Multinuclear NMR study and crystal structures of complexes of the types cis- and trans-Pt(Ypy)(2)X-2, where Ypy = pyridine derivative and X = Cl and I

Complexes of the types cis- and trans-Pt(Ypy)(2)X-2 where Ypy is a methyl d erivative of pyridine and X = Cl or I were studied by spectroscopic methods , especially by multinuclear NMR spectroscopy. In Pt-195 MNR, the cis-dichl oro compounds were observed between - 1998 and - 2021 ppm in CDCl3, while t he trans compounds were found at slightly lower field, between - 1948 and - 1973 ppm. The diiodo species were observed at much higher field, between - 3199 and - 3288 ppm for the cis isomers and between - 3122 and - 3264 ppm f or the trans isomers. In H-1 NMR, the (3)J(Pt-195-H-1) coupling constants a re larger for the cis compounds (about 42 ppm) than for the trans isomers ( about 33 ppm). In C-13 NMR, the values of (3)J(Pt-195-C-13) were also found to be larger for the cis complexes. There seems to be a slight dependence of the pK(a) values of the protonated ligands on the delta(Pt) chemical shi fts. The presence of pi-bonding between Pt and the pyridine ligands do not seem very important. The crystal structures of three dichloro and five diio do complexes were determined, in an attempt to obtain information on the tr ans influence of the three ligands. The results have shown that the iodo li gand has the greatest trans influence. Chloro and pyridine ligands seem to have similar trans influence, although, the chloro ligand seems to have a s lightly larger influence than pyridine derivatives. One structure, trans-Pt (2-pic)(2)I-2, has shown a sm conformation of the two 2-picoline ligands. ( C) 1999 Elsevier Science S.A. All rights reserved.