Abstract
Hydrolysis of γ Cu₂ (OH)₂CrO₄ at 160°C gives a new stable compound. It was possible to definitely attribute the complex formula Cu₁₁ (OH)₁₄ (CrO₄)₄ to this compound only after its complete structural investigation. This hydroxychromate crystallises in the triclinic system, with space groupe P-1 and Z = 1 formula units Cu₁₁ (OH)₁₄ (CrO₄)₄ per unit cell. The crystal structure of this compound was investigated after computation of a three-dimensional Patterson function which revealed the positions of the copper and chromium atoms. The positions of the oxygen atoms were investigated by Fourier difference synthesis. In this structure the distribution of copper atoms is as follows : seven copper atoms are set in octahedral layers where all the octahedral sites are occupied by Cu²⁺ ; equidistant from two octahedral layers of this first type are set four copper atoms forming octahedral links in which four of the possible octahedral sites are filled by copper. The chromate groups make the bond between these octahedral layers and links. The oxygen atoms or hydroxyl groups are set in parallel planes pratically equidistant but in the unit cell there are sometimes 7, sometimes 8 oxygen atoms or hydroxyls per layer.
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