Abstract
The aqueous solution UV spectra of the aqueous Rh(III) sulfito complexes trans-Rh(NH3)4(SO3)(X)n− (X = CN− (I) or SO32− (II) are dominated by intense (ϵmax∼104 M−1 s−1) absorption bands at λmax 226 (I) and 266 (II) nm attributed to ligand to metal charge transfer (LMCT) transitions. Both compounds are photoactive. Photolysis of II at 313 nm leads to Rh(NH3)4(SO3)(H2O)+ formation with a quantum yield (0.16±0.01) independent of light intensity (Ia) and of air, behavior consistent with excitation to a substitution labile ligand field excited state. More complicated behavior was observed with 254 nm photolysis of both I and II which indicates the possible contributions of photoredox pathways originating in the LMCT state(s). The luminescence spectra and lifetimes at 77 K of I and II and of the two cyano complexes [Rh(NH3)5CN]Cl2 and [trans-RhNH3)4CNCl]Cl are also reported. Each of these compounds displays broad bands attributed to emission from ligand field triplet states. Also described is the equilibrium constant for reaction of trans-Rh(NH3)4(SO3)(H2O)+ with Cl− in aqueous solution (K = 0.053 ± 0.007 M).
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