COMPETING MAGNETIC EXCHANGE INTERACTIONS IN TETRANUCLEAR D(1) SYSTEMS- SYNTHESIS, STRUCTURE, AND MAGNETOCHEMISTRY OF A NEUTRAL VANADIUM(IV) COMPLEX WITH A ((VO)(4)(MU(3)-OR)(2)(MU(2)-OR)(4))(2+)

The complex [{VO(L)}(2){VO(acac)}(2)(mu(2)-OMe)(2)1 1 can be synthesiz ed by reaction of the Schiff base ligand xyethyl)-N'-(2-pyrrolylmethyl idene)ethylenediamine (H2L) with [VO(acac)(2)] (Hacac = 2,4-pentanedio ne). The compound 1 . MeOH has been characterized by IR, UV/vis, and E SR spectroscopy as well as magnetic susceptibility measurements. A sin gle-crystal diffraction study performed on 1 . MeOH gives the followin g crystal data: triclinic, P (1) over bar, a = 7.352(2) Angstrom, b = 12,584(4) Angstrom, c = 12.826(4) Angstrom, alpha 107.61(2)degrees, be ta = 102.96(2)degrees, gamma = 95.25(2)degrees, Z = 1. The tetranuclea r {(VO)(4)(mu(3)-OR)(2)(mu(2)-OR)(4)}(2+) core of 1 is composed of thr ee different types of edge-shared binuclear units, an anti-coplanar, t wo syn-coplanar, and two twist configurations. Consistent with this co nnectivity pattern, analysis of the magnetic data reveals competing fe rritmagnetic and antiferromagnetic exchange interactions within the te tranuclear con structure. Both ESR and magnetic data indicate a single t ground state for 1. In addition, the general magnetic behavior of ox ovanadium(IV) clusters is discussed on the basis of classification sch emes derived from simple binuclear fragmentation patterns. Consistent with the superexchange mechanism expected to be operative for binuclea r oxovanadium(IV) units with syn-coplanar configuration, the correspon ding magnetic exchange parameter J(sc) of 1 (V ... V = 3.410(2) Angstr om) is determined to be antiferromagnetic at -153 cm(-1).