ABSTRACT
Carbonyl adducts to CuMCl(4) (M = Al and Ga) have been characterized by single-crystal and/or powder X-ray diffraction, IR and diffuse reflectance UV/vis spectroscopy. Up to two equivalents of carbon monoxide ( approximately 200 cm(3)/g relative to stp) are sorbed at room temperature, with equilibrium binding pressures of below 0.5 atm of CO. The carbonyl bonding is shown to be nonclassical, implicating the dominance of sigma-bonding and absence of pi-back-bonding. Analysis of the crystalline structures of the parent and adduct phases provides an atomistic picture of the sorptive reconstruction reaction. Comparison of the reactivity of CO and ethylene with these CuMCl(4) materials, as well as other copper(I) halide compounds that exhibit classical and nonclassical modes of bonding, demonstrates the ability to tune the reactivity of the crystalline frameworks with selectivity for carbon monoxide or olefins, respectively.
ABSTRACT
Three ethylene adducts to CuAlCl(4) have been characterized by single crystal and/or powder X-ray diffraction, (13)C, (27)Al and (63)Cu MAS NMR and diffuse reflectance UV-vis spectroscopy. (C(2)H(4))(2)CuAlCl(4), a = 7.1274(5) b = 12.509(1) c = 11.997(3) beta = 91.19 degrees, Pc, Z = 4; alpha-(C(2)H(4))CuAlCl(4), a =7.041(3) b = 10.754(8) c =11.742(9) beta = 102.48(6), P2(1), Z = 4 and beta-(C(2)H(4))CuAlCl(4), a = 7.306(2), b = 16.133(3), c = 7.094(1), Pna2(1), Z = 4. Up to 2 equiv of ethylene ( approximately 200 cm(3)/g relative to stp) are sorbed at room temperatures and pressures as low as 300 Torr. The ethylene ligands are bound to copper (I) primarily through a sigma-interaction, because the AlCl(4)(-) groups also bound to copper prevent any significant pi-back-bonding. The olefin binding is reversible and has been characterized by gravimetric and volumetric adsorption analysis and by time and pressure resolved synchrotron powder X-ray diffraction. Comparison of the parent crystal structure to those of the adduct phases provide an atomistic picture of the sorptive reconstruction reactions. These are proposed to proceed by a classic substitution mechanism that is directed by the van der Waals channels of the parent crystalline lattice.
ABSTRACT
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.
