DOE OSTI2020
(K)2K2Hg2Sn21 crystallizes in the orthorhombic Ama2 space group. The structure is three-dimensional and consists of eight potassium molecules and one K2Hg2Sn21 framework. In the K2Hg2Sn21 framework, there are two inequivalent K sites. In the first K site, K is bonded in a 8-coordinate geometry to eight Sn atoms. There are a spread of K–Sn bond distances ranging from 3.91–3.96 Å. In the second K site, K is bonded in a 8-coordinate geometry to eight Sn atoms. There are a spread of K–Sn bond distances ranging from 4.17–4.22 Å. There are two inequivalent Hg sites. In the first Hg site, Hg is bonded to four Sn atoms to form HgSn4 tetrahedra that share corners with four SnSn3Hg tetrahedra and corners with six SnKSn4 trigonal bipyramids. All Hg–Sn bond lengths are 2.89 Å. In the second Hg site, Hg is bonded to four Sn atoms to form HgSn4 tetrahedra that share corners with four SnSn4 tetrahedra and corners with eight SnKSn4 trigonal bipyramids. There are three shorter (2.86 Å) and one longer (2.87 Å) Hg–Sn bond lengths. There are thirteen inequivalent Sn sites. In the first Sn site, Sn is bonded in a 5-coordinate geometry to one K and four Sn atoms. There are three shorter (2.88 Å) and one longer (2.90 Å) Sn–Sn bond lengths. In the second Sn site, Sn is bonded to one K and four Sn atoms to form distorted SnKSn4 trigonal bipyramids that share corners with three HgSn4 tetrahedra, corners with six SnSn4 tetrahedra, corners with two SnKSn4 trigonal bipyramids, and edges with three SnKSn4 trigonal bipyramids. There are a spread of Sn–Sn bond distances ranging from 2.87–2.96 Å. In the third Sn site, Sn is bonded to one K and four Sn atoms to form distorted SnKSn4 trigonal bipyramids that share corners with two HgSn4 tetrahedra, corners with seven SnSn4 tetrahedra, corners with three SnKSn4 trigonal bipyramids, and edges with two SnKSn4 trigonal bipyramids. There are a spread of Sn–Sn bond distances ranging from 2.87–2.93 Å. In the fourth Sn site, Sn is bonded to one K and four Sn atoms to form distorted SnKSn4 trigonal bipyramids that share corners with two HgSn4 tetrahedra, corners with seven SnK2Sn4 tetrahedra, corners with three SnKSn4 trigonal bipyramids, and edges with two SnKSn4 trigonal bipyramids. There are a spread of Sn–Sn bond distances ranging from 2.87–2.89 Å. In the fifth Sn site, Sn is bonded to four Sn atoms to form distorted SnSn4 tetrahedra that share a cornercorner with one HgSn4 tetrahedra, corners with seven SnSn4 tetrahedra, and corners with three SnKSn4 trigonal bipyramids. There are one shorter (2.94 Å) and one longer (2.96 Å) Sn–Sn bond lengths. In the sixth Sn site, Sn is bonded to two equivalent K and four Sn atoms to form distorted SnK2Sn4 tetrahedra that share a cornercorner with one HgSn4 tetrahedra, corners with fourteen SnSn4 tetrahedra, corners with two equivalent SnKSn4 trigonal bipyramids, edges with two SnK2Sn3Hg tetrahedra, and a faceface with one SnK2Sn4 tetrahedra. There are one shorter (2.93 Å) and one longer (2.95 Å) Sn–Sn bond lengths. In the seventh Sn site, Sn is bonded to one Hg and three Sn atoms to form distorted SnSn3Hg tetrahedra that share a cornercorner with one HgSn4 tetrahedra, corners with seven SnSn4 tetrahedra, and corners with two SnKSn4 trigonal bipyramids. The Sn–Sn bond length is 2.96 Å. In the eighth Sn site, Sn is bonded to one Hg and three Sn atoms to form distorted SnSn3Hg tetrahedra that share corners with eight SnSn3Hg tetrahedra and corners with three SnKSn4 trigonal bipyramids. In the ninth Sn site, Sn is bonded to two equivalent K, one Hg, and three Sn atoms to form distorted SnK2Sn3Hg tetrahedra that share corners with fifteen SnK2Sn4 tetrahedra, corners with four SnKSn4 trigonal bipyramids, edges with two SnK2Sn4 tetrahedra, and a faceface with one SnK2Sn3Hg tetrahedra. The Sn–Sn bond length is 2.95 Å. In the tenth Sn site, Sn is bonded to one Hg and three Sn atoms to form distorted SnSn3Hg tetrahedra that share a cornercorner with one HgSn4 tetrahedra, corners with seven SnSn4 tetrahedra, and corners with four SnKSn4 trigonal bipyramids. The Sn–Sn bond length is 2.96 Å. In the eleventh Sn site, Sn is bonded to two equivalent K and four Sn atoms to form distorted SnK2Sn4 tetrahedra that share a cornercorner with one HgSn4 tetrahedra, corners with fourteen SnSn4 tetrahedra, corners with four SnKSn4 trigonal bipyramids, edges with two SnK2Sn3Hg tetrahedra, and a faceface with one SnK2Sn4 tetrahedra. The Sn–Sn bond length is 2.94 Å. In the twelfth Sn site, Sn is bonded to two equivalent K, one Hg, and three Sn atoms to form distorted SnK2Sn3Hg tetrahedra that share corners with fifteen SnSn4 tetrahedra, corners with two equivalent SnKSn4 trigonal bipyramids, edges with two SnK2Sn4 tetrahedra, and a faceface with one SnK2Sn3Hg tetrahedra. In the thirteenth Sn site, Sn is bonded to four Sn atoms to form SnSn4 tetrahedra that share corners with four SnSn3Hg tetrahedra and corners with four SnKSn4 trigonal bipyramids.