Layered basic copper anion exchangers: chemical characterisation and X-ray absorption study

The local structure around copper in Cu2(OH)3OAc·H2O, and in the anhydrous iodide analogue prepared by ion exchange, has been determined by X-ray absorption spectroscopy at 77 K. For both compounds, the copper environment is compatible with a botallackite-type Cu2(OH)3Br arrangement, in which two crystallographically distinct copper atoms lie in 4 + 2 (oxygen + X) and 4 + 1 + 1 (oxygen + oxygen + X) environments (X = exchangeable anion OAc, I, Br etc.). Interatomic distances between copper and the exchangeable anion have been determined to be 2.78 and 3.15 Å in Cu2(OH)3OAc·H2O and Cu2(OH)3I, respectively, the latter representing an unusual example of a direct CuII—I bond. At least two Cu—Cu distances could be identified in the radial distribution function: r(CuCu)= 3.16 and 6.32 Å, signals from second and more distant neighbours being reinforced by a focussing effect along the linear chain of copper atoms in the layers.