Structural, magnetic and optical properties of an FeIII dimer bridged by the meridional planar divergent N,N′-bis(salicyl)hydrazide and its photo- and electro-chemistry in solution

Abstract

{Fe^IIICl(DMF)₂}₂(L) where L is N,N′-bis(salicyl)hydrazide has been synthesized as red crystals and characterized using single-crystal diffraction, infrared and UV-vis spectroscopies, and its magnetic properties studied. The dimeric unit in the structure is formed through the two meridional sets of divergent O, N, O coordinating atoms of the hexacoordinated and quadruply charged ligand. With the presence of the inversion symmetry the Fe atoms are strictly planar with the ligand. The magnetic exchange interaction is found to be antiferromagnetic with a J = −5.98(3) cm⁻¹ through the rare Fe–N–N–Fe pathway. Irradiation of the FeCl₃/H₄L red DMF solution in the visible region of the spectrum resulted in its complete discoloration and from which the unknown colorless salt [Fe^II(DMF)₆][Fe^IICl₄] and the neutral ligand have been identified by single crystal diffraction. The UV-visible spectra of FeCl₃, H₄L and their mixture in DMF solution indicate that the iron complex is the absorbing species and the presence of the free ligand in the irradiated solution suggests that the ligand is potentially acting as a catalyst to the photoreduction of Fe^III to Fe^II, while electrochemistry points to a mixed-valent (Fe^II–Fe^III) intermediate in the process.