Conformational influence of quinoline moieties in the crystal packing of bis(quinolinecarboxamide)alkane derivatives

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Six new compounds of the homologous series of N,N′-bis(2-quinolinecarboxamide)alkane (4a–c) and N,N′-bis(6-quinolinecarboxamide)alkane (5a–c) derivatives having two, four and six carbon atoms in the alkyl spacer were synthesized and their crystal structures were determined by single crystal X-ray diffraction. These solid-state structures have been analyzed finding that the two series exhibit interesting differences between them. The remarkable preference of the bis(6-quinolinecarboxamide)alkanes to form one- or two-dimensional networks via N–H⋯O intermolecular hydrogen bonds appears total or partially disrupted by the intramolecular N–H⋯Nquinoline hydrogen bond in bis(2-quinolinecarboxamide)alkanes. These interactions, theoretically sorted as a ‘very weak and purely electrostatic’, seems to play a fundamental role in the crystal packing of bis(2-quinolinecarboxamide) derivatives. On the other hand, the rationalization of the bis(6-quinolinecarboxamide) structures are completely in agreement with the statement that the amide-to-amide hydrogen bond formation and network (β-sheets or 4,4-network), in these systems, depends on the interplanar angle between the amide group and the heterocyclic ring.