Nb3B3C crystallizes in the orthorhombic Cmcm space group. There are three inequivalent Nb sites. In the first Nb site, Nb(1) is bonded to two equivalent B(2), four equivalent B(3), and six equivalent B(1) atoms to form NbB12 cuboctahedra that share corners with two equivalent Nb(2)BC5 square pyramids, edges with eight equivalent Nb(1)B12 cuboctahedra, and faces with six equivalent Nb(1)B12 cuboctahedra. In the second Nb site, Nb(2) is bonded to one B(2) and five equivalent C(1) atoms to form distorted NbBC5 square pyramids that share corners with two equivalent Nb(1)B12 cuboctahedra, corners with four equivalent Nb(2)BC5 square pyramids, and edges with eight equivalent Nb(2)BC5 square pyramids. In the third Nb site, Nb(3) is bonded in a 7-coordinate geometry to two equivalent B(3), four equivalent B(2), and one C(1) atom. There are three inequivalent B sites. In the first B site, B(1) is bonded in a 9-coordinate geometry to six equivalent Nb(1), one B(3), and two equivalent B(1) atoms. In the second B site, B(2) is bonded in a 9-coordinate geometry to one Nb(2), two equivalent Nb(1), four equivalent Nb(3), and two equivalent B(3) atoms. In the third B site, B(3) is bonded in a 9-coordinate geometry to two equivalent Nb(3), four equivalent Nb(1), one B(1), and two equivalent B(2) atoms. C(1) is bonded to one Nb(3) and five equivalent Nb(2) atoms to form a mixture of corner and edge-sharing CNb6 octahedra. The corner-sharing octahedral tilt angles are 1°.
Nb3B3C crystallizes in the orthorhombic Cmcm space group. There are three inequivalent Nb sites. In the first Nb site, Nb(1) is bonded to two equivalent B(2), four equivalent B(3), and six equivalent B(1) atoms to form NbB12 cuboctahedra that share corners with two equivalent Nb(2)BC5 square pyramids, edges with eight equivalent Nb(1)B12 cuboctahedra, and faces with six equivalent Nb(1)B12 cuboctahedra. Both Nb(1)-B(2) bond lengths are 2.50 Å. All Nb(1)-B(3) bond lengths are 2.46 Å. There are two shorter (2.43 Å) and four longer (2.45 Å) Nb(1)-B(1) bond lengths. In the second Nb site, Nb(2) is bonded to one B(2) and five equivalent C(1) atoms to form distorted NbBC5 square pyramids that share corners with two equivalent Nb(1)B12 cuboctahedra, corners with four equivalent Nb(2)BC5 square pyramids, and edges with eight equivalent Nb(2)BC5 square pyramids. The Nb(2)-B(2) bond length is 2.90 Å. There is one shorter (2.17 Å) and four longer (2.27 Å) Nb(2)-C(1) bond lengths. In the third Nb site, Nb(3) is bonded in a 7-coordinate geometry to two equivalent B(3), four equivalent B(2), and one C(1) atom. Both Nb(3)-B(3) bond lengths are 2.36 Å. All Nb(3)-B(2) bond lengths are 2.39 Å. The Nb(3)-C(1) bond length is 2.15 Å. There are three inequivalent B sites. In the first B site, B(1) is bonded in a 9-coordinate geometry to six equivalent Nb(1), one B(3), and two equivalent B(1) atoms. The B(1)-B(3) bond length is 1.84 Å. Both B(1)-B(1) bond lengths are 1.81 Å. In the second B site, B(2) is bonded in a 9-coordinate geometry to one Nb(2), two equivalent Nb(1), four equivalent Nb(3), and two equivalent B(3) atoms. Both B(2)-B(3) bond lengths are 1.84 Å. In the third B site, B(3) is bonded in a 9-coordinate geometry to two equivalent Nb(3), four equivalent Nb(1), one B(1), and two equivalent B(2) atoms. C(1) is bonded to one Nb(3) and five equivalent Nb(2) atoms to form a mixture of corner and edge-sharing CNb6 octahedra. The corner-sharing octahedral tilt angles are 1°.