Halide Anion Effects\nand Magnetostructural Relationships\nin Iron(III) Spin Crossover Complexes

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