Magnetic circular dichroism spectra of tris-chelate complexes of 2,2′-bipyridyl and 1,10-phenanthroline with iron(II), ruthenium(II), and osmium(II) at 4.2 K

Abstract

The magnetic circular dichroism (m.c.d.) spectra, in alcoholic glasses at 4.2 K, are reported for the tris-chelates of 2,2′-bipyridyl and 1,10-phenanthroline of iron(II), ruthenium(II), and osmium(II), including those of the substituted bipyridyl ligands, 4,4′-diphenyl-, 4,4′-diethoxy-, 4,4′-di(ethoxycarbonyl)-, and 5,5′-di(ethoxycarbonyl)-2,2′-bipyridine. The spectra in the region of the spin-allowed metal-to-ligand charge-transfer bands show good resolution and a number of the expected A-terms are apparent. The osmium(II) complexes also show well defined A-terms in the region of the formally spin-forbidden transitions. Calculation of the signs and magnitudes of the A-terms has been carried out using a theoretical model proposed previously. Good agreement is obtained between the experimental results and the theoretical predictions in the case of tris(2,2′-bipyridyl)osmium(II). The relationship between the form of the spectrum of this complex and the others studied is discussed. The m.c.d. spectra of the triplet states do not help to resolve the controversy over the assignment of the luminescing states.