Unknown isopolyoxovanadate species detected by electrospray mass spectrometry

Electrospray mass spectrometry (ES MS) has been used to identify many previously unknown isopolyvanadate anions and cations in aqueous solutions under non-equilibrium conditions. There is direct evidence that the evaporation process in ES MS has resulted in significant chemical effects, thereby generating many of these previously undetected species. As a consequence, ES MS offers insight into the polymerisation process. For the ammonium metavanadate system, negative-ion ES MS yielded two series, namely: [HxVyOz]− (x=0 to 1; y=1 to 10; z=3 to 26) and [HxVyOz]2− (x=0, 1; y=3 to 17; z=9 to 44). Also, the [H2VO4]−, [V10O28]6− and [H5V10O28]− anions were detected. In the positive-ion mode, three series of polyoxovanadate cations were observed, namely: [Hm+1(VO3)m]+, [Hm−1VmO3m−1]+ and [Hm−3VmO3m−2]+. For the alkali metal metavanadate systems ions of the form [AVmO3m−2]− (m=2, 4, 6; A=Li+, Na+ and K+) were detected. In the positive-ion mode, at least two series of the form [Am+1(VO3)m]+ and [Am+3VmO3m+1]+ were observed. In all series, the protonated and unprotonated ions differed by {V2O5} mass units (characterised by ES MS as the formal building block in these clusters). At high cone-voltages, mixed-valence polyoxovanadate anions were observed for all the systems studied. On the other hand, for the positive-ion mode, the only mixed-valence polyoxovandates cations detected were for the potassium system.