METAL-ION COMPLEXATION BY TETRAESTER DERIVATIVES OF BRIDGED CALIX[4]ARENES

A series of bridged calix [4] arenes (5-10 methylene groups in the bridge) were synthesized and transformed into their tetraester derivatives by reaction with ethyl bromoacetate. The stability constants for complexes of the tetraester derivatives with sodium, potassium and silver cations, determined in methanol by spectroscopic or potentiometric techniques, show a drastic decrease (more than 10(5) for Na+) for the shorter methylene chains. H-1 NMR studies demonstrate a conformational rearrangement of the calixarene part to fourfold symmetry to be necessary for the complexation of a cation, which is prevented by the shorter chains. This is further confirmed by the X-ray structure of a tetraester derivative with a CH2CH2COCH2CH2 bridge; crystals. were monoclinic, space group P2(1)/c, a = 11.847(2), b = 39.773(5), c = 12.127(2) angstrom, beta = 109.24(1)-degrees, V = 5395.1 angstrom3, Z = 4, D(x) = 1.186 Mg m-3.