Neutral transition-metal complexes as probes for solvent structure. The spectrophotometric properties of [NN′-1-methylethylenebis(o-aminobenzylideneiminato)]cobalt(II) in some pure and mixed solvents

Abstract

The visible spectrum of the rigid planar complex [NN′-1-methylethylenebis(o-aminobenzylideneiminato)]-cobalt (II), [Co(meab)], has been studied in a range of pure and mixed aqueous solvent systems under deoxygenated conditions. Beer's law is obeyed in each system up to the solubility limit. Although the visible spectrum of [Co(meab)] in water is essentially featureless, maxima at 421–435 and 522–531 nm develop on addition of methanol, ethanol, n-propanol, t-butyl alcohol, acetone, and pyridine. The close similarity of the visible spectra in pure pyridine and benzene solvents suggests that this effect is not due to discrete axial ligation of [Co(meab)] by solvent molecules, as confirmed by magnetic-moment measurements in aqueous pyridine and by the isolation of a solvate, rather than a pyridine-containing complex, from saturated solutions of [Co(meab)] in pyridine. The absorption coefficient of [Co(meab)] in binary aqueous mixtures appears to be related to the structure of the bulk solvent environment.