The spectroscopic and luminescent properties of the heterobimetallic [PtRh (dppm)2(CN)2(CN-t-Bu)2] ClO4, [AuRh(dppm)2(CN-t-Bu)2] (ClO4)2, and [AgRh(dppm)2(CN-t-Bu)2](ClO4)2 complexes were investigated. All the three complexes display an intense 1(dσ* → pσ) transition at 473 nm (εmax = 1.34 × 104 M- cm-1), 455 nm (εmax = 2.40 × 104 M-1 cm-1), and 425 nm (εmax = 1.68 × 104 M-1 cm-1), respectively. A molecular orbital calculation on the model complex [PtRh(dmpm)2(CN)2(CN-t-Bu)2]+ (dmpm = bis(dimethylphosphino)methane) suggests that the dσ* orbital is mainly derived from the 4dz2 of Rh and the pσ is made up of π* of isocyanide and 5pz of Rh. In each case, the 1(dσ* → pσ) transition has substantial Rh → π*(isocyanide, phosphine) charge-transfer character. Excitation of solid samples of the complexes leads to phosphorescence derived from the 3(dσ*pσ) excited state.
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Yip et al. (1993) studied this question.