MgB2C2 crystallizes in the orthorhombic Cmce space group. There are two inequivalent Mg sites. In the first Mg site, Mg(1) is bonded in a 12-coordinate geometry to two equivalent B(3), four equivalent B(1), two equivalent C(3), and four equivalent C(1) atoms. In the second Mg site, Mg(2) is bonded in a 12-coordinate geometry to two equivalent B(1), two equivalent B(2), two equivalent B(3), two equivalent C(1), two equivalent C(2), and two equivalent C(3) atoms. There are three inequivalent B sites. In the first B site, B(1) is bonded in a distorted trigonal planar geometry to one Mg(2), two equivalent Mg(1), one C(1), one C(2), and one C(3) atom. In the second B site, B(2) is bonded in a distorted trigonal planar geometry to two equivalent Mg(2), one C(2), and two equivalent C(1) atoms. In the third B site, B(3) is bonded in a distorted trigonal planar geometry to two equivalent Mg(1), two equivalent Mg(2), one C(3), and two equivalent C(1) atoms. There are three inequivalent C sites. In the first C site, C(3) is bonded in a distorted trigonal planar geometry to two equivalent Mg(1), two equivalent Mg(2), one B(3), and two equivalent B(1) atoms. In the second C site, C(1) is bonded in a distorted trigonal planar geometry to one Mg(2), two equivalent Mg(1), one B(1), one B(2), and one B(3) atom. In the third C site, C(2) is bonded in a distorted trigonal planar geometry to two equivalent Mg(2), one B(2), and two equivalent B(1) atoms.
MgB2C2 crystallizes in the orthorhombic Cmce space group. There are two inequivalent Mg sites. In the first Mg site, Mg(1) is bonded in a 12-coordinate geometry to two equivalent B(3), four equivalent B(1), two equivalent C(3), and four equivalent C(1) atoms. There is one shorter (2.34 Å) and one longer (2.50 Å) Mg(1)-B(3) bond length. There are two shorter (2.41 Å) and two longer (2.55 Å) Mg(1)-B(1) bond lengths. There is one shorter (2.46 Å) and one longer (2.49 Å) Mg(1)-C(3) bond length. There are two shorter (2.41 Å) and two longer (2.44 Å) Mg(1)-C(1) bond lengths. In the second Mg site, Mg(2) is bonded in a 12-coordinate geometry to two equivalent B(1), two equivalent B(2), two equivalent B(3), two equivalent C(1), two equivalent C(2), and two equivalent C(3) atoms. Both Mg(2)-B(1) bond lengths are 2.43 Å. Both Mg(2)-B(2) bond lengths are 2.31 Å. Both Mg(2)-B(3) bond lengths are 2.49 Å. Both Mg(2)-C(1) bond lengths are 2.36 Å. Both Mg(2)-C(2) bond lengths are 2.25 Å. Both Mg(2)-C(3) bond lengths are 2.49 Å. There are three inequivalent B sites. In the first B site, B(1) is bonded in a distorted trigonal planar geometry to one Mg(2), two equivalent Mg(1), one C(1), one C(2), and one C(3) atom. The B(1)-C(1) bond length is 1.58 Å. The B(1)-C(2) bond length is 1.56 Å. The B(1)-C(3) bond length is 1.59 Å. In the second B site, B(2) is bonded in a distorted trigonal planar geometry to two equivalent Mg(2), one C(2), and two equivalent C(1) atoms. The B(2)-C(2) bond length is 1.58 Å. Both B(2)-C(1) bond lengths are 1.57 Å. In the third B site, B(3) is bonded in a distorted trigonal planar geometry to two equivalent Mg(1), two equivalent Mg(2), one C(3), and two equivalent C(1) atoms. The B(3)-C(3) bond length is 1.58 Å. Both B(3)-C(1) bond lengths are 1.58 Å. There are three inequivalent C sites. In the first C site, C(3) is bonded in a distorted trigonal planar geometry to two equivalent Mg(1), two equivalent Mg(2), one B(3), and two equivalent B(1) atoms. In the second C site, C(1) is bonded in a distorted trigonal planar geometry to one Mg(2), two equivalent Mg(1), one B(1), one B(2), and one B(3) atom. In the third C site, C(2) is bonded in a distorted trigonal planar geometry to two equivalent Mg(2), one B(2), and two equivalent B(1) atoms.