Solvation structure of metal ions in nitrogen-donating solvents

Abstract

The solvation structure of the Mn(II), Fe(II), Co(II), Ni(II), and Zn(II) ions has been determined in various nitrogen-donating solvents of n-propylamine (PA), trimethylenediamine (TA), ethylenediamine (EN), pyridine (PY), 2-methylpyridine (2MPY), 4-methylpyridine (4MPY), and acetonitrile (AN) by the X-ray absorption spectroscopy. The 6-coordinate octahedral structure has been observed for all the ions except for the species of Zn(II) in PA and 2MPY. The mixed formation of 4- and 6-coordinate species is found for Zn(II) in TA, of which the electron donicity is compared with that of PA. A similar mixed formation of solvated species has been observed for the Co(II) ion in PA. The M–N bond distances vary in the order Mn(II) > Fe(II) > Co(II) > Ni(II) < Zn(II) as expected from the ligand field theory. There are systematic shifts in the series of the M–N bond distances in the aliphatic amines, pyridines, and nitriles, which may be related to the electronic structure of the coordinating nitrogen atoms.