Bis-phenol a cyclophanes: Synthesis, crystal structures and binding studies

The synthesis and structural characterisation of three new macrocyclic bis- phenol A cyclophane ethers are described. The solid state structures of two of the cyclophanes were determined by single crystal X-ray diffraction. Cy clophane 3 crystallises in the orthorhombic space group Pbca with unit cell dimensions of a = 11.533(7), b = 29.383(8), c = 14.927(8) Angstrom and cyc lophane 4 in the monoclinic space group P2(1)/n with cell dimensions of a = 11.585(4), b = 11.839(2), c = 18.866(2) Angstrom, beta = 94.48(2)degrees. The X-ray crystal structures reveal distorted conformations, thus supportin g the weak binding of quats in solution observed by the NMR studies. In the crystalline state both macrocycles were found to form self-complementary d imers held together by weak intermolecular pi-pi and CH-pi interactions. Th e binding behaviour towards a series of tetralkylammonium cations was deter mined by H-1 NMR titration in CDCl3 solution. The interactions between the hosts and the quats were clearly detectable but too weak to be translated i nto meaningful equilibrium constants.