Polarisations of the copper(II) and uranyl electronic spectra of meta-zeunerite single crystals

Abstract

The electronic spectra of meta-zeunerite, Cu(UO₂)₂(AsO₄)₂,8H₂O, show clear separation of the copper(II)d–d bands and the bands due to the uranyl ion. The polarisations of the copper(II) bands are consistent with the following order of one-electron orbitals, d_x²–y² > d_xy > d_z² > d_xz, d_yz. From the crystal g-values the molecular orbital coefficients are calculated and then compared with the values for other copper(II)–oxygen systems of known crystal structure. The extents of in-plane and out-of-plane π-bonding are discussed. The polarisations of the uranyl bands are consistent with their assignment to the components of a ³Πâ†�¹Σ⁺ transition. Interpretation of the presence of z-intensity requires the use of acentric point-groups (C_∞v or C_4v). The vibrational interval in the band structure is related to the length of the U–O bonds.