The potential energy curves associated with the interconversion between square planar (SP) and tetrahedral (Td) conformations of the formally d 10 [M(biphosphinine)2]q complexes (M = Ni, Pt, Co, Rh and Ru) were obtained by means of DFT calculations with the B3LYP functional. In agreement with the experimental data, the complexes with M = Ni, Pt, Co and Rh were found to adopt a distorted tetrahedral conformation, the flatness of the computed potential energy curves accounting for the experimental characterization of several independent molecules and the fluxional behaviour observed in solution for M = Co and Rh. As expected for formal d10 complexes, the tetrahedral structure was always found to be more stable than the square planar structure. However, the computed energy difference is rather small (between 3.1 kcal mol-1 for M = Ru and 13.6 kcal mol -1 for M = Ni) and it is shown that, for a given column of the periodic table, the lower the d orbitals on the metal centre (Ni < Pt and Co < Rh), the less favoured the square planar conformation. Finally, for M = Ru, the slight preference for the tetrahedral conformation found in the isolated complex is not preserved in the presence of two counter cations (Na +): in agreement with the experimental data for the uncryptated complex, the two cations were found to be located above and below the plane of a nearly square planar dianionic [Ru(biphosphinine)2]2- unit.
|Journal||New Journal of Chemistry|
|Publication status||Published - 1 Jul 2004|