Transition metal chelates of some quinquedentate and tridentate ligands

Abstract

Transition metal chelates containing tridentate and quinquedentate ligands have been prepared and studied. Three bis-Schiff bases, N,N'-disalicylidene-4-R-2, 6-di(aminomethyl) anisole (R = Cl, Br, CH3) were synthesized by the condensation of corresponding diamines and salicylaldehyde. The bis-hydroxymethyl derivatives of p-substituted phenolic ethers, were treated with acetonitrile in presence of sulphuric acid, to give the corresponding bis-amides, which on hydrolysis gave the diamines. By the loss of two protons the Schiff bases act as doubly nega tively charged M(ONONO)quinquedentate ands,Storming neutral complexes of the type M(ONONO) (M ='~i, Cu, Fe, Co). FAB mAss spectra in all causes short the:parent protonated molecular ion (M(NONOH) for each metal complex, except for copper, where no such fan was observed . Although this could indicate the presence of five-cordinate monomeric species a detailed study of the electronic spectra suggests otherwise. It is therefore concluded t ha t nickel (II), copper(II), iron(II) and coba1t(II) form high-spin, po1ymeric six-coordinate complexes, presumably with oxygen bridging. However the uranyl complexes, U02(ONONO) have a pentagonal bipyramidal structure with the ligand acting as a dinegatively charged quinquedentate. The Schiff base, N-salicylidene-6-aminomethyl- .Z, 4-dichlorophenol was synthesized by the same procedure as above. Due to the loss of two protons, the Schiff base acts as doubly negatively charged ONO-tridentate ligand and neutral copper complex of the type CUZLZ was formed. A binuclear dimeric structure has been suggested for the complex. Structural elucidation entailed the use of reflectance spectra, Fast Atomic Bombardment mass spectra, X-ray diffraction patterns and magnetic susceptibility. 1,he C, Hand N -micro analysis and metal determination were carried out on all compounds which were synthesized Gravimetric methods were used to determine a~l metals (Ni, Cu, Co, Fe), except for uranium which was determined by calorimetric method.