Synthesis, structure and DFT/TDDFT study of diimido-bridged asymmetric dimolybdenum complex

Abstract

The homobimetallic complex (Bu₄N)₂[MoO(mnt)Mo{o-aminobenzothiolato (3-)-N,S}₂(mnt)] (2; mnt = 1,2-dicyanoethylenedithiolate) has been synthesized as a dark green solid by treating (Bu₄N)₂ [Mo₂O₄ (mnt)₂] (1) with ο -aminothiophenol in CH₃CN. An X-ray crystal structure analysis of 2 reveals that it possesses an asymmetric structure where one Mo has a distorted octahedral geometry and the other a square-pyramidal geometry. The basal plane of the two Mo centers makes an angle of 26.41°, which is nearly one quarter of 90°. The shape of the ν (Mo=O) band in the IR spectrum of 2 suggests that these Mo atoms may have different oxidation states. The different reactivity of 1 with o-aminothiophenol and 2-aminoethanethiol was followed by EPR spectroscopy, and analysis of the different end-products from these reactions supports the proposal that 2 is a mixed-valence compound containing Mo^VI and Mo^IV centers. The electronic structures of 1 and 2 have been calculated at the DFT level of theory to analyse the effect of a deviation of the basal plane on the metal-metal bond in 2. The cyclic voltammetric responses of 1 and 2 have been measured to correlate the data with the computational results. TDDFT calculations have been performed on 1 and 2 in the gas phase and also in a solvent medium to assign the transitions corresponding to the peaks found in the respective experimental electronic absorption spectra of these complexes.