Aftereffects in zeolite‐encapsulated ⁵⁷Co‐complexes

Abstract

Tris(2,2'-bipyridyl)-⁵⁷Co^II and bis(2,2':6',2'-terpyridine)-⁵⁷Co^II complexes were synthesised in the supercages of zeolite‐Y in order to study the effect of molecular isolation on the aftereffects of the ⁵⁷Co(EC)⁵⁷Fe decay. As compared to the regular crystalline salts of the complex ions where, according to the emission Mössbauer spectra, the most abundant species is low‐spin Fe^II, the molecular isolation in the zeolite resulted in a larger fraction of low‐spin Fe^III and a varying amount of high‐spin Fe²⁺ species. In the investigated temperature range, 20 K to 295 K, the majority of the changes was observed above 80 K. In the case of tris (2,2'-bipyridyl)-⁵⁷Co^II-Y, the most characteristic change occurred in valence states, while for bis (2,2':6',2'-terpyridine)-⁵⁷Co^II‐Y, the temperature dependence of the spin states was more prominent. The change in the low spin valence states is explained partly by donor-acceptor properties of the zeolite lattice. The variation in the high spin fraction is explained by radiation damage of the ligand sphere and/or fragmentation of the complex ion followed by incomplete recombination in the supercage. Molecular isolation itself did not seem to increase the chance of fragmentation (as a consequence of charge neutralization following Auger ionization) of these highly conjugated complex molecules.