Layered Assembly Formed by Benzyl Viologen and <i>p</i>-Sulfonatothiacalix[4]arene and Their Complexation Thermodynamics

A novel layered assembly, possessing 5,11,17,23-tetrasulfonatothiacalix[4]arene (STCA) and benzyl viologen dication (BV2+), has been prepared in the solid state. The crystal structure of the layered assembly reveals that the intermolecular interaction between STCA and BV2+ is a 1:2 stoichiometry, and meanwhile, the STCA forms a layered array in an up-and-down fashion. To investigate the thermodynamic origin of the inclusion complexation between STCA and dicationic BV2+ molecules, microcalorimetric titrations have been performed in phosphate buffer solution (pH 7.2) at 25 °C to calculate the complex stability constants (KS) and thermodynamic parameters (ΔG°, ΔH°, and TΔS°) for stepwise binding to form the stoichiometric 1:2 inclusion complex between STCA and BV2+. Thermodynamically, the resulting complex of BV2+ with STCA is absolutely enthalpy-driven in buffer solution, typically showing larger negative enthalpy changes due to the hydrophobic, electrostatic, and π−π interactions. 1H NMR spectroscopic investigations indicate that not only the resulting complex between STCA and BV2+ but also two BV2+ guest molecules bond to the upper and lower rim of STCA in sequence. Therefore, the comprehensive evaluation of the binding behavior in solution and the solid state by thermodynamics and crystallography will serve us in designing and preparing the claylike materials, in which organic or inorganic counterparts are intercalated to the organic−organic layer.