Materials Data on Nb7(BC)4 by Materials Project

Abstract

Nb(Nb3C2)2(B)4 crystallizes in the orthorhombic Immm space group. The structure is two-dimensional and consists of two niobium molecules; two B ribbons oriented in the (1, 0, 0) direction; and two Nb3C2 sheets oriented in the (0, 0, 1) direction. In each B ribbon, there are two inequivalent B sites. In the first B site, B is bonded in a 3-coordinate geometry to three B atoms. There is two shorter (1.83 Å) and one longer (1.85 Å) B–B bond length. In the second B site, B is bonded in a 2-coordinate geometry to two equivalent B atoms. In each Nb3C2 sheet, there are three inequivalent Nb+2.29+ sites. In the first Nb+2.29+ site, Nb+2.29+ is bonded in a single-bond geometry to one C4- atom. The Nb–C bond length is 2.14 Å. In the second Nb+2.29+ site, Nb+2.29+ is bonded to six C4- atoms to form NbC6 octahedra that share corners with four equivalent NbC6 octahedra, a cornercorner with one NbC5 square pyramid, edges with eight equivalent NbC6 octahedra, and edges with four equivalent NbC5 square pyramids. The corner-sharing octahedral tilt angles are 2°. There are a spread of Nb–C bond distances ranging from 2.19–2.29 Å. In the third Nb+2.29+ site, Nb+2.29+ is bonded to five C4- atoms to form NbC5 square pyramids that share a cornercorner with one NbC6 octahedra, corners with four equivalent NbC5 square pyramids, edges with four equivalent NbC6 octahedra, and edges with four equivalent NbC5 square pyramids. The corner-sharing octahedral tilt angles are 0°. There are one shorter (2.20 Å) and four longer (2.26 Å) Nb–C bond lengths. There are two inequivalent C4- sites. In the first C4- site, C4- is bonded to six Nb+2.29+ atoms to form a mixture of edge and corner-sharing CNb6 octahedra. The corner-sharing octahedra tilt angles range from 0–2°. In the second C4- site, C4- is bonded to six Nb+2.29+ atoms to form a mixture of edge and corner-sharing CNb6 octahedra. The corner-sharing octahedra tilt angles range from 0–1°.