Barium (III) Thiocyanate Trihydrate

Barium Thiocyanate trihydrate—Ba(SCN)₂•3H₂O—is a colorless crystalline solid.  It is soluble in water and polar organic solvents like ethanol, but has limited applications due to its toxicity.

Metal thiocyanates are fascinating from a fundamental structural chemistry perspective.  There are two resonance structures for the thiocyanate ion.  The predominant resonance structure has the negative charge carried by the sulfur atom.  Thiocyanate is sometimes referred to as a “pseudo-halogen” because it is a monovalent anion.

The crystal structure of the trihydrate exhibits a coordination polymer, indicating that the barium atoms are nine-coordinate. These Barium atoms interact with four nitrogen (N) atoms and one sulfur (S) atom from the thiocyanate ions, as well as four oxygen (O) atoms from the water molecules.  The structure can be described as chains oriented along one axis of the unit cell, with hydrogen bonding bridging secondary chains.

A group of researchers from three different chemical and geological research institutions in Russia recently published the crystal structure of a Barium iodide-thiocyanate tetrahydrate complex.  It was prepared by evaporation of an aqueous solution of Barium Thiocyanate trihydrate and Barium Iodide dihydrate in a 1:1 stoichiometric ratio. The structure can be described as layers of cations and anions.  The Barium ions are ten-coordinate, interacting with two S atoms and two N atoms from the thiocyanate ions, and six O atoms from the water molecules.

References

1. Cliffe, M. J. Inorganic Metal Thiocyanates.(opens in new tab) Chem. 2024, 63 (29), 13137–13156. https://doi.org/10.1021/acs.inorgchem.4c00920
2. Mereiter, K.; Preisinger, A. Barium Thiocyanate Trihydrate(opens in new tab). Acta Crystallogr. B 1982, 38 (2), 382–385. https://doi.org/10.1107/S0567740882003033
3. Kireev, V. E.; Khasanov, K. A.; Charkin, D. O.; Aksenov, S. M. Synthesis and Crystal Structure of a New Non-Centrosymmetrical Layered Barium Iodide-Thiocyanate Tetrahydrate .(opens in new tab) Struct. Chem. 2024, 65 (12), 2522–2532. https://doi.org/10.1134/S0022476624120151