A collisionally activated dissociation (CAD) and computational investigation of doubly and singly charged DMSO complexes of Cu2+

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The singly and doubly charged Cu(II)–DMSO complexes formed by electrospray have been examined by CAD and computation. The CAD spectra were obtained as a function of collision energy. The doubly charged ions, [Cu(DMSO)n]2+, were observed only for n ≥ 2. For n = 3, dissociation leads mainly to [Cu(DMSO)2]+ + DMSO+, with only a trace of [Cu(DMSO)2]2+. Although [Cu(DMSO)]2+ was never detected, computation shows that the n = 1 complex exists in a potential well. Loss of DMSO+ is computed to be exothermic for n = 1–3, the exothermicity decreasing as n increases. The singly charged complexes in the ESI spectra were [CuX(DMSO)n]+ (X = Cl, Br, NO3, HSO4, n = 1 or 2). The CAD spectra showed competition between electron transfer from anion to metal followed by loss of X and loss of DMSO+. Experiment and computation show that for [CuX(DMSO)]+, loss of X is the preferred decomposition at low collision energy. NBO analysis shows that electron transfer to Cu from DMSO decreases in [Cu(DMSO)n]2+ as n increases, the bonding becoming more electrostatic and less covalent. In [CuX(DMSO)n]+, the negative charge on X is much less than unity with most of the difference appearing on the DMSO ligand(s).Key words: copper–DMSO complexes, electrospray, CAD, structures.