Nanoelectrospray MS and MS-MS investigation of two polydendate Lewis acids, (C6F4Hg)3 and o-C6F4(HgCl)2, characterization and halide binding selectivity
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The coordination of halide anions by two polyfunctional Lewis acids, namely trimeric perfluoro-ortho-phenylene mercury (1) and 1,2-bis(chloromercurio)tetrafluorobenzene (2) has been monitored by negative ion nanoelectrospray mass spectrometry using a hybrid quadrupole time-of-flight instrument. Experiments carried out on compound 1 in the presence of halide anions show the formation of the anionic complexes, [1X]- and [(1)2X]-. The latter are likely to exhibit a bridged structure in which the halide anion is sandwiched by two molecules of 1. In order to determine the anion binding selectivity of 1, relative affinity measurements were carried out and reveal the following order: I->Br->Cl->F-. After normalization of the halide binding affinities to that of iodide, the following values could be obtained: I- 100%, Br- 9.51.6%, Cl- 2.41.5%, and F- 0.30.1% indicating that 1 is 10 less likely to bind bromide, 40 less likely to bind chloride, and 400 less likely to bind fluoride than iodide. Two fragmentation methods, namely nozzle-skimmer fragmentation and CID MS-MS, were used to further characterize the anionic complexes of 1. Experiments carried out on 2 in the presence of different halides gave widely varied results. With excess chloride, the anionic complex [2Cl]- is formed. In the presence of excess bromide, 2 is converted into 1,2-bis(bromomercurio)tetrafluorobenzene (3) and detected as the bromide complex [3Br]-. With excess iodide, 2 undergoes a condensation reaction to form 1, which is detected as the iodide complex [1I]-. 2002 Elsevier Science B.V. All rights reserved.
