Strong antiferromagnetic interaction in µ-Oxo-bridged diiron(III) complex and paramagnetic nickel(II) complex of pyridoxal Schiff base ligands

Dinuclear and mononuclear pyridoxal Schiff base complexes, specifically [{FeL} 2 ( µ -O)]·2.2H 2 O ( 1 ) and [NiL’(H 2 O)]·2H 2 O ( 2 ) (where L 2– is the dianion of tetradentate pyridoxal Schiff base generated in situ by the iron-catalyzed oxidative C − N bond cleavage of the initial pentadentate Schiff base, and L’ 2– is the dianion of pentadentate Schiff base ligand formed from pyridoxal and N -(2-aminoethyl)propane-1,3-diamine) have been synthesized and characterized by elemental analysis, Fourier transform infrared spectroscopy, and mass spectrometry. The crystal structures of these complexes were determined using single-crystal X-ray diffraction. The Fe atoms in complex 1 exhibit a distorted square pyramidal coordination geometry, while Ni atom in complex 2 displays a distorted octahedral geometry. The most significant finding is the strong antiferromagnetic exchange coupling observed in the diiron complex 1 . Magnetic susceptibility data revealed an exchange coupling constant of J = − 173 cm –1 , confirming its potential role as a model for non-heme diiron metalloenzymes. In contrast, complex 2 exhibits typical paramagnetic behavior of an octahedral Ni(II) complex with two unpaired electrons. Calculations based on density functional theory confirmed the high-spin state of the Fe(III) centers in the diiron complex and verified the magnitude of the strong antiferromagnetic exchange coupling. For the nickel complex, these calculations also revealed a significant degree of bond covalency, providing a comprehensive understanding of the structural and magnetic properties of these pyridoxal-based coordination compounds.