While determination of the crystal structure of 1,3;2,4-biscrown-5-calix[4] arene (chloroform solvate, triclinic. space group Pī, a 11.151(4), b 16.832(6), c 21.929(8) Ǻ, α 98.78(3), β 92.02(3), γ 92.12(3)°, Z = 4 f.u ., conventional R on |F| 0.085 for 4699 'observed', I > 2σ(I), reflections) shows that this ligand has a closely similar solid state conformation to that of its previously characterized, substituted analogue, 1,3;2,4-biscrown-5-p-t-butylcalix[4] arene, the two ligands do differ significantly in their interactions with alkali metal picrates in chloroform solution. Most obviously, the t-butyl substituents of the latter ligand appear to inhibit caesium binding. changing the nature of the interactions to a form similar to that of both ligands with Li+ and Na+, for which 1H n.m.r. spectroscopy indicates weak exocyclic binding to some of the polyether oxygen atoms. 1H n.m.r. spectroscopy also provides evidence of picrate binding to the metals in isomeric forms.
The phenoxyl group-modulated interplay of cation–π and σ-type interactions in the alkali metal series