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Issue 26, 2019
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Gold(i) sulfide: unusual bonding and an unexpected computational challenge in a simple solid

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Abstract

We report the experimental high-pressure crystal structure and equation of state of gold(I) sulfide (Au2S) determined using diamond-anvil cell synchrotron X-ray diffraction. Our data shows that Au2S has a simple cubic structure with six atoms in the unit cell (four Au in linear, and two S in tetrahedral, coordination), no internal degrees of freedom, and relatively low bulk modulus. Despite its structural simplicity, Au2S displays very unusual chemical bonding. The very similar and relatively high electronegativities of Au and S rule out any significant metallic or ionic character. Using a simple valence bond (Lewis) model, we argue that the Au2S crystal possesses two different types of covalent bonds: dative and shared. These bonds are distributed in such a way that each Au atom engages in one bond of each kind. The multiple arrangements in space of dative and shared bonds are degenerate, and the multiplicity of configurations imparts the system with multireference character, which is highly unusual for an extended solid. The other striking feature of this system is that common computational (DFT) methods fail quite spectacularly to describe it, with 20% and 400% errors in the equilibrium volume and bulk modulus, respectively. We explain this by the poor treatment of static correlation in common density-functional approximations. The fact that the solid is structurally very simple, yet presents unique chemical bonding and is unmodelable using current DFT methods, makes it an interesting case study and a computational challenge.

Graphical abstract: Gold(i) sulfide: unusual bonding and an unexpected computational challenge in a simple solid

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Supplementary files

Article information


Submitted
22 Jan 2019
Accepted
19 May 2019
First published
22 May 2019

This article is Open Access
All publication charges for this article have been paid for by the Royal Society of Chemistry

Chem. Sci., 2019,10, 6467-6475
Article type
Edge Article

Gold(I) sulfide: unusual bonding and an unexpected computational challenge in a simple solid

D. Santamaría-Pérez, D. Daisenberger, J. Ruiz-Fuertes, T. Marqueño, R. Chulia-Jordan, C. Muehle, M. Jansen, P. Rodriguez-Hernandez, A. Muñoz, E. R. Johnson and A. Otero-de-la-Roza, Chem. Sci., 2019, 10, 6467
DOI: 10.1039/C9SC00371A

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