Structural and Electronic Properties of Iron(II) and Nickel(II) Complexes of 2,6-Bis(triazol-3-yl)pyridines

Abstract

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 N4 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) Ǻ, β 122.20(1)°, Z 4. Bis [2,6-bis(1,2,4-triazol-3-yl)pyridine]iron(II) dinitrate tetrahydrate : tetragonal, space group 14₁/a, a 11.488(2), c 21.055(7) Ǻ, 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 77K. The complex of the 5-methyl derivative undergoes a continuous singlet ↔ quintet transition below room temperature.