Synthesis and characterisation of some lanthanide Schiff base complexes

Abstract

The formation of a novel complex of praseodymium with the Schiff base ligand 3,5-dibromo-2-[3-hydroxypropylimino)methyl]phenol, or 3,5-dibromosalicylaldimine (Br2SalH.PrH) is reported. This ligand was chosen to prevent polymerisation, which is common in Schiff base complexes of lanthanides. It was postulated that the relatively bulky bromine substituents on the ligand would hinder this polymerisation from taking place. It was also hoped that the complexes formed would have greater solubility, to allow better characterisation, following the work of Attard in 1996 on lanthanide complexes of SalH.PrH and Cl-SalH.PrH, which proved to be insoluble in most solvents except DMF and the coordinating solvent DMSO. The perchlorate and bromide salts of praseodymium and lanthanum were prepared. In addition, the Schiff base ligand Br2SalH.PrH was prepared. The Reimer-Tiemann reaction was also used in the synthesis of two isomers of dimethyl-2-hydroxybenzaldehyde in the expectation that they could be converted to the respective Schiff base ligands. The lanthanide complexes of these ligands were expected to display a greater degree of solubility than those formed from the ligands used by Attard. This, however, was not confirmed since the yields of the reaction to prepare the precursors of the Schiff base ligands were too low to permit formation of the respective Schiff bases and subsequent preparation of their lanthanide complexes. The metal salts were reacted with the Schiff base ligand in order to synthesize the complexes, and different methods were utilized to encourage crystallization, with varying degrees of success. The products obtained were analyzed by means of infrared, ultraviolet and nuclear magnetic resonance techniques (where possible). Another objective of this dissertation was also to analyse the products by means of elemental analysis and magnetic susceptibility. This, however, was not possible, because of time constraints as well as problems with departmental apparatus.