Encapsulation‐Induced Remarkable Stability of a Hydrogen‐Bonded Heterocapsule

Remarkably enhanced stability of the self‐assembled hydrogen‐bonded heterocapsule 1?2 by the encapsulation of 1,4‐bis(1‐propynyl)benzene 3 a was found with K_a=1.14×10⁹ M ^?1 in CDCl₃ and K_a2=1.59×10⁸ M ^?2 in CD₃OD/CDCl₃ (10 % v/v) at 298 K. The formation of 3 a @( 1?2 ) was enthalpically driven (ΔH°<0 and ΔS°<0) and there was a unique inflection point in the correlation between ΔH° versus ΔS° as a function of polar solvent content. The ab initio calculations revealed that favorable guest–capsule dispersion and electrostatic interactions between the acetylenic parts (triple bonds) of 3 a and the aromatic inner space of 1?2 , as well as less structural deformation of 1?2 upon encapsulation of 3 a , play important roles in the remarkable stability of 3 a @( 1?2 ).     

Unique Hydrogen‐Bonded Complex of Hydronium and Hydroxide Ions

H₃O⁺ and OH^?, formed by the self‐ionization of two coordinating water molecules during the crystal growing of a host molecule [1,3,5‐tris(hydroxymethyl)2,4,6‐triethylbenzene ( 1 )], could be effectively stabilized by hydrogen‐bonding interactions with the preorganized hydroxy groups of three molecules of 1. The binding motifs observed in the complex ( 1 )₃?H₃O⁺?HO^? show remarkable similarity to those postulated for the hydrated hydronium and hydroxide ion complexes, which play important roles in various chemical, biological, and atmospheric processes, but their molecular structures are still not fully understood and remain a subject of intensive research.     

Hydrogen‐Bonding Interactions and Properties of Energetic Nitroamino[1,3,5]triazine‐Based Guanidinium Salts: DFT‐D and QTAIM Studies

The intramolecular hydrogen‐bonding interactions and properties of a series of nitroamino[1,3,5]triazine‐based guanidinium salts were studied by using the dispersion‐corrected density functional theory method (DFT‐D). Results show that there are evident LP(N or O; LP=lone pair)→σ*(N? H) orbital interactions related to O???H? N or N???H? N hydrogen bonds. Quantum theory of atoms in molecules (QTAIM) was applied to characterize the intramolecular hydrogen bonds. For the guanidinium salts studied, the intramolecular hydrogen bonds are associated with a seven‐ or eight‐membered pseudo‐ring. The guanylurea cation is more helpful for improving the thermal stabilities of the ionic salts than other guanidinium cations. The contributions of different substituents on the triazine ring to the thermal stability increase in the order of ? NO₂23 (? ONO₂)2. Energy decomposition analysis shows that the salts are stable owing to electrostatic and orbital interactions between the ions, whereas the dispersion energy has very small contributions. Moreover, the salts exhibit relatively high densities in the range of 1.62–1.89 g cm^?3. The detonation velocities and pressures lie in the range of 6.49–8.85 km s^?1 and 17.79–35.59 GPa, respectively, which makes most of them promising explosives.     

Microporosity of a Guanidinium Organodisulfonate Hydrogen‐Bonded Framework

Guanidinium organosulfonates (GSs) are a large and well‐explored archetypal family of hydrogen‐bonded organic host frameworks that have, over the past 25 years, been regarded as nonporous. Reported here is the only example to date of a conventionally microporous GS host phase, namely guanidinium 1,4‐benzenedisulfonate ( p ‐G₂BDS ). p ‐G₂BDS is obtained from its acetone solvate, AcMe@ G₂BDS , by single‐crystal‐to‐single‐crystal (SC‐SC) desolvation, and exhibits a Type I low‐temperature/pressure N₂ sorption isotherm (SA_BET=408.7(2) m² g^?1, 77 K). SC‐SC sorption of N₂, CO₂, Xe, and AcMe by p ‐G₂BDS is explored under various conditions and X‐ray diffraction provides a measurement of the high‐pressure, room temperature Xe and CO₂ sorption isotherms. Though p ‐G₂BDS is formally metastable relative to the “collapsed”, nonporous polymorph, np ‐G₂BDS , a sample of p ‐G₂BDS survived for almost two decades under ambient conditions. np ‐G₂BDS reverts to zCO₂@ p ‐G₂BDS or yXe@ p ‐G₂BDS (y,z=variable) when pressure of CO₂ or Xe, respectively, is applied.     

A C3‐Symmetric Macrocycle‐Based,Hydrogen‐Bonded,Multiporous Hexagonal Network as a Motif of Porous Molecular Crystals

A C₃‐symmetric π‐conjugated macrocycle combined with an appropriate hydrogen bonding module (phenylene triangle) allowed the construction of crystalline supramolecular frameworks with a cavity volume of up to 58 %. The frameworks were obtained through non‐interpenetrated stacking of a hexagonal sheet possessing three kinds of pores with different sizes and shapes. The activated porous material absorbed CO₂ up to 96 cm³ g^?1 at 195 K under 1 atm.     

On‐Surface Assembly of Hydrogen‐ and Halogen‐Bonded Supramolecular Graphyne‐Like Networks

Demonstrated here is a supramolecular approach to fabricate highly ordered monolayered hydrogen‐ and halogen‐bonded graphyne‐like two‐dimensional (2D) materials from triethynyltriazine derivatives on Au(111) and Ag(111). The 2D networks are stabilized by N???H?C(sp) bonds and N???Br?C(sp) bonds to the triazine core. The structural properties and the binding energies of the supramolecular graphynes have been investigated by scanning tunneling microscopy in combination with density‐functional theory calculations. It is revealed that the N???Br?C(sp) bonds lead to significantly stronger bonded networks compared to the hydrogen‐bonded networks. A systematic analysis of the binding energies of triethynyltriazine and triethynylbenzene derivatives further demonstrates that the X₃‐synthon, which is commonly observed for bromobenzene derivatives, is weaker than the X₆‐synthon for our bromotriethynyl derivatives.     

An Enantiopure Hydrogen‐Bonded Octameric Tube: Self‐Sorting and Guest‐Induced Rearrangement

The assembly of a discrete hydrogen‐bonded molecular tube from eight small identical monomers is reported. Tube assembly was accomplished by means of selective heterodimerization between isocytosine and ureidopyrimidinone hydrogen‐bonding motifs embedded in an enantiopure bicyclic building block, leading to the selective formation of an octameric supramolecular tube. Upon introduction of a fullerene guest molecule, the octameric tube rearranges into a tetrameric inclusion complex and the hydrogen‐bonding mode is switched. The dynamic behavior of the system is further explored in solvent‐ and guest‐responsive self‐sorting experiments.     

An AAA–DDD Triply Hydrogen‐Bonded Complex Easily Accessible for Supramolecular Polymers

For a complementary hydrogen‐bonded complex, when every hydrogen‐bond acceptor is on one side and every hydrogen‐bond donor is on the other, all secondary interactions are attractive and the complex is highly stable. AAA–DDD (A=acceptor, D=donor) is considered to be the most stable among triply hydrogen‐bonded sequences. The easily synthesized and further derivatized AAA–DDD system is very desirable for hydrogen‐bonded functional materials. In this case, AAA and DDD, starting from 4‐methoxybenzaldehyde, were synthesized with the Hantzsch pyridine synthesis and Friedländer annulation reaction. The association constant determined by fluorescence titration in chloroform at room temperature is 2.09×10⁷ M ^?1. The AAA and DDD components are not coplanar, but form a V shape in the solid state. Supramolecular polymers based on AAA–DDD triply hydrogen bonded have also been developed. This work may make AAA–DDD triply hydrogen‐bonded sequences easily accessible for stimuli‐responsive materials.     

Characterization of Supramolecular Hidden Chirality of Hydrogen‐Bonded Networks by Advanced Graph Set Analysis

Supramolecular hidden chirality of hydrogen‐bonded (HB) networks of primary ammonium carboxylates was exposed by advanced graph set analysis from a symmetric viewpoint in topology. The ring‐type HB (R‐HB) networks are topologically regarded as faces, and therefore exhibit prochirality and positional isomerism due to substituents attached on the faces. To describe the symmetric properties of the faces, additional symbols, Re (right‐handed or clockwise), Si (left‐handed or anticlockwise), and m (mirror), were proposed. According to the symbols, various kinds of faces were classified based on the symmetry. This symmetry consideration of the faces enables us to precisely evaluate supramolecular chirality, especially its handedness, of 0D‐cubic, 1D‐ladder and 2D‐sheet HB networks that are composed of the faces. The 1D‐ladder and 2D‐sheet HB networks generate chirality by accumulating the chiral faces in 1D and 2D manners, respectively, whereas 0D‐cubic HB networks generate chirality based on combinations of eight kinds of faces, similar to the chirality of dice.     

Formation of a Hydrogen‐Bonded Heptazine Framework by Self‐Assembly of Melem into a Hexagonal Channel Structure

Self‐assembly of melem C₆N₇(NH₂)₃ in hot aqueous solution leads to the formation of hydrogen‐bonded, hexagonal rosettes of melem units surrounding infinite channels with a diameter of 8.9 Å. The channels are filled with strongly disordered water molecules, which are bound to the melem network through hydrogen bonds. Single‐crystals of melem hydrate C₆N₇(NH₂)₃ ? xH₂O (x≈2.3) were obtained by hydrothermal treatment of melem at 200 °C and the crystal structure (R $\bar 3$ c, a=2879.0(4), c=664.01(13) pm, V=4766.4(13)×10⁶ pm³, Z=18) was elucidated by single‐crystal X‐ray diffraction. With respect to the structural similarity to the well‐known adduct between melamine and cyanuric acid, the composition of the obtained product was further analyzed by solid‐state NMR spectroscopy. Hydrolysis of melem to cyameluric acid during syntheses at elevated temperatures could thus be ruled out. DTA/TG studies revealed that, during heating of melem hydrate, water molecules can be removed from the channels of the structure to a large extent. The solvent‐free framework is stable up to 430 °C without transforming into the denser structure of anhydrous melem. Dehydrated melem hydrate was further characterized by solid‐state NMR spectroscopy, powder X‐ray diffraction, and sorption measurements to investigate structural changes induced by the removal of water from the channels. During dehydration, the hexagonal, layered arrangement of melem units is maintained whereas the formation of additional hydrogen bonds between melem entities requires the stacking mode of hexagonal layers to be altered. It is assumed that layers are shifted perpendicular to the direction of the channels, thereby making them inaccessible for guest molecules.     

Guanidinium Alkynesulfonates with Single‐Layer Stacking Motif: Interlayer Hydrogen Bonding Between Sulfonate Anions Changes the Orientation of the Organosulfonate R Group from “Alternate Side” to “Same Side”

Hydrolyses of HC?CSO₃SiMe₃ ( 1 ) and CH₃C?CSO₃SiMe₃ ( 2 ) lead to the formation of acetylenic sulfonic acids HC?CSO₃H?2.33 H₂O ( 3 ) and CH₃C?CSO₃H?1.88 H₂O ( 4 ). These acids were reacted with guanidinium carbonate to yield [⁺C(NH₂)₃][HC?CSO₃^?] ( 5 ) and [⁺C(NH₂)₃][CH₃C?CSO₃^?] ( 6 ). Compounds 1 – 6 were characterized by spectroscopic methods, and the X‐ray crystal structures of the guanidinium salts were determined. The X‐ray results of 5 show that the guanidinium cations and organosulfonate anions associate into 1D ribbons through ${{\rm R}{{2\hfill \atop 2\hfill}}}$ (8) dimer interactions, whereas association of these ions in 6 is achieved through ${{\rm R}{{2\hfill \atop 2\hfill}}}$ (8) and ${{\rm R}{{1\hfill \atop 2\hfill}}}$ (6) interactions. The ribbons in 5 associate into 2D sheets through ${{\rm R}{{2\hfill \atop 2\hfill}}}$ (8) dimer interactions and ${{\rm R}{{3\hfill \atop 6\hfill}}}$ (12) rings, whereas those in 6 are connected through ${{\rm R}{{1\hfill \atop 2\hfill}}}$ (6) and ${{\rm R}{{2\hfill \atop 2\hfill}}}$ (8) dimer interactions and ${{\rm R}{{4\hfill \atop 6\hfill}}}$ (14) rings. Compound 6 exhibits a single‐layer stacking motif similar to that found in guanidinium alkane‐ and arenesulfonates, that is, the alkynyl groups alternate orientation from one ribbon to the next. The stacking motif in 5 is also single‐layer, but due to interlayer hydrogen bonding between sulfonate anions, the alkynyl groups of each sheet all point to the same side of the sheet.     

Docking Strategy To Construct Thermostable,Single‐Crystalline,Hydrogen‐Bonded Organic Framework with High Surface Area

Enhancing thermal and chemical durability and increasing surface area are two main directions for the construction and improvement of the performance of porous hydrogen‐bonded organic frameworks (HOFs). Herein, a hexaazatriphenylene (HAT) derivative that possesses six carboxyaryl groups serves as a suitable building block for the systematic construction of thermally and chemically durable HOFs with high surface area through shape‐fitted docking between the HAT cores and interpenetrated three‐dimensional network. A HAT derivative with carboxybiphenyl groups forms a stable single‐crystalline porous HOF that displays protic solvent durability, even in concentrated HCl, heat resistance up to 305 °C, and a high Brunauer–Emmett–Teller surface area [SA_(BET)] of 1288 m² g^?1. A single crystal of this HOF displays anisotropic fluorescence, which suggests that it would be applicable to polarized emitters based on robust functional porous materials.     

A Supramolecular Hydrogen‐Bonded Network as a Diffusion Barrier for Metal Adatoms

Confined in a molecular corral : A supramolecular network changes the mechanism by which underpotential deposition (UPD) of copper proceeds on a gold electrode modified by a self‐assembled monolayer (SAM). Lateral diffusion of Cu adatoms is suppressed between adjacent cells of a network/SAM hybrid structure. Instead, UPD occurs by direct deposition into the SAM filled pores of the network, where the Cu adatoms are confined.

     

Rational Construction of 2D and 3D Borromean Arrayed Organic Crystals by Hydrogen‐Bond‐Directed Self‐Assembly

Borromean organic networks: The rigid and trigonal pyramidal molecule, 1,3,5‐tris(4‐carboxyphenyl)adamantane (TCA), self‐assembles into a 2D Borromean linked network by hydrogen bonds. Different linkers (methanol, phenazine, 4,4′‐bipyridine, and 4,4′‐azopyridine) result in more complex Borromean networks or a 3D polycatenation network.

     

Iodinated ortho‐Carboranes as Versatile Building Blocks to Design Intermolecular Interactions in Crystal Lattices

The crystal structures of numerous iodinated ortho‐carboranes have been studied, which has revealed the diversity of intermolecular interactions that these substances can adopt in the solid state. The nature—mostly as it relates to hydrogen and/or halogen bonds—and relative strength of such interactions can be adjusted by selectively introducing substituents onto the cluster, thus enabling the rational design of crystal lattices. In this work we present the newly determined crystal structures of the following iodinated ortho‐carboranes: 9‐I‐1,2‐closo‐C₂B₁₀H₁₁, 4,5,7,8,9,10,11,12‐I₈‐1,2‐closo‐C₂B₁₀H₄, 3,4,5,6,7,8,9,10,11,12‐I₁₀‐1,2‐closo‐C₂B₁₀H₂, 1‐Me‐8,9,10,12‐I₄‐1,2‐closo‐C₂B₁₀H₇, 1,2‐Me₂‐8,9,10,12‐I₄‐1,2‐closo‐C₂B₁₀H₆, and 1,2‐Ph₂‐8,9,10,12‐I₄‐1,2‐closo‐C₂B₁₀H₆. Their 3D supramolecular organization has been thoroughly investigated and compared to similar previously published crystal structures. Such a systematic survey has allowed us to draw some general trends. C_c? H???I? B hydrogen bonds (C_c= cluster carbon atoms) appear to be significant in the growth of the crystal lattices of these compounds, given the acidity of hydrogen atoms bonded to C_c, and the polarization of B? I bonds. These hydrogen bonds can be disrupted by selectively blocking the positions next to C_c, that is, B(3) and B(6), with bulky substituents that prevent iodine atoms from approaching as hydrogen acceptors. Halogen bonds of the type B? I???I? B are frequently observed in most cases, thus suggesting that these interactions could be attractive in boron clusters. In addition, different substituents can be grafted onto the ortho‐carborane surface, thereby providing further possibilities for homomeric or heteromeric molecular assembly.     

Investigation of Steric Influences on Hydrogen‐Bonding Motifs in Cyclic Ureas by Using X‐Ray,Neutron, and Computational Methods

A series of urea‐derived heterocycles, 5N‐substituted hexahydro‐1,3,5‐triazin‐2‐ones, has been prepared and their structures have been determined for the first time. This family of compounds only differ in their substituent at the 5‐position (which is derived from the corresponding primary amine), that is, methyl ( 1 ), ethyl ( 2 ), isopropyl ( 3 ), tert‐butyl ( 4 ), benzyl ( 5 ), N,N‐(diethyl)ethylamine ( 6 ), and 2‐hydroxyethyl ( 7 ). The common heterocyclic core of these molecules is a cyclic urea, which has the potential to form a hydrogen‐bonding tape motif that consists of self‐associative (8) dimers. The results from X‐ray crystallography and, where possible, Laue neutron crystallography show that the hydrogen‐bonding motifs that are observed and the planarity of the hydrogen bonds appear to depend on the steric hindrance at the α‐carbon atom of the N substituent. With the less‐hindered substituents, methyl and ethyl, the anticipated tape motif is observed. When additional methyl groups are added onto the α‐carbon atom, as in the isopropyl and tert‐butyl derivatives, a different 2D hydrogen‐bonding motif is observed. Despite the bulkiness of the substituents, the benzyl and N,N‐(diethyl)ethylamine derivatives have methylene units at the α‐carbon atom and, therefore, display the tape motif. The introduction of a competing hydrogen‐bond donor/acceptor in the 2‐hydroxyethyl derivative disrupts the tape motif, with a hydroxy group interrupting the N? H???O?C interactions. The geometry around the hydrogen‐bearing nitrogen atoms, whether planar or non‐planar, has been confirmed for compounds 2 and 5 by using Laue neutron diffraction and rationalized by using computational methods, thus demonstrating that distortion of O‐C‐N‐H torsion angles occurs to maintain almost‐linear hydrogen‐bonding interactions.