The electronic spectra of the cobalt(II) ion in anhydrous cobalt(II) zeolite A in the presence of adsorbed unsaturated hydrocarbons demonstrate that olefins and acetylene are π bonded to cobalt in well defined surface complexes. Gravimetric adsorption data show that one ethylene molecule is bound by each cobalt ion with an energy of about −68 kJ mol−1. Theoretical analysis treating the unsaturated hydrocarbon as a low symmetry electrostatic perturbation to a tetrahedral Co(II) ion gives a quantitative interpretation of the band splitting in the electronic spectra. This splitting is distinguished from that occurring through the dynamic Jahn-Teller effect in purely tetrahedral Co(II) complexes. The low symmetry field contributions to the ligand field stabilization energies have been determined from the fine structure in the experimental spectra and have been found to decrease from ethylene to trans-2-butene in accord with increasing steric hindrance from substitutional methyl groups. These contributions are small, however, and do not exceed 5 kJ mol−1. The spectrum of the Co(II) zeolite A acetylene complex is similar to that of the ethylene complex but shows in addition features characteristic of charge transfer processes.

Optical absorption, mass spectroscopy, magnetic susceptibility, electron spin resonance, and gas adsorption studies of the activated dehydration of silver-exchanged zeolite A show that principally diamagnetic silver clusters are formed by the activated extraction of oxygen from (oxidation of) the zeolite lattice. This oxidation is formally two-electron and, coupled with intrazeolitic silver ion mobility, can account for the concerted reduction of pairs of silver ions without the formation of stable paramagnetic clusters. The predominant charged cluster (B) formed in the sodalite unit has a low-energy absorption band centered at 2.72 eV and a higher lying excitation at 3.8-3.9 eV. The nuclearity of this cluster is uncertain, although it is >6 and <14. Another cluster (C) appears to coexist with cluster B and has excitations at 3.5-3.6, 4.1-4.2, and 4.9-5 eV. Sorption of olefins induces the competitive and reversible desorption of silver ions from cluster B and leads to the formation of C. Three distinct intermediates (absorption maxima at 2.9, 3.1, and 3.3 eV) have been identified during silver ion desorption from cluster B. Another intermediate (cluster A; band maximum at 3-3.1 eV) has also been identified en route to the formation of cluster B. A superposition of this 3-3.1-eV intermediate absorption of cluster A with the 2.72-eV absorption of cluster B gives the so-called yellow form of silver zeolite A. This yellow color had previously been assigned to linear and doubly charged (paramagnetic) silver trimers trapped in the sodalite unit by Gellens et al.

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