Spin-crossover behavior in a new series of iron (II) compounds based on the ligand 5-(2-pyridyl)-1,2,4-triazole

The title ligand (hereafter LL), is found to form an exciting new series of pseudo-octahedral Fe(II) compounds with formula Fe(LL)₃X₂. N Solvent, which exhibit conveniently studied spin-crossover transformations between nominal⁵T and¹A states of Fe(II). Mössbauer spectra indicate that the spin-crossover transformations for these new systems are probably of the continuous type. There is considerable variation in the degree of conversion to low spin with decreasing temperature depending on gegen ion, solvation and/or location of methyl substituent on the triazole - ligand. The Mössbauer spectra for particular complexes in this group show an absence of both noticeable hysteresis and mechanical grinding effects.