Formation of pseudo[3]rotaxanes containing calix-bis-crowns and secondary ammonium ions and their thermodynamic stabilities in a solution: preorganization by second macrocycle and nonallosteric behavior exhibited by large crown cavities

This Letter describes the formation of pseudo3]rotaxanes containing calix4]-bis-crowns, exhibiting a 1,3-alternate conformation and large crown cavities, and secondary ammonium ions. The first and second association constants of pseudo3]rotaxane formation are moderate (K₁ = 175, K₂ = 100 M⁻¹) and are higher than that of the corresponding pseudo2]rotaxane (K = 24 M⁻¹), consisting of a calix4]-mono-crown and the same secondary ammonium ion.