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Sorptive Reconstruction of the CuAlCl4 Framework upon Reversible Ethylene Binding

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posted on 14.08.2003, 00:00 by Roger M. Sullivan, Haiming Liu, D. Steve Smith, Jonathan C. Hanson, Derek Osterhout, Michael Ciraolo, Clare P. Grey, James D. Martin
Three ethylene adducts to CuAlCl4 have been characterized by single crystal and/or powder X-ray diffraction, 13C, 27Al and 63Cu MAS NMR and diffuse reflectance UV−vis spectroscopy. (C2H4)2CuAlCl4, a = 7.1274(5) b = 12.509(1) c = 11.997(3) β = 91.19°, Pc, Z = 4; α-(C2H4)CuAlCl4, a =7.041(3) b = 10.754(8) c =11.742(9) β = 102.48(6), P21, Z = 4 and β-(C2H4)CuAlCl4, a = 7.306(2), b = 16.133(3), c = 7.094(1), Pna21, Z = 4. Up to 2 equiv of ethylene (∼200 cm3/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 σ-interaction, because the AlCl4- groups also bound to copper prevent any significant π-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.