Structure and magnetism of dibridged vanadium(IV) hydrotris(pyrazolyl)borate dimers

The synthesis and characterization of four dinuclear V(IV) complexes are described: 1, [LVO(mu-(Ph)(2)PO2)LVO]; 2, [LVO(mu-(Ph)HPO2)(2)LVO]; 3, [LVO(mu-OH)(2)LVO]; and 4, [LVO(mu-OH)(mu u-OAc)LVO] (where L = hydrotris-(pyrazolyl)borate). X-ray crystal structural analysis of 1-4 gave the following parameters: 1, C46H46B2N14O6P2V2, P1, a = 12.249(2) Angstrom, b = 13.951(3) Angstrom, c = 16.391(3) Angstrom, alpha = 93.95(3)degrees, beta = 100.53(3)degrees, gamma = 110.01(3)degrees, Z = 2; 2, C47H48B2N19O9P3V3, <P(1)over bar> a = 9.927(2) Angstrom, b = 12.307(2) Angstrom, c = 24.878(3) Angstrom, alpha = 98.12(1)degrees, beta = 100.79(1)degrees, gamma = 91.05(1)degrees, Z = 2; 3, C22H28B2N14O4V2, Pbca, a = 10.698(1) Angstrom, b = 15.414(3) Angstrom, c = 17.865(3) Angstrom, Z = 4; 4, C24H24B2N12O5V2, C2/C, a = 34.252(4) Angstrom, b = 14.623(2) Angstrom, c = 15.387(2) Angstrom, beta = 102.32(1)degrees, Z = 8. Magnetic measurements indicate that all the compounds except 4 are moderately antiferromagnetically coupled. A rationalization for the magnetic behavior of these and other complexes of this type based on a direct overlap model modulated by the conformation of the eight-membered V(mu-OXO)(2)V ring is proposed.