Author(s)

Hans Hermann Otto

Materialwissenschaftliche Kristallographie, Clausthal University of Technology, Clausthal-Zellerfeld, Germany.

Low-dimensional quantum spin systems with the Cu²⁺ central ion are still in the focus of experimental and theoretical research. Here is reported on growth of mm-sized single-crystals of the low-dimensional S = 1/2 spin compound Cu₆(Ge,Si)₆O₁₈·6H₂O by a diffusion technique in aqueous solution. A route to form Si-rich crystals down to possible dioptase, the pure silicate, is discussed. Motivated by previously reported incorrect assignments of UV-VIS spectra, the assignment of dd excitations from such spectra of the hexahydrate and the fully dehydrated compound is proposed in comparison to dioptase and selected Cu(II) oxo-compounds using bond strength considerations. Non-doped cuprates as layer compounds show higher excitation energies than the title compound. However, when the antiferromagnetic interaction energy as J_z·ln(2) is taken into account for cuprates, a single linear relationship between the Dq_e excitation energy and equatorial Cu(II)-O bond strength is confirmed for all compounds. A linear representation is also confirmed between ²A_1g energies and a function of axial and equatorial Cu-O bond distances if auxiliary axial bonds are used for four-coordinated compounds. The quotient Dt/Ds of experimental orbital energies deviating from the general trend to smaller values indicates the existence of H₂O respectively Cl⁻ axial ligands in comparison to oxo-ligands, whereas larger Dt/Dq_e values indicate missing axial bonds. The quotient of the excitation energy ²A_1g by 2·²E_g-²B_2g allows checking for correctness of the assignment and to distinguish between axial oxo-ligands and others like H₂O or Cl⁻.

Dioptase, Ge-Dioptase, Copper(II) Compounds, Cuprates, Crystal Growth, UV-VIS Spectroscopy, EPR, Color, d-d Excitations, Bond Strength, Super-Exchange Interaction

Otto, H. (2017) Crystal Growth of Cu6(Ge,Si)6O18·6H2O and Assignment of UV-VIS Spectra in Comparison to Dehydrated Dioptase and Selected Cu(II) Oxo-Compounds Including Cuprates. World Journal of Condensed Matter Physics, 7, 57-79. doi: 10.4236/wjcmp.2017.73006.