KEu 2 In 3 B 12 S 13 : a novel type of thioborate featuring B 12 S 12 cluster and unique In 6 S 6 12-membered ring.

Both borates and sulfides are important inorganic multifunctional materials. Encouraged by this background, thioborates attract considerable interest. However, their investigations are highly hindered by the scarcity of the available ones and the synthetic difficulty of the new ones. Here, we report a new thioborate KEu 2 In 3 B 12 S 13 (1), which was obtained via a facile solid-state reaction in KI flux. It crystallizes in the trigonal R 3̄ m structure, and the three-dimensional structure features a six InS 6 octahedron consolidated B 12 icosahedron built {[In 3 B 12 S 12 ] 5- } ∞ polyanionic framework and a unique In 6 S 6 12-membered ring, representing a new type of compound. The B 12 S 12 cluster is also different from the other known thioborates. The structural chemistry, optical and magnetic properties, as well as theoretical calculations of 1 were systematically studied. This study not only provides a new type of thioborate but also makes a breakthrough in the synthesis of thioborates.