title: Reversible extrusion and uptake of HCl molecules by crystalline solids involving coordination bond cleavage and formation.
abstract: Yellow crystalline salts (3-XpyH)2[CuCl4] (3-XpyH = 3-halopyridinium, X = Cl, Br) lose HCl upon exposure to air in an open vessel, yielding quantitatively blue crystalline coordination compounds [CuCl2(3-Xpy)2]. The reaction is prevented if the vessel is sealed, but can be driven forward under such conditions by providing a trapping agent for HCl, such as an aqueous solution of AgNO3. The reaction requires cleavage of Cu-Cl and N-H bonds and formation of Cu-N bonds. The metal coordination geometry also changes from distorted tetrahedral to square planar. Remarkably, the reaction is fully reversible upon exposure of the blue coordination compound to vapor from a concentrated aqueous solution of HCl, and the initial yellow crystalline salt results. The structural changes occurring in these reactions have been followed by X-ray powder diffraction, including Rietveld refinement, of the crystal structures.
authors.affiliation: Department of Chemistry, University of Sheffield, Sheffield S3 7HF, United Kingdom.
authors.forename: Guillermo
authors.initials: G
authors.lastname: Mínguez Espallargas
authors.forename: Lee
authors.initials: L
authors.lastname: Brammer
authors.forename: Jacco
authors.initials: J
authors.lastname: van de Streek
authors.forename: Kenneth
authors.initials: K
authors.lastname: Shankland
authors.forename: Alastair J
authors.initials: AJ
authors.lastname: Florence
authors.forename: Harry
authors.initials: H
authors.lastname: Adams