Co-crystallization experiments of thiocarbamides with bipyridine-type molecules

Abstract

Co-crystallization experiments conducted between thiocarbamide derivatives, (E)-O-alkyl N-aryl-thiocarbamide, ROC(S)N(H)R′, for R = Me, Et and iPr, and R′ = Ph and PhNO₂-4, containing a pharmaceutically active chromophorei.e. –C(S)–N(H)–, and the bipyridine-type molecules, 4,4′-bipyridine, trans-1,2-bis(4-pyridyl)ethene and 1,2-bis(4-pyridyl)ethane, showed the formation of stable 2 : 1 co-crystals, i.e. {[ROC(S)N(H)R′]₂(bipyridine-type molecule)}. Novel species were formed by grinding and solvent drop grinding methods, and characterized by powder X-ray diffraction. Five 2 : 1 co-crystals were isolated as single crystals by slow evaporation methods and fully characterized by spectroscopic and X-ray crystallographic methods. Uniformly, trimeric aggregates were formed where each pyridine-nitrogen was connected to an amide-H via a N_pyridine⋯H–N_amide hydrogen bond. This study shows that the eight-membered {⋯H–N–CS}₂ homosynthon found in the parent thiocarbamides is readily disrupted in the presence of bipyridine-type molecules to enable the formation of the stable heterosynthon, {N⋯H–N}.