Synthesis and characterisation of ligand-bridged tungsten and chromium penta- and tetra-carbonyl complexes
Ligand bridged metal carbonyl complexes of the form [5(CO)MLM(CO)5], [4(CO)MLM(CO)4] and [4(CO)ML], where M is either tungsten or chromium and L is either trans-l,2-(bis-4-pyridyl)ethylene(TBE) or 3,6-di-2-pyridyl-l,2,4,5-tetrazine (DPT) have been synthesised. They were characterised using IR, UV-Vis and NMR, MS, TLC and microanalysis. Electronic spectral studies showed that both the dinuclear, [4(CO)CrDPTCr(CO)4] and mononuclear, [4(CO)CrDPT] complexes have MLCT transitions at 900.88 nm and 652.52 nm respectively. The dinuclear MLCT is more intense and broad and is deemed to have overlapped with the d-d transitions observed in the mononuclear complex at 909.45 nm. However, intra-ligand transitions were observed at 279.97 nm, 303.53 nm and 382.75 nm for both mononuclear and dinuclear complexes. Photoluminescence spectra showed two emissions for [TBE{W(CO)5}2]; with the emission at 530 nm originating from an MLCT transition, and the one at 353 nm originating from an intra-ligand transition. For [4(CO)CrDPTCr(CO)4] and [4(CO)CrDPT], a single broad emission was observed at 523 nm and 460 nm respectively. A small peak at 400 nm in the dinuclear complex is observed and is tentatively attributed to an intra-ligand transition. A structure of distorted octahedron is proposed for pentacarbonyl/ro^-l^-(bis-4-pyridyl) emyIenetungsten.
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