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Tungsten(0)-carbonyl complexes of naphthylazoimidazoles

Datta, Papia and Patra, Ashis Kumar and Sinha, Chittaranjan (2009) Tungsten(0)-carbonyl complexes of naphthylazoimidazoles. In: Polyhedron, 28 (3). pp. 525-533.

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The reaction of W(CO)(6) with 1-alkyl-2-(naphthyl-alpha-azo)imidazole (alpha-NaiR) has synthesized [W(CO)(5)(alpha-NaiR-N)] (alpha-NaiR-N refers to the monodentate imidazole-N donor ligand) at room temperature. The structure of[W(CO)(5)(alpha-NaiMe-N)] shows a monodentate imidazole-N coordination of 1-methyl-2-(naphthyl-alpha-azo)imidazole (alpha-NaiMe). The complexes are characterized by elemental, mass and other spectroscopic data (IR, UV-Vis, NMR). On refluxing in THF at 323 K, [W(CO)(5)(alpha-NaiR-N)] undergoes decarbonylation to give [W(CO)(4)(alpha-NaiR-N,N')] (alpha-NaiR-N,N' refers to the imidazole-N(N), azo-N(N') bidentate chelator). Cyclic voltammetry shows metal oxidation (W-0/W-1) and ligand reductions (azo/azo(-), azo(-)/azo(=)). The redox and electronic properties are explained by theoretical calculations using an optimized geometry. DFT computation of [W(CO)(5)(alpha-NaiMe-N)] suggests that the major contribution to the HOMO/HOMO - 1 come from W cl-orbitals and the orbitals of CO. The LUMOs are occupied by alpha-NaiMe functions. The back bonding interaction thus originates from the W(CO)(n) moiety to the LUMO of alpha-NaiR. A TD-DFT calculation has ascribed that HOMO/HOMO - 1 -> LUMO is a mixture of metal-to-ligand and ligand-to-ligand charge transfer underlying the CO -> azoimine contribution. The complexes show emission spectra at room temperature. [W(CO)(4)(alpha-NaiR-N,N')] shows a higher fluorescence quantum yield (phi = 0.05-0.07) than [W(CO)(5)(alpha-NaiR-N)] (phi = 0.01-0.02). (C) 2008 Elsevier Ltd. All rights reserved.

Item Type: Journal Article
Publication: Polyhedron
Publisher: Elsevier Science
Additional Information: Copyright of this article belongs to Elsevier Science.
Keywords: W(0)-carbonyl;Naphthylazoimidazole;X-ray structure;Electrochemistry;DFT-TD-DFT calculations
Department/Centre: Division of Chemical Sciences > Inorganic & Physical Chemistry
Date Deposited: 16 Nov 2009 09:42
Last Modified: 19 Sep 2010 05:29
URI: http://eprints.iisc.ac.in/id/eprint/19669

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