Wydział Chemii

Oleg A. Varzatskii

Sergey V. Shul'ga

Henryk Kozłowski

Elżbieta Gumienna-Kontecka

Łukasz Szyrwiel

Ekaterina G. Lebed

Yan Z. Voloshin

2014

Macroheterocycles

7

302-310

10.6060/mhc140496v

Naukowa

Angielski

Artykuł

Ionization pathways of iron(II) di- and hexachloro-mono- and bis-clathrochelates and their oximehydrazonate, dimethyl- and diamine-containing macrobicyclic analogs, and the cation-receptor properties of such cage compounds towards alkali metal cations (as individual species or the mixtures) as well as their competitive complexation in the presence of 18-crown-6 have been studied by ESI-MS method. Ionization of iron(II) mono- and bis-clathrochelates under the conditions of ESI-MS experiments was found to proceed via different pathways. The macrobicyclic iron(II) oximehydrazonate as an ionic associate of the macrobicyclic cation with BF₄^– anion undergoes the ionization by its heterolytic dissociation. The main pathways of ionization of the dioximate cage and bis-cage intracomplexes are substantially affected by ribbed substituents in their chelate fragments. The methyl- and amine-containing macrobicyclic complexes easily form anion-radical species by one-electron oxidation of their polyazomethine cage frameworks, whereas in the case of iron(II) dihalogenoclathrochelates the most intensive peaks correspond to their ionic associates with monocharged alkali metal cations. ESI-MS positive-mode spectrum of the iron(II) hexachloroclathrochelate contains no detectable peaks of the cationic species, which resulted either from its oxidation to the corresponding cation-radical or from its ionic associates with alkali metal cations. In the negative mode, an intensive peak assigned to the anion-radical product of one-electron reduction has been observed. As ESI mass spectrometry allows maintaining precise concentrations of the complex under study and that of “cationization agents” (i.e., the compounds that promote formation of cationic species of the analyte and are used in the case of low-ionizable complexes), the alkali metal tetraphenylborates were used as such agents to study cation-receptor properties of the iron(II) mono- and bis-clathrochelates with ribbed substituents of the different nature towards these metal ions. Iron(II) monoclathrochelates form two types of ionic associates with alkali metal cations with both the 1:1 and 2:1 stoichiometries, which are more and less intensive in their ESI-MSs, respectively, whereas those of bis-cage complexes contain the intensive peaks of only 1:1 ionic associates with high affinity towards Cs⁺ cation.

Macrocyclic compounds, Clathrochelates, iron complexes, ionic mass spectrometry, receptors

http://dx.doi.org/10.6060/mhc140496v