Synthesis, structural, and magnetic studies on a redox family of tetrametallic vanadium clusters: {VIV4}, {VIII2VIV2}, and {VIII4} butterfly complexes

The synthesis, crystal structures, and magnetic properties are reported for a redox family of butterfly-type tetrametallic vanadium alkoxide clusters, namely V2(VO)2(acac)4(RC{CH2O}3)2] (R=Me 1, Et 2, CH2OH 3), V2(VO)2(acac)2(O2CPh)2(MeC{CH2O}3)2] (5), (VO)4(MeOH)2(O2CPh)2({HOCH2}C{CH2O}3)2] (6), V4Cl2(dbm)4(RC{CH2OH}3)2] (R=Me 7, Et 8, CH2OH 9), and V4Cl2(dbm)4(MeO)6] (10). The cluster cores are {VIV4} (6), {VIII2VIV2} (1-5), and {VIII4} (7-10), with examples of both isomeric forms of the of the mixed-valence cores (either VIII or VIV ions forming the butterfly body). Magnetic studies reveal the clusters to be dominated by antiferromagnetic exchange interactions in each case. The magnetic exchange parameters are determined for representative examples of each core type. {VIV4} and {VIII4} have diamagnetic ground states. The two isomeric {VIII2VIV2} types are found to give rise to either an S=0 ground state with a number of low-lying excited states due to competing antiferromagnetic exchange interactions (VIII2 butterfly body) or to a well-isolated S=1 ground state (VIV2 butterfly body).