Conformation variation of tris(2-carboxyethyl)isocyanuric acid induced by cocrystallized N-heterocyclic organic molecules

Crystallizations of tris(2-carboxyethyl) isocyanuric acid (H(3)tci) without or with N-heterocyclic organic molecules result in three distinct supramolecular complexes, [(H(3)tci)] (1), organic salt [(Hma)(+)center dot(H(2)tci)(-)] (2) and cocrystal [(H(3)tci)center dot(bipy)(1.5)] (3) (ma = melamine, bipy = 4,4'-bipyridine). In the absence of N-heterocyclic organic molecules, three 2-carboxyethyl arms of H(3)tci show a cis(anti)-cis(anti)-trans(anti) conformation. The H(3)tci molecules are extended to a 2D 4(4)-sql net via O-H center dot center dot center dot O hydrogen bonds. However, in the presence of ma or bipy, the conformation of the 2-carboxyethyl arms of H(3)tci in both 2 and 3 is transformed to cis(anti)-cis(anti)-cis(gauche)induced by cocrystallized N-heterocyclic organic molecules. In 2, ma plays a crucial role in the formation of O-H center dot center dot center dot N, N-H center dot center dot center dot O and O-H center dot center dot center dot O hydrogen bonds which direct the binary species to form the 2D double-layer structure containing 24-membered supramolecular macrocycles. Complex 3 is a 1D chain based on a [(H(3)tci)(2)center dot(bipy)(2)] 42-membered macrocycle incorporating the carboxyl-pyridyl H-bonding supramolecular synthons, which are extended by another bipy molecule to form the 1D chain. The 1D chains are further extended by means of a C-H center dot center dot center dot O non-classic hydrogen bond to form the resulting 2D layer containing three kinds of macrocycles. The 2D layers are packed into a 3D framework through pi/pi interaction between the triazinyl and pyridyl rings. Based on the structural analysis, we found that the conformation of H(3)tci could be modulated by introduction of the cocrystallized N-heterocyclic organic molecules. Moreover, the thermal stabilities of 2 and 3 are discussed.