Effect of alkali metal coordination on gas-phase chemistry of the diphosphate ion:: The MH2P2O7- ions

Systematic experimental and theoretical studies on anionic phosphate species in the gas phase are almost nonexistent, even though they could provide a benchmark for enhanced comprehension of their liquid-phase chemical behavior. Gaseous MH2P2O7- ions (M=Li, Na, K, Rb, Cs), obtained from electrospray ionization of solutions containing H4P2O7 and MOH or M salts as a source of M+ ions were Structurally assayed by collisionally activated dissociation (CAD) mass spectrometry and theoretical calculations at the B3LYP/6-31 + G* level of theory. The joint application of mass spectrometric techniques and theoretical methods allowed the MH2P2O7- ions to be identified as having a structure in which the linear diphosphate anion is coordinated to the M+ ion (I) and provides information oil gas-phase isomerization processes in the [(PO3MH2PO4)-M-...](-) clusters II and the [(P2O6MH2O)-M-...-H-...](-) clusters IV. Studies of gas-phase reactivity by Fourier transform ion cyclotron resonance (FTICR) and triple quadrupole (TQ) mass spectrometry revealed that the MH2P2O7- ions react with selected nucleophiles by clustering, proton transfer and addition-elimination mechanisms. The influence of the coordination of alkali metal ions oil the chemical behavior of pyrophosphate is discussed.