Electron Spin Resonance of Re2(μ-H)2(CO)8+. and Re2(μ-H)2(CO)6(μ-dppm)-. (dppm = (Ph2P)2CH2). An Indication of Large 5d-6p Mixing in the Odd-Electron Orbital

Article abstract of DOI:10.1021/ja00309a008

Re2(μ-H)2(CO)8^-., Re2(μ-D)2(CO)8^-., and Re2(μ-H)2(CO)6(μ-dppm)^-. have been examined with electron spin resonance spectroscopy.They have planar Re2H2 rhomboids and their odd-electron orbitals are the ?^*_ReRe orbital lying in the rhomboid.Rhenium hyperfine splitting tensors are interpreted most reasonable with the ?^*_ReRe orbital consisting of rhenium 5d and 6p AO's.The odd-electron density on the 5d AO is estimated to be around 0.26 for Re2(μ-H)2(CO)8^-..The anisotropy of the rhenium hyperfine interaction due to the odd-electron density on the 6p AO is estimated as 42 * 10^-4 cm^-1, a magnitude similar to that due to the 5d odd-electron density, 57 * 10^-4 cm^-1.This large 5d-6p mixing is likely to arise from contraction and stabilization of 6p AO's and expansion and destabilization of 5d AO's due to relativistic effects.