Crystal and Molecular Structure of Benzo-13-crown-4 and Its Complex with Lithium Thiocyanate

The crystal structures of the title compounds have been determined from single-crystal X-ray diffractometry data. There are 4 molecules of polyether in the unit cell of dimensions a = 8.014 Á, b = 8.309 Á, and c = 18.964 Á. The space group is P2₁2₁2₁. The structure was solved by direct methods and refined by least-squares methods to a value of 0.042 for R with use of 1243 independent observations. Crystals of the complex with LiSCN in the space group Pbca have 8 molecules in unit cell of dimensions a = 11.870 Á, b= 13.453 Á, and c = 19.105 Á. The structure was solved by Patterson and direct methods and refined by least-squares methods to 0.069 for R with use of 1612 independent observations. The free crown ether is “bent”: three oxygens are pointing to the interior and one to the exterior of the macrocyclic ring. In the complex, Li is pentacoordinated to four crown oxygens and the N of the SCN anion. Li-O distances are in the range of 2.01-2.16 Á, and the Li-N distance is 1.945 Á. Complexation of the ether changes its conformation. A rotation of ~ 145° about the CC-CO bond in the C-C-C-O dihedral angle brings one of the oxygens inward, allowing simultaneous coordination of all four oxygens to the Li cation. All of the remaining torsion angles are similar to those which are typical in these systems. Also, the C-C aliphatic bonds are short (average C-C ~ 1.49 Á) in both molecular structures, in agreement with known structures of a similar kind.