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Two new aromatic pyrimidine-based derivatives designed specifically for halogen bond directed self-assembly are investigated through a combination of high-resolution Raman spectroscopy, X-ray crystallography, and computational quantum chemistry. The vibrational frequencies of these new molecular building blocks, pyrimidine capped with furan (PrmF) and thiophene (PrmT), are compared to those previously assigned for pyrimidine (Prm). The modifications affect only a select few of the normal modes of Prm, most noticeably its signature ring breathing mode, ν1. Structural analyses afforded by X-ray crystallography, and computed interaction energies from density functional theory computations indicate that, although weak hydrogen bonding (C–H···O or C–H···N interactions) is present in these pyrimidine-based solid-state co-crystals, halogen bonding and π-stacking interactions play more dominant roles in driving their molecular-assembly. 

Recent advancements in material science exploit non-covalent interactions, such as halogen bonding (XB) or π-stacking within solid-state molecular frameworks for application in organic electronic devices. Herein, we focus on these and other non-covalent interactions and the effect that furan and thiophene substituents play on the solid-state properties of co-crystals formed between pentafluoro(iodoethynyl)benzene ( F 5 BAI ; XB donor) and a pyridine disubstituted with either furans or thiophenes ( PyrFur 2 and PyrThio 2 ; XB acceptors). Spectroscopic and thermal analyses of 1 : 1 mixtures provide indirect evidence of XB interactions, whereas X-ray crystallography provides direct evidence that XB and π-stacking are present in both co-crystals. Density functional theory (DFT) computations provide insight into the relative electronic energetics of each pair-wise contact observed in the experimental F 5 BAI-PyrFur 2 and F 5 BAI-PyrThio 2 co-crystals.