DOE OSTI2020
Ca7Tl3N2 crystallizes in the orthorhombic Cmmm space group. The structure is three-dimensional. there are four inequivalent Ca sites. In the first Ca site, Ca is bonded in a linear geometry to four Tl and two equivalent N atoms. There are two shorter (3.49 Å) and two longer (3.60 Å) Ca–Tl bond lengths. Both Ca–N bond lengths are 2.48 Å. In the second Ca site, Ca is bonded in a single-bond geometry to six equivalent Tl and one N atom. There are two shorter (3.43 Å) and four longer (3.49 Å) Ca–Tl bond lengths. The Ca–N bond length is 2.33 Å. In the third Ca site, Ca is bonded in a linear geometry to four equivalent Tl and two equivalent N atoms. All Ca–Tl bond lengths are 3.48 Å. Both Ca–N bond lengths are 2.56 Å. In the fourth Ca site, Ca is bonded in a linear geometry to four Tl and two equivalent N atoms. There are two shorter (3.50 Å) and two longer (3.65 Å) Ca–Tl bond lengths. Both Ca–N bond lengths are 2.45 Å. There are two inequivalent Tl sites. In the first Tl site, Tl is bonded to twelve Ca atoms to form TlCa12 cuboctahedra that share corners with twelve TlCa12 cuboctahedra, faces with six TlCa12 cuboctahedra, and faces with eight equivalent NCa6 octahedra. In the second Tl site, Tl is bonded to ten Ca and two equivalent Tl atoms to form distorted TlCa10Tl2 cuboctahedra that share corners with eight TlCa12 cuboctahedra, corners with two equivalent NCa6 octahedra, edges with four equivalent TlCa10Tl2 cuboctahedra, faces with seven TlCa12 cuboctahedra, and faces with four equivalent NCa6 octahedra. The corner-sharing octahedral tilt angles are 45°. Both Tl–Tl bond lengths are 3.29 Å. N is bonded to six Ca atoms to form NCa6 octahedra that share corners with two equivalent TlCa10Tl2 cuboctahedra, corners with five equivalent NCa6 octahedra, and faces with eight TlCa12 cuboctahedra. The corner-sharing octahedra tilt angles range from 0–4°.