Spectra-structure correlations from the infrared spectra of some transition metal complexes of 8-hydroxyquinoline

Abstract

The IR spectra of twenty-one transition metal complexes of 8-hydroxyquinoline over the range 700-50 cm −1 are discussed in relation to their known or inferred structures. The complexes are of three types: (a) the bis(aquo) complexes of the 3 d metal(II) ions trans-[M(ox) 2(H 2O) 2] (M = Mn, Fe, Co, Ni, Cu, Zn); (b) the corresponding anhydrous complexes, [M(ox) 2] (M = Mn, Co, Ni, Cu, Zn); and (c) the complexes of the metal(III) ions, [M(ox) 3] (M = Sc, V, Cr, Mn, Fe, Co, Ga). 8-Hydroxyquinoline- d 7 has been synthesized and used to assist in the metal-ligand assignments which are further based on 64,68Zn labelling of the bis(aquo) zinc complex and on the effects of metal ion substitution in relation to expectations based on crystal field theory. The effects of Jahn-Teller distortion on the spectra of the complexes of Cu(II) and Mn(III) are discussed. The spectra of the bis(aquo) adducts support the previously proposed trans-octahedral structure. The spectra of the anhydrous complexes are consistent with tetrahedral Mn, Ni and Zn but suggest that the Co complex has polymeric octahedral coordination rather than the previously-proposed tetrahedral structure. The six-coordinate α-Cu complex and five-coordinate β-Cu complex exhibit distinctive differences in their spectra which support the elongated axial Cu-O bonds observed in crystal structure determinations. The spectra of the metal(III) tris(oxinates) are consistent with the facial ( cis-cis) coordination previously proposed. The spectra of these complexes are discussed in relation to bonding considerations based on crystal field theory.