title: New chemistry of the triply bonded divanadium (V2 4+) unit and reduction to an unprecedented V2 3+ core.
abstract: We report here the synthesis and characterization of seven new divanadium compounds with the paddlewheel geometry bridged by nitrogen-donating ligands. Five of these contain the diamagnetic V(2)(4+) core with short V-V distances of less than 2.0 A, consistent with a formal triple bond. The V-V distances vary with the basicity of the bridging ligands; more basic ligands such as those of the guanidinate type have the shorter metal-metal separations, and those with the less basic formamidinate groups have longer separations. One compound, V(2)(DPhF)(4) (DPhF = the anion of N,N'-diphenylformamidine), has been reduced by one electron, and two structures, [K(THF)(3)]V(2)(DPhF)(4) and [K(18-crown-6)(THF)(2)]V(2)(DPhF)(4), have been obtained. These have an unprecedented V(2)(3+) core where the formal oxidation state of each vanadium atom is +1.5. The decrease in V-V bond distance and the multiline EPR spectrum in the reduced species provide evidence that these two molecules contain a bond of order 3.5.
authors.affiliation: Department of Chemistry and Laboratory for Molecular Structure and Bonding, P.O. Box 30012, Texas A&M University, College Station, TX 77842-3012, USA. cotton@tamu.edu
authors.forename: F Albert
authors.initials: FA
authors.lastname: Cotton
authors.forename: Elizabeth A
authors.initials: EA
authors.lastname: Hillard
authors.forename: Carlos A
authors.initials: CA
authors.lastname: Murillo
authors.forename: Xiaoping
authors.initials: X
authors.lastname: Wang