Electronic structure of rhodium(II) dimers of formula [Rh2X2(µ-O2CH)2(HNCHCHNH)2](X = halide)

Abstract
The electronic structures of the dirhodium complexes [Rh2(µ-O2CH)4(H2O)2] and [Rh2X2(µ-O2CH)2(HNCHCHNH)2](X = Cl, Br or I) have been calculated by the Fenske–Hall method. The calculations gave the electronic configurations σ2π4δ2δ*2π*4σ* with σ* as the lowest unoccupied molecular orbital for [Rh2(µ-O2CH)4(H2O)2] and highest occupied molecular orbital < 18a1, 16b1(π* HNCHCHNH) < 17b1(σ*) for [Rh2X2(µ-O2CH)2(HNCHCHNH)2]. All Rh–Rh orbitale of the latter complexes have considerably higher ligand contributions than those of [Rh2(O2CH)4(H2O)2]. The strength of the Rh–Rh bond and the electronic spectra of the complexes are discussed.