Search

Proton transfer realized through intermolecular H-bonds enables charge and energy transfer in biological systems, particularly in enzymes.1 Protonation of the donor from acidic acceptors are generally a route for the formation of ion pair adducts. Chloranilic acid (CLA) exhibits electron-acceptor properties on one hand and acidic properties leading to formation of H-bonds on the other hand, and usually utilized as a template for generating tightly bound self assemblies with various organic bases, and also as a model compound for investigating hydrogen transfer motions in O–H·N and N–H·O hydrogen bond systems.2 Benzimidazole (BIZ) is an organic base, and has H-bond donor site as well as acceptor site. The synthesis and spectroscopic studies, as well as crystallographic studies3,4 of charge transfer complexes formed between CLA and BIZ derivatives have been reported and the knowledge utilized in the field of drug-receptor binding mechanisms in medicinal chemistry. However, there is no report on BIZ complex with CLA, and is being pursued by our group. Our attempt to obtain such a complex resulted in the formation of BIZ with CLA hydrate adduct. As per our interest in studying proton transfer complexes, we found it prudent to report the role played by water in influencing proton transfer in the adduct, as well as contributing to increased number of H-bonds. The complex was obtained by dissolving a 1:1 mixture of BIZ (0.24 g, 2 mmol) and CLA (0.42 g, 2 mmol) in 20 ml methanol and allowed to evaporate slowly at room temperature. Suitable crystals were obtained after two weeks and characterized through X-ray diffraction at 150 K. Crystal data and details of data collection are given in Table 1. The structure solution was carried out with direct methods using the programs SIR 92 or superflip within the CRYSTALS software suite, and refined by full-matrix leastsquares methods based on F2. The chemical structure of BIZ/CLA·H2O adduct is shown in X-ray Structure Analysis Online

Pyrazoles are promising model compounds and convenient components for building up supramolecular systems. Due to the presence of an =N–N(H) fragment, pyrazole derivatives possess a unique ability to form various self-associates in the gaseous phase, in crystal, and in solution.1 Studies of such kind have useful applications in pharmacology, typically as non-narcotic analgesics, as well as the field of drug-receptor binding mechanisms in medicinal chemistry.2 Thus, the complexes of pyrazole derivatives with proton donor and acceptors compounds are being studied by many supramolecular chemists. Recently, we obtained an adduct of 3,5-dimethylpyrazole (3,5DMP, an orally active hypoglycemic agent, and effective on carbohydrate and free fatty acid metabolism) with chloranilic acid (CLA, a proton donor). We subsequently investigated the effect of methyl substituents on the packing mode in the adduct, since; either of the methyl groups may have a propensity to be out-of-plane of the pyrazole ring, and thus influence the packing fashion and hydrogen-bond patterns. We also considered how the presence of competitive hydrogen bond donor-acceptor groups can enhance a possible proton transfer process. Thus, in this manuscript the aforementioned aims are discussed. The crystal complex was obtained by dissolving a 1:1 mixture of 3,5DMP (0.20 g, 2 mmol) and CLA (0.42 g, 2 mmol) in 20 ml of methanol and allowed to evaporate slowly at room temperature. Suitable crystals were obtained after eight days, and characterized through X-ray diffraction at 150 K. Crystal data and details of data collection are given in Table 1. The structure solution was carried out with direct methods using the programs SIR 92 or superflip within the CRYSTALS software suite, and refined by full-matrix least-squares methods based on F2. The chemical structure of the adduct is shown in Fig. 1, while the atom numbering follows the scheme indicated in Fig. 2. The bond lengths and angles in CLA are insignificantly different from those in the crystal structure of CLA.3 The geometry of the 3,5DMP ring shows a similar pattern of bond distances and angles as pyrazole,4 and shows an insignificant effect of the hydrogen-bonding interaction on the bonded X-ray Structure Analysis Online

Crystal engineering is a focus area for constructing interesting H-bond zigzag channel-like network structures with some special tectons. In such a system, the host and guest components construct extended structures in the solid state through non-covalent interactions between the molecular subunits.1 Such studies are utilized in separation science and pharmacological profiles,2 and have received great attention in supramolecular chemistry. As per our interest to identify different kinds of potential building blocks that form zigzag channels and entrap organic guest molecules, we have found that sulfamethoxazole (SMZ, known for its antitumor or protease inhibitor activity3) forms H-bond zigzag channel and entraps 8-hydroxyquinoline (8-HQN, known for antibacterial, and carcinogenic activities4). Due to the important roles of both drugs in biological systems, we found it prudent to perform crystal structure studies on complexes of SMZ with 2-hydroxyquinoline (2-HQN), 4-hydroxyquinoline (4-HQN), and 8-HQN in order to understand the effects of the position(s) of N in the quinoline molecule on complex formation with SMZ, the molecular association of the SMZ molecules, and the H-bond network between interacting groups in SMZ and quinoline derivatives. Unfortunately, we obtained only the SMZ/8-HQN complex after several unsuccessful attempts, and herein report on its crystal structure regarding the aforementioned aims. The crystals were grown by dissolving SMZ and 8-HQN in a 1:1 stoichiometry ratio in methanol/ethanol mixed solvents, warmed, and left for slow evaporation to obtain crystals after five days and characterized through X-ray diffraction. Crystal intensity data were collected using graphite-monochromated X-ray Structure Analysis Online

The crystal structures of [XnE]+[(η7-C7H7)Mo(CO)2GaI3]- [XnE = (C4H8O)4Li (1), (C6H11)3PH (2)] are reported, revealing: (1) monoclinic, P21/c, a = 11.2388(1), b = 17.3201(3), c = 17.5473(2)A, β = 101.623(1)°, Z = 4, R = 0.038 and wR2 = 0.090 for 7614 observed reflections [I > 2σ(I)]; (2) monoclinic, P21/n, a = 9.2979(5), b = 18.4632(8), c = 19.9789(9)A, σ = 99.325(3)°, Z = 4, R = 0.073 and wR2 = 0.184 for 5554 observed reflections [I > 2σ(I)].