trans-Pyridyl and naphthyridyl cinnamides as alternatives for urea in complexation of carboxylic acid and formation of water-templated assemblies in the solid state.

A series of alpha,beta-unsaturated amides of pyridine and naphthyridine (1-4) derived from trans-cinnamic acid and its derivatives has been synthesized. The hydrogen-bonding behavior of these simple amides in the solid state has been established by solving X-ray structures. In solution and in the solid state, the above compounds 1-4 were found to bind carboxylic acid utilizing both conventional and unconventional hydrogen bonds. Hence, the possibility has been revealed of using this motif as an alternative of urea for the design of task-specific hosts. The experimental results have been rationalized with an accompanying theoretical study involving density functional calculations on the structure and the relative energies of different rotamers of the host systems as well as the binding energy of the complexes formed with trans-cinnamic acid. Generally, small binding energies (0.58-0.70 eV) are calculated for the complexes in the gas phase which become even smaller in chloroform solvent.