The reaction of vanadium(III) acetylacetonate with HBF4 in acetonitrile yields [(CH3CN)(5)V-O-V(CH3CN)(5)][BF4](4), a material that serves as a-convenient precursor to other [V-O-V](4+) species such as [(bipy)(2)(CH3CN)V-O-V(CH3CN)(bipy)(2)][BF4](4) (bipy = 2,2 '-bipyridine). Single-crystal X-ray diffraction shows that the V-O-V linkage of [(CH3CN)(5)V-O-V(CH3CN)(5)](4+) is linear. An Evans method measurement of the solution-phase magnetic susceptibility indicates strong ferromagnetic coupling between the vanadium centers. Magnetic susceptibility (chi) and magnetization (M(H)) data for a powdered sample and for a single crystal oriented with its V-O-V axis parallel to the applied field were measured over 1.8-300 K The results suggest that the V(III) centers are ferromagnetically coupled with J approximate to 72 K (similar to 50 cm(-1)) yielding a ground state with a total spin S-total = 2. Theoretical fit to the M(H) plot for the single crystal yielded g(parallel to) = 2.01 +/- 0.01 and the zero-field splitting parameter D = 0.60 +/- 0.04 K (0.42 +/- 0.03 cm(-1)). EPR measurements at 34 and 101.6 GHz are consistent with the S-total = 2 ground state and yield g(parallel to) = 1.9825, g(perpendicular to) = 1.9725 and D = 0.57 +/- 0.03 K.