Lithium thiocyanate

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Lithium thiocyanate
Li+[N≡C−S−]
Names
Other names
  • Lithium sulfocyanate
Identifiers
3D model (JSmol)
ChemSpider
ECHA InfoCard 100.008.306 OOjs UI icon edit-ltr-progressive.svg
EC Number
  • 209-135-1
  • monohydrate:629-475-8
PubChem CID
  • InChI=1S/CHNS.Li/c2-1-3;/h3H;/q;+1/p-1
    Key: ZJZXSOKJEJFHCP-UHFFFAOYSA-M
  • monohydrate:InChI=1S/CHNS.Li.H2O/c2-1-3;;/h3H;;1H2/q;+1;/p-1
    Key: UNTVNJAFDYEXLD-UHFFFAOYSA-M
  • dihydrate:InChI=1S/CHNS.Li.2H2O/c2-1-3;;;/h3H;;2*1H2/q;+1;;/p-1
    Key: TWRGRNSGEYGNBV-UHFFFAOYSA-M
  • [Li+].C(#N)[S-]
  • monohydrate:[Li+].C(#N)[S-].O
  • dihydrate:[Li+].C(#N)[S-].O.O
Properties
LiSCN
Molar mass 65.02 g/mol
AppearanceWhite hygroscopic solid
Density 1.44 g/cm3 [1]
Melting point 274 °C (525 °F; 547 K) [2]
Boiling point 550 °C (1,022 °F; 823 K) (decomposition)
125 g/100 ml
Solubility Soluble in alcohol [1]
Structure [2] [3]
Orthorhombic (anhydrous, α-monohydrate, dihydrate)
Monoclinic (β-monohydrate)
C2/m (α-monohydrate)
Pnam (β-monohydrate)
Pnma (anhydrous, dihydrate)
a = 1215.1 pm, b = 373.6 pm, c = 529.9 pm (anhydrous)
4 (α, β-monohydrate)
6 (anhydrous, dihydrate)
Tetrahederal (α and β-monohydrate)
Thermochemistry
Std molar
entropy (S⦵298)
9 e.u. [1]
5.0 kcal/mol [1]
Hazards
GHS labelling:
GHS-pictogram-exclam.svg
Warning
H302+H312+H332, H412
NFPA 704 (fire diamond)
NFPA 704.svgHealth 4: Very short exposure could cause death or major residual injury. E.g. VX gasFlammability 1: Must be pre-heated before ignition can occur. Flash point over 93 °C (200 °F). E.g. canola oilInstability 1: Normally stable, but can become unstable at elevated temperatures and pressures. E.g. calciumSpecial hazards (white): no code
4
1
1
Related compounds
Other cations
Sodium thiocyanate, Potassium thiocyanate
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).

Lithium thiocyanate is a chemical compound with the formula LiSCN. It is an extremely hygroscopic white solid that forms the monohydrate and the dihydrate. It is the least stable of the alkali metal thiocyanates due to the large electrostatic deforming field of the lithium cation. [1]

Contents

Properties and preparation

Lithium thiocyanate is hygroscopic and forms the anhydrous, monohydrate, and dihydrate, which melts at 274, 60, and 38 °C, respectively. [2] The monohydrate supercools after melting, as it recrystallizes at 36 °C. It is soluble in many organic solvents, such as ethanol, methanol, 1-propanol, and acetone. However, it is insoluble in benzene. [1]

Due to its hygroscopicity, the anhydrous form is hard to prepare. The anhydrous form is usually prepared by the reaction of lithium hydroxide and ammonium thiocyanate, then the water was removed by vacuum, then the resulting solid was dissolved in diethyl ether, followed by adding to petroleum ether to form the ether salt, then it was heated in vacuum at 110 °C to result in the anhydrous salt. The overall reaction is the following: [1]

LiOH + NH4SCN → LiSCN + NH4OH

The ether can be replaced by THF. [2]

Crystallography

The monohydrate has 2 forms, the α form, and the β form; the α form reversibly converts to the β form at 49 °C. The α form has the space group C2/m while the β form has the space group Pnam. More info on its crystallography are listed in the table below.

Crystallographic data for the 4 forms of lithium thiocyanate
CompoundLiSCN [3] α-LiSCN·H2O [2] β-LiSCN·H2O [2] LiSCN·2H2O [3]
Molar mass (g/mol)65.0283.0483.04101.05
Crystal Structure Orthorhombic Orthorhombic Monoclinic Orthorhombic
Space GroupPnmaC2/mPnamPnma
Lattice constant a (Å)12.15115.02713.2265.721
Lattice constant b (Å)3.7367.5977.0628.093
Lattice constant c (Å)5.2996.7078.1669.66.9
β96.147°
Coordination number6446
Calculated density (g/cm3)1.801.451.451.50

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References

  1. 1 2 3 4 5 6 7 D. A. Lee (1964). "Anhydrous Lithium Thiocyanate". Inorganic Chemistry. 3 (2). ACS Publications: 289–290. doi:10.1021/ic50012a039.
  2. 1 2 3 4 5 6 Markus Joos; Maurice Conrad; Sebastian Bette; Rotraut Merkle; Robert E. Dinnebier; Thomas Schleid; Joachim Maier (2022). "On the crystal structures of lithium thiocyanate monohydrate LiSCN 1 H2O and the phase diagram LiSCN – H2O". Journal of Physics and Chemistry of Solids. 160. doi:10.1016/j.jpcs.2021.110299.
  3. 1 2 3 Olaf Reckeweg; Armin Schulz; Björn Blaschkowski; Thomas Schleid; Francis J. DiSalvo (2014). "Single-Crystal Structures and Vibrational Spectra of Li[SCN] and Li[SCN] · 2H2O". Zeitschrift für Naturforschung B. 69 (1). De Gruyter: 17–24. doi:10.5560/znb.2014-3220. S2CID   52235581.
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