Electrospray mass spectrometric analysis of transition-metal halide complexes

A general electrospray mass spectrometric (ESMS) survey of uncharged transition-metal coordination complexes containing ancillary halide ligands has been carried out, in order to determine the dominant ionisation process(es). Ionisation via loss of the halide ligand was observed for most complexes, though ions containing coordinated solvent molecules, such as MeCN, were also seen, depending on the cone voltage employed. Protonation of parent complexes was rarely observed, even when ligands containing basic groups such as tri-isopropylphosphite were present, but aggregates with NH4+ cations were observed for cis-[PtCl2(Et2S)(2)] and for [p-cymene)OsCl2(PPh3)]. In a limited number of cases, displacement of (weakly-bonded) ancillary ligands as well as the halide occurred, e.g. Et2S in cis-[PtCl2(Et2S)(2)] and PPh3 in [RuCl2(PPh3)(3)] and [OsHCl(CO)(PPh3)(3)]. The formation of cleaner and more intense spectra can usually be facilitated by the addition of a small quantity of the volatile, stronger donor ligand pyridine (py) to the analyte solution, resulting in [M - halide + py](+) ions. This forms the method of choice for the routine analysis of the majority of neutral transition-metal halide complexes, and in particular, mononuclear complexes, except when labile ligands are present. In the case of the dinuclear complex [Pd2Cl2(dppm)(2)] (dppm = Ph2PCH2PPh2) addition of pyridine led to a more complex spectrum indicating a range of solvated dications formed by loss of both chlorides. (C) 1999 Elsevier Science S.A. All rights reserved.