Three conformational polymorphs and order-disorder phase transition in a calix

Three polymorphs of a calix[4]arene fixed in the 1,3-alternate conformation by two bridges, a crown-6 on one side and a crown-6 including a photoisomerizable azobenzene unit on the other, 8,11,14,28,31,34,37,40,43,57,60,63-dodecaoxa-2,3-diazanonacyclo[62.2.2.2(4,7).1(16,45).1(26,55).0(15,20).0(22,27).0(44,49).0(51,56)]doheptaconta-1(66),2,4,6,15,17,19,22,24,26,44,46,48,51,53,55,64,67,69-nonadecene, have been characterized by single-crystal X-ray diffraction. In all the polymorphs the azobenzene group is in the more stable trans conformation. The polymorphism arises from the high conformational flexibility of the bridges, which are arranged differently and are highly disordered in the two monoclinic forms (1) and (2a). Form (2a) presents a phase transition near 268 (2) K, leading to a triclinic form (2b), differing from the high-temperature form by some ordering of the chains and a subsequent reduction in crystallographic site multiplicity. The evolution of the cell parameters and peak width with temperature has been investigated down to 173 (2) K. Adiabatic calorimetry measurements indicate a smooth transition centered at 265.0 (1) K, with a heat capacity jump of 60 mJ g(-1) K(-1), suggesting a second-order nature for the transition.

Calix Crowns Derived from para-Bridged Calix

Two calix[4]arenes, bridged by aliphatic chains of five and eight carbon atoms spanning two opposite para positions, have been converted into their 1,3-crown ether derivatives by reaction with tetraethylene and pentaethylene glycol ditosylates. Of the two possible 1,3-crown derivatives, only the formation of those isomers is observed in which the phenolic units connected at the para positions are etherified. This has been established in one case by a single-crystal X-ray analysis. Preliminary results for the extraction of selected alkali and alkaline-earth metals are reported.