Structural Studies of Iron(III) Complexes with N4O2 Coordination Sphere

The Spin-Crossover (SCO) phenomenon implicates a switchable between a low-spin (LS) diamagnetic state, which is stable at low temperatures and a paramagnetic high-spin state (HS), which is stable at higher temperatures. This transition is generated by an external perturbation such as temperature, pressure or light. In general, the switching process in solid-state systems is controlled by cooperative intermolecular interactions. The correlation of structure with physical properties is crucial to the identification of these interactions and ultimately the understanding of the complex processes that control the SCO phenomenon[1]. With the aim of developing new SCO materials, we carried out the syntheses and crystal structure analysis of seven iron(III) complexes, mixing 5-bromo-salicylaldehyde or 5-chloro-salicylaldehyde and ethylendiamine with iron(III) chloride and/or ammonium hexafluorophosphate solutions by slow diffusion or reflux in methanol or 2-propanol (figure 1). The crystal structures show the iron(III) centre is hexacoordinated (FeN4O2) and the coordination polyhedron can be described as a distorted octahedron formed by the 4 N atoms of the ethylenediamine fragment and 2 hydroxyl O atoms from the salicylaldehyde fragment, this distortion was evaluated at 120 and 298 K, the major distortion were observed in complexes [2]+ PF6-· MeOH, [2]+ PF6-·iPrOH and [1]+ PF6-·MeOH, which is characteristic in HS states, while the complexes [2]+ Cl-·iPrOH, [1]+ PF6-·iPrOH [2]+ and [2]+ClO4-, shows a minor distortion according to LS states. On the other hand, [1]+ClO4- is a SCO complex with a typical geometry for both spin states at 120 K (LS) and 298 K (HS). Finally, we studied the intermolecular interactions using Crystal Explorer Software[2] between the iron complexes, the counterion and/or the solvate molecule, for instance, in the [2]+PF6-·MeOH complex, the most remarkable feature observed are Br···Br intermolecular interactions (figure 2). ACKNOWLEDGMENTS: FONDECYT N⁰ 1130640, FONDEQUIP EQM120095 and Beca CONICYT folio 21130944

Structural Characterization of Iron(iii) Dinuclear Complexes

Dinuclear complexes have been studied for different purposes: magnetic materials[1], Non-linear optics materials[2], molecular switches [3], mixed-valence systems, etc. With these antecedents in mind, we present in this work a new series of dinuclear Iron(III) complexes formed by different Schiff bases ligands. The reaction starting from the iron chloride salts with the 5-chloro or 5-bromo-salycilaldehyde and ethylendiamine yields two different kinds of dinuclear iron complexes in different reaction conditions. The first one (Fig N°1), are methoxo-bridged dinuclear iron(III) complexes in which each metal centre is coordinated with one mono-condensated Schiff base ligand, one 4-chloro or 4-bromo-2-(dimethoxymethyl)phenoxo ligand and two bridging methoxo ligands. The iron(III) centres are hexacoordinated (FeN2O4), the coordination sphere is formed by 2 nitrogen atoms of the ethylendiamine fragment, 2 oxygen atoms from the hydroxyl of the Schiff base and two O atoms from the methoxo ligands. Both iron(III) centres are related by a inversion centre. The second one (Fig N°2), the dinuclear complex is formed for the double condensation of ethylendiamine with 5-chloro or 5-bromo-salycilaldehyde and one oxygen from the dianionic ligand act as bridge with another unit. The iron (III) centres are also hexaccordinated (FeN2O3Cl) formed by 2 nitrogen atoms from ethylendiamine fragment and 3 oxygen atoms from hydroxyl from Schiff base ligands and one chloro ligand. Finally, the electronic and redox properties have been studied by UV-Visible and cyclic voltammetry. ACKNOWLEDGMENT FONDECYT N⁰ 1130640, FONDEQUIP EQM120095 and Beca CONICYT folio 21130944