The infrared spectra of pyridine N-oxide complexes of transition metal perchlorates in relation to their structures

The infrared spectra of the complexes [M(pyO)6](ClO4)2 (pyO = pyridine N-oxide; M = Mn, Fe, Co, Ni, Zn) are discussed. Assignments of v(M-O) and other significant vibrations are based on the band shifts induced by deuteration of the heterocyclic ring and the effects of metal ion substitution. Earlier spectroscopic evidence suggesting distortion from regular octahedral site symmetry is discounted by the far-infrared spectra. In agreement with recent crystallographic evidence for Oh site symmetry in these complexes, one infrared-active v(M-O) band is expected and observed. The effects on the spectra of structural distortion in the 6-coordinate CuII complex [Cu(pyO)6](ClO4)2, reduced coordination number in the 4-coordinate complex [Cu(pyO)4](C1O4)2, and increased cationic charge in the GaIII complex [Ga(pyO)6](C1O4)3are discussed.