ESI activity of Br⁻, BF₄⁻ , ClO₄⁻ and BPh₄⁻ anions in the presence of Li⁺ and NBu⁴⁺ counter-ions

To improve our understanding of the electrospray ionization (ESI) process, we have subjected equimolar mixtures of salts A⁺ X^- (A⁺  = Li⁺ , NBu₄⁺ ; X^-  = Br^- , ClO₄^- , BF₄^- , BPh₄^- ) in different solvents (CH₃ CN, tetrahydrofuran, CH₃ OH, H₂ O) to negative-ion mode ESI and analyzed the relative ESI activity of the different anionic model analytes. The ESI activity of the large and hydrophobic BPh₄^- ion greatly exceeds that of the smaller and more hydrophilic anions Br^- , ClO₄^- and BF₄^- , which we ascribe to its higher surface activity. Moreover, the ESI activity of the anions is modulated by the action of the counter-ions and their different tendency toward ion pairing. The tendency toward ion pairing can be reduced by the addition of the chelating ligands 12-crown-4 and 2.2.1 cryptand and is, although to a smaller degree, further influenced by the variation of the solvent. Complementary electrical conductivity measurements afford additional information on the interactions of the ionic constituents of the sample solutions. Copyright © 2017 John Wiley & Sons, Ltd.

Copper-63 NMR line width study of the copper(I)-acetonitrile system

The principal focus of this study is the (63)Cu NMR line widths in Cu(I)-acetonitrile (AN) solutions. The variations with the concentrations of Cu(I) salts (trifluoromethanesulfonate and perchlorate), added salts, water, chloride ion, and temperature have been studied. A quantitative analysis shows that the anomalous temperature dependence of the line widths is not due to ion pairing or anion complexation but results primarily from formation of a species with a different coordination number or less symmetrical arrangement of AN ligands than in the normal tetrahedral Cu(AN)(4)(+) ion. Solvent viscosity and ion pairing (with triflate) also are identified as factors having the expected effects on the line widths. The results of earlier studies also are discussed and analyzed by the current model where possible.