Charge-transfer and intraligand electronic spectra of bipyridyl complexes of iron, ruthenium, and osmium. I. Bivalent complexes

Abstract

A series of spin-paired bivalent bipyridyl complexes of iron, ruthenium, and osmium, of the type [M(bipy)₃]²⁺, [M(bipy)₂X₂]ⁿ⁺, [M(bipy)₂XY]ⁿ⁺, [M(bipy)X₄]ⁿ⁺, [M(bipy)(X₂)₂]ⁿ⁺, and [M(bipy)X₂Y₂]ⁿ⁺ (X and Y include a range of monodentate ligands and X₂ a range of bidentate ligands) have been prepared. Their electronic spectra within the range 41000-7000 cm^-1 have been recorded. All the complexes show two intraligand transitions which are present in free bipyridyl. The iron and ruthenium complexes have two metal oxidation charge-transfer bands, while the osmium complexes have a more complex charge-transfer pattern. Trends in the positions of the bands have been related to the bonding of the ligands X and Y to the metal ions. It is suggested that the energy of the metal t₂ type orbitals relative to the ligand π and π* orbitals is the main factor in determining the intense electronic spectra of these complexes.