Electron Spin Resonance Studies of Bis (acetylacetonato)copper(II) Adsorbed on X-Type Zeolite. II. The Substitution Reaction of Ligands with Pyridine

Abstract

Abstract The interaction of bis(acetylacetonato)copper(II) (Cu(acac)2) adsorbed on X-type zeolite of the sodium form with pyridine was investigated by means of ESR. When a pyridine vapor was introduced to Cu(acac)2 on the zeolite, the spectral lines of the perpendicular g component for Cu(acac)2 were replaced by those consisting of a superhyperfine structure, which arises from the ligand nitrogen atoms. The observed spectrum was assigned to [Cu(pyridine)4]2+. Such a characteristic substitution reaction of Cu(acac)2 with pyridine was not, however, observed on silica gel nor in ordinary solvents. It is pointed out, on the basis of these results and of the considerations described in a preceding paper, that the reaction involves the following mechanism: the interaction of quasi-π-electrons in Cu(acac)2 with an electrostatic field originating from the cation on the zeolite lowers the stability of Cu(acac)2, and the complex is attacked by two adsorbed pyridine molecules and two pyridinium ions which are formed by the combination with protons on acid sites, resulting in the substitution reaction. In addition, [Cu-(pyridine)4]2+ was produced on other cation-exchanged zeolites and silica-alumina. The substitution reaction was also found when α-, β-, or γ-picoline was used instead of pyridine.