The crystal structure of KCu(CN)2

Abstract

KCu(CN)2 is monoclinic, space group P21/c(C2h5) with four formula units per unit cell. The cell constants are α = 7.57, b = 7.82, c = 7.45 Å. and β = 102.2°. The trial structure was deduced from a three-dimensional Patterson followed by a three-dimensional Fourier synthesis. This structure was refined by the least-squares method. All computations were made on the Maniac. The analogous silver and gold compounds have discrete linear complex ions formed by sp hybridization of the metal. The copper compound has an entirely different structure. The complex ions form spiral polymer chains of composition [Cu(CN)2-]∞. The twofold screw axes pass through the centers of the chains. The chains are held together by the K+ ions. The Cu atom has assumed a threefold hybridized state, probably a distorted sp2 hybrid. The Cu(CN)2- units are held together by a Cu-N bond of 2.05 ± 0.02 Å. One CN group forms this bond while the other CN group protrudes from the chain Good evidence is presented for making a distinction between the C and N atoms. The two Cu-O bond lengths are 1.92 ± 0.02 Å. The C-N bonds are 1.15 ± 0.03 and 1.13 ± 0.03 Å. The C-Cu-C angle is 134.2 ± 0.9°.