Synthesis, Structure, and Properties of (Ba₆Co₂₅S₂₇): A Perovskite-Like Superstructure of Co₈S₆ and Ba₆S Clusters

We have prepared single crystals of a new ternary barium cobalt sulfide, Ba₆Co₂₅S₂₇, by cooling a melt containing BaS, CoS, and Co from 975 °C. The structure, determined by single-crystal X-ray diffraction, is cubic (Pm3m) with a = 10.033 (3) Å, Z = 1, and R = 2.6%, R_w= 2.4%. The structure contains an octahedrally coordinated cobalt atom, nearly cubic clusters of eight cobalt atoms, and an unusual arrangement of barium atoms. The electric resistivity and magnetic susceptibility measurements show that Ba₆Co₂₅S₂₇is a poor metal with a resistance minimum at 8 K and is Pauli paramagnetic with a small Curie contribution indicating that either the Co₈cluster or the octahedrally coordinated cobalt atom has a magnetic moment.