Antiferromagnetically coupled iso-structural CrIII, MnIII and FeIII complexes of a tetradentate Schiff base ligand derived from o-phenylenediamine

Three isostructural, Iron(III), Manganese(III) and Chromium complexes, with a tetradentate Schiff base ligand (H₂L²) from o-phenylenediamine and o-vanillin having the general formulae, [M(H₂L²)(C₂H₃O₂)(H₂O)], where M = Cr, Mn, Fe) have been prepared. The complexes were then subsequently characterized by physico-chemical and spectroscopic methods and further investigated for their magnetic nature. All the complexes are neutral mononuclear species and crystallize in a triclinic space group P-1(2). Single-crystal diffraction studies reveal that the ligand, H₂L², coordinates to the central metal ion in a tetradentate fashion through both the azomethine nitrogen and the deprotonated phenolic oxygen generating neutral complexes. One of the acetate counter anions and a water molecule is involved in the coordination, generating a distorted octahedral geometry in all the complexes. Temperature dependence magnetic susceptibility was measured in a squid magnetometer in the temperature range 300–1.8 K and reveals that all of the three complexes show antiferromagnetic behavior in the temperature range studied. The experimental susceptibility data fitting, by considering the intermolecular interactions, enabled to estimate the magnetic anisotropy D and lead to the parameters (D =  + 0.14 cm⁻¹ and zJ =  − 0.35 cm⁻¹) for Fe^III and (D =  − 3.95 cm⁻¹; E =  + 0.54 cm⁻¹; zJ =  − 0.35 cm⁻¹) for Mn^III ions. This study is aiming and boosting to 'open up' our interest to focus more on mononuclear complexes with SMM character with first-row transition metals, which will be more interesting as far as the application side is concerned.