Complexes between macrobicyclic polyethers and hydrogen bond donors; the crystal structure of ammonium iodide and 1,5,12,16,23,26,29,32-octaoxa [10][5.5]orthocyclophane

Abstract

Interaction between hydrogen bonding donor molecules and four macrobicyclic polyethers derived from dibenzo-14-crown-4 with the bridge which forms the second ring containing (1) three, (2) four, (4) five oxygen atoms separated by (CH₂)₂units, or else (3) by two aliphatic and two more oxygen atoms on a benzene ring has been investigated by potentiometric titration, and by i.r. and u.v. spectroscopy. Hydrated complexes have been isolated from (2), with ammonium salts, glycine, hydrochloric acid, picric acid, and trichloroacetic acid and from (4) with ammonium bromide. Crystal structure of the ammonium iodide complex of (2), with stoicheiometry NH₄I:(2):H₂O of 1:1:n, has shown it to contain centrosymmetric dimeric [NH₄⁺(2)]₂ cations and iodide anions with n ca.1.5 in a unit cell a= 22.734(3), b= 14.288(3), c= 17.514(4)Å, β= 100.46(2)°, space group C2/c. The phase problem was solved by direct methods and the parameters refined to R= 0.062 for 3 021 observations. Each ammonium nitrogen atom is nearly coplanar with six oxygen atoms of one ligand [N–O, 2.718(7)–2.868(7)Å], and is hydrogen bonded to one oxygen atom [N–O, 2.981(7)Å] of the other ligand in the dimer. The complex dimeric cations pack to form channels which contain iodide ions and water molecules held by hydrogen bonding.