Solvation structure of metal ions in nitrogen-donating solvents

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.