The neutron structure of complex Cp*MoH3(dppe)
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The structure of compounds containing more than one H atom bonded to a transition metal may lay on a continuum between two extremes: separate bonds between the metal (M) and each H atom with no direct H-H bonds (classical polyhydride), and a dihydrogen complex in which the metal is covalently bonded to an H2 molecule.
To investigate the nature of the M-H interactions in transition metal polyhydrides, we have determined the structure of the complex Cp*MoH3(dppe) by single crystal neutron diffraction using SXD. This complex reveals an unexpected geometry, with two H atoms being placed at a distance from each other that is too long for a direct H-H interaction (H2-H3 ~ 1.4 Å), but short compared to typical classical polyhydrides (~ 1.8 Å). Furthermore, one-electron oxidation of the metal induces a significant closing of the H-H separation. This the first structurally characterised example of two polyhydride complexes having the same composition but differing by one electron, illustrating the effect of the metal oxidation state on the tendency of polyhydrides to undergo collapse and elimination of H2.
M Baya, J Houghton, J-C Daran, R Poli (Laboratoire de Chimie de Coordination, France), L Male, A Albinati (Università di Milano, Italy), M Gutmann (ISIS)
Research date: December 2007
M Baya et al., Chem. Eur. J. 13 (2007) 5347
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