Inorgunic Chemistry COS rRIBU 110s FROM
THE D E P A R TMEK
rNIVERSITY O F CALIFORNIA,
r
O F CHEXISTRY,
RIVERSIDE, CALIFORNIA 92502
Proton Nuclear Magnetic Resonance Studies of Nitrilotriacetic Acid, N-Methyliminodiacetic Acid, and Iminodiacetic Acid Complexes of Palladium(I1) BY B. B. S M I T H
AND
DOS.4LD T. SAWYER
Received Febmaujl 21, 1968 Several 1: 1 and 1:2 (metal ion: ligand) complexes of nitrilotriacetic acid (NTA4),?*'-rnetliyli~iiiriodi~c~tic acid (MTD:i), and iminodiacetic acid i1D.A) with palladiuiiiill) have been synthesized arid isolated, arid their proton iirnr spwtra Iiavc heeti studied in aqueous solutions (DzO) as a function of pH and temperature. In the 1: 1 complexes M I D X and 1Il.A functioti a s tridentate ligands forming two imns (with respect to the two carboxylate oxygen atoms) acetate chelate rings, with the fourth site of the square-planar Pd(I1) occupied by a solvent niolecule. Their spectra exhibit relatively sharp AB splitting patterns for the ligand acetate protons, which establishes t h a t 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 t o be a dimer or a polymer in which the ligand acts as a bridge between adjacent metal ions. T h e 1: 2 complexes appear to have the imns (with respect t o the nitrogen atoms) configuration, with each ligand forming one acetate ring. Infrared spectra of the complexes have been measured t o characterize their structures further.
Nitrilotriacetic acid (NTA), IS-methyliminodiacetic acid ( M I DA), and iminodiacetic acid (1 DA) form
in which the metal-ligand bonding is characteristically nonlabile, exhibit such AB patterns. The spectra of other complexes, in which the metal---ligandbonding is more labile,3~4~7~10-12 can exhibit AB patterns for the RAT/CH2CooH in the MIDA and IDA cases, although acetate protons ,\ CHzCOOH they are not observed in the corresponding KTA comXTA, R = CHzCOOH plexes. MIDA, R CH3 I n the present paper the synthesis and isolation of IDA, R = H several new Pd(I1)-NTA, -XIDA, and -IDA comstable metal complexes in solution which have been plexes and the results of a detailed study of their prostudied extensively in terms of their formation conton nmr spectra in aqueous solutions (DzO) as a funcstants.' NTA forms complexes containing three tion of pH and temperature are summarized. Pd(I1) chelate rings while both MIDA and IDA form comcharacteristically forms four-coordinate, square-planar plexes with two rings.2 complexes, in which the metal-ligand bonding is exRecently, several proton nmr studies of diamagpected to be nonlabile. The spectra, which provide netic3-ln and paramagnetic11%12 metal-NTA, -MIDA, insight to the structures of the complexes and their and -IDA complexes in aqueous solutions have been metal-ligand bond dynamics, represent the first proton reported. These, and those reported for related comnmr studies of square-planar metal-NTA, -MIDA, and plexes,13-16have proved useful in elucidating the struc-IDA complexes. The system is of interest in terms of tural and bonding features of the complexes. The metal-ligand bond lability because it probably repreprevious work has established that AB splitting patsents an intermediate case between the inert Co(1II) terns are observed for the ligand acetate protons with and Rh(II1) systems and more labile systems. certain metal ions. Thus, the spectra of the C O ( I I I ) ~ I ~ Two proton nmr studies of Pd(I1) and Pt(I1) comand Rh(III)8complexes with NTA, MIDA, and IDA, plexes with ethylenediaminetetraacetic acid (EDTA) and amino acidsl6 have been discussed recently; their (1) L. G. Sillen a n d A. E. Martell, "Stability Constants of Metal-Ion spectra exhibit AB patterns for the acetate protons. Complexes," Special Publication S o . 17. T h e Chemical Society, London. 1964, and references given therein. The infrared spectra of the complexes have been (2) G. Schwarzenbach, E. Kampitsch, and I
