Water Oxidation by a Copper(II) Complex with 6,6'-Dihydroxy-2,2'-Bipyridine Ligand: Challenges and an Alternative Mechanism.

Recently, copper(II) complexes have been extensively investigated as oxygen-evolution reaction (OER) catalysts through a water-oxidation reaction. Herein, new findings regarding OER in the presence of a Cu(II) complex with 6,6'-dihydroxy-2,2'-bipyridine ligand are reported. Using scanning electron microscopy, energy dispersive spectrometry, X-ray diffraction, Raman spectroscopy, in situ visible microscopy, in situ visible spectroelectrochemistry, X-ray absorption spectroscopy, and electrochemistry, it is hypothesized that the film formed on the electrode's surface in the presence of this complex causes an appropriated matrix to produce Cu (hydr)oxide. The resulting Cu (hydr)oxide could be a candidate for OER catalysis. The formed film could form Cu (hydr)oxide and stabilize it. Thus, OER activity increases in the presence of this complex.

Water oxidation reaction in the presence of a dinuclear Mn(II)-semicarbohydrazone coordination compound.

Water splitting, producing of oxygen, and hydrogen molecules, is an essential reaction for clean energy resources and is one of the challenging reactions for artificial photosynthesis. The Mn4Ca cluster in photosystem II (PS-II) is responsible for water oxidation in natural photosynthesis. Due to this, water oxidation reaction by Mn coordination compounds is vital for mimicking the active core of the oxygen-evolving complex in PS-II. Here, a new dinuclear Mn(II)-semicarbohydrazone coordination compound, [Mn(HL)(µ-N3)Cl]2 (1), was synthesized and characterized by various methods. The structure of compound 1 was determined by single crystal X-ray analysis, which revealed the Mn(II) ions have distorted octahedral geometry as (MnN4OCl). This geometry is created by coordinating of oxygen and two nitrogen donor atoms from semicarbohydrazone ligand, two nitrogen atoms from azide bridges, and chloride anion. Compound 1 was used as a catalyst for electrochemical water oxidation, and the surface of the electrode after the reaction was investigated by scanning electron microscopy, energy dispersive spectrometry, and powder X-ray diffraction analyses. Linear sweep voltammetry (LSV) experiments revealed that the electrode containing 1 shows high activity for chemical water oxidation with an electrochemical overpotential as low as 377 mV. Although our findings showed that the carbon paste electrode in the presence of 1 is an efficient electrode for water oxidation, it could not withstand water oxidation catalysis under bulk electrolysis and finally converted to Mn oxide nanoparticles which were active for water oxidation along with compound 1.

Investigation of electrocatalytic activity of a new mononuclear Mn(II) complex for water oxidation in alkaline media.

Water splitting is a promising way to alleviate the energy crisis. In nature, water oxidation is done by a tetranuclear manganese cluster in photosystem II. Therefore, the study of water oxidation by Mn complexes is attractive in water splitting systems. In this report, a new mononuclear Mn(II) complex, MnL2 (HL = (E)-3-hydroxy-N'-(pyridin-2-ylmethylene)-2-naphthohydrazide) was prepared and characterized by spectroscopic techniques and single-crystal X-ray diffraction. Crystallographic analysis indicated that the geometry around the Mn(II) ion is distorted octahedral. The MnN4O2 coordination moiety is achieved by bounding of oxygen and two nitrogen donor atoms of two hydrazone ligands. The synthesized complex was also investigated for electrochemical water oxidation using electrochemical techniques, scanning electron microscopy, energy dispersive spectrometry, and PXRD analysis. Linear sweep voltammetry experiment showed that the modified carbon paste electrode by the complex displays high activity for water oxidation reaction with an overpotential of 565 mV at a current density of 10 mA cm-2 and Tafel slope of 105 mV dec-1 in an alkaline solution. It was found that the complex structure finally changes during the reaction and converts to Mn oxide nanoparticles which act as active catalytic species and oxidize the water.

Investigation of the Hg(II) biosorption from wastewater by using garlic plant and differential pulse voltammetry.

In this work, the bio sorption of mercury ion by garlic bio-adsorbent was studied. A batch and a continuous up-flow fixed-bed column system were used in this report. Differential pulse voltammetry was used to detecting the amount of mercury ion. Using Differential pulse voltammetry prevents the production of carcinogenic mercury vapor. In the batch system, various doses of bio-adsorbent were investigated. After that, the experimental data was fitted using Langmuir and Freundlich models. The experimental data were also fitted to the Thomas, Bohart-Adams, and Yan models for the continuous mode in a fixed bed of garlic bio-adsorbent. The maximum adsorption capacity estimated by the Thomas models was 23.5 mg g-1 and τ was 135.3 min. This adsorbent is also suitable for absorbing mercury from a real-life well water sample. It is renewable and can be used to absorb mercury several times.

Synthesis, Study, and Application of Pd(II) Hydrazone Complexes as the Emissive Components of Single-Layer Light-Emitting Electrochemical Cells.

For the first time, square planar Pd(II) complexes of hydrazone ligands have been investigated as the emissive components of light-emitting electrochemical cells (LECs). The neutral transition metal complex, [Pd(L1)2]·2CH3OH (1), (HL1 = (E)-N'-(phenyl(pyridin-2-yl)methylene)isonicotinhydrazide), was prepared and structurally characterized. Complex 1 displays quasireversible redox properties and is emissive at room temperature in solution with a λmax of 590 nm. As a result, it was subsequently employed as the emissive material of a single-layer LEC with configuration FTO/1/Ga/In, where studies reveal that it has a yellow color with CIE(x, y) = (0.33, 0.55), a luminance of 134 cd cm-2, and a turn-on voltage of 3.5 V. Protonation of the pendant pyridine nitrogen atoms of L1 afforded a second ionic complex [Pd(L1H)2](ClO4)2 (2) which is also emissive at room temperature with a λmax of 611 nm, resulting in an orange LEC with CIE(x, y) = (0.43, 0.53). The presence of mobile anions and cations in the second inorganic transition metal complex resulted in more efficient charge injection and transport which significantly improved the luminance and turn-on voltage of the device to 188.6 cd cm-2 and 3 V, respectively. This study establishes Pd(II) hydrazone complexes as a new class of materials whose emissive properties can be chemically tuned and provides proof-of-concept for their use in LECs, opening up exciting new avenues for potential applications in the field of solid state lighting.

Inhibition of quorum sensing related virulence factors of Pseudomonas aeruginosa by pyridoxal lactohydrazone.

Pseudomonas aeruginosa quorum sensing (QS) system is a cell to cell signaling mechanism that regulates virulence factors and pathogenicity. Therefore, the QS system in P. aeruginosa may be an important target for pharmacological intervention. The present study aimed to investigate the effects of sub-MIC concentrations of (S,E)-2-hydroxy-N-(3-hydroxy-5-(hydroxymethyl)-2-methylpyridin-4-yl)propane hydrazide (pyridoxal lactohydrazone) against P. aeruginosa QS related virulence factors. We investigated the effect of sub-MIC concentrations of chiral pyridoxal lactohydrazone, which formed by the reaction of chiral lactic acid hydrazide and pyridoxal (one form of Vitamin B6) as bioactive reagents, on virulence factors. Treated PAO1 cultures in the presence of tested compound at 1/4 and 1/16 MIC (32 and 8 µg/mL respectively) showed significant inhibition of virulence factors including motility, alginate and pyocyanin production and susceptibility to H2O2 (P < 0.001). Also, the pyridoxal lactohydrazone showed anti-QS activity in Chromobacterium violaceum CV026 biosensor bioassay. Because of quorum sensing is a promising target for anti-virulence therapy and also important role of LasR regulatory protein in the initiation of P. aeruginosa QS system, we carried out molecular docking for understanding the interactions of pyridoxal lactohydrazone with the LasR receptor. The results of docking study suggested that the pyridoxal lactohydrazone has potential to inhibit the LasR protein. The results indicated that sub-MIC concentrations of this compound exhibited inhibitory effect on P. aeruginosa QS related virulence factors.

Molecular oxygen reduction catalyzed by a highly oxidative resistant complex of cobalt-hydrazone at the liquid/liquid interface.

A new complex of Co(III) using an oxidative stable hydrazone ligand, CoL, was synthesized and characterized by elemental analysis, spectroscopic methods and single crystal X-ray analysis where HL is bis-[(E)-N'-(phenyl(pyridin-2-yl)methylene)]carbohydrazide. X-ray analysis revealed that the complex is mononuclear and the coordination environment around the Co(III) core is trans-[CoN4Cl2]. The catalytic activity of the complex in the oxygen reduction reaction was investigated. The complex is a highly oxidative resistant cobalt-hydrazone which can efficiently catalyze the reduction of oxygen (O2) by a weak electron donor ferrocene, (Fc), at the polarized water/1,2-dichloroethane (DCE) interface. Oxygen reduction is coupled with proton transfer from water to the organic phase to form hydrogen peroxide, which is extracted into the aqueous phase.

Synthesis of chiral Cu(II) complexes from pro-chiral Schiff base ligand and investigation of their catalytic activity in the asymmetric synthesis of 1,2,3-triazoles.

A pro-chiral Schiff base ligand (HL) was synthesized by the reaction of 2-amino-2-ethyl-1,3-propanediol and pyridine-2-carbaldehyde in methanol. The reaction of HL with CuCl2·2H2O and CuBr2 in methanol gave neutral mononuclear Cu(II) complexes with general formula of [Cu(HL)Cl2] (1) and [Cu(HL)Br2] (2), respectively. By slow evaporation of the methanolic solutions of 1 and 2, their enantiomers were isolated in crystalline format. The formation of pure chiral crystals in the racemic mixture was amply authenticated by single crystal X-ray analysis, which indicated that S-[Cu(HL)Cl2], R-[Cu(HL)Cl2], and S-[Cu(HL)Br2] are crystallized in chiral P212121 space group of orthorhombic system. Preferential crystallization was used to isolate the R and S enantiomers as single crystals and the isolated compounds were also studied by CD analysis. Structural studies indicated that the origin of the chirality in these compounds is related to the coordination mode of the employed pro-chiral ligand (HL) because one of its carbon atoms has been converted to a chiral center in the synthesized complexes. Subsequently, these complexes were used in click synthesis of a ß-hydroxy-1,2,3-triazole and the results of catalytic studies indicated that 1 and 2 can act as enantioselective catalysts for the asymmetric synthesis of ß-hydroxy-1,2,3-triazole product under mild condition. This study illustrates the significant capacity of the use of pro-chiral ligands in preparing chiral catalysts based on complexes which can also be considered as an effective approach to cheap chiral catalysts from achiral reagents.

Exploring C-F···π Interactions: Synthesis, Characterization, and Surface Analysis of Copper ß-Diketone Complexes.

Synthesis and characterization of two novel copper ß-diketone complexes, where halogen bonds play a pivotal role in shaping their multifaceted structural landscape, have been done in the present study. This study employs X-ray diffraction, ultraviolet-visible (UV-vis) spectroscopy, and infrared (IR) spectroscopy to investigate two copper ß-diketone complexes, [Cu(L1)2(ttfa)2]·2CH3OH (1) and [Cu(L1)(dfpb)2] (2), where Httfa is 4,4,4-trifluoro-1-(thiophen-2-yl)butan-3,1-dione and Hdfpb is 4,4-difluoro-1-phenylbutane-1,3-dione. Complex 1 displays a halogen bond, which contributes to its uniqueness. The coordination sphere around the copper atoms was found to be octahedral for complex 1 and pyramid with a square base for complex 2. The study also extensively discusses the interactions present in these complexes. Hirshfeld surface analysis was employed to gain a more detailed understanding of these interactions, and the results showed that hydrogen-bond interactions contributed above 30% of the whole surface area in both complexes. Additionally, the halogen bond in complex 1 was found to contribute approximately 8% of the surface. Overall, this study provides valuable insights into the structural properties and interactions of copper ß-diketone complexes, which could have potential applications in various fields.

N,N'-(Pyridine-2,6-di-yl)dibenzamide.

The mol-ecule of the title compound, C19H15N3O2, is completed by the application of crystallographic twofold symmetry, with the pyridine N atom lying on the rotation axis. The mol-ecular structure is approximately planar, the dihedral angle between the mean planes of the pyridine and benzene rings being 7.53 (11)°. In the crystal, N-H⋯O hydrogen bonds link the mol-ecules into a two-dimensional array perpendicular to the c axis.

Green carbon-carbon homocoupling of terminal alkynes by a silica supported Cu(II)-hydrazone coordination compound.

A Cu(II) complex, [Cu(HL)(NO3)(CH3OH)]·CH3OH (1), was obtained by the reaction of Cu(NO3)2·3H2O and H2L in methanol solvent (H2L is (E)-4-amino-N'-(2-hydroxy-3-methoxybenzylidene)benzohydrazide). H2L and compound 1 were characterized by various spectroscopic analyses and the molecular structure of [Cu(HL)(NO3)(CH3OH)]·CH3OH was determined by single-crystal X-ray analysis. The results indicated the product is a mononuclear Cu(II) complex and contains a free NH2 functional group on the structure of the ligand. [Cu(HL)(NO3)(CH3OH)]·CH3OH was used for the preparation of a heterogeneous catalyst by supporting it on functionalized silica gel. The heterogeneous catalyst (Si-Cu) was prepared by an amidification reaction of [Cu(HL)(NO3)(CH3OH)]·CH3OH with functionalized silica gel. The resulting silica-supported catalyst (Si-Cu) was characterized by TGA, FT-IR, EPR, DRS, EDS, XRD, SEM and XPS analyses. Si-Cu was employed in a carbon-carbon coupling reaction and the effects of the amount of Si-Cu and temperature were investigated in the catalytic coupling. The structure of one of the products of the catalytic reactions (C16H22O2, CP1) was determined by single-crystal X-ray analysis, which proved the formation of a C-C bond and the production of di-acetylene by homocoupling of terminal alkyne. This catalytic system is stable and it can be reused for a coupling reaction without a significant change in its catalytic activity.

Highly regioselective and diastereoselective synthesis of novel pyrazinoindolones via a base-mediated Ugi-N-alkylation sequence.

An efficient base-mediated/metal-free approach has been developed for the synthesis of 1-oxo-1,2,3,4-tetrahydropyrazino[1,2-a]indole-3-carboxamide derivatives via intramolecular indole N-H alkylation of novel bis-amide Ugi-adducts. In this protocol the Ugi reaction of (E)-cinnamaldehyde derivatives, 2-chloroaniline, indole-2-carboxylic acid and different isocyanides was designed for the preparation of bis-amides. The main highlight of this study is the practical and highly regioselective preparation of new polycyclic functionalized pyrazino derivatives. This system is facilitated by Na2CO3 mediation in DMSO and 100 °C conditions.

Role of decomposition products in the oxidation of cyclohexene using a manganese(III) complex.

Metal complexes are extensively explored as catalysts for oxidation reactions; molecular-based mechanisms are usually proposed for such reactions. However, the roles of the decomposition products of these materials in the catalytic process have yet to be considered for these reactions. Herein, the cyclohexene oxidation in the presence of manganese(III) 5,10,15,20-tetra(4-pyridyl)-21H,23H-porphine chloride tetrakis(methochloride) (1) in a heterogeneous system via loading the complex on an SBA-15 substrate is performed as a study case. A molecular-based mechanism is usually suggested for such a metal complex. Herein, 1 was selected and investigated under the oxidation reaction by iodosylbenzene or (diacetoxyiodo)benzene (PhI(OAc)2). In addition to 1, at least one of the decomposition products of 1 formed during the oxidation reaction could be considered a candidate to catalyze the reaction. First-principles calculations show that Mn dissolution is energetically feasible in the presence of iodosylbenzene and trace amounts of water.

{(E)-4-Hy-droxy-N'-[phen-yl(pyridin-2-yl-κN)methyl-idene]benzohydrazide-κN',O}bis-(nitrato-κO,O')copper(II).

In the title compound, [Cu(NO(3))(2)(C(19)H(15)N(3)O(2))], the coordination geometry around the Cu(II) ion can be described as distorted square-pyramidal, with two N atoms and one O atom from an (E)-4-hy-droxy-N'-[phen-yl(pyridin-2-yl)methyl-ene]benzohydrazide ligand and one nitrate O atom in the basal plane and one nitrate O atom at the apical site. The other two nitrate O atoms also bind to the Cu atom with long Cu-O distances [2.607 (4) and 2.853 (5) Å]. The crystal packing is stabilized by inter-molecular N-H⋯O and O-H⋯O hydrogen bonds.

(E)-4-{2-[(2-Hy-droxy-naphthalen-1-yl)methyl-idene]hydrazinecarbon-yl}pyridinium nitrate.

The title compound, C(17)H(14)N(3)O(2) (+)·NO(3) (-), is an aroylhydrazone-based material consisting of a 4-(hydrazinecarbon-yl)pyridinium cation and a nitrate anion. In the cation, the dihedral angle between the benzene ring and the naphthalene ring system is 2.20 (7)°. In the cation, the configuration about the C=N bond is E. There is an intra-molecular O-H⋯N hydrogen bond in the cation, and the supra-molecular structure is stabilized by inter-molecular N-H⋯O hydrogen bonds and weak C-H⋯O contacts between the cation and the nitrate anion.

2-[((E)-2-{2-[(E)-2-Hy-droxy-benzyl-idene]hydrazinecarbon-yl}hydrazinyl-idene)meth-yl]phenol.

The mol-ecule of the title compound, C(15)H(14)N(4)O(3), is completed by the application of crystallographic twofold symmetry, with the carbonyl group lying on the rotation axis. The mol-ecule is close to planar: the greatest deviation of a torsion angle from 0° is 7.3 (2)° about the bond linking the phenol ring to the rest of the mol-ecule. An intra-molecular O-H⋯N(imine) hydrogen bond is formed in each half of the mol-ecule. The carbonyl O atom is anti with respect to the amine H atoms and this allows for the formation of N-H⋯O(hydrox-yl) hydrogen bonds in the crystal, which results in supra-molecular layers lying parallel to (100).

N'-[(2Z)-4-Oxo-4-phenyl-but-2-en-2-yl]pyridine-4-carbohydrazide.

There are significant twists in the title compound, C(16)H(15)N(3)O(2), as seen in the dihedral angle between the benzene and adjacent but-2-enal group [29.26 (4)°] and between the pyridine ring and amide group [24.79 (6)°]. A twist is also evident around the hydrazine bond [the C-N-N-C torsion angle is -138.25 (13)°]. The conformation about the ethene bond is Z. An intra-molecular N-H⋯O hydrogen bond involving the benzoyl O atom and leading to an S(6) motif is formed. Significant delocalization of π-electron density is found in this part of the mol-ecule. In the crystal, helical supra-molecular chains aligned along the b axis and mediated by N-H⋯O hydrogen bonds are formed.

N'-[(E)-2-Hy-droxy-5-iodo-benzyl-idene]furan-2-carbohydrazide monohydrate.

The organic mol-ecule of the title monohydrate, C(12)H(9)IN(2)O(3)·H(2)O, features a disordered furyl ring with the major component [site occupancy = 0.575 (18)] having the carbonyl O and furyl O atoms syn, and the other conformation having these atoms anti. The mol-ecule is slightly twisted with the dihedral angle between the benzene and furyl rings being 10.3 (6)° (major component). An intra-molecular O-H⋯N(imine) hydrogen bond is formed. In the crystal, the water mol-ecule accepts a hydrogen bond from an amine H atom, and forms two O-H⋯O(carbon-yl) hydrogen bonds, thereby linking three different carbohydrazide mol-ecules. The result is a supra-molecular layer parallel to (001). The closest contacts between layers are of the type I⋯I, at a distance of 3.6986 (6) Å.

(E)-2-(2-Hy-droxy-5-iodo-benzyl-idene)hydrazinecarboxamide.

In the title mol-ecule, C(8)H(8)IN(3)O(2), there is an intra-molecular O-H⋯N hydrogen bond between the hy-droxy group and the imine N atom, which generates an S(6) ring. In the crystal, the carbonyl O atom accepts two different N-H⋯O hydrogen bonds, which connect mol-ecules with two R(2) (2)(8) motifs.

(E,E)-N'-{4-[(2-Benzoyl-hydrazin-1-yl-idene)meth-yl]benzyl-idene}benzo-hydrazide.

In the title compound, C(22)H(18)N(4)O(2), the mol-ecules lie across an inversion centre. The dihedral angle between the mean planes of the central and terminal benzene rings is 66.03 (2)°. The mol-ecule displays trans and anti conformations about the C=N and N-N bonds, respectively. In the crystal, N-H⋯O hydrogen bonds, with the O atoms of C=O groups acting as acceptors, link the mol-ecules into a chain along [101].