Galina S. Matouzenko

A spin-crossover iron(II) 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)

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 A 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.

SYNTHESIS OF C3-CYCLOTRIVERATRYLENE LIGANDS FOR IRON(II) AND IRON(III) COORDINATION

Abstract The design and synthesis of a new family of siderophores based on cyclotriveratrylene is described. The ligands consist of a C3-cyclotriveratrylene unit provided with three arms (spacers) ending with hydroxamate, catecholate, bipyridine, or iminopyridine units suitable for the octahedral coordination of transition metals and particularly for the complexation of iron(II) and iron(III).

Spin Crossover in a Family of Iron(II) Complexes with Hexadentate ligands: Ligand Strain as a Factor Determining the Transition Temperature

This paper reports the synthesis of a family of mononuclear complexes [Fe(L)]X(2) (X=BF(4), PF(6), ClO(4)) with hexadentate ligands L=Hpy-DAPP ({bis[N-(2-pyridylmethyl)-3-aminopropyl](2-pyridylmethyl)amine}), Hpy-EPPA ({[N-(2-pyridylmethyl)-3-aminopropyl][N-(2-pyridylmethyl)-2-aminoethyl](2-pyridylmethyl)amine}) and Hpy-DEPA ({bis[N-(2-pyridylmethyl)-2-aminoethyl](2-pyridylmethyl)amine}). The systematic change of the length of amino-aliphatic chains in these ligands results in chelate rings of different size: two six-membered rings for Hpy-DAPP, one five- and one six-membered rings for Hpy-EPPA, and two five-membered rings for Hpy-DEPA. The X-ray analysis of three low-spin complexes [Fe(L)](BF(4))(2) revealed similarities in their molecular and crystal structures. The magnetic measurements have shown that all synthesized complexes display spin-crossover behavior. The spin-transition temperature increases upon the change from six-membered to five-membered chelate rings, clearly demonstrating the role of the ligand strain. This effect does not depend on the nature of the counter ion. We discuss the structural features accountable for the strain effect on the spin-transition temperature.