Insights into Selective Removal by Dye Adsorption on Hydrophobic vs Multivalent Hydrophilic Functionalized MWCNTs.

Hydrophilic functionalized carbon nanotubes (MWCNT-COOH) were developed via hydrothermal glucose-coated carbonization, mixing MWCNTs with glucose in different weight ratios. Methyl violet (MV), methylene blue (MB), alizarin yellow (AY), and methyl orange (MO) were used as dye models for adsorption studies. Comparative dye adsorption capacity onto the pristine (MWCNT-raw) and functionalized (MWCNT-COOH-11) CNTs was evaluated in aqueous solution. These results revealed that MWCNT-raw is capable of adsorbing either anionic or cationic dyes. In contrast, an induced selective cation dye adsorption capacity is significantly enhanced on multivalent hydrophilic MWCNT-COOH, in comparison to a pristine surface. This ability can be tuned to the selective adsorption of cations over anionic dyes or between anionic mixtures from binary systems. An insight into adsorbate-adsorbent interactions shows that hierarchical supramolecular interactions dominate the adsorption processes, which is ascribed to the chemical modification by switching from a hydrophobic to a hydrophilic surface, dye charge, temperature, and potential matching multivalent acceptor/donor capacity between chemical groups in the adsorbent interface. The dye adsorption isotherm and thermodynamics on both surfaces were also studied. Changes in the Gibbs free energy (ΔG°), enthalpy (ΔH°), and entropy (ΔS°) were evaluated. Thermodynamic parameters were endothermic on MWCNT-raw, whereas the adsorption process on MWCNT-COOH-11 revealed that adsorption processes were spontaneous and exothermic, accompanied by a significant reduction of entropy values as a consequence of a multivalent effect. This approach provides an eco-friendly, low-cost alternative for the preparation of supramolecular nanoadsorbents with unprecedented properties to achieve remarkable selective adsorption independent of the presence of intrinsic porosity.

1,2,4,5-Benzenetetracarboxylic acid: a versatile hydrogen bonding template for controlling the regioselective topochemical synthesis of head-to-tail photodimers from stilbazole derivatives.

The crystal engineering of hydrogen bonded organic assemblies based on 1,2,4,5-benzenetetracarboxylic acid (H4bta) and stilbazole derivatives (1-10) is exploited to provide regio-controlled [2 + 2] photocycloadditions in the solid state. Single crystal X-ray diffraction analyses have revealed that all the arrays are built-up from the self-assembly of the (H2bta)2- dianion with two stilbazolium cations via O-HO- and N+-HO- charge-assisted H-bonding synthons: (4-Hstilbazolium+)2(H2bta2-). The dianion displays an interesting diversity of H-bonding motifs. Such structural flexibility allowed us to obtain four structure-types defined by the preferential formation of intramolecular or intermolecular hydrogen bonds between carboxylate-carboxylic groups. In these ionic assemblies two predominant structural H-bonding patterns were observed. The first pattern is characterised by the formation of intramolecular H-bonds in the dianion, leading to discrete assemblies based on ternary arrays. The second hydrogen pattern consists of 2-D hydrogen networks built-up from the self-assembly of anions via intermolecular H-bonds that are linked to the cations. Two additional examples, in which the dianion is self-assembled in two types of ribbons, were also observed. Another supramolecular feature predominant in all these arrays is the stacking of the cations in a head-to-tail fashion, which is controlled via cation-π interactions. These arrays are photoactive in the solid state upon UV-irradiation leading to the regioselective synthesis of rctt-cyclobutane head-to-tail-isomers in high to quantitative yield. In this work, the template tolerance either to steric or electronic effects by changing the number or positions of the supramolecular interactions exerted by distinctive functional groups was also explored. In addition, assemblies bearing 2-chloro (7 and 8) and 3-chloro-4-stilbazole (1 and 9) crystallize in two different crystalline forms, leading to novel examples of supramolecular isomers with similar solid state reactivity.

Novel MoO2/carbon hierarchical nano/microcomposites: synthesis, characterization, solid state transformations and thiophene HDS activity.

Novel MoO(2)/C nano/microcomposites were prepared via a bottom-up approach by hydrothermal carbonization of a solution of glucose as a carbon precursor in the presence of polyoxometalates (POMs: phosphomolybdic acid [H(3)PMo(12)O(40)] and ammonium heptamolybdate tetrahydrate [(NH(4))(6)Mo(7)O(24)]·4H(2)O). The structural characterization by FT-IR, XRPD, SEM and TEM analyses revealed the controlled formation of hierarchical MoO(2)/C composites with different morphologies: strawberry-like, based on carbon microspheres decorated with MoO(2) nanoparticles; MoO(2)/C core-shell composites; and irregular aggregates in combination with ring-like microstructures bearing amorphous Mo species. These composites can be fine-tuned by varying reaction time, glucose/POM ratio and type of POM precursor. Subsequent transformations in the solid state through calcinations of MoO(2)/C core-shell composites in air lead to hollow nanostructured molybdenum trioxide microspheres together with nanorods and plate microcrystals or cauliflower-like composites (MoO(2)/C). In addition, the MoO(2)/C composite undergoes a morphology evolution to urchin-like composites when it is calcined under nitrogen atmosphere (MoO(2)/C-N(2)). The MoO(2)/C strawberry-like and MoO(2)/C-N(2) composites were transformed into Mo carbide and nitride supported on carbon microspheres (Mo(2)C/C, MoN/C, and MoN/C-N(2)). These phases were tested as precursors in thiophene hydrodesulphurization (HDS) at 400 °C, observing the following trend in relation to the thiophene steady-state conversion: MoN/C-N(2) > MoN/C > Mo(2)C/C > MoO(2)/C-N(2) > MoO(2)/C. According to these conversion values, a direct correlation was observed between higher HDS activity and decreasing crystal size as estimated from the Scherrer equation. These results suggest that such composites represent interesting and promising precursors for HDS catalysts, where the activity and stability can be modified either by chemical or structural changes of the composites under different conditions.

Crotofolane diterpenoids from Croton caracasanus.

Four new crotofolane-type diterpenoids, crotocarasin (A-D) (1-4), together with the known crotofolin E, were isolated from a dichloromethane extract of the stems of Croton caracasanus Pittier. The structures of the new compounds were determined by spectroscopic methods, and the structure of 3 was further confirmed by single-crystal X-ray data analyses.

Synthesis and characterization of rhodium complexes with phosphine-stabilized germylenes.

The reaction of phosphine-stabilized germylenes (1a,b) with dimer complex [Rh(2)(µ-Cl)(2)(COD)(2)] leads to the corresponding phosphine-germylene-Rh(I) complexes (2a,b). Interestingly, the stability of these complexes depends strongly on the nature of the substituent of the germylene fragment. Indeed, the complex (2a) with the chloro-germylene ligand isomerizes into a metallacycle rhodium complex (3a) via germylene insertion into the Rh-Cl bond, while the complex with the phenyl-substituted germylene (2b) was isolated and represents the first stable Rh(I)-germylene complex with a Rh-Cl bond.

1-[5-(4,5-Dimethyl-1,3,2-dioxaborolan-2-yl)thiophen-2-yl]ethanone and 4-(4,4,5,5-tetramethyl-1,3,2-dioxaborolan-2-yl)benzaldehyde.

In both title compounds, C(10)H(13)BO(3)S, (I), and C(13)H(17)BO(3), (II), the molecules adopt nearly planar conformations. The crystal packing of (I) consists of a supramolecular two-dimensional network with a herringbone-like topology formed by self assembly of centrosymmetric pairs of molecules linked via dipole-dipole interactions. The crystal structure of (II) consists of a supramolecular two-dimensional network built up from centrosymmetric pairs of molecules via π-π interactions. These pairs of molecules are self-organized in an offset fashion related by a symmetry centre, generating supramolecular ribbons running along the [101] direction. Neighbouring ribbons are stacked via complementary van der Waals and hydrophobic methyl-methyl interactions.

4-Carboxypiperidinium 1-carboxycyclobutane-1-carboxylate.

The title salt, C(6)H(12)NO(2)(+)·C(6)H(7)O(4)(-) or ISO(+)·CBDC(-), is an ionic ensemble assisted by hydrogen bonds. The amino acid moiety (ISO or piperidine-4-carboxylic acid) has a protonated ring N atom (ISO(+) or 4-carboxypiperidinium), while the semi-protonated acid (CBDC(-) or 1-carboxycyclobutane-1-carboxylate) has the negative charge residing on one carboxylate group, leaving the other as a neutral -COOH group. The -(+)NH(2)- state of protonation allows the formation of a two-dimensional crystal packing consisting of zigzag layers stacked along a separated by van der Waals distances. The layers extend in the bc plane connected by a complex network of N-H···O and O-H···O hydrogen bonds. Wave-like ribbons, constructed from ISO(+) and CBDC(-) units and described by the graph-set symbols C(3)(3)(10) and R(3)(3)(14), run alternately in opposite directions along c. Intercalated between the ribbons are ISO(+) cations linked by hydrogen bonds, forming rings described by the graph-set symbols R(6)(6)(30) and R(4)(2)(18). A detailed analysis of the structures of the individual components and the intricate hydrogen-bond network of the crystal structure is given.

2-Ethyl-6-(2-pyrid-yl)-5,6,6a,11b-tetra-hydro-7H-indeno[2,1-c]quinoline.

The title compound, C(23)H(22)N(2), was obtained using the three-component imino Diels-Alder reaction via a one-pot condensation between anilines, α-pyridine-carboxy-aldehyde and indene using BF(3)·OEt(2) as the catalyst. The mol-ecular structure reveals the cis-form as the unique diastereoisomer. The crystal structure comprises one-dimensional zigzag ribbons connected via N-H⋯N hydrogen bonds. C-H⋯π inter-actions also occur.

Combining hydrogen bonding and metal coordination for controlling topochemical [2 + 2] cycloaddition from multi-component assemblies.

The crystal engineering of hydrogen bonded metal assemblies based on stilbene-type compounds is exploited in order to drive [2 + 2] cycloaddition in the solid state. Harmonization of hydrogen bonding and metal coordination is shown as an alternative supramolecular approach for the rational design of novel supramolecular photoreactive networks. This approach was extended to prepare five compounds based on Mn/trans-1,2'-(4-pyridyl)ethylene (4,4'-bpe). The structure-templating features of such arrangements are discussed in terms of their encoded self-complementary stereochemical information (persistence of O-H...N hydrogen bonds and the presence of multiple short contacts between double bonds of the 4,4'-bpe molecules). In this work, the tolerance of this approach to diverse structural factors such as number of hydrogen bonding sites on the metal centre, nature of the counterion and coordinating solvent is shown. All the arrays 1-5 are photoreactive in the solid state upon UV-irradiation leading to the regioselective synthesis of rctt-tetrakis(4-pyridyl)cyclobutane isomer (rctt-4,4'-tpcb) in high to moderate yield. An unprecedented example of supramolecular isomers (2 and 4) with similar solid state reactivity is also reported. In addition, the compound 5 exhibits unexpected formation of the rctt-4,4'-tpcb isomer in the solid state, then a structural change induced by the desolvation of the material.

A non-photochemical route for the regioselective preparation of rtct-pyridylcyclobutanes via hydrothermal isomerisation promoted by polymolybdates.

A novel approach for the regioselective preparation of rtct-tpcb (tpcb = tetrapyridylcyclobutanes) compounds promoted by polymolybdates under hydrothermal conditions is reported; these isomers are stabilised as counterions in inorganic-organic hybrid solids and are obtained in high to fair yield.

(Z)-3-Chloro-3-phenyl-N-[(S)-1-phenyl-ethyl]prop-2-enamide.

The asymmetric unit of the title compound, C(17)H(16)ClNO, contains two crystallographically independent mol-ecules. These mol-ecules are connected in an alternating fashion through N-H⋯O and C-H⋯O hydrogen bonds, generating one-dimensional chains of graph sets R(2) (1)(6) and C(4) along the a axis.

rac-1-Acetyl-5-benzyl-2-thioxoimidazolidin-4-one.

In the title compound, C(12)H(12)N(2)O(2)S, the mol-ecules have a wing-like conformation, with a distance of 3.797 (2) Šbetween the centroids of the five- and six-membered rings. In the crystal structure, mol-ecules are linked by N-H⋯O hydrogen bonds, forming infinite one-dimensional zigzag chains, running along [001], with a C(4) graph-set motif.

Exploiting the use of hydrogen bonding and metal-coordination in the self-assembly of photoreactive multicomponent networks.

An unprecedented example of concomitant harmonisation of hydrogen bonding and metal-templating to direct a topochemical [2+2] cycloaddition with quantitative yield is reported.

Hydrogen-bonded networks in trans-3-(3-pyridyl)acrylic acid and rctt-3,3'-(3,4-dicarboxycyclobutane-1,2-diyl)dipyridinium dichloride.

The structure of trans-3-(3-pyridyl)acrylic acid, C(8)H(7)NO(2), (I), possesses a two-dimensional hydrogen-bonded array of supramolecular ribbons assembled via heterodimeric synthons between the pyridine and carboxyl groups. This compound is photoreactive in the solid state as a result of close contacts between the double bonds of neighbouring molecules [3.821 (1) A] along the a axis. The crystal structure of the photoproduct, rctt-3,3'-(3,4-dicarboxycyclobutane-1,2-diyl)dipyridinium dichloride, C(16)H(16)N(2)O(4)(2+).2Cl(-), (II), consists of a three-dimensional hydrogen-bonded network built from crosslinking of helical chains integrated by self-assembly of dipyridinium cations and Cl(-) anions via different O-H...Cl, C-H...Cl and N(+)-H...Cl hydrogen-bond interactions.

(S)-5-Benzylimidazolidine-2,4-dione monohydrate.

The crystal structure of the title compound, C(10)H(10)N(2)O(2).H(2)O, also known as L-5-benzylhydantoin monohydrate, is described in terms of two-dimensional supramolecular arrays built up from infinite chains assembled via N-H...O and O-H...O hydrogen bonds among the organic molecules and solvent water molecules, with graph-set R(3)(3)(10)C(5)C(2)(2)(6). The hydrogen-bond network is reinforced by stacking of the layers through C-H...pi interactions.

(2S)-1-Carbamoylpyrrolidine-2-carboxylic acid.

In the title compound, also known as N-carbamoyl-L-proline, C(6)H(10)N(2)O(3), the pyrrolidine ring adopts a half-chair conformation, whereas the carboxyl group and the mean plane of the ureide group form an angle of 80.1 (2) degrees. Molecules are joined by N-H...O and O-H...O hydrogen bonds into cyclic structures with graph-set R(2)(2)(8), forming chains in the b-axis direction that are further connected via N-H...O hydrogen bonds into a three-dimensional network.

2,6-Bis[1-(2-isopropyl-phenyl-imino)-ethyl]-pyridine.

The title compound, C(27)H(31)N(3), has E substitution at each imine double bond where the two N atoms adopt a trans-trans relationship. The benzene rings are twisted out of the mean plane of the pyridine ring; the mean planes of the aromatic groups are rotated by 63.0 (1) and 72.58 (8)°. The crystal structure is sustained mainly by C-H⋯π and hydro-phobic methyl-methyl inter-actions.

Supramolecular isomerism in multivalent metal-templated assemblies with topochemical influence in the regioselective synthesis of tetrakis(2-pyridyl)cyclobutane isomers.

An unprecedented example of supramolecular isomerism based on 2D hydrogen-bonded multi-component networks that leads to the preparation of different photoproducts via a topochemical transformation is reported.

A mesoporous hydrogen-bonded organic-inorganic framework bearing the isopolymolybdate [Mo36O112(OH2)16]8-.

The mesoporous H-bonded organic-inorganic hybrid material is built up from the assembly of the isopolymolybdate [Mo36O112(OH2)16]8- and H2bipy2+, which displays large interconnected cavities and exhibits a reversible water sorption behaviour while maintaining its striking crystal integrity.

Robust hydrogen-bonded self-assemblies from biimidazole complexes. Synthesis and structural characterization of [M(biimidazole)2(OH2)2]2+ (M = Co2+, Ni2+) complexes and carboxylate modules.

A robust heteromeric hydrogen-bonded synthon [R2(2) (9)-Id] is exploited to drive the modular self-assembly of four coordination complexes [M(H2biim)2(OH2)2]2+ (M = Co2+, Ni2+) and carboxylate counterions. This strategy allowed us to build molecular architectures of 0-, 1-, and 2-dimensions. A hydrogen-bonded 2D-network with cavities has been designed, which maintains its striking integrity after reversible water desorption-resorption processes.