A COMPARISON OF THE SOLUTION BEHAVIOR OF PT(II) COMPLEXES OF N,N'-ETHYLENEDIAMINEDIACETATE AND N,N-ETHYLENEDIAMINEDIACETATE (EDDA AND UEDDA)

Pt(II) complexes of N,N'-ethylenediaminediacetate (edda) and N,N-ethyl enediaminediacetate (uedda) have been prepared from K2PtCl4 by stepwis e addition of the nitrogen backbone donors at pH similar to 2.9 (50-60 degrees C, 60 h) and further coordination of the deprotonated carboxy late donors at pH 24 (65-75 degrees C, 24 h). Coordination of the glyc inato donors was shown by H-1 and C-13 NMR and IR methods. The symmetr ical edda ligands form 38.3% (R,R)/(S,S)-[Pt(edda)] isomers and 61.7% mesa (R,S)/(S,R)-EPt(edda)] isomers. All four forms of [Pt(edda)] unde rgo aquation of one in-plane glycinato donor in 72 h as detected by th e appearance of a 13-line H-1 NMR pattern which may be deconvoluted in to four AB glycinato sets. These results are indicative of a pendant o r ion-paired glycinato donor for [Pt(edda)(H2O)] which is placed eithe r on the same side, or the opposite side, of the PtN2O2 plane and coor dinated glycinato donor. Pt-195 NMR shows that H2O is actually replace d by Cl-, i.e. [Pt(edda)Cl](-). The unsymmetrical [Pt-II(uedda)X] (X = H2O, Cl-, OH-) complex exhibits no major change over long time interv als (greater than or equal to 10 days, pD similar to 6). The presence of a minor species at 15% abundance may be a similarly structured spec ies as for [Pt(edda)(H2O)] with a pendant glycinato functionality. The major complex in solution is shown by the H-1 NMR with [NaCl] and [Na ClO4]-dependence studies to be [Pt(uedda)(H2O)] at low [Cl-] and [Pt(u edda)Cl](-) at 1.0 M Cl-. Pt-195 NMR confirms the formulation of X = H 2O at low [Cl-]. H-1 and C-13 NMR evidence supports one axially associ ated and one in-plane coordinated glycinato donor each for the major [ Pt(uedda)(H2O)] complex. The C-13 NMR shows only one type of glycinato donor with a chemical shift of 189.3 ppm for the major species, and t wo types for the 15% species (185.6 and 170.5 ppm). The major species of [Pt(uedda)(H2O)] has only one type of carboxylate stretch in the IR spectra (1661 cm(-1); shoulder feature at 1639 cm(-1)) which compares favorably with the fully-coordinated pair of glycinato donors of [Pt( edda)] (1640 cm(-1)). It is proposed that the structures of [Pt(uedda) (H2O)] and [Pt(uedda)Cl](-) are pseudosquare pyramids which illustrat es the capacity of Pt(II) to adopt five-coordinate, 18-electron comple xes when a suitable chelate ligand offers a fifth associable donor. Th ese species are similar to the five-coordinate intermediates of ligand substitution reactions of typical square-planar Pt(II) complexes.