High-pressure synthesis of an arsenopyrite-type polymorph of <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:msub> <mml:mi>ReS</mml:mi> <mml:mn>2</mml:mn> </mml:msub> </mml:math> recoverable to ambient conditions

Transition-metal dichalcogenides have attracted a great deal of attention in the context of two-dimensional materials because of their electronic properties, derived from their layered crystal structures, as well as their exfoliability. Surprisingly, the combination of high pressure and high temperature has been rarely exploited in the study of these systems, although it is expected to be an efficient way of inducing the formation of novel polymorphs. Here, rhenium and carbon disulfide were observed to react at a pressure of 54 GPa in a laser-heated diamond anvil cell to form a hitherto unknown polymorph of rhenium disulfide, denoted as <a:math xmlns:a="http://www.w3.org/1998/Math/MathML"> <a:mrow> <a:mi>m</a:mi> <a:mi>P</a:mi> <a:mn>12</a:mn> <a:mtext>−</a:mtext> <a:msub> <a:mi>ReS</a:mi> <a:mn>2</a:mn> </a:msub> </a:mrow> </a:math> in the Pearson notation. Its crystal structure was solved and refined using synchrotron single-crystal x-ray diffraction data, revealing that <b:math xmlns:b="http://www.w3.org/1998/Math/MathML"> <b:mrow> <b:mi>m</b:mi> <b:mi>P</b:mi> <b:mn>12</b:mn> <b:mtext>−</b:mtext> <b:msub> <b:mi>ReS</b:mi> <b:mn>2</b:mn> </b:msub> </b:mrow> </b:math> adopts the arsenopyrite structure type (space group <c:math xmlns:c="http://www.w3.org/1998/Math/MathML"> <c:mrow> <c:mi>P</c:mi> <c:msub> <c:mn>2</c:mn> <c:mn>1</c:mn> </c:msub> <c:mo>/</c:mo> <c:mi>c</c:mi> </c:mrow> </c:math> ). The structure is characterized by an extended three-dimensional framework of corner- and edge-sharing distorted <d:math xmlns:d="http://www.w3.org/1998/Math/MathML"> <d:msub> <d:mi>ReS</d:mi> <d:mn>6</d:mn> </d:msub> </d:math> octahedra. Raman spectroscopy data further confirm the formation and structure of <e:math xmlns:e="http://www.w3.org/1998/Math/MathML"> <e:mrow> <e:mi>m</e:mi> <e:mi>P</e:mi> <e:mn>12</e:mn> <e:mtext>−</e:mtext> <e:msub> <e:mi>ReS</e:mi> <e:mn>2</e:mn> </e:msub> </e:mrow> </e:math> . Remarkably, upon decompression, <f:math xmlns:f="http://www.w3.org/1998/Math/MathML"> <f:mrow> <f:mi>m</f:mi> <f:mi>P</f:mi> <f:mn>12</f:mn> <f:mtext>−</f:mtext> <f:msub> <f:mi>ReS</f:mi> <f:mn>2</f:mn> </f:msub> </f:mrow> </f:math> was recovered to ambient conditions and found to be stable in air. Thermodynamic, electronic, and bonding properties of the new phase were also studied computationally within the framework of density functional theory. From these, <g:math xmlns:g="http://www.w3.org/1998/Math/MathML"> <g:mrow> <g:mi>m</g:mi> <g:mi>P</g:mi> <g:mn>12</g:mn> <g:mtext>−</g:mtext> <g:msub> <g:mi>ReS</g:mi> <g:mn>2</g:mn> </g:msub> </g:mrow> </g:math> is found to be semimetallic at 0 GPa, and to have a lower enthalpy than the previously known <h:math xmlns:h="http://www.w3.org/1998/Math/MathML"> <h:msub> <h:mi>ReS</h:mi> <h:mn>2</h:mn> </h:msub> </h:math> polymorph from <i:math xmlns:i="http://www.w3.org/1998/Math/MathML"> <i:mrow> <i:mo>∼</i:mo> <i:mn>0.5</i:mn> <i:mspace width="0.28em"/> <i:mi>GPa</i:mi> </i:mrow> </i:math> onwards. The discovery of this new compound warrants further investigations of its physical properties, and may open new possibilities for applications.