Synthesis, Crystal Structure, and Properties of Two Modifications of MgB12C2
- 3 April 2007
- journal article
- research article
- Published by Wiley in Chemistry – A European Journal
- Vol. 13 (12), 3450-3458
- https://doi.org/10.1002/chem.200601002
Abstract
Single crystals of two modifications of the new magnesium boride carbide MgB12C2 were synthesized from the elements in a metallic melt by using tantalum ampoules. Crystals were characterized by single‐crystal X‐ray diffraction and electron microprobe analysis (energy‐dispersive (EDX) and wavelength‐dispersive (WDX) X‐ray spectroscopy). Orthorhombic MgB12C2 is formed in a Cu/Mg melt at 1873 K. The crystal structure of o‐MgB12C2 (Imma, Z=4, a=5.6133(10), b=9.828(2), c=7.9329(15) Å, 574 reflections, 42 variables, R1(F)=0.0208, wR2(I)=0.0540) consists of a hexagonal primitive array of B12 icosahedra with Mg atoms and C2 units in trigonal‐prismatic voids. Each icosahedron has six exohedral BB and six BC bonds. Carbon is tetrahedrally coordinated by three boron atoms and one carbon atom with a remarkably long CC distance of 1.727 Å. Monoclinic MgB12C2 is formed in an Al/Mg melt at 1573 K. The structure of m‐MgB12C2 (C2/c, Z=4, a=7.2736(11), b=8.7768(13), c=7.2817(11) Å, β=105.33(3)°, 1585 reflections, 71 variables, R1(F)=0.0228, wR2(I)=0.0610) may be described as a distorted cubic close arrangement of B12 icosahedra. Tetrahedral voids are filled by C atoms and octahedral voids are occupied by Mg atoms. The icosahedra are interconnected by four exohedral BB bonds to linear chains and by eight interstitial C atoms to form a three‐dimensional covalent network. Both compounds fulfill the electron‐counting rules of Wade and Longuet‐Higgins.This publication has 52 references indexed in Scilit:
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