The crystal structures of 1,5,12,16,23,26,29,32,35-nonaoxa[13][5.5]orthocyclophane and its complex with rubidium picrate

Abstract

The crystal structures of the macrobicyclic polyether (Ic) systematically named in the title, and of its complex with rubidium picrate have been determined from observations collected on a CAD4 diffractometer. Crystals of the uncomplexed ether are monoclinic with four molecules in a unit cell having a= 8.859(4), b= 11.555(10), c= 25.325(11)Å and β= 102.49(4)° and space group P2₁/c. The structure was solved by direct methods and refined by full matrix least squares to R 0.068 for 3 285 observed reflections. The molecules take up a folded conformation, with the aliphatic bridge much nearer one benzene ring than the other. There are several unexpected values for the torsion angles. The rubidium picrate complex is triclinic with space group P. In the unit cell a= 16.280(4), b= 16.660(5), c= 16.077(3)Å, α= 111.62(2), β= 116.29(2), γ= 91.32(2)°, there are two crystallographically independent rubidium ions, ligand molecules (Ic), picrate ions, and water molecules. One rubidium, Rb(1), is nine-co-ordinated by the oxygen atoms of (Ic)(1) with Rb–O ranging from 2.952(7) to 3.368(11)Å, giving a complex cation [Rb(1)(Ic)(1)]⁺. The second rubidium, Rb(2), is eleven-co-ordinated by the nine oxygen atoms of (Ic)(2)[Rb–O 2.922(11)–3.277(15)Å], by a nitro-oxygen atom from picrate (2)[Rb–O 2.933(16)Å], and by a water molecule on a centre of symmetry [Rb–O 3.077(2)Å]. This water molecule bridges two complexed ion pairs so that the entity is {[Rb(2)(Ic)(2)picrate(2)]₂H₂O}⁰. There may be hydrogen bonding contacts between the second water molecule, the co-ordinating picrate(2) and the unco-ordinated picrate(1). Disorder is evident in the aliphatic chains of each ligand and in the picrate(1). Least squares refinement in two blocks of full matrices gave R 0.105 for 4 746 observed reflections. The conformations of the complexed forms of the macrobicyclic molecule are similar and differ markedly from that of the uncomplexed molecule.