METAL-TO-LIGAND CHARGE-TRANSFER SPECTRA OF SOME CHLORO-BRIDGED COMPLEXES OF RHODIUM(I) AND IRIDIUM(I)

Electronic absorption and magnetic circular dichroism (MCD) spectra are reported for the chloro-bridged dimers [RhCl(CO)2]2, [RhCl(COD)]2, [RhCl(NBD)]2, and [IrCl(COD)]2 (COD=1, 5-cyclooctadiene; NBD=norbornadiene) in dichloromethane solution. Absorption spectra are also reported for the less stable [RhCl(C2H4)2]2, [RhCl(COT)2]2, and [IrCl(COT)2]2 (COT=cyclooctene) complexes. Spectra at 77 K were also obtained for [RhCl(CO)2]2 and several of the olefin complexes in glassy EPA or methylcyclohexane/pentane solution. Dissolution of [RhCl(CO)2]2, [RhCl(COD)]2, [RhCl(NBD)]2, and [IrCl(COD)]2 in acetonitrile gives a bridge-cleavage reaction, and spectral data are reported for the monomeric products [RhCl(CO)2(CH3CN)], [RhCl(COD)(CH3CN)], [RhCl(NBD)(CH3CN)], and [IrCl(COD)(CH3CN)]. The intense bands observed in the visible and near-ultraviolet regions of the spectra of all these complexes are assigned as metal-to-ligand charge-transfer (MLCT) transitions from occupied metal d orbitals to low-energy ligand À orbitals. Detailed spectral assignments are presented, and comparisons are made between the chloro-bridged complexes and related monomeric complexes. © 1979, American Chemical Society. All rights reserved.