Novel Combination of Coordination Polyhedra in Mg₂Co₃Sn_10+x ‐ The First Phase in the Mg/Co/Sn System

Abstract

Abstract Mg 2 Co 3 Sn 10+x is the first compound in the ternary system Mg/Co/Sn. Single crystals for structure analysis were grown from the elements by a tin flux method. The structure ( P6 3 /mmc, a = 9.490(1) Å and c = 33.555(7) Å) was determined by X‐ray single crystal analysis ( R 1 = 0.037). A small phase width of 0 ≤ x ≤ 0.15, due to the partial occupancy of one out of ten tin positions is observed. There are two crystallographically different cobalt sites each with a unique tin coordination sphere. The Co1 site has a square antiprismatic coordination with tin atoms comparable to the ones observed in the tin rich binary stannides. The Co2 site is characterized by a trigonal prismatic coordination with tin similar to previously known ternary stannides. The different polyhedra are arranged in alternating layers in an intricate way which gives rise to tin‐tin distances shorter than 3Å. Magnesium is only found in those layers which have cobalt trigonal prismatically coordinated to tin atoms. Thus, the structure shows an unprecedented arrangement of different coordination spheres, and furthermore provides evidence for homoatomic tin bonding within a metallic framework. Magnetic susceptibility measurements show temperature independent Pauli‐paramagnetism down to 50 K.