Cyclic Octamer of Hydroxyl-functionalized Cations with Net Charge Q=+8e Kinetically Stabilized by a ‘Molecular Island’ of Cooperative Hydrogen Bonds

Cyclic octamers are well-known structural motifs in chemistry, biology and physics. These include covalently bound cyclic octameric sulphur, cylic octa-alkanes, cyclo-octameric peptides as well as hydrogen-bonded ring clusters of alcohols. In this work, we show that even calculated cyclic octamers of hydroxy-functionalized pyridinium cations with a net charge Q=+8e are kinetically stable. Eight positively charged cations are kept together by hydrogen bonding despite the strong Coulomb repulsive forces. Sufficiently long hydroxy-octyl chains prevent “Coulomb explosion” by increasing the distance between the positive charges at the pyridinium rings, reducing the Coulomb repulsion and thus strengthen hydrogen bonds between the OH groups. The eightfold positively charged cyclic octamer shows spectroscopic properties similar to those obtained for hydrogen-bonded neutral cyclic octamers of methanol. Thus, the area of the hydrogen bonded OH ring represents a ‘molecular island’ within an overall cationic environment. Although not observable, the spectroscopic properties and the correlated NBO parameters of the calculated cationic octamer support the detection of smaller cationic clusters in ionic liquids, which we observed despite the competition with ion pairs wherein attractive Coulomb forces enhance hydrogen bonding between cation and anion.     

CH‐Directed Anion–π Interactions in the Crystals of Pentafluorobenzyl‐Substituted Ammonium and Pyridinium Salts

Simple pentafluorobenzyl‐substituted ammonium and pyridinium salts with different anions can be easily obtained by treatment of the parent amine or pyridine with the respective pentafluorobenzyl halide. Hexafluorophosphate is introduced as the anion by salt metathesis. In the case of the ammonium salt 4 , water co‐crystallisation seems to suppress effective anion–π interactions of bromide with the electron‐deficient aromatic system, whereas with salts 5 and 6 such interactions are observed despite the presence of water. However, due to asymmetric hydrogen‐bonding interactions with ammonium side chains, the anion of 5 is located close to the rim of the pentafluorophenyl group (η¹ interaction). In 6 the CH–anion hydrogen bonding is more symmetric and fixes the anion on top of the ring (η⁶). A similar structure‐controlling effect is observed in case of the 1,4‐diazabicyclo[2.2.2]octane derivatives 7 . Here the position of the anion (Cl, Br, I) is shifted according to the length of the weak CH–halide interaction. The hexafluorophosphate 7 d reveals that this “non‐coordinating” anion can be located on top of an aromatic π system. In the methyl‐substituted pyridinium salts 9 and 10 different locations of the bromide anions with respect to the π system are observed. This is due to different conformations of the mono‐ versus disubstituted pyridine, which leads to different directions of the weak, but structurally important, H_Me? Br bonds.     

Density functional studies on hydrogen‐bonded clusters of hydrogen halides and the interaction on halide anions

Density functional theory (DFT) calculations have been performed to study the structures and stability of X^?·(HX)_n=2–5 clusters where X = F, Cl, Br at B3LYP/6‐311++G** level of theory. The presence of halide ions in these clusters disintegrates the hydrogen halide clusters. All the hydrogen halides are then hydrogen bonded to the centrally placed halide ions, thereby forming multiple hydrogen bonds. The interaction energies have been corrected for the basis set superposition error (BSSE) using Boy's counterpoise correction method. Evidence for the destruction of hydrogen bonds in hydrogen halide clusters due to the presence of halide ions is further obtained from topological analysis and natural bond orbital analysis. The chemical hardness and chemical potential have been calculated for all the anion clusters. The above analysis reveals that hydrogen bonding in these systems is not an essentially electrostatic interaction. The nature of the stabilization interactions operative in these multiple hydrogen‐bonded clusters has been explained in terms of many‐body contribution to interaction energies. From these studies, an attempt has been made to understand the nature of the molecular properties resulting from different electronegativities of the halogens. © 2005 Wiley Periodicals, Inc. Int J Quantum Chem, 2005     

Carboxylate–phenolate tautomerism in 5‐[(nitrophenyl)diazenyl]salicylate anions

Aryldiazenyl derivatives of salicylic acid and their salts are used as dyes. In these structures, the carboxylate groups are engaged in short contacts with the cations and in hydrogen bonds with water molecules, if present. If both O atoms of the carboxylate group take part in such interactions, the negative charge is delocalized over the two atoms. In the absence of hydrogen bonds and contacts with cations, the negative charge is localized on one of the O atoms. In the crystal structures of tetramethylammonium 2‐hydroxy‐5‐[(E)‐(4‐nitrophenyl)diazenyl]benzoate and tetramethylammonium 2‐hydroxy‐5‐[(E)‐(2‐nitrophenyl)diazenyl]benzoate, both C₄H₁₂N⁺·C₁₃H₈N₃O₅⁻, all the interactions between the cations and anions are weak, and their effect on the geometry of the anions is negligible. Under these conditions, the 2‐nitro‐substituted anion is an almost pure phenol–carboxylate tautomer, whereas in the 4‐nitro‐substituted anion, the phenolic H atom is shifted towards the carboxylate group, and thus the structure of this anion is intermediate between the phenol–carboxylate and phenolate–carboxylic acid tautomeric forms. The probable formation of such an intermediate form is supported by quantum chemical calculations. Being the characteristic feature of this form, a short distance between the phenolic and carboxylate O atoms is observed in the 4‐nitro‐substituted anion, as well as in the structures of some 3,5‐dinitrosalicylates reported in the literature.     

β-卤素取代对杯[4]吡咯构象及主-客体相互作用的影响II. 密度泛函理论研究

应用密度泛函理论对杯[4]吡咯及卤素取代杯[4]吡咯模型分子的自由主体以及其卤素离子复合物体系进行计算研究. 结果表明, 杯[4]吡咯β位被卤素拉电子基团取代后, 主体分子的构象特征受吡咯单元的偶极影响; β-卤素取代导致了杯[4]吡咯对卤素离子的结合作用增强, 且当β位为氯取代时, 杯[4]吡咯对卤素离子的结合能力最强. 并从振动光谱、NBO电荷布居、相互作用的前线轨道、“活性”构象的偶极矩和Mulliken成键布居等方面阐述β-卤素取代对杯[4]吡咯与卤素离子之间的主-客体相互作用的影响.     

Highly Dense Nitranilates‐Containing Nitrogen‐Rich Cations

High density energetic salts containing nitrogen‐rich cations and the nitranilic anion were readily synthesized in high yield by metathesis reactions of sodium nitranilate 2 and an appropriate halide. All of the new compounds were fully characterized by elemental, spectral (IR, ¹H, ¹³C NMR), and thermal (DSC) analyses. The structure of hydrazinium nitranilate ( 4 ) was also determined by single‐crystal X‐ray analysis. The high symmetry and oxygen content of the anion give these salts extensive hydrogen bonding capability which further results in the high densities, low water solubilities, and high thermal stabilities (T_d> 200 °C) of these compounds. Theoretical performance calculations were carried out by using Gaussian 03 and Cheetah 5.0. The calculated detonation pressures (P) for these new salts fall between 17.5 GPa ( 10 ) and 31.7 GPa ( 4 ), and the detonation velocities (νD) range between 7022 m s^?1 ( 13 ) and 8638 m s^?1 ( 4 ).     

Tris(1‐ethyl‐3‐methyl­imidazolium) hexa­chloro­lanthanate

In the title complex, (C₆H₁₁N₂)₃[LaCl₆], centrosymmetric octahedral hexa­chloro­lanthanate anions are located at the corners and face‐centers of the monoclinic unit cell. The ring H atoms of the cations interact with the Cl atoms of the anions via hydrogen bonding, and bifurcation of the hydrogen bonding is observed. Cation–cation interactions via hydrogen bonding between the ring H atoms and π‐electrons of aromatic rings are also observed as in other imidazolium salts.     

The Structures and Hydrogen Bonding Networks in Crystals of Alkylenediammonium Salts of Galactaric Acid

The crystal structures of five alkylenediammonium galactarates (1– 5) were determined because the information from these structures may provide some insight into the solid state structures of the poly(alkylene galactaramides) derived from these salts. In each case the meso-galactarate anion is in the extended conformation. In four out of the five cases associations between galactarate units led to alternating layers of anions and cations rather than the expected alternation of anion and cation found in ionic solids. All five salts display extensive hydrogen bonding involving ammonium and carboxylate groups and in some cases hydroxyl groups of the anion.     

2‐Ethyl‐6‐methylpyridin‐3‐ol and its salt bis(2‐ethyl‐3‐hydroxy‐6‐methylpyridinium) succinate

The title compounds, C₈H₁₁NO, (I), and 2C₈H₁₂NO⁺·C₄H₄O₄²⁻, (II), both crystallize in the monoclinic space group P2₁/c. In the crystal structure of (I), intermolecular O—H...N hydrogen bonds combine the molecules into polymeric chains extending along the c axis. The chains are linked by C—H...π interactions between the methylene H atoms and the pyridine rings into polymeric layers parallel to the ac plane. In the crystal structure of (II), the succinate anion lies on an inversion centre. Its carboxylate groups interact with the 2‐ethyl‐3‐hydroxy‐6‐methylpyridinium cations via intermolecular N—H...O hydrogen bonds with the pyridine ring H atoms and O—H...O hydrogen bonds with the hydroxy H atoms to form polymeric chains, which extend along the [01] direction and comprise R₄⁴(18) hydrogen‐bonded ring motifs. These chains are linked to form a three‐dimensional network through nonclassical C—H...O hydrogen bonds between the pyridine ring H atoms and the hydroxy‐group O atoms of neighbouring cations. π–π interactions between the pyridine rings and C—H...π interactions between the methylene H atoms of the succinate anion and the pyridine rings are also present in this network.     

Crystallographic characterization of the first reported crystalline form of the potent hallucinogen (R)‐2‐amino‐1‐(8‐bromobenzo[1,2‐b;5,4‐b′]difuran‐4‐yl)propane or `bromodragonfly': the 1:1 anhydrous proton‐transfer compound with 3,5‐dinitrosalicylic acid

The 1:1 proton‐transfer compound of the potent substituted amphetamine hallucinogen (R)‐2‐amino‐1‐(8‐bromobenzo[1,2‐b;5,4‐b′]difuran‐4‐yl)propane (common trivial name `bromodragonfly') with 3,5‐dinitrosalicylic acid, namely 1‐(8‐bromobenzo[1,2‐b;5,4‐b′]difuran‐4‐yl)propan‐2‐aminium 2‐carboxy‐4,6‐dinitrophenolate, C₁₃H₁₃BrNO₂⁺·C₇H₃N₂O₇⁻, forms hydrogen‐bonded cation–anion chain substructures comprising undulating head‐to‐tail anion chains formed through C(8) carboxyl–nitro O—H...O associations and incorporating the aminium groups of the cations. The intrachain cation–anion hydrogen‐bonding associations feature proximal cyclic R₃³(8) interactions involving both an N⁺—H...O_phenolate and the carboxyl–nitro O—H...O associations and aromatic π–π ring interactions [minimum ring centroid separation = 3.566 (2) Å]. A lateral hydrogen‐bonding interaction between the third aminium H atom and a carboxyl O‐atom acceptor links the chain substructures, giving a two‐dimensional sheet structure. This determination represents the first of any form of this compound and is in the (R) absolute configuration. The atypical crystal stability is attributed both to the hydrogen‐bonded chain substructures provided by the anions, which accommodate the aminium proton‐donor groups of the cations and give crosslinking, and to the presence of the cation–anion aromatic ring π–π interactions.     

DFT Study of the Geometrical and Electronic Structures of Geminal Dicationic Ionic Liquids 1,3‐Bis[3‐methylimidazolium‐1‐yl]hexane Halides

In this work, the geometrical and electronic properties of the mono cationic ionic liquid 1‐hexyl‐3‐methylimidazolium halides ([C₆(mim)]⁺_X^?, X=Cl, Br and I) and dicationic ionic liquid 1,3‐bis[3‐methylimidazolium‐1‐yl]hexane halides ([C₆(mim)₂X₂], X=Cl, Br and I) were studied using the density functional theory (DFT). The most stable conformer of these two types ionic liquids (IL) are determined and compared with each other. Results show that in the most stable conformers, in both monocationic ILs and dicationic ILs, the Cl^? and Br^? anions prefer to locate almost in the plane of the imidazolium ring whereas the I^? anion prefers nearly vertical location respect to the imidazolium ring plan. Comparison of hydrogen bonding and ionic interactions in these two types of ionic liquids reveals that these ionic liquids can be formed hydrogen bond by Cl^? and Br^? anion. The calculated thermodynamic functions show that the interaction of cation — anion pair in the dicationic ionic liquids are more than monocationic ionic liquids and these interactions decrease with increasing the halide anion atomic weight.     

Dissecting Noncovalent Interactions in Carboxyl-Functionalized Ionic Liquids Exhibiting Double and Single Hydrogens Bonds Between Ions of Like Charge

We show that the carboxyl-functionalized ionic liquid 1-(carboxymethyl)pyridinium bis(trifluoromethylsulfonyl)imide [HOOC-CH₂-py][NTf₂] exhibits three types of hydrogen bonding: the expected single hydrogen bonds between cation and anion, and, surprisingly, single and double hydrogen bonds between the cations, despite the repulsive Coulomb forces between the ions of like charge. Combining X-ray crystallography, differential scanning calorimetry, IR spectroscopy, thermodynamic methods and DFT calculations allows the analysis and characterization of all types of hydrogen bonding present in the solid, liquid and gaseous states of the ionic liquid (IL). We find doubly hydrogen bonded cationic dimers (c⁺=c⁺) in the crystalline phase. With increasing temperature, this binding motif opens in the liquid and is replaced by (c⁺−c⁺−a⁻ species, with a remaining single cationic hydrogen bond and an additional hydrogen bond between cation and anion. We provide clear evidence that the IL evaporates as hydrogen-bonded ion pairs (c⁺−a⁻) into the gas phase. The measured transition enthalpies allow the noncovalent interactions to be dissected and the hydrogen bond strength between ions of like charge to be determined.     

Anion–π Interactions in Salts with Polyhalide Anions: Trapping of I42−

The directionality of interaction of electron‐deficient π systems with spherical anions (e.g,. halides) can be controlled by secondary effects like NH or CH hydrogen bonding. In this study a series of pentafluorophenyl‐substituted salts with polyhalide anions is investigated. The compounds are obtained by aerobic oxidation of the corresponding halide upon crystallization. Solid‐state structures reveal that in bromide 2 , directing NH–anion interactions position the bromide ion in an η¹‐type fashion over but not in the center of the aromatic ring. The same directing forces are effective in corresponding tribromide salt 3 . In the crystal, the bromide ion is paneled by four electron‐deficient aromatic ring systems. In addition, compounds 4 and 6 , which have triiodide and the rare tetraiodide dianion as anions, are described. Computational studies reveal that the latter is highly unstable. In the present case it is stabilized by the crystal lattice, for example, by interaction with electron‐deficient π systems.     

Hydrogen bonding interactions between <Emphasis Type="Italic">N</Emphasis>,<Emphasis Type="Italic">N</Emphasis>-dimethylformamide and cysteine: DFT studies of structures,properties, and topologies

The hydrogen bonding interactions between cysteine and N,N-dimethylformamide (DMF) were studied at the extended hybrid functional DFT-X3LYP/6-311++G(d,p) level regarding their geometries, energies, vibrational frequencies, and topological features of the electron density. The quantum theory of atoms in molecules (QTAIM) and natural bond orbital (NBO) analyses were employed to elucidate the interaction characteristics in the complexes. The results show that two intermolecular hydrogen bonds (H-bonds) are formed in one complex except few complexes with one intermolecular H-bond. The H-bonds involving O atom of DMF as H-bond acceptor usually are red-shifting H-bonds, while the blue-shifting H-bond usually involve methyl of DMF or methenyl of cysteine moiety as H-bond donors. Both hydrogen bonding interaction and structural deformation play important roles in the relative stabilities of the complexes. Due to the π-bond cooperativity, the strongest H-bond is formed between hydroxyl of cysteine moiety and O atom of DMF, however, the serious deformation counteract the hydrogen bonding interaction to a great extent. The complex involves a stronger hydrogen bonding interaction as well as the smaller deformation is the most stable one. The electron density (ρ_b) as well as its Laplacian (∇²ρ_b) at the H-bond critical point predicted by QTAIM is strongly correlated with the H-bond structural parameter (δR _H···Y) and the second-perturbation energies E(2) in the NBO scheme.     

镁铝水滑石层板与层间阴离子相互作用的理论研究

本文采用以ASED-MO(含原子对排斥的EHMO法)为基础的结构自动优化的EHTOPT程序,对镁铝水滑石(LDHs)层板与层间阴离子相互作用进行了理论研究.以Mg6Al2(OH)16X@H2O为分子结构单元,计算并分析了与不同层间阴离子形成稳定结构的能量变化、成键状况及电荷转移情况,揭示了层间作用力的本质.结果表明,LDHs层板与层间阴离子间存在静电吸引、氢键等非共价键弱相互作用,且氢键作用为主,其强弱与阴离子电荷分布、空间排布方式密切相关;层间阴离子电荷分布同时还影响着层板酸碱性的变化.     

The Double‐Faced Nature of Hydrogen Bonding in Hydroxy‐Functionalized Ionic Liquids Shown by Neutron Diffraction and Molecular Dynamics Simulations

We characterize the double‐faced nature of hydrogen bonding in hydroxy‐functionalized ionic liquids by means of neutron diffraction with isotopic substitution (NDIS), molecular dynamics (MD) simulations, and quantum chemical calculations. NDIS data are fit using the empirical potential structure refinement technique (EPSR) to elucidate the nearest neighbor H???O and O???O pair distribution functions for hydrogen bonds between ions of opposite charge and the same charge. Despite the presence of repulsive Coulomb forces, the cation–cation interaction is stronger than the cation–anion interaction. We compare the hydrogen‐bond geometries of both “doubly charged hydrogen bonds” with those reported for molecular liquids, such as water and alcohols. In combination, the NDIS measurements and MD simulations reveal the subtle balance between the two types of hydrogen bonds: The small transition enthalpy suggests that the elusive like‐charge attraction is almost competitive with conventional ion‐pair formation.     

Hexaaquanickel(II) bis[2‐carboxylato‐2‐(isothiouronium‐S‐ylmethyl)propane‐1,3‐diyl phosphate] hexahydrate

In the title complex, [Ni(H₂O)₆](C₆H₁₀N₂O₆PS)₂·6H₂O, the asymmetric unit consists of one‐half of an Ni atom (which lies on an inversion centre) with three coordinated water molecules, one complete 2‐carboxylato‐2‐(isothiouronium‐S‐ylmethyl)propane‐1,3‐diyl phosphate anion and three noncoordinated water molecules. The hexaaquanickel(II) cations have distorted octahedral coordination and are connected via water chains to form two‐dimensional supramolecular networks parallel to the ab plane. The phosphate ester anion is linked via N—H...O and O—H...O hydrogen bonds, thus creating various ring, dimer and chain hydrogen‐bonding patterns, and building up a second two‐dimensional supramolecular network parallel to the ab plane. The crystal structure is further stabilized by an intra‐ and interlayer hydrogen‐bond network. This work illustrates that a carboxylate with a caged phosphate ester can open its ring in the presence of dichloridotetrakis(thiourea)nickel, and the resulting polyfunctional anion can be used for constructing a complex hydrogen‐bonding scheme.     

Understanding cellulose dissolution: effect of the cation and anion structure of ionic liquids on the solubility of cellulose

The effect of ionic liquids (ILs) on the solubility of cellulose was investigated by changing their anions and cations. The structural variation included 11 kinds of cations in combination with 4 kinds of anions. The interaction between the IL and cellobiose, the repeating unit of cellulose, was clarified through nuclear magnetic resonance (NMR) spectroscopy. The reason for different dissolving capabilities of various ILs was revealed. The hydrogen bonding interaction between the IL and hydroxyl was the major force for cellulose dissolution. Both the anion and cation in the IL formed hydrogen bonds with cellulose. Anions associated with hydrogen atoms of hydroxyls, and cations favored the formation of hydrogen bonds with oxygen atoms of hydroxyls by utilizing activated protons in imidazolium ring. Weakening of either the hydrogen bonding interaction between the anion and cellulose, or that between the cation and cellulose, or both, decreases the capability of ILs to dissolve cellulose.     

Anion Binding Properties of N-Confused Porphyrins at the Peripheral Nitrogen

Ni(II), Pd(II), and Cu(II) complexes of N-confused porphyrin (NCP) exhibit anion binding properties through a hydrogen bonding interaction at the peripheral NH of confused pyrrole ring. The binding constants of the tetrakis(pentafluorophenyl)-NCP metal complexes (1-M, M= Ni, Pd, Cu) for various halide anions in CH₂C1₂ increase in the order of F^? > Cl^? > Br^? > I^?, respectively. Zwitterionic resonance form of the NCP complexes as well as interactions between halide anions and a pentafluorophenyl group are suggested to be important for efficient anion binding.     

Multiple hydrogen bonds in cytosinium zoledronate trihydrate

The asymmetric unit of the title compound [systematic name: 4‐amino‐2‐oxo‐2,3‐dihydropyrimidin‐1‐ium 1‐hydroxy‐2‐(1H,3H‐imidazol‐3‐ium‐1‐yl)ethylidenediphosphonate trihydrate], C₄H₆N₃O⁺·C₅H₉N₂O₇P₂⁻·3H₂O, contains one cytosinium cation, one zoledronate anion and three water molecules. The zoledronate anion has a zwitterionic character, in which each phosphonate group is singly deprotonated and an imidazole N atom is protonated. Furthermore, proton transfer takes place from one of the phosphonic acid groups of the zoledronate anion to one of the N atoms of the cytosinium cation. The cytosinium cation forms a C(6) chain, while the zoledronate anion forms a rectangular‐shaped centrosymmetric dimer through N—H...O hydrogen bonds. The cations and anions are held together by N—H...O and O—H...O hydrogen bonds to form a one‐dimensional polymeric tape. The three water molecules play a crucial role in hydrogen bonding, resulting in a three‐dimensional hydrogen‐bonded network.