CRYSTAL-STRUCTURE OF ZEOLITE-A WITH POTASSIUM CLUSTERS AND CONTINUA

A single crystal of fully dehydrated sodium zeolite A reacted with 0.3 Torr of potassium vapor at 300-degrees-C. Its structure was determined by X-ray diffraction methods at 24-degrees-C in the cubic space group Pm3mBAR. Not only have all Na+ ions have been replaced with K+ by redox reaction, but additional potassium atoms were sorbed to give K(n)-A, n = 14 to 15, per 12.298(2) angstrom unit cell. Crystallographic results show that cationic tetrahedral K4 and/or triangular K3 Clusters have formed in the sodalite cavities of zeolite A. The partially reduced ions of these clusters interact primarily with oxygen atoms of the zeolite structure rather than with each other. Four potassium ions per unit cell lie on 3-fold axes in the large cavity where each coordinates trigonally to three oxygens of a six-oxygen ring. All remaining potassium ions, three in the eight-oxygen-ring windows and four opposite four-oxygen rings, are loosely bound together by ca. one or two electrons per unit cell. In each large cavity, four four-ring potassium ions form a square which is capped by an eight-ring potassium ion. Each such unit is connected to four others by bridging eight-ring potassium ions to form layers. These layers appear structurally to be two-dimensional metallic continua.