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The first page of this article is displayed as the abstract.

Currently, more than half of available drugs on the market are chiral, and approximately 90% of these drugs are marketed as racemates. When these racemic medications are exposed to the chiral environment of the human body, differences in their activity appear. The enantiomers of a chiral drug may potentially have distinct pharmacokinetic, metabolic, and toxicological features. As a result, regulatory requirements promote the production of enantiopure drugs to reduce the complexity of pharmacodynamics and the administration dose or to eliminate unwanted side effects, while also providing some economic savings by enabling a totally effective pharmaceutical formulation. There are a variety of procedures employed in the pharmaceutical industry for chiral separation of racemic drugs, such as developing de novo enantiomerically pure pharmaceuticals by asymmetric synthesis or chiral resolution of currently available racemic compounds via different approaches like chiral chromatography methods, diastereoisomeric salt formation, and cocrystallization-based methods. This review will focus on cocrystallization techniques such as the generation of host–guest inclusion compounds, diastereomeric cocrystal pairs, enantiospecific cocrystals, conglomerates, ionic cocrystals, and preferential enrichment of cocrystals. Overall, this review outlined the crucial importance of pharmaceutical cocrystals in chiral resolution techniques of racemic compounds.

The first page of this article is displayed as the abstract.

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A graphical abstract is available for this content

Ligands capable of simultaneous metal coordination and hydrogen bond donation provide useful structural features to enhance cooperativity and favour specific geometries within the coordination sphere. Here we present the first structurally characterised examples of coordination compounds containing protonated 7-azaindole-N-oxide HL, bearing a neutral oxo donor capable of terminal or bridging coordination modes adjacent to a convergent hydrogen bond donor. The ligand itself shows a strong tendency for dimeric assembly in the solid state, but is easily deprotonated to give the chelate complex [CuL2] 1. In the presence of lanthanide ions, however, four new complexes [Eu(NO3)3(HL)3] 2, [Gd(NO3)3(HL)3] 3, [Eu2(μ2-HL)2(HL)4Cl6] 4 and [YbCl3(HL)3][YbCl(HL)5OH2]2Cl 5 were prepared and crystallographically characterised. All four species show strong tendencies for hydrogen bonding from the ligand to impact their overall structures, including a C3 propellor-like macrocyclic motif in 2 and 3 and a combination of intramolecular N–H⋯Cl contacts, and intermolecular tridentate anion binding in 5. Solution studies including HRMS and phosphorescence emission spectroscopy reveal persistence of the europium complex 2 in solution, despite the multiple possible binding modes of this ligand, hinting at a degree of cooperativity in these systems. These results show the utility of hydrogen bonding within the coordination sphere for influencing structural outcomes, relevant to the construction of stable higher-order crystalline assemblies.

In situ construction of polymetallic layered double hydroxide (LDH) @sulfide heterostructures (LDH@sulfides) is a promising strategy to achieve excellent electrochemical performance by providing more redox active sites and facilitating ion/electron pathways. Herein, nickel cobalt molybdenum based LDH@sulfide core–shell composites (NCM-LDH@NCMS) grown on Ni foam have been successfully prepared via a facile hydrothermal method, followed by controllable sulfidation methods. The effect of sulfidation time on the electrochemical performance of NCM-LDH@NCMS was investigated. The NCM-LDH nanosheets minimized the diffusion path of electrolyte ions and accelerated the kinetics of redox reactions, and the outer Ni–Co–Mo sulfides effectively improved the conductivity of LDHs and exposed more active sites. With sulfidation for 2 h, the obtained NCM-LDH@NCMS-2 exhibited excellent electrochemical performance, with a specific capacitance of ∼7.73 F cm−2 at 10 mA cm−2, and better capacitance rate performance of 56.7% at 50 mA cm−2. Furthermore, hybrid NCM-LDH@NCMS-2//activated carbon supercapacitors provided a high energy density of 0.25 mW h cm−2 at 40 mW cm−2 and excellent cycling stability of 89.82% after 8000 cycles at 8 mA−2.

Acentric structures host numerous important applications such as second harmonic generation, nonreciprocal responses, etc. In this work, a heteroanionic system of La3AsS5Br2 and La5As2S9Cl3 exhibits a good example of how the alignment of lone pair electrons affects crystal structure. Noncentrosymmetric (NCS) chalcohalide La3AsS5Br2, isostructural to Pr3AsS5Cl2, and centrosymmetric chalcohalide La5As2S9Cl3 were successfully synthesized by a salt flux growth method. Crystal structures were determined by single crystal X-ray diffraction. Both compounds contain trigonal pyramidal [AsS3] units with stereochemically active lone pairs in As3+, aligning in the same direction in La3AsS5Br2 and in opposite directions in La5As2S9Cl3, which account for their acentric crystal structure and centrosymmetric structure, respectively. Electron localization function (ELF) calculations confirmed that the alignment of the [AsS3] motifs contributes to the acentric nature of La3AsS5Br2. La3AsS5Br2 is predicated to be an indirect bandgap semiconductor by theory calculations with a bandgap of 2.27 eV, which is verified by UV-Vis spectroscopy measurements to be 2.8(1) eV. The acentric structural nature of La3AsS5Br2 was demonstrated by a moderate second harmonic generation (SHG) response of 0.23× AgGaS2, where La5As2S9Cl3 exhibited no response under the same conditions.

Two new isostructural 2D coordination polymers, denoted 1(Mn) and 2(Fe), have been synthesized using the layer diffusion method. These polymers, {[Mn(PDA)(4-bpdb)(H2O)2]·4-bpdb}n and {[Fe(PDA)(4-bpdb)(H2O)2]·4-bpdb}n, incorporated 1,4-phenylenediacetate (PDA) and 1,4-bis(4-pyridyl)-2,3-diaza-1,3-butadiene (4-bpdb) ligands. Structural analysis through the single-crystal X-ray study revealed that compound 1(Mn) and compound 2(Fe) exhibited a one-dimensional connectivity along the a-axis between metal ions (Mn(II)/Fe(II)) and 1,4-phenylenediacetate ligands and formed a 2D layered structure interconnected with 4-bpdb. These layers are arranged in an AAA… pattern along the b-axis, forming a three-dimensional supramolecular structure. Non-bonded 4-bpdb molecules occupy voids within this arrangement, stabilized by hydrogen bonds and π⋯π interactions. The redox-active metal centers (Mn2+/Fe2+) present in the coordination polymers hold promise for electrochemical studies. Supercapacitor assessment revealed an intriguing discrepancy: compound 1(Mn) demonstrated nearly 2.5 times greater specific capacitance than compound 2(Fe) in a 1 M H2SO4 medium, despite their isostructural nature. However, cyclic stability testing showed a reverse trend, with compound 2(Fe) exhibiting excellent stability, retaining 98% capacity after 5000 cycles compared to 1(Mn)'s 78%. Conductivity measurements indicated that compound 1(Mn) possesses conductivity 10 times superior to that of compound 2(Fe). Notably, both compounds exhibited potential for Schottky diode fabrication. Overall, this study highlights the influence of specific metal ions on distinctive supercapacitor characteristics and conductivity within isostructural coordination polymers.