Why are there (almost) no molecular actinide complexes containing unsupported metal-metal bonds?

NUCL 35

Nikolas Kaltsoyannis, n.kaltsoyannis@ucl.ac.uk, Department of Chemistry, University College London, 20 Gordon Street, London, WC1H 0AJ, United Kingdom and German E Cavigliasso, german.cavigliasso@anu.edu.au, Department of Chemistry, Australian National University, Faculty of Science, Canberra, ACT 0200, Australia.
By contrast to the d-block elements, actinide compounds containing unsupported metal-metal bonds have proved extremely difficult to synthesize. In this presentation, we shall report the results of DFT investigations of analogous 4d, 5d and 5f compounds, aimed at understanding why this should be the case. The target systems are M2X6 (M = Mo, W, U; X = Cl, F, OH, NH2, CH3) and [M2X8]2- (M = Mo, Tc, Ru, W, Re, Os, U, Np, Pu; X = Cl, Br). A detailed analysis of the metal-metal interactions has been carried out using MO and energy decomposition methods. Generally, the results suggest that the overall metal-metal interaction is considerably weaker, or unfavourable, in the actinide systems relative to the d-block analogues, in agreement with the scarcity of actinide dimers. The origins of this weakness are analysed in the context of the energy decomposition scheme and the MO structure of the target systems.