Ferromagnetic coupling by the spin-polarization mechanism in a trinuclear VIV triplesalen complex

The first trinuclear vanadium complex [(talen(t-Bu2) )V-IV=O)(3) ( 1) of a triple tetradentate triplesalen ligand has been synthesized and characterized. The triplesalen ligand talen(t-Bu2))(6-) provides three salen- like coordination environments bridged in a meta- phenylene arrangement by a phloroglucinol backbone. In the electronic absorption spectrum of 1 all four ligand field transitions are detected below 21400 cm(-1). The region above 23000 cm(-1) is dominated by strong absorption from imine pi ->pi* and ligand-to-ligand CT transitions. The latter may also be described by a combined phenolate-to-vanadium LMCT and vanadium-to-imine MLCT through the empty metal d orbitals in a push-pull type interaction. The temperature-dependent magnetic susceptibility measurements reveal a ferromagnetic coupling of the three V (IV)= O units in the triplesalen complex with J = + 0.44 cm(-1). The correlation of the electronic structure to the weakness of the ferromagnetic coupling by the spin- polarization mechanism in the trinuclear V= O system is discussed. (c) 2007 Elsevier B. V. All rights reserved.