Topological Classification and Supramolecular Chirality of 21-Helical Ladder-Type Hydrogen-Bond Networks Composed of Primary Ammonium Carboxylates: Bundle Control in 21-Helical Assemblies

Polymorphs with Remarkably Distinct Physical and/or Chemical Properties

Polymorphism in crystals is known since 1822 and the credit goes to Mitscherlich who realized the existence of different crystal structures of the same compound while working with some arsenate and phosphate salts. Later on, this phenomenon was observed also in organic crystals. With the advent of different technologies, especially the easy availability of single crystal XRD instruments, polymorphism in crystals has become a common phenomenon. Almost 37 % of compounds (single component) are polymorphic to date. As the energies of the different polymorphic forms are very close to each other, small changes in crystallization conditions might lead to different polymorphic structures. As a result, sometimes it is difficult to control polymorphism. For this reason, it is considered to be a nuisance to crystal engineering. It has been realized that the property of a material depends not only on the molecular structure but also on its crystal structure. Therefore, it is not only of interest to academia but also has widespread applications in the materials science as well as pharmaceutical industries. In this review, we have discussed polymorphism which causes significant changes in materials properties in different fields of solid-state science, such as electrical, magnetic, SHG, thermal expansion, mechanical, luminescence, color, and pharmaceutical. Therefore, this review will interest researchers from supramolecular chemistry, materials science as well as medicinal chemistry.

Primary Ammonium Terephthalate Salts with High Moisture Resistance and Their Use in the Detection of OH Radicals

A novel and practical method is proposed for the detection of gaseous OH radicals using a moisture-resistant organic salt composed of terephthalic acid (TPA) and n-alkylamine. When the alkyl chain length was greater than 8, the organic salt had a crystal structure in which the alkyl chains were arranged parallel to each other and zero-dimensional voids were adjacent to terephthalate (TA). Since the parallelly arranged alkyl chains acted as a hydrophobic block, the organic salts had excellent humidity durability. The highly hydrophobic bis(n-octylammonium) terephthalate (nOA-TA) powder was exposed to gaseous OH radicals generated by a low-pressure mercury lamp and a fluorescence response suggesting the formation of bis(n-octylammonium) hydroxyterephthalate (nOA-HTA) was observed. The presence of the zero-dimensional voids in the nOA-TA crystal caused the formation of nOA-HTA. In addition, a sheet was prepared in which nOA-TA crystals were uniformly immobilized in the pores of a membrane filter, and the spatial distribution of OH radicals was evaluated.

Ethylammonium hydrogen oxalate–oxalic acid (2/1)

The reaction between ethylamine and oxalic acid in water in a 1:1 molar ratio afforded the title salt, C2H8N+·C2HO4 −·0.5C2H2O4. The hydrogen oxalate anions interact through hydrogen bonding and are organized into a chains propagating along the c-axis direction. The chains are connected to the neighbouring cations and oxalic acid molecules by N—H...O and O—H...O hydrogen bonds and N...O dipole–dipole contacts, leading to a supramolecular three-dimensional network.

π-Choreography in aromatic ammonium formate solids

Eight novel benzylammonium formate complexes are combed for evidence suggesting “π-stacking” interactions, and are compared with similar published lamellar structures.

Structures of N-acetyl-DL-isoleucine, N-acetyl-DL-alloisoleucine and their ammonium salts; role of ammonium ions in crystal structure formation

The crystal structures of N-acetyl-DL-isoleucine, N-acetyl-DL-alloisoleucine and their ammonium salts show that these four compounds exist as racemic compounds around room temperature. The two ammonium salts are arranged around a 21 screw axis, forming a helical column which consists of ammonium ions and single enantiomeric anions similar to the crystals of the ammonium salts of optically active N-acetyl-L-isoleucine and N-acetyl-D-alloisoleucine. The ammonium ion and the carboxylate ion in the helix are connected by three hydrogen bonds, the fourth hydrogen bond being formed between the ammonium ion and an external acetyl amino group of the neighboring helical column. The fourth hydrogen bond is formed between the ammonium ion and an external acetyl amino group of the neighboring 21 column. Ammonium N-acetyl-DL-alloisoleucinate was revealed to exist as an unstable racemic compound due to conformational similarity between the racemic and optically active compounds in the solid state and was optically resolved by fractional crystallization at 293 K.

Construction and Systematical Symmetric Studies of a Series of Supramolecular Clusters with Binary or Ternary Ammonium Triphenylacetates

Functions of clusters in nano or sub-nano scale significantly depend on not only kinds of their components but also arrangements, or symmetry, of their components. Therefore, the arrangements in the clusters have been precisely characterized, especially for metal complexes. Contrary to this, characterizations of molecular arrangements in supramolecular clusters composed of organic molecules are limited to a few cases. This is because construction of the supramolecular clusters, especially obtaining a series of the supramolecular clusters, is difficult due to low stability of non-covalent bonds compare to covalent bonds. From this viewpoint, utilization of organic salts is one of the most useful strategies. A series of the supramolecules could be constructed by combinations of a specific organic molecule with various counter ions. Especially, primary ammonium carboxylates are suitable as typical examples of supramolecules because various kinds of carboxylic acids and primary amines are commercially available, and it is easy to change their combinations. Previously, it was demonstrated that primary ammonium triphenylacetates using various kinds of primary amines specifically construct supramolecular clusters, which are composed of four ammoniums and four triphenylacetates assembled by charge-assisted hydrogen bonds, in crystals obtained from non-polar solvents. This study demonstrates an application of the specific construction of the supramolecular clusters as a strategy to conduct systematical symmetric study for clarification of correlations between molecular arrangements in supramolecules and kinds and numbers of their components. In the same way with binary salts composed of triphenylacetates and one kind of primary ammoniums, ternary organic salts composed of triphenylacetates and two kinds of ammoniums construct the supramolecular clusters, affording a series of the supramolecular clusters with various kinds and numbers of the components.

Chirality control of self-assembled achiral nanofibers using amines in their solid state

Although there are numerous examples of helical and spiral conformations in nature, including plant tendrils, snail shells, and even collagen, the occurrence of supramolecular systems that are able to reversibly undergo solid-to-solid helical transformation based on environmental chiral triggers is rare. In this work, we present a supramolecular, non-helical nanofiber which shows a distinct helical rearrangement in the presence of specific diamines and monoamines, such as cyclohexanediamines, alanine, lysine, and phenylalanine, depending on the molecular chirality of the surrounding analytes. A detailed investigation on the structural organization of the nanofibers using SEM and CD spectra analysis confirmed the repeatable and reversible nature of this amplification of chiral information. Further preparation of an electrospun nanofiber film was demonstrated for distinguishing chiral diamines and monoamines in solution by film immersion and CD analysis, which is the first example of amplification of chiral information in the solid-state using electrospun nanofiber films. With this system, we could demonstrate a reusable means for detecting the molecular chirality, which also provided a unique example of reversible control of solid state rearrangement in supramolecular helicity.

Crystal structure of the bis-(cyclo-hexyl-ammonium) succinate succinic acid salt adduct

The crystal structure of the title salt adduct, 2C6H14N(+)·C4H4O4 (2-)·C4H6O4, consists of two cyclo-hexyl-ammonium cations, one succcinate dianion and one neutral succinic acid mol-ecule. Succinate dianions and succinic acid mol-ecules are self-assembled head-to-tail through O-H⋯O hydrogen bonds and adopt a syn-syn configuration, leading to a strand-like arrangement along [101]. The cyclo-hexyl-ammonium cations have a chair conformation and act as multidentate hydrogen-bond donors linking adjacent strands through inter-molecular N-H⋯O inter-actions to both the succinate and the succinic acid components. This results in two-dimensional supra-molecular layered structures lying parallel to (010).

Exocyclic self-assembly behavior of carboxylic acid and lariat ether macrocyclic hosts: regulation by pendent arm

An exocyclic supramolecular building block through O–H⋯N hydrogen bonding interaction for the assembly of di-sidearm dibenzo-diazacrown ethers bearing a flexibility sidearm with PTA acid.

Linkage control between molecular and supramolecular chirality in 2₁-helical hydrogen-bonded networks using achiral components

Chiral molecules preferentially form one-handed supramolecular assemblies that reflect the absolute configuration of the molecules. Under specific conditions, however, the opposite-handed supramolecular assemblies are also obtained because of flexibility in the bond length and reversibility of non-covalent interactions. The mechanism of the handedness selectivity or switching phenomenon remains ambiguous, and most phenomena are observed by chance. Here we demonstrate the construction of chiral hydrogen-bonded twofold helical assemblies with controlled handedness in the crystalline state based on crystallographic studies. Detailed investigation of the obtained crystal structures enabled us to clarify the mechanism, and the handedness of the supramolecular chirality was successfully controlled by exploiting achiral factors. This study clearly reveals a connection between molecular chirality and supramolecular chirality in the crystalline state.

Structural study of six cycloalkylammonium cinnamate salt structures featuring one-dimensional columns and two-dimensional hydrogen-bonded networks

Six ammonium carboxylate salts, namely cyclopentylammonium cinnamate, C(5)H(12)N(+)·C(9)H(7)O(2)(-), (I), cyclohexylammonium cinnamate, C(6)H(14)N(+)·C(9)H(7)O(2)(-), (II), cycloheptylammonium cinnamate form I, C(7)H(16)N(+)·C(9)H(7)O(2)(-), (IIIa), and form II, (IIIb), cyclooctylammonium cinnamate, C(8)H(18)N(+)·C(9)H(7)O(2)(-), (IV), and cyclododecylammonium cinnamate, C(12)H(26)N(+)·C(9)H(7)O(2)(-), (V), are reported. Salts (II)-(V) all have a 1:1 ratio of cation to anion and feature three N(+)-H···O(-) hydrogen bonds forming one-dimensional hydrogen-bonded columns consisting of repeating R(4)(3)(10) rings, while salt (I) has a two-dimensional network made up of alternating R(4)(4)(12) and R(6)(8)(20) rings. Salt (III) consists of two polymorphic forms, viz. form I having Z' = 1 and form II with Z' = 2. The latter polymorph has disorder of the cycloheptane rings in the two cations, as well as whole-molecule disorder of one of the cinnamate anions. A similar, but ordered, Z' = 2 structure is seen in salt (IV).

2-(Ammonio-meth-yl)pyridinium sulfate monohydrate

In the crystal of the title hydrated molecular salt, C₆H₁₀N₂²⁺·SO₄²⁻·H₂O, N—H⋯O and O—H⋯O hydrogen bonds link the mol­ecules into layers parallel to the ab plane. C—H⋯O hydrogen bonds are observed both within these layers and between mol­ecules and ions in adjacent layers.

Enantioseparation of 1-arylethanols via a supramolecular chiral host consisting of N-(2-naphthoyl)-L-aspartic acid and an achiral diamine

A supramolecular chiral host consisting of N-(2-naphthoyl)-L-aspartic acid (L-1) and meso-1,2-diphenylethylenediamine (2) is effective in enantioseparation of 1-arylethanols (up to 96% ee with 100% inclusion ratio). Here we report three different methods to prepare the inclusion crystals and discuss the chiral recognition mechanism on the basis of X-ray crystallography results.

Organic Zeolite Analogues Based on Multi-Component Liquid Crystals: Recognition and Transformation of Molecules within Constrained Environments

In liquid crystals (LCs), molecules are confined in peculiar environments, where ordered alignment and certain mobility are realized at the same time. Considering these characteristics, the idea of "controlling molecular events within LC media" seems reasonable. As a suitable system for investigating this challenge, we have recently developed a new class of ionic LCs; the salts of amphiphilic carboxylic acids with 2-amino alcohols, or those of carboxylic acids with amphiphilic 2-amino alcohols, have a strong tendency to exhibit thermotropic LC phases. Because of the noncovalent nature of the interaction between molecules, one of the two components can easily be exchanged with, or transformed into, another molecule, without distorting the original LC architecture. In addition, both components are common organic molecules, and a variety of compounds are easily available. Taking advantage of these characteristics, we have succeeded in applying two‑component LCs as chiral media for molecular recognition and reactions. This review presents an overview of our recent studies, together with notable reports related to this field.