A structural profile of the bis(2,2′-bipyridyl)monochlorocopper(<scp>II</scp>) cation. Crystal structures of bis(2,2′-bipyridyl)monochlorocopper(<scp>II</scp>) perchlorate and the nitrate trihydrate

The crystal structures of the title compounds [Cu(bipy)2Cl][ClO4], (1), and [Cu(bipy)2Cl][NO3]·3H2O, (2), have been determined by X-ray diffraction methods using three-dimensional diffractometer data; the structures were solved by heavy-atom techniques and successive Fourier synthesis. Compound (1) crystallises in the monoclinic space group P21/c with a= 10.761(5), b= 12.253(5), c= 16.990(5)Å, β= 112.18(5)°, Z= 4, and (2) crystallises in the monoclinic space group P21/a with a= 14.305(5), b= 21.213(5), c= 8.234(5)Å, β= 114.90(4)°, Z= 4. The [Cu(bipy)2Cl]+ cation in both (1) and (2) involves a square-pyramidal distorted trigonal-bipyramidal CuN4Cl chromophore with the distortion in (1) greater than in (2). From a correlation of the bond-length and bond-angle distortion of the structures of five[Cu(bipy)2Cl]+ cation distortion isomers a structural profile has been constructed between a near regular trigonal-bipyramidal CuN4Cl chromophore of C2 symmetry, and a square-pyramidal chromophore. The electronic reflectance spectra have been established as an 'electronic criteria of stereochemistry' for the CuN4Cl chromophore, which involves a single peak at 12 500 cm–1 for the trigonalbipyramidal geometry and twin peaks at 13 240 and 10 470 cm–1 for the square-pyramidal distorted structure.