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Summary: The photocatalytic reduction of carbon dioxide (CO2) into multi-electron carbon products remains challenging due to the inherent stability of CO2 and slow multi-electron transfer kinetics. Here in, we synthesized a hybrid material, cesium copper halide (Cs3Cu2I5) intercalated onto two-dimensional (2D) cobalt-based zeolite framework (ZIF-9-III) nanosheets (denoted as Cs3Cu2I5@ZIF-1) through a simple mechanochemical grinding. The synergy in the hybrid effectively reduces CO2 to carbon monoxide (CO) at 110 μmol/g/h and methane at 5 μmol/g/h with high selectivity, suppressing hydrogen evolution. Further, we have investigated additional Cs3Cu2I5@ZIF hybrids with varying ZIF-9-III amounts, confirming their selective CO2 reduction to methane over hydrogen. Density functional theory (DFT) calculations reveal a non-covalent interaction between Cs3Cu2I5 and ZIF-9-III, with electron transfer suggesting potential for improved photocatalysis.

Herein, we have explored the effects of chlorinated mononuclear Cu(II) complex upon binding with BSA protein (bovine serum albumin) and its in vitro anti-proliferative potentiality against SiHa cell. The complex was synthesized involving a Schiff base ligand having N,N,O donor centers and characterized by several spectroscopic studies. Structure, DFT studies and Hirshfeld surface (HS) analyses were identified using crystallographic computational studies. The binding interaction with BSA depicts the efficacy of the complex towards promising binding of it with BSA. Further, the complex shows a moderate cytotoxicity against SiHa cancer cell signifying its potentiality as an anti-proliferative agent for human cervix uteri carcinoma.

The work carried out by our research group over the last couple of decades in the context of quantitative crystal engineering involves the analysis of intermolecular interactions such as carbon (tetrel) bonding, pnicogen bonding, chalcogen bonding, and halogen bonding using experimental charge density methodology is reviewed. The focus is to extract electron density distribution in the intermolecular space and to obtain guidelines to evaluate the strength and directionality of such interactions towards the design of molecular crystals with desired properties. Following the early studies on halogen bonding interactions, several “sigma-hole” interaction types with similar electrostatic origins have been explored in recent times for their strength, origin, and structural consequences. These include interactions such as carbon (tetrel) bonding, pnicogen bonding, chalcogen bonding, and halogen bonding. Experimental X-ray charge density analysis has proved to be a powerful tool in unraveling the strength and electronic origin of such interactions, providing insights beyond the theoretical estimates from gas-phase molecular dimer calculations. In this mini-review, we outline some selected contributions from the X-ray charge density studies to the field of non-covalent interactions (NCIs) involving elements of the groups 14–17 of the periodic table. Quantitative insights into the nature of these interactions obtained from the experimental electron density distribution and subsequent topological analysis by the quantum theory of atoms in molecules (QTAIM) have been discussed. A few notable examples of weak interactions have been presented in terms of their experimental charge density features. These examples reveal not only the strength and beauty of X-ray charge density multipole modeling as an advanced structural chemistry tool but also its utility in providing experimental benchmarks for the theoretical studies of weak interactions in crystals.

Hirshfeld atom refinement (HAR) is a novel X-ray structure refinement technique that employs aspherical atomic scattering factors obtained from stockholder partitioning of a theoretically determined tailor-made static electron density. HAR overcomes many of the known limitations of independent atom modelling (IAM), such as too short element–hydrogen distances, r(X—H), or too large atomic displacement parameters (ADPs). This study probes the accuracy and precision of anisotropic hydrogen and non-hydrogen ADPs and of r(X—H) values obtained from HAR. These quantities are compared and found to agree with those obtained from (i) accurate neutron diffraction data measured at the same temperatures as the X-ray data and (ii) multipole modelling (MM), an established alternative method for interpreting X-ray diffraction data with the help of aspherical atomic scattering factors. Results are presented for three chemically different systems: the aromatic hydrocarbon rubrene (orthorhombic 5,6,11,12-tetraphenyltetracene), a co-crystal of zwitterionic betaine, imidazolium cations and picrate anions (BIPa), and the salt potassium hydrogen oxalate (KHOx). The non-hydrogen HAR-ADPs are as accurate and precise as the MM-ADPs. Both show excellent agreement with the neutron-based values and are superior to IAM-ADPs. The anisotropic hydrogen HAR-ADPs show a somewhat larger deviation from neutron-based values than the hydrogen SHADE-ADPs used in MM. Element–hydrogen bond lengths from HAR are in excellent agreement with those obtained from neutron diffraction experiments, although they are somewhat less precise. The residual density contour maps after HAR show fewer features than those after MM. Calculating the static electron density with the def2-TZVP basis set instead of the simpler def2-SVP one does not improve the refinement results significantly. All HARs were performed within the recently introduced HARt option implemented in the Olex2 program. They are easily launched inside its graphical user interface following a conventional IAM.

Rubrene is one of the most studied organic semiconductors to date due to its high charge carrier mobility which makes it a potentially applicable compound in modern electronic devices. Previous electronic device characterizations and first principles theoretical calculations assigned the semiconducting properties of rubrene to the presence of a large overlap of the extended π-conjugated core between molecules. We present here the electron density distribution in rubrene at 20 K and at 100 K obtained using a combination of high-resolution X-ray and neutron diffraction data. The topology of the electron density and energies of intermolecular interactions are studied quantitatively. Specifically, the presence of Cπ...Cπ interactions between neighbouring tetracene backbones of the rubrene molecules is experimentally confirmed from a topological analysis of the electron density, Non-Covalent Interaction (NCI) analysis and the calculated interaction energy of molecular dimers. A significant contribution to the lattice energy of the crystal is provided by H—H interactions. The electron density features of H—H bonding, and the interaction energy of molecular dimers connected by H—H interaction clearly demonstrate an importance of these weak interactions in the stabilization of the crystal structure. The quantitative nature of the intermolecular interactions is virtually unchanged between 20 K and 100 K suggesting that any changes in carrier transport at these low temperatures would have a different origin. The obtained experimental results are further supported by theoretical calculations.

Synchrotron radiation has many compelling advantages over conventional radiation sources in the measurement of accurate Bragg diffraction data. The variable photon energy and much higher flux may help to minimize critical systematic effects such as absorption, extinction and anomalous scattering. Based on a survey of selected published results from the last decade, the benefits of using synchrotron radiation in the determination of X-ray electron densities are discussed, and possible future directions of this field are examined.

In the title molecule, C28H20Cl2N2O2, the dihedral angle between the 2-chloroquinoline and 6-chloroquinoline rings is 7.55 (6)°. The dihedral angle between the phenyl ring and its attached quinoline ring is 62.59 (4)°. In the crystal, aromatic π–π stacking interactions [centroid–centroid distances = 3.771 (3) and 3.612 (3) Å] help to establish the packing.

The title compound, C18H16N2O, crystallizes in the triclinic space group P1, with four independent molecules in the asymmetric unit wherein two molecules have an irregular -ac, -ac, +ap conformation (ap, antiperiplanar; ac, anticlinal), while the other molecules exhibit a different, +ac, +ac, +ap conformation. The planar (r.m.s. deviation = 0.006 Å in each of the four molecules) quinoline ring systems of the four molecules are oriented at dihedral angles of 32.8 (2), 33.4 (2), 31.7 (2) and 32.3 (2)° with respect to the benzene rings. Intramolecular N—H...N interactions occur in all four independent molecules. The crystal packing is stabilized by intermolecular N—H...O and C—H...O hydrogen bonds, and are further consolidated by C—H...π and π–π stacking interactions [centroid–centroid distances = 3.728 (3), 3.722 (3), 3.758 (3) and 3.705 (3) Å].

In the title molecule, C22H21N3, the isoquinoline ring is almost planar [maximum deviation = 0.046 (1) Å] and makes dihedral angles of 52.01 (4) and 14.61 (4)° with the pyrazole and phenyl rings, respectively. The phenyl ring and the pyrazole ring are twisted by 44.20 (6)° with respect to each other. The terminal C atoms of both of the ethyl groups attached to the pyrazole ring are disordered over two sites with occupancy ratios of 0.164 (7):0.836 (7) and 0.447 (16):0.553 (16). A weak intramolecular C—H...N contact may influence the molecular conformation. The crystal structure is stabilized by C—H...π contacts involving the phenyl and pyrazole rings, and by π–π stacking interactions involving the pyridine and benzene rings [centroid–centroid distance = 3.5972 (10) Å].

In the title molecule, C19H14ClN3O, the quinoline and quinazoline ring systems form a dihedral angle of 80.75 (4)°. In the crystal, the molecules are linked by pairs of C—H...N hydrogen bonds into centrosymmetric dimers, generating R22(6) ring motifs. The structure is further stabilized by C—H...π interactions and π–π stacking interactions [centroid–centroid distances = 3.7869 (8) and 3.8490 (8) Å].

The title compound, C11H10ClNO, is close to being planar (r.m.s deviation for the non-H atoms = 0.026 Å). In the crystal, molecules are linked by O—H...O hydrogen bonds, generating C(2) chains, and weak C—H...π interactions and aromatic π–π stacking interactions [centroid–centroid distance = 3.713 (3) Å] help to consolidate the structure.

In the title compound, C11H10ClNO2·H2O, the organic molecule is roughly planar (r.m.s. deviation = 0.074 Å). In the crystal structure, molecues are linked by O—H...O and O—H...N hydrogen bonds and weak C—H...π and π–π interactions [centroid–centroid distance = 3.578 (3) Å] consolidate the packing. A short Cl...O contact [3.147 (3) Å] is also observed.

In the title compound, C28H20Cl2N2O2, the 2-chloroquinoline and 6-chloroquinoline ring systems are twisted slightly, making a dihedral angle of 4.05 (3)°. The dihedral angle between the 2-quinoline ring system and the phenyl ring attached to it is 74.43 (5)°. In the crystal structure, a pair of intermolecular C—H...O hydrogen bonds connect the molecules, forming centrosymmetric dimers with R22(16) motifs. The dimers are further consolidated by a C—H...π interaction and a π–π stacking interaction with a centroid–centroid distance of 3.6562 (10) Å.

In the title compound, C27H18Cl2N2O2, the 2-chloroquinoline and 6-chloroquinoline rings are almost planar, with maximum deviations from their mean planes of 0.072 (1) and 0.044 (1) Å, respectively, for the Cl atoms. The interplanar angle between these rings is 14.36 (5)°. The interplanar angle between the 6-chloroquinoline and phenyl rings is 66.00 (8)°. In the crystal, molecules are interlinked by weak C—H...O, C—H...π and π–π stacking [centroid–centroid distances = 3.7453 (10) and 3.7557 (9) Å] interactions.

There are two independent molecules in the asymmetric unit of the title compound, C11H9Cl2N, both of which are essentially planar [maximum deviations of 0.072 (5) and 0.072 (7) Å]. In the crystal structure, weak π–π stacking interactions [centroid-centroid distances = 3.791 (3) Å and 3.855 (3) Å] link pairs of molecules.

In the title compound, C15H11Cl2NO2, the dihedral angle between the two benzene rings is 74.83 (5)°. The N-bound and terminal benzene rings are inclined at dihedral angles of 4.09 (10) and 78.38 (9)°, respectively, to the mean plane through the acetamide group. Intramolecular C—H...O and N—H...O hydrogen bonds both generate S(6) rings.

The title molecule, C5H7N3O2, has an almost planar conformation, with a maximum deviation of 0.043 (3) Å, except for the methyl H atoms. In the crystal structure, intermolecular C—H...O hydrogen bonds link the molecules into layers parallel to the bc plane. Intermolecular π–π stacking interactions [centroid–centroid distances = 3.685 (2) and 3.697 (2) Å] are observed between the parallel triazole rings.

The title compound, C13H14OS, crystallizes with two independent molecules in the asymmetric unit. The unit cell contains three voids of 197 Å3, but the residual electron density (highest peak = 0.24 e Å−3 and deepest hole = −0.18 e Å−3) in the difference Fourier map suggests no solvent molecule occupies this void. The crystal structure is stabilized by π–π interactions between the isocoumarin ring systems, with centroid–centroid distances of 3.6793 (14) and 3.6566 (15) Å.

In the title molecule, C22H14ClN3, the triazoloisoquinoline ring system is approximately planar, with an r.m.s. deviation of 0.033 (2) Å and a maximum departure from the mean plane of 0.062 (1) Å for the triazole ring C atom, bonded to the benzene ring. The benzene and phenyl rings are twisted by 57.02 (6) and 62.16 (6)°, respectively, to the mean plane of the triazoloisoquinoline ring system. The molecule is stabilized by a weak intramolecular π–π interaction [centroid–centroid distance = 3.7089 (10) Å] between the benzene and phenyl rings. In the crystal structure, weak intermolecular C—H...N hydrogen bonds and C—H...π interactions link the molecules.

In the title molecule, C20H12ClN3O, the triazoloisoquinoline ring system is nearly planar, with an r.m.s. deviation of 0.018 (3) Å and a maximum deviation of 0.034 (3) Å from the mean plane for the triazole ring C atom which is bonded to the benzene ring. The furan and benzene rings are twisted by 59.71 (14) and 66.95 (10)°, respectively, with respect to the mean plane of the triazoloisoquinoline ring system. The molecular conformation is stabilized by an intramolecular π–π interaction [centroid-to-centroid distance = 3.5262 (18) Å]. The crystal packing is stabilized by weak C—H...π interactions and weak π–π interactions [centroid-to-centroid distance = 3.9431 (17) Å].

In the title compound, C15H12ClN3O, the quinoline ring system is essentially planar, with a maximum deviation of 0.017 (1) Å. The crystal packing is stabilized by π–π stacking interactions between the quinoline rings of adjacent molecule, with a centroid–centroid distance of 3.5913 (8) Å. A weak C—H...π contact is also observed between molecules.

In the title compound, C16H13ClN2O, the quinoline ring system is approximately planar [maximum deviation 0.021 (2) Å] and forms a dihedral angle of 85.93 (6)° with the pyridone ring. Intermolecular C—H...O hydrogen bonding, together with weak C—H...π and π–π interactions [centroid-to-centroid distances 3.5533 (9) and 3.7793 (9) Å], characterize the crystal structure.

In the title compound, C18H11ClN2O2, the isatin and 2-chloro-3-methylquinoline units are both almost planar, with r.m.s. deviations of 0.0075 and 0.0086 Å, respectively, and the dihedral angle between the mean planes of the two units is 83.13 (7)°. In the crystal, a weak intermolecular C—H... O interaction links the molecules into chains along the c axis.

In the title molecule, C23H14N4, the triazoloisoquinoline ring system is nearly planar, with an r.m.s. deviation of 0.038 (2) Å and a maximum deviation of −0.030 (2) Å from the mean plane of the triazole ring C atom which is bonded to the benzene ring. The benzene and phenyl rings are twisted by 57.65 (8) and 53.60 (9)°, respectively, with respect to the mean plane of the triazoloisoquinoline ring system. In the crystal structure, molecules are linked by weak aromatic π–π interactions [centroid–centroid distance = 3.8074 (12) Å]. In addition, the crystal structure exhibits a nonclassical intermolecular C—H...N hydrogen bond.

In the title molecule, C21H15ClN4S, the triazoloisoquinoline ring system is approximately planar, with an r.m.s. deviation of 0.054 (2) Å and a maximum deviation of 0.098 (2) Å from the mean plane for the triazole ring C atom that is bonded to the thiazole ring. The thiazole and benzene rings are twisted by 66.36 (7) and 56.32 (7)°, respectively, with respect to the mean plane of the triazoloisoquinoline ring system. In the crystal structure, molecules are linked by intermolecular C—H...N interactions along the a axis. The molecular conformation is stabilized by a weak intramolecular π–π interaction involving the thiazole and benzene rings, with a centroid–centroid distance of 3.6546 (11) Å. In addition, two other intermolecular π–π stacking interactions are observed, between the triazole and benzene rings and between the dihydropyridine and benzene rings [centroid–centroid distances = 3.6489 (11) and 3.5967 (10) Å, respectively].

In the title compound, C30H24Cl2N2O3, the two quinoline ring systems are almost planar [maximum deviations = 0.029 (2) and 0.018 (3) Å] and the dihedral angle between them is 4.17 (8)°. The dihedral angle between the phenyl ring and its attached quinoline ring is 69.06 (13)°. The packing is stabilized by C—H...O, C—H...N, weak π–π stacking [centroid–centroid distances = 3.7985 (16) and 3.7662 (17) Å] and C—H...π interactions.

In the title molecule, C14H10ClNO, all non-H atoms are coplanar (r.m.s deviation = 0.0266 Å). In the crystal, symmetry-related molecules are hydrogen bonded via intermolecular O—H...O interactions, forming chains along the b axis.

In the title compound, C17H15ClN2O, the quinoline ring system is nearly planar, with a maximum deviation from the mean plane of 0.074 (2) Å, and makes a dihedral angle of 81.03 (7)° with the pyridone ring. The crystal packing is stabilized by π–π stacking interactions between the pyridone and benzene rings of the quinoline ring system [centroid–centroid distance = 3.6754 (10) Å]. Furthermore, weak intermolecular C—H...O hydrogen bonding links molecules into supramolecular chains along [001].

In the title compound, C16H13ClN2O, the quinoline ring system is essentially planar, with a maximum deviation of 0.021 (2) Å. The pyridone ring is oriented at a dihedral angle of 85.93 (6)° with respect to the quinoline ring system. In the crystal structure, intermolecular C—H...O hydrogen bonds link the molecules along the b axis. Weak π–π stacking interactions [centroid–centroid distances = 3.7218 (9) and 3.6083 (9) Å] are also observed.

The title compound, C22H20ClN3, is composed of a dialkyl-substituted pyrazole ring connected to an aryl-substituted isoquinoline ring system with a dihedral angle of 55.8 (1)° between the pyrazole ring and and the isoquinoline ring system. The dihedral angle between the chlorophenyl ring and the isoquinoline ring system is 28.3 (1)°.

The molecular conformation of the title compound, C19H18O2, is stabilized by an intramolecular O—H—O hydrogen bond. In addition, intermolecular O—H—O interactions link the molecules into zigzag chains running along the c axis.

The title compound, C25H19N3, is composed of an aryl-substituted pyrazole ring connected to an aryl-substituted isoquinoline ring system with a dihedral angle of 52.7 (1)° between the pyrazole ring and the isoquinoline ring system. The dihedral angle between the pyrazole ring and the phenyl ring attached to it is 27.4 (1)° and the dihedral angle between the isoquinoline ring system and the phenyl ring attached to it is 19.6 (1)°.

In the title molecule, C20H13N3S, the triazoloisoquinoline ring system is approximately planar, with an r.m.s. deviation of 0.045 Å and a maximum deviation of 0.090 (2) Å from the mean plane for the triazole ring C atom which is bonded to the thiophene ring. The phenyl ring is twisted by 52.0 (1)° with respect to the mean plane of the triazoloisoquinoline ring system. The thiophene ring is rotationally disordered by approximately 180° over two sites, the ratio of refined occupancies being 0.73 (1):0.27 (1).

All the non-H atoms of the title compound, C10H11NO2, are almost coplanar [maximum deviation = 0.040 (3) Å]. The crystal structure is stabilized by C—H...O hydrogen bonds.

All the non-H atoms of the title compound, C11H10ClNO2, are roughly coplanar (r.m.s. deviation = 0.058 Å). In the crystal, adjacent molecules are linked by an O—H...N hydrogen bond, generating chains running along the a axis.

All non-H atoms of the title compound, C12H12ClNO, are co-planar (r.m.s. deviation = 0.055 Å). The hydroxy H atom is disordered over two positions of equal occupancy. In the crystal, molecules are linked by O—H...O hydrogen bonds, generating zigzag chains running along the b axis.

In the title compound, C18H14ClNO3, the dihydroquinolin-2-one ring system is almost planar (r.m.s. deviation = 0.033 Å). The carboxylate plane and the phenyl group are twisted away from the dihydroquinolin-2-one ring system by 50.3 (1) and 64.9 (1)°, respectively. In the crystal structure, inversion-related molecules form R22(8) dimers via pairs of N—H...O hydrogen bonds.

The asymmetric unit of the title compound, C20H20ClNO2, contains two crystallographically independent molecules of similar geometry. The piperidine ring adopts a distorted boat conformation in both molecules, in which the N atom assumes an almost planar configuration.

In the molecule of the title compound, C20H23NO3, the bulky methoxyphenyl substituents at the equatorial 2,6-positions crowd the vicinity of the equatorial amino H atom and prevent it from forming intermolecular hydrogen bonds. The piperidine ring adopts a distorted chair conformation.