Bonding in Dinuclear Metalloradicals

Metal-metal interactions in paramagnetic, multinuclear transition metal complexes are critical to the reactivity of metalloproteins, and understanding them is important in the development of functional metal-containing polymers. Particularly, the bonding and spectroscopic properties of the interesting unbridged paramagnetic dimers that are held together only by metal-metal bonds have remained unexplored.

In a combined experimental and computational study, researchers from PNNL have, for the first time, syntesized and isolated a stable unbridged dimetal radical, [{CpW(CO)2(PMe3)}2]•+ (1•+). Relativistic density functional calculations revealed that the SOMO is an M-M antibonding π orbital, and aided spectroscopic assignments. Calculated TDDFT spectra were in agreement with experiment and assigned the characteristic near-infrared (NIR) absorption at λmax = 966 nm to a ππ* transition to the SOMO. Spin-orbit coupling DFT yielded EPR parameters in very good agreement with the experiments.

Measured and calculated (vertical lines) VIS/NIR spectra of [{CpW(CO)2(PMe3)}2] (1) and the stable metal-metal radical formed upon its oxidation, [{CpW(CO)2(PMe3)}2]•+ (1•+). The charateristic NIR transition at 966 nm results from a ππ* transition to the SOMO as shown in the inset.

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E. F. van der Eide, P. Yang, E. D. Walter, T. Liu, and R. M. Bullock, Dinuclear Metalloradicals Featuring Unsupported Metal-Metal Bonds Angew. Chem. Int. Ed. 51, 8361-8364 (2012)

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