Semiempirical INDO/S calculations on the absorption spectrum of mono‐ and trinuclear vanadium(II) complexes

This work is concerned with prospective starting materials for the synthesis of larger molecules used as functional models of the substrate binding and reducing site of the vanadium nitrogenase. It is well known that the mononuclear adduct of vanadium(II) chloride with N,N,N′,N′ ‐tetramethylethylenediamine, henceforth referred to as [VCl 2 (tmeda) 2 ], is a good starting material for the synthesis of trinuclear vanadium complexes. We now report the results of semiempirical calculations on the spectroscopy of [VCl 2 (tmeda) 2 ] using the intermediate neglect of differential overlap (INDO) method. For the mononuclear complex, the ground state was calculated to be a quartet, about 45 kcal/mol below the doublet. For the positively charged trinuclear vanadium complex, [V 3 (μ‐Cl) 3 (μ 3 ‐Cl) 2 (tmeda) 3 ] + , the ground state was calculated to be a decatet, about 47 kcal/mol below the octet. For both complexes the frontier orbitals are dominated by the vanadium 3d manifold, and accordingly the electronic spectra are dominated by d‐d* excitations within this manifold. The INDO/S‐calculated spectra are in good agreement with the observed UV‐visible spectra in both cases. © 2002 Wiley Periodicals, Inc. Int J Quantum Chem 88: 245–251, 2002