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Abstract Electrochemical hydrogen evolution reaction (HER) refers to the process of generating hydrogen by splitting water molecules with applied external voltage on the active catalysts. HER reaction in the acidic medium can be studied by different mechanisms such as Volmer reaction (adsorption), Heyrovsky reaction (electrochemical desorption) or Tafel reaction (recombination). In this paper, facile hydrothermal methods are utilized to synthesis a high-performance metal-inorganic composite electrocatalyst, consisting of platinum nanoparticles (Pt) and molybdenum disulfide nanosheets (MoS2) with different platinum loading. The as-synthesized composite is further used as an electrocatalyst for HER. The as-synthesized Pt/Mo-90-modified glassy carbon electrode shows the best electrocatalytic performance than pure MoS2 nanosheets. It exhibits Pt-like performance with the lowest Tafel slope of 41 mV dec−1 and superior electrocatalytic stability in an acidic medium. According to this, the HER mechanism is related to the Volmer-Heyrovsky mechanism, where hydrogen adsorption and desorption occur in the two-step process. According to electrochemical impedance spectroscopy analysis, the presence of Pt nanoparticles enhanced the HER performance of the MoS2 nanosheets because of the increased number of charge carriers transport.

This paper reports the synthesis, characterization, anticancer screening and quantum chemical calculation of a tetradentate Schiff base 2,2'-((1E,1'E)-((2,2-dimethylpropane-1,3-diyl)bis- (azanylylidene))bis(methanylylidene))bis(4-fluorophenol) (L2F) and its Pd (II) complex (PdL2F). The compounds were characterized via UV-Visible, NMR, IR spectroscopy and single crystal x-ray diffraction. Density Functional Theory (DFT) and time-dependent DFT calculations in gas and solvent phases were carried out using B3LYP, B3P86, CAM-B3LYP and PBE0 hybrid functionals combined with LanL2DZ basis set. Complexation of L2F to form PdL2F was observed to cause a bathochromic shift of the maximum absorption bands of n-π* from 327 to 410 nm; an upfield shift for δ (HC = N) from 8.30 to 7.96 ppm and a decreased wavenumber for ν(C = N) from 1637 to 1616 cm-1. Overall, the UV-Vis, NMR and IR spectral data are relatively well reproduced through DFT and TD-DFT methods. L2F and PdL2F showed IC50 of 90.00 and 4.10 μg/mL, respectively, against human colorectal carcinoma (HCT116) cell lines, signifying increased anticancer activity upon complexation with Pd (II).

This paper reports the synthesis, characterisation and DFT analysis of an N,O bidentate Schiff base, ((E)-(4-methoxybenzylimino)methyl)phenol, (L1c) and its Ni(II) and Pd(II) complexes. The structures were elucidated via elemental analysis, UV–Visible, NMR, IR and single crystal X-ray diffraction. Complexation of L1c with Ni(II) and Pd(II) was observed to induce different degrees of bathochromic effect on n → π∗ and π → π∗ electronic transitions. A comparison of the experimental data of UV–Visible, NMR, IR and X-ray with those calculated using DFT and TD-DFT methods where five hybrid functionals were tested in gas, IEF-PCM and SS-PCM models was also carried out. The results show that the reproduction of maximum absorption bands n → π∗ and π → π∗ is strongly related to the tested hybrid functionals and solvatochromic effects. Relatively good concordance was obtained between experimental and calculated NMR chemical shifts, IR and X-ray parameters. A bioactivity evaluation against HCT116 and Escherichia coli displayed that the parent ligand L1c is a more superior anticancer and antibacterial agent than the positive controls of 5FU and gentamicin respectively. However, both complexes showed poor activity as anticancer agent and no activity observed against tested bacteria.

The asymmetric unit of the title complex, [Pd(C15H13FNO)2], contains one half of the molecule with the PdII cation lying on an inversion centre and is coordinated by the bidentate Schiff base anion. The geometry around the cationic PdII centre is distorted square planar, chelated by the imine N- and phenolate O-donor atoms of the two Schiff base ligands. The N- and O-donor atoms of the two ligands are mutually trans, with Pd—N and Pd—O bond lengths of 2.028 (2) and 1.9770 (18) Å, respectively. The fluorophenyl ring is tilted away from the coordination plane and makes a dihedral angle of 66.2 (2)° with the phenolate ring. In the crystal, molecules are linked into chains along the [101] direction by weak C—H...O hydrogen bonds. Weak π–π interactions with centroid–centroid distances of 4.079 (2) Å stack the molecules along c.

The asymmetric unit of the title complex, [Ni(C14H11FNO)2], contains one-half of the molecule with the NiII cation lying on an inversion centre coordinated by a bidentate Schiff base anion. The cationic NiII center is in a distorted square-planar coordination environment chelated by the imine N and phenolate O donor atoms of the two Schiff base ligands. The N and O donor atoms of the two ligands are mutually trans with Ni—N and Ni—O bond lengths of 1.9242 (10) and 1.8336 (9) Å, respectively. The fluorophenyl ring is almost orthogonal to the coordination plane and makes a dihedral angle of 82.98 (7)° with the phenolate ring. In the crystal, molecules are linked into screw chains by weak C—H...F hydrogen bonds. Additional C—H...π contacts arrange the molecules into sheets parallel to the ac plane.

The asymmetric unit of the title compound, [Ni(C15H14NO2)2], comprises an NiII cation, lying on an inversion centre, and a Schiff base anion that acts as a bidentate ligand. The NiII cation is in a square-planar coordination environment binding to the imine N and phenolate O atoms of the two Schiff base ligands. The N- and O-donor atoms of the two ligands are mutually trans, with Ni—N and Ni—O bond lengths of 1.9191 (11) and 1.8407 (9) Å, respectively. The plane of the methoxybenzene ring makes a dihedral angle of 84.92 (6)° with that of the phenolate ring. In the crystal, molecules are linked into screw chains by weak C—H...O hydrogen bonds. Additional C—H...O hydrogen bonds, together with C—H...π contacts, arrange the molecules into sheets parallel to the ac plane.

In the title complex, [Pd(C16H16NO2)2]·CHCl3, the PdII cation lies on an inversion center. One Cl atom of the CHCl3 solvent molecule lies on a twofold axis and the C—H group is disordered with equal occupancies about this axis with the other Cl atom in a general position with full occupancy. The PdII cation is four-coordinate and adopts a square-planar geometry via coordination of the imine N and phenolic O atoms of the two bidentate Schiff base anions. The N and O atoms of these ligands are mutually trans. The plane of the benzene ring makes a dihedral angle of 73.52 (10)° with that of the methoxyphenolate ring. In the crystal, molecules of the PdII complex are arranged into sheets parallel to the ac plane, and the chloroform solvent molecules are located in the interstitial areas between the complex molecules. Weak intermolecular C—H...O and C—H...π interactions stabilize the packing.

In the title compound, C25H26N2O4·CHCl3, the aromatic rings of the iminomethyl-6-methoxyphenol fragments make dihedral angles of 58.33 (6) and 87.74 (6)° with the central benzene ring. The molecular conformation is stabilized by intramolecular O—H...N hydrogen bonds. In the crystal, an intermolecular C—H...O hydrogen bond involving the chloroform solvent molecule is observed. The crystal packing is further stabilized by π–π stacking interactions [centroid–centroid distances = 3.739 (3)–3.776 (3) Å] between the benzene rings of centrosymmetrically related molecules.

In the title compound, [Ni(C15H13FNO2)2], the NiII atom is tetracoordinated by two N atoms and two O atoms from two 2-[(4-fluorobenzyl)iminomethyl]-6-methoxyphenolate ligands in a square-planar geometry. The two N atoms and two O atoms around the NiII atom are trans to each other, as the NiII atom lies on an inversion centre. In the fluorophenyl group, five C atoms and an F atom are disordered over two sets of positions of equal occupancy. In the crystal, the complex molecules are linked via intermolecular C—H...F hydrogen bonds, forming chains along [001].

The title compound, C16H15NO4, exists as a zwitterion in the solid state, with the carboxylic acid group being deprotonated and the imine N atom being protonated. The molecule adopts an E configuration about the C=N double bond. The dihedral angle between the benzene rings is 46.34 (4)°. An intramolecular N—H...O hydrogen bond generates an S(6) ring motif. In the crystal, adjacent molecules are connected by intermolecular O—H...O and C—H...O hydrogen bonds, forming supramolecular ribbons along the a axis.

In the title compound, [Pd(C15H14NO)2], the Pd atom lies on an inversion center and is coordinated by two ligand molecules through the O and N atoms in a bidentate manner, forming a slightly distorted square-planar geometry. The dihedral angle between the two benzene rings in the ligand is 76.53 (19)°. The molecular packing is stablized by C—H...O and C—H...π interactions.

The title Schiff base compound, C14H12BrClN2O, exists in an E configuration with respect to the central C=N double bond. The amino group adopts a pyramidal configuration. The dihedral angle between the two benzene rings is 76.88 (10)° and an intramolecular O—H...N hydrogen bond forms a six-membered ring, generating an S(6) ring motif. In the crystal structure, molecules are linked into chains along [010] via N—H...O hydrogen bonds. The presence of π–π interactions [centroid–centroid distance = 3.6244 (12) Å] further stabilizes the crystal structure.

The title compound, C22H19ClN2O4, has the appearance of a warped butterfly. One 2-hydroxy-3-methoxybenzylideneamino fragment is planar [with a maximum deviation of 0.056 (3) Å] and forms a dihedral angle of 9.85 (9)° with the central benzene ring. The other fragment is not planar; however, the methoxyphenol group is planar [with the maximum deviation of 0.033 (2) Å] and makes a dihedral angle of 41.7 (3)° with the central benzene ring. The molecule is stabilized by intramolecular O—H...N hydrogen bonding. The crystal structure is stabilized by weak intermolecular C—H...O hydrogen bonding and C—H...π interactions.

Anew series of7V,0-bidentate ligands, LI, L2, L3 and L4, and their Pd(II) complexes, PdLl, PdL2, PdL3 and PdL4 have been synthesised and characterised using various physico-chemical techniques, namely elemental analyses, IR and 1H and 13C NMR spectroscopies, and conductivity analysis. The molecular geometries of PdL2 and PdL4 have been elucidated through single crystal X-ray crystallography revealing 2:1 molar equivalence of ligand: Pd with the Schiff bases that exhibited bidentate ligands behaviour, in which they coordinated through the phenolic O donor atoms and imine N. Upon complexation, the v(C=N) around 1629-1639 cm'1 andv(C-O) around 1251 to 1252 cm-1 shifted to lower frequencies by 4 to 23 cm 1. In this study, three parameters were chosen for the reaction conditions optimisation, which were types of bases, loadings for the catalyst, and temperatures of the reaction. Pd(II) complexes exhibited good catalytic activities for Heck coupling reaction with 100% conversion at 100°C within 12 hours of reaction time. Reducing the reaction temperature to 80°C reduced the conversion to a maximum of 80%. [ABSTRACT FROM AUTHOR]

Chemical industries are greatly assisted by catalysts; and commonly used catalysts for C-C formation reactions are mainly phosphine-based complexes which are air and moisture sensitive. New air stable Schiff base Pd(II) complexes have been synthesised, characterised and screened for their catalytic potential. This paper reports three ONNO Schiff bases, namely, L2C [2,2'-((l E ,l'E)-((2,2-dimethylpropane-l,3- diyl) bis (azanylylidene)) bis (methanylylidene)-) bis (4-chlorophenol)], L2M [2,2'-((lE ,l'E)-((2,2- dimethylpropane-l,3-diyl)bis(azanylyli-dene)) bis (methanylylidene)) bis (4-methylphenol)] and L2H [2,2'-((lE ,l'E) - ((2,2-dimethyl-propane-l,3-diyl)bis (azanylylidene)) bis (methanylylidene)) diphenol]. These were synthesised from 2,2-dimethyl-l,3-propanediamine and salicylaldehyde derivatives with Cl, CH3 and H at the meta position, respectively. The compounds were reacted with palladium(II) acetate yielding three palladium(II) complexes denoted as PdL2C, PdL2M and PdL2H. The structures of all compounds were elucidated through elemental analysis, 1H and 13C NMR, FTIR and melting point. The complexes were screened for catalytic activities in Sonogashira coupling reaction between iodobenzene and phenylacetylene in DMSO. PdL2H was found to be the most active catalyst with 87% iodobenzene conversion after 12 hours of reaction. [ABSTRACT FROM AUTHOR]

The syntheses of salicylideneaniline (LIa) and 4-hydroxybenzalaniline (Lib) was carried out via condensation reaction giving yields of 80.74% and 81.65% respectively. The compounds were characterised by physical and spectroscopic techniques, namely melting point, micro elemental analysis (C, H and N), 'H Nuclear Magnetic Resonance (NMR) and Infrared (IR) spectroscopy. The characteristic n(C=N) peaks were observed at 1615 cnr1 and 1575 cm'1 respectively. Chronoamperometry (CA) was employed to electrodeposit both compounds on mild steel at 0.1 M inhibitor concentration in 0.3 M NaOH at three different potentials, +0.8 V, +1.05 V and +1.7 V. Formation of yellow imine films was observed on the mild steel. The corrosion behaviour of coated and uncoated mild steel was studied using Linear Polarization Resistance (LPR) in 0.5 M NaCl. Coated mild steel showed better corrosion resistance and with the highest inhibition efficiency of 90.34%, LI a provides a better protection against corrosion for mild steel than Lib. [ABSTRACT FROM AUTHOR]

A mononuclear and new tetranuclear metal complexes of Zn(II) with Schiff base ligands LI and L2 respectively, were synthesised. LI was obtained through the condensation of salicylaldehyde with orthophenylenediamine while L2 was the product of reaction between of ortho-\anillin with 2,4,6-trimethylm- phenylenediamine. The ligands and complexes were characterised via elemental analysis, melting point, IR and NMR spectroscopy. The shifting of v(C=N), v(C-OH) and v(0-CH3) infrared peaks upon coordination with Zn(II) indicated that these three moieties play a significant role in the complexation. It was found that LI acted as tetradentate ligand, coordinating with Zn(II) centres through phenolic oxygen and imine nitrogen. The ligand L2 acted as a hexadentate ligand, bonded to metal via phenolic oxygen, imine nitrogen and methoxy oxygen, where four Zn(II) centres formed bridges to connect two ligands. [ABSTRACT FROM AUTHOR]

Two imines of different molecular sizes namely 3-(phenylimino) indolin-2-one (PII) and 3,3- (1,4-phenylenebis (azan-l-yl-l-ylidene) diindolin-2-one (PDI) were investigated for their corrosion inhibition on mild steel in 1 M HC1 solution using electrochemical impedance spectroscopy (EIS). The bigger molecule PDI containing double the amount of isatin moiety exhibited higher inhibition efficiency of 87.3% while PII that contained monoisatin moiety showed a lower inhibition efficiency of 74.8%. Both compounds had an increase in inhibition efficiencies percentage as concentrations increased. Density functional theory (DFT) was used to detennine the correlation between the corrosion inhibition efficiency and electronic parameters. The DFT calculations indicated that the corrosion inhibition efficiency was mainly dependant on the frontier orbital energy gap and the chemical softness/hardness of the imines. [ABSTRACT FROM AUTHOR]