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)pyri dine and the substituted derivatives 2-(1(N)-methyltriazol-3-yl) pyrid ine and 2-(1,5-dimethyltriazol-3-yl)pyridine have been prepared. Coord ination of the dimethyl-substituted ligand via N(4) of the triazolyl m oieties is confirmed by structure determination of [FeL(3)][BF4](2), w hich has the mer configuration. Tris(2-(1,5-dimethyltriazol-3-yl)pyrid ine)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 substit uents 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 [F eN6](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 s uggest that there is a fundamental change with time in the geometry of the complex cation. The metastable form of the complex hexafluorophos phate 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 mult iple iron(II) sites in the lattice for salts containing either the N-m ethyl or the unsubstituted ligand.