Iron(II) 2-methylimidazolate and copper(II) 1,2,4-triazolate complexes: systems exhibiting long-range ferromagnetic ordering at low temperatures

Abstract

Crystals of [Fe (2methylimidazolate)2·0.13(FeCp2)]x,1, are orthorhombic, a = 8.0654(11), b = 15.3504(5), c = 19.3388(9) Å, Z = 8, space group Pnnm. The structure was solved by direct methods and refined by full-matrix least-squares procedures to R (F, I [Formula: see text] 3σ(I)) = 0.057 (Rw (F2, all data) = 0.142). The structure involves tetrahedral iron(II) centers linked in chains by single imidazolate ligand bridges. The chains are cross-linked by additional imidazolates to generate a complex 3-D network of linear channels in which ferrocene molecules are trapped. [Cu(1,2,4-triazolate)2]x, 2, is shown by indirect evidence to have a polymeric structure in which copper(II) ions are bridged by triazolate ligands. Magnetic susceptibilities were measured on powdered samples over the temperature range 2-300 K at applied fields of 0-55 000 G. Both materials exhibit antiferromagnetic exchange at temperatures above a magnetic phase transition: 27 K for 1 and 35 K for 2. At temperatures below these transitions the compounds exhibit weak ferromagnetism, likely resulting from canted spin structures. Cycling the applied magnetic field between +55 000 G and -55 000 G at 4.8 K generates hysteresis loops for both materials. Remnant magnetizations of 200 and 55 cm3 G mol-1 and coercive fields of 5000 and 2500 G are obtained for 1 and 2, respectively.Key words: iron, 2-methylimidazolate, copper, 1,2,4-triazolate, canted spins, ferromagnets.