Single crystal structure refinement and high-pressure properties of CoSn

Using single crystal data we have refined the crystal structure of CoSn in space group P6/mmm, a = 5.2790(7) Angstrom, c = 4.2597(10) Angstrom 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 structure 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 structure of an intermetallic compound is a 20-atom void which is located between the Kagome nets. Powder diffraction experiments under high hydrostatic 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 orbitals in the Kagome nets and of Sn2 forming the graphite nets. The layers are connected by bonding interactions between Co and Sn2. Calculations of the electron localization function showed no indications of localized electron pairs within the 20-atom void.