Crystal structures of complexes between alkali-metal salts and cyclic polyethers. Part IX. Complex formed between dibenzo-24-crown-8 (6,7,9,10,12,13,20,21,23,24,26,27-dodecahydrodibenzo[b, n][1,4,7,10,13,16,19,22]octaoxacyclotetracosin) and two molecules of sodium o-nitrophenolate

Abstract

The crystal structure of the title complex has been determined by direct methods from X-ray diffractometer data. Crystals are monoclinic, space group C2/c, a= 19.629(11), b= 10.755(6), c= 17.425(31)Å, β= 90.21(6)°. Z= 4. Refinement of atomic parameters by full-matrix least-squares methods gave R 0.084 for 1 894 reflections.

The two halves of the complex are related by a two-fold symmetry axis which passes through a pair of aliphatic C–C bonds on opposite sides of the crown ring. The polyether ring folds around the pair of sodium ions. Each cation interacts with three oxygen atoms of the ligand; each of the fourth pair of oxygen atoms is 2.965 Å from a cation, not directed towards the cation, and not involved in co-ordination. Torsion angles in the crown ring differ considerably from normal; about the two-fold axis, the torsion angle of one C–C bond (where there is slight site disorder) is 117°, an eclipsed arrangement, and of the other bond is 139°.

An o-nitrophenolate anion on each side of the crown ring completes the six-fold co-ordination of the cations. Each anion chelates a cation and the phenolate oxygen (carrying most of the anionic charge) bridges the pair of cations. Molecular dimensions are as expected. Packing in the crystal is by van der Waals' interactions, including the parallel arrangement of benzene rings of crown ligands about a centre of symmetry.