Electrospray ionization mass spectrometric study of platinum(II) complexes with 1,3,4-thiadiazoles and dimethyl sulfoxide

Abstract

By mixing 2,5-disubstituted-1,3,4-thiadiazoles (L) with platinum(II) chloride and dimethyl sulfoxide (DMSO) a number of complexes have been obtained and studied by the electrospray ionization mass spectrometry. Excellent correlation between the types of complexes observed and the arrangement of pyridine and thiadiazole nitrogen atoms has confirmed that we really deal with structurally defined complexes, not with electrostatic adducts which are very common in ESI. For platinum(II) coordinated by one nitrogen atom (from the thiadiazole ring or pyridine nitrogen atom), the observed complexes has been found to contain two DMSO molecules ([PtL(DMSO) 2Cl] + ion). For the compounds containing 1,3,4-thiadiazole ring substituted by 2-pyridyl moiety, platinum(II) has been coordinated by two nitrogen atoms (one pyridine and one from the thiadiazole ring) and the complex formed contained one DMSO molecule ([PtL(DMSO)Cl] + ion). The compounds containing 2,6-di(1,3,4-thiadiazol-2-yl)-pyridine moiety have formed non-DMSO containing complexes ([PtLCl] + ion) since the platinum(II) cation was coordinated by two nitrogen atoms of the thiadiazole ring and by one pyridine nitrogen atom. For the compounds able to form two types of complexes, their relative amounts have been shown to be substantially affected be the solvent used indicating that the recorded ESI mass spectra reflect the condensed phase. The compounds not containing pyridyl moieties but containing two thiadiazole rings have also yielded two types of complexes (containing one and two DMSO molecules), however, their relative amounts can be affected by the solvent used only if the thiadiazole rings are close to each other.