A spin-crossover iron(<scp>ii</scp>) coordination polymer with the 8-aminoquinoline ligand: synthesis, crystal structure and magnetic properties of [Fe(aqin)₂(4,4′-bpy)](ClO₄)₂·2EtOH (aqin = 8-aminoquinoline, 4,4′-bpy = 4,4′-bipyridyl)

Abstract

We report here on the synthesis and characterisation of a new iron(II) spin-crossover coordination polymer of formula [Fe(aqin)2(4,4′-bpy)](ClO4)2·2EtOH (aqin = 8-amino-quinoline, 4,4′-bpy = 4,4′-bipyridyl), with a linear chain structure. Variable temperature magnetic susceptibility measurements revealed a relatively abrupt HS ↔ LS spin transition, with T1/2 = 220 K (temperature for which the HS fraction is equal to 0.5). The crystal structure was resolved at 293 K (HS form) and 80 K (LS form). Both spin state structures belong to the monoclinic space group C2/c (Z = 4). The complex assumes a one-dimensional linear chain structure, in which the active iron(II) sites are linked to each other by rigid rodlike 4,4′-bipyridyl molecules acting as chemical bridges. The Fe–Fe distance through the 4,4′-bpy ligand is 11.485 and 11.147 Å in the high-spin and low-spin structures, respectively. The polymeric chains extend in the b direction and form sheets parallel to the bc plane. They are linked together by π-stacking interactions and H-bonding between the H-donor aqin ligands and the perchlorate ions. Those structural features provide a basis for cooperative interactions.