DOE OSTI2020
TaNb2TeI7Ta3TeI7 crystallizes in the monoclinic Cm space group. The structure is two-dimensional and consists of one Ta3TeI7 sheet oriented in the (0, 0, 1) direction and one TaNb2TeI7 sheet oriented in the (0, 0, 1) direction. In the Ta3TeI7 sheet, there are two inequivalent Ta+3.50+ sites. In the first Ta+3.50+ site, Ta+3.50+ is bonded to one Te2- and five I1- atoms to form distorted edge-sharing TaTeI5 octahedra. The Ta–Te bond length is 2.73 Å. There are a spread of Ta–I bond distances ranging from 2.75–3.07 Å. In the second Ta+3.50+ site, Ta+3.50+ is bonded to one Te2- and five I1- atoms to form distorted edge-sharing TaTeI5 octahedra. The Ta–Te bond length is 2.73 Å. There are a spread of Ta–I bond distances ranging from 2.75–3.07 Å. Te2- is bonded in a 12-coordinate geometry to three Ta+3.50+ atoms. There are three inequivalent I1- sites. In the first I1- site, I1- is bonded in a water-like geometry to two equivalent Ta+3.50+ atoms. In the second I1- site, I1- is bonded in a 3-coordinate geometry to two equivalent Ta+3.50+ atoms. In the third I1- site, I1- is bonded in a distorted trigonal non-coplanar geometry to three Ta+3.50+ atoms. In the TaNb2TeI7 sheet, Ta+3.50+ is bonded to one Te2- and five I1- atoms to form distorted TaTeI5 octahedra that share edges with four equivalent NbTeI5 octahedra. The Ta–Te bond length is 2.72 Å. There are a spread of Ta–I bond distances ranging from 2.75–3.05 Å. Nb2+ is bonded to one Te2- and five I1- atoms to form distorted NbTeI5 octahedra that share edges with two equivalent TaTeI5 octahedra and edges with two equivalent NbTeI5 octahedra. The Nb–Te bond length is 2.74 Å. There are a spread of Nb–I bond distances ranging from 2.76–3.06 Å. Te2- is bonded in a 12-coordinate geometry to one Ta+3.50+ and two equivalent Nb2+ atoms. There are five inequivalent I1- sites. In the first I1- site, I1- is bonded in a water-like geometry to two equivalent Nb2+ atoms. In the second I1- site, I1- is bonded in a water-like geometry to one Ta+3.50+ and one Nb2+ atom. In the third I1- site, I1- is bonded in a 3-coordinate geometry to two equivalent Nb2+ atoms. In the fourth I1- site, I1- is bonded in a 2-coordinate geometry to one Ta+3.50+ and one Nb2+ atom. In the fifth I1- site, I1- is bonded in a distorted trigonal non-coplanar geometry to one Ta+3.50+ and two equivalent Nb2+ atoms.