Quantitative assessment of the nature of noncovalent interactions in N -substituted-5-(adamantan-1-yl)-1,3,4-thiadiazole-2-amines: insights from crystallographic and QTAIM analysis

Three adamantane-1,3,4-thiadiazole hybrid derivatives namely; -ethyl-5-(adamantan-1-yl)-1,3,4-thiadiazole-2-amine I, -(4-fluorophenyl)-5-(adamantan-1-yl)-1,3,4-thiadiazole-2-amine II and (4-bromophenyl)-5-(adamantan-1-yl)- -1,3,4-thiadiazole-2-amine III, have been synthesized and crystal structures have been determined at low temperature. The structures revealed that the orientation of the amino group is different in non-halogenated structures. Intra- and intermolecular interactions were characterized on the basis of the quantum theory of atoms-in-molecules (QTAIM) approach. Intermolecular interaction energies for different molecular pairs have been obtained using the PIXEL method. Hirshfeld surface analysis and 2D-fingerprint plots revealed that the relative contributions of different non-covalent interactions are comparable in compounds with halogen (Br and F) substitutions. Crystal structures of II and III show isostructural behaviour with 1D supramolecular constructs. In all three structures, the N-H⋯N hydrogen bond was found to be stronger among other noncovalent interactions. The H-H bonding showed a closed shell in nature and played significant roles in the stabilization of these crystal structures.