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Issue 34, 2009
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Structural and spectroscopic properties of a copper(I)–bis(N-heterocyclic)carbene complex

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The structural and spectroscopic properties of a Cu(I) complex bearing a methylene-linked bis(N-heterocyclic carbene) ligand, [Cu2(μ-Me-mbim)2](PF6)2 were investigated. X-ray single crystal structure analysis revealed that the complex is binuclear similar to the corresponding silver(I) complex. In [Cu2(μ-Me-mbim)2](PF6)2, cation–π interaction between copper and the adjacent carbene carbon is observed. On the other hand, the coppercopper interaction is very weak in the crystal and almost negligible in solution. The absorption spectrum of [Cu2(μ-Me-mbim)2](PF6)2 in methanol shows a strong absorption band (ε = 23 000 dm3 mol−1 cm−1) and a weaker shoulder (ε = 6200 dm3 mol−1 cm−1) at 261 nm and 300 nm, respectively. From molecular orbital calculations using TD-DFT, these absorption bands are assigned to the metal-centered transitions with some contribution from the NHC orbitals. The powdered sample of [Cu2(μ-Me-mbim)2](PF6)2 shows bright blue-green phosphorescence with a high quantum yield (43%). The phosphorescence is of dual-emission character at room temperature with peak maxima at 374 nm and 482 nm whereas it changes to a single emission band centered around 500 nm at 77 K. Molecular orbital calculations indicate that the luminescence derives from the triplet MC and MLCT mixed excited states. A methanolic solution of [Cu2(μ-Me-mbim)2](PF6)2 shows yellow-green phosphorescence with a peak maximum at 542 nm. Unlike in the solid state, no dual-emission was observed. These results suggest that the dual emission is caused by differences in the contribution of metal–metal interactions at room temperature in the solid state. The differences in the absorption and emission properties between [Cu2(μ-Me-mbim)2](PF6)2 and the related Cu(I)–diphosphine complex, [Cu2(μ-dcpm)2](BF4)2 are discussed.

Graphical abstract: Structural and spectroscopic properties of a copper(I)–bis(N-heterocyclic)carbene complex

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The article was received on 10 Dec 2008, accepted on 12 Jun 2009 and first published on 06 Jul 2009

Article type: Paper
DOI: 10.1039/B822109J
Citation: Dalton Trans., 2009,0, 6795-6801

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    Structural and spectroscopic properties of a copper(I)–bis(N-heterocyclic)carbene complex

    K. Matsumoto, N. Matsumoto, A. Ishii, T. Tsukuda, M. Hasegawa and T. Tsubomura, Dalton Trans., 2009, 0, 6795
    DOI: 10.1039/B822109J

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