Reversible extrusion and uptake of HCl molecules by crystalline solids involving coordination bond cleavage and formation

Espallargas, G.M. and Brammer, L. and van de Streek, J. and Shankland, K. and Florence, A.J. and Adams, H. (2006) Reversible extrusion and uptake of HCl molecules by crystalline solids involving coordination bond cleavage and formation. Journal of American Chemical Society, 128 (30). pp. 9584-85. ISSN 0002-7863

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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.