Abstract This study presents a systematic investigation of a possible odd–even effect in a homologous series of acylated 2-aminopyrazine derivatives, focusing on the relationship between alkyl chain length and macroscopic properties. A series of N-(pyrazin-2-yl)alkylamides (PZ2–PZ9) was synthesized and structurally characterized (PZ2-PZ8) using single-crystal X-ray diffraction. The results revealed that even-numbered alkyl chains promote more efficient crystal packing, with all chains aligned in the same direction, whereas odd-numbered compounds exhibit alternating orientations, leading to packing inefficiencies. The even-numbered derivatives consistently exhibited higher melting points and densities compared to the odd-numbered derivatives. The results also indicate that decreasing molecular polarity can translate into increased resistance to water uptake at the bulk level. In this series, only the shortest alkyl chain and the most polar compound (PZ2) exhibited moisture sensitivity. Overall, subtle variations in molecular structure are shown to significantly affect macroscopic properties in predictable ways, thus providing further insights for the rational bottom-up design of functional organic materials.

Previous studies observed one-, two-, and three-dimensional H-bonded supramolecular assemblies in crystal structures of primary amides. However, no systematic study of alpha/beta/gamma-alkyl- and alpha/beta/gamma-aryl-substituted primary amides has been undertaken thus far. In this paper, we report molecular and supramolecular structures of six pharmaceutically relevant primary amides. These include four alpha-substituted amides (2-methylpropionamide, 2-propylvaleramide, 2-phenylacetamide, and 2-methyl-2-phenylpropionamide), one beta-substituted amide (3-methylbutyramide), and one gamma-substituted amide (4-phenylbutyramide). Crystal structures of these compounds are stabilized by the N-H & ctdot;O hydrogen bonds. One-dimensional H-bonded ribbons are observed in 2-propylvaleramide, and two-dimensional H-bonded layers are observed in the other five compounds. By comparing our results to the structures of primary amides (substituted acetamides) previously published by our group and other groups, we were able to formulate the following new structural insights: (i) in crystals of substituted primary amides, ribbons and layers are equally common; (ii) 4-phenylbutyramide molecules form an unusual type of layer based on the R24(8) R44(16) synthon; (iii) the preference for either layer or ribbon is determined by the bulkiness of substituents as well as their positions.

In this study, nine cocrystals of N-(5-nitropyridin-2-yl)amide derivatives with 3-dimethylaminobenzoic acid (3DMABA) and 4-aminobenzoic acid (4ABA) were synthesized and structurally characterized in order to fine-tune photophysical properties by systematically modifying targets and coformers while maintaining overall structural consistency. The influence of competing factors, such as hydrogen-bonding motifs and steric effects, was examined through deliberate coformer selection and alkyl chain-length variation. The compounds exhibited visible color changes during grinding experiments, which were investigated using UV-visible spectroscopy and computational chemistry. The results show that changing the coformer can effectively modulate photophysical behavior while largely preserving crystal structure, and the competing intermolecular forces do not limit control over key solid-state structural parameters. Furthermore, the observed photophysical properties and colors can be rationalized and predicted based on calculated HOMO-LUMO gaps of donor-acceptor pairs, demonstrating a strategy for controlled design of functional cocrystals.

In search of new green and renewable energy sources, the use of hydrogen fuel cells continues to be a promising avenue. However, to unlock the full potential of these cells, the production of hydrogen remains to be the limiting factor, rooted in the need for new efficient catalyst development. To this end, we believe that placing proton shuttles (pendent group) in secondary coordination sphere close to catalytically active metal centre, mimicking that of natural enzymes and in some synthetic catalysts. In this, it will provide protons and electrons, which can decrease overpotential (energy to bring electron) and increase catalytical activity.To be discussed are three palladium complexes bearing calixpyrrole ligands with functionalities in the secondary coordination sphere. The pendent groups varying about the aniline, with no substitution (R= NH 2 ; 1A), an acetate (R=NHC(O)CH 3; 1B) and a Boc group (R=NHC(O)OC(CH) 3 ; 1C). Each of these were electrochemically characterized and electrocatalytic activities for hydrogen production were explored. They showed very fast reaction kinetics in acetonitrile, with high turnover frequencies up to 4,630,000 s -1 for 1A at an overpotential of 0.86 V, up to 4, 689, 000 s -1 for 1B at an overpotential of 0.92 V, and up to 3,690,000 s -1 for 1C at an overpotential of 0.94 V with anilinium tetrafluoroborate (pKa=10.62). To check the importance of pendent groups in hydrogen production, Ni complexes bearing calixpyrrole ligands with the same pendent groups (R=NHC(O)CH 3 ; NHC(O)OC(CH) 3 ) and without pendent group (R=H) were synthesized and electrochemically analyzed. The inclusion of Ni metal, rather than Pd, makes these catalysts far more economic. In this, the Ni compound decreased overpotential for hydrogen production from 0.98V (R=H) to 0.81V (R= NHC(O)OC(CH) 3 ) with anilinium tetrafluoroborate and showed high turnover frequency from 32891s -1 (R=H) to 48931s -1 (R=NHC(O)OC(CH) 3 ) and is giving idea of faster reaction kinetics. The results based on the pendent groups give significant insights into controlling secondary coordination sphere and showed how pendent groups can increase the catalytical activity for hydrogen evolution. Figure 1

This study examines the structural landscape of 14 crystal structures across two acetylated series of 2-aminopyridine derivatives (5-NO2 and 3-Cl, 5-CF3), which often display diverse solid-state interactions that complicate the prediction of supramolecular self-assembly. Comparative analysis of the NO2 series revealed that sterics alone has a significant impact on the formation of supramolecular assemblies in this family of compounds, as increasing steric demand shifts the bonding pattern from N-H center dot center dot center dot C=O chains to N-H center dot center dot center dot N(pyridine) dimers. In contrast, in the second series (3-Cl, 5-CF3), infinite N-H center dot center dot center dot O=C chains were present in all structures, indicating that increasing the steric factor does not affect the molecular assemblies in this series. Rather, this series demonstrated that the charge of pyridine nitrogen has a significant influence on the formation of supramolecular assemblies. Overall, these two series indicated that both sterics and charge have a great impact on the determination of final supramolecular assembly, and subtle changes in the structure were found to have a significant impact on solid-state assembly. In addition, infrared (IR) spectroscopy was shown to be a reliable tool for distinguishing between different hydrogen-bonding modes in the solid-state acetylated derivatives of 2-aminopyridines.

A systematic structural investigation of acetylated 2-aminopyrimidine derivatives was conducted to understand the balance between hydrogen and halogen bonds in supramolecular assembly. The 2-aminopyrimidine derivatives were grouped into three series to examine the effects of alkyl chain length, chain nature, and halogen substitution on supramolecular assembly. A total of twenty-one new crystal structures across these targets indicate that steric effects (alkyl chain length), the nature of the carbon chain, and halogen-atom substitution did not influence the assembly, with primary bonding motifs remaining largely consistent within each series. Notably, the study demonstrated that hydrogen bonds could be replaced by halogen bonds without disrupting overall crystal assembly when the halogen bond donor was sufficiently strong. Analysis of bond directionality illustrated that halogen bonds are more directional than hydrogen bonds, with hydrogen bond angles ranging from 126 degrees to 166 degrees, chlorine halogen bonds from 170 degrees to 175 degrees, and bromine halogen bonds from 168 degrees to 177 degrees. These findings highlight the potential of halogen bonds as reliable alternatives to hydrogen bonding in crystal engineering and expand possibilities for designing molecular structures with tailored noncovalent interactions.

Organochalcogen species have recently emerged as potential alternative candidates for chemotherapeutic drug design. From a molecular recognition perspective, the chalcogen atoms in these compounds offer variable sigma-hole potentials through electron-withdrawing groups, sp-hybridization, and atom-to-atom substitution. This adaptability does, in turn, provide some control over the way in which the selectivity and binding strength of small molecules capable of chalcogen bonding (ChB) can be fine-tuned in a biological system. In this context, a total of eight molecules were synthesized 4Cl-Ch, 4CN-Ch, 4NO 2 -Ch, and 35DN-Ch (Ch = Se/Te), and their single crystal structures were examined. Electronic structure calculations show that the electrostatic potential at the two sigma-holes on the chalcogen atom can be tuned by substituting selenium with tellurium, by modifying the electron-withdrawing capacity of the phenyl group substituents from 4Cl to 35DN and by varying the orientation of the phenyl groups. The two sigma-holes show different degrees of sensitivity to these parameters, allowing for further tunability of these bidirectional sigma-hole interactions. Biological evaluations showed a strong correlation between sigma-hole activation and anticancer activity, with tellurium compound 35DN-Te demonstrating potent activity against HeLa cells (IC5 0 = 2.9 mu M), outperforming traditional drugs like cis-platin. These findings highlight ChB's potential for developing novel chemotherapeutics.

The reactivity of hydroxyl-bearing MOF linkers with isocyanates is influenced by their mutual confinement with amine-bearing linkers within the pores of the framework.

To explore the structural landscape of a variety of 1,3,4-chalcogenadiazoles, more than 150 cocrystallization reactions with carboxylic acids as potential coformers were attempted, and the outcome of each was characterized and classified using FTIR. The results from the FTIR screen were subsequently confirmed using single-crystal X-ray diffraction of products (12 were found to be salts, and the remaining 5 were cocrystals). It was noted that the common Delta pK a "rule" did not provide reliable information on salt vs cocrystal formation in these systems, whereas the use of calculated interaction energies for neutral vs salt-based heteromeric dimers identified a noticeable separation between the two, indicating that such calculations can offer a useful predictor for the outcome of cocrystallization reactions.

Robust and reliable synthons can facilitate the synthesis of predictable and complex supramolecular assemblies. In this study, we employ triply activated halogen-bond donors as a driver for cocrystal formation and examine the influence of the sigma-hole potential for controlling the stoichiometry of binary cocrystals of phenazine. Six new crystal structures are presented for ketone:phenazine binary cocrystals as well as six crystal structures for ester:phenazine cocrystals. The combination of structural chemistry and theory provides an increased understanding of how controlled variation of the molecular electrostatic potential on the halogen-bond atom can control the stoichiometry in the resulting binary cocrystals.

Designing ligand architectures that can mimic enzyme active sites is a promising approach for developing efficient small molecule activation catalysts for sustainable energy applications. Some key design features include chemically distinct binding pockets for multiple metal centers and a three-dimensional structure that controls the positioning of catalytic sites. With these principles in mind, mono- and bimetallic unsymmetric cofacial palladium complexes, 2 and 3, respectively, bearing ligands with calixpyrrole and salen coordination sites, or "salixpyrrole" ligands, are reported. These species were accessed in a straightforward Schiff-base reaction with appreciable yields. In addition, both 2 and 3 were found to be active hydrogen evolution electrocatalysts using para-toluenesulfonic acid monohydrate as the proton source. The two salixpyrrole species displayed different mechanisms of action, with 2 showing a second-order dependence on acid concentration, whereas 3 exhibited a first-order dependence. Moreover, the bimetallic catalyst was significantly more efficient, with higher turnover frequencies, 4640 s-1 vs 1680 s-1 for 2, and lower overpotentials, 0.39 V vs 0.69 V for 2. The results reported herein provide proof-of-concept that bimetallic catalysts with chemically distinct binding sites demonstrate enhanced catalytic properties in comparison to monometallic or symmetric analogues.

An entry from the Cambridge Structural Database, the world’s repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.

An entry from the Cambridge Structural Database, the world’s repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.

Incorporating design elements from homogeneous catalysts to construct well defined active sites on electrode surfaces is a promising approach for developing next generation electrocatalysts for energy conversion reactions. Furthermore, if functionalities that control the electrode microenvironment could be integrated into these active sites it would be particularly appealing. In this context, a square planar nickel calixpyrrole complex, Ni(DPMDA) (DPMDA=2,2'-((diphenylmethylene)bis(1H-pyrrole-5,2-diyl))bis(methaneylylidene))bis-(azaneylylidene))dianiline) with pendant amine groups is reported that forms a heterogeneous hydrogen evolution catalyst using anilinium tetrafluoroborate as the proton source. The supported Ni(DPMDA) catalyst was surprisingly stable and displayed fast reaction kinetics with turnover frequencies (TOF) up to 25,900 s(-1) or 366,000 s(-1) cm(-2). Kinetic isotope effect (KIE) studies revealed a KIE of 5.7, and this data, combined with Tafel slope analysis, suggested that a proton-coupled electron transfer (PCET) process involving the pendant amine groups was rate-limiting. While evidence of an outer-sphere reduction of the Ni(DPMDA) catalyst was observed, it is hypothesized that the control over the secondary coordination sphere provided by the pendant amines facilitated such high TOFs and enabled the PCET mechanism. The results reported herein provide insight into heterogeneous catalyst design and approaches for controlling the secondary coordination sphere on electrode surfaces.

For a series of substituted dithieno[3,2- a :2′,3′- c ]phenazine derivatives X-ray diffraction studies have been carried out.

An entry from the Cambridge Structural Database, the world’s repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.

The ability of halogen-bond donors to form strong and directional intermolecular interactions remains integral to their prospects of becoming reliable synthetic tools for the bottom-up assembly of functional materials. An activation strategy involving three different electron-withdrawing groups in parallel, was employed in order to develop new halogen-bond donors possessing some of the highest sigma-hole potentials reported to date.

An entry from the Cambridge Structural Database, the world’s repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.

A series of three calixpyrrole ligands (1a-c) with pendant nitrogen-based hydrogen bond donors, R, were syn-thesized and coordinated to palladium to produce metal complexes (2a-c), where R = NH2 (a); NHC(O)CH3 (b); or NHC(O)OC(CH3)3 (c). The calixpyrrole compounds were generated using a Schiff-base reaction starting with 5,5 & PRIME;-diformyl-2,2 & PRIME;-diphenyldipyrromethane and an aniline precursor. The deprotonated calixpyrrole species were subsequently bound to palladium to generate distorted square planar complexes. The pendant groups were not coordinated to the metal with Pd-N distances of 3.36 to 4.79 & ANGS;. The electrochemical properties of the palladium complexes were also explored, and 2a-c displayed two irreversible oxidations above 0.0 V vs ferrocene/ferro-cenium (Fc/Fc+), as well as two irreversible reductions below -0.70 V vs Fc/Fc+. Interestingly, the free ligands showed similar electrochemical features, suggesting redox non-innocence. Preliminary reactivity studies indi-cated the palladium complexes did not activate small molecules, but they did catalyze H2 evolution in the presence of acid. The onset of catalysis for 2a-c was approximately 0.4-0.5 V more positive than a glassy carbon electrode, and the active species could undergo 500 scans without significant changes in activity. The catalysts were found to be heterogeneous in nature and adsorbed onto the working electrode.