Crystal structure and electronic properties of bis(2,2′-bipyridyl)-cyanocopper(II) nitrate dihydrate: a correlation of the in-plane angular distortion with the splitting of the electronic spectrum

Abstract

The crystal structure of the title compound [Cu(bipy)₂(CN)][NO₃]·2H₂O has been determined by X-ray analysis. It crystallises in the monoclinic space group, P2₁/n with a= 9.263(3), b= 24.678(4), c= 10.123(3)Å, β= 109.83(8)°, and Z= 4. The five-co-ordinate CuN₂N₂C chromophore has a distorted trigonal-bipyramidal stereochemistry related to a regular trigonal-bipyramidal stereochemistry by distortion towards square pyramidal. The cyanide ion is bonded to the copper atom in the trigonal plane, via the carbon atom at a distance of 1.974(5)Å. The three in-plane trigonal angles of 138.0, 126.5, and 95.4° show considerable distortion from 120°, and are considered responsible for the splitting in the twin-peaked electronic reflectance spectrum (12 820 and 14 920 cm^–1).