3 NEW POLYNUCLEAR BIS(MU-PHOSPHATO) VANADYL CLUSTERS - [HB(PZ)(3)VO(MU-(C6H5O)(2)PO2)](2), [HB(3,5-ME(2)PZ)(3)VO(MU-(C6H5O)(2)PO2)]CENTER-DOT-C7H8, AND H2O-SUBSET-OF[T-BUPZ(MU-C6H5OPO3)VO](6)(H2O)(2)CENTER-DOT-2CH(3)CH(2)OH - ADAPTABILITY OF THE CYCLIC (OV)(OPO)(2)(VO) BRIDGING UNIT

The dinuclear complexes [LVO(mu-(C6H5O)(2)PO2)](2) (I) and [L'VO(mu-C6H5O)(2)PO)](2)) (II) (L = hydridotris(pyrazolyl)borate; L' = hydridotris(3,5-dimethylpyrazolyl)borate) and the hexanuclear complex H2O subset of[t-Bupz(mu-C6H5OPO3)VO](6)(H2O)(2) . 2CH(3)CH(2)OH (III) (t-Bupz = 3-tert-butylpyrazole) can be prepared by self-assembly of the components in solution under ambient conditions. These compounds have been characterized by UV-vis, IR, and EPR spectroscopies, magnetic susceptibility measurements, cyclic voltammetry, and X-ray structure determinations. Crystallographic parameters: for I, monoclinic, P2(1)/n, a = 9.418(1) Angstrom, b = 19.526(1) Angstrom, c = 13.186(1) Angstrom, beta = 90.08(1)degrees, V = 2424.8(3) Angstrom(3), Z = 2, T = 298 K, R = 0.0380, R(W) = 0.0496, 2743 unique, observed (\F\ greater than or equal to 4 sigma(F)) data, 316 least-squares parameters; for II, monoclinic, P2(1)/c, a = 13.367(3) Angstrom, b = 16.909(2) Angstrom, c = 15.560(2) Angstrom, beta = 105.89(1)degrees, V = 3382.6(9) Angstrom(3), Z = 2, T = 298 K, R = 0.0752, R(W) = 0.0830, 2100 unique, observed (\F greater than or equal to 4 sigma(F)) data, 395 least-squares parameters; for III, monoclinic, C2/c, a = 25.750(4) Angstrom, b = 15.171(2) Angstrom, c = 27.537(5) Angstrom, beta = 95.00(1)degrees, V = 10716(2) Angstrom(3), Z = 4, T = 298 K, R = 0.0687, R(W) = 0.0699, 3216 unique, observed (\F\ greater than or equal to 4 sigma(F)) data, 583 least-squares parameters. The structures of I and II consist of bis(mu-diphenyl phosphato-O,O') divanadyl complexes in which the vanadyl oxygens of the two metal centers are oriented anti to one another. Compound III consists of a vaselike shell of mu-phenyl phosphato-O,O',O'' vanadyl octahedra that encapsulate a molecule of water. The shell of this cluster is composed of fused, cyclic (OV)(OPO)(2)(VO) units such as those found at the core of the isolated dimeric species in I and II. This central bridging unit varies widely in its form in response to various structural forces. The presence of the sterically encumbered dimethylpyrazole groups in II forces a flattening of this central ring relative to that found in the unsubstituted dinuclear complex, I, while the presence of the template molecule in III generates four distinct bridging unit types in order to optimize interaction with the central water molecule and maintain the integrity of the cluster framework. Examination of the structures of the cyclic bridging units in these and other vanadyl phosphate systems shows that variation of the bridge structure can occur by (1) changing the coordination of the bridging phosphates in the equatorial planes of the metal centers or (2) changing the ring conformation through a continuous bending deformation. Structural variation is also reflected in the magnetic properties. Susceptibility measurements for the dinuclear complex I show weak ferromagnetic coupling (J/k = 3.3(4) K) while EPR measurements for the sterically encumbered dimethylpyrazolyl analog II indicate an uncoupled magnetic system. Antiferromagnetic coupling in the hexanuclear cluster is best fit to a model described by a pair of isolated divanadyl units (J/k = -14.4(3) K). These differences in exchange coupling among the three compounds can be explained by differences in the direct overlap of the vanadyl orbitals in the dinuclear bridging units.