Abstract Two main species are formed when nitrilotriacetic acid (H3nta) displaces Cl− ligands from PtCl42−. The resultant [PtII(nta)Cl]2− and [Pt(ntaH, Cl]− complexes were examined by 1H and 13C NMR methods. The 1:1 complex is responsive to changes in pH, indicating a titratable glycinato arm in [PtII(nta)Cl]2− rather than a [PtII(nta)], polymer previously prepared by Smith and Sawyer. The major species (∼82% at pH 4.5) has two in-plane glycinato donors exhibiting an AB 1 NMR quartet (Ha = 4.40 ppm, Hb = 4.25 ppm, Jab = 16.3 Hz, area 2) and a singlet for the third glycinato donor (3.85 ppm, area 1). The latter is assigned as a weakly axially-associated glycinato donor which renders [PtII(nta)Cl]2− as a five-coordinate entity. The minor component (∼ 17%) is the dichloro derivative having two pendant glycinato arms (AB quartet: Ha = 3.91 ppm, Hb = 3.83 ppm, Jab = 16.7 Hz, area 2) and a lone in-plane glycinato donor (singlet, 4.03 ppm, area 1). At pH=3.0 the major species exhibits proton exchange-induced shifts of the glycinato singlet as well as near coalescence of the in-plane glycinato donors, indicative of an associative/dissociative equilibrium of the axial glycinato donor which alters the coordination number of the PtII center. This exchange is frozen out at pH 1.2 where the axial donor is fully removed by protonation as a pendant group in [Pt(ntaH)Cl]− (1H NMR singlet, 4.08 ppm, area 1, pendant glycinato; AB quartet, Hb = 4.36 ppm, Hb = 4.26 ppm, Jab = 16.4 Hz area 2, in-plane pair of glycinato donors). Further proton-induced dechelations of the in-plane glycinato donors occur over a 14 day period, forming a monodentate N-bound species thought to be [PtII(ntaH3)Cl3]− with one glycinato 1H NMR singlet (4.30 ppm). The existence of one chloride in [PtII(nta)Cl]2−, the major (82%) species, and two chlorides in the lesser (17%) species was confirmed by 195Pt NMR. The 195Pt NMR spectra indicate that the axial interaction in [PtII(nta)Cl]2− is very weak, with δPt shifts of −1309 ppm compared to −1317 ppm for mer-[Pt(mida)Cl]−, an authentic four-coordinate analogue.