Metal Ion Complexes of Aromatic Amino Acids. II. N-Substituted Amino Benzoic Acids

Abstract

This study has indicated that substitution on the nitrogen atom in aminobenzoic acid markedly decreases complex forming ability; this is especially true in the case of bulky electrophilic groups such as phenyl and acetyl. In these cases, the usual evidence accepted for the formation of coordination complexes was not present, and it was therefore concluded that only salts were formed from ligands bearing these groups on the nitrogen atom. The presence of the methyl group on the amino nitrogen reduces the ability to form complexes and also reduces the stability of the few complexes formed; this is in contrast to the substitution of methyl and other small groups on the ring. Using carbon-hydrogen ratios and infrared data, the structures assigned to the complexes are square planar with the exception of tetrahedral zinc (II) complexes. Usually water was present in the complex which stubbornly resisted removal; at least some of this water may have been coordinated, particularly in the cases where cations are known to prefer octahedral symmetry. The ratios for the complexes prepared from N-methylanthranilic acid were in every case two ligand anions to one metal cation. Ultraviolet-visible data were obtained with difficulty and in general substantiated the evidence obtained by infrared analysis. The presence of water tended to obscure these results, and the very limited solubility of the complexes in water and in other appropriate solvents precluded intensive analysis via ultraviolet-visible absorption spectrophotometry. Five coordination complexes and twenty-eight salts were produced of the forty-four combinations possible with these four acids as ligand source. The five complexes studied were previously unreported; however, the copper (II) and cadmium (II) complexes of N-methyl- and of N-phenylarthranilic acid reported by other workers 2 were, on the basis of the criteria used in this study, salts rather than coordination complexes. The stability series as determined from the degree of shifting in the infrared regions around 3400 cm-1 and 1000 cm-1 were shown to differ markedly from those series obtained for ring substituted aminobenzoic acids.