Spectroscopic and Theoretical Studies of Metal Cluster Complexes. 1. The He(I) Photoelectron Spectrum of ReaClg. Calculations by the SCC DV Xγ Method of Re₃Cl₉ and Re₂Cl₈^2-

The gas-phase photoelectron spectrum of Re₃Cl₉ has been measured at ca. 800 K. The first vertical ionization potential occurs at 8.85 eV Results of a discrete variational Hartree-Fock-Slater calculationsuggest that this ionization be attributed to a E state. Spin-orbit splitting of the first ionization band alsosupports this assignment. Charge density contributions to this orbital are distributed over the Re 5d, bridgingCl3p, and axial CI 3p orbitals in a 5:2:3 ratio. Remaining features in the photoelectron spectrum and the proposedorbital assignments are as follows: 9.80 eV, 22e” 9.90 eV, 18a₂”, 12a₂’, 40e’ 10.47 eV, 21e” 10.83 eV, 39e’, 17a₂”, 5a₁” 11.09 eV, 28a₁’, 20e”, 38e’ 11.83 eV,16a₂”, 37e’ 12.21 eV, 11a₂’, 36e’ 13.06 eV, 27a₁’ 13.39 eV, 15a₂”, 19e”, 26a₁’ 13.86 eV, 35e’. A unique feature of bonding in this complex is the great stability of 25a₁’, the cluster c-bonding orbital. Chemically, this manifests itself in a trans effect at the vertices of the trinuclear cluster framework. To allow a fair comparison between Re₃Cl₉ and the well-studied Re₂Cl₈^2- ion, a calculation of the latter complex's electronic structure was also performed. A detailed comparison of the valence orbitals in these two molecules follows.