DOE OSTI2020
ZrNb(RuSi)2 crystallizes in the monoclinic Pm space group. The structure is three-dimensional. there are three inequivalent Zr2+ sites. In the first Zr2+ site, Zr2+ is bonded to five Si4- atoms to form ZrSi5 square pyramids that share corners with five ZrSi5 square pyramids, corners with five NbSi5 square pyramids, corners with six RuSi4 tetrahedra, edges with two NbSi5 square pyramids, edges with four ZrSi5 square pyramids, and edges with six RuSi4 tetrahedra. There are four shorter (2.74 Å) and one longer (2.77 Å) Zr–Si bond lengths. In the second Zr2+ site, Zr2+ is bonded to five Si4- atoms to form ZrSi5 square pyramids that share a cornercorner with one ZrSi5 square pyramid, corners with nine NbSi5 square pyramids, corners with six RuSi4 tetrahedra, edges with two equivalent ZrSi5 square pyramids, edges with four NbSi5 square pyramids, and edges with six RuSi4 tetrahedra. There are three shorter (2.75 Å) and two longer (2.77 Å) Zr–Si bond lengths. In the third Zr2+ site, Zr2+ is bonded to five Si4- atoms to form ZrSi5 square pyramids that share corners with four equivalent ZrSi5 square pyramids, corners with six NbSi5 square pyramids, corners with six RuSi4 tetrahedra, edges with two NbSi5 square pyramids, edges with four ZrSi5 square pyramids, and edges with six RuSi4 tetrahedra. There are a spread of Zr–Si bond distances ranging from 2.74–2.77 Å. There are three inequivalent Nb2+ sites. In the first Nb2+ site, Nb2+ is bonded to five Si4- atoms to form distorted NbSi5 square pyramids that share corners with three equivalent NbSi5 square pyramids, corners with seven ZrSi5 square pyramids, corners with six RuSi4 tetrahedra, edges with three ZrSi5 square pyramids, edges with three NbSi5 square pyramids, and edges with six RuSi4 tetrahedra. There are a spread of Nb–Si bond distances ranging from 2.68–2.76 Å. In the second Nb2+ site, Nb2+ is bonded to five Si4- atoms to form NbSi5 square pyramids that share corners with two equivalent NbSi5 square pyramids, corners with eight ZrSi5 square pyramids, corners with six RuSi4 tetrahedra, edges with three ZrSi5 square pyramids, edges with three NbSi5 square pyramids, and edges with six RuSi4 tetrahedra. There are a spread of Nb–Si bond distances ranging from 2.69–2.72 Å. In the third Nb2+ site, Nb2+ is bonded to five Si4- atoms to form NbSi5 square pyramids that share corners with five ZrSi5 square pyramids, corners with five NbSi5 square pyramids, corners with six RuSi4 tetrahedra, edges with two equivalent ZrSi5 square pyramids, edges with four NbSi5 square pyramids, and edges with six RuSi4 tetrahedra. There are two shorter (2.70 Å) and three longer (2.72 Å) Nb–Si bond lengths. There are six inequivalent Ru2+ sites. In the first Ru2+ site, Ru2+ is bonded to four Si4- atoms to form RuSi4 tetrahedra that share corners with two equivalent NbSi5 square pyramids, corners with four ZrSi5 square pyramids, corners with ten RuSi4 tetrahedra, edges with two equivalent ZrSi5 square pyramids, edges with four NbSi5 square pyramids, and edges with two RuSi4 tetrahedra. There are a spread of Ru–Si bond distances ranging from 2.48–2.51 Å. In the second Ru2+ site, Ru2+ is bonded to four Si4- atoms to form RuSi4 tetrahedra that share corners with two equivalent ZrSi5 square pyramids, corners with four NbSi5 square pyramids, corners with ten RuSi4 tetrahedra, edges with two equivalent NbSi5 square pyramids, edges with four ZrSi5 square pyramids, and edges with two RuSi4 tetrahedra. There are a spread of Ru–Si bond distances ranging from 2.51–2.54 Å. In the third Ru2+ site, Ru2+ is bonded to four Si4- atoms to form RuSi4 tetrahedra that share corners with two equivalent NbSi5 square pyramids, corners with four ZrSi5 square pyramids, corners with ten RuSi4 tetrahedra, edges with two equivalent ZrSi5 square pyramids, edges with four NbSi5 square pyramids, and edges with two RuSi4 tetrahedra. There are a spread of Ru–Si bond distances ranging from 2.46–2.52 Å. In the fourth Ru2+ site, Ru2+ is bonded to four Si4- atoms to form RuSi4 tetrahedra that share corners with two equivalent ZrSi5 square pyramids, corners with four NbSi5 square pyramids, corners with ten RuSi4 tetrahedra, edges with two equivalent NbSi5 square pyramids, edges with four ZrSi5 square pyramids, and edges with two RuSi4 tetrahedra. There are a spread of Ru–Si bond distances ranging from 2.48–2.57 Å. In the fifth Ru2+ site, Ru2+ is bonded to four Si4- atoms to form RuSi4 tetrahedra that share corners with two equivalent ZrSi5 square pyramids, corners with four NbSi5 square pyramids, corners with ten RuSi4 tetrahedra, edges with two equivalent ZrSi5 square pyramids, edges with four NbSi5 square pyramids, and edges with two RuSi4 tetrahedra. There are a spread of Ru–Si bond distances ranging from 2.44–2.57 Å. In the sixth Ru2+ site, Ru2+ is bonded to four Si4- atoms to form RuSi4 tetrahedra that share corners with two equivalent NbSi5 square pyramids, corners with four ZrSi5 square pyramids, corners with ten RuSi4 tetrahedra, edges with two equivalent NbSi5 square pyramids, edges with four ZrSi5 square pyramids, and edges with two RuSi4 tetrahedra. There are a spread of Ru–Si bond distances ranging from 2.45–2.58 Å. There are six inequivalent Si4- sites. In the first Si4- site, Si4- is bonded in a 9-coordinate geometry to two equivalent Zr2+, four Nb2+, and three Ru2+ atoms. In the second Si4- site, Si4- is bonded in a 9-coordinate geometry to four Zr2+, two equivalent Nb2+, and three Ru2+ atoms. In the third Si4- site, Si4- is bonded in a 9-coordinate geometry to two equivalent Zr2+, four Nb2+, and three Ru2+ atoms. In the fourth Si4- site, Si4- is bonded in a 9-coordinate geometry to four Zr2+, two equivalent Nb2+, and three Ru2+ atoms. In the fifth Si4- site, Si4- is bonded in a 9-coordinate geometry to one Zr2+, two Nb2+, and six Ru2+ atoms. In the sixth Si4- site, Si4- is bonded in a 9-coordinate geometry to two Zr2+, one Nb2+, and six Ru2+ atoms.