Aftereffects in zeolite‐encapsulated 57Co‐complexes

Tris(2,2'-bipyridyl)-57CoII and bis(2,2':6',2'-terpyridine)-57CoII 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 Mossbauer spectra, the most abundant species is low‐spin FeII, the molecular isolation in the zeolite resulted in a larger fraction of low‐spin FeIII 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)-57CoII-Y, the most characteristic change occurred in valence states, while for bis (2,2':6',2'-terpyridine)-57CoII‐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.