Synthesis and study of Iron(II) perrhenate complexes with 4-propyl-1,2,4-triazole exhibiting 1A1 ? 5T2 spin transition

Coordination compounds of iron(II) perrhenate with 4-propyl-1,2,4-triazole (L), Fe₃L₆(ReO₄)₄(H₂O)₂](ReO₄)₂(I), Fe₃L₆(H₂O)₆](ReO₄)₆·H₂O(II), and FeL₃(ReO₄)₂(III), were synthesized. Compounds I and III were studied by static magnetic susceptibility measurements and by IR and electronic spectroscopy. These complexes exhibit a reversible ¹ A ₁ ⇄ ⁵ T ₂ spin transition and thermochromism. Compound I exhibits a spin transition without hysteresis at 185 K. The temperatures of forward and reverse transition for III are 250 and 244 K, respectively. Complex II isolated by crystallization from an acidified aqueous solution of compound I has a linear trinuclear structure of the cation (X-ray diffraction data). The structure of complex I was assumed to be similar, while compound III has a polymeric structure. Original Russian Text ? M.B. Bushuev, L.G. Lavrenova, Yu.G. Shvedenkov, A.V. Virovets, L.A. Sheludyakova, S.V. Larionov, 2007, published in Zhurnal Neorganicheskoi Khimii, 2007, Vol. 52, No. 1, pp. 51–56.