SINGLE-CRYSTAL STRUCTURE REFINEMENT AND HIGH-PRESSURE PROPERTIES OF COSN

Using single crystal data we have refined the crystal structure of CoS n in space group P6/mmm, a = 5.2790(7) Angstrom, c = 4.2597(10) Angstr om with Sn1 at Wyckoff position 1a, Sn2 at 2d, and Co at 3f. The space group used for the structure refinement was confirmed by a subsequent convergent beam electron diffraction investigation. The crystal struc ture contains graphite-like 6(3) nets of Sn2 atoms and Kagome nets of Co centred by the Sn1 atoms. An unusual feature for a crystal structur e of an intermetallic compound is a 20-atom void which is located betw een the Kagome nets. Powder diffraction experiments under high hydrost atic pressures show that -- despite a space filling of only 55% -- the ambient pressure modification is stable up to 26 Gpa. Extended Huckel computations revealed significant overlap populations of Co and Sn1 o rbitals in the Kagome nets and of Sn2 forming the graphite nets. The l ayers are connected by bonding interactions between Co and Sn2. Calcul ations of the electron localization function showed no indications of localized electron pairs within the 20-atom void.