PH-DEPENDENT COORDINATION OF THE GLYCINATO DONORS OF NITRILOTRIACETATOPLATINATE(II), [PT-II(NTA)](-)

Two main species are formed when nitrilotriacetic acid (H(3)nta) displ aces Cl- ligands from PtCl42-. The resultant [Pt-II(nta)Cl](2-) and [P t(ntaH)Cl](-) complexes were examined by H-1 and C-13 NMR methods. The 1:1 complex is responsive to changes in pH, indicating a titratable g lycinato arm in [Pt-II(nta)Cl](2-) rather than a [Pt-II(nta)](x) polym er previously prepared by Smith and Sawyer. The major species (similar to 82% at pH 4.5) has two in-plane glycinato donors exhibiting an AB H-1 NMR quartet (H-a=4.40 ppm, H-b=4.25 ppm, J(ab)=16.3 Hz, area 2) an d a singlet for the third glycinato donor (3.85 ppm, area 1). The latt er is assigned as a weakly axially-associated glycinato donor which re nders [Pt-II(nta)Cl](2-) as a five-coordinate entity. The minor compon ent (similar to 17%) is the dichloro derivative having two pendant gly cinato arms (AB quartet: H-a=3.91 ppm, H-b=3.83 ppm, J(ab)=16.7 Hz, ar ea 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 o f the glycinato singlet as well as near coalescence of the in-plane gl ycinato donors, indicative of an associative/dissociative equilibrium of the axial glycinato donor which alters the coordination number of t he Pt-II 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](-) (H-1 NMR singlet, 4.08 ppm, area 1, pendant glycinato; AB quart et, H-a=4.36 ppm, H-b=4.26 ppm, J(ab)=16.4 Hz, area 2, in-plane pair o f glycinato donors). Further proton-induced dechelations of the in-pla ne glycinato donors occur over a 14 day period, forming a monodentate N-bound species thought to be [Pt-II(ntaH(3))Cl-3](-) with one glycina to H-1 NMR singlet (4.30 ppm). The existence of one chloride in [Pt-II (nta)Cl](2-), the major (82%) species, and two chlorides in the lesser (17%) species was confirmed by Pt-195 NMR. The Pt-195 NMR spectra ind icate that the axial interaction in [Pt-II(nta)Cl](2-) is very weak, w ith delta(Pt) shifts of -1309 ppm compared to -1317 ppm for mer-[Pt(mi da)Cl](-), an authentic four-coordinate analogue.