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High-Valent Manganese in Polyoxotungstates. 3. Dimanganese Complexes of γ-Keggin Anions† Xiao-Yan Zhang,‡ Charles J. O’Connor,§ Geoffrey B. Jameson,‡,| and Michael T. Pope*,‡ Department of Chemistry, Georgetown University, Washington, D.C. 20057, and Department of Chemistry, University of New Orleans, New Orleans, Louisiana 70148 ReceiVed June 23, 1995X Dimanganese-substituted γ-Keggin heteropoly tungstates have been synthesized by reaction of the lacunary species γ-[(SiO4)W10O32]8- with appropriate mixtures of MnII and MnO4-. The crystal structure of [(CH3)3(C6H5)N]4[(SiO4)W10MnIII2O36H6]‚2CH3CN‚H2O (anion 1) was determined by X-ray diffraction. Crystallographic data: space group P1h, a ) 12.951(3) Å, b ) 14.429(3) Å, c ) 20.347(4) Å, R ) 81.95(3)°, β ) 88.92(3)°, γ ) 67.48(3)°, V ) 3475.2(13) Å3, and Z ) 2. The final R value is 7.29% for 15861 reflections with I > 2σ(I). The anion has the anticipated γ-Keggin structure with virtual C2V symmetry. The two Mn cations occupy adjacent, edge-shared octahedra with bridging hydroxo and terminal aqua ligands. Anion 1 can be oxidized and reduced to the corresponding MnIIIMnIV (2) and MnII2 (3) species respectively. The magnetic susceptibility of 1 between 2 and 300 K indicates that the MnIII cations are antiferromagnetically coupled, with J ) -17.0 cm-1 and g ) 1.965. No simple magnetic behavior was observed for 2 or 3.
Introduction In the course of our investigations of high-valent tungstomanganates, we have examined species with one-,1,2 three-,3 and four4 manganese centers. The mono- and trimanganese heteropolyanions are known to exhibit significant catalytic activity for epoxidation of alkenes.5-11 In this paper we report the synthesis and characterization of dimanganese complexes derived from the divacant lacunary polyanion γ-[(SiO4)W10O36]8-. Comparison of the catalytic activities of the various manganese-containing polyanions will be reported elsewhere. The redox activity of dimanganese complexes is also of interest in view of the roles such moieties play in redox-active enzymes, such as Mn catalase and ribonucleotide reductase, and in photosystem II.12 The catalase and reductase enzymes each contain two adjacent manganese atoms bridged by oxo, hydroxo, †
Parts 1 and 2: see refs 2 and 4, respectively. Georgetown University. § University of New Orleans. | Present address: Department of Chemistry and Biochemistry, Massey University, Palmerston North, New Zealand. X Abstract published in AdVance ACS Abstracts, December 1, 1995. (1) Tourne´, C. M.; Tourne´, G. F.; Malik, S. A.; Weakley, T. J. R. J. Inorg. Nucl. Chem. 1970, 32, 3875-3890. (2) Zhang, X. Y.; Pope, M. T.; Chance, M. R.; Jameson, G. B. Polyhedron 1995, 14, 1381-1392. (3) Liu, J. F.; Orte´ga, F.; Sethuraman, P.; Katsoulis, D. E.; Costello, C. E.; Pope, M. T. J. Chem. Soc. Dalton Trans. 1992, 1901-196. (4) Zhang, X. Y.; Jameson, G. B.; O’Connor, C. J.; Pope, M. T. Polyhedron, in press. (5) Katsoulis, D. E.; Pope, M. T. J. Chem. Soc., Chem. Commun. 1986, 15, 1186-1188. (6) Hill, C. L.; Brown, R. B., Jr. J. Am. Chem. Soc. 1986, 108, 536-538. (7) (a) Hill, C. L.; Zhang, X. Nature, 1995, 373, 324. (b) Khenkin, A. M.; Hill, C. L. J. Am. Chem. Soc. 1993, 15, 8178-8186 and cited papers. (8) Lyon, D. K.; Miller, W. K.; Novet, T.; Domaille, P. J.; Evitt, E.; Johnson, D. C.; Finke, R. G. J. Am. Chem. Soc. 1991, 113, 72097221; Mansuy, D.; Bartoli, J. F.; Battioni, P.; Lyon, D. K.; Finke, R. G. J. Am. Chem. Soc. 1991, 113, 7222-7226. (9) Neumann, R.; Abu-Gnim, C. J. Chem. Soc., Chem. Commun. 1989, 1324-1325. (10) (a) Neumann, R.; Abu-Gnim, C. J. Am, Chem. Soc. 1990, 112, 60256031. (b) Neumann, R.; Gara, M. J. Am. Chem. Soc. 1994, 116, 55095510. (11) Liu, J. F. Private communication, 1993. (12) Que, L., Jr.; True, A. E. Prog. Inorg. Chem. 1990, 38, 180. ‡
0020-1669/96/1335-0030$12.00/0
or carboxylate ligands, and although four manganese centers are believed to be involved in the oxygen evolving protein of photosystem II, current activity is centered on a “dimer of dimers” model. Since Herve´ et al. reported the synthesis of the lacunary polyoxoanion γ-[(SiO4)W10O36]8-,13 only two derivatives have been described. One is the divanadate(V)-substituted anion, γ-[(SiO4)W10V2O36]6-, of C2V symmetry, which was structurally characterized by NMR.14 The other complex is the dichromium(III)-substituted anion in [(n-C4H9)4N]3H2[(SiO4)W10O32{Cr2(OH)(CH3CO2)2-(OH2)2}]‚3H2O, which has an unexpected structure in which the Cr atoms are bridged by hydroxo and two acetato ligands.15 Experimental Section Tetra-n-butylammonium decatungstodimangano(III)silicate (SiW10MnIII2, anion 1) was prepared starting with γ-K8[(SiO4)W10O32]‚12H2O (γ-SiW10) reported in the literature.13 A solution of γ-SiW10 (6.0 g, 2.0 mmol) in 15 mL of deionized water was quickly adjusted to pH ) 3.9 with concentrated nitric acid. The pH of this solution was kept between 3.8 and 4.5 with nitric acid while solutions A and B as described below were added. The addition of solution A [0.784 g, 3.2 mmol, of manganese(II) acetate, Mn(OAc)2‚2H2O, in 10 mL of water] afforded an orange solution. After the solution had been stirred for 2 min, solution B [potassium permanganate (0.126 g, 0.8 mmol) in 10 mL of water] was added dropwise. The proportions of MnII and MnVII were chosen to yield MnIII. The color of the solution changed from orange to brown. After about 5 min, addition of solid tetra-nbutylammonium (TBA) nitrate (3.0 g) resulted in a brown precipitate. The precipitate was filtered off and purified by twice dissolving it in CH3CN and then adding water to reprecipitate the product. About 6 g of purified compound was obtained. Anal. Calcd for [(C4H9)4N]4[(SiO4)W10MnIII2O36H6]‚1.5CH3CN‚2H2O: C, 21.13; N, 2.02; H, 4.06; W, 48.33; Mn, 2.89; Si, 0.74. Found: C, 21.55; N, 1.99; H, 4.14; W, 47.57; Mn, 2.83; Si, 0.80. The manganese oxidation state(s) for all SiW10Mn2 salts were confirmed by coulometry. Trimethylphenylammonium Decatungstodimangano(III)silicate. Addition of a saturated solution (10 mL) of trimethylphenylammonium (13) (a) Canny, J.; Te´ze´, A.; Thouvenot, R.; Herve´, G. Inorg. Chem. 1986, 25, 2114-2118. (b) Te´ze´, A.; Herve´, G. Inorg. Synth. 1990, 27, 8596. (14) Canny, J.; Thouvenot, R.; Te´ze´, A.; Herve´, G.; Leparulo-Loftus, M.; Pope, M. T. Inorg. Chem. 1991, 30, 976-981. (15) Wassermann, K. Ph.D. Thesis, Humboldt University, Berlin, 1995.
© 1996 American Chemical Society
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Inorganic Chemistry, Vol. 35, No. 1, 1996 31
Table 1. Crystal Data and Structure Refinement for (Me3PhN)4[(SiO4)W10MnIII2O36H6]‚2CH3CN‚H2O temp: 293(2) K wavelength: 0.71073 Å space group: P1h unit cell dimenss a ) 12.951(3) Å b ) 14.429(3) Å c ) 20.347(4) Å R ) 81.95(3)° β ) 88.92(3)° γ ) 67.48(3)° volume ) 3475.2(13) Å3 Z)2 density (calcd): 3.000 g/cm3 abs coeff: 16.935 mm-1 F(000): 2828 cryst size: 0.3 × 0.2 × 0.08 mm3 θ range for data collcn 1.54 to 27.50° index ranges: -1
