STRUCTURAL AND ELECTRONIC-PROPERTIES OF IRON(II) AND NICKEL(II) COMPLEXES OF 2,6-BIS(TRIAZOL-3-YL)PYRIDINES

Iron(II) and nickel(II) bis(ligand) complexes of 2,6-bis(1,2,4-triazol-3-yl)pyridine and the substituted derivatives 2,6-bis(1(N)-methyl-1,2,4-triazol-3-yl)pyridine, 2,6-bis(5-methyl-1,2,4-triazol-3-yl)pyridine and 2,6-bis(1,5-dimethyl-1,2,4-triazol-3-yl)pyridine have been prepared. Coordination of the unsubstituted ligand through N 4 of the triazolyl moieties is confirmed by structure determination of [FeL2][NO3]2.4H2O and [NiL2]Cl2.3H2O. In both of these complex salts there is an extensive hydrogen-bonded network involving the N 1-H group, the anions and the water molecules. Bis[2,6-bis(1,2,4-triazol-3-yl)pyridine]nickel(II) dichloride trihydrate: monoclinic, space group C2/c, a 17.971(5), b 11-433(1), c 14.849(5) angstrom, beta 122.20(1)-degrees, Z 4. Bis[2,6-bis(1,2,4-triazol-3-yl)pyridine]iron(ii) dinitrate tetrahydrate: tetragonal, space group I 4(1)/a, a 11.488(2), c 21.055(7) angstrom, Z 4. [FeL2]Cl2.3H2O is isostructural with the nickel complex and is high-spin but undergoes a partial transition to low-spin at low temperature. Conversion to low-spin is complete when the complex is dehydrated, and this change is associated with the effects of the hydrogen bonding. The solid iron complexes of the N-methyl-substituted ligands in which the hydrogen-bonding potential is reduced are entirely high-spin down to 77 K. The complex of the 5-methyl derivative undergoes a continuous singlet reversible quintet transition below room temperature.