INFLUENCES OF LIGAND AND OF ZEOLITE TOPOLOGY ON THE STRUCTURE OF CO-II SCHIFF-BASE CHELATES IN FAUJASITE-TYPE ZEOLITES

The reaction in dehydrated faujasite zeolites of two different topolog ies between charge-compensating Co-II cations and five different Schif f base ligands was studied by EPR and vis-near-IR spectroscopy. Tetrad entate as well as pentadentate ligands were used for this comparison, while the behavior of a faujasite with cubic symmetry (zeolite Y) was compared to that of EMT, a faujasite with hexagonal symmetry. After re action of the Schiff bases salen (bis(salicylaldehyde) ethylenediimine ) (1) and acacen (bis(acetylacetone) ethylenediimine) (2) with CoNaY z eolite, low-spin square-planar Co-II was observed in low concentration s in [Co-II(acacen)]NaY. In [Co-II(salen)]NaY, formation bf planar com plexes is doubtful. Use of these tetradentate ligands for oxygen activ ation in zeolite Y results in low concentrations of active, oxygen-bin ding Co-II. Incorporation of a nitrogen base into these Schiff bases r esults in the pentadentate ligands smdpt (bis(salicylaldehyde) methyln itrilodipropylenediimine) (3) and amdpt (bis(acetylacetone) methylnitr ilodipropylenediimine) (4). Use of these ligands greatly raises the fr action of the Co-II participating in the oxygen activation. When the C o-II form of the hexagonal faujasite NaEMT is loaded with smdpt (3), u p to 25% of the total Co-II reversibly binds dioxygen. Intrazeolitic C o-II was also reacted with pyren (bis(2-pyridinecarboxaldehyde) ethyle nediimine) (5), a ligand which occupies a position structurally interm ediate between Schiff bases and bipyridine. Different EPR parameters w ere observed for [Co-III(smdpt).O-2(-)] occluded in cubic faujasite (N aY) and hexagonal faujasite (NaEMT), reflecting the influence of the z eolite topology on complex formation. The dioxygen sorption of these n ew materials was studied quantitatively.