Carbon-tetrel bonds: cooperative existence and disappearance in elastically bendable fluorescent organic single crystals by operating within the hierarchy of non-covalent interactions

Abstract

The crystal structures of 4-Cl/Br/I/Me-chalcones have revealed the formation of an unexpected molecular packing, space group, and elastically bendable fluorescent crystal, wherein the molecules are packed with a combination of intermolecular interactions, including carbon tetrel bonds, π–π stacking and other non-bonding interactions. All four compounds crystallize in the tetragonal space group. The structure is unique as four-fold symmetry is observed at the centre of the carbon bond. The carbon bond strength gets weakened as the substitution changes from chlorine to bromine and eventually vanishes with a highly polarizable iodine substituted analogue. The fine tuning of the mechanical properties in fluorescent single crystals using carbon-tetrel bonds is hitherto unreported. The nature of the carbon bond is analysed and corroborated as co-operative in nature. These findings are supported by DFT calculations.