Fluxional chromophores of bis(di-2-pyridylamine)nitritocopper(II) cations: crystal structures and electronic properties of the complexes bis(di-2-pyridylamine)nitritocopper(II) nitrate and bis(di-2-pyridylamine)nitritocopper(II) perchlorate

The X-ray crystal structures of two cation-distortion isomers of [Cu(dpyam)2(ONO)](NO3) (1) and [Cu(dpyam)2(ONO)](ClO4) (2) complexes are reported and shown to contain an asymmetric cis-distorted CuN4O2 chromophore. In 1 the copper atom and the asymmetrically bonded nitrito group lie on a crystallographic C2 axis. The nitrito group is clearly disordered about the C2 axis giving a square pyramidal cis-distorted octahedral (4+1+1*) chromophore rather than a pseudo regular cis-distorted octahedral chromphore. In 2 a distortion of the CuN4O2 chromophore towards a square pyramidal (4+1+1*) geometry is also present, but with well-ordered and less asymmetric nitrito group. The polycrystalline ESR spectra of 1 and 2 are temperature independent suggesting that both complexes appear to be near the static distortion limit of the fluxional CuN4O2 chromophore geometry. The electronic reflectance spectra of 1 and 2 involve two bands at approximately 14 700 and 9800 cm−1 for 1, and approximately 14 970 and 10 000 cm−1 for 2 and relate to the underlying static CuN4O2 (4+1+1*) chromophore geometry.