alpha- and beta-CuAlCl(4): Framework Construction Using Corner-Shared Tetrahedral Metal-Halide Building Blocks.
Rapid quenching of a melt of CuCl and AlCl(3) results in the formation of the metastable framework structure, beta-CuAlCl(4). The structure, determined by single-crystal X-ray crystallography (space group Pna2(1), a = 12.8388(5) Å, b = 7.6455(3) Å, and c = 6.1264(3) Å, Z = 2), can be derived from a distorted hexagonal closest packed anion sublattice. Annealing at temperatures above 100 degrees C results in a phase transition to the more thermodynamically stable alpha-CuAlCl(4). The solid solution CuAlCl(4)(-)(x)()Br(x)() is described for both alpha and beta phases. The structures of alpha-CuAlCl(4) and alpha-CuAlBr(4), determined by single-crystal X-ray diffraction (space group P&fourmacr;2c, a = b 5.4409(1) Å and c = 10.1126(3) Å, V = 299.37(1) Å(3), Z = 2, and a = b = 5.7321(2) Å and c = 10.6046(8) Å, Z = 2, respectively), are derived from a distorted cubic closest packed anion sublattice. The mechanism for this phase transition is described in relation to that previously described for cristobalite-type structures. The structures of both alpha- and beta-CuAlCl(4) reveal large van der Waals channels, which are proposed to be important for the reversible adsorption of carbon monoxide and ethylene by these materials.
Martin
James D.
JD
Department of Chemistry, North Carolina State University, Raleigh, North Carolina 27695.
Leafblad
Brian R.
BR
Sullivan
Roger M.
RM
Boyle
Paul D.
PD