Abstracts Chemistry

Studies of the coordination behavior of substituted nitrogen donor ligands

by Frank C. March

This work is concerned with metal-complexes of extensively conjugated heterocyclic nitrogen donor ligands. Part I Four-coordinate complexes of zinc(II), cadmium(II), mercury(II) and palladium(II) of general formula MLLuPc₂ have been prepared with the ligands 4,4'-dicarboxyethyl-3,3',5,5' tetramethyldipyrromethene and 3,4'-dicarboxyethyl-5-chloro-3',4,5'-trimethyldipyrromethene. The complexes involve bidentate coordination of the dipyrromethene ligands. Those of the Group IIb metals are near regular tetrahedral while the palladium complex shown in this work to be square plansar. Complexes of palladium(II) of general formulae Pd₂Cl₂L₂ and PdX(L)(LH), where X is Cl⁻ and Br⁻ and L is either of the dipyrromethenes have also been prepared. Both types are square planar four-coordinate complexes, the first being chloro-bridged with two bidentate dipyrromethene ligands, and the second having one monodentate and one bidentate dipyrromethene ligand. The electronic absorption spectra of all the complexes have been measured and the observed bands have been assigned to intraligand π → π* transitions and to metal → ligand charge transfer transitions The proton magnetic resonance spectra of the complexes have been recorded and resonance peaks have been assigned to protons of particular groups substituted on the dipyrromethene ligands. The results of both these spectral studies are discussed with reference to the stereochemistry about the metal ion and the influence of ligand substituents on the metal-ligand bonding. The crystal and molecular structure of bis-(4,4'-dicarboxyethyl-3,3'-5,5'-tetramethyldipyrrometheneto-palladium(II) has been determined from a single crystal diffraction study. The compound is “stepped" square planar and the dipyrromethene ligands are found to deviate considerably from planarity. The structure of this compound is compared with those which have studied previously. The influences are found to similar compounds on stereochemistry of the metal ion (copper(II), nickel(II) and palladium(II)) and of bulky ligand substituents are discussed. Part II A number of o-phenanthroline complexes of iron(II) and ruthenium(II) have been prepared. These are all six-coordinate and have general formulae M(phen)₃²⁺ and M(phen)₂X₂ where X is Cl-, Br-, I-, SCN- and ON-, and phen is o-phenanthroline, 5-methyl-o-phenanthroline, 5-chloro-o-phenanthroline or 5-nitro-o-phenanthroline.. The electronic spectra of these complexes have been investigated in solution or in the solid state. Bands have been assigned to metal → ligand charge transfer transitions and intraligand π → π* transitions from comparisons with the results of earlier studies. Energies of the electronic transitions are discussed with reference to both the influence of the ligands and of the substituents on the phenanthroline ligand on the metal-ligand π-interactions.