Crystal structure, XANES and charge distribution investigation of krennerite and sylvanite: analysis of Au—Te and Te—Te bonds in Au<sub>1–<i>x</i> </sub>Ag<sub> <i>x</i> </sub>Te<sub>2</sub> group minerals - Université de Lorraine Access content directly
Journal Articles Acta Crystallographica Section B : Structural Science, Crystal Engineering and Materials [2014-...] Year : 2022

Crystal structure, XANES and charge distribution investigation of krennerite and sylvanite: analysis of Au—Te and Te—Te bonds in Au1–x Ag x Te2 group minerals

Ginga Kitahara
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Makoto Tokuda
Hidetomo Hongu
Koichi Momma

Abstract

The structure refinement and XANES study of two gold-silver-tellurides [Au 1+x Ag x Te 2 , krennerite (x = 0.11-0.13) and sylvanite (x = 0.29-0.31)] are presented and the structures are compared with the prototype structure of calaverite (x = 0.08-0.10). Whereas the latter is well known for being incommensurately modulated at ambient conditions, neither krennerite nor sylvanite present any modulation. This is attributed to the presence of relatively strong Te-Te bonds (bond distances < 2.9 A ˚) in the two minerals, which are absent in calaverite (bond distances > 3.2 A ˚). In both tellurides, trivalent gold occurs in slightly distorted square planar coordination, whereas monovalent gold, partly substituted by monovalent silver, presents a 2+2+2 coordination, corresponding to distorted rhombic bipyramids. The differentiation between bonding and non-bonding contacts is obtained by computation of the Effective Coordination Number (ECoN). The CHARge DIstribution (CHARDI) analysis is satisfactory for both tellurides but suggests that the Te-Te bond in the [Te 3 ] 2À anion is not entirely homopolar. Both tellurides can therefore be described as Madelung-type compounds, despite the presence of Te-Te in both structures.
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hal-03633784 , version 1 (07-04-2022)

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Ginga Kitahara, Akira Yoshiasa, Makoto Tokuda, Massimo Nespolo, Hidetomo Hongu, et al.. Crystal structure, XANES and charge distribution investigation of krennerite and sylvanite: analysis of Au—Te and Te—Te bonds in Au1–x Ag x Te2 group minerals. Acta Crystallographica Section B : Structural Science, Crystal Engineering and Materials [2014-..], 2022, 78 (2), pp.117-132. ⟨10.1107/s2052520622000804⟩. ⟨hal-03633784⟩
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