Salophen Complex Research Articles

Efficient and selective oxidation of alcohols and hydrocarbons catalyzed by oxovanadium(IV) unsymmetrical salophen complex supported on silica-coated CoFe2O4 magnetic nanoparticles

Efficient and selective oxidation of alcohols and hydrocarbons catalyzed by oxovanadium(IV) unsymmetrical salophen complex supported on silica-coated CoFe2O4 magnetic nanoparticles

Enhanced Efficiency of Silicon Solar Cell by New Salophen Complexes Embedded PMMA as Light Concentrators

The Schiff base N,N-bis(salicylidene)-o-phenylenediamine (salophen) was prepared by the condensation of salicylaldehyde with o-phenylenediamine in ethanol solution. Two new Zn(II) and Ni(II) salophen complexes, were synthesized, fully characterized by infrared (IR), 1H NMR spectroscopic measurements, UV–Vis spectra, photoluminescence (PL), and X-ray diffraction (XRD). The prepared complexes were used as phosphors to fabricate complexes/PMMA slab-based luminescent solar concentrators (LSC). The thermal stability of pure and doped PMMA polymer was examined by differential scanning calorimetry. Various parameters such as the optical energy gap, refractive index, AC and DC conductivity, dielectric constant, dielectric loss, Urbach energy, fluorescence quantum yield, and Stokes shift have been calculated and discussed. Optical absorption is carried out in wavelength region 200–900 nm at room temperature before and after the samples have been exposed to sunlight for up to 8 h. Photodegradation studies showed that the Zn(II) complex/PMMA LSC has the lowest rate of degradation compared with Ni(II) complex/PMMA LSC with the same concentration (0.06% weight). I–V characteristics of the photovoltaic devices with and without collectors were examined. The PV cell coupled with LSC shows an increase in maximum efficiency by about 50% compared to the normal one. This indicates that the proposed technique is very useful for improving the efficiency of solar cells.

CO2 to Cyclic Carbonate: A Mechanistic Insight of a Benign Route Using Zinc(II) Salophen Complexes

AbstractZinc(II) Schiff base complexes with different substituents at 5, 5’ positions have been synthesized to study the effect of the electronic environment of the metal towards the cycloaddition reaction between CO2 and epoxide. The complexes have been characterized by FT‐IR, XPS, NMR, electronic spectroscopy, LC–MS, and TGA. We have used density functional theory to study the electronic structure of the Zn(II) complexes and modelled the electronic spectra and the mechanism of catalysis. Results obtained from DFT and LC–MS indicate the dimeric structures for all the complexes except ZnL4. The monomeric ZnL4 has the strongest electron withdrawing group, i. e., −NO2 at 5, 5’ positions along with two labile water molecules attached to the Zn center. The dimeric complexes exhibit good to moderate yield for cycloaddition reaction to styrene carbonate under solvent‐free conditions and a relatively low reaction temperature of 80 °C, with CO2 pressure of ~1 atm. The best yield has been achieved by ZnL4. Different rate‐determining steps are captured by the DFT studies for dimeric and monomeric complexes. Without taking any preventing measure of dimerization by attaching the bulky tBu groups, relatively lesser catalytic amounts of all the complexes have shown yields of cyclic carbonate between 53–74 %, depending on the nature of the substituent present.

Retraction: The anchoring of a Cu(ii)-salophen complex on magnetic mesoporous cellulose nanofibers: green synthesis and an investigation of its catalytic role in tetrazole reactions through a facile one-pot route.

[This retracts the article DOI: 10.1039/D1RA01913A.].

Spiral gas-solid two-phase flow continuous mechanochemical synthesis of salophen complexes and catalytic thermal decomposition of ammonium perchlorate.

Although mechanochemistry is increasingly becoming an alternative to traditional chemical synthesis, highly efficient continuous mechanochemical synthesis techniques are still rare. In this work, a novel spiral gas-solid two-phase flow (S-GSF) synthesis technique for the mechanochemical synthesis of salophen complexes has been reported, which is an approach for continuous synthesis based solely on airflow impacting the reaction. The synthesis of salophen-Br-Cu was used as a model reaction to optimize the reaction conditions, and three other salophen complexes, namely, salophen-Br-Co, salophen-Br-Ni, and salophen-Br-Zn were synthesized on this basis. The structure and thermal stability of the obtained products were characterized by Fourier transform infrared spectroscopy, X-ray diffraction, UV-vis spectroscopy, nuclear magnetic resonance spectroscopy, scanning electron microscopy, and differential thermal analysis (DTA). The results showed that these complexes can be obtained continuously at a rate close to 4 g min-1, and the corresponding space-time yield is close to 1.2 × 105 kg m-3 day-1. In addition, DTA was used to analyze the catalytic performance of the complex for ammonium perchlorate (AP). The results showed that compared to the conditions for pure AP, salophen-Br-Co and salophen-Br-Cu could significantly reduce the high-temperature decomposition of AP pyrolysis to 77.0 and 102.1 °C, respectively. According to the method of Kissinger calculations, the Ea of AP decomposition decreased from 217.3 kJ mol-1 to 131.0 and 118.5 kJ mol-1, respectively. The TG data at different heating rates were analyzed using two isoconversion methods, i.e. Flynne-Walle-Ozawa (FWO) and Kissinger-Akahira-Sunose (KAS). The activation energies of AP, AP + 10 wt% salophen-Br-Co, and AP + 10 wt% salophen-Br-Cu were calculated. When the conversion degree (α) is between 0.1 and 0.9, the Ea values obtained from the two isoconversion methods are similar and exhibit certain matching. These two isoconversion methods also confirm Kissinger's calculations.

Salophen chromium(iii) complexes functionalized with pyridinium salts as catalysts for carbon dioxide cycloaddition to epoxides.

The catalytic properties of a series of novel chromium(iii) salophen complexes having different pyridinium chloride units (pyridinium, 2,6-dimethylpyridinium or 4-(dimethylamino)pyridinium ones) have been studied in the reaction of carbon dioxide cycloaddition to phenyl glycidyl ether. The examined complexes were found to be capable of catalyzing cycloaddition under relatively mild reaction conditions without any additional nucleophilic co-catalyst. However, their catalytic activity depended strongly on the structure and number of pyridinium salt units in the ligand molecule. The complex with a single unit of 4-(dimethylamino)pyridinium chloride turned out to be the most active among the examined ones. A TOF of up to 1480 h-1 was obtained in the presence of this catalyst under the following conditions: 120 °C, 2 h, 6 bar, 0.05 mol% (74% epoxide conversion, and >99% selectivity). The most active complex has also been examined as a catalyst in the reactions of CO2 with a series of ten other terminal epoxides. High catalytic activity (TOF = 220-5045 h-1) was observed in most cases, except for the reaction of CO2 with allyl glycidyl ether.

Oxovanadium(IV) unsymmetrical salophen complex supported on modified silica-coated CoFe2O4 nanoparticles: A magnetically recoverable nanocatalyst for efficient and selective oxidation of sulfides and thiols

In this study, an oxovanadium(IV) unsymmetrical salophen complex, VO(salophen-OH) where salophen-OH = 4-[(E)-{(2-[(E)-2-hydroxybenzylidene)amino]phenyl}imino)methyl]benzene-1,3-diol, was synthesized and immobilized on the surface of chloro-functionalized silica-coated CoFe2O4 (CoFe2O4@SiO2@CPTMS) magnetic nanoparticles. FT-IR and EDX spectra, TEM and SEM images, XRD pattern, TGA, ICP, and VSM measurements were applied to characterize the resulting CoFe2O4@SiO2@CPTMS@VO(salophen-OH) nanoparticles. The developed CoFe2O4@SiO2@CPTMS@VO(salophen-OH) magnetic nanoparticle was used as a remarkably efficient nanocatalyst, which facilitates the chemo-selective oxidation of sulfides to sulfoxides using 30 % H2O2 and also enables the oxidative coupling of thiols to disulfides using urea/H2O2 (UHP) in ethanol at room temperature. This catalytic system presented disulfides and sulfoxides as optimal products that showed good to excellent yields, and there was no over-oxidation of disulfides and sulfoxides to undesirable by-products. An external magnet can be used to recover this nanocatalyst magnetically, and it can be recycled up to five times in both oxidation reactions without losing its catalytic action. Moreover, the recycled catalyst shows no major differences in its XRD pattern and FT-IR spectrum compared to the fresh catalyst.

Biodiesel from Waste Cooking Oil: Highly Efficient Homogeneous Iron(III) Molecular Catalysts

This article presents an efficient iron(III) molecular catalyst for the production of biodiesel from waste vegetable oils. The approach involved an initial screening of eight salophen complexes with various substituents on the arene rings, leading to the selection of the simplest unsubstituted species as the most active catalyst. Under optimized conditions, this catalyst demonstrated the capability to achieve complete conversion of the oil at a low catalyst loading (0.10% mol/mol) and convenient conditions (160 °C, 20/1 MeOH/oil ratio).

Syntheses, Characterization, and DNA Binding Studies of a Series of Copper(II), Nickel(II), Platinum(II) and Zinc(II) Complexes Derived from Schiff Base Ligands

AbstractThree series of metal salophen complexes derived from Zn2+, Cu2+, Pt2+ and Ni2+ have been synthesized and their interaction with quadruplex DNA has been evaluated. The compounds differ on the number of ethyl piperidine substituents. They have been characterized by 1H NMR, IR and UV‐visible spectroscopies and by HR‐mass spectrometry. Their luminescent properties have been also evaluated and we can observe that, as expected, Zn2+ and Pt2+ complexes are those displaying more interesting luminescence with an emission band red‐shifted with respect to the corresponding uncoordinated ligand. DNA interactions with G4 and duplex DNA were evaluated by FRET melting assays (for the Zn2+, Cu2+ and Ni2+ complexes) and by emission titrations (for one Pt2+ complex) which indicated that the disubstituted compounds 2‐Ni and 2‐Pt are the only ones that display good affinity for G4 DNA structures.

Ni(II)-Salophen-Comprehensive Analysis on Electrochemical and Spectral Characterization and Biological Studies.

New aspects of the Ni(II)-salophen complex and salophen ligand precursor were found during deep electrochemical and optical characterization, as well as biological studies for new pharmacological applications. Physicochemical and spectroscopic methods (1H- and 13C-NMR, FT-IR and UV-Vis, electrospray ionization mass spectroscopy, thermogravimetric analysis, and molar conductance measurements) were also used to prove that the salophen ligand acts as a tetradentate and coordinates to the central metal through nitrogen and oxygen atoms. The electrochemical behavior of the free Schiff salophen ligand (H2L) and its Ni(II) complex (Ni(II)L) was deeply studied in tetrabutylammonium perchlorate solutions in acetonitrile via CV, DPV, and RDE. Blue films on the surfaces of the electrodes as a result of the electropolymerization processes were put in evidence and characterized via CV and DPV. (H2L) and Ni(II)L complexes were tested for their antimicrobial, antifungal, and antioxidant activity, showing good antimicrobial and antifungal activity against several bacteria and fungi.

Design of simple salophen chromium complexes for a two-steps oxidative carboxylation of styrene with CO2 and O2

In this work, chromium(III) Salophen complexes bearing tertiary dimethyl or diethyl amino substituents were synthesized and tested as homogeneous co-catalysts associated with n-Bu4NBr for the cycloaddition of CO2 on styrene epoxide under 11 bar of CO2. Full conversion of styrene oxide into styrene carbonate was obtained after 23 h reaction at 50 °C using Salophen-Me2N-Cr. These results emphasized that tertiary amine groups born by the aromatic cycles of Salophen clearly enhanced the co-catalytic activity of the corresponding Cr(III) complex. The direct conversion of styrene into styrene carbonate was then conducted at 80 °C with O2 and CO2 either under a single set of conditions (reactants and catalysts together) or using a two-steps transformation. The latter was based on the prior epoxidation of styrene in the presence of isobutyraldehyde and O2 (3.5 bar) with a delayed addition of the cycloaddition catalysts (n-Bu4NBr and Salophen-Me2N-Cr) and CO2 (11 bar). Using these conditions, the maximum yield of styrene carbonate, obtained after 3 h of epoxidation and 20 h of cycloaddition (with Salophen-Me2N-Cr), was 31 % at 80 °C. This work demonstrates that the key-point to afford a high styrene carbonate global yield with that system was related to the implementation of a two-step protocol, since it allowed to minimize the amounts of undesired by-products.

Aluminium(III) Salophen complex as a luminescent turn-off/turn-on sensor for nitrobenzene, Fe3+, and toluene

An Al(III) complex, Al-Salp-(H2O)2NO3 (Salp-Al, Salp = N,N’-bis(salicylidene)-1,2-phenylenediamine), is synthesized from the Schiff base ligand Salp. Salp-Al can emit green light in DMF/H2O solution or in solid state and is characterized by XPS, SEM, FT-IR, NMR and TGA. The Salp-Al shows a response to Fe3+ and nitrobenzene in DMF/H2O as a turn-off chemosensor with a limit of detection of 0.4 × 10−4 M and 4.6 × 10−5 M, respectively. Salp-Al can also be applied to detect toluene in DMF/H2O as a turn-on chemosensor with an excellent limit of detection of 4.3 × 10−4 M. The fluorescence lifetime of Salp-Al is 1.94 ns.

Heterobimetallic conducting polymers based on salophen complexes via electrosynthesis

Heterobimetallic polymers: the best of both worlds? The copolymers electrosynthesized in this work can benefit from both the conducting polymer structure and the presence of two metals. Their potential application in sensing ascorbic acid was also explored.

Effect of regio-specific arylamine substitution on novel π-extended zinc salophen complexes: density functional and time-dependent density functional study on DSSC applications.

A series of π-extended salophen-type Schiff-base zinc(ii) complexes, e.g., zinc-salophen complexes (ZSC), were investigated toward potential applications for dye-sensitized solar cells. The ZSC dyes adopt linear-, X-, or π-shaped geometries either with the functionalization of 1 donor/1 acceptor or 2 donors/2 acceptors to achieve a push-pull type molecular structure. The frontier molecular orbitals, light-harvesting properties as well as charge transfer characters against regio-specific substitution of donor/acceptor groups were studied by using density functional theory (DFT) and time-dependent density functional theory (TDDFT). The results reveal that all ZSC dyes of D-ZnS-π-A geometry (where D, S, and A denote to donor, salophen ligand, and acceptor, respectively) exhibit relatively lower HOMO energy compared to the structurally resembled porphyrin dye YD2-o-C8. Natural transition orbital (NTO) and electron-hole separation (EHS) approaches clearly differentiate the linear type YD-series dyes from CL-, AJ1-, and AJ2-series dyes because of poor charge transfer (CT) properties. In contrast, the π-shaped AJ2-series and X-shaped AJ1-series dyes outperform the others in a manner of stronger CT characteristics, broadened UV-vis absorption as well as tunable bandgap simply via substitution of p-ethynylbenzoic acids (EBAs) and arylamine donors at salophen 7,8- and 2,3,12,13-positions, respectively. Both EHS and calculated exciton binding energies suggest the strength of CT character for ZSC dyes with an amino donor in the trend TPA > AN > DPA. This work has provided clear illustration toward molecular design of efficient dyes featuring a zinc-salophen backbone.

Oxovanadium(IV)‐salophen covalently immobilized on silica‐coated Fe3O4 nanoparticles: A magnetically recoverable nanocatalyst for the selective oxidation of sulfides

The current study introduces an approach toward the development of heterogeneous, magnetically recoverable oxovanadium(IV)‐salophen complex to employ in the selective oxidation of sulfides using H2O2 as oxidant. A salophen ligand containing hydroxyl functional group was synthesized, which is conducive to successful, covalent immobilization of metal complex onto the silica‐modified Fe3O4 magnetic nanoparticles (SMNPs). This type of metal anchoring is achieved through an intermolecular condensation reaction. The in‐depth investigation on the catalyst (Fe3O4@SiO2@VO(salophen)) productivity and lifetime in the oxidation of a wide range of linear and aromatic sulfides is well represented and discussed. The use of the current catalyst in the selective oxidation of prototype substrate (methyl phenyl sulfide) resulted in an appreciable increase in the selectivity toward the desired sulfoxide (92%) and conversion rate (95%) compared with similar studies, reported to this day. Analytical techniques such as field emission scanning electron micrograph (FE‐SEM), energy‐dispersive X‐ray spectroscopy (EDX), Fourier transform infrared (FT‐IR), X‐ray diffraction (XRD) analysis, and inductively coupled plasma optical emission spectrometer (ICP‐OES) provided data on structural/compositional characterization of materials in catalyst preparation steps.

Efficient electrochemical water oxidation mediated by different substituted manganese-salophen complexes

• The electrocatalytic role of different substituted Mn II salophen complexes was investigated for water oxidation. • It was revealed that the studied complexes show excellent activity for OER. • The overpotential for the OER was in the range of 345–420 mV. • It was speculated that the O O bond formation occurs by oxidizing the active center of Mn complexes. • The Mn II complexes catalyzed the OER as real electrocatalysts. Developing robust and efficient water oxidation catalysts is an essential challenge in water splitting. In this work, the electrocatalytic behavior of the modified carbon paste electrodes with different substituted Mn II salophen complexes, MnL 1 -MnL 3 , (H 2 L 1 = N,N′-bis(salicylidene)-1,2-diaminobenzene, H 2 L 2 = N,N′-bis(salicylidene)-4-bromo-1,2-diaminobenzene and H 2 L 3 = N,N′-bis(2-hydroxy-3-methoxybenzilidine)-1,2-diaminobenzene) was evaluated for water oxidation by electrochemical methods. All three complexes were found highly effective, stable, and robust catalysts for water oxidation. Electrochemical experiments, Field emission-scanning electron microscope (SEM), energy-dispersive X-ray (EDX), and powder X-ray diffraction (PXRD) analyses indicated that the studied Mn II salophen complexes are molecular catalysts for water oxidation in origin. Cyclic voltammetry experiments in different pHs displayed that the O O bond formation probably occurs by oxidizing the active center of Mn II complexes through proton-coupled electron transfer (PCET). The results showed that the nature of the substituent on the salophen ligand could not affect the stability of the complexes under applied electrochemical conditions. It was found that Mn oxide nanostructures obtained by the thermal decomposition of MnL 1 can also effectively catalyze the reaction, but in comparison with MnL 1 , they have lower activity.

Excited state dynamics of Zn–salophen complexes

Zn–salophen complexes are a promising class of fluorescent chemosensors for nucleotides and nucleic acids. We have investigated, by means of steady state UV–Vis, ultrafast transient absorption, fluorescence emission and time dependent density functional theory (TD-DFT) the behavior of the excited states of a salicylidene tetradentate Schiff base (Sal), its Zn(II) coordination compound (Zn–Sal) and the effect of the interaction between Zn–Sal and adenosine diphosphate (ADP). TD-DFT shows that the deactivation of the excited state of Sal occurs through torsional motion, due to its rotatable bonds and twistable angles. Complexation with Zn(II) causes rigidity so that the geometry changes in the excited states with respect to the ground state structure are minimal. By addition of ADP to a freshly prepared Zn–Sal ethanol solution, a longer relaxation constant, in comparison to Zn–Sal, was measured, indicative of the interaction between Zn–Sal and ADP. After a few days, the Zn–Sal–ADP solution displayed the same static and dynamic behavior of a solution containing only the Sal ligand, demonstrating that the coordination of the ADP anion to Zn(II)leads to the demetallation of the Sal ligand. Fluorescence measurements also revealed an enhanced fluorescence at 375 nm following the addition of ADP to the solution, caused by the presence of 2,3-diamino naphthalene that is formed by demetallation and partial decomposition of the Sal ligand. The efficient fluorescence of this species at 375 nm could be selectively detected and used as a probe for the detection of ADP in solution.Graphical abstract

Aluminium(Ш) Salophen Complex as a Luminescentturn-On/Turn-Off Sensor for Nitrobenzene, Fe3+, and Toluene

Aluminium(Ш) Salophen Complex as a Luminescentturn-On/Turn-Off Sensor for Nitrobenzene, Fe3+, and Toluene

Schiff base metal complexes driven quantum dots of ZnSe and CdSe

The Schiff base metal complexes of Cd and Zn (popularly known as the salophen complexes) when reacted with cycloocteno-1,2,3-selenadiazole lead to formation of CdSe and ZnSe quantum dots (QDs) via thermal reaction employing octadecenoic acid. Such metal precursors offer versatility in the field of nanomaterials. The QDs were analysed by UV-Visible and Photoluminescence spectroscopy, XRD, TEM and TGA. The method leads to selective formation of cubic quantum dots of less than 3 nm with typical quantum yields of as-prepared samples was estimated to be 15.34% for ZnSe and 7.25% for CdSe.

Modulating carbon dioxide activation on carbon nanotube immobilized salophen complexes by varying metal centers for efficient electrocatalytic reduction

Electrocatalytic CO2 reduction (ECR) into valuable chemicals, especially driven by renewable energy, presents a promising pattern to realize carbon neutrality. Site-isolated metal complexes flourish in the area of ECR as single-atom-like catalysts because of their competent and tailorable activity. In this study, salophen-based metal (Fe, Co, Ni and Cu) complexes were anchored onto carbon nanotubes (CNTs) to construct efficient catalysts for electrochemically converting CO2 to CO. Both experimental and theoretical results verified that CO2 activation was the rate-determining step for the catalytic performance of these hybrid molecular catalysts. The coordinate activation ability can be manipulated by varying the metal centers. The as-synthesized Fe-salophen hybrid CNT (Fe-salophen/CNT) shows the best activity and selectivity of −13.24 mA·cm−2 current density with 86.8% Faradaic efficiency for generating CO (FECO) at −0.76 V vs. RHE in aqueous solution, whereas Cu-salophen/CNT only achieved a −2.22 mA·cm−2 current density and 57.9% FECO under the same reaction conditions. These distinct catalytic performances resulted from the different coordination activation abilities of CO2 on various metal centers.