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Synthesis, Structure, and Magnetic Properties of [(CH3CN)5V−O−V(CH3CN)5][BF4]4

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journal contribution
posted on 12.11.2007, 00:00 by Julie A. Cissell, Narpinder Kaur, Saritha Nellutla, Naresh S. Dalal, Thomas P. Vaid
The reaction of vanadium(III) acetylacetonate with HBF4 in acetonitrile yields [(CH3CN)5V−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)5V−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 (χ) 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 ≈ 72 K (∼50 cm-1) yielding a ground state with a total spin Stotal = 2. Theoretical fit to the M(H) plot for the single crystal yielded g|| = 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 Stotal = 2 ground state and yield g|| = 1.9825, g = 1.9725 and D = 0.57 ± 0.03 K.