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 Pt-195, H-1 and C-13 NMR, X-ray crystallography, UV-Vis spectroscopy and high-resolution mass spectrometry. Pt-195 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 H-1 and C-13 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 Pt-195 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-, N-3(-), SCN-, CN-, Cl- and SO42-) gives strong evidence for the formation of pseudo five-coordinate complexes of the type [Pt(bipy-kappa N-2,N')(bipy-kappa N)(L)(n+) in the cases of OH-, S2O32-, N-3(-) and SCN-. The results of calculations aimed at determining the Pt-195 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-kappa N-2,N')(bipy-kappa N)(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+). (C) 2013 Elsevier Ltd. All rights reserved.