Nine Supramolecular Adducts of 4-dimethylaminopyridine and Carboxylic acids Assembled by Classical Hydrogen Bonds and Other Noncovalent Intermolecular Interactions

Cocrystallization of the widely available 4-dimethylaminopyridine, with a series of carboxylic acids gave nine molecular adducts 4-dimethylaminopyridinium trifluoroacetate (1) , 4-dimethylaminopyridinium glycolate glycolic acid (2) , 4-dimethylaminopyridinium 2-furoate dihydrate (3) , tri(4-dimethylaminopyridinium) tri(o-chlorobenzoate) tetrahydrate (4) , 4-dimethylaminopyridinium 4-bromobenzoate 4-bromobenzoic acid (5) , 4-dimethylaminopyridinium 4-formylbenzoate 4-formylbenzoic acid (6) , 4-dimethylaminopyridinium 2,4-dichlorobenzoate (7) , 4-dimethylaminopyridinium 2-aminobenzoate 2-aminobenzoic acid (8) and bis(4-dimethylaminopyridinium) 5-nitroisophthalate 5-nitroisophthalic acid methanol solvate (9) . The nine adducts have been characterised by X-ray diffraction, IR and elemental analysis, the melting points were also reported. Their structural and supramolecular aspects are fully analyzed. The result reveals that among the nine investigated crystals only the ring Ns in the 4-dimethylaminopyridine moieties are protonated when the carboxylic acids are deprotonated. The crystal packing is interpreted by the strong charge-assisted N-H center dot center dot center dot O hydrogen bond between the NH+ and the deprotonated acidic groups. Except the N-H center dot center dot center dot O hydrogen bonds, the charge assisted or neutral O-H center dot center dot center dot O hydrogen bonds were also found at 2-6, 8 and 9 . The COOH center dot center dot center dot COO- synthon has been at 2, 5-6 and 8-9. Further analysis of the crystal packing indicated that a different family of additional CH-O/CH2-O/CH3-O, F-F, Br-Br, CH-Cl, CH3-Cl, CH-pi/CH3-pi, C-H center dot center dot center dot C-pi, C-pi, Cl-O, O-C, O-pi and pi-pi contacts contribute to the stabilization and expansion of the total high-dimensional (2D-3D) framework structures. For the synergism of the various nonbonding contacts there created homo/hetero supramolecular synthons or both. (C) 2021 Elsevier B.V. All rights reserved.

Automated summary

In this study, cocrystallization of 4-dimethylaminopyridine with a series of carboxylic acids yielded nine molecular adducts, which were characterized by X-ray diffraction, IR, and elemental analysis. The results showed that only the ring Ns in the 4-dimethylaminopyridine moieties were protonated in the investigated crystals. The crystal packing was interpreted by the strong charge-assisted N-H···O hydrogen bond between the NH+ and the deprotonated acidic groups, with additional nonbonding contacts contributing to the stabilization and expansion of the high-dimensional framework structures.