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

Two new trigonal and tetragonal polymorphs of the title compound, iodidotris(tetrahydrofuran-kappaO)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 I41cd. 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