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

Abstract

Crystallizations of tris(2-carboxyethyl)isocyanuric acid (H₃tci) without or with N-heterocyclic organic molecules result in three distinct supramolecular complexes, [(H₃tci)] (1), organic salt [(Hma)⁺·(H₂tci)⁻] (2) and cocrystal [(H₃tci)·(bipy)_1.5] (3) (ma = melamine, bipy = 4,4′-bipyridine). In the absence of N-heterocyclic organic molecules, three 2-carboxyethyl arms of H₃tci show a cis^anti–cis^anti–trans^anti conformation. The H₃tci molecules are extended to a 2D 4⁴-sql net via O–H⋯O hydrogen bonds. However, in the presence of ma or bipy, the conformation of the 2-carboxyethyl arms of H₃tci 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⋯N, N–H⋯O and O–H⋯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 [(H₃tci)₂·(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⋯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 π⋯π interaction between the triazinyl and pyridyl rings. Based on the structural analysis, we found that the conformation of H₃tci could be modulated by introduction of the cocrystallized N-heterocyclic organic molecules. Moreover, the thermal stabilities of 2 and 3 are discussed.