Iron(III) induced 2-phenyl imidazolidine ring hydrolysis of a new binucleating Schiff base ligand: X-ray structure of the mononuclear Fe III(NNO) 2 end product

Abstract

The reaction of triethylenetetramine, salicylaldehyde and benzaldehyde in 1:2:1 mole ratio in methanol at room temperature affords a novel μ-bis(tridentate) ligand H 2L′ through the formation of an imidazolidine ring within the parent hexadentate precursor in a two step reaction. The ligand H 2L′ reacts with Fe(ClO 4) 2 · 6H 2O in aqueous methanol in the presence of triethylamine to form the mononuclear [Fe IIIL](ClO 4) complex, (where L 2− is the anion of the parent hexadentate H 2saltrien ligand) after the cleavage of the imidazolidine ring. The mononuclear complex has a structure with an N 4O 2 donor atom set of the hexadentate ligand forming a distorted octahedral coordination geometry around the metal atom as established from a crystal structure determination. The Fe–N(imine) distances are 1.934(10) and 1.948(9) Å, Fe–N(amine) distances are 2.062(8) and 2.076(9) Å and Fe–O(phenol) distances are 1.864(8) and 1.872(7) Å. The terminal oxygen donor atoms occupy cis positions and the remaining four nitrogen atoms (two cis amine and two trans imine) complete the coordination sphere. The mononuclear complex has a magnetic moment 1.89 μ B corresponding to the low-spin 3d 5 configuration. The UV–Vis spectrum of the end product, after the imidazolidine ring hydrolysis, is different from the spectrum of the initial reaction mixture containing the μ-bis(tridentate) ligand H 2L′.