COORDINATION-COMPOUNDS OF POLYOXOVANADATES WITH A HEXAMETALATE CORE - CHEMICAL AND STRUCTURAL CHARACTERIZATION OF [V(V)6O13((OCH2)3CR(2]2-, [V(V)6O11(OH)2((OCH2)3CR(2], [V(IV)4V(V)2O9(OH)4((OCH2)3CR(2]2-, AND [V(IV)6O7(OH)6((OCH2)3CR(2]2-

Reactions of the tris(hydroxymethyl)methane-derived ligands, (HOCH2)3Cr, R = NO2, CH2OH, and CH3, with [(C4H9)4N]3[H3V10O28] in CH3CN yield in the polyoxovanadate coordination complexes [(C4H9)4N]2[V6O13{(OCH2)3Cr}2] (R = NO2, 1; CH2OH, 2; CH3, 3). Complexes of this general class are electrochemically active, displaying a reversible one-electron reduction in the range -0.67 to -1.20 V, relative to the ferrocene/ferrocenium couple. The reduced species [V(IV)V(V)5O13{(OCH2)3CNO2}2]3-exhibits an eight-line EPR spectrum at 4.2 K, approximately centered at g = 1.95. Broadening of EPR spectral features as the temperature is raised from 4.2 to 83 K is evidence for increased motion of the unpaired electron consistent with thermally induced electron transfer between V(IV) and V(V) states. In contrast, chemical reductions of [(C4H9)4N]2[V6-O13{(OCH2)3CCH3}2] with organohydrazines yield the reduced, hydroxy-bridged species [(C4H9)4N]2[V(IV)4V(V)2O9(OH)4{(O-CH2)3CCH3}2] (6) and [(C4H9)4N]2[V(IV)6O7(OH)6{(OCH2)3CCH3}2].2CH2Cl2.0.5C6H5NNC6H5 (7). The protonation sites have been established by X-ray crystallography. Protonation and reduction can be decoupled such that reaction of 3 with HBF4.O(C2H5)2 yields the diprotonated species [V6O11(OH)2{CH3C(CH2O)3}2] (5) wherein the site of protonation has been established by X-ray crystallography as two of the bridging oxo groups. Crystal data are as follows. 1: triclinic P1BAR; a = 11.470 (2) angstrom, b = 12.149 (2) angstrom, c = 12.433 (2) angstrom, alpha = 63.24 (1)-degrees, beta = 63.45 (1)-degrees, gamma = 79.31 (1)-degrees, V = 1383.5 (5) angstrom3, Z = 1, D(calcd) = 1.55 g cm-3; structure solution and refinement (in all cases: Mo K-alpha, lambda = 0.71073 angstrom) converged at R = 0.049. 2.DMF: monoclinic P2(1)/c, a = 12.003 (2) angstrom, b = 16.900 (3) angstrom, c = 16.769 (3) angstrom, beta = 106.95 (1)-degrees, V = 3253.8 (11) angstrom 3, Z = 2, D(calcd) = 1.37 g cm-3; R = 0.054. 3: triclinic P1BAR, a = 11.460 (2) angstrom, b = 12.237 (2) angstrom, c = 12.331 (2) angstrom, alpha = 62.88 (1)-degrees, beta = 63.50 (1)-degrees, gamma = 77.52 (1)-degrees, V = 1377.4(5) angstrom3, Z = 1, D(calcd) = 1.49 g cm-3; R = 0.055. 5.2DMF.(C2H5)2O: triclinic P1BAR, a = 10.362 (3) angstrom, b = 10.513 (3) angstrom, c = 10.366 (2) angstrom, alpha = 116.33 (1)-degrees, beta = 93.56 (1)-degrees, gamma = 62.40 (1)-degrees, V = 882.2 (7) angstrom3, Z = 1, D(calcd) = 1.83 g cm-3; R = 0.043. 6: triclinic P1BAR, a = 11.534 (2) angstrom, b = 12.161 (3) angstrom, c = 12.483 (4) angstrom, alpha = 62.86 (2)-degrees, beta = 63.15 (2)-degrees, gamma = 78.87 (2)-degrees, V = 1389.7 (7) angstrom3, Z = 1, D(calcd) = 1.48 g cm-3; R = 0.043. 7: triclinic P1BAR, a = 13.613 (3) angstrom, b = 16.090 (4) angstrom, c = 16.077 (4) angstrom, alpha = 86.36 (1)-degrees, beta = 80.71 (2)-degrees, gamma = 80.46 (1)-degrees, V = 3424.1 (12) angstrom3, Z = 2, D(calcd) = 1.45 g cm-3; R = 0.042.