Amar Ballabh

Hydrogen bonded supramolecular network in organic salts: crystal structures of acid–base salts of dicarboxylic acids and amines

Four new organic salts, namely bis(2-aminopyridinium) fumarate–fumaric acid (1∶1) 1, benzylammonium hydrogen fumarate 2, 2-aminopyridinium hydrogen cyclobutane-1,1-dicarboxylate 3 and benzylammonium hydrogen cyclobutane-1,1-dicarboxylate 4 have been synthesized and characterized by FT-IR, 1H NMR and single crystal X-ray crystallography in order to analyse their supramolecular structures. While 1, 2 and 4 form two-dimensional layer structures, 3 displays a one-dimensional network. The role of stronger O–H⋯O and N–H⋯O interactions and weak C–H⋯O interactions on the supramolecular arrangement have been discussed based on the single crystal X-ray structures.

Facile preparation and structure–property correlation of low molecular mass organic gelators derived from simple organic salts

Secondary ammonium salts namely dicyclohexylammonium 4-nitrocinnamate 1, 3-nitrocinnamate 2, 2-nitrocinnamate 3 and the corresponding benzoate salts namely dicyclohexylammonium 4-nitrobenzoate 4, 3-nitrobenzoate 5 and 2-nitrobenzoate 6 have been prepared and scanned for gelation. Salts 1 and 2 display excellent gelation properties. Structure–property correlations of these salts based on various X-ray diffraction data have been attempted and compared with the earlier results reported by our group. Single crystal structures of the gelator dicyclohexylammonium 3-bromocinnamate 7 reported earlier by us, and 4- and 2-methylbenzoate 8 and 10, both nongelators, have also been reported in the context of drawing important conclusions on structure–property correlations of dicyclohexylammonium cinnamate based gelators.

Probing the O/Br-Br halogen bonding in X-ray crystal structures with ab initio calculations†

Halogen bonding is a class of non-covalent interaction in which a halogen atom interacts with an electronegative atom such as oxygen or nitrogen in an attractive fashion. In this work, we investigate the X-ray crystallographically observed non-bonded C–O⋯Br–Br interactions with methanol, 1,4-dioxane and acetone by quantum chemical calculations. The C–O⋯Br–Br interaction was further extended with dimethyl ether, 1,3-dioxane and formaldehyde. The CBS-QB3 calculated results show that the oxygen and bromine non-bonded interactions are in the order of 3–5 kcal mol−1, which are comparable to the typical O–H⋯O and N–H⋯O type hydrogen bond strengths [S. J. Grabowski, Chem. Rev., 2011, 111, 2597]. The AIM calculations show good correlation between the density at the intermolecular critical point and the interaction energy. This study has also explored the directionality of bromine molecule addition to the lone pairs at the sp2 and sp3oxygen atoms of methanol, 1,4-dioxane, acetone, dimethyl ether, 1,3-dioxane and formaldehyde. The calculated results show that the directionality of bromine molecules towards interacting with the oxygen atoms of 1,4-dioxane and acetone is in accord with the observed X-ray crystal structure analysis. However, in the case of methanol, the approach of the bromine molecule seems to be influenced by the crystal forces. The influence of stereoelectronic effects towards the approach of the bromine molecule to 1,3-dioxane is more prominent than that of the 1,4-dioxane system. The existence and magnitude of the positive regions (σ-hole) on the other side of the bromine molecule complexed with the donor molecule seem to facilitate the bridge formation as observed in the X-ray crystal structures.