Crystal structure and optical absorption spectra of LiCo(SO4)OH and its remarkable relationship to the Zn-Mn-silicate hodgkinsonite

Author(s)
Manfred Wildner, Gerald Giester
Abstract

Crystals of the compound LiCo(SO

4)OH were synthesised at low-hydrothermal conditions, and the crystal structure was determined and refined from single crystal X-ray diffraction data. LiCo(SO

4)OH crystallises monoclinic, space group P2

1/c, Z = 4, a = 9.586(2), b = 5.425(1), c = 7.317(1) Å, β = 109.65(1)°, V = 358.3 Å

3, wR2 = 0.0485 (2215 unique reflections, 78 variables). The structure is built from chains of edge-sharing, quite strongly bond-length and -angle distorted Co(OH)

3O

3 octahedra (< Co–O > = 2.126 Å), which are further linked by common corners, hydrogen bonds, and by properly shaped SO

4 tetrahedra (< S–O > = 1.476 Å) to sheets parallel (100). These sheets are connected to a three-dimensional framework by sharing corners with distorted LiO

4 polyhedra (< Li–O > = 1.956 Å). Apart from the isotypic sulfates of Mn

2+ and Fe

2+, only the molybdate LiCd(MoO

4)OH crystallises isostructural with LiCo(SO

4)OH. However, a very close structural relationship exists with the rare mineral hodgkinsonite, Zn

2Mn(SiO

4)(OH)

2, yielding crystal chemically very uncommon topological equivalents of Zn

2+ ≡ S

6+ and Si

4+ ≡ Li

+, aside from the expectable substitution Mn

2+ ≡ Co

2+. Polarised optical absorption spectra of LiCo(SO

4)OH reveal that the dominating spin-allowed

4T

1(P) band system of Co

2+ (d

7 configuration) is strongly split up and covers a prominent part (~ 15,500–24,500 cm

−1) of the visible spectral range, in accordance with the significant distortion of the Co(OH)

3O

3 polyhedron. The spectra are interpreted in terms of the Superposition Model of crystal fields, yielding a new set of intrinsic and interelectronic repulsion parameters for Co

2+.

Organisation(s)
Department of Mineralogy and Crystallography
Journal
Mineralogy and Petrology
Volume
117
Pages
317-324
No. of pages
8
ISSN
0930-0708
DOI
https://doi.org/10.1007/s00710-022-00807-w
Publication date
2023
Peer reviewed
Yes
Austrian Fields of Science 2012
105116 Mineralogy, 105105 Geochemistry
Keywords
ASJC Scopus subject areas
Geochemistry and Petrology, Geophysics
Portal url
https://ucrisportal.univie.ac.at/en/publications/c1465487-9a66-4bac-b13f-669cd538fd25