Spectroscopy of cobalt–ethylenediamine–oxygen adducts in the supercages of zeolites

Abstract

The complex [Co(en)₃]²⁺(en = ethylenediamine) can be synthesized in the supercages of faujasite-type zeolites by adsorption of gaseous en. On dehydrated cobalt–zeolites additional heating is necessary to enhance the mobility of Co²⁺ from the small cages to the supercages. Upon heating, [Co(en)₃]²⁺ decomposes to [Co(en)₂]²⁺ and to [Co(en)]²⁺. The mono and tris complexes are not capable of binding O₂ whereas the bis complex forms the 1 : 1 superoxo-complex [Co(en)₂(O₂)]²⁺ and the 2 : 1 monobridged peroxo-complex [{Co(en)₂}₂(O₂)]⁴⁺ with O₂. The former is preferentially formed when not more than one cobalt atom is in each supercage, the latter when more than one cobalt, statistically, is in each supercage. The 1 : 1 superoxo-complex is unstable, and its formation is only partially reversible. The amount of electron transfer from cobalt to O₂ is estimated to be 0.46 e, indicating a weak σ-donor ligand trans to O₂^– in the complex. When [Co(en)₃]²⁺ and physisorbed en are present in the supercages the interaction with O₂ is complex and involves oxidation of en with formation of water.