The coordination behaviour of 2-((E)-(tert-butylimino)methyl) phenol towards lanthanide nitrate and chloride salts

Abstract

Five novel complexes were prepared by reacting 2-((E)-(tert-butylimino)methyl)phenol (HL2) with Ln(NO3)3∙xH2O (Ln = Gd and Dy ; x = 6 and 5, respectively) and LnCl₃∙6H₂O (Ln = Nd, Gd and Dy). The crystal structures of the former two Ln(III) nitrate complexes are isostructural and the coordination sphere is composed of three monodentate HL₂ ligands bonded to the metal centre through the phenolic oxygen atom and three nitrate ions coordinated in a bidentate fashion. Both complexes are nine-coordinate and SHAPE analysis reveals that they adopted a muffin polyhedra geometric type. The average Ln-O_nitrate and Ln-O_phenolate bond lengths are 2.5059 and 2.2816 Å, respectively. The complexes derived from the chloride salts exhibited an octahedral geometry with four monodentate Schiff base ligands [Ln-O_phenolate distances range from 2.229(4) to 2.2797(18) Å] coordinating in the equatorial positions and two chloride ions [average Ln-Cl bond length is 2.6530 Å, and average Cl-Ln-Cl angles is 180°] in axial positions. The ligand coordinated through the phenolate oxygen with the phenolic proton migrating to the imino nitrogen to give a zwitterionic form of the ligand. There are weak C-H∙∙∙Cl interactions present and O-H∙∙∙N hydrogen bonds are also observed in the crystal packing.