On the crystal structures of lithium thiocyanate monohydrate LiSCN • 1 H2O and the phase diagram LiSCN - H2O

Hydration of anhydrous LiSCN by stoichiometric amounts of water vapor leads to the formation of LiSCN center dot 1 H2O. At room temperature, LiSCN center dot 1 H2O crystallizes in the monoclinic space group C2/m with a = 15.0271(3) angstrom, b = 7.5974(1) angstrom, c = 6.7070(1) angstrom, beta = 96.147(6) degrees and V = 761.32(2) angstrom(3) (alpha-phase). At 49 degrees C, the material transforms into a high temperature beta-phase with the orthorhombic space group Pnam and a = 13.2258(2) angstrom, b = 7.0619(9) angstrom, c = 8.1663(1) A and V = 762.72(2) 3 . Structural and thermodynamic investigations were conducted using infrared (IR) spectroscopy, ex situ and in situ X-ray powder diffraction (XRPD) while varying temperature or water partial pressure PH2O , differential scanning calorimetry (DSC) and direct measurements of equilibrium PH2O. The results indicate that LiSCN center dot 1 H2O is a special case when compared to LiSCN center dot n H2O (n = 0 or 2), both regarding crystal structure and hydration thermodynamics. These results are combined with literature date into an updated phase diagram of the LiSCN - H2O system, showing a detailed picture of the phase formation behavior of the LiSCN center dot n H2O hydrates.

Automated summary

Hydration of anhydrous LiSCN by water vapor leads to the formation of LiSCN•H2O, with an α-phase crystallizing at room temperature and transforming into a higher temperature β-phase at 49 degrees C. Structural and thermodynamic investigations suggest that LiSCN•H2O is a unique case compared to other LiSCN hydrates.