Self assembly of dialkoxo bridged dinuclear Fe(III) complex of pyridoxal Schiff base with C[sbnd]C bond formation – Structure, spectral and magnetic properties

Abstract

The new dinuclear Fe(III) complex, [Fe2(µ-L)2]·3(H2O)·0.38(O), [L=(E)-2-(((5-(hydroxymethyl)-2-methyl-3-oxido-1κO-pyridin-4-yl)methylene)amino-1κN)-3-(3-(hydroxymethyl)-2-methyl-5-oxido-1κO-pyridin-1-ium-4-yl)-3-oxido-1:2κ2O-propanoato-2κO]∗ (∗The second ligand has swapped indices 1 and 2, denoting the individual Fe centers.), was synthesized by reaction of FeCl3·6H2O with potassium pyridoxylidenglycinate in ethanol-water solution. Pentadentate pyridoxal Schiff base ligand was generated in situ by aldol condensation of potassium pyridoxylidenglycinate and pyridoxal. A CC coupling was achieved at room temperature under metal template reaction. The complex was characterized by X-ray structural analysis at 100K, elemental analysis, spectral and magnetic measurements. The compound crystallizes in the monoclinic space group P 21/n, with unit cell parameters: a=9.7445(15)Å, b=19.489(3)Å, c=20.862(6)Å, β=92.595(17)°. Structural analysis of the complex showed that each Fe(III) center has a distorted octahedral FeNO5 core, which is sixfold coordinated through iminic nitrogen atom, two phenoxido oxygen atoms, alkoxo oxygen atom and carboxylato oxygen atom from two Schiff-base ligands forming a rhombic arrangement of metal ions and oxygen atoms. In the structure, two Fe(III) atoms are connected with two alkoxo-bridging ligands providing covalent superexchange pathway by linkage Fe1–O–Fe2 with the Fe1⋯Fe2 distance of 3.195Å. In the crystal lattice, the noncovalent interactions, hydrogen bonds, and π-π stacking interactions expand the mononuclear units to 3D supramolecular network. The temperature dependent magnetic susceptibility data (6.5–300K)indicate that the octahedral Fe(III) centers in this complex retain high-spin S=5/2 (6A1g) in the whole temperature range. The effects of zero-field splitting (D=7.67cm−1) and an antiferromagnetic coupling (J=−14.66cm−1) between the two alkoxo-oxygen bridged Fe(III) ions are discussed.