Materials Data on UNb6O16 by Materials Project
UNb6O16 crystallizes in the monoclinic C2 space group. The structure is three-dimensional. U4+ is bonded to six O2- atoms to form distorted UO6 octahedra that share corners with four equivalent NbO6 octahedra, corners with four equivalent NbO6 pentagonal pyramids, and edges with two equivalent UO6 octahedra. The corner-sharing octahedra tilt angles range from 36–64°. There are a spread of U–O bond distances ranging from 2.28–2.41 Å. There are three inequivalent Nb+4.67+ sites. In the first Nb+4.67+ site, Nb+4.67+ is bonded to six O2- atoms to form distorted NbO6 octahedra that share corners with two equivalent UO6 octahedra, corners with two equivalent NbO6 octahedra, a cornercorner with one NbO6 pentagonal pyramid, an edgeedge with one NbO6 octahedra, and edges with two equivalent NbO6 pentagonal pyramids. The corner-sharing octahedra tilt angles range from 36–64°. There are a spread of Nb–O bond distances ranging from 1.84–2.34 Å. In the second Nb+4.67+ site, Nb+4.67+ is bonded to six O2- atoms to form distorted NbO6 pentagonal pyramids that share corners with two equivalent UO6 octahedra, corners with four NbO6 pentagonal pyramids, and edges with two equivalent NbO6 octahedra. The corner-sharing octahedra tilt angles range from 58–67°. There are a spread of Nb–O bond distances ranging from 1.92–2.28 Å. In the third Nb+4.67+ site, Nb+4.67+ is bonded to six O2- atoms to form a mixture of distorted edge and corner-sharing NbO6 pentagonal pyramids. The corner-sharing octahedral tilt angles are 9°. There are a spread of Nb–O bond distances ranging from 1.95–2.16 Å. There are eight inequivalent O2- sites. In the first O2- site, O2- is bonded in a 3-coordinate geometry to one U4+ and two equivalent Nb+4.67+ atoms. In the second O2- site, O2- is bonded in a 3-coordinate geometry to three Nb+4.67+ atoms. In the third O2- site, O2- is bonded in a distorted trigonal non-coplanar geometry to two equivalent U4+ and one Nb+4.67+ atom. In the fourth O2- site, O2- is bonded in a 3-coordinate geometry to three Nb+4.67+ atoms. In the fifth O2- site, O2- is bonded in a linear geometry to two Nb+4.67+ atoms. In the sixth O2- site, O2- is bonded in a linear geometry to two Nb+4.67+ atoms. In the seventh O2- site, O2- is bonded in a linear geometry to two Nb+4.67+ atoms. In the eighth O2- site, O2- is bonded in a 3-coordinate geometry to three equivalent Nb+4.67+ atoms.