LAYERED BASIC COPPER ANION-EXCHANGERS - CHEMICAL CHARACTERIZATION 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 angstrom in Cu2(OH)3OAc.H2O and CU2(OH)3I, respectively, the latter representing an unusual example of a direct Cu(II)-I bond. At least two Cu-Cu distances could be identified in the radial distribution function: r(Cu - - - Cu)=3.16 and 6.32 angstrom, signals from second and more distant neighbours being reinforced by a focussing effect along the linear chain of copper atoms in the layers.