Multinuclear magnetic resonance studies of the aqueous products of the complexes cis- and trans-Pt(amine)2(NO3)2

Abstract

The hydrolyis or the aquation reactions of the compounds cis- and trans-Pt(amine)2(NO3)2 were studied in D2O in different conditions of pH. The products were characterized by multinuclear (195Pt, 13C, and 1H) magnetic resonance spectroscopy. In acidic medium, the product was [Pt(amine)2(D2O2)]2+ and for a few amines, trans- [Pt(amine)2(D2O)(NO3)]+ was detected. The 195Pt NMR resonances of the diaqua complexes were observed at higher fields for the cis compounds (avg. –1727 ppm) than for the trans isomers (avg. –1560 ppm). At basic pH, Pt(amine)2(OD)2 was formed and for ethylamine, trans-Pt(EtNH2)2(OD)(NO3) was detected. The cis compounds were also observed at higher fields than the trans isomers (–1706 ppm vs. –1574 ppm). The coupling constants with 195Pt were geometry dependent. The avg. 2J(195Pt-1H) values for the diaqua species were 66 (cis) and 57 (trans) Hz, while the avg. 3J(195Pt-1H) were 43 (cis) and 34 (trans) Hz for the diaqua compounds, and 43 and 37 Hz, respectively, for the dihydroxo species. The 2J(195Pt-13C) avg. values were 18 (cis) and 12 (trans) Hz and the avg. 3J(195Pt-13C) were 31 (cis) and 23 (trans) Hz for both the diaqua and dihydroxo compounds. For the cis isomers, at neutral pH, the monoaqua–monohydroxo species (avg. –1721 ppm) and the dihydroxo-bridged dimer (avg. –1353 ppm) were observed. For a few amines, the monohydroxo-bridged dimer was observed (avg. –1684 ppm) and its concentration increased with time. For the trans compounds, the monoaqua–monohydroxo species was observed at –1563 ppm (avg.). For a few amines, the hydroxo-bridged dimer was present. For methylamine, a third species assigned to a higher oligomer was observed after 6 months.Key words: platinum, amine, nitrato, hydrolysis, NMR, aquation.