Interligand communication in a metal mediated LL'CT system - a case study.

A series of oxo-Mo(iv) complexes, [MoO(Dt)(Dt)] (where Dt = benzene-1,2-dithiol (bdt), toluene-3,4-dithiol (tdt), quinoxaline-2,3-dithiol (qdt), or 3,6-dichloro-benzene-1,2-dithiol (bdtCl); Dt = ,'-dimethylpiperazine-2,3-dithione (MeDt) or ,'-diisopropylpiperazine-2,3-dithione ( PrDt)), possessing a fully oxidized and a fully reduced dithiolene ligand have been synthesized and characterized. The assigned oxidation states of coordinated dithiolene ligands are supported with spectral and crystallographic data. The molecular structure of [MoO(tdt)( PrDt)] () demonstrates a large ligand fold angle of 62.6° along the S⋯S vector of the Dt ligand. The electronic structure of this system is probed by density functional theory (DFT) calculations. The HOMO is largely localized on the Dt ligand while virtual orbitals are mostly Mo and Dt in character. Modeling the electronic spectrum of with time dependent (TD) DFT calculations attributes the intense low energy transition at ∼18 000 cm to a ligand-to-ligand charge transfer (LL'CT). The electron density difference map (EDDM) for the low energy transition depicts the electron rich Dt ligand donating charge density to the redox-active orbitals of the electron deficient Dt ligand. Electronic communication between dithiolene ligands is facilitated by a Mo-monooxo center and distortion about its primary coordination sphere.