevant crystallographic data are listed in Table 1.
Directed Synthesis of Noncentrosymmetric Molybdates Powder X-ray Diffraction. Powder diffraction patterns were recorded on a GBC-Difftech MMA powder diffractometer. Samples were mounted on aluminum plates. Calculated powder patterns were generated from single-crystal data using ATOMS, version 6.0.26 Infrared Spectroscopy. Infrared measurements were obtained using a Perkin-Elmer Fourier transform infrared Spectrum 1000 spectrophotometer. Samples were diluted with spectroscopic-grade KBr and pressed into a pellet. A scan was run over the range of 400-4000 cm-1. Nonlinear-Optical Measurements. Powder SHG measurements were conducted using a modified Kurtz-NLO system, with a 1064nm light source.27,28 Polycrystalline 4 and 5 were ground and sieved into distinct particle size ranges:
