Photochemically generated superoxides of rhodium(III)

Abstract

Bis(ethylenediamine)rhodium(III) compounds containing N-co-ordinated nitrite ion photoreact with molecular oxygen to give the monomeric superoxorhodium(III) ion, [Rh(en)₂(OH₂)(O₂)]²⁺, and dimeric superoxo-bridged dirhodium(III,III) species. Irradiation of cis- and trans-bis(ethylenediamine)- dinitrorhodium(III) salts, both in the presence and the absence of oxygen, results in nitro–nitrito-isomerization. The visible spectra of the monomers (λ= 490 nm) and dimers (λ= 550 nm) and their Raman frequencies [ν(O–O) at 1 080 and 1 050 cm^–1, and 1 050 cm^–1 respectively] indicate the presence of the Rh^III–O₂^– moiety in the complexes. The e.s.r. spectra (g tensor ca. 2.03) also agree with this formulation. Both monomeric and dimeric species act as one-electron oxidizing agents towards I^– and Fe²⁺.