ChemInform Abstract: THE ELECTRONIC STRUCTURE OF COPPER IN THE POLYMER POTASSIUM BIS(CARBONATO)CUPRATE(II) AS DETERMINED FROM PRECISE X‐RAY DIFFRACTION DATA

Abstract

The crystal structure of the polymer potassium bis(carbonato)cuprate(II), K2[Cu(CO3)2], has been investigated in terms of the electronic structure of the copper atom. Single-crystal X-ray diffraction data with (sinθ)/λ⩽ 10.8 nm–1, which were previously used in a 3σ(I) refinement of the crystal structure, were employed. Crystals are orthorhombic, space group Fdd2, Z= 8, a= 1.142 5(3), b= 1.765 8(4), c= 0.615 4(2) nm. All 1 693 independent reflections were used in a least-squares refinement on intensity values. Final agreement indices were R 0.029 and χ 2.027. The copper atom is in an essentially square-planar environment of four oxygen atoms from the bridging carbonato-groups [Cu–O 192.9(1) and 193.3(1) pm]. The final difference-Fourier synthesis showed non-centrosymmetric areas of positive and negative deformation charge density on opposite sides of the CuO4‘plane.’ These regions of charge were included in the scattering model as spherical scatterers, and their populations refined to ±0.31 (4) electrons at fixed axial positions 55 pm from the copper atom. The dipole moment on the copper atom, parallel to the c crystal axis, is of magnitude 0.5(1)× 10–29 C m. The symmetry of these deformation density features does not follow the local (bonded) square-planer symmetry of the copper atom environment. Two Cu ⋯ CO contacts of ca. 280 pm, which occur in only one axial direction, seem to be involved in the polarisation of the valence electrons of the copper atom. The non-centrosymmetry of these deformation density features precludes their modelling in terms of 3d or 4s atomic orbital populations.