Structural Features and Thermal Stability of 25,26,27,28-Tetrahydroxycalix[4]arene Molecular Complexes with Solvents

A single crystal of 25,26,27,28-tetrahydroxycalix[4]­arene molecular complex with n-hexane was grown by slow evaporation of a solution in n-hexane allowing a complete elucidation of its structure. For the first time a 25,26,27,28-tetrahydroxycalix[4]­arene molecular complex with toluene was obtained. In addition, its thermal stability was studied. The kinetic sorption curves of acetone, acetonitrile, n-hexane, and toluene saturated vapors within 25,26,27,28-tetrahydroxycalix[4]­arene were derived experimentally. It was shown that the kinetic sorption curve of acetonitrile saturated vapor within 25,26,27,28-tetrahydroxycalix[4]­arene has a distinct peak corresponding to the 1:1 stoichiometry. It was suggested that the structural reorganization of 25,26,27,28-tetrahydroxycalix[4]­arene provides transport of acetonitrile molecules into the molecular crystal and subsequent complexation with the formation of a thermodynamically stable hexagonal structure. A conclusion was drawn that the high thermal stability of 25,26,27,28-tetrahydroxycalix[4]­arene solvates is due to strict compliance with the shape and size of the “guest” molecule and “host” cavity size.