Halide Anion Effects and Magnetostructural Relationships in Iron(III) Spin Crossover Complexes

A series of three compounds [Fe(salEen-5-I)2]Cl 1, [Fe(salEen-5-I)2]Br 2, and [Fe(salEen-5-I)2]I 3 in which salEen-5-I = 2-{[(2-(ethylamino)ethyl]imino)methyl}-4-iodophenolate is reported. Magnetic studies reveal that 2 exhibits an abrupt 2-step spin crossover close to room temperature around 288 K, while 1 and 3 exhibit gradual incomplete spin crossover spanning over 200 K. The use of structural parameters A–C to describe the nearest and next nearest neighbor contacts allows us to rationalize not only the abruptness of the spin crossover but also the stepped nature of the spin crossover in 2. Comparisons with previously reported [Fe(salEen-5-Br)2]ClO4 and [Fe(salEen-5-I)2]ClO4 reveal that this magnetostructural relationship is applicable to a wider range of members of this family of complexes.