A Density Functional Study of the Systems [MH 3 (PMe 3 ) 4 ] + (M = FE, RU, OS)

The structures and relative energies of various isomers of [FeH 3 (PMe 3 ) 4 ) + ( 1 ), [RuH 3 (PMe 3 ) 4 ]. ( 2 ) and [OsH 3 (PMe 3 ) 4 ]. ( 3 ) have been studies by density functional theory. The stereoisomers considered are derived from a tetrahedral (T), square planar (P), and C 2v ‐butterfly (C) arrangement of the phosphane ligands. For the latter two, classical trihydride ( I ) and nonclassical hydride/dihydrogen ( II ) geometries have been considered 1 and 2 prefer coordination mode II , whereas 3 favours coordination mode I . This trend is explained by relativistic effects. For Fe and Os, the C and T type structures are preferred over a P geometry. for Ru, the C and P structures are close in energy, and the T arrangement represents the highest energy isomer.