Abstract: The invention is directed to a process for the separation of oxygen from an oxygen containing gas using an oxygen selective material comprising a transition element complex comprising a first transition element ion and one or more chelating ligands, wherein: i) said first transition element ion is capable of accepting intermolecular donation; ii) said chelating ligand or ligands provides up to four intramolecular donor sites to said transition element ion; iii) said chelating ligand or ligands provides an intermolecular donor site to a second transition element ion which is contained in second discrete transition element complex; and iv) said chelating ligand or ligands contains at least one substituent that inhibits &mgr;-peroxo dimer formation on said sorbent; wherein when said material is in deoxy form, the total number of donor sites to said first transition element ion is five.