An unusually stable five-coordinate monomeric divalent rhodium complex, [RhII(H)(CO)(PPh3)3]+, is produced by bulk oxidative electrolysis or chemical oxidation of RhI(H)(CO)(PPh3)3 in dichloromethane. Consequently, odd as well as even electronic configurations are available in this well-known catalytic system. The EPR and electronic spectra of electrogenerated paramagnetic 17-electron cation [RhII(H)(CO)(PPh3)3]+ have been obtained at low temperatures as has the EPR spectrum of the deuterated analogue. Computer simulation of the EPR spectra of the hydride and deuteride complexes reveals three g-values and anisotropic coupling constants for hydrogen, phosphorus, and rhodium. One of the phosphorus coupling constants is very large (A1 = 175.0 G; A2 = 176.0 G; A3 = 230.0 G). This may be accounted for if [RhII(H)(CO)(PPh3)3]+ has the square pyramidal structure, and substantial mixing of the singly occupied metal orbital and the apical phosphorus s-orbital are considered. NMR measurements on mixtures of RhI(H)(...