The nature of species derived from [Pt(bipy)2]2+ in aqueous solution: X-ray structural, mass spectral, NMR, and computational studies

The reaction of [Pt(bipy)2]2+ with a variety of organic and inorganic ligands in aqueous solution has been studied by 195Pt, 1H and 13C NMR, X-ray crystallography, UV–Vis spectroscopy and high-resolution mass spectrometry. 195Pt NMR spectra of D2O solutions containing equimolar amounts of [Pt(bipy)2]2+ and the heterocyclic N donor ligands pyridine, 3-methylpyridine and 4-methylpyridine give evidence for the formation of at least one species, while quinoline appears to give only a single product under the same conditions. These results are supported by 1H and 13C NMR data. The complex [Pt(bipy)(py)2](ClO4)2 was isolated from a reaction mixture containing equimolar amounts of [Pt(bipy)2]2+ and pyridine, and was characterised by X-ray crystallography. The 195Pt NMR chemical shift of this material suggested the presence of [Pt(bipy)(R-py)2]2+ species in aqueous solutions containing equimolar amounts of [Pt(bipy)2]2+ and R-py (R-py = py, 3-Mepy, 4-Mepy). High-resolution mass spectral analysis of aqueous solutions containing [Pt(bipy)2]2+ and inorganic ligands L (L = OH−, S2O32-, N3-, SCN−, CN−, Cl− and SO42-) gives strong evidence for the formation of pseudo five-coordinate complexes of the type [Pt(bipy-κ2N,N′)(bipy-κN)(L)]n+ in the cases of OH−, S2O32-, N3- and SCN−. The results of calculations aimed at determining the 195Pt NMR chemical shifts of the possible species resulting from the reaction of [Pt(bipy)2]2+ with OH− in aqueous solution are consistent with the formation of pseudo five-coordinate [Pt(bipy-κ2N,N′)(bipy-κN)(OH)]+, but are not absolutely conclusive. However, the bonding energy of this complex is calculated to be significantly lower than that of any species resulting from OH− attack at a bipy ligand of [Pt(bipy)2]2+.

X-ray crystallography, 195Pt, 1H and 13C NMR spectroscopy, high-resolution mass spectrometry, UV–Vis spectroscopy and computational techniques are used to investigate the nature of species formed on addition of organic and inorganic ligands to [Pt(bipy)2]2+ in aqueous solution.Figure optionsDownload as PowerPoint slide