On the crystal structures of lithium thiocyanate monohydrate LiSCN ⋅ 1 H2O and the phase diagram LiSCN – H2O

Abstract Hydration of anhydrous LiSCN by stoichiometric amounts of water vapor leads to the formation of LiSCN ⋅ 1 H2O. At room temperature, LiSCN ⋅ 1 H2O crystalizes in the monoclinic space group C2/m with a = 15.0271(3) A, b = 7.59742(1) A, c = 6.70700(1) A, β  = 96.1470(6) ° and V = 761.32(2) A³ (α-phase). At 49 °C, the material transforms into a high temperature β-phase with the orthorhombic space group Pnam and a = 13.22578(2) A, b = 7.06191(9) A, c = 8.16628(1) A and V = 762.724(2) A³. 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 p H 2 O , differential scanning calorimetry (DSC) and direct measurements of equilibrium p H 2 O . The results indicate that LiSCN ⋅ 1 H2O is a special case when compared to LiSCN ⋅ 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 ⋅ n H2O hydrates.