Flux Crystal Growth, Crystal Structure, and Magnetic Properties of a Ternary Chromium Disulfide Ba9Cr4S19 with Unusual Cr4S15 Tetramer Units

A new ternary chromium disulfide, Ba9Cr4S19, has been grown out of BaCl2 molten salt. Single-crystal structure analysis revealed that it crystallizes in the centrosymmetric space group C2/c with lattice parameters: a = 12.795(3) Å, b = 11.3269(2) Å, c = 23.2057(6) Å, β = 104.041(3)°, and Z = 4. Ba9Cr4S19 comprises four face-sharing Cr-centered octahedra with disulfide ions occupying sites on each terminal face. The resulting Cr4S15 tetramer units are isolated by nonmagnetic Ba-centered polyhedra in the ab plane and barium disulfide (=Ba4(S2)2) layers along the c-axis. Following the structure analysis, the title compound should be expressed as [Ba2+]9[Cr3+]4[(S2)2–]4[S2–]11, which is also consistent with Cr2p X-ray photoemission spectra showing trivalent states of the Cr atoms. The unique Cr-based zero-dimensional structure with the formation of these disulfide ions can be achieved for the first time in ternary chromium sulfides, which adopt 1–3 dimensional frameworks of Cr-centered polyhedra.