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

Abstract

In the crystal structures of the two imidazole derivatives 5-chloro-1,2-dimethyl-4-nitro-1H-imidazole, C(5)H(6)ClN(3)O(2), (I), and 2-chloro-1-methyl-4-nitro-1H-imidazole, C(4)H(4)ClN(3)O(2), (II), C-Cl...O halogen bonds are the principal specific interactions responsible for the crystal packing. Two different halogen-bond modes are observed: in (I), there is one very short and directional C-Cl...O contact [Cl...O = 2.899 (1) A], while in (II), the C-Cl group approaches two different O atoms from two different molecules, and the contacts are longer [3.285 (2) and 3.498 (2) A] and less directional. In (I), relatively short C-H...O hydrogen bonds provide the secondary interactions for building the crystal structure; in (II), the C-H...O contacts are longer but there is a relatively short pi-pi contact between molecules related by a centre of symmetry. The molecule of (I) is almost planar, the plane of the nitro group making a dihedral angle of 6.97 (7) degrees with the mean plane of the imidazole ring. The molecule of (II) has crystallographically imposed mirror symmetry and the nitro group lies in the mirror plane.

Dihydrogen phosphate mediated supramolecular frameworks in 2- and 4-chloroanilinium dihydrogen phosphate salts

“…The N1-H1AÁ Á ÁO4 and N1-H1CÁ Á ÁO4 ii hydrogen bonds [symmetry code: (ii) x, y + 1, z], along with O2-H2DÁ Á ÁO3 ii , form a chain of edgefused R 3 3 (10) ring motifs extending along the [010] direction, as observed in the structure of 3-acetylanilinium dihydrogen phosphate (Cinčić & Kaitner, 2008). The ClÁ Á ÁO1 interaction, which acts as a pseudo-hydrogen bond (Bryant et al, 1998;Kubicki & Wagner, 2007), with the Cl1 atom at (x, y, z) as donor and atom O1 at (Àx + 1 2 , Ày + 1 2 , Àz + 1 2 ) as acceptor, along with the N-HÁ Á ÁO hydrogen bonds, forms a chain of fused R 2 4 (10) motifs extending along the [010] direction. The 2 1 screw-related chains of R 3 3 (10) and R 2 4 (10) motifs along ( 1 4 , y, 1 4 ) ( Fig.…”

Bifurcated and Monocentric Halogen Bonds in Cocrystals of Metal(II) Acetylacetonates with p-Dihalotetrafluorobenzenes

“…In the seminal paper by Laurence et al, bifurcated halogen bonds are found to be unlikely for any strong (inorganic) halogen donor, while it may be possible for weaker halogen bond donors (which will form less covalent bonds) to form symmetric halogen bonds. Indeed, numerous experimental (in particular with heterocycles − and nitro groups − as acceptors) and theoretical studies − have shown the existence of bifurcated halogen bonds. However, in the vast majority of cases the bifurcated halogen bonds show pronounced asymmetry, one contact being shorter and straighter and the other longer and more bent.…”

Intermolecular Interactions in Bromo-, Methyl-, and Cyanoimidazole Derivatives

“…Despite the difficulty in obtaining positively charged 4,5dicyano-2-halo-imidazolium compounds, given the results discussed above, it appeared likely that the neutral heterocycle could be sufficiently electron-withdrawing to induce a σ hole on the polarizable halogen, and thus provide a new uncharged motif for halogen bond formation. Such interactions have been observed in both 2-and 5-chloro-1-methyl-4-nitroimidazole, 35 which is, in principle, less favorably disposed to halogen bond formation than 2-bromo-4,5-dicyanoimidazole, possessing fewer electron-withdrawing groups and a less polarizable halogen. Single crystals suitable for X-ray diffraction were obtained for 2-bromo-4,5-dicyanoimidazole to examine its hydrogen bonding behavior, and for its N-benzyl derivative to provide a second perspective on any halogen-bonding properties.…”