Host proficiency of N,N′-bis(9-phenyl-9-thioxanthenyl)ethylenediamine for pyridine and the methylpyridine guests – a competition study

AbstractN,N′-Bis(9-phenyl-9-thioxanthenyl)ethylenediamine proved to be an extremely efficient host compound for pyridine and the isomeric methylpyridines. Furthermore, this host displayed selective behaviour during equimolar guest competitions, consistently favouring 3-methylpyridine in binary, ternary and quaternary experiments. Selectivity orders were 3-methylpyridine >> 4-methylpyridine > 2-methylpyridine, and 3-methylpyridine > pyridine > 4-methylpyridine > 2-methylpyridine, for equimolar ternary and quaternary solutions, respectively. When guest concentrations in binary competitions were varied, 3-methylpyridine remained the favoured guest, even at low 3-methylpyridine concentrations. Single crystal X-ray diffraction showed that all four complexes were isostructural (monoclinic, P21/n) while guests occupy discrete cavities in the crystal. Only 3-methylpyridine experiences (guest methyl)C–H∙∙∙π(host) and (guest methyl)C–H∙∙∙H–Ar(host) interactions, explaining the observed affinity of the host for this...