The influence of ligand substituents and donor atom sets on the gas phase electron attachment reactions of bis‐chelates of nickel(II)

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Abstract
Electron attachment reactions and negative ion mass spectra which were obtained under negative chemical ionization conditions have been examined for a series of 21 nickel(II) bis‐chelates of formula Ni[R1CXCHCYR2]2. Three ligand donor atom sets (X, Y), respectively O4, O2S2, S4 were investigated for each of the substituent combinations, viz.: R1=CH3, CF3 or C2H5O, R2=CH3; R1=C6H5, CH3 or CF3, R2=C6H5; and R1 = R2 = tert−C4H9. While the ligand substituent combinations exerted considerable influence over the various ion decomposition reactions, the relative molecular ion stabilities were largely dependent on the ligand donor atom sets and followed the sequence O4⩾ O2S2>S4 for most substituent combinations. Rationalizations are offered in terms of reductive electron capture reactions involving metal‐based orbitals, as well as the increasing stabilities of reaction products as sulphur is incorporated into the ligand donor atom sets. A comparison is also given of negative ion mass spectral data obtained under electron impact conditions as well as negative chemical ionization conditions when methane was used as an electron energy moderating gas.

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