PROTON NUCLEAR MAGNETIC RESONANCE STUDIES OF NITRILOTRIACETIC ACID N-METHYLIMINODIACETIC ACID AND IMINODIACETIC ACID COMPLEXES OF PALLADIUM(2)

Several 1:1 and 1:2 (metal ion:ligand) complexes of nitrilotriacetic acid (XTA), N-methyliminodiacetic acid (MIDA), and iminodiacetic acid (IDA) with palladium(II) have been synthesized and isolated, and their proton nmr spectra have been studied in aqueous solutions (D2O) as a function of pH and temperature. In the 1:1 complexes MIDA and IDA function as tridentate ligands forming two trans (with respect to the two carboxylate oxygen atoms) acetate chelate rings, with the fourth site of the square-planar Pd(II) occupied by a solvent molecule. Their spectra exhibit relatively sharp AB splitting patterns for the ligand acetate protons, which establishes that metal-ligand bonding is nonlabile. In the presence of added ammonia the spectra indicate the formation of several mixed ammine-MIDA and -IDA complexes. The 1:1 NTA complex appears to be a dimer or a polymer in which the ligand acts as a bridge between adjacent metal ions. The 1:2 complexes appear to have the trans (with respect to the nitrogen atoms) configuration, with each ligand forming one acetate ring. Infrared spectra of the complexes have been measured to characterize their structures further. © 1968, American Chemical Society. All rights reserved.