Iron(II) Complexes Containing 1,2,4-Triazole-Pyridine and the Substituted Derivatives; Electronic Properties and Magnetic Moments

Abstract

Iron(II) complexes of [FeL3][X]2, where L = trzp, 1-mtrzp, and 1,5-dmtrzp, X = NO3 and I, and nickel(II) analogous, have been prepared and characterized in the electronic properties and magnetism. The complexes were found to be yellow to brownish for the dihydrates, [FeL3](X)2.2H2O. An additional complex of [Fe(1,5-dmtrzp)2Cl2] was also isolated and found as an orange powder. The complexes, [Fe(trzp)3](NO3)2, [Fe(1,5-dmtrzp)3](NO3)2 and [Fe(1,5-dmtrzp)3](I)2 are fully paramagnetic at room temperature, the μ300K being about 5.2 BM. These are, however, significantly temperature-dependent associated with thermally spin-state transition in iron(II), singlet1A1g ( l.s) quintet 5T2g (h.s), and the transitions are continuous and incomplete within the range of experimental temperature, down to 90K. The degree of incompleteness varies among them, and the least thermally induced was observed for [Fe(1-mtrzp)3](NO3)2. The bis chlorido-ligand complex of [Fe(1,5-dmtrzp)2Cl2], shows a normal high-spin nature down to ~ 100 K (μ100K ~ 5.4 BM). The particular nickel complexes analogous show a normal paramagnet with μ300K ~ 2.9 - 3.0 BM. The electronic spectrum for these complex reveals an octahedral geometry with ν2/ν1 being 1.58-1.59. The ligand field strength of about 11700-11800 cm-1 is in the range in which the spin-state transition in the corresponding iron(II) complexes can be thermally induced.