Structural Characterization of a Calix[4]arene Constrained to a 1,3-Alternate Conformation by Polyether Bridging

Abstract

Despite evidence of coordinative interactions with alkali metal picrates in solution, attempts to crystallize Li⁺, Na⁺, K⁺, Rb⁺ or Cs⁺ complexes of a 'doubly crowned' calix [4] arene (obtained by reaction of tetraethylene glycol ditosylate with p-t- butylcalix [4] arene ) have resulted only in the deposition of crystals of the free ligand . A room-temperature single-crystal X-ray study has shown the crystals to be hexagonal, space group P6₄22, a (= b) 17.092(5), c 20.147(7) Ǻ, V 5097(5) Ǻ³, Z 3, conventional R (on |F|) 0.082 for 1397 'observed' reflections [I > 3σ(I)]. The highly symmetrical oblate-globular shape of this doublecrowncalix allows the enclosure of an extended narrow cavity possibly better suited to the binding of two small metal ions rather than one large.