Na_4.25Mo₁₅S₁₉: a novel ternary reduced molybdenum sulfide containing Mo₆ and Mo₉ clusters

The structure of tetra­sodium penta­deca­molybdenum nona­deca­sulfide, Na_4.25Mo₁₅S₁₉, is isotypic with Na_3.9Mo₁₅Se₁₉ [Salloum et al. (2013). Acta Cryst. E69, i67-i68]. It is characterized by Mo₆Sⁱ₈S^a₆ and Mo₉Sⁱ₁₁S^a₆ (where i represents inner and a apical atoms) cluster units that are present in a 1:1 ratio. The cluster units are centered at Wyckoff positions 2b and 2c, and have point-group symmetry -3 and -6, respectively. The clusters are inter­connected through additional Mo-S bonds. The Na⁺ cations occupy inter­unit voids formed by six or seven S atoms. One Mo, one S and one Na site [occupancy 0.751 (12)] are situated on mirror planes, and two other S atoms and one Na site (full occupancy) are situated on threefold rotation axes.