The photochemistry of some cis-dihalo rhodium(III) complexes

Abstract

JAMES SELLAN and ROF~ERT RUMFELDT. Can. J. Chem. 54, 1061 (1976).The photochemistry of cis-[Rh(cyclarn)X21f (where X = CI, Br, or I) and cis-[Rh(en)2Cl2]+ have been studied. Whilst only halide aquation is observed for the cyclarn complexes, amine aquation is the principal reaction mode for the ethylenediamine complex. In each case, the photosensitivity was greater for charge transfer excitation than ligand field excitation. Although this wavelength dependence was also exhibited for the corresponding tr~11s complexes, the dependence on the leaving group which was &I-) < +(Br-) < +(I-) for tile tru~ls complexes is completely reversed for cis- (111) haloamines. Whilst the photoreactions of the trans complexes were accurately predicted by Zink's model (2), the cis complexes exhibited an apparently inconsistent behaviour. Thus, the photolysis of ci~-[Rh(en)~Cl~]+ was characterized by the anti-thermal ethylenediamine aquation whereas the analogous complex, cis-[Rh(cyclam)C12]+, (cyclam = 1,4,8,11-tetraazocyclotetradecane) exhibited chloride aquation exclusively. In principle, if a cis complex possessed tetragonal symmetry then Zink's model would predict that the strongest ligand on the weak field axis would be preferentially labilized. Therefore, the ethylenediamine aquation in the photolysis of cis-