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The crystal structures and packing features of a family of 13 aminophenols, or supraminols, are analyzed and correlated. The findings indicate that even for compounds with complex crystal structures the packing may be reasonably anticipated provided a sufficient number of examples are available.

Research has been conducted on the hydrogen bonds. The features common to all hydrogen bonds termed hydrogen bridges in this article for their ability to interact without borders are discussed..

Research has been conducted on the hydrogen bonding. The description of the N-H...O hydrogen bond pattern in the primary cubanecarboxamides family is presented.

The synthesis and structural characterization of a family of 4-substituted-1-cubanecarboxylic acids are described. The results showed that four of the seven crystal structures contain the unusual syn-anti O-H...catemer. These compounds were 4-chloro-1-cubanecarboxylic acid, 4-bromo-1-cubanecarboxylic acid, 4-iodo-1-cubanecarboxylic acid and 4-(methoxycarbonyl)-1-cubanecarboxyillic acid. This is attributed to the stabilization from C-H...O bonds formed by the acidic cubyl C-H donors and the carboxyl O-acceptor atoms.

The role played by C-H***F interactions in the crystal structures of fluorobenzenes has been studied. The significance of the C-F group in crystal packing has also been analyzed in order to understand the binding of a fluorinated substrate to a macromolecular receptor. F***F interactions have further been examined to assess their value in the chemistry of fluorobenzenes. Results show that C-H***F interactions are as important as C-H***O and C-H***N hydrogen bonds in stabilizing fluorobenzene crystals.

Organometallic crystal engineering supports an organic outlook of crystal engineering. Its scope focuses on the characterization of molecular crystals for a range of physical and chemical applications. A number of factors are considered critical in the crystal engineering of organomettalic compounds. These factors are correlated with the location of the metal centers in the compounds within the molecular cores. The features of organometallic molecules support dependencies related to the relationship between the electronic nature of the metals and the intermolecular bonding of ligands.

Distinct aims and goals in crystal engineering are discerned as strategic and methodological, aesthetically motivated supramolecular synthesis and efforts towards functional materials. The polar molecule-based crystal engineering of nonlinear optics (NLO) materials aims to establish the noncentrosymmetric assembly of molecular dipoles. The crystal structures and NLO properties of 2,4,6-triaryloxy-1,3,5-triazines are reported.

Low-temperature neutron diffraction was utilized to determine the crystal structure of 2- and 3-aminophenols and their tetrahedral hydrogen-bonded networks. The 2- and 3-aminophenols are composed of N-H...pi bonds that are located in electron-rich aromatic rings. The crystal structure of 2-aminophenol was also composed of phenyl rings that were arranged in a herringbone fashion with a T-shaped geometry.

The structure of 2-ethynyladamantan-1-ol is analyzed using neutron diffraction techniques to determine the types of hydrogen bonds it contains. Results indicate the presence of an unusual hydrogen bond of the type O-H...pi, aside from the more common O-H...O and C-H...O bonds. The novel bond points to its center, rather than the alkynic carbon atoms, when it is directed towards a -C=C- bond. A very short and straight C-H...0 bond is also shown to be present.

Intermolecular interactions lead to the formation of structural units called synthons in crystals. It has been hypothesized that a lack of correspondence between molecular and crystal structures resulting from synthon interference could cause problems in the engineering of crystals. To test this hypothesis, the structural chemistry of a series of 1,4-disubstituted 2,3-dicyano-5,6-dichlorobenzenes and related compounds is determined.

The crystal structure of organic diamondoid solids is simplified into a network that is dissected into nodes and node connections. The effects of the node connections, or supramolecular synthons, on crystal packing and their interchangeability with molecular synthons show that simplifying the crystal structure can be a useful strategy for crystal structure design, particularly in complex networks.

The influence of intermolecular and intramolecualr C-H...O hydrogen bonds on the crystal structures of metal-coordinated CO ligand compounds is investigated. The investigation reveals that the metal-coordinated CO ligands are involved in the formation of hydrogen bonding reaction with H atoms of the ligands. Preferential reactions with the terminal bonds are established by the bridging COs. The formation of C-H...O bonds is favored by the terminal and bridging COs.

The supramolecular synthon concept recognizes the complexities inherent in crystallization, and the synthon approach to crystal structure prediction (CSP) recognizes that the kinetic issue is not easily resolved with exhaustive computation. It is indicated that as the amount of structural information in crystallographic databases increases, structural prediction is likely to move toward fingerprinting.

Solid solutions (SS) of benzoic acid (BA) and 4-fluorobenzoic acid (4FBA) are monitored with respect to increasing fluorine content. All 10 SS studied take a crystal structure that is different from the crystal structures of either BA or 4FBA and retain structural uniformity over a wide range of composition. Adoption of a crystal structure different from either of the parent structure types is a unique observation in the context of SS. It implies the influence of directional interactions in the formation of the SS; this idea is strengthened by the observations made in this study. All the structural and interaction parameters monitored follow trends with respect to fluorine content. There is indication of the effect of C–H···F hydrogen bonds in the structures. [ABSTRACT FROM AUTHOR]

The acid…amide dimer heterosynthon in cocrystals of aromatic acids and primary amides is identified by marker peaks in the IR spectra that are characteristic of individual N-H…O and O-H…O interactions and also of the extended synthon. The O-H…O hydrogen bond is crucial to heterodimer formation in contrast to the N-H…O bond. A combinatorial study, tuning the chemical nature of acid and amide functionalities, leads to 22 cocrystals out of 36 crystallization attempts. Four quadrants I-IV are defined based on acidity and basicity of the acid and amide components. The strong acid-strong base combination in quadrant I favors the planar acid…amide heterodimer in its eight cocrystals. Quadrant IV with its weak acid-weak base combination is the least favored for the planar heterosynthon and synthon diversity is observed in the eight cocrystals obtained. The strong-weak and weak-strong combinations in quadrants II and III are expectedly ambivalent. This exercise highlights the effect of molecular features on supramolecular behavior. Quadrant I crystals, with their propensity for the planar acid…amide heterodimer are suitable for the engineering of crystals that can be sheared. This quadrant favors the formation of elastic crystals too. The overall result is that 57% (4 in 7) of all crystals in this quadrant are deformable, compared with 14% (1 in 7) in the three other quadrants. This work is a complete crystal engineering exercise from synthon identification to a particular desired crystal packing to property selection. One can virtually anticipate the mechanical property of a putative acid…amide cocrystal from a knowledge of just the molecular structures of the constituent acid and amide molecules. [ABSTRACT FROM AUTHOR]

A strategy is outlined for the design of hand-twisted helical crystals. The starting point in the exercise is the one-dimensional (1D) plastic crystal, 1,4-dibromobenzene, which is then changed to a 1D elastic crystal, exemplified by 4-bromophenyl 4'-chlorobenzoate, by introduction of a molecular synthon -O-CO- in lieu of the supramolecular synthon Br···Br in the precursor. The 1D elastic crystals are next modified to two-dimensional (2D) elastic crystals, of the type 4-bromophenyl 4'-nitrobenzoate where the halogen bonding and C-H···O hydrogen bonding are well-matched. Finally, varying the interaction strengths in these 2D elastic crystals gives plastic crystals with two pairs of bendable faces but without slip planes. Typical examples are 4-chlorophenyl and 4-bromophenyl 4'-nitrobenzoate. This type of 2D plasticity represents a new type of bendable crystals in which plastic behavior is seen with a fair degree of isotropic character in the crystal packing. The presence of two sets of bendable faces, generally orthogonal to each other, allows for the possibility of hand-twisting of the crystals to give grossly helical morphologies. Accordingly, we propose the name hand-twisted helical crystals for these substances. [ABSTRACT FROM AUTHOR]

Gliclazide (GCZ), tolbutamide (TOL), and glipizide (GPZ) are BCS class II antidiabetic drugs with poor aqueous solubility. Multicomponent solid forms, salts, and cocrystals of GCZ were obtained upon liquid assisted grinding with coformers of catechol, resorcinol, p-toluenesulfonic acid, and piperazine. The solubility of TOL was also modified by salt formation with piperazine (PPZ). The multicomponent solids were characterized by single crystal X-ray diffraction, powder X-ray diffraction, Fourier transform infrared spectroscopy, differential scanning calorimetry, and thermal gravimetric analysis and further subjected to solubility studies. The cocrystals/salts, in all cases, showed improvements in the solubility and dissolution rates compared to the parent active pharmaceutical ingredients. GCZ-PPZ and TOL-PPZ(I) showed 6.6 and 80 and fold enhancements respectively in the solubility. The reasons for the improved solubility of the cocrystals/salts in terms of drug-coformer interactions are discussed. [ABSTRACT FROM AUTHOR]

A strategy is outlined for the design of hand-twisted helical crystals. The starting point in the exercise is the one-dimensional (1D) plastic crystal, 1,4-dibromobenzene, which is then changed to a 1D elastic crystal, exemplified by 4-bromophenyl 4'-chlorobenzoate, by introduction of a molecular synthon -O-CO- in lieu of the supramolecular synthon Br⋯Br in the precursor. The 1D elastic crystals are next modified to two-dimensional (2D) elastic crystals, of the type 4-bromophenyl 4'-nitrobenzoate where the halogen bonding and C-H⋯O hydrogen bonding are well-matched. Finally, varying the interaction strengths in these 2D elastic crystals gives plastic crystals with two pairs of bendable faces but without slip planes. Typical examples are 4-chlorophenyl and 4-bromophenyl 4'-nitrobenzoate. This type of 2D plasticity represents a new type of bendable crystals in which plastic behavior is seen with a fair degree of isotropic character in the crystal packing. The presence of two sets of bendable faces, generally orthogonal to each other, allows for the possibility of hand-twisting of the crystals to give grossly helical morphologies. Accordingly, we propose the name hand-twisted helical crystals for these substances. [ABSTRACT FROM AUTHOR]

Analyses of the character and importance of hydrogen bonds, of the type X bonded to H...C (X double bonded to O,N), focused on extraordinary interactions and crystallographic investigations on 17-alpha-ethynylandrosta-2,4-dieno(2,3-d)dihydroxazol-17beta-ol (donazole) prove that these extraordinary O bonded to H...C interactions exist. The energetic and structural importance of there hydrogen bonds has been revealed by database investigating IR spectroscopy and ab initio calculations.

Thecrystal structure landscape of the 2:1 benzoic acid:dipyridylethylenecocrystal (BA:DPE-I) is explored experimentally with fluoro-substitutedbenzoic acids and extended with studies employing the Cambridge StructuralDatabase (CSD). The interpretation of the cocrystal landscape is facilitatedby considering the kinetically favored and robust acid–pyridineheterosynthon as a modular unit. Information based on high-throughputcrystallography shows that polymorphs and pseudopolymorphs may belongto the same landscape but arise from different crystallization pathwaysbecause of complex and different kinetic features, and secondary synthonpreferences. Using the CSD as a guide, the coformer was changed from1,2-bis(4-pyridyl)ethylene (DPE-I) to 1,2-bis(4-pyridyl)ethane (DPE-II) and this provides an extendedinterpretation of the BA:DPE-I cocrystal landscape, also highlightingthe complexity of the kinetic–thermodynamic dichotomy duringthe molecule-to-crystal progression. [ABSTRACT FROM AUTHOR]

Tetrakis(4-nitrophenyl)methane inclusion compounds were studied focusing on C-H...O networks, structural transformations and pseudopolymorphism.

How do molecules aggregate in solution, and how do these aggregates consolidate themselves in crystals? What is the relationship between the structure of a molecule and the structure of the crystal it forms? Why do some molecules adopt more than one crystal structure? Why do some crystal structures contain solvent? How does one design a crystal structure with a specified topology of molecules, or a specified coordination of molecules and/or ions, or with a specified property? What are the relationships between crystal structures and properties for molecular crystals? These are some of the questions that are being addressed today by the crystal engineering community, a group that draws from the larger communities of organic, inorganic, and physical chemists, crystallographers, and solid state scientists. This Perspective provides a brief historical introduction to crystal engineering itself and an assessment of the importance and utility of the supramolecular synthon, which is one of the most important concepts in the practical use and implementation of crystal design. It also provides a look to the future from the viewpoint of the author, and indicates some directions in which this field might be moving. [ABSTRACT FROM AUTHOR]

A family of 4-hydroxybenzamide–dicarboxylic acidcocrystals has been designed and subsequently isolated and characterized.The design strategy follows from an understanding of synthon modularityin crystal structures of monocomponent crystals such as γ-quinol,4,4′-biphenol and 4-hydroxybenzoic acid. These monocomponentstructures contain infinite O–H···O–H···O–H···cooperative synthons linked with molecular connectors such as phenyland biphenyl, and supramolecular connectors such as the acid dimerin 4-hydroxybenzoic acid. The cocrystal design was influenced by theanticipation that dicarboxylic acids can form a supramolecular connectormediated by acid–amide synthons with 4-hydroxybenzamide, whichcan then form the phenol O–H···O–H···O–H···infinite synthon. Effectively, the acid–amide and phenol synthonsare insulated. The short axis of such a structure will be around 5.12Å and this is borne out in 2:1 cocrystals of 4-hydroxybenzamidewith oxalic, succinic, fumaric, glutaric (two forms) and pimelic acids.Hydrated variations of this structure type are seen in the cocrystalsobtained with adipic and sebacic acids. [ABSTRACT FROM AUTHOR]

Thirteen host−guest compounds of 3,5-dihydroxybenzoic acid (DHBA) have been structurally characterized. Water molecules occupy the peripheries of a hexagonal void, created with DHBA molecules, and act as “hooks” to connect the guest molecules with the host-framework via hydrogen bonding. The “water hook” is an OH group acting as a donor. Consequently, the guest molecules were chosen so that they contain good hydrogen bond acceptor functionalities. A number of multicomponent hydrates were isolated with stoichiometries (DHBA)x(H2O)y(guest)z. Of these, compounds with the following as guests were obtained as crystals that were good enough for single crystal work: ethyl acetate (EtOAc), diethyl oxalate, dimethyl oxalate, di(n-propyl) oxalate, diethyl malonate, diethyl succinate, chloroacetonitrile, N,N-dimethyl formamide (DMF), acetone, dimethyl sulfoxide (DMSO), 1-propanol, and 2-butanol. From 2-butanol, a hemihydrate, (DHBA)2(H2O), was also obtained concomitantly. Further to guest stabilization, water acts as a good mediator of effective crystal packing and also determines the topology of the host framework. In the present series of compounds, the role of water is wide ranging, and it is not easy to classify it specifically as a host or as a guest. [ABSTRACT FROM AUTHOR]