Mixed‐valence Compounds: AuO₂ and AuS

Abstract

Mixed-valence compounds are of great interest due to their interesting properties and wide applications. Recently, gold (Au) chemistry has experienced an unprecedented development. However, Au with mixed-valence states in Au-O compounds has not been reported thus far. Here, two hitherto unknown AuO and AuS compounds with mixed-valence character were identified with the aid of first-principles swarm structure searching calculations. AuO consists of quasi-square AuO moiety and AuO octahedron in which Au shows the mixed-valence states of III and V, the first example in Au-O binary compounds. AuS contains the linear AuS and quasi-square AuS units exhibiting Au mixed-valence states. The analysis of electronic property demonstrates that AuO and AuS are narrow band gap semiconductors with strong hybridization between Au 5d and O 2p or S 3p. With the increase of pressure, Au-O and Au-S compounds show completely different thermodynamic stabilities, resulting from distinct shifting of pressure-induced atomic orbital energy levels of O and S atoms. Our work provides an opportunity for understanding mixed-valence character in Au-O and Au-S compounds.

Au with sp3 Hybridization in Li5AuP2

“…Unexpectedly, there disappears stable Au–P composition (Figure S1). A similar structural instability induced by pressure has been reported in binary Au–H and Au–S systems, originating from the similar electronegativity between Au and H/S atoms, which is unfavorable for charge transfer and impedes the stabilization of high-pressure compounds. Breaking such charge balance via introduction of an electron or hole has been demonstrated to be an effective route to stabilize new ternary Au–H compounds. , …”

Pressure-induced new chemistry*

“…1(c)). [58] These studies not only provide a controllable method for achieving the diverse oxidation states of Au, but also widen the understanding of Au element.…”

Exploitation of mixed-valency chemistry for designing a monolayer with double ferroelectricity and triferroic couplings

“…Mixed-valence (MV) compounds with an element being in more than one oxidation state [1][2][3][4][5][6][7][8] (e.g., Prussian blue with a cyanide-bridged Fe(II)-Fe(III) structure) have been extensively studied as excellent model systems for the investigation of the intriguing physical chemistry of electron-and charge-transfer phenomena. In particular, the thermally and optically induced charge-transfer in MV compounds, as depicted by Marcus theory, is a fundamental topic and also has broad implications in complex biophysical processes such as photosynthesis.…”

“…Mixed-valence (MV) compounds with an element being in more than one oxidation state 1–8 ( e.g. , Prussian blue with a cyanide-bridged Fe( ii )–Fe( iii ) structure) have been extensively studied as excellent model systems for the investigation of the intriguing physical chemistry of electron- and charge-transfer phenomena.…”