Molecular Hydrogen Complex vs Dihydride in ML<inf>4</inf>+ H<inf>2</inf> Systems: Influence of the ML<inf>4</inf> Fragment Geometry

The influence of the d8ML4[Rh(PH3)4]+ metallic fragment geometry on the H2 coordination shape is analyzed with the ab initio MO method. The potential energy surface minima are found to be essentially different when the fragment has a classic form C2v or a rigid pyramidal C3v structure. In C2v, symmetry, the stable species turns out to be the dihydride, whereas in C3v symmetry the η2 molecular complex is the stable structure, in good agreement with experimental data. Through the analysis of a few selected molecular orbitals, the different hybridization of the Rh d orbitals is shown to be the key factor to explain the experimental behavior. © 1989, American Chemical Society. All rights reserved.