Molecular Hirshfeld Surface Research Articles

Synthesis, characterization, crystal structure and theoretical simulation of novel ethyl 2-(7-hydroxy-4-methyl-2-oxo-2H-chromen-3-yl)acetate

Abstract Novel coumarin derivative, ethyl 2-(7-hydroxy-4-methyl-2-oxo-2H-chromen-3-yl)acetate has been synthesized by Pechmann condensation reaction and the single crystals of the compound were obtained by slow evaporation technique using ethanol as crystallization solvent. The compound C28H28O10 was spectroscopically characterized using 1H NMR, 13C NMR and IR techniques. Finally single crystal X-ray diffraction studies revealed the molecular structure conformation of the coumarin derivative. The compound crystallized in the orthorhombic crystal system with P212121 space group. The crystal structure of C28H28O10 is stabilized by various intra and inter (O--H...O and C--H...O) intermolecular hydrogen bond interactions. The existence and nature of various intermolecular interactions are quantified by the 3-D molecular Hirshfeld surface and 2-D fingerprint plot analysis. Further, the DFT calculations were performed to optimize structural coordinates and the minima point on the potential energy surface is confirmed by the frequency calculation. The optimized structural parameters showed very good correlation with the single crystal XRD results. Frontier molecular orbitals (HOMO-LUMO), their energy gap and associated reactive parameters were determined to understand the properties of the molecule.

Simple Trans-Platinum Complex Bearing 3-Aminoflavone Ligand Could Be a Useful Drug: Structure-Activity Relationship of Platinum Complex in Comparison with Cisplatin.

Following previous studies devoted to trans–Pt(3-af)2Cl2, in this paper, the molecular structure and intermolecular interactions of the title complex are compared with other cisplatin analogues of which the crystal structures are presented in the Cambridge Structural Database (CSD). Molecular Hirshfeld surface analysis and computational methods were used to examine a possible relationship between the structure and anticancer activity of trans–Pt(3-af)2Cl2. The purpose of the article was also to investigate the effect of hyperthermia on the anticancer activity of cisplatin, cytostatics used in the treatment of patients with ovarian cancer and a new analogue of cisplatin-trans–Pt(3-af)2Cl2. The study was conducted on two cell lines of ovarian cancer sensitive to Caov-3 cytostatics and the OVCAR-3 resistant cisplatin line. The study used the MTT (3-(4,5-dimethylthiazol-2,5-diphenyltetrazolium bromide) cell viability assay, LDH (lactate dehydrogenase), and the quantitative evaluation method for measuring gene expression, i.e., qPCR with TagMan probes. Reduced survivability of OVCAR-3 and Caov-3 cells exposed to cytostatics at elevated temperatures (37 °C, 40 °C, 43 °C) was observed. Hyperthermia may increase the sensitivity of cells to platinum-based antineoplastic drugs and paclitaxel, which may be associated with the reduction of gene expression related to apoptotic processes.

Synthesis, crystal structure and optical properties of Anderson-type heteropolyanion with cobalt cations

A sample inorganic A-type Anderson polyoxometalate (POM) (TeMo6) compound formulated as [Co(H2O)6]3[TeMo6O24] is synthesized in aqueous solution by slow evaporation technique. Single-crystal X-ray diffraction analysis reveals that the obtained compound crystallizes in the centrosymmetric hexagonal space group (R-3c) with a formula unit made up of one [TeMo6O24]6− A-type Anderson anion and three [Co(H2O)3]2+ cations. The molecular Hirshfeld surface indicates that the crystal packing is stabilized by H-bonds interactions to generate 3D supramolecular frameworks. Furthermore, some optical properties such as bandgap energy, refractive index, dielectric constant and optical conductivity of the sample are investigated. The large value of refractive index known in the visible region of electromagnetic spectrum (n = 3.5 at 1.8 eV) reveals that this sample can become a promising candidate for visible optical communication devices. The emission fluorescent spectrum in the solid state at room temperature is measured and the decay lifetime curves are obtained by monitoring the ligand-to-metal charge transfer transition (LMCT). The studies of the colorimetric properties of the sample reveal that the color coordinates (x = 0.33667; y = 0.25564) are located in the region of National Television System Committee (NTSC) in the CIE chromaticity chart and the calculated correlated color temperature value (CCT ~ 5085 K) indicates that the optimized compound could be applied as a cool light emission diode.

Synthesis, crystal structure, Hirshfeld surface analysis, DFT calculations and characterization of 1,3-propanediylbis(triphenylphosphonium) monotribromide as brominating agent of double bonds and phenolic rings

This paper presents synthesis and structural characterization of new members of phosphorus-based organic bromides. 1,3-Propanediylbis(triphenylphosphonium) dibromide I and 1,3-propanediylbis(triphenylphosphonium) monotribromide II, as a new brominating agent for double bonds and phenolic rings, were synthesized. 1H NMR, 13C NMR, 31P NMR, FT-IR, single crystal X-ray diffraction crystallography, differential scanning calorimetry, thermogravimetric analysis and differential thermal analysis were used to characterize these salts. Thermal and physicochemical stability, simple working up, non-toxicity in comparison to liquid bromine and high yield are some of the advantages of these salts. These salts have good solubility in organic solvents, such as methanol, ethanol, acetone, dichloromethane and THF. Crystallographic data showed that compound I crystallized in the monoclinic crystal system, in P21 space group and compound II crystallized in the monoclinic crystal system, in P21/c space group and one of the bromide ions was replaced by tribromide ion in II. The crystal packing structures of title compounds were stabilized by various intermolecular interactions, especially of the type C-H∙∙∙π contacts. The molecular Hirshfeld surface analysis and 2D fingerprint analysis revealed that the C∙∙∙H (30.4% for the compound I and 28.3% for compound II) contact, which was related to C-H∙∙∙π interactions, had the major contribution in the crystal architectures. To get more insight about molecular structures of titled compounds, DFT calculations were performed (energy, structural optimization and natural bond orbital analysis). Bromination of double bonds and phenolic rings was carried out to prove the ability of the tribromide salt to bromine such organic substrates.

A Synthetic, Spectroscopic, Theoretical and Biological Perspective on a Novel Schiff Base Included 4-Aminoantipyrine

A novel Schiff base, 4-(([1,1'-biphenyl]-4-ylmethylene)amino)-1,5-dimethyl-2-phenyl-1,2-dihydro-3H-pyrazol-3-one (BiPhAAP), obtained from biphenyl carboxaldehyde with 4-aminoantipyrine was characterized using elemental analysis, FT-IR, and 1H and 13C NMR spectroscopic methods. In addition to the spectroscopic findings, geometrical descriptions and the extent of surface interactions in the compound were determined by X-ray single crystallographic and Molecular Hirshfeld surface (MHS) analysis techniques. The distinctions between experimental and calculated FT-IR results have proved the presence of intra-molecular (C–H….O type) hydrogen bonds in the crystal structure. The in vitro antimicrobial potential, which was studied against two Gram-negative (Escherichia coli and Proteus vulgaris) and two Gram-positive (Bacillus subtilis and Micrococcus luteus) bacterial strains, and three yeast strains (Candida albicans, Aspergillus niger and Candida globrata) was examined by using the agar well diffusion method at concentrations of 250, 125 and 62.5 mg/mL. The in vitro antioxidant activities of this compound were estimated by five different antioxidant assays (DPPH radical scavenging, reducing power, metal chelating activity, superoxide scavenging, and total antioxidant). Cytotoxic activity of the new compound was sought against human breast carcinoma cells (MCF-7). The IC50 values were established with respect to the MTT test.

Growth and characterization of 2-bromo-5-methoxybenzohydrazide derivative—a nonlinear optical single crystal

A nonlinear optically active single crystal of 2-bromo-5-methoxybenzohydrazide derivative has been synthesized using standard method. Using solution growth technique the compound obtained was successfully grown as single crystals. FT-IR spectrum determines the different functional groups of the newly synthesized molecule. The single crystal x-ray diffraction analysis confirms the molecular structure and characterizes the crystal as non centrosymmetric as it crystallized in an orthorhombic crystal system having P212121 space group and also calculates the lattice parameters. The optical study reveals the maximum absorption at 289 nm wavelength and wide transparency of the crystal was observed near visible region. Green light emitting property of the crystal was determined by photoluminescence study. Thermo gravimetric (TG) and Differential thermal (DT) analysis discloses the thermal strength of the material. 0.41 SHG efficiency of title molecule was estimated by powder SHG test. Molecular Hirshfeld surface analysis of the crystal structure reveals the intermolecular interaction exhibited by various inter contacts and the corresponding 2-dimensional finger print analysis further estimates the individual contribution from each atom. Density functional theory (DFT) analysis calculates the energy gap of the molecule using HOMO-LUMO values. Various global chemical reactivity descriptor (GCRD) parameters have been calculated. Using molecular electrostatic potential (MEP) map the suitable sites for electrophilic and nucleophilic reactive sites were predicted. The NLO properties such as first order molecular hyperpolarizabilities (β), polarizability (α), molecular dipole moment (μ) and anisotropy polarizability (Δα) was theoretically estimated using DFT.

Electron densities of two cyclononapeptides from invariom application

Abstract The nonapeptides cyclo(Val-Leu-Pro-Ile-Leu-Leu-Leu-Val-Leu) (I) and cyclo(Val-Leu-Pro-Ala-Leu-Leu-Leu-Val-Leu) (II) were identified as promising candidates for the development as potential anti-cancer drugs. We report a re-refinement of deposited single-crystal X-ray diffraction data with aspherical scattering factors from the invariom database. A subsequent evaluation of the molecular electron density distribution and of the differences in their molecular electrostatic potentials provides insight in their activities. The sequences differ only in residue 4, Ile in (I) and Ala in (II). Since the anti-tumor potency is reduced for the Ala peptide (II), the causes for the differences seen in activity between (I) and (II) were examined from a structural and from an electron density (ED) point of view. The exchange at residue 4 does not lead to significant changes in molecular geometry. Molecular Hirshfeld surfaces and electrostatic potential (ESP) isosurfaces show accumulations of intermolecular interactions in regions adjacent to the Ile/Ala residues indicating preferred interactions with a potential receptor in these regions. The concentrations of intermolecular interactions were localized on the Hirshfeld surfaces through an extended basin of ED concentration close to the Ile/Ala residues. Differences in the electrostatic potentials (ESPs) between (I) and (II) were only found at the Ile/Ala site and were very close to zero otherwise.

Crystal structure and mol-ecular Hirshfeld surface analysis of acenaphthene derivatives obeying the chlorine-methyl exchange rule.

Instances of crystal structures that remain isomorphous in spite of some minor changes in their respective mol-ecules, such as change in a substituent atom/group, can provide insights into the factors that govern crystal packing. In this context, an accurate description of the crystal structures of an isomorphous pair that differ from each other only by a chlorine-methyl substituent, viz. 5''-(2-chloro-benzyl-idene)-4'-(2-chloro-phen-yl)-1'-methyl-dispiro-[acenaphthene-1,2'-pyrrolidine-3',3''-piperidine]-2,4''-dione, C34H28Cl2N2O2, (I), and its analogue 1'-methyl-5''-(2-methyl-benzyl-idene)-4'-(2-methyl-phen-yl)di-spiro-[acenaphthene-1,2'-pyrrolidine-3',3''-piperidine]-2,4''-dione, C36H34N2O2, (II), is presented. While there are two C-H⋯O weak inter-molecular inter-actions present in both (I) and (II), the change of substituent from chlorine to methyl has given rise to an additional weak C-H⋯O inter-molecular inter-action that is relatively stronger than the other two. However, the presence of the stronger C-H⋯O inter-action in (II) has not disrupted the validity of the chloro-methyl exchange rule. Details of the crystal structures and Hirshfeld analyses of the two compounds are presented.

Evaluation of structural, optical and mechanical behaviour of L-argininium bis(trifluoroacetate) single crystal: An efficient organic material for second harmonic generation applications

In the present technologically advanced era, non-linear optical materials especially organic derivatives are in the limelight due to their fast response in electro-optic switches and high nonlinear efficiency. Therefore, with respect to this behaviour, single crystals of L-argininium Bis(trifluoroacetate) (here in after called LABTF) an organic material was grown by slow evaporation solution growth technique. The grown single crystal was subjected to single crystal X-Ray diffractometer to validate its chemical structure and compound formation. The titled compound crystallizes into an asymmetric entity that comprises of one divalent L-argininium cation and two monovalent trifluoroacetic anion. All the intermolecular hydrogen bonds present in the LABTF crystal structure are investigated by 3D molecular Hirshfeld surface analysis and their relative involvements are disintegrated using 2D fingerprint plots. Further, the crystalline perfection assessment was performed using high-resolution X-Ray diffractometer which divulges the absence of structural grain boundaries in the obtained crystal. Thermal transport parameters of the titled compound were measured through Photoacoustic spectroscopy. The shock strength above which the crystal induces damage was found by the shock damage threshold technique. In addition, mechanical property related parameters such as hardness, stiffness and Young's Modulus were evaluated using the nanoindentation technique. These mechanical parameters resolve the reliability of devices and it can be enhanced by improving the crystal quality.

Analysis of two [2]catenanes based on electron densities from invariom refinement and results from DFT calculations

AbstractCatenanes are of considerable interest as potential building blocks for molecular machines. The simplest [2]catenanes, Hopf links, consist of two macrocycles that are mechanically interlocked. This unusual architecture cannot be opened without breaking at least one covalent bond. Based on these structural characteristics, unusual properties on Hirshfeld or electrostatic potential surfaces could be expected. For a comparison of their structural and electronic properties, the electron densities (EDs) of two [2]catenanes, codedH22andH4L7in the original papers, were examined after application of the invariom formalism, relying on X-ray diffraction data collected earlier. The obtained electron density distributions were subjected to an analysis using the QTAIM formalism to yield bond and atomic properties. Moreover, molecular Hirshfeld surfaces and electrostatic potentials (ESP) were calculated. There are different types of intra- and intermolecular interactions in these two [2]catenanes. In addition to classical N–H···N and C–H···O hydrogen bonds, various types of π···π interactions inH22and inH4L7exist. Most of them are verified by local ED concentrations visible on the corresponding Hirshfeld surfaces, except for the parallel π···π interactions inH22, which are either too weak or too diffuse to generate an ED signal on the Hirshfeld surface between the contributing aromatic rings. The electrostatic potentials (ESPs) were calculated and displayed on molecular surfaces. The interaction in the cavity of one macrocycle with the penetrated fragment of the second one was examined and it was found that corresponding to the above-mentioned contacts attractive and repulsive interactions exist. Additionally the ED was examined using results of density functional calculations, including non-covalent interaction index (NCI) and electron localizability indicator (ELI-D) surface analysis, complementing experimental findings.

Synthesis, single crystal, structure and Hirshfeld surface analysis of (E)-4-toluic-N′-(2,4-dihydroxy-benzylidene) benzohydrazide

Abstract The structure of the title Schiff base, C15H14N2O3, displays a trans configuration with respect to the C N bond, with a dihedral angle of 53.16(13)° between the benzene rings. The compound crystallizes in the monoclinic system, space group P21/a with unit cell parameters a = 12.43(2) A, b = 9.846(14) A,c = 12.55(2)A, β= 115.256(13)° and Z = 4. The molecular packing is controlled by intermolecular hydrogen bonds and π−π stacking interactions. The intermolecular O H···O and N H···O hydrogen bonds are involved in crystal structure stabilization. An intramolecular O H···N hydrogen bond is observed between the phenolic OH (O2) group and the azomethine nitrogen atom. Further, the molecular Hirshfeld surface analysis was carried out to reveal the nature of intermolecular contacts and the fingerprint plot provides the information about the percentage contribution and reveals that the H···H (54.7%) interactions have the major contribution to form the crystal.

Synthesis of 1,1′-(2,6-dihydroxy-2,6-dimethyl-3,7-dioxabicyclo [3.3.1]nonane-1,5-diyl)diethanone dihydrate: crystal structure and quantitative analysis of molecular interaction via molecular electrostatic potential and Hirshfeld surface analysis

ABSTRACTA new bicyclononane derivative, 1,1′-(2,6-dihydroxy-2,6-dimethyl-3,7-dioxa-bicyclo[3.3.1]nonane-1,5-diyl) diethanone dihydrate (1), has been synthesized and structurally characterized by the single-crystal X-ray diffraction technique. In the solid-state structure of the compound, molecular units are interlinked via strong hydrogen bonds as well as non-classical weak hydrogen bonds leading to a three-dimensional supramolecular architecture. Solid-state DFT optimized geometry in (1) agrees closely with that obtained from the crystallographic analysis. The C(dioxa-bicyclononane)–H … O(hydroxy) hydrogen bond generates cyclic (10) ring in (1) which are further connected through C–H … O and O–H … O hydrogen bonds into a three-dimensional framework in the title compound. Hirshfeld surface analysis of the title compound along with some related nonane derivatives retrieved from the Cambridge Structural Database shows that the most of the Hirshfeld surface area in this class of compounds is due to H … H and O … H interactions.

X-ray, dielectric, piezoelectric and optical analyses of a new nonlinear optical 8-hydroxyquinolinium hydrogen squarate crystal

The 1:1 complex of 8-hydroxyquinoline with squaric acid has been characterized using single-crystal X-ray diffraction, UV–vis spectroscopy, density functional theory (DFT) calculations, and photoluminescence, dielectric, piezoelectric and second-harmonic generation (SHG) studies. The title compound (8-hydroxyquinolinium hydrogen squarate; HQS) contains one protonated 8-hydroxyquinoline cation (C9H8NO+) and one hydrogen squarate mono-anion (C4HO4 −). All the intermolecular hydrogen-bonding interactions present in the HQS crystal structure are analyzed by three-dimensional molecular Hirshfeld surface analysis and their relative contributions are determined from two-dimensional fingerprint plots. The structure of C9H8NO+·C4HO4 − molecular complex has been optimized at the DFT/B3LYP/6-31G(d,p) level. The UV–vis spectroscopic data calculated by time-dependent density functional theory are compared with the experimental data. The LUMO+1, LUMO, HOMO and HOMO−1 energy values, their shapes and energy gaps are calculated using the B3LYP/6-31G(d,p) level of theory. The HQS material exhibits high SHG output (2.6 times of that of potassium dihydrogen phosphate), high photoluminescence emission centred at 474 nm and a piezoelectric charge coefficient of 3 pC N−1. Henceforth, HQS can serve as an alternative potential candidate for multifunctional nonlinear optically active and piezoelectric crystals.

An insight into the synthesis, crystal structure, geometrical modelling of crystal morphology, Hirshfeld surface analysis and characterization ofN-(4-methylbenzyl)benzamide single crystals

A versatile approach for the synthesis ofN-(4-methylbenzyl)benzamide, C15H15NO, using CuI as catalyst has been reported. Single crystals of the synthesized compound were grown using the slow evaporation solution technique. The crystal structure of theN-(4-methylbenzyl)benzamide crystals has been determined by single-crystal X-ray diffraction. The compound crystallizes in an orthorhombic lattice, noncentrosymmetric space groupPna21. The crystal structure is stabilized by intermolecular N—H...O hydrogen bonds and weak C—H...π interactions to form layers parallel to theaaxis. A user-friendly approach based on centre of mass propagation vector theory was used to predict the crystal morphology. The framework developed here utilizes the concept of intermolecular bond strength to discern the crystal morphology. Fourier transform IR, NMR and high-resolution mass spectrometry analytical techniques were used for the identification of functional groups and confirmation of the structure of the title compound. All of the intermolecular interactions present in the crystal structure, including the C—H...π, C—H...O and N—H...O interactions, were investigated and confirmed by molecular Hirshfeld surface analysis. From linear optical spectroscopy, the transmittance, optical band gap and UV cutoff wavelength were determined. The photoluminescence emission spectrum was recorded for a grown crystal. Dielectric measurements were performed at room temperature for various frequencies. The mechanical strength of the (001) plane of the title compound was measured using the Vickers micro-hardness technique. A piezo-coefficient of 15 pC N−1was found along the (001) plane of the title crystals. The thermal stability and melting point were also investigated. In addition, density functional theory simulations were used to calculate the optimized molecular geometry and the UV–vis spectrum, and to determine the highest occupied molecular orbital/lowest unoccupied molecular orbital energy gap. The results show thatN-(4-methylbenzyl)benzamide is a potential candidate for multifunctional optical and piezoelectric crystals.

Crystal structure studies, Hirshfeld surface analysis and DFT calculations of novel 1-[5-(4-methoxy-phenyl)-[1,3,4]oxadiazol-2-yl]-piperazine derivatives

Abstract Two new compounds 1-(4-tert-butyl-benzenesulfonyl)-4-[5-(4-methoxy-phenyl)-[1,3,4]oxadiazol-2-yl]-piperazine (I) and 1-[5-(4-methoxyphenyl)-[1,3,4]oxadiazol-2-yl]-4-[(4-bromo)benzene sulfonyl]-piperazine (II) of 1-[5-(4-methoxy-phenyl)-[1,3,4]oxadiazol-2-yl]- piperazine derivatives have been synthesized and the structures were confirmed by single crystal X-ray diffraction studies. The computational density functional theory (DFT) calculations have been carried out to shed light on reactive sites for electrophilic and nucleophilic nature of the molecules. Both the compounds were crystallized in the monoclinic crystal system, in P21/n space group wherein the piperazine ring in both the structures adopts a chair conformation. Both the compounds I and II exhibit intermolecular hydrogen bonds of the type C—H…O and contribute to the crystal packing. Further, the molecular Hirshfeld surface analysis was carried out which reveals the nature of intermolecular contacts, the fingerprint plot provides the information about the percentage contribution and revealed that the H…H (54.7% for compound I and 40.2% for compound II) interactions has the major contribution.

Exploring potent ligand for proteins: insights from knowledge-based scoring functions and molecular interaction energies

Two different scoring functions, Hirshfeld fingerprint-based scoring (HFBS) and molecular operating environment (MOE), and the kernel energy method (KEM) along with counterpoise (CP)-corrected approach were used to estimate the binding energies of protein–ligand complexes and tested against a series of inhibitors of human aldose reductase enzyme. The new scoring function, HFBS, is based on Hirshfeld fingerprints, which are 2D histogram plots of the distances from the molecular Hirshfeld surface to the nearest atomic nuclei inside versus outside the surface and are highly sensitive to the immediate environment of the molecule. The Hirshfeld surface plotted over the ligand molecule helped to visualize the contacts with the active site residues and solvents, which were then taken into account for interaction energy calculations. Application of KEM-assisted CP-corrected approach facilitated an efficient way of calculating interaction energies in protein complex systems. Interaction energies calculated using MP2/6-31G(d) level of theory allowed us to rank the ligands by potency. We find that both the KEM-assisted CP-corrected interaction energies and the scoring functions used here predict comparable rankings for the strength of binding of the series of ligands as docked to the active site of the protein, which are also in good agreement with the experimental binding affinities in this case.

Supramolecular architecture based on [Fe(CN)6]3− metallotectons and melaminium synthons

Assembly involving [Fe(CN)6]3− metallotectons as building units and melaminium organic cation has been envisioned in order to elaborate a hybrid supramolecular based on ionic H-bonds with formula {(H-mel)4[Fe(CN)6]Cl} (H-mel+: melaminium cation). The compound has been prepared by diffusion method and characterized by single-crystal X-ray diffraction, EDX analysis, and Raman-IR spectroscopies with assignment from ab initio calculations. The melaminium exhibit self cationic coupling with cyclic hydrogen bonds to give a one dimensional {[H-mel]+}∝ synthon. Therefore, these cationic ribbons are inter-linked via hydrogen bonds by the anionic tectons [Fe(CN)6]3− and chlorine anion resulting on a 3D network. Molecular hirshfeld surfaces revealed that the crystal structure has been supported mainly by NH⋯N and NH⋯Cl intermolecular Hydrogen bonds and by favoured C⋯C and C⋯N weak interactions.

Invariom-based comparative electron density studies of iso-sildenafil and sildenafil

Abstract The title compounds have raised considerable medical and broad public interest in that sildenafil is used as an agent against male erectile dysfunction; iso-sildenafil is not in clinical use. A comparison of their structural and electronic properties therefore seems of interest. The electron densities of iso-sildenafil and the cationic and neutral forms of sildenafil were examined by the application of the invariom formalism relying on diffraction data reported in the literature. The electron-density distributions obtained were subjected to topological analysis using the quantum theory of atoms in molecules (QTAIM) formalism to yield bond topological and atomic properties. Moreover, molecular Hirshfeld surfaces and electrostatic potentials (ESPs) were calculated. A number of structural and electronic differences were thus identified between sildenafil and the iso-analog. In both sildenafil structures, the phenyl ring and the pyrazolopyrimidine fragment are practically coplanar (planar conformation), whereas in the iso-analog they exhibit an angle of 44° (inclined form). Related to differences in molecular structure are completely different hydrogen bonding patterns and differences in the ESPs, the latter ones being influenced by different methylation at the pyrazolopyrimidine fragment. Iso-sildenafil is present as a hydrogen-bond dimer in the crystal, and the ESP of this dimer is dominated by a surrounding positive potential.

Mono- and binuclear copper(II) complexes of the bipyridine ligand: Structural, electrochemical and biological studies

The copper(II) complexes [Cu(bpy)2(ClO4)](ClO4) (1), [Cu(bpy)2(Cl)](ClO4) (2), [Cu(bpy)2(CH3COO)](ClO4) (3), [Cu2(bpy)2(μ-OH)2(μ-ClO4)2] (4) and [Cu2(bpy)2(μ-OH)(μ-H2O)(μ-CH3COO)](ClO4)2 (5) (where bpy=2,2′-bipyridine) have been synthesized and characterized by single crystal analysis, elemental analysis and spectroscopic methods. Complexes 2 and 4 crystallize in the monoclinic P21/n and C2/m space groups respectively, and the other complexes crystallize in the triclinic P1¯ space group. The molecular Hirshfeld surfaces and fingerprint plots of the complexes were investigated. Complexes 1–3 exhibit one quasi-reversible and complexes 4 and 5 exhibit two quasi-reversible redox cyclic voltammetric responses near the cathodic region in DMF. Binding studies of the complexes with BSA and ctDNA showed good binding affinity. Cleavage of pBR322 DNA by the complexes shows efficient oxidative cleavage in the presence of MPA through the formation of singlet oxygen. The complexes were also screened for their antimicrobial activities, which indicated that the complexes exhibit a zone of inhibition like that of standard drugs.

Trinuclear {Sr[UO2L3]2(H2O)4} and pentanuclear {Sr[UO2L3]4}2−uranyl monocarboxylate complexes (L-acetate or n-butyrate ion)

Crystals of two acetate complexes, Cs2{Sr[UO2L3]4} (1) and [Sr(H2O)6][UO2L3]2{Sr(H2O)4[UO2L3]2}2 (2), and one n-butyrate complex, {Sr(H2O)4[UO2L3]2}·2H2O (3), of uranium(VI), where L is a corresponding monocarboxylate ion, were studied by means of FTIR spectroscopy and single crystal X-ray analysis. The structure of 1 contains pentanuclear anionic complexes, {Sr[UO2L3]4}2−, bonded in a three dimensional framework by electrostatic interactions with Cs+ cations. The structure of 2, in addition to ‘typical’ uranyl triacetate complexes of [UO2L3]− and [Sr(H2O)6]2+ cations, contains neutral trinuclear complexes, {Sr(H2O)4[UO2L3]2}. The structure of 3 with n-butyrate ions consists of neutral complexes of {Sr(H2O)4[UO2L3]2} and molecules of crystallized water. Analysis of intermolecular interactions in 2 and 3 by means of two independent approaches (molecular Voronoi–Dirichlet polyhedra and molecular Hirshfeld surfaces) revealed that discrete complex groups are connected with one another mostly due to H/O hydrogen bonds and H/H dispersion interactions. A dynamic balance among mono- and poly-nuclear complexes in aqueous solutions containing R2+ and [UO2L3]− ions is proposed. The effect of the alkyl chain and the nature of the R2+ cation on the balance is discussed.