Crystal structures of complexes between alkali-metal salts and cyclic polyethers. Part IV. The crystal structures of dibenzo-30-crown-10 (2,3:17,18-dibenzo-1,4,7,10,13,16,19,22,25,28-decaoxacyclotriaconta-2,17-diene) and of its complex with potassium iodide

Abstract

The crystal structures of the title compounds have been determined from X-ray diffractometer observations. The molecules of the cyclic ether are centrosymmetric with Z= 2 in a monoclinic unit cell having a= 16·960, b= 8·920, c= 9·096 Å, β= 90·03°, and space group P2₁/c. They form loops approximately parallel to the a axis. The structure was solved by the iterative application of Sayres' equation, and refined by least-squares methods to R 0·056 for 1414 independent observations.

In the complex Z= 4 in an orthorhombic unit cell having a= 19·576, b= 12·405, and c= 12·965 Å with space group Pnna. The structure was solved by conventional Patterson and Fourier methods and refined by least-squares techniques to R 0·046 for 1102 independent observations. Each potassium ion lies on a two-fold axis, and is enclosed by a ligand molecule wrapped round to give ten K–O distances in the range 2·850(6)–2·931(6)Å. The iodide ions also lie on two-fold axes and are not in contact with potassium. The packing of the complex cations and the iodide ions is a distorted sodium chloride structure.

Bond lengths and angles in the complexed and free molecules are the same; the conformations and different. Four of the C–C–O–C angles change from trans in the free molecule to gauche in the complex; the remaining torsion angles are of the same type in both forms but corresponding ones differ by as much as 30° and the sign may be reversed.