Proton Intercalation into an Open-Tunnel Bronze Phase with Near-Zero Volume Change.

Managing safety and supply-chain risks associated with lithium-ion batteries (LIBs) is an urgent task for sustainable development. Aqueous proton batteries are attractive alternatives to LIBs because using water and protons addresses these two risks. However, most host materials undergo large volume changes upon H+ intercalation, which induces intraparticle cracking to accelerates parasitic reactions. Herein, we report that Mo3Nb2O14 bronze exhibits reversible H+ intercalation (200 mAh g-1) with a Coulombic efficiency of 99.7% owing to near-zero volume change and solid-solution-type phase transition. Combination of experimental and theoretical analyses clarifies that rotation and shrinkage of open tunnels, which consist of flexible corner-sharing Mo/NbOn polyhedra, relieve local structural distortions upon H+ intercalation to suppress intraparticle cracking. The prototype full cell of an aqueous proton battery with a Mo3Nb2O14 anode operates stably over 1000 charge/discharge cycles. This study reveals the importance of implementing distortion-relieving voids in host materials to reduce volume change upon charge/discharge.

MgO-Template Synthesis of Extremely High Capacity Hard Carbon for Na-Ion Battery.

Extremely high capacity hard carbon for Na-ion battery, delivering 478 mAh g-1 , is successfully synthesized by heating a freeze-dried mixture of magnesium gluconate and glucose by a MgO-template technique. Influences of synthetic conditions and nano-structures on electrochemical Na storage properties in the hard carbon are systematically studied to maximize the reversible capacity. Nano-sized MgO particles are formed in a carbon matrix prepared by pre-treatment of the mixture at 600 °C. Through acid leaching of MgO and carbonization at 1500 °C, resultant hard carbon demonstrates an extraordinarily large reversible capacity of 478 mAh g-1 with a high Coulombic efficiency of 88 % at the first cycle.

Crystal structures of four isomeric hydrogen-bonded co-crystals of 6-methyl-quinoline with 2-chloro-4-nitro-benzoic acid, 2-chloro-5-nitro-benzoic acid, 3-chloro-2-nitro-benzoic acid and 4-chloro-2-nitro-benzoic acid.

The structures of the four isomeric compounds of 6-methyl-quinoline with chloro- and nitro-substituted benzoic acids, C7H4ClNO4·C10H9N, namely, 2-chloro-4-nitro-benzoic acid-6-methyl-quinoline (1/1), (I), 2-chloro-5-nitro-benzoic acid-6-methyl-quinoline (1/1), (II), 3-chloro-2-nitro-benzoic acid-6-methyl-quinoline (1/1), (III), and 4-chloro-2-nitro-benzoic acid-6-methyl-quinoline (1/1), (IV), have been determined at 185-190 K. In each compound, the acid and base mol-ecules are linked by a short hydrogen bond between a carboxyl O atom and an N atom of the base. The O⋯N distances are 2.5452 (12), 2.6569 (13), 2.5640 (17) and 2.514 (2) Å, respectively, for compounds (I)-(IV). In the hydrogen-bonded acid-base units of (I), (III) and (IV), the H atoms are each disordered over two positions with O site:N site occupancies of 0.65 (3):0.35 (3), 0.59 (4):0.41 (4) and 0.48 (5):0.52 (5), respectively, for (I), (III) and (IV). The H atom in the hydrogen-bonded unit of (II) is located at the O-atom site. In all of the crystals of (I)-(IV), π-π inter-actions between the quinoline ring system and the benzene ring of the acid mol-ecule are observed. In addition, a π-π inter-action between the benzene rings of adjacent acid mol-ecules and a C-H⋯O hydrogen bond are observed in the crystal of (I), and C-H⋯O hydrogen bonds and O⋯Cl contacts occur in the crystals of (III) and (IV). These inter-molecular inter-actions connect the acid and base mol-ecules, forming a layer structure parallel to the bc plane in (I), a column along the a-axis direction in (II), a layer parallel to the ab plane in (III) and a three-dimensional network in (IV). Hirshfeld surfaces for the title compounds mapped over d norm and shape index were generated to visualize the weak inter-molecular inter-actions.

Reaction Behavior of a Silicide Electrode with Lithium in an Ionic-Liquid Electrolyte.

Silicides are attractive novel active materials for use in the negative-electrodes of next-generation lithium-ion batteries that use certain ionic-liquid electrolytes; however, the reaction mechanism of the above combination is yet to be clarified. Possible reactions at the silicide electrode are as follows: deposition and dissolution of Li metal on the electrode, lithiation and delithiation of Si, which would result from the phase separation of the silicide, and alloying and dealloying of the silicide with Li. Herein, we examined these possibilities using various analysis methods. The results revealed that the lithiation and delithiation of silicide occurred.

Crystal structure of 4-chloro-2-nitro-benzoic acid with 4-hy-droxy-quinoline: a disordered structure over two states of 4-chloro-2-nitro-benzoic acid-quinolin-4(1H)-one (1/1) and 4-hy-droxy-quinolinium 4-chloro-2-nitro-benzoate.

The title compound, C9H7.5NO·C7H3.5ClNO4, was analysed as a disordered structure over two states, viz. co-crystal and salt, accompanied by a keto-enol tautomerization in the base mol-ecule. The co-crystal is 4-chloro-2-nitro-benzoic acid-quinolin-4(1H)-one (1/1), C7H4ClNO4·C9H7NO, and the salt is 4-hy-droxy-quinolinium 4-chloro-2-nitro-benzoate, C9H8NO+·C7H3ClNO4 -. In the compound, the acid and base mol-ecules are held together by a short hydrogen bond [O⋯O = 2.4393 (15) Å], in which the H atom is disordered over two positions with equal occupancies. In the crystal, the hydrogen-bonded acid-base units are linked by N-H⋯O and C-H⋯O hydrogen bonds, forming a tape structure along the a-axis direction. The tapes are stacked into a layer parallel to the ab plane via π-π inter-actions [centroid-centroid distances = 3.5504 (8)-3.9010 (11) Å]. The layers are further linked by another C-H⋯O hydrogen bond, forming a three-dimensional network. Hirshfeld surfaces for the title compound mapped over shape-index and d norm were generated to visualize the inter-molecular inter-actions.

Crystal structures of the two isomeric hydrogen-bonded cocrystals 2-chloro-4-nitro-benzoic acid-5-nitro-quinoline (1/1) and 5-chloro-2-nitro-benzoic acid-5-nitro-quinoline (1/1).

The structures of two isomeric com-pounds of 5-nitro-quinoline with chloro- and nitro-substituted benzoic acid, namely, 2-chloro-4-nitro-benzoic acid-5-nitro-quinoline (1/1), (I), and 5-chloro-2-nitro-benzoic acid-5-nitro-quinoline (1/1), (II), both C7H4ClNO4·C9H6N2O2, have been determined at 190 K. In each com-pound, the acid and base mol-ecules are held together by an O-H⋯N hydrogen bond. In the crystal of (I), the hydrogen-bonded acid-base units are linked by a C-H⋯O hydrogen bond, forming a tape structure along [10]. The tapes are stacked into a layer parallel to the ab plane via N-O⋯π inter-actions between the nitro group of the base mol-ecule and the quinoline ring system. The layers are further linked by other C-H⋯O hydrogen bonds, forming a three-dimensional network. In the crystal of (II), the hydrogen-bonded acid-base units are linked into a wide ribbon structure running along [10] via C-H⋯O hydrogen bonds. The ribbons are further linked via another C-H⋯O hydrogen bond, forming a layer parallel to (110). Weak π-π inter-actions [centroid-centroid distances of 3.7080 (10) and 3.7543 (9) Å] are observed between the quinoline ring systems of adjacent layers. Hirshfeld surfaces for the 5-nitro-quinoline mol-ecules of the two com-pounds mapped over shape index and d norm were generated to visualize the weak inter-molecular inter-actions.

Crystal structures of 3-chloro-2-nitro-benzoic acid with quinoline derivatives: 3-chloro-2-nitro-benzoic acid-5-nitro-quinoline (1/1), 3-chloro-2-nitro-benzoic acid-6-nitro-quinoline (1/1) and 8-hy-droxy-quinolinium 3-chloro-2-nitro-benzoate.

The structures of three compounds of 3-chloro-2-nitro-benzoic acid with 5-nitro-quinoline, (I), 6-nitro-quinoline, (II), and 8-hy-droxy-quinoline, (III), have been determined at 190 K. In each of the two isomeric compounds, (I) and (II), C7H4ClNO4·C9H6N2O2, the acid and base mol-ecules are held together by O-H⋯N and C-H⋯O hydrogen bonds. In compound (III), C9H8NO+·C7H3ClNO4 -, an acid-base inter-action involving H-atom transfer occurs and the H atom is located at the N site of the base mol-ecule. In the crystal of (I), the hydrogen-bonded acid-base units are linked by C-H⋯O hydrogen bonds, forming a tape structure along the b-axis direction. Adjacent tapes, which are related by a twofold rotation axis, are linked by a third C-H⋯O hydrogen bond, forming wide ribbons parallel to the (03) plane. These ribbons are stacked via π-π inter-actions between the quinoline ring systems [centroid-centroid distances = 3.4935 (5)-3.7721 (6) Å], forming layers parallel to the ab plane. In the crystal of (II), the hydrogen-bonded acid-base units are also linked into a tape structure along the b-axis direction via C-H⋯O hydrogen bonds. Inversion-related tapes are linked by further C-H⋯O hydrogen bonds to form wide ribbons parallel to the (08) plane. The ribbons are linked by weak π-π inter-actions [centroid-centroid distances = 3.8016 (8)-3.9247 (9) Å], forming a three-dimensional structure. In the crystal of (III), the cations and the anions are alternately linked via N-H⋯O and O-H⋯O hydrogen bonds, forming a 21 helix running along the b-axis direction. The cations and the anions are further stacked alternately in columns along the a-axis direction via π-π inter-actions [centroid-centroid distances = 3.8016 (8)-3.9247 (9) Å], and the mol-ecular chains are linked into layers parallel to the ab plane through these inter-actions.

Negative dielectric constant of water confined in nanosheets.

Electric double-layer capacitors are efficient energy storage devices that have the potential to account for uneven power demand in sustainable energy systems. Earlier attempts to improve an unsatisfactory capacitance of electric double-layer capacitors have focused on meso- or nanostructuring to increase the accessible surface area and minimize the distance between the adsorbed ions and the electrode. However, the dielectric constant of the electrolyte solvent embedded between adsorbed ions and the electrode surface, which also governs the capacitance, has not been previously exploited to manipulate the capacitance. Here we show that the capacitance of electric double-layer capacitor electrodes can be enlarged when the water molecules are strongly confined into the two-dimensional slits of titanium carbide MXene nanosheets. Using electrochemical methods and theoretical modeling, we find that dipolar polarization of strongly confined water resonantly overscreens an external electric field and enhances capacitance with a characteristically negative dielectric constant of a water molecule.

Crystal structures of two hydrogen-bonded compounds of chloranilic acid-ethyl-eneurea (1/1) and chloranilic acid-hydantoin (1/2).

The structures of the hydrogen-bonded 1:1 co-crystal of chloranilic acid (systematic name: 2,5-di-chloro-3,6-dihy-droxy-1,4-benzo-quinone) with ethyl-eneurea (systematic name: imidazolidin-2-one), C6H2Cl2O4·C3H6N2O, (I), and the 1:2 co-crystal of chloranilic acid with hydantoin (systematic name: imidazolidine-2,4-dione), C6H2Cl2O4·2C3H4N2O2, (II), have been determined at 180 K. In the crystals of both compounds, the base mol-ecules are in the lactam form and no acid-base inter-action involving H-atom transfer is observed. The asymmetric unit of (I) consists of two independent half-mol-ecules of chloranilic acid, with each of the acid mol-ecules lying about an inversion centre, and one ethyl-eneurea mol-ecule. The asymmetric unit of (II) consists of one half-mol-ecule of chloranilic acid, which lies about an inversion centre, and one hydantoin mol-ecule. In the crystal of (I), the acid and base mol-ecules are linked via O-H⋯O and N-H⋯O hydrogen bonds, forming an undulating sheet structure parallel to the ab plane. In (II), the base mol-ecules form an inversion dimer via a pair of N-H⋯O hydrogen bonds, and the base dimers are further linked through another N-H⋯O hydrogen bond into a layer structure parallel to (01). The acid mol-ecule and the base mol-ecule are linked via an O-H⋯O hydrogen bond.

Surface modification effects on the tensile properties of functionalised graphene oxide epoxy films.

Graphene oxide (GO) is a candidate for nanofillers to improve the mechanical and thermal stability of nanocomposites. In order to determine the molecular interaction to improve the mechanical properties of GO-epoxy resin composites, we investigated the relationship between GO oxidation properties and the tensile strength of the epoxy resin. With respect to GO preparation, graphite was oxidised by the Brodie or Hummers method, and the oxidised GO was reduced or chloride substituted. The X-ray photoelectron spectroscopy (XPS) spectral patterns indicate that a shorter Brodie oxidation method GO (B-GO) is associated with a higher proportion of hydroxyl groups. The oxidised GO materials, with the exception of the sample produced by the 54 h Brodie oxidation method, improved the tensile strength of the composites while the epoxy resin with reduced or chlorinated GO did not increase the tensile strength of the film. Based on XPS and elemental analyses, the improvement in the tensile strength is due to the presence of O atom based functional groups, such as hydroxyl groups, on the GO surface. The interaction between the epoxy resin and O atom based functional groups on the GO contributes to improving the tensile strength of the composites.

Crystal structures of three hydrogen-bonded 1:2 compounds of chloranilic acid with 2-pyridone, 3-hy-droxy-pyridine and 4-hyroxypyridine.

The crystal structures of the 1:2 compounds of chloranilic acid (systematic name: 2,5-di-chloro-3,6-dihy-droxy-1,4-benzo-quinone) with 2-pyridone, 3-hy-droxy-pyridine and 4-hyroxypyridine, namely, bis-(2-pyridone) chloranilic acid, 2C5H5NO·C6H2Cl2O4, (I), bis-(3-hy-droxy-pyridinium) chloranilate, 2C5H6NO+·C6Cl2O42-, (II), and bis-(4-hy-droxy-pyridinium) chloranilate, 2C5H6NO+·C6Cl2O42-, (III), have been determined at 120 K. In the crystal of (I), the base mol-ecule is in the lactam form and no acid-base inter-action involving H-atom transfer is observed. The acid mol-ecule lies on an inversion centre and the asymmetric unit consists of one half-mol-ecule of chloranilic acid and one 2-pyridone mol-ecule, which are linked via a short O-H⋯O hydrogen bond. 2-Pyridone mol-ecules form a head-to-head dimer via a pair of N-H⋯O hydrogen bonds, resulting in a tape structure along [201]. In the crystals of (II) and (III), acid-base inter-actions involving H-atom transfer are observed and the divalent cations lie on an inversion centre. The asymmetric unit of (II) consists of one half of a chloranilate anion and one 3-hy-droxy-pyridinium cation, while that of (III) comprises two independent halves of anions and two 4-hy-droxy-pyridinium cations. The primary inter-molecular inter-action in (II) is a bifurcated O-H⋯(O,O) hydrogen bond between the cation and the anion. The hydrogen-bonded units are further linked via N-H⋯O hydrogen bonds, forming a layer parallel to the bc plane. In (III), one anion is surrounded by four cations via O-H⋯O and C-H⋯O hydrogen bonds, while the other is surrounded by four cations via N-H⋯O and C-H⋯Cl hydrogen bonds. These inter-actions link the cations and the anions into a layer parallel to (301).

Crystal structures of two 1:2 dihydrate compounds of chloranilic acid with 2-carb-oxy-pyridine and 2-carb-oxy-quinoline.

The crystal structure of the 1:2 dihydrate compound of chloranilic acid (systematic name: 2,5-di-chloro-3,6-dihy-droxy-1,4-benzo-quinone) with 2-carb-oxy-pyridine (another common name: picolinic acid; systematic name: pyridine-2-carb-oxy-lic acid), namely, 2C6H5.5NO20.5+·C6HCl2O4-·2H2O, (I), has been determined at 180 K, and the structure of the 1:2 dihydrate compound of chloranilic acid with 2-carb-oxy-quinoline (another common name: quinaldic acid; systematic name: quinoline-2-carb-oxy-lic acid), namely, 2C10H7NO2·C6H2Cl2O4·2H2O, (II), has been redetermined at 200 K. This determination presents a higher precision crystal structure than the previously published structure [Marfo-Owusu & Thompson (2014 ▸). X-ray Struct. Anal. Online, 30, 55-56]. Compound (I) was analysed as a disordered structure over two states, viz. salt and co-crystal. The salt is bis-(2-carb-oxy-pyridinium) chloranilate dihydrate, 2C6H6NO2+·C6Cl2O42-·2H2O, and the co-crystal is bis-(pyridinium-2-carboxyl-ate) chloranilic acid dihydrate, 2C6H5NO2·C6H2Cl2O4·2H2O, including zwitterionic 2-carb-oxy-pyridine. In both salt and co-crystal, the water mol-ecule links the chloranilic acid and 2-carb-oxy-pyridine mol-ecules through O-H⋯O and N-H⋯O hydrogen bonds. The 2-carb-oxy-pyridine mol-ecules are connected into a head-to-head inversion dimer by a short O-H⋯O hydrogen bond, in which the H atom is disordered over two positions. Compound (II) is a 1:2 dihydrate co-crystal of chloranilic acid and zwitterionic 2-carb-oxy-quinoline. The water mol-ecule links the chloranilic acid and 2-carb-oxy-quinoline mol-ecules through O-H⋯O hydrogen bonds. The 2-carb-oxy-quinoline mol-ecules are connected into a head-to-tail inversion dimer by a pair of N-H⋯O hydrogen bonds.

Crystal structures of 4-meth-oxy-benzoic acid-1,3-bis-(pyridin-4-yl)propane (2/1) and biphenyl-4,4'-di-carb-oxy-lic acid-4-meth-oxy-pyridine (1/2).

The crystal structures of two hydrogen-bonded compounds, namely 4-meth-oxy-benzoic acid-1,3-bis-(pyridin-4-yl)propane (2/1), C13H14.59N2·C8H7.67O3·C8H7.74O3, (I), and biphenyl-4,4'-di-carb-oxy-lic acid-4-meth-oxy-pyridine (1/2), C14H9.43O4·C6H7.32NO·C6H7.25NO, (II), have been determined at 93 K. In (I), the asymmetric unit consists of two crystallographically independent 4-meth-oxy-benzoic acid mol-ecules and one 1,3-bis-(pyridin-4-yl)propane mol-ecule. The asymmetric unit of (II) comprises one biphenyl-4,4'-di-carb-oxy-lic acid mol-ecule and two independent 4-meth-oxy-pyridine mol-ecules. In each crystal, the acid and base mol-ecules are linked by short O-H⋯N/N-H⋯O hydrogen bonds, in which H atoms are disordered over the acid O-atom and base N-atom sites, forming a linear hydrogen-bonded 2:1 or 1:2 unit of the acid and the base. The 2:1 units of (I) are linked via C-H⋯π, π-π and C-H⋯O inter-actions into a tape structure along [101], while the 1:2 units of (II) form a double-chain structure along [-101] through π-π and C-H⋯O inter-actions.

Crystal structures of hydrogen-bonded co-crystals as liquid crystal precursors: 4-(n-pent-yloxy)benzoic acid-(E)-1,2-bis-(pyridin-4-yl)ethene (2/1) and 4-(n-hex-yloxy)benzoic acid-(E)-1,2-bis-(pyridin-4-yl)ethene (2/1).

The crystal structures of title hydrogen-bonded co-crystals, 2C12H16O3·C12H10N2, (I), and 2C13H18O3·C12H10N2, (II), have been determined at 93 K. In (I), the asymmetric unit consists of one 4-(n-pent-yloxy)benzoic acid mol-ecule and one half-mol-ecule of (E)-1,2-bis-(pyridin-4-yl)ethene, which lies about an inversion centre. The asymmetric unit of (II) comprises two crystallographically independent 4-(n-hex-yloxy)benzoic acid mol-ecules and one 1,2-bis-(pyridin-4-yl)ethene mol-ecule. In each crystal, the acid and base components are linked by O-H⋯N hydrogen bonds, forming a linear hydrogen-bonded 2:1 unit of the acid and the base. The 2:1 units are linked via C-H⋯π and π-π inter-actions [centroid-centroid distances of 3.661 (2) and 3.909 (2) Šfor (I), and 3.546 (2)-3.725 (4) Šfor (II)], forming column structures. In (II), the base mol-ecule is orientationally disordered over two sets of sites approximately around the N⋯N mol-ecular axis, with an occupancy ratio of 0.647 (4):0.353 (4), and the average structure of the 2:1 unit adopts nearly pseudo-C2 symmetry. Both compounds show liquid-crystal behaviour.

Crystal structures of four co-crystals of (E)-1,2-di(pyridin-4-yl)ethene with 4-alk-oxy-benzoic acids: 4-meth-oxy-benzoic acid-(E)-1,2-di(pyridin-4-yl)ethene (2/1), 4-eth-oxy-benzoic acid-(E)-1,2-di(pyridin-4-yl)ethene (2/1), 4-n-propoxybenzoic acid-(E)-1,2-di(pyridin-4-yl)ethene (2/1) and 4-n-but-oxy-benzoic acid-(E)-1,2-di(pyridin-4-yl)ethene (2/1).

The crystal structures of four hydrogen-bonded co-crystals of 4-alk-oxy-benzoic acid-(E)-1,2-di(pyridin-4-yl)ethene (2/1), namely, 2C8H8O3·C12H10N2, (I), 2C9H10O3·C12H10N2, (II), 2C10H12O3·C12H10N2, (III) and 2C11H14O3·C12H10N2, (IV), have been determined at 93 K. In compounds (I) and (IV), the asymmetric units are each composed of one 4-alk-oxy-benzoic acid mol-ecule and one half-mol-ecule of (E)-1,2-di(pyridin-4-yl)ethene, which lies on an inversion centre. The asymmetric unit of (II) consists of two crystallographically independent 4-eth-oxy-benzoic acid mol-ecules and one 1,2-di(pyridin-4-yl)ethene mol-ecule. Compound (III) crystallizes in a non-centrosymmetric space group (Pc) and the asymmetric unit comprises four 4-n-propoxybenzoic acid mol-ecules and two (E)-1,2-di(pyridin-4-yl)ethane mol-ecules. In each crystal, the acid and base components are linked by O-H⋯N hydrogen bonds, forming a linear hydrogen-bonded 2:1 unit of the acid and the base. In (I), (II) and (III), inter-molecular C-H⋯O inter-actions are observed. The 2:1 units of (I) and (II) are linked via C-H⋯O hydrogen bonds, forming tape structures. In (III), the C-H⋯O hydrogen bonds, except for those formed in the units, link the two crystallographically independent 2:1 units. In (IV), no C-H⋯O inter-actions are observed, but π-π and C-H⋯π inter-actions link the units into a column structure.

Sodium-Ion Intercalation Mechanism in MXene Nanosheets.

MXene, a family of layered compounds consisting of nanosheets, is emerging as an electrode material for various electrochemical energy storage devices including supercapacitors, lithium-ion batteries, and sodium-ion batteries. However, the mechanism of its electrochemical reaction is not yet fully understood. Herein, using solid-state (23)Na magic angle spinning NMR and density functional theory calculation, we reveal that MXene Ti3C2Tx in a nonaqueous Na(+) electrolyte exhibits reversible Na(+) intercalation/deintercalation into the interlayer space. Detailed analyses demonstrate that Ti3C2Tx undergoes expansion of the interlayer distance during the first sodiation, whereby desolvated Na(+) is intercalated/deintercalated reversibly. The interlayer distance is maintained during the whole sodiation/desodiation process due to the pillaring effect of trapped Na(+) and the swelling effect of penetrated solvent molecules between the Ti3C2Tx sheets. Since Na(+) intercalation/deintercalation during the electrochemical reaction is not accompanied by any substantial structural change, Ti3C2Tx shows good capacity retention over 100 cycles as well as excellent rate capability.

Crystal structures of morpholinium hydrogen bromanilate at 130, 145 and 180†K.

Crystal structures of the title compound (systematic name: morpholin-4-ium 2,5-di-bromo-4-hy-droxy-3,6-dioxo-cyclo-hexa-1,4-dien-1-olate), C4H10NO(+)·C6HBr2O4 (-), were determined at three temperatures, viz. 130, 145 and 180 K. The asymmetric unit comprises one morpholinium cation and two halves of crystallographically independent bromanilate monoanions, which are located on inversion centres. The conformations of the two independent bromanilate anions are different from each other with respect to the O-H orientation. In the crystal, the two different anions are linked alternately into a chain along [211] through a short O-H⋯O hydrogen bond, in which the H atom is disordered over two positions. The refined site-occupancy ratios, which are almost constant in the temperature range studied, are 0.49 (3):0.51 (3), 0.52 (3):0.48 (3) and 0.50 (3):0.50 (3), respectively, at 130, 145 and 180 K, and no significant difference in the mol-ecular geometry and the mol-ecular packing is observed at the three temperatures. The morpholinium cation links adjacent chains of anions via N-H⋯O hydrogen bonds, forming a sheet structure parallel to (-111).

Crystal structures of three co-crystals of 4,4'-bipyridyl with 4-alk-oxy-benzoic acids: 4-eth-oxy-benzoic acid-4,4'-bipyridyl (2/1), 4-n-propoxybenzoic acid-4,4'-bipyridyl (2/1) and 4-n-but-oxy-benzoic acid-4,4'-bipyridyl (2/1).

The crystal structures of three hydrogen-bonded co-crystals of 4-alk-oxy-benzoic acid-4,4'-bipyridyl (2/1), namely, 2C9H10O3·C10H8N2, (I), 2C10H12O3·C10H8N2, (II) and 2C11H14O3·C10H8N2, (III), have been determined at 93 K. Although the structure of (I) has been determined in the space group P21 with Z = 4 [Lai et al. (2008 ▸). J. Struct. Chem. 49, 1137-1140], the present study shows that the space group is P21/n with Z = 4. In each crystal, the components are linked by O-H⋯N hydrogen bonds, forming a linear hydrogen-bonded 2:1 unit of the acid and the base. The 2:1 unit of (I) adopts nearly pseudo-C 2 symmetry, viz. twofold rotation around an axis passing through the mid-point of the central C-C bond of 4,4'-bipyridyl, while the units of (II) and (III), except for the terminal alkyl chains, have pseudo-inversion symmetry. The 2:1 units of (I), (II) and (III) are linked via C-H⋯O hydrogen bonds, forming sheet, double-tape and tape structures, respectively.

Crystal structures of three co-crystals of 1,2-bis-(pyridin-4-yl)ethane with 4-alk-oxy-benzoic acids: 4-eth-oxy-benzoic acid-1,2-bis-(pyridin-4-yl)ethane (2/1), 4-n-propoxybenzoic acid-1,2-bis(pyridin-4-yl)ethane (2/1) and 4-n-but-oxy-benzoic acid-1,2-bis-(pyridin-4-yl)ethane (2/1).

The crystal structures of three hydrogen-bonded co-crystals of 4-alk-oxy-benzoic acid-1,2-bis-(pyridin-4-yl)ethane (2/1), namely, 2C9H10O3·C12H12N2, (I), 2C10H12O3·C12H12N2, (II), and 2C11H14O3·C12H12N2, (III), have been determined at 93, 290 and 93 K, respectively. In (I), the asymmetric unit consists of one 4-eth-oxy-benzoic acid mol-ecule and one half-mol-ecule of 1,2-bis-(pyridin-4-yl)ethane, which lies on an inversion centre. In (II) and (III), the asymmetric units each comprise two crystallographically independent 4-alk-oxy-benzoic acid mol-ecules and one 1,2-bis-(pyridin-4-yl)ethane mol-ecule. In each crystal, the two components are linked by O-H⋯N hydrogen bonds, forming a linear hydrogen-bonded 2:1unit of the acid and the base. Similar to the structure of 2:1 unit of (I), the units of (II) and (III) adopt nearly pseudo-inversion symmetry. The 2:1 units of (I), (II) and (III) are linked via C-H⋯O hydrogen bonds, forming tape structures.

Crystal structures of iso-quinoline-3-chloro-2-nitro-benzoic acid (1/1) and isoquinolinium 4-chloro-2-nitro-benzoate.

In each of the title isomeric compounds, C9H7.3N·C7H3.7ClNO4, (I), and C9H8N·C7H3ClNO4, (II), of iso-quinoline with 3-chloro-2-nitro-benzoic acid and 4-chloro-2-nitro-benzoic acid, the two components are linked by a short hydrogen bond between a base N atom and a carb-oxy O atom. In the hydrogen-bonded unit of (I), the H atom is disordered over two positions with N and O site occupancies of 0.30 (3) and 0.70 (3), respectively, while in (II), an acid-base inter-action involving H-atom transfer occurs and the H atom is located at the N site. In the crystal of (I), the acid-base units are connected through C-H⋯O hydrogen bonds into a tape structure along the b-axis direction. Inversion-related adjacent tapes are further linked through π-π inter-actions [centroid-centroid distances = 3.6389 (7)-3.7501 (7) Å], forming a layer parallel to (001). In the crystal of (II), the acid-base units are connected through C-H⋯O hydrogen bonds into a ladder structure along the a-axis direction. The ladders are further linked by another C-H⋯O hydrogen bond into a layer parallel to (001).