DOE OSTI2020
Ag2HgI4 crystallizes in the monoclinic Cm space group. The structure is two-dimensional and consists of two I ribbons oriented in the (0, 1, 0) direction; one Ag3Hg2I5 sheet oriented in the (0, 0, 1) direction; and one Ag3HgI5 sheet oriented in the (0, 0, 1) direction. In each I ribbon, I1- is bonded in a 2-coordinate geometry to two equivalent I1- atoms. Both I–I bond lengths are 2.81 Å. In the Ag3Hg2I5 sheet, there are three inequivalent Ag1+ sites. In the first Ag1+ site, Ag1+ is bonded to four I1- atoms to form AgI4 tetrahedra that share corners with three equivalent HgI4 tetrahedra and corners with nine AgI4 tetrahedra. There are a spread of Ag–I bond distances ranging from 2.86–2.99 Å. In the second Ag1+ site, Ag1+ is bonded to four I1- atoms to form corner-sharing AgI4 tetrahedra. There are a spread of Ag–I bond distances ranging from 2.85–3.08 Å. In the third Ag1+ site, Ag1+ is bonded to four I1- atoms to form corner-sharing AgI4 tetrahedra. There are a spread of Ag–I bond distances ranging from 2.87–3.04 Å. There are two inequivalent Hg2+ sites. In the first Hg2+ site, Hg2+ is bonded in a 1-coordinate geometry to three equivalent I1- atoms. There are one shorter (3.52 Å) and two longer (3.91 Å) Hg–I bond lengths. In the second Hg2+ site, Hg2+ is bonded to four I1- atoms to form HgI4 tetrahedra that share corners with three equivalent AgI4 tetrahedra and corners with six equivalent HgI4 tetrahedra. There are a spread of Hg–I bond distances ranging from 2.69–3.28 Å. There are five inequivalent I1- sites. In the first I1- site, I1- is bonded in a 2-coordinate geometry to four Hg2+ atoms. In the second I1- site, I1- is bonded to one Ag1+ and three equivalent Hg2+ atoms to form corner-sharing IAgHg3 tetrahedra. In the third I1- site, I1- is bonded to four Ag1+ atoms to form corner-sharing IAg4 tetrahedra. In the fourth I1- site, I1- is bonded to four Ag1+ atoms to form corner-sharing IAg4 tetrahedra. In the fifth I1- site, I1- is bonded in a trigonal non-coplanar geometry to three equivalent Ag1+ atoms. In the Ag3HgI5 sheet, there are three inequivalent Ag1+ sites. In the first Ag1+ site, Ag1+ is bonded to four I1- atoms to form corner-sharing AgI4 tetrahedra. There are a spread of Ag–I bond distances ranging from 2.71–3.02 Å. In the second Ag1+ site, Ag1+ is bonded to four I1- atoms to form corner-sharing AgI4 tetrahedra. There are a spread of Ag–I bond distances ranging from 2.81–2.97 Å. In the third Ag1+ site, Ag1+ is bonded to four I1- atoms to form AgI4 tetrahedra that share corners with three equivalent HgI4 tetrahedra and corners with nine AgI4 tetrahedra. There are a spread of Ag–I bond distances ranging from 2.81–2.96 Å. Hg2+ is bonded to four I1- atoms to form HgI4 tetrahedra that share corners with three equivalent AgI4 tetrahedra and corners with six equivalent HgI4 tetrahedra. There are a spread of Hg–I bond distances ranging from 2.83–3.27 Å. There are five inequivalent I1- sites. In the first I1- site, I1- is bonded in a single-bond geometry to one Ag1+ atom. In the second I1- site, I1- is bonded to four Ag1+ atoms to form corner-sharing IAg4 tetrahedra. In the third I1- site, I1- is bonded to four Ag1+ atoms to form corner-sharing IAg4 tetrahedra. In the fourth I1- site, I1- is bonded to three equivalent Ag1+ and one Hg2+ atom to form corner-sharing IAg3Hg tetrahedra. In the fifth I1- site, I1- is bonded in a distorted T-shaped geometry to three equivalent Hg2+ atoms.