New Metal-Rich Sulfides Ni6SnS2 and Ni9Sn2S2 with a 2D Metal Framework: Synthesis, Crystal Structure, and Bonding

Two new, metal-rich nickel-tin sulfides Ni6SnS2 and Ni9Sn2S2 were found by establishing phase relations in the ternary Ni-Sn-S system at 540 °C. Their single crystals were prepared by means of chemical vapor transport reactions. Single crystal X-ray diffraction was used for the determination of their crystal structures. Both compounds crystallize in a tetragonal system (I4/mmm, No. 139, Z = 2, a = 3.646(1) (angstrom), c = 18.151(8) (angstrom) for Ni6SnS2, and a = 3.678(1) (angstrom), c = 25.527(8) (angstrom) for Ni9Sn2S2). Their crystal structures represent a new structure type and can be considered as assembled from bimetallic nickel-tin and nickel-sulfide slabs alternating along the crystallographic c axis. DFT band structure calculations showed the bonding within the bimetallic slabs to have a delocalized, multicenter nature, typical for metallic systems, and predominantly classical, pairwise bonding between nickel and sulfur.