© 2014 Elsevier Ltd. All rights reserved. DFT calculations at the B3LYP/Def2-SVP level have been conducted on the half-sandwich cycloheptatrienyl molybdenum complexes [Mo(CO)3(η-C7H7)]+, + and [MoBrL2(η-C7H7)]n + (L2 = 2 CO, n = 0, 2; L2 = bpy, n = 0, 3; L2 = bpy, n = 1, +; bpy = 2,2′-bipyridyl). In all cases, strong δ-bonding interactions operate between the e2 level of the C7H7 ring and metal dxy and d x2-y2 orbitals resulting in a metal-centred HOMO with substantial d z2 character in the 18-electron, closed shell systems. The experimental electronic UV-Vis spectra of +, 2 and 3 are accurately reproduced by TD-DFT methods. For complexes 2 and 3, assignments made with the assistance of calculated spectra indicate that absorptions in the region 390-770 nm originate from a series of MLCT (metal-ligand charge transfer) or ILCT (inter-ligand charge transfer) transitions in which carbonyl, C7H7 and 2,2′-bipyridyl ligands act as acceptor systems from the metal or mixed metal and bromide donor groups. The metal-centred, one-electron oxidation of 3 to 3[PF6] results in almost complete quenching of the visible region MLCT/ILCT absorptions of 3 and replacement with weak transitions probably arising from bromide to metal LMCT (ligand to metal charge transfer) processes.
Roberts, K. A. E., Brown, N. J., Roberts, H. N., Mcdouall, J. J. W., Low, P., & Whiteley, M. W. (2015). Electronic structure and spectroscopy of the cycloheptatrienyl molybdenum halide complexes [MoBrL2(η-C7H7)]n + (L2 = 2CO, n = 0; L2 = 2,2′-bipyridyl, n = 0 or 1). Polyhedron, 86, 89-97. https://doi.org/10.1016/j.poly.2014.05.027