STRENGTH AND TRANS INFLUENCE OF RH-RH BOND IN RHODIUM(II) CARBOXYLATE DIMERS

SCF-Xa-SW calculations of Rh2(02CH)4(H20)2 and Rh2(O2CH)4 are used to discuss the electronic structures of rhodium(Il) carboxylates, Rh2(CO3)4 4-, Rh2(S04)4 4-, and Rh2 4+(aq). The Rh-Rh bonds in these compounds are predicted to be single, not triple; the basic orbital configuration is 2 4 2 *4 *2. Reasons for the short Rh-Rh distance of 2.39 in Rh2(02CCH3)4(H20)2 are discussed in this context. Both a detailed description and a simple orbital picture of how the Rh-Rh bond so dramatically weakens the trans Rh-OH2 bonds are given; the key is the Rh-OH2 antibonding character of Rh-Rh and a* orbitals. The converse effect of axial ligands on the Rh-Rh bond is also discussed. Comparisons are made with previous calculations on quadruply bonded complexes, particularly Mo2(02CH)4. The peaks at 17.1, 22.7, 40 sh, and 45.9 X 10-3 cm-1 in the electronic spectrum of Rh2(o2CCH3)4(H20)2 are assigned to* -*. *, *-Rh-0 *, -*. *, and La -* a* transitions, respectively. The recently isolated diatomic Rh2 is predicted to have an S = 2 ground state at Rh-Rh = 2.39 A, based on a “dns'” configuration; comparisons are made to Mo2. The ground state of [Ru2(O2CR)4]+ compounds is predicted to be 27 4 2 *2 *1. © 1978, American Chemical Society. All rights reserved.