Surface Analysis Studies Research Articles

Wettability alteration of calcite rock from gas- repellent to gas-wet using a fluorinated nanofluid: A surface analysis study

Wettability alteration analysis form gas-repellent to gas-wet with the aid of chemical agents has been subjected of numerous studies. However, fundamental understanding of the effect of surface tension of liquid on repellency strength, the change in the intermolecular forces due to the adsorption of nanoparticles onto the rock surfaces, and exposure of treated rock in brine are not well discussed in the available literature. In this study, X-ray diffraction, Atomic Force Microscopy, scanning electron microscopy, and energy-dispersive X-ray spectroscopy were applied to characterize the treated and fresh samples. Dynamic and static contact angle measurements were then combined with six methods of surface free energy analysis; Neumann, Zisman plot, geometric, harmonic, acid-base, and Chibowski, to model liquid intermolecular forces effect on contact angle and to calculate the surface forces. Surface characterization results showed that adsorbed fluorine and silicon elements onto the calcite surface due to treatment in the nanofluid resulted in an increment of surface roughness. The weight percent of 0.93 and 1.22 and surface fraction of 0.265 and 0.014 for adsorbed Fluorine and Silicon were observed, respectively. A reduction for surface free energy in the range of 20–35 mN/m was observed for different applied approaches. The results of geometric, harmonic, and acid-base models indicated that calcite intrinsically has a mildly polar surface with a negative surface charge. It was revealed that the magnitude of the dispersive component was nearly 1.6 times greater than the polar component. For the treated surfaces, the geometric, harmonic, and acid-base methods showed a high reduction in the polar force of surface (<4 mN/m), which implied that the dispersive forces of the surfaces were dominant (~13 mN/m). The acid-base model estimated a negative surface charge for calcite and treated calcite. Also, a reversible reduction in water repellency due to exposure of treated samples in brine was observed.

New (N,O) Schiff bases of 2-hydroxynaphthaldehyde and their homoleptic Zn(II) and Cu(II) complexes – Synthesis, structural characterization, Hirshfeld surface analysis and antimicrobial activity studies

New Schiff bases L1H and L2H have been synthesized by condensation of 2-hydroxynaphthaldehyde with 2,3-dimethoxyaniline and 2-(3,4-dimethoxyphenyl) ethan-1-amine respectively. Their complexes are [M(L1-2)2] where, M: Zn (1 and 2) and Cu (3 and 4). They were prepared by the reaction of ligands with Zn(OAc)2·2H2O and CuCl2·6H2O in the molar ratios of 2:1 (L:M). Both ligands and their four complexes were characterized by CHN analysis, FT-IR and UV–Visible spectroscopy. In addition, the ligands and complexes 1 and 2 were characterized by 1H and 13C{1H} NMR spectroscopy. The molecular structures of the four compounds L1H, L2H, 3 and 4 were determined by single crystal X-ray diffraction. In all complexes, the deprotonated (L1 and L2) ligands coordinated to M(II) ions hence, acting as bidentate (NO) donors using imine nitrogen (>CN) and phenolate oxygen (PhO−) atoms. The ligands (L1H and L2H) and complexes (1–4) were screened in different dosages for antimicrobial activity by the agar well diffusion method against the pathogenic bacterial strains E. coli and E. aerogenes and a fungal strain C. albicans. These compounds showed moderate antibacterial activity but, significant antifungal activity. The antimicrobial activity results also revealed that the metal complexes were more active than their corresponding free ligands. The zinc complexes (1–2) showed higher antibacterial activity than copper ones. Surprisingly, the compounds related to 3,4-dimethoxy aniline (L1H, 1 and 3) showed higher activity than those containing 2-(3,4-dimethoxyphenyl)ethan-1-amine (L2H, 2 and 4) especially towards E. coli. Unlike the antibacterial activity, the antifungal activity of L1H was higher than that of its complexes and that of L2H was lower than that of L1H as well as its complexes.

Cold atmospheric pressure plasma treatment for adhesion improvement on polypropylene surfaces

Cold atmospheric pressure plasma from a plasma jet was used to improve the adhesion properties of polypropylene (PP). Differences in adhesion were at first observed for either air or N2 as process gas, tested on a PP-acrylic pressure sensitive adhesive (PSA) model system. For a deeper understanding changes in the surface chemistry and topography on PP after plasma jet treatment, using several different O2/N2 mixtures, were investigated in a comprehensive surface analytical study. Independent of the gas composition a majority of plasma induced polar groups exist as water soluble low molecular weight oxidized material (LMWOM), located within the first few nanometers. Consequently, the observed changes in the surface chemistry for various process gas compositions are mainly attributed to differences in the formed LMWOM. However, these chemical changes indicated also differences in the interaction mechanism of plasma reactive species with the polymer surface and therefore, in the resulting plasma-polymer etching process. Hence, significant changes in the topography have been observed for different process gas compositions, which could be reliably correlated with the obtained adhesion results.

Crystal structure, Hirshfeld surface analysis and DFT studies of (E)-4-methyl-2-{[(2-methyl-3-nitro-phen-yl)imino]-meth-yl}phenol.

The title compound, C15H14N2O3, was prepared by condensation of 2-hy-droxy-5-methyl-benzaldehyde and 2-methyl-3-nitro-phenyl-amine in ethanol. The configuration of the C=N bond is E. An intra-molecular O-H⋯N hydrogen bond is present, forming an S(6) ring motif and inducing the phenol ring and the Schiff base to be nearly coplanar [C-C-N-C torsion angle of 178.53 (13)°]. In the crystal, mol-ecules are linked by C-H⋯O inter-actions, forming chains along the b-axis direction. The Hirshfeld surface analysis indicates that the most important contributions to the crystal packing are from H⋯H (37.2%), C⋯H (30.7%) and O⋯H (24.9%) inter-actions. The gas phase density functional theory (DFT) optimized structure at the B3LYP/ 6-311 G(d,p) level is compared to the experimentally determined mol-ecular structure in the solid state. The HOMO-LUMO behaviour was elucidated to determine the energy gap.

Cinnamaldehyde-modified chitosan as a bio-derived corrosion inhibitor for acid pickling of copper: Microwave synthesis, experimental and computational study

Chitosan (CS) was cross-linked using cinnamaldehyde (Cinn) in a single step procedure following microwave irradiation to produce cinnamaldehyde-modified chitosan (Cinn-CS). The synthesized Cinn-CS was used as a novel corrosion inhibitor for copper in 1 M hydrochloric acid. A comprehensive electrochemical investigation using the impedance measurements, and potentiodynamic polarization was undertaken, supported with surface analysis and computational studies. The inhibitor Cinn-CS functioned by adsorption on the copper surface and showed an inhibition efficiency of >89% at a dose of 1000 mgL−1. The charge transfer resistance showed a rise with increase in inhibitor dosage to the corrosive medium, and the corrosion currents showed a significant decrease with the addition of the inhibitor. The Cinn-CS displayed a mixed type of inhibition performance with cathodic nature. The study of the copper surface using scanning electron microscopy depicted a considerably smooth morphology in the presence of the adsorbed Cinn-CS. The computational studies indicated that the Cinn-CS Schiff base shows better adsorption behavior compared to the parent molecules of chitosan and cinnamaldehyde and can show an inhibition performance in the neutral, and the protonated form.

Electrochemical behaviour of Ni-Ti (Super elastic) alloy in artificial saliva in the presence of phexin

Corrosion resistance of super elastic Ni-Ti alloy has been evaluated in artificial saliva in presence and absence of antibiotic sulfa drugs like phexin and almox 500. The amounts of drugs were taken in 50 ppm and 100 ppm amounts and they were added to the artificial saliva in which the metal is immersed. They were allowed to settle down for 1 day and 30 days batch at 37 ± 0.1 °C. Electrochemical techniques such as Potentio dynamic polarization and AC impedance studies were carried out to investigate the corrosion behaviour of Ni-Ti alloy. The surface analysis study, SEM technique was also used to analyze the surface of the alloys in absence and presence of the drugs. And also to investigate the corrosion behaviour of this metal alloy surface.

Study of adsorption mechanism of chalcone derivatives on mild steel-sulfuric acid interface

Chalcone derivatives namely: (E)-3-(4-methoxyphenyl)-1-(p-tolyl)prop-2-en-1-one (MTP), (E)-1,3-di-p-tolylprop-2-en-1-one (DTP), and (E)-3-(4-(diethylamino)phenyl)-1-(p-tolyl)prop-2-en-1-one (DEP) were synthesized and characterized by nuclear magnetic resonance (NMR), Mass spectroscopy (MS) and Infrared spectroscopy (IR). The corrosion mitigation of mild steel (MS) in 0.5 M H2SO4 by these compounds has been investigated by weight loss, electrochemical technique, surface analysis and theoretical studies. The investigations were performed at three optimum concentrations (10−4, 10−5, and 10−6 M) at three temperatures (298, 313 and 328 K) The weight loss Potentiodyanamic polarization (PDP) and Electrochemical impedance spectroscopy (EIS) measurements showed that DEP has the maximum inhibition efficiency (93.3% for highest concentration i.e. 10−4 M) at 298 K among all three inhibitors. The inhibition efficiencies vary directly and inversely with respect to concentration and temperature respectively for all the additives. Potentiodynamic polarization (PDP) measurements revealed that the chalcones are mixed-type corrosion inhibitors and obeyed the Langmuir adsorption isotherms. Electrochemical impedance spectroscopy (EIS) technique further proposes that the inhibitor molecules mitigate corrosion process by adsorbing at the metal/electrolyte interfaces. Further the adsorption of chalcones at the metallic surface was supplemented by SEM and AFM studies where the decreased surface roughness of the inhibited mild steel specimens was observed as compared to the uninhibited specimen. Several thermodynamic parameters (ΔGads0,ΔHads0andΔSads0), DFT and MD theoretical parameters were calculated to explain the adsorption behaviour of these compounds on specimen surface.

Crystal structure, Hirshfeld surface analysis and DFT studies of (E)-2-{[(3-chloro-4-methyl-phen-yl)imino]-meth-yl}-4-methyl-phenol.

The title compound, C15H14ClNO, was synthesized by condensation reaction of 2-hy-droxy-5-methyl-benzaldehyde and 3-chloro-4-methyl-aniline, and crystallizes in the monoclinic space group P21/c. The 3-chloro-benzene ring is inclined to the phenol ring by 9.38 (11)°. The configuration about the C=N bond is E and an intra-molecular O-H⋯N hydrogen bond forms an S(6) ring motif. The Hirshfeld surface analysis of the crystal structure indicates that the most important contributions for the packing arrangement are from H⋯H (43.8%) and C⋯H/H⋯C (26.7%) inter-actions. The density functional theory (DFT) optimized structure at the B3LYP/ 6-311 G(d,p) level is compared with the experimentally determined mol-ecular structure and the HOMO-LUMO energy gap is provided.

Crystal structure, Hirshfeld surface analysis and DFT studies of 4-methyl-2-({[4-(tri-fluoro-meth-yl)phen-yl]imino}-meth-yl)phenol.

The title compound, C15H12F3NO, crystallizes with one mol-ecule in the asymmetric unit. The configuration of the C=N bond is E and there is an intra-molecular O-H⋯N hydrogen bond present, forming an S(6) ring motif. The dihedral angle between the mean planes of the phenol and the 4-tri-fluoro-methyl-phenyl rings is 44.77 (3)°. In the crystal, mol-ecules are linked by C-H⋯O inter-actions, forming polymeric chains extending along the a-axis direction. The Hirshfeld surface analysis indicates that the most important contributions to the crystal packing are from C⋯H/H⋯C (29.2%), H⋯H (28.6%), F⋯H/H⋯F (25.6%), O⋯H/H⋯O (5.7%) and F⋯F (4.6%) inter-actions. The density functional theory (DFT) optimized structure at the B3LYP/6-311 G(d,p) level is compared with the experimentally determined mol-ecular structure in the solid state. The HOMO-LUMO behaviour was elucidated to determine the energy gap. The crystal studied was refined as an inversion twin.

Surface and bulk characterization of reservoir and cap-rocks: Past, present, and future

Geologic formations provide potentially some of the largest volume capacities for CO2 storage or sequestration. Potential storage sites can be deep saline aquifers, depleted oil reservoirs, and coal seams, surrounded by sealing layers to prevent CO2 from leaking. It is therefore critical to understand mechanisms contributing to CO2 trapping and CO2 leaks. Both phenomena are governed by reactions at the interfaces of the reservoir and cap-rocks and are controlled by the complex chemistry and pore structures of rocks. Mechanisms at the macroscale are affected by the processes occurring at the nanoscale. This review highlights the necessity of multitechnique, multiscale characterization of rocks and points to the importance of surface analysis and surface science studies. Two shale rocks (seals) from Niobrara and Agardhfjellet formations with complex surface chemistry are used as examples throughout the paper. Typically, evaluation of rocks with x-ray diffraction, thermogravimetric analysis, Rock-Eval pyrolysis, gas adsorption, and electron microscopy combined with energy dispersive x-ray spectroscopy is conducted to provide valuable information about the bulk mineralogy, elemental composition, pore volume, and adsorbed species on the sample surface. These studies are necessary prior to designing surface sensitive experiments with x-ray photoelectron spectroscopy (XPS), guiding both sample preparation and sample analysis. XPS has been widely used to study the surface composition of rocks during the investigations of their fine-scale wettability, and the main findings are highlighted here. This paper also reviews the existing literature on ambient-pressure XPS, which provides new opportunities to study in situ chemical alteration due to interactions with CO2 and offers recommendations for adapting this technique to study rock-fluid interactions, allowing for the identification of fundamental interactions during CO2 sequestration and guide selection of formation sites for improved storage.

Synthesis, Hirshfeld surface analysis, DFT calculations, photoluminescence, spectroscopic and second order non linear optical studies on ammonium hydrogensquarate squaric acid monohydrate crystal

A new nonlinear optical material, Ammonium hydrogensquarate squaric acid monohydrate (AHSAM) has been synthesized. Single crystals of AHSAM have been grown successfully by slow evaporation solution technique (SEST). The grown AHSAM crystals have been subjected to Single crystal X-ray diffraction analysis (XRD), Hirshfeld surface analysis, Fourier transform infrared spectroscopy (FT-IR), Fourier transform Raman (FT-R) spectroscopy, Calculated and experimental ultraviolet–visible spectral analysis, Photoluminescence, Microhardness and second harmonic generation (SHG). From X-ray diffraction studies it shows that the structure belongs to monoclinic structure with space group C2/c. Hirshfeld surface analysis used to clarify the intra and intermolecular interactions in a visual manner. The molecular geometries are compared with AM1, HF and Density Functional Theory calculations and it shows good agreement with experimental data. The Frontier molecular orbital energy gap is found by TD-DFT method with HOMO-LUMO calculation. The second order NLO studies for AHSAM crystal is done by Kurtz and Perry powder technique.

2-[(1E)-[(Z)-2-({[(1Z)-[(E)-2-[(2-Hydroxyphenyl)methylidene]hydrazin-1-ylidene]({[(4-methylphenyl)methyl]sulfanyl})methyl]disulfanyl}({[(4-methylphenyl)methyl]sulfanyl})methylidene)hydrazin-1-ylidene]methyl]phenol: crystal structure, Hirshfeld surface analysis and computational study

The complete mol-ecule of the title hydrazine carbodi-thio-ate derivative, C32H30N4O2S4, is generated by a crystallographic twofold axis that bis-ects the di-sulfide bond. The mol-ecule is twisted about this bond with the C-S-S-C torsion angle of 90.70 (8)° indicating an orthogonal relationship between the symmetry-related halves of the mol-ecule. The conformation about the imine bond [1.282 (2) Å] is E and there is limited delocalization of π-electron density over the CN2C residue as there is a twist about the N-N bond [C-N-N-C torsion angle = -166.57 (15)°]. An intra-molecular hydroxyl-O-H⋯N(imine) hydrogen bond closes an S(6) loop. In the crystal, methyl-ene-C-H⋯π(tol-yl) contacts assemble mol-ecules into a supra-molecular layer propagating in the ab plane: the layers stack without directional inter-actions between them. The analysis of the calculated Hirshfeld surfaces confirm the importance of H⋯H contacts, which contribute 46.7% of all contacts followed by H⋯C/C⋯H contacts [25.5%] reflecting, in part, the C-H⋯π(tol-yl) contacts. The calculation of the inter-action energies confirm the importance of the dispersion term and the influence of the stabilizing H⋯H contacts in the inter-layer region.

Synthesis, crystal structure, hirshfeld surface analysis, spectroscopic, biological and first-principles studies of novel aminocoumarins

Two novel aminocoumarins 3-(1-(2 aminophenylamino) ethylidene)chromene-2,4‑dione, noted (1) and 3-(1-(2–1-(2, 4-dioxochromene-3-ylidene) ethylamino)phenylamino) ethylidene) chromene -2,4‑dione,noted (2), were synthesized from 3-acetyl-4-hydroxycoumarin and ortho-phenylenediamine in absolute ethanol and characterized by spectroscopies methods (FT-IR, UV–vis and fluorescence). The crystal structures of the mentioned compounds were solved from single-crystal diffraction data at low temperature. The compound (1) crystallizes in the orthorhombic system with space group Iba2 while (2) is monoclinic with space group P21/c. Hirshfeld surface analysis indicates the presence of the π-π stacking in the aminocoumarin structures with the contribution of 7.8% for (1) and 8.7% for (2) of the total Hirshfeld area. The optimized DFT geometries (B3PW91/6–311 G (2df, p)) and the spectral simulations agree well with the experimental data. Theoretical reactivity behavior was assessed, taking into account HOMO-LUMO diagrams and Molecular Electrostatic Potential maps. The two aminocoumarins derivatives have fluorescence properties. Analysis of the photoluminescence spectra shows that the emission intensity is high for the solutions of the two compounds in polar aprotic solvents (DMSO, DMF). The aminocoumarins were monitored for antimicrobial activity using the disk diffusion method. The coumarin (1) is effective against S. aureus (gram-positive bacteria) and S. typhy (gram-negative bacteria), but the coumarin (2) showed markedly weak antibacterial activity.

Synthesis, Hirshfeld Surface Analysis and DFT Studies of Ethano-tetracyclic Tetracene Derivatives

The syntheses of ethano-tetracyclic tetracenes; 14-cyano-5,12-dihydro-5,12-ethanotetracen-14-yl acetate (2a and 2b) and 5,12-dihydro-5,12-ethanotetracen-13-one (3) are reported. The tetracenes isomers 2a and 2b are equally obtained via DA reaction and the tetracene 3 is synthesized from the alkaline hydrolysis of 2a and 2b. The DFT calculations of tetracenes isomers 2a and 2b are performed and gave good agreement to the experimental result. The structure of tetracene 3 is elucidated by X-ray technique and its intermolecular interactions are determined by Hirshfeld surface analysis. The crystal system of tetracene 3 is orthorhombic with a Pca21 space group; a = 28.589 (5) A, b = 6.5023 (14) A, c = 7.5101 (11) A, V = 1396.1 (4) A3, Z = 4. This is the first report describing syntheses Ethano-tetracyclic tetracenes 2a, 2b, 3. DFT studies were used to explain the reaction regioselectivity of the two tetracene isomers 2a, 2b. The x-ray is performed to elucidate the structure of tetracene 3. Hirshfeld surface analysis is performed to determine the intermolecular interactions in the crystal structure of the tetracene 3.

DFT calculations, Hirshfeld surface analysis and docking studies of 3-anisaldehyde thiosemicarbazone

We report herein the synthesis, quantum chemical electronic structure, Hirshfeld surface and molecular docking studies of 3-anisaldehyde thiosemicarbazone (I). The compound has been characterized by NMR (1H, 13C) and IR spectroscopy. Hirshfeld surface analysis has been performed to understand the intermolecular interactions. The quantum chemical calculations show good consistency between the predicted and experimental parameters. Molecular docking studies of I with two different cancer target enzymes exhibit higher binding energy than its ortho substituted analogue. Synthesis, spectroscopic characterization, quantum chemical calculations, Hirshfeld surface analysis and molecular docking studies have been investigated for the compound 3-anisaldehyde thiosemicarbazone (I). The theoretical results gave a better understanding of the molecular interactions and the docking results suggest I can be used for in vitro anticancer study.

Crystal structure, Hirshfeld surface analysis and DFT studies of 2-[(2-hy-droxy-5-methyl-benzyl-idene)amino]-benzo-nitrile.

The title compound, C15H12N2O, was synthesized by condensation reaction of 2-hy-droxy-5-methyl-benzaldehyde and 2-amino-benzo-nitrile, and crystallizes in the ortho-rhom-bic space group Pbca. The phenol ring is inclined to the benzo-nitrile ring by 25.65 (3)°. The configuration about the C=N bond is E, stabilized by a strong intra-molecular O-H⋯N hydrogen bond that forms an S(6) ring motif. In the crystal, C-H⋯O and C-H⋯N inter-actions lead to the formation of sheets perpendicular to the a axis. C-H⋯π inter-actions, forming polymeric chains along the a-axis direction, connect these sheets into a three-dimensional network. A Hirshfeld surface analysis indicates that the most important contributions for the packing arrangement are from H⋯H and C⋯H/H⋯C inter-actions. The density functional theory (DFT) optimized structure at the B3LYP/6-311 G(d,p) level is compared with the experimentally determined mol-ecular structure and the HOMO-LUMO energy gap is given.

Synthesis, characterization, crystal structures, Hirshfeld surface analysis and DFT computational studies of new Schiff Bases derived from Phenylhydrazine

In this research, four novel ligands were synthesized from hydrazine derivatives. The hydrazine compounds via reacting 2, 4-dinitrophenylhydrazine with 2-hydroxy-4-methoxybenzaldehyde (HL1), 2-hydroxy- 5-bromobenzaldehyde (HL2), 2-hydroxy-naphtaldehyde (HL3) and 4-nitrophenylhydrazine with 2-hydroxy-4-methoxybenzaldehyde (HL4) were synthesized, characterized using FT-IR, Raman and UV–Vis spectrum and it structure were confirmed by X-ray diffraction studies. Novel compounds were recovered to crystallize the systems in monoclinic, orthorhombic, triclinic and monoclinic, crystal structures with P21/n, Pbcn, P-1, and P21/c space groups in ligands (HL1), (HL2), (HL3) and (HL4), respectively. Afterwards, the present study compared the experimental parameters in the UV–Vis and FT-IR spectra with the theoretical values.The results showed that at B3LYP/6-311 + G (d, p) level, DFT was able to properly reproduce the structure of the title ligands. Moreover, Hirshfeld surface (HS) analyses, particularly dnorm surface and FPs (fingerprint plots), were employed to decode intermolecular interactions in the crystal system and contribution of component units in the construction of the 3D architecture. These examinations presented the general description of such inter-contact interactions by means of an attractive graphical approach by 3D Hirshfeld surfaces and 2D fingerprint plots derived from the surfaces. Hirshfeld surface analysis indicated the dominant role of various hydrogen intermolecular interactions such as H⋯H, C⋯H/H⋯C and O⋯H/H⋯O for all compounds and H⋯Br contacts for the HL2 (because of the) into the crystal packing which are discussed.

Unexpected synthesis of novel 2-pyrone derivatives: crystal structures, Hirshfeld surface analysis and computational studies

Here we report synthesis of three new compounds namely, 1-acetyl-1H-benzimidazolo-2(3H)-one (I), N-(5-acetyl-6-methyl-2-oxo-2H-pyran-4-yl)-N-(2-acetamidophenyl)acetamide (II) and N-(2-acetamidophenyl)-N-2-oxo-2H-pyran-4-yl)acetamide (III) have been synthesized and characterized by single crystal X-ray diffraction. Compounds I and II crystallize in the monoclinic space groups P21/n, and P21/c, respectively, while III crystallizes in the triclinic space group P-1. The theoretical parameters of I–III have been calculated through density functional theory (DFT) by using the hybrid functional B3LYP and basis set 6-311++G**. These theoretical parameters have been compared with the experimental ones obtained by XRD. The significant intermolecular interactions arising in crystal packing are rationalized by means of the Hirshfeld surface analysis method. The major intermolecular contacts in the Hirshfeld surfaces of I–III are from H…H contacts. In addition, binding modes of I–III within Tyrosine-protein kinase JAK2 were investigated using molecular docking and molecular dynamics simulation studies. Communicated by Ramaswamy H. Sarma

Synthesis of new α-amino-1H indazolyl-phosphonate derivatives: Crystal structure, Hirshfeld surface analysis and DFT studies

A new α-amino-1H Indazolyl-phosphonates derivative 3a–e were synthesized and subjected to solid state characterization by single-crystal X-ray diffraction analysis, and to study their NMR and Hirshfeld surface analysis. The P atom exhibits tetrahedral geometry involving two O-ethyl groups, a C atom and a double-bonded O atom. The P–C bond has an approximately staggered conformation, with the aniline and substituted groups in gauche positions with respect to the PO double bond. The molecules are arranged as centrosymmetric or pseudocentrosymmetric dimers connected by two N–H⋯OP hydrogen bonds and also by C–H … π interaction in the case of structures 3a–e, which are responsible for the formation and stability of the molecular assemblies. Hirshfeld surface analysis (dnorm surface and two-dimensional (2D) fingerprint plots) revealed the nature of intermolecular contacts. The most important contributions for the crystal packing are from H⋯H, H⋯C/C⋯H, O⋯H/H⋯O, and H⋯N/N⋯H interactions. In addition, frontier molecular orbitals and Molecular Electrostatic Potential map of the compounds was produced by using the optimized structures.

Crystal structure, Hirshfeld surface analysis and DFT studies of (E)-4-methyl-2-{[(4-methyl-phen-yl)imino]-meth-yl}phenol.

In the title compound, C15H15NO, the configuration of the C=N bond of the Schiff base is E, and an intra-molecular O-H⋯N hydrogen bond is observed, forming an intra-molecular S(6) ring motif. The phenol ring is inclined by 45.73 (2)° from the plane of the aniline ring. In the crystal, mol-ecules are linked along the b axis by O-H⋯N and C-H⋯O hydrogen bonds, forming polymeric chains. The Hirshfeld surface analysis of the crystal structure indicates that the most important contributions for the packing arrangement are from H⋯H (56.9%) and H⋯C/C⋯H (31.2%) inter-actions. The density functional theory (DFT) optimized structure at the B3LYP/ 6-311 G(d,p) level is compared with the experimentally determined mol-ecular structure, and the HOMO-LUMO energy gap is provided. The crystal studied was refined as an inversion twin.