Studies on Mass Spectrometry of Metal Chelates. II. Mass Spectrometric Investigation of Thiooxine Metal Chelates

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In every mass spectrum of the metal thiooxinates, the peak being attributable to the molecular ion was observed, and the mass units correspond to a 2 : 1 molar ratio chelate (ligand : metal). The loss of 160 mass units from the molecular ion was observed. This indicates that a cleavage of one molecule of the coordinated thiooxine from the molecular ions affords the fragment ion of a 1 : 1 ratio chelate. In the following fragmentation process, the group of Mn, Co, Ni, Cu, and Pd chelates and the group of Zn, Cd, Hg, and Pb chelates showed different pathway. In order to examine the stabilities of these metal thiooxinates under electron impact, the intensity ratio of a fragment ion peak of a 1 : 1 molar ratio chelate to a molecular ion peak was calculated and the following decreasing stability order in the central metal atom was observed ; Cd>Zn>Ni>Pd∼Co>Mn>Cu>Hg>Pb. This order is found to be quite similar to that of metal oxinates, reported in a previous paper. A definite correlation between these intensity ratios and the chargeradius ratio, e/r, and the ionization potential of the central metal atoms was shown.