Studies of polyhalide ions in aqueous and non-aqueous solution by electrospray mass spectrometry

Solutions of I2+ X–(X = Cl, Br, I. NCS) in both water and acetonitrile have been studied by electrospray mass spectrometry in order to identify the anions present. For I2/I–, there is no evidence of the I5– anion proposed earlier to explain deviations from ideality in the formation of I3– in aqueous solution; rather, the equilibrium I3–+ I– I42– is shown to be compatible with the mass spectrometric results, and with the earlier literature. With Cl–, Br– and NCS–, both classes of solution contain members of the series X3– X2I– XI2– I3–; this is ascribed to rapid redistribution processes rather than to the redox and/or photochemical reactions suggested by earlier workers. There is little qualitative difference between aqueous and acetonitrile solutions, except that aqueous I2/Cl– systems contain the ICl4– anion, whose decomposition in the gas phase produces the previously unknown ICl3– radical anion. No I2X– adducts were identified when X = OH–, NCO–, N3– or NO2–.