STRUCTURAL AND ELECTRONIC-PROPERTIES OF IRON(II) COMPLEXES OF 2-(1,2,4-TRIAZOL-3-YL) PYRIDINE AND SUBSTITUTED DERIVATIVES

Iron(II) and nickel(II) tris(ligand) complexes of 2-(triazol-3-yl)pyridine and the substituted derivatives 2-(1(N)-methyltriazol-3-yl) pyridine and 2-(1,5-dimethyltriazol-3-yl)pyridine have been prepared. Coordination of the dimethyl-substituted ligand via N(4) of the triazolyl moieties is confirmed by structure determination of [FeL(3)][BF4](2), which has the mer configuration. Tris(2-(1,5-dimethyltriazol-3-yl)pyridine)iron(II) bis(tetrafluoroborate): orthorhombic, space group Pbca, a 11.568(3), b 19.442(4), c 30.551(8) Angstrom, Z 8. The methyl substituents appear to have only a minor influence on the donor properties of the ligands, all three of which have field strengths in the iron(Ir) quintet reversible arrow singlet crossover region. Temperature-induced singlet reversible arrow quintet transitions occur in salts of the [FeN6](2+) derivatives in both the solid and solution states. Mossbauer effect studies reveal the complexity of the solid state properties of salts of the iron complex of 2-(1(N)-methyltriszol-3-yl)pyridine and suggest that there is a fundamental change with time in the geometry of the complex cation. The metastable form of the complex hexafluorophosphate salt shows virtually no quadrupole splitting in the spectrum for the quintet state species, which implies high symmetry for the metal ion environment. Mossbauer studies further reveal the presence of multiple iron(II) sites in the lattice for salts containing either the N-methyl or the unsubstituted ligand.