Comparative Theoretical Study of O- and S-Containing Hydrogen-Bonded Supramolecular Structures

摘要

We report a computational density-functional theory (DFT) study of planar hydrogen-bonded supramolecular structures (dimers, chains, and networks) of cyanuric acid (CA) and trithiocyanuric acid (TTCA). We confirm that the electronegative atom (oxygen or sulfur) influences both the geometry and the strength of hydrogen bonds and therefore affects the order of stabilities of the two-dimensional networks of CA and TTCA. The N—H···O bonds are stronger and have the energy of ～ —0.27 eV in a CA dimer, compared to ～ —0.18 eV for N—H···S bonds. Our analysis, based entirely on available hydrogen bonding connections, predicts that six 2D network structures are possible both for CA and TTCA. Our DFT calculations show that all these network structures are stable for CA, however, only four out of the six networks are stable for TTCA. We compare our results with the available experimental data on the structure of self-assembled networks on some flat crystal surfaces and with X-ray data on the bulk crystal structure of these molecules. For CA, the calculated most stable network closely corresponds to the bulk crystal structure of CA, the two next most stable 2D structures have been observed as self-assembled networks on the Au(111) and graphite surfaces. For TTCA, however, only indirect comparison with the available bulk crystal data is possible, and we find that our most stable TTCA network does not match the layers in the observed crystal structure.