Crystal and electronic structures of the new ternary silicide Sc12Co41.8Si30.2

Sc12Co41.8Si30.2 was prepared from the elements by arc melting under argon and subsequent tempering at 800 degrees C for 350 h. Single-crystal X-ray diffraction reveals Sc12Co41.8Si30.2 to crystallize in a new hexagonal structure type: Pearson's symbol (PS) hP168, space group P6/mmm, a = 17.291(1), c = 8.0293(8) angstrom. The crystal structure is formed of three types of atomic layers along the [001] direction - two flat at z = 0 and z = 0.5 and one corrugated at z = 0.16-0.33 and z = 0.67-0.84, shows a substantial degree of positional and occupational disorder and close structural relationships to a series of hexagonal structures with PS hP164-hP171. Quantum chemical calculations have been performed to analyze the electronic structure and provide deeper insight into the structure-property relationships. The quantum chemical calculation indicates that the material features both two-center, two-electron localized bonding and multi-center multi-electron delocalized bonding.