Synthesis and characterisation of two lithium-thiocyanate solvates with tetrahydrofuran: Li[SCN]·THF and Li[SCN]·2THF

Abstract

Li[SCN]·THF and Li[SCN]·2THF can be obtained from solutions of anhydrous Li[SCN] in tetrahydrofuran (C₄H₈O, THF). Both compounds are very hygroscopic and slowly decompose even at room temperature. At ambient conditions Li[SCN]·THF crystallizes in the monoclinic space group P2₁/c with the lattice parameters a = 574.41(2), b = 1643.11(6), c = 830.15(3) pm and β = 99.009(1)° for Z = 4 as determined by laboratory X-ray powder diffraction. Its crystal structure contains Li⁺ cations surrounded by one THF molecule and three thiocyanate anions [SCN]⁻ forming {Li[NCS]₂[SCN](OC₄H₈)}²⁻ tetrahedra, which join together as pairs via shared N⋯N edges. CHNS combustion analysis and vibrational spectroscopy confirmed its composition, whereas differential scanning calorimetry and thermogravimetric analysis coupled with a mass spectrometer were applied to record its thermal behaviour. Li[SCN]·2THF crystallises in a primitive monoclinic lattice as well, but in the space group P2₁/n with the lattice parameters a = 1132.73(3), b = 1637.98(3), c = 1264.88(2) pm and β = 94.393(2)° for Z = 8 as determined from single-crystal X-ray diffraction data at 100 K. Its structure contains two crystallographically independent Li⁺-centred tetrahedra {Li[NCS]₂(OC₄H₈)₂}⁻, which form dimers {(C₄H₈O)₂Li[μ₂-NCS]₂Li(OC₄H₈)₂} via shared N⋯N edges. They are merely stabilised by weak agostic H⋯S interactions between some CH₂-groups of the C₄H₈O molecules and the [NCS]⁻ ligands.