Electronic properties of mixed valence iron(II,III) dinuclear complexes with carboxylate bridges

Mixed valence dinuclear iron(II,III) complexes of the type [Fe2L2(H2O)4](NO3)(H2O)3, where L is the dianion of a Schiff base ligand derived from α-amino acids (glycine and l-isoleucine) and 5-bromosalicylaldehyde, have been prepared and characterised using different spectroscopic methods, magnetic susceptibility, conductivity, and electrochemical measurements. The mixed valence iron complexes can be described as hexacoordinated species, in which the metal ion is surrounded by water molecules, the salicylidenimine ligand and two bridging carboxylate groups. The presence of bromine as a substituent in the salicylaldehyde ring stabilises the mixed valence species.

Graphical abstractTwo mixed valence dinuclear iron(II,III) complexes with carboxylate bridges of the type [Fe2L2(H2O)4](NO3)(H2O)3, where L = Schiff base derived from an α-amino acid (glycine or l-isoleucine) and 5-bromosalicylaldehyde have been prepared and characterised by different spectroscopic techniques, magnetic susceptibility, conductivity, and electrochemical measurements. The existence of the mixed valence species was corroborated by Mössbauer spectroscopy and electrochemical measurements. Temperature dependence of the reciprocal molar susceptibility indicates a weakly antiferromagnetically coupled system (−J ∼ 0.17 and 0.14 cm−1). The conproportionation constant values, at 298 K, are approximately 3.7 × 104 and 5.4 × 104. The obtained values are in agreement with a moderate electron coupling between the redox sites.Figure optionsDownload full-size imageDownload as PowerPoint slide