Salt-Templated Open Frameworks (CU-2): Novel Phosphates and Arsenates Containing M3(X2O7)22- (M = Mn, Cu; X = P, As) Micropores 5.3 Å and 12.7 Å in Diameter
journal contributionposted on 26.10.1999, 00:00 by Qun Huang, Mutlu Ulutagay, Patrick A. Michener, Shiou-Jyh Hwu
We have recently isolated a novel family of salt-templated phosphates and arsenates, A2M3(X2O7)2·(salt) [where A = K, Rb, Cs; M = Mn, Cu; X = P, As]. The space-filling, charge-compensation alkali metal chloride salts can be removed conveniently without destroying the MXO framework. These materials (designated as CU-2-MXO) exhibit microporous structures (ca. 5.3 and 12.7 Å in diameter) in which the active transition metal sites are distributed in a spatially uniform manner throughout the bulk. The salt lattice functions as a structure-directing template. The single-crystal structure shows that the large pore contains a remarkable ACl/CsCl lattice that consists of two interpenetrating, square antiprismatic columns of ions. In contrast to organically templated microporous solids, these new materials were synthesized by conventional solid-state reactions at high temperatures. Consequently, the resulting compounds can endure extensive heating to ca. 650 °C. These materials, in fact, possess the highest thermal stability found thus far among zeolite and related materials. Along with the synthesis and structure of four CU-2-MXO compounds, we also report some preliminary results concerning studies of ion-exchange and topotactic deintercalation−intercalation reactions.