Exocyclic self-assembly behavior of carboxylic acid and lariat ether macrocyclic hosts: regulation by pendent arm

Abstract

Interaction of 1,4-dicarboxybenzene (PTA) with N,N′-disubstituented dibenzo-diaza-18-crown-6-ethers (I, II, III, IV) bearing flexible side chain arms afforded the exocyclic supramolecular complexes of compositions 1 (I·PTA), 2 (II·PTA·0.2H₂O), 3 (III·PTA) and 4 (IV·PTA), while with N-substituented dibenzo-aza-18-crown-6-ethers (V, VI, VII) afforded the endo-coordinated H₂O salts 5 [3(V·H₂O)·(3PTA·7H₂O)], 6 [(VI·H₂O)·(PTA·3H₂O)] and 7 [2(VII·H₂O)·(PTA·11H₂O)], whose structures were determined by a single crystal X-ray method. These products were also obtained by the same synthetic conditions. Single crystal X-ray structural investigations on these solids confer: P space symmetry for compound III and complexes 3, 5 and 7; C2/c space symmetry for the complexes 1, 2 and 4; P2₁/n space symmetry for compound I; P2₁2₁2₁ for complex 6. The macrocyclic entities in compounds I, III and complexes 1, 2, 3, 4 with the ‘chair-like’ conformation of the crown ether ring and the extended arrangement of the pendent arms, adopt the structure as ‘out–out’ cyclic amines. But the macrocyclic entities in salts 5 and 6 adopt the C-shape conformation. The side chain arm may introduce minor crystal structure disparity, particularly 3D packing types in the exocyclic complexes 1, 2, 3 and 4, with the arrangement of the pendent arms in protonated mono-sidearm crown ethers. Moreover, each complex with distinct ionic states, indicates that the proton transfer depends also upon the solid state environment.