Theoretical studies on the interaction mechanisms between tetrachloro-p-benzoquinone and hydrogen peroxide

A detailed knowledge of the initial complexes is crucial for the better understanding of the reaction mechanisms between tetrachloro-p-benzoquinone (TCBQ) and hydrogen peroxide (H₂O₂). In the present study, the interaction modes and interaction mechanisms between TCBQ and H₂O₂ in the absence and presence of one, two, and three water molecules have been systematically investigated employing the B3LYP/6-311++G** level of theory in combination with the atoms in molecules theory and natural bond orbital (NBO) method. It was found that the introduction of water molecules can influence the original interaction modes between TCBQ and H₂O₂ through the formation of the intermolecular H-bonds. The interaction energies between TCBQ and H₂O₂ range from ?0.37 to ?2.75 kcal/mol for four stable complexes, which are smaller than that of the interaction between H₂O₂ and water molecule. Further energy decomposition analyses suggest that the coupling interactions between TCBQ and H₂O₂ are predominated by the electrostatic interactions regardless of the presence or absence of water molecules. In addition, the significant heat released from the interaction process in the presence of water molecules is expected to be favorable for the following reactions involving the production of the hydroxyl radical.     

Water‐mediated intermolecular interactions in 1,2‐O‐cyclohexylidene‐myo‐inositol: a quantitative analysis

The syntheses of new myo‐inositol derivatives have received much attention due to their important biological activities. 1,2‐O‐Cyclohexylidene‐myo‐inositol is an important intermediate formed during the syntheses of certain myo‐inositol derivatives. We report herein the crystal structure of 1,2‐O‐cyclohexylidene‐myo‐inositol dihydrate, C₁₂H₂₀O₆·2H₂O, which is an intermediate formed during the syntheses of myo‐inositol phosphate derivatives, to demonstrate the participation of water molecules and hydroxy groups in the formation of several intermolecular O—H…O interactions, and to determine a low‐energy conformation. The title myo‐inositol derivative crystallizes with two water molecules in the asymmetric unit in the space group C 2/c , with Z = 8. The water molecules facilitate the formation of an extensive O—H…O hydrogen‐bonding network that assists in the formation of a dense crystal packing. Furthermore, geometrical optimization and frequency analysis was carried out using density functional theory (DFT) calculations with B3LYP hybrid functionals and 6‐31G(d), 6‐31G(d,p) and 6‐311G(d,p) basis sets. The theoretical and experimental structures were found to be very similar, with only slight deviations. The intermolecular interactions were quantitatively analysed using Hirshfeld surface analysis and 2D (two‐dimensional) fingerplot plots, and the total lattice energy was calculated.     

Methyl 3‐O‐β‐l‐fucopyranosyl α‐d‐glucopyranoside trihydrate

The water content of the title compound, C₁₃H₂₄O₁₀·3H₂O, creates an extensive hydrogen‐bonding pattern, with all the hydroxyl groups of the disaccharide acting as hydrogen‐bond donors and acceptors. The water molecules are arranged in columns along the crystallographic b axis and form, together with one of the hydroxyl groups, infinite hydrogen‐bonded chains. The conformation of the disaccharide is described by glycosidic torsion angles of −38 and 18°.     

Gold(III) Chloride Catalyzed Synthesis of Chiral Substituted 3‐Formyl Furans from Carbohydrates: Application in the Synthesis of 1,5‐Dicarbonyl Derivatives and Furo[3,2‐c]pyridine

This report describes a gold(III)‐catalyzed efficient general route to densely substituted chiral 3‐formyl furans under extremely mild conditions from suitably protected 5‐(1‐alkynyl)‐2,3‐dihydropyran‐4‐one using H₂O as a nucleophile. The reaction proceeds through the initial formation of an activated alkyne–gold(III) complex intermediate, followed by either a domino nucleophilic attack/anti‐endo‐dig cyclization, or the formation of a cyclic oxonium ion with subsequent attack by H₂O. To confirm the proposed mechanistic pathway, we employed MeOH as a nucleophile instead of H₂O to result in a substituted furo[3,2‐c]pyran derivative, as anticipated. The similar furo[3,2‐c]pyran skeleton with a hybrid carbohydrate–furan derivative has also been achieved through pyridinium dichromate (PDC) oxidation of a substituted chiral 3‐formyl furan. The corresponding protected 5‐(1‐alkynyl)‐2,3‐dihydropyran‐4‐one can be synthesized from the monosaccharides (both hexoses and pentose) following oxidation, iodination, and Sonogashira coupling sequences. Furthermore, to demonstrate the potentiality of chiral 3‐formyl furan derivatives, a TiBr₄‐catalyzed reaction of these derivatives has been shown to offer efficient access to 1,5‐dicarbonyl compounds, which on treatment with NH₄OAc in slightly acidic conditions afforded substituted furo[3,2‐c]pyridine.     

Understanding LiOH Chemistry in a Ruthenium‐Catalyzed Li–O2 Battery

Non‐aqueous Li–O₂ batteries are promising for next‐generation energy storage. New battery chemistries based on LiOH, rather than Li₂O₂, have been recently reported in systems with added water, one using a soluble additive LiI and the other using solid Ru catalysts. Here, the focus is on the mechanism of Ru‐catalyzed LiOH chemistry. Using nuclear magnetic resonance, operando electrochemical pressure measurements, and mass spectrometry, it is shown that on discharging LiOH forms via a 4 e⁻ oxygen reduction reaction, the H in LiOH coming solely from added H₂O and the O from both O₂ and H₂O. On charging, quantitative LiOH oxidation occurs at 3.1 V, with O being trapped in a form of dimethyl sulfone in the electrolyte. Compared to Li₂O₂, LiOH formation over Ru incurs few side reactions, a critical advantage for developing a long‐lived battery. An optimized metal‐catalyst–electrolyte couple needs to be sought that aids LiOH oxidation and is stable towards attack by hydroxyl radicals.     

Poly[[hexaaquabis[μ4‐2‐hydroxy‐5‐(4‐sulfonatophenyldiazenyl)benzoato]dibarium(II)] 4,4′‐bipyridine solvate]

The title compound, {[Ba₂(C₁₃H₈N₂O₆S)₂(H₂O)₆]·C₁₀H₈N₂}_n, possesses a novel two‐dimensional porous coordination network, in which each Ba^II ion is nine‐coordinated by three carboxylate O atoms, two sulfonate O atoms and four water molecules in an irregular coordination environment. Hydrogen‐bond interactions between coordinated water molecules and sulfonate/hydroxyl groups hold the network layers together and produce a three‐dimensional supramolecular architecture.     

A novel three‐dimensional framework constructed by 2‐[(1H‐imidazol‐1‐yl)methyl]‐1H‐benzimidazole and infinite chains of hydrogen‐bonded water molecules

A novel three‐dimensional framework of 2‐[(1H‐imidazol‐1‐yl)methyl]‐1H‐benzimidazole dihydrate, C₁₁H₁₀N₄·2H₂O or L·2H₂O, (I), in which L acts as both hydrogen‐bond acceptor and donor in the supramolecular construction with water, has been obtained by self‐assembly reaction of L with H₂O. The two independent water molecules are hydrogen bonded alternately with each other to form a one‐dimensional infinite zigzag water chain. These water chains are linked by the benzimidazole molecules into a three‐dimensional framework, in which each organic molecule is hydrogen bonded by three water molecules. This study shows that the diversity of hydrogen‐bonded patterns plays a crucial role in the formation of the three‐dimensional framework. More significantly, as water molecules are important in contributing to the conformation, stability, function and dynamics of biomacromolecules, the infinite chains of hydrogen‐bonded water molecules seen in (I) may be a useful model for water in other chemical and biological processes.     

Water‐induced pseudo‐quadruple hydrogen‐bonding motifs in xanthine–inorganic acid complexes

In xanthinium nitrate hydrate [systematic name: 2,6‐dioxo‐1,2,3,6‐tetrahydro‐9H‐purin‐7‐ium nitrate monohydrate], C₅H₅N₄O₂⁺·NO₃⁻·H₂O, (I), and xanthinium hydrogen sulfate hydrate [systematic name: 2,6‐dioxo‐1,2,3,6‐tetrahydro‐9H‐purin‐7‐ium hydrogen sulfate monohydrate], C₅H₅N₄O₂⁺·HSO₄⁻·H₂O, (II), the xanthine molecules are protonated at the imine N atom with the transfer of an H atom from the inorganic acid. The asymmetric unit of (I) contains a xanthinium cation, a nitrate anion and one water molecule, while that of (II) contains two crystallographically independent xanthinium cations, two hydrogen sulfate anions and two water molecules. A pseudo‐quadruple hydrogen‐bonding motif is formed between the xanthinium cations and the water molecules via N—H...O and O—H...O hydrogen bonds in both structures, and leads to the formation of one‐dimensional polymeric tapes. These cation–water tapes are further connected by the respective anions and aggregate into two‐dimensional hydrogen‐bonded sheets in (I) and three‐dimensional arrangements in (II).     

Active role of hydrogen bond and ambient water in Meyer–Schuster rearrangements in high‐temperature water

Meyer–Schuster rearrangements of 2‐phenyl‐3‐butyn‐2‐ol with H₃O⁺ and (H₂O)₆ model in high‐temperature water (HTW) have been investigated by the use of density functional theory calculations. In the substrate 2‐phenyl‐3‐butyn‐2‐ol catalyzed by H₃O⁺ and (H₂O)₆, the Meyer–Schuster rearrangements were predicted by the frontier molecular orbital theory. The results show that the rearrangement does not involve the carbonium ion intermediates, but the first transition state is carboniumion like. Dehydration and hydration may occur via the intermolecular proton relay along the hydrogen‐bond chains and the second step of reaction path is a total acid–base catalytic process. Based on the results, a model considered both HTW ambient and water molecules are proposed to represent mechanisms of other reactions in HTW. © 2011 Wiley Periodicals, Inc. Int J Quantum Chem, 2011     

Electrophile‐Induced Nucleophilic Substitution of the nido‐Dicarbaundecaborate Anion nido‐7,8‐C2B9H12− by Conjugated Heterodienes

Substitution of the dicarbaundecaborate anion nido‐7,8‐C₂B₉H₁₂^? ( 1 ) by precise hydride abstraction followed by nucleophilic attack usually leads to symmetric products 10‐R‐nido‐7,8‐C₂B₉H₁₁. However, thioacetamide (MeC(S)NH₂) as nucleophile and acetone/AlCl₃ as hydride abstractor gave asymmetric 9‐[MeC(NHiPr)S]‐nido‐7,8‐C₂B₉H₁₁ ( 2 ), whereas N,N‐dimethylthioacetamide (MeC(S)NMe₂) gave the expected symmetric 10‐[MeC(NMe₂)S]‐nido‐7,8‐C₂B₉H₁₁ ( 4 ). For the formation of 2 , acetone and thioacetamide are assumed to give the intermediate MeC(S)N(CMe₂) ( 3 ), which then attacks 1 with formation of 2 . Similarly, reaction of acetyliminium chloride [MeC(O)NH(CPh₂)]Cl ( 5 ) with 1 in THF gave a mixture of 9‐ and 10‐substituted [MeC(NHCHPh₂)O]‐nido‐7,8‐C₂B₉H₁₁ ( 6 and 7 , respectively). These reactions are the first examples in which compounds (here heterodienes) that unite the functionalities of both hydride acceptor and nucleophilic site react with 1 in a bimolecular fashion. Furthermore, the analogous reaction of 1 and 5 (in an equilibrium mixture with acetyl chloride and benzophenone imine) in MeCN afforded 10‐[MeC(NCPh₂)NH]‐nido‐7,8‐C₂B₉H₁₁ ( 8 ) and MeC(O)NHCHPh₂ ( 9 ).     

The monohydrates of the four polar dipeptides l‐seryl‐l‐asparagine,l‐seryl‐l‐tyrosine,l‐tryptophanyl‐l‐serine and l‐tyrosyl‐l‐tryptophan

The crystal structures of the four dipeptides l ‐seryl‐l ‐asparagine monohydrate, C₇H₁₃N₃O₅·H₂O, l ‐seryl‐l ‐tyrosine monohydrate, C₁₂H₁₆N₂O₅·H₂O, l ‐tryptophanyl‐l ‐serine monohydrate, C₁₄H₁₇N₃O₄·H₂O, and l ‐tyrosyl‐l ‐tryptophan monohydrate, C₂₀H₂₁N₃O₄·H₂O, are dominated by extensive hydrogen‐bonding networks that include cocrystallized solvent water molecules. Side‐chain conformations are discussed on the basis of previous observations in dipeptides. These four dipeptide structures greatly expand our knowledge on dipeptides incorporating polar residues such as serine, asparagine, threonine, tyrosine and tryptophan.     

Poly[diaquabis(μ‐4,4′‐bipyridine‐κ2N:N′)bis(ethane‐1,2‐diol)di‐μ‐sulfato‐dicopper(II)]

The title compound, [Cu₂(SO₄)₂(C₁₀H₈N₂)₂(C₂H₆O₂)₂(H₂O)₂]_n, contains two crystallographically unique Cu^II centres, each lying on a twofold axis and having a slightly distorted octahedral environment. One Cu^II centre is coordinated by two bridging 4,4′‐bipyridine (4,4′‐bipy) ligands, two sulfate anions and two aqua ligands. The second is surrounded by two 4,4′‐bipy N atoms and four O atoms, two from bridging sulfate anions and two from ethane‐1,2‐diol ligands. The sulfate anion bridges adjacent Cu^II centres, leading to the formation of linear ...Cu1–Cu2–Cu1–Cu2... chains. Adjacent chains are further bridged by 4,4′‐bipy ligands, which are also located on the twofold axis, resulting in a two‐dimensional layered polymer. In the crystal structure, extensive O—H...O hydrogen‐bonding interactions between water molecules, ethane‐1,2‐diol molecules and sulfate anions lead to the formation of a three‐dimensional supramolecular network structure.     

Bis[diaquabis(2,2‐bipyridine N,N′‐dioxide‐κ2O,O′)cobalt(II)] ξ‐octamolybdate dihydrate

The title organic–inorganic hybrid compound, [Co(C₁₀H₈N₂O₂)₂(H₂O)₂]₂[Mo₈O₂₆]·2H₂O, consists of [Co(bpdo)₂(H₂O)₂]²⁺ (bpdo is 2,2‐bipyridine N,N′‐dioxide) and ξ‐[Mo₈O₂₆]⁴⁻ groups in a 2:1 ratio, plus two water solvent molecules. The independent Co atom in the cation is coordinated by four O atoms from two bpdo ligands and two water molecules, in a distorted octahedral geometry. The counter‐anions, built up around a symmetry center, are linked by solvent water molecules through O—H...O hydrogen bonds to generate two‐dimensional layers, which are in turn linked by coordinated water molecules from the cationic units through further O—H...O hydrogen bonds, forming a three‐dimensional supramolecular structure.     

The double‐stranded ladder‐like structure of poly[[bis(μ2‐acetato‐κ2O:O′)bis(acetato‐κO)bis(μ‐4,4′‐bipyridine‐κ2N:N′)dicopper(II)] 4‐nitrophenol disolvate tetrahydrate]

The reaction of 4,4′‐bipyridine with copper acetate in the presence of 4‐nitrophenol led to the formation of the title compound, {[Cu(CH₃COO)₂(C₁₀H₈N₂)]·C₆H₅NO₃·2H₂O}_n. The complex forms a double‐stranded ladder‐like coordination polymer extending along the b axis. The double‐stranded polymers are separated by 4‐nitrophenol and water solvent molecules. The two Cu^II centres of the centrosymmetric Cu₂O₂ ladder rungs have square‐pyramidal coordination environments, which are formed by two acetate O atoms and two 4,4′‐bipyridine N atoms in the basal plane and another acetate O atom at the apex. The ladder‐like double strands are separated from each other by one unit‐cell length along the c axis, and are connected by the water and 4‐nitrophenol molecules through a series of O—H...O and C—H...O hydrogen‐bonding interactions and two unique intermolecular π–π interactions.     

Triaqua(μ‐7‐iodo‐8‐oxidoquinoline‐5‐sulfonato‐κ2N,O8)dioxidouranium(VI) dihydrate

In the title compound, [U(C₉H₄INO₄S)O₂(H₂O)₃]·2H₂O, the asymmetric unit contains a UO₂²⁺ ion coordinated by the N and O atoms of a 7‐iodo‐8‐oxidoquinoline‐5‐sulfonate dianion (ferron anion) and three coordinated water molecules, and two uncoordinated water molecules. The UO₂²⁺ ion exhibits a seven‐coordinate pentagonal bipyramidal geometry. The usual sulfonate oxygen coordination is absent but the sulfonate O atoms, along with the coordinated and lattice water molecules, play a vital role in assembling the three‐dimensional structure via an extensive network of intermolecular O—H...O hydrogen bonds and π–π stacking interactions.     

Correlation of the solid‐state reactivities of racemic 2,4(6)‐di‐O‐benzoyl‐myo‐inositol 1,3,5‐orthoformate and its 4,4′‐bipyridine cocrystal with their crystal structures

Racemic 2,4(6)‐di‐O‐benzoyl‐myo‐inositol 1,3,5‐orthoformate, C₂₁H₁₈O₈, (1) , shows a very efficient intermolecular benzoyl‐group migration reaction in its crystals. However, the presence of 4,4′‐bipyridine molecules in its cocrystal, C₂₁H₁₈O₈·C₁₀H₈N₂, (1)·BP , inhibits the intermolecular benzoyl‐group transfer reaction. In (1) , molecules are assembled around the crystallographic twofold screw axis (b axis) to form a helical self‐assembly through conventional O—H...O hydrogen‐bonding interactions. This helical association places the reactive C6‐O‐benzoyl group (electrophile, El) and the C4‐hydroxy group (nucleophile, Nu) in proximity, with a preorganized El...Nu geometry favourable for the acyl transfer reaction. In the cocrystal (1)·BP , the dibenzoate and bipyridine molecules are arranged alternately through O—H...N interactions. The presence of the bipyridine molecules perturbs the regular helical assembly of the dibenzoate molecules and thus restricts the solid‐state reactivity. Hence, unlike the parent dibenzoate crystals, the cocrystals do not exhibit benzoyl‐transfer reactions. This approach is useful for increasing the stability of small molecules in the crystalline state and could find application in the design of functional solids.     

Zn(NCS)2‐3‐cyanopyridine Coordination Compounds: Synthesis,Crystal Structures,and Thermal Properties

The reaction of different stoichiometric amounts of Zn(NCS)₂ with 3‐cyanopyridine in different solvents leads to the formation of several new coordination compounds, which were structurally characterized and investigated for their thermal behavior. In Zn(NCS)₂(3‐cyanopyridine)₄ ( 1 ) and Zn(NCS)₂(3‐cyanopyridine)₂(H₂O)₂ · (3‐cyanopyridine)₂ ( 2 ) the zinc cations are octahedrally coordinated by two terminally N‐bonded thiocyanate anions and four 3‐cyanopyridine ( 1 ) or two 3‐cyanopyridine and two water molecules ( 2 ) within slightly distorted octahedra. Zn(NCS)₂(3‐cyanopyridine)₂ ( 3 ) and Zn(NCS)₂(3‐cyanopyridine)₂ · (H₂O)_0.5 ( 3‐H₂O ) also form discrete complexes but with tetrahedrally coordinated Zn cations. Upon heating compound 1 decomposes without the formation of any intermediate compound. In contrast, compound 2 loses the water molecules in the first step and transforms into compound 1 . Surprisingly, upon further heating a second TG step is observed, in which compound 3 is formed as an intermediate, which is not observed if compound 1 is heated directly. The tetrahedral complex 3 melts leading to the formation of an amorphous phase. If the hemihydrate 3‐H₂O is heated, it transforms into 3 via melting and crystallization but there are hints that a metastable phase might form as intermediate on water removal.     

4‐Carboxypyridinium perchlorate 18‐crown‐6 dihydrate clathrate and 4‐carboxypyridinium tetrafluoroborate 18‐crown‐6 dihydrate clathrate

Mixtures of 4‐carboxypyridinium perchlorate or 4‐carboxypyridinium tetrafluoroborate and 18‐crown‐6 (1,4,7,10,13,16‐hexaoxacyclooctadecane) in ethanol and water solution yielded the title supramolecular salts, C₆H₆NO₂⁺·ClO₄⁻·C₁₂H₂₄O₆·2H₂O and C₆H₆NO₂⁺·BF₄⁻·C₁₂H₂₄O₆·2H₂O. Based on their similar crystal symmetries, unit cells and supramolecular assemblies, the salts are essentially isostructural. The asymmetric unit in each structure includes one protonated isonicotinic acid cation and one crown ether molecule, which together give a [(C₆H₆NO₂)(18‐crown‐6)]⁺ supramolecular cation. N—H...O hydrogen bonds between the protonated N atoms and a single O atom of each crown ether result in the 4‐carboxypyridinium cations `perching' on the 18‐crown‐6 molecules. Further hydrogen‐bonding interactions involving the supramolecular cation and both water molecules form a one‐dimensional zigzag chain that propagates along the crystallographic c direction. O—H...O or O—H...F hydrogen bonds between one of the water molecules and the anions fix the anion positions as pendant upon this chain, without further increasing the dimensionality of the supramolecular network.     

Hydrogen‐bonded network in the trichloroacetate salts of 2‐amino‐5‐chloropyridinium and 2‐methyl‐5‐nitroanilinium monohydrate

In the crystal structures of 2‐amino‐5‐chloropyridinium trichloroacetate, C₅H₆ClN₂⁺·C₂Cl₃O₂⁻, (I), and 2‐methyl‐5‐nitroanilinium trichloroacetate monohydrate, C₇H₉N₂O₂⁺·C₂Cl₃O₂⁻·H₂O, (II), the protonated planar 2‐amino‐5‐chloropyridinium [in (I)] and 2‐methyl‐5‐nitroanilinium [in (II)] cations interact with the oppositely charged trichloroacetate anions to form hydrogen‐bonded one‐dimensional chains in (I) and, together with water molecules, a three‐dimensional network in (II). The crystals of (I) exhibit nonlinear optical properties. The second harmonic generation efficiency in relation to potassium dihydrogen phosphate is 0.77. This work demonstrates the usefulness of trichloroacetic acid in crystal engineering for obtaining new materials for nonlinear optics.