Molecular Pedal Motion Influences Thermal Expansion Properties within Isostructural Hydrogen-Bonded Co-crystals

摘要

The influence of molecular pedal motion on the thermal expansion properties of three isostructural hydrogen-bonded co-crystals based upon resorcinol is reported. The resulting co-crystals all exhibit discrete four-component assemblies held together by O–H···N hydrogen bonds and comprise resorcinol ( res ) with a series of isosteric bipyridines, namely, 4,4′-azopyridine ( 4,4′-AP ), trans -1,2-bis(4-pyridyl)ethylene ( 4,4′-BPE ), and 1,2-bis(4-pyridyl)acetylene ( 4,4′-BPA ). The ability to change the core of the hydrogen bond acceptor molecules from an azo (N═N) to an ethylene (C═C) and finally an acetylene (C≡C) group affords co-crystals that differ in their tendency to undergo dynamic pedal motion in the organic solid state. All three co-crystals, 2( res )?2( 4,4′-AP ), 2( res )?2( 4,4′-BPE ), and 2( res )?2( 4,4′-BPA ), exhibit thermal expansions that correlate with the strength of the noncovalent interactions, as well as the propensity of the core to undergo pedal motion.