Cite this: CrystEngComm, 2013, 15, 7212 Conformational influence of quinoline moieties in the crystal packing of bis(quinolinecarboxamide)alkane derivatives3 Received 7th May 2013, Accepted 6th June 2013 DOI: 10.1039/c3ce40807h www.rsc.org/crystengcomm Nicole Parra, a Luz Guarda, a Julio B. Belmar, a Paulina I. Hidalgo, a Claudio A. Jime ´nez,* a Jorge Pasa ´n* b and Catalina Ruiz-Pe ´rez b Six new compounds of the homologous series of N,N9-bis(2-quinolinecarboxamide)alkane (4a–c) and N,N9-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 … N quinoline 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 (b-sheets or 4,4-network), in these systems, depends on the interplanar angle between the amide group and the heterocyclic ring. Introduction Crystal engineering is an emerging area of research encom- passing various domains of chemistry, physics, biology, material sciences, engineering, and pharmaceuticals. Despite of the great advanced level that this discipline has reached, with a plethora of successful design strategies and properties that can be engineered, several fundamental questions remain unanswered. 1 Challenges in small molecule crystallography today have more to do with understanding the reasons why a compound chooses a particular conformational in the crystal lattice and not another. Crystal engineering is a part of such an endeavour because it attempts to establish packing trends in families of compounds as a whole. 2 The crystal packing viewed as the result of the optimization of various possible inter- molecular interactions between several functional groups simplifies the understanding and prediction of crystal structures to some extent. 3 Although it is accepted by the crystal engineering community that the crystal building process is a hierarchical process, sometimes weak interactions can have a considerable effect on the crystal packing as a few strong ones. 4 The disruption of a robust synthon of a particular functional group by the presence of another functional group has been termed as ‘‘interaction interfer- ence’’. 5 Hydrogen bonds formed by weak donor and acceptors were somehow disregarded during the first years of crystal engineering. Although small in energy, weak interactions outnumber covalent bonds in crystals and they often govern molecular packing and hence the crystal structures and bulk properties. 1,6 C–H … O, 7 C–H … N, 8 and C–H … p 9 are some examples of important weak hydrogen interactions that have been found controlling the conformational behaviour, mole- cular recognition, crystal engineering and hydrophobic effect in organic molecules and protein structures, even over stronger ones. The amide functional group is pervasive in nature and technology as structural materials. 10 This chemical function plays an important role in structural chemistry because of the great ability to form prevalent supramolecular homo and heterosynthons. 11 Bis and tris(pyridylcarboxamide)-based organic molecules are excellent aromatic N-containing supra- molecular synthons and have been widely employed in crystal engineering for studying the role of hydrogen bonding, p … p a Departamento de Quı ´mica Orga ´nica, Facultad de Ciencias Quı ´micas, Universidad de Concepcio´n, Casilla 160-C, Concepcio´n, Chile. E-mail: cjimenez@udec.cl b Laboratorio de Rayos X y Materiales Moleculares, Departamento de Fı ´sica Fundamental II, Facultad de Fı ´sica, Universidad de La Laguna, Avda, Astrofı ´sico Francisco Sa ´nchez s/n, E-38204 La Laguna, Spain. E-mail: jpasang@ull.es 3 Electronic supplementary information (ESI) available: Crystallographic information files in CIF format, figures of the crystal packing of compounds 4a– 5a, and histogram of bond separations from a CSD survey. CCDC 879084– 879089. For ESI and crystallographic data in CIF or other electronic format see DOI: 10.1039/c3ce40807h CrystEngComm PAPER 7212 | CrystEngComm, 2013, 15, 7212–7221 This journal is ß The Royal Society of Chemistry 2013