About the polymorphism of Li(C4H8O)3I: crystal structures of trigonal and tetra­gonal polymorphs

摘要

Two new trigonal and tetra­gonal polymorphs of the title compound, iodido­tris­(tetra­hydro­furan-κO)lithium, are presented, which both include the isolated ion pair Li(THF)3 ⁺·I⁻. One Li—I ion contact and three tetra­hydro­furan (THF) mol­ecules complete the tetra­hedral coordination of the lithium cation. The three-dimensional arrangement in the two polymorphs differs notably. In the trigonal structure, the ion pair is located on a threefold rotation axis of space group P-3 and only one THF mol­ecule is present in the asymmetric unit. In the crystal, strands of ion pairs parallel to [001] are observed with an eclipsed conformation of the THF mol­ecules relative to the Li⋯I axis of two adjacent ion pairs. In contrast, the tetra­gonal polymorph shows a much larger unit cell in which all atoms are located on general positions of the space group I41 cd. The resulting three-dimensional arrangement shows helical chains of ion pairs parallel to [001]. Apart from van der Waals contacts, no remarkable inter­molecular forces are present between the isolated ion pairs in both structures.