Molecular tapes based on CN ⋯ Cl interactions

Abstract

Weak C=N.-CI interactions may be used to design linear molecular tapes.The construction of molecular ensembles, utilising the directional characteristics of intermolecular forces, is one of the key elements of contemporary supramolecular chemistry. 1 Linear or zig-zag arrays of flat molecules have been described by Lehn2 and by Whitesides3 who has referred to such arrays as 'molecular tapes'. Tapes, such as those found in the crystal structures of molecular complexes of substituted aminopyrimidines or melamines and substituted barbituric acids,2.3 have been designed using the directional properties of strong N-H.e.0 bonds.4.5 The underlying rationale is that these bonds are so specific and important in crystal packing that molecular assembly can proceed in a regular, anticipated manner. In this communication, we show that molecular tapes may be constructed with forces that are far weaker than conventional hydrogen bonds. Short C=N...Cl contacts were first postulated by Hassel6 and later reviewed by Britton.7 We have shown that N...Cl distances, D , in crystals range between 3.00 and 3.45 A and that GN...Cl angles, 8, vary between 80 and 18V.8 This CkN..-Cl contact arises owing to the polarisability of C1, and the crystal packing of several simple chloro cyano compounds, for example the polymorphs of 4-chlorobenzonitrile, may be understood on the basis of a secondary motif built up via these CkN*-CP+ interactions. Accordingly, it was felt that substituted 2,3-dicyano-5,6-dichlorobenzenes would be good candidates for the formation of a CkN...Cl mediated molecular tape such as is shown in Fig. 1.

Crystal Engineering Involving C−H···N Weak Hydrogen Bonds: A Diquinoxaline Lattice Inclusion Host with a Preference for Polychlorocarbon Guests

“…[22] The N···Cl distances are typically 3.00Ϫ3.45 Å . [23] When the nitrogen atom is present in an aromatic ring the N···ClϪC angle tends to be around 180°depending on distortions induced by crystal packing. A computational study has estimated the energy of association for N···Cl at around 5 kJ mol Ϫ1 .…”

Two different modes of halogen bonding in two 4-nitroimidazole derivatives

“…The attractive interactions between halogens and atoms that have lone electron pairs have been known for some time (e.g. Halogen bonds have been utilized successfully in the creation of supramolecular systems; for example, it has been shown that these interactions can create molecular tapes (Reddy, Panneerselvam et al, 1993) or a diamondoid structure (Reddy, Craig et al, 1993). This interaction was termed halogen bonding (Dumas et al, 1983; Legon, 1998), in order to stress some geometrical correspondences with hydrogen bonding, for instance the striking tendency towards the linearity of the CÐXÁ Á ÁY system [for reviews, see, for example, Legon (1999) and Metrangolo et al (2005)].…”

“…The molecule of (I) is almost planar, the plane of the nitro group making a dihedral angle of 6.97 (7) with the mean plane of the imidazole ring. Halogen bonds have been utilized successfully in the creation of supramolecular systems; for example, it has been shown that these interactions can create molecular tapes (Reddy, Panneerselvam et al, 1993) or a diamondoid structure (Reddy, Craig et al, 1993). the supramolecular architecture of molecular crystals) via interactions with the electron pairs of other atoms, interactions with other halogen atoms or acceptance of weak hydrogen bonds.…”

Crystal Engineering: Strategies and Architectures

“…Recently, I-• .O2N--R contacts (Desiraju, Pedireddi, Sarma & Zacharias, 1993) and cyano...halogen interactions (Reddy, Panneerselvam, Pilati & Desiraju, 1993;Desiraju & Harlow, 1989) have all been identified as influencing spatial orientation of substituted aromatic solids.…”