Crystal structure, electronic absorption spectra, and crystal field superposition model analysis of Li2Co3(SeO3)4

Abstract Single crystals of the new compound Li 2 Co 3 (SeO 3 ) 4 have been synthesized under low-hydrothermal conditions. The structure was determined by direct methods from single crystal X-ray diffraction data (monoclinic, space group P 2 1 / c , a = 8.095(2) Å, b = 9.236(3) Å, c = 7.781(2) Å, β = 115.76(1)°, V = 523.9 Å 3 , Z = 2; R 1 = 0.034 for 1613 F o > 4 σ ( F o ) and 98 variables). Li 2 Co 3 (SeO 3 ) 4 builds a framework structure composed of one type of [4 + 2] coordinated Li atoms and each two crystallographically different CoO 6 octahedra and pyramidal SeO 3 groups. The polyhedra of lithium and of one type of the cobalt atoms exhibit uncommonly strong irregular distortions. Polarized electronic absorption spectra of Li 2 CO 3 (SeO 3 ) 4 from 35000 to 4000 cm −1 were obtained by microscope-spectrometric techniques. The spectra were evaluated in terms of crystal field superposition model calculations for both triclinic Co 2+ sites giving the first complete set of superposition model parameters for Co 2+ , i.e. the intrinsic parameters [unk] 2 = 7000 cm −1 and [unk] 4 = 4740 cm −1 , and the power-law exponents t 2 = 5.5 and t 4 = 3.1. The interelectronic repulsion parameters are Racah B = 805 cm −1 and Racah C = 3630 cm −1 . As already observed for several other selenite compounds, the derived crystal field strength parameters Dq cub again indicate a rather low position of the [SeO 3 ] 2− anion within the range of oxygen-based ligands in the spectrochemical series.