Crystal structure and electronic properties of bis(2,2′-bipyridyl)-nitratocopper( II ) nitrate monohydrate

The crystal structure of the title compound [Cu(bipy)2(ONO2)][NO3]·H2O (bipy = 2,2′-bipyridyl) has been redetermined by X-ray analysis in the triclinic space group P with a= 7.488(2), b= 10.017(2), c= 15.061 (2)Å, α= 106.183(4), β= 91.335(3), γ= 89.662(3)°, and Z= 2. The six-co-ordinate CuN2N′2OO′ chromophore has a (4 + 1 + 1*) stereochemistry related to the original square-based pyramidal stereochemistry by an asymmetrically co-ordinated nitrate group to give an unsymmetrical bicapped square-pyramidal structure. The single-crystal e.s.r. and polarised electronic spectra are reported and together are shown to offer the possibility of distinguishing this bicapped square-pyramidal structure from that of a (4 + 1 + 1*) distorted square-pyramidal structure or cis-distorted octahedral structure. A structural pathway is suggested to connect these three geometries of the [Cu(bipy)2(OXO)]+(OXO = ONO–, O2CMe–, or O2CH–) cation by a linear combination of the S1a and S2a modes of vibration of the parent tris(chelate)copper(II) complex.