Ammonium N‐acetyl‐l‐threoninate and methyl­ammonium N‐acetyl‐l‐threoninate

Ammonium N‐acetyl‐l ‐threoninate, NH₄⁺·C₆H₁₀NO₄^?, and methyl­ammonium N‐acetyl‐l ‐threoninate, CH₆N⁺·­C₆H₁₀NO₄^?, crystallize in the orthorhombic P2₁2₁2₁ and monoclinic P2₁ space groups, respectively. The two crystals present the same packing features consisting of infinite ribbons of screw‐related N‐acetyl‐l ‐threoninate anions linked together through pairs of hydrogen bonds. The cations interconnect neighbouring ribbons of anions involving all the nitrogen‐H atoms in three‐dimensional networks of hydrogen bonds. The hydrogen‐bond patterns include asymmetric `three‐centred' systems. In both structures, the Thr side chain is in the favoured (g^?g⁺) conformation.     

2‐Amino­anilinium phosphite

The solid‐state structure of the title compound, alternatively called 2‐amino­anilinium hydrogen phosphonate, C₆H₉N₂⁺·H₂PO₃^?, shows the monoprotonated di­amine mol­ecule to be multiply hydrogen bonded to HPO₃H^? anions. There is no inter‐phosphite hydrogen bonding, contrary to previous solid‐state observations of the species.     

Anion Receptors Containing ‐NH Binding Sites: Hydrogen‐Bond Formation or Neat Proton Transfer?

When the amide‐containing receptor 1 ⁺ is in a solution of dimethyl sulfoxide (DMSO) in the presence of basic anions (CH₃COO^?, F^?, H₂PO₄^?), it undergoes deprotonation of the ‐NH fragment to give the corresponding zwitterion, which can be isolated as a crystalline solid. In the presence of less basic anions (Cl^?, Br^?, NO₃^?), 1 ⁺ establishes true hydrogen‐bond interactions of decreasing intensity. The less acidic receptor 2 ⁺ undergoes neat proton transfer with only the more basic anions CH₃COO^? and F^?, and establishes hydrogen‐bond interactions with H₂PO₄^?. An empirical criterion for discerning neutralisation and hydrogen bonding, based on UV/Vis and ¹H NMR spectra, is proposed.     

2(S)‐Amino‐3‐[1H‐imidazol‐4(5)‐yl]­propyl cyclo­hexylmethyl ether di­hydro­chloride and 2(S)‐amino‐3‐[1H‐imidazol‐4(5)‐yl]­propyl 4‐bromo­benzyl ether di­hydro­chloride

(Cyclo­hexyl­methyl­oxy­methyl)(1H‐imidazol‐4‐io­methyl)‐(S)‐ammonium dichloride, C₁₃H₂₅N₃O⁺·2Cl^?, and (4‐bromo­benzyl)(1H‐imidazol‐4‐io­methyl)‐(S)‐ammonium dichloride, C₁₃H₁₈BrN₃O⁺·2Cl^?, are model compounds with different biological activities for evaluation of the hist­amine H3‐receptor activation mechanism. Both title compounds occur in almost similar extended conformations.     

Ethyl­ammonium and diethyl­ammonium salts of chloranilic acid

In the crystals of two title salts of chloranilic acid (2,5‐di­chloro‐3,6‐di­hydroxy‐p‐benzo­quinone), namely ethyl­ammonium chloranilate, C₂H₈N⁺·C₆HCl₂O₄^?, (I), and diethyl­ammonium chloranilate, C₄H₁₂N⁺·C₆HCl₂O₄^?, (II), the chloranilate ions are present as a hydrogen‐bonded dimer which has an inversion center. The ethyl­ammonium and diethyl­ammonium ions link the dimers through N—H?O hydrogen bonds, forming a three‐dimensional hydrogen‐bond network in (I) and a one‐dimensional chain in (II).     

Gutmann's Donor Numbers Correctly Assess the Effect of the Solvent on the Kinetics of SNAr Reactions in Ionic Liquids

We report an experimental study on the effect of solvents on the model S_NAr reaction between 1‐chloro‐2,4‐dinitrobenzene and morpholine in a series of pure ionic liquids (IL). A significant catalytic effect is observed with reference to the same reaction run in water, acetonitrile, and other conventional solvents. The series of IL considered include the anions, NTf₂^?, DCN^?, SCN^?, CF₃SO₃^?, PF₆^?, and FAP^? with the series of cations 1‐butyl‐3‐methyl‐imidazolium ([BMIM]⁺), 1‐ethyl‐3‐methyl‐imidazolium ([EMIM]⁺), 1‐butyl‐2,3‐dimethyl‐imidazolium ([BM₂IM]⁺), and 1‐butyl‐1‐methyl‐pyrrolidinium ([BMPyr]⁺). The observed solvent effects can be attributed to an “anion effect”. The anion effect appears related to the anion size (polarizability) and their hydrogen‐bonding (HB) abilities to the substrate. These results have been confirmed by performing a comparison of the rate constants with Gutmann's donicity numbers (DNs). The good correlation between rate constants and DN emphasizes the major role of charge transfer from the anion to the substrate.     

A theoretical study of dihydrogen bonds in small protonated rings: Aziridine and azetidine cations

B3LYP/6-311++G(d,p) calculations were used to predict some molecular properties of the C₂H₆N⁺?BeH₂, C₂H₆N⁺?MgH₂, C₃H₈N⁺?BeH₂ and C₃H₈N⁺?MgH₂ dihydrogen-bonded complexes. In these systems, it was demonstrated that the C₂H₆N⁺ and C₃H₈N⁺ protonated rings are potential candidates to bind with protonic hydrogens derived from alkaline earth metal compounds, BeH₂ and MgH₂. In terms of structural parameters and quantification of the dihydrogen bond energies, we should mention that the C₂H₆N⁺ three-membered ring provides the formation of stronger bound systems, which are 4.0 kJ mol^?1 more stables than C₃H₈N⁺ four-membered ones. As complement, the analysis of the infrared spectrum indicated that red-shifts and blue-shifts are occurring in the N–H bonds of both C₂H₆N⁺ and C₃H₈N⁺ cationic rings. However, these two vibrational shifts were also verified on BeH₂ and MgH₂, what lead us to affirm that cationic compounds derived from small nitrogen rings and earth alkaline molecules are able to form unusual dihydrogen-bonded complexes by means of distinct spectroscopic phenomena, the red-shits and blue-shifts.     

Vibrational spectroscopy of complex compounds of gold pentafluoride

IR and Raman spectra of X⁺ AuF₆ ^? (X=CIF₂, CIO₂, CIOF₂, CIF₄, CIF₆) were studied. The vibration frequencies of these compounds in the solid phase and in solutions in anhydrous HF were assigned. Peculiar features of the vibrational spectra of solid X⁺ AuF₆ ^?, associated both with structural transformations of cations and anions in the crystal lattice field and cation—anion interactions and also with the Jahn—Teller effect, Fermi resonance, non-rigid intramoleciular rearrangements.,etc., were discussed.     

Hexa­methyl­enetetraminium 2,4,6‐tri­nitro­phenolate

In the title complex, the 1:1 ionic adduct of hexa­methyl­enetetraminium and 2,4,6‐tri­nitro­phenolate, C₆H₁₃N₄⁺·­C₆H₂N₃O₇^?, the cation acts as a donor for bifurcated hydrogen bonds to the O atoms of the phenolate and one of the nitro groups of the 2,4,6‐tri­nitro­phenolate anion. The crystal structure is built from sheets of cations and anions, and is stabilized by intermolecular C—H?O and C—H?π interactions.     

Aqueous Self‐Assembly and Cation Selectivity of Cobaltabisdicarbollide Dianionic Dumbbells

The anion [3,3′‐Co(C₂B₉H₁₁)₂]^? ([COSAN]^?) produces aggregates in water. These aggregates are interpreted to be the result of C?H???H?B interactions. It is possible to generate aggregates even after the incorporation of additional functional groups into the [COSAN]^? units. The approach is to join two [COSAN]^? anions by a linker that can adapt itself to act as a crown ether. The linker has been chosen to have six oxygen atoms, which is the ideal number for K⁺ selectivity in crown ethers. The linker binds the alkaline metal ions with different affinities; thus showing a distinct degree of selectivity. The highest affinity is shown towards K⁺ from a mixture containing Li⁺, Na⁺, K⁺, Rb⁺ and Cs⁺; this can be indicative of pseudo‐crown ether performance of the dumbbell. One interesting possibility is that the [COSAN]^? anions at the two ends of the linker can act as a hook‐and‐loop fastener to close the ring. This facet is intriguing and deserves further consideration for possible applications. The distinct affinity towards alkaline metal ions is corroborated by solubility studies and isothermal calorimetry thermograms. Furthermore, cryoTEM micrographs, along with light scattering results, reveal the existence of small self‐assemblies and compact nanostructures ranging from spheres to single‐/multi‐layer vesicles in aqueous solutions. The studies reported herein show that these dumbbells can have different appearances, either as molecules or aggregates, in water or lipophilic phases; this offers a distinct model as drug carriers.     

Tetra­butyl­ammonium α‐acetyl‐γ‐butyrolactonate containing a three‐dimensional hydrogen‐bonded network

The title compound, C₁₆H₃₆N⁺·C₆H₇O₃^?, crystallizes with two independent anions and two independent cations in the asymmetric unit. Each anion adopts an s‐trans conformation and forms O?H—C hydrogen bonds to the α‐methyl­ene groups of four neighbouring tetra­butyl­ammonium cations, to create a three‐dimensional hydrogen‐bonded network.     

Acyclic Schiff base salts derived from 1,3‐diaminopropane and 1,3‐diamino‐2‐hydroxypropane

Two salts of acyclic Schiff base cationic ligands, namely N,N′‐bis(2‐nitrobenzyl)propane‐1,3‐diammonium dichloride monohydrate, C₁₇H₂₂N₄O₄²⁺·2Cl⁻·H₂O, (I), and 2‐hydroxy‐N,N′‐bis(2‐nitrobenzyl)propane‐1,3‐diammonium dichloride, C₁₇H₂₂N₄O₅²⁺·2Cl⁻, (II), were synthesized as precursors in order to obtain new acyclic and macrocyclic multidentate ligands and complexes. The cation conformations in compounds (I) and (II) are different in the solid state, although the cations are closely related chemically. Similarly, the hydrogen‐bonding networks involving ammonium cations, hydroxyl groups and chloride anions are also different. In the cation of compound (II), the hydroxyl group is disordered over two sets of sites, with occupancies of 0.785 (8) and 0.215 (8).     

Metal Complexes with Macrocyclic Ligands Part XXX. Synthesis and structure of halocuprates of tetraprotonated 1,4,8,11-tetraazacyclotetradecane and its Cu2+ complex

By mixing acidic solutions of 1,4,8,11-tetraazacyclotetradecane (Cy) with CuX₂ (X = Cl^?, Br^?), either the hexahalocuprates of the tetraprotonated form of the macrocycle ([CyH₄] [CuX₆]) or the tetrahalocuprates of its Cu²⁺ complex ([CuCy] [CuX₄]) are obtained. The structures of the chloro derivatives are established by X-ray diffraction analysis. In [CyH₄] [CuCl₆], the Cu²⁺ is in a tetragonally distorted octahedral geometry with four short and two long Cu? Cl bonds. The tetraprotonated macrocycle is centrosymmetric, and its conformation is exodentate, so that the four ammonium groups are as far as possible from each other to minimize the electrostatic repulsion. In [CuCy] [CuCl₄], the Cu²⁺ ion complexed by the macrocycle is surrounded by four N-atoms in a square-planar arrangement. In addition, the axial positions are occupied by two Cl^? ions of two CuCl units, which act as bridges. The macrocycle is in the trans-III-configuration. The other Cu²⁺ ion is coordinated by four Cl^? ions in a distorted tetrahedral geometry. IR and VIS spectra of the chloro and bromo derivatives are used to discuss the structure of the bromo species.     

Amide-based Fluorescent Macrocyclic Anion Receptors

Introduction Interest in the selective recognition and sensing of anionic species continues to attract the attention of su-pramolecular chemistry community.1 The importance of anions in chemical and biological process can not be underestimated. It is well known that in nature neutral proteins bind anions only via hydrogen bonding interac-tions.2 Several anion receptors have been constructed from five-membered heterocycle,3 amide,4 (thio) urea,5 since these groups form relatively strong NHanio…     

Tri- and tetraurea piperazine cyclophanes: synthesis and complexation studies of preorganized and folded receptor molecules

A series of symmetrical tri‐ and tetrameric N‐ethyl‐ and N‐phenylurea‐functionalized cyclophanes have been prepared in nearly quantitative yields (86–99 %) from the corresponding tri‐ and tetraamino‐functionalized piperazine cyclophanes and ethyl or phenyl isocyanates. Their conformational and complexation properties have been studied by single‐crystal X‐ray diffraction, variable‐temperature NMR spectroscopy, and ESI‐MS analysis. The rigid 27‐membered trimeric cyclophane skeleton assisted by a seam of intramolecular hydrogen bonds results in a preorganized ditopic recognition site with an all‐syn conformation of the urea moieties that, complemented by a lipophilic cavity of the cyclophane, binds molecular and ionic guests as well as ion pairs. The all‐syn conformation persists in acidic conditions and the triprotonated triurea cyclophane binds an unprecedented anion pair, H₂PO₄^????HPO₄^2?, in the solid state. The tetra‐N‐ethylurea cyclophane is less rigid and demonstrates an induced‐fit recognition of diisopropyl ether in the solid state. The guest was encapsulated within the lipophilic interior of a quasicapsule, formed by intramolecular hydrogen‐bond‐driven folding of the 36‐membered cyclophane skeleton. In the gas phase, the essential role of the urea moieties in the binding was demonstrated by the formation of monomeric 1:1 complexes with K⁺, TMA⁺, and TMP⁺ as well as the ion‐pair complexes [KI+K]⁺, [TMABr+TMA]⁺ and [TMPBr+TMP]⁺. In the positive‐mode ESI‐MS analysis, ion‐pair binding was found to be more pronounced with the larger tetraurea cyclophanes. In the negative mode, owing to the large size of the binding site, a general binding preference towards larger anions, such as the iodide, over smaller anions, such as the fluoride, was observed.     

l‐Prolinium picrate and 2‐methyl­pyridinium picrate

In the structure of l ‐prolinium picrate, C₅H₁₀NO₂⁺·C₆H₂N₃O₇⁻, the C^γ atom of the pyrrolidine ring has conformational disorder. Both the major and minor conformers of the pyrrolidine ring adopt conformations inter­mediate between a half‐chair and an envelope. Both the cation and anion are packed through chelated three‐centred N—H⋯O hydrogen bonds. The prolinium cation connects two different picrate anions, leading to an infinite chain running along the b axis. In 2‐methyl­pyridinium picrate, C₆H₈N⁺·C₆H₂N₃O₇⁻, the cations and anions are packed separately along the a axis and are inter­connected by N—H⋯O hydrogen bonds. Intra­molecular contacts between phenolate O atoms and adjacent nitro groups are identified in both structures. A graph‐set motif of R₁²(6) is observed in both structures.     

Differences and similarities among hypoxanthinium nitrate hydrate structures

Crystals of hypoxanthinium (6‐oxo‐1H,7H‐purin‐9‐ium) nitrate hydrates were investigated by means of X‐ray diffraction at different temperatures. The data for hypoxanthinium nitrate monohydrate (C₅H₅N₄O⁺·NO₃^?·H₂O, Hx1 ) were collected at 20, 105 and 285 K. The room‐temperature phase was reported previously [Schmalle et al. (1990). Acta Cryst. C 46 , 340–342] and the low‐temperature phase has not been investigated yet. The structure underwent a phase transition, which resulted in a change of space group from Pmnb to P2₁/n at lower temperature and subsequently in nonmerohedral twinning. The structure of hypoxanthinium dinitrate trihydrate (H₃O⁺·C₅H₅N₄O⁺·2NO₃^?·2H₂O, Hx2 ) was determined at 20 and 100 K, and also has not been reported previously. The Hx2 structure consists of two types of layers: the `hypoxanthinium nitrate monohydrate' layers (HX) observed in Hx1 and layers of Zundel complex H₃O⁺·H₂O interacting with nitrate anions (OX). The crystal can be considered as a solid solution of two salts, i.e. hypoxanthinium nitrate monohydrate, C₅H₅N₄O⁺·NO₃^?·H₂O, and oxonium nitrate monohydrate, H₃O⁺(H₂O)·NO₃^?.     

Influence of protonation on the geometry of 2-{[(2,6-dimethylphenoxy)ethyl]amino}-1-phenylethan-1-ol: crystal structures of the free base and of its chloride and 3-hydroxybenzoate salt forms

The aroxyalkylaminoalcohol derivatives are a group of compounds known for their pharmacological action. The crystal structures of four new xylenoxyaminoalcohol derivatives having anticonvulsant activity are reported, namely, 2-{[2-(2,6-dimethylphenoxy)ethyl]amino}-1-phenylethan-1-ol, C₁₈H₂₃NO₂, 1 , the salt N-[2-(2,6-dimethylphenoxy)ethyl]-1-hydroxy-1-phenylethan-2-aminium 3-hydroxybenzoate, C₁₈H₂₄NO₂⁺·C₇H₅O₃^?, 2 , and two polymorphs of the salt (R)-N-[2-(2,6-dimethylphenoxy)ethyl]-1-hydroxy-1-phenylethan-2-aminium chloride, C₁₈H₂₄NO₂⁺·Cl^?, 3 and 3p . Both polymorphs crystallize in the space group P2₁2₁2 and each has two cations and two anions in the asymmetric unit (Z′ = 2). The molecules in the polymorphs show differences in their molecular conformations and intermolecular interactions. The crystal packing of neutral 1 is dominated by intermolecular O—H…N hydrogen bonds, resulting in the formation of one-dimensional chains. In the crystal structures of the salt forms ( 2 , 3 and 3p ), each protonated N atom is engaged in a charge-assisted hydrogen bond with the corresponding anion. The protonation of the N atom also influences the conformation of the molecular linker between the two aromatic rings and changes the orientation of the rings. The crystal packing of the salt forms is dominated by intermolecular O—H…O hydrogen bonds, resulting in the creation of chains and rings. Structural studies have been enriched by the calculation of Hirshfeld surfaces and the corresponding fingerprint plots.     

Density Functional Theoretical Study of Polynitrogen Compounds N5+Y− (Y=B(CF3)4, BF4, PF6 and B(N3)4)

The structures and the stabilities of polynitrogen compounds N₅⁺Y^? [Y=B(CF₃)₄, BF₄, PF₆, and B(N₃)₄], as the potential high energy density compounds, have been investigated at the B3LYP/6‐31G(d,p) and B3LYP/6‐311+G(d,p) levels. On the basis of our geometry optimization calculations, the structural properties of the N₅⁺Y^? compounds are discussed, and it is found that the combination of the N₅⁺ cation and the Y^? anions leads to distortion of the structures of the Y^? anions. Based on the TS calculations for the N₂‐loss dissociations of the N₅⁺Y^? compounds, the stabilities of these compounds are discussed, and the following conclusion can be drawn that among the four compounds, N₅⁺B(CF₃)₄^? is the most stable one and N₅⁺B(N₃)₄^? is the most unstable, and the relative stability of these compounds is always consistent using different basis sets. From these discussions, it is revealed that there are close correlations between the stuctrual distortions of the Y^? anions and the stabilities of the N₅⁺Y^? compounds, and between the nitrogen content in the compounds and the stabilities of the N₅⁺Y^? compounds.     

Synthesis and crystal structures of 2,4,6-pyridine-tricarboxylic anions/guanidinium and tetraalkylammonium inclusion compounds

Two different hydrogen-bonded inclusion compounds, [2,4,6-C₅H₂N(COO^?)₃]_0.5·[C(NH₂) ₃ ⁺ ]_0.5·[(C₂H₅)₄N⁺]·2H₂O (1) and [2,4,6-C₅H₂N(COO^?)₃]·[C(NH₂) ₃ ⁺ ]·[(C₂H₅)₄N⁺]·[(C₃H₇)₄N⁺]·6H₂O (2) are reported in this paper, in which 2,4,6-pyridine-tricarboxylic anions, guanidiniums and water molecules jointly construct host lattices while tetraalkylammonium cations are accommodated as guest species. Both two compounds formed sandwich-like hydrogen-bond inclusion compounds. In compound 1, the dimers composed of 2,4,6-pyridine-tricarboxylic anions and guanidiniums form 2D hydrogen-bonded layers by connecting with water molecules. In compound 2, 2,4,6-pyridine-tricarboxylic anions, guanidiniums and water molecules contribute to generate an undulate rosette hydrogen-bonded architecture. Interestingly, in compound 2, there are two species of guest molecules, tetraethylammonium and tetrapropylammonium, which are alternately arranged between the neighboring layers. Mixed guest cations accommodated in hydrogen-bonded inclusion compounds are seldom seen.