The structure of a crystalline monolayer of 1,3,5-triazine has been characterised using X-ray diffraction. The monolayer is found to exhibit a hexagonal unit cell with a lattice parameter of 6.161(5) Å, indicating the formation of C–H … N hydrogen bonds. DFT simulations have been performed exhibiting close agreement with the experimental structure. By comparing the strength of the intermolecular interactions both with and in the absence of Van der Waals corrections, it is possible to estimate an interaction strength for the weak C–H … N hydrogen bonds.
Using a combination of X-ray diffraction and simulation techniques, we are able to identify a crystalline monolayer of 1,3,5-triiodotrifluorobenzene formed on graphite. The monolayer is found to exhibit an incommensurate hexagonal unit cell with a lattice parameter of 9.28(7) Å, exhibiting a trigonal arrangement of iodine atoms not found in the bulk structure. DFT simulations have been performed exhibiting close agreement with the experimental structure. Importantly these simulations can be used to compare the strength of the intermolecular interactions both with and without Van der Waals corrections. Thus it is possible to estimate that halogen bonding consists of approximately half the total interaction energy. This demonstrates that despite the presence of strong directional non-covalent bonding, dispersion interactions account for a very significant proportion of the total energy.
A homologous series of halogen bonding
monolayers based on terminally
iodinated perfluoroalkanes and 4,4′-bipyridine have been observed
on a graphitic surface and noninvasively probed using powder X-ray
diffraction. An excellent agreement is observed between the X-ray
structures and density functional theory calculations with dispersion
force corrections. Theoretical analysis of the binding energies of
the structures indicate that these halogen bonds are strong (25 kJ
mol
–1
), indicating that the layers are highly stable.
The monolayer structures are found to be distinct from any plane of
the corresponding bulk structures, with limited evidence of partitioning
of hydrocarbon and perfluoro tectons. The interchain interactions
are found to be slightly stronger than those in related aromatic systems,
with important implications for 2D crystal engineering.
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