Two-dimensional zeolite-like network in the new caesium copper aluminate Cs2CuAl4O8

Abstract

Monoclinic dicaesium copper tetraaluminate, Cs2CuAl4O8, space groupP21/c,a= 8.4551 (7),b= 10.012 (1),c= 17.073 (2) Å, β = 101.643 (9)°,Z= 6, was obtained by high-temperature crystallization from a phosphate flux. Its microporous crystal structure presents the first example of double layers built from [AlO4] tetrahedra combined in 4-, 6- and 8-rings, topologically similar to those found in theATT-type zeolites and isostructural minerals armstrongite, davanite and dalyite. These layers show a rare arrangement of three [AlO4] tetrahedra sharing one oxygen vertex. The aluminate slabs are further linked by chains of edge-sharing [CuO4] square planes to form a mixed anionic three-dimensional framework with Cs+cations in channels and cavities. An unusually short Cu...Cs distance of 3.166 Å is ascribed to the strong Jahn–Teller effect of Cu2+. The magnetic subsystem demonstrates properties of an alternating antiferromagnetic chain with a gap in the spectrum of magnetic excitations.