Salophen Ligand Research Articles

An unsymmetrical dinuclear scandium complex comprising salophen ligands [H2salophen = N,N'-bis-(salicyl-idene)-1,2-phenyl-enedi-amine

Treatment of scandium nitrate tetra-hydrate with the tetra-dentate ligand H2salophen [N,N'-bis-(salicyl-idene)-1,2-phenyl-enedi-amine] afforded the yellow dinuclear complex Sc(NO3)2(μ-salophen)Sc(salophen)(EtOH) or [Sc2(C20H14N2O2)2(NO3)2(C2H6O)] (systematic name: (ethanol-κO)bis-(nitrato-κ2 O,O'){μ-2,2'-[1,2-phenyl-enebis(nitrilo-methanylyl-idene)]diphenolato-κ4 N,N',O,O':κ2 O,O'}{2,2'-[1,2-phenyl-enebis(nitrilo-methanylyl-idene)]diphenolato-κ4 O,N,N',O'}discandium). In this compound, one salophen ligand displays a bridging coordination via the two oxygen atoms, while the other salophen ligand is attached to only one Sc center. This arrangement is stabilized by a hydrogen-bonded EtOH co-ligand, and by π-π stacking inter-actions between the two salophen ligands.

Structural, photophysical and electrochemical properties of a novel cardanol-based salophen ligand and its Mn(II) complex

A new cardanol-based salophen (hpbp) ligand and its manganese complex [Mn(hpbp)] were obtained by microwave-assisted synthesis method, with yields and reaction times of 65% in 20 min and 85% in 5min, respectively. The structural features of compounds were confirmed by electronic (UV–vis and fluorescence), infrared and NMR (1H, 13C) spectroscopic techniques. The photophysical study of the ligand showed ketoenamine-enolimine tautomeric equilibrium, which was discussed based on the excited state intramolecular proton transfer (ESIPT) mechanism and was dependent on the solvent, concentration and molecular structure. The energy of the HOMO and LUMO orbitals (−5.41 and −2.12 eV, respectively), determinated by cyclic voltammetry and UV–Vis, the energy was very close to the values determined by the theoretical calculations. The studies revealed that the hpbp is a tetradentate ligand bonded to the metal ion by phenolic oxygens and by azomethine nitrogens. Therefore, this work contributes to the science of salophen compounds, in addition to stimulating the synthesis of new ligands from renewable sources for the coordination chemistry.

Deep red PhOLED from dimeric salophen Platinum(II) complexes

The condensation of 3,3′-diaminobenzidine with different substituted salicylaldehyde afforded three dimeric salophen ligands H4L1-H4L3. Subsequently, their corresponding dimeric salophen platinum(II) complexes Pt2L1-Pt2L3 were prepared through the metallation of ligands with K2PtCl4. The ligands and complexes were characterized by 1H NMR, infrared spectroscopy, mass spectrometry and elemental analysis and their thermal stabilities, photophysical properties, and electrochemical behavior were further investigated in detail. Using Pt2L1 as phosphorescent emitting materials, deep red light-emitting devices were fabricated with moderate efficiency. The maximum current efficiency, power efficiency, and brightness for the 3.0 wt % Pt2L1 doped OLED are 1.39 cd A−1, 0.74 lm·W−1 and 1774 cd m−2, respectively. Given the synthetic simplicity and ease of structural variation, the preliminary results here indicate that these dimeric salophen complexes are good candidates for phosphorescent OLED.

Tetradentate Palladium(II) Salophen Complexes: Synthesis, Characterization and Catalytic Activities in Copper-Free Sonogashira Coupling Reaction

This paper reports the synthesis and characterization of three salophen ligands; 2,2'-((1E,1'E)-(1,2 phenylenebis(azanylylidene))bis(methanylylidene))diphenol [L1H], 2,2'-((1E,1'E)-(1,2-phenylenebis(azanylylidene))bis (methanylylidene))bis(4-chlorophenol) [L1C] and 2,2'-((1E,1'E)-(1,2-phenylenebis(azanylylidene))bis(methanylylidene))bis(4-methoxylphenol) [L1OME]. The compounds were prepared from condensation reaction between salicylaldehyde, and its derivatives, with ortho-phenylenediamine. Their palladium(II) complexes, namely PdL1H, PdL1C and PdL1OME were synthesized through insertion reaction between the ligands with palladium(II) acetate. All compounds were characterized through melting point, elemental analysis, infrared spectroscopy, 1H and 13C NMR spectroscopy. Palladium(II) complexes were tested as homogenous catalysts in copper-free Sonogashira coupling reaction between iodobenzene and phenylacetylene in DMSO using triethylamine as base with 1.0 mmol% catalyst loading. The most performing catalyst was PdL1OME with 91% conversion followed by PdL1H (83%) and PdL1C (27%).

Synthesis and Antibacterial Evaluation of 1,2,3‐Triazole‐based Quinazolines Using Click Chemistry in the Presence of Salophen Schiff Base Ligand

The reaction of 2‐chloro‐4‐(prop‐2‐ynyloxy)quinazoline or 2‐chloro‐N‐(prop‐2‐ynyl)quinazolin‐4‐amine with aromatic azides in the presence of the salophen Schiff base ligand afforded new derivatives of 1,2,3‐triazole‐based quinazoline scaffold in high‐to‐excellent reaction yields. The main advantage of this procedure is that the toxicity of the copper catalyst used could be decreased to 2 mol% by complexation with the salophen ligand. All the synthesized compounds were screened for their in vitro antibacterial activities against the Gram‐positive and Gram‐negative bacteria using the well‐diffusion method.

Alternating ring-opening copolymerization of phthalic anhydride with epoxides catalysed by salophen chromium(iii) complexes. An effect of substituents in salophen ligands

The effect of a ligand structure on the catalytic activity of salophen chromium(iii) complexes in the ring-opening copolymerization of phthalic anhydride with a series of epoxides was studied.

Solid-state structural elucidation and electrochemical analysis of uranyl naphthylsalophen.

A salophen ligand derivative incorporating naphthalene (naphthylsalophen = [H2L]) and the corresponding uranyl (UO22+) complex have been synthesized and characterized both in solution and the solid-state. A hydrogen bonding uranyl tetramer and the electrochemical analysis of [H2L] and UO2[L] are described.

Electronic and magnetic properties of the [Ni(salophen)]: An experimental and DFT study

The effect of the coordination of a Ni(II) ion on the electronic and magnetic properties of the ligand salophen were experimentally and theoretically evaluated. The complex [Ni(salophen)] was synthesized and characterized through FTIR and an elemental analysis. Spectral data obtained using DMSO as a solvent showed that the ligand absorption profile was significantly disturbed after the coordination of the metal atom. In addition to a redshift of the salophen ligand absorption bands, mainly composed by π → π∗electronic transitions, additional bands of around 470 nm were observed, resulting in a partial metal-to-ligand charge transfer. Furthermore, a significant increment of its band intensities was observed, favoring a more intense absorption in a broader range of the visible spectrum, which is a desired characteristic for applications in the field of organic electronics. This finding is related to an increment of the planarity and consequent electron delocalization of the macrocycle in the complex, which was estimated by the calculation of the current strengths at the PBE0/cc-pVTZ (Dyall.v3z for Ni(II)) level.

Monomeric and Dimeric Oxidomolybdenum(V and VI) Complexes, Cytotoxicity, and DNA Interaction Studies: Molybdenum Assisted C═N Bond Cleavage of Salophen Ligands.

Four novel dimeric bis-μ-imido bridged metal-metal bonded oxidomolybdenum(V) complexes [MoV2O2L'21-4] (1-4) (where L'1-4 are rearranged ligands formed in situ from H2L1-4) and a new mononuclear dioxidomolybdenum(VI) complex [MoVIO2L5] (5) synthesized from salen type N2O2 ligands are reported. This rare series of imido-bridged complexes (1-4) have been furnished from rearranged H3L'1-4 ligands, containing an aromatic diimine (o-phenylenediamine) "linker", where Mo assisted hydrolysis followed by -C═N bond cleavage of one of the arms of the ligand H2L1-4 took place. A monomeric molybdenum(V) intermediate species [MoVO(HL'1-4)(OEt)] (Id1-4) was generated in situ. The concomitant deprotonation and dimerization of two molybdenum(V) intermediate species (Id1-4) ultimately resulted in the formation of a bis-μ-imido bridge between the two molybdenum centers of [MoV2O2L'21-4] (1-4). The mechanism of formation of 1-4 has been discussed, and one of the rare intermediate monomeric molybdenum(V) species Id4 has been isolated in the solid state and characterized. The monomeric dioxidomolybdenum(VI) complex [MoVIO2L5] (5) was prepared from the ligand H2L5 where the aromatic "linker" was replaced by an aliphatic diimine (1,2-diaminopropane). All the ligands and complexes have been characterized by elemental analysis, IR, UV-vis spectroscopy, NMR, ESI-MS, and cyclic voltammetry, and the structural features of 1, 2, 4, and 5 have been solved by X-ray crystallography. The DNA binding and cleavage activity of 1-5 have been explored. The complexes interact with CT-DNA by the groove binding mode, and the binding constants range between 103 and 104 M-1. Fairly good photoinduced cleavage of pUC19 supercoiled plasmid DNA was exhibited by all the complexes, with 4 showing the most promising photoinduced DNA cleavage activity of ∼93%. Moreover, in vitro cytotoxic activity of all the complexes was evaluated by MTT assay, which reveals that the complexes induce cell death in MCF-7 (human breast adenocarcinoma) and HCT-15 (colon cancer) cell lines.

A novel spectrophotometric method for the determination of copper ion by using a salophen ligand, N,N′-disalicylidene-2,3-diaminopyridine

In this study, a novel, selective and highly sensitive spectrophotometric method has been developed for the determination of copper(II) by using a new chromogenic reagent N,N′-bissalicylidene-2,3-diaminopyridine (H2IF). The absorbance was measured at λmax=414nm. Experimental conditions were optimized, and Beer’s law was observed in the concentration range of 6.35–318μgL−1 of copper. The molar absorptivity of the complex was calculated and found to be 1.46×105Lmol−1cm−1. The detection and quantification limits were calculated and found to be 6.38μgL−1 and 21.27μgL−1, respectively. The calculated relative standard deviation (n=5) was 0.62% for a standard solution including 63.5μgL−1 copper(II). The interference effects of the common ions have been studied and the statistical assessment of the obtained results is presented. The developed method was applied for the determination of copper in water samples. The reliability and accuracy of the developed method was proven by the analysis of a waste water standard.

Syntheses, structural characterization, luminescence and optical studies of Ni(II) and Zn(II) complexes containing salophen ligand

Some Ni(II) (1a-d) and Zn(II) (2a-d) salophen complexes were prepared by the treatment of 5-bromosalicylaldehyde, 5-(trimethylsilylethynyl)salicylaldehyde, 5-(4-nitrophenyl)ethynylsalicylaldehyde or 5-(4-methoxyphenyl)ethynylsalicylaldehyde with nickel acetate or zinc acetate followed by addition of 2,3-diamino-5-bromopyridine. All complexes were characterized by elemental analyses, IR, 1H NMR and mass spectral studies. X-ray powder diffraction of representative complexes 1c and 2b and SEM studies of 1b and 2d are used to elucidate the crystal structure and morphology of the complexes. The electrochemical behavior reveals that the redox responses of Ni(II) complexes shifted to more negative potential in order to increase the π-conjugation in the complexes. Room temperature luminescence is observed for all complexes corresponding to π→π* ILCT transition with some MLCT character in DMF and is finely tuned by the degree of extended π-conjugation and variation of the substituent group with different electronic effects in the complexes. The second harmonic generation (SHG) efficiency of the complexes was screened by Kurtz-powder technique indicating that all complexes possesses promising potential for the application as a useful nonlinear optical material.

Potentiometric Anion Selectivity and Analytical Applications of Polymer Membrane Electrodes Based on Novel Mn(III)‐ and Mn(IV)‐Salophen Complexes

AbstractNew Mn(III)‐L and Mn(IV)‐L complexes were prepared from the highly lipophilic salophen ligand (L): phenol 2,2′‐[(4,5‐dimethyl‐1,2‐phenylene)bis[(E)‐nitrilomethylidyne]]bis[4,6‐bis(1,1‐dimethylethyl). The prepared complexes were fully characterized and used for the construction of thiocyanate membrane electrodes. Optimized membrane electrodes contained 33.0 mg PVC, 66.0 mg o‐nitrophenyloctylether, 50 or 5 (mole %) tetrakis(trifluoromethyl)phenyl borate and 1 mg Mn(III)‐L (sensor 2) or Mn‐(IV)‐L (sensor 12), respectively. Such electrodes exhibited linear responses toward thiocynate in a concentration range of 10−1–10−5 M and detection limits of 8.3×10−6, 8.9×10−6 M for sensor 2 and 12, respectively. Optimized membrane electrodes exhbited high selectivty toward thiocayante compared to more lipophilic anions. The observed thiocyanate selectivity of the optimized membranes was confirmed by formation constant calculations for Mn(III)‐L and Mn(IV)‐L with SCN−, β=1014.1 and 1012.5, which was measured potentiometrically using the sandwich membrane method. Furthermore, computational study using DFT calculations was performed to at DFT/B3LYP level of theory to confirm the observed selectivity data. The response times were 3 and 0.5 min for low and high concentrations. The lifetimes of the optimized electrodes were ∼4–6 weeks. The analytical utility of the optimized membrane electrodes was demonstrated by the analysis of thiocyanate level in different saliva samples.

Syntheses, crystal structures and thermal properties of two novel isostructural Co(III) complexes with salophen ligand

Abstract Two new isostructural octahedral complexes [CoX(H2O)(salophen)]·H2O·EtOH (X=Cl (1), Br (2); salophen=N,N′-bis(salicylidene)-1,2-diaminobenzene) have been prepared by reaction of CoX2 and H2 salophen in a mixture of ethanol and dichloromethane (1:1) and characterized by IR spectroscopy and elemental analysis. Crystal structures of both 1 and 2 are molecular and built up of [CoX(H2O)(salophen)] complex molecules and solvate water and ethanol molecules. The salophen ligand occupies the equatorial plane of the hexacoordinated Co(III) atom while halogenido and aqua ligands are placed in the axial positions. The crystal packings are formed by O–H···O hydrogen bonds and additional π–π stacking interactions. The results of thermogravimetric studies of 1 and 2 revealed that the loss of solvating molecules takes place first.

Excited-State and Two-Photon Absorption in Salicylidene Molecules: The Role of Zn(II) Planarization

This paper report on the excited-state (ESA) and two-photon absorption (2PA) features of two novel salicylidene compounds: N,N′-bis(salicylidene)-1,2-phenylenediamine (salophen) and its Zn(II) coordination compound ([Zn(salophen) (OH2)]). The molecular structure of salophen is a tetradentated ligand with iminic and phenolic bonding sites, allowing the coordination of metal ions such as zinc(II) forming [Zn(salophen) (OH2)]. According to our data, the Zn(II) coordination complex modifies the ESA and 2PA spectrum of the salophen ligand, increasing significantly its hyperpolarizability and improving its optical properties due to the increase of the planarity and rigidity of the ligand framework. In order to obtain more information about optical properties of these molecules, theoretical calculations were performed at the DFT/TD-DFT level using aug-cc-pVDZ/CAM-B3LYP. Our results suggest that the molecular geometries of the ligand, corresponding to S0 and S1 states, are quite similar. However, the coordination...

Investigation of VO–salophen complexes electronic structure

Vanadyl N,N′-bis(salicylidene)-o-phenylenediamine (salophen) complexes have been extensively investigated by cyclic voltammetry, UV–visible spectroscopy and theoretical calculations in MeCN, THF (tetrahydrofuran) and DMF (N,N-dimethylformamide), in order to elucidate the overall factors that influence the electronic density of the metal and therefore the properties of these complexes in various applications. Different substituents were introduced into the salophen skeleton to change the vanadium electron density. Results obtained and here presented showed that the substituents influence the metal electronic character in a way that cannot be easily predicted by considering only the electronic effect. Similarly, the solvent polarity or coordination ability affects the metal complex properties in an unpredictable way. Therefore, experimental and theoretical data here collected are a powerful tool to a priori design salophen ligands to obtain vanadyl complexes having the specific electronic properties suitable for desired applications.

Near-infrared (NIR) luminescent homoleptic linear tetranuclear [Ln4((OH)2-Salophen)4] (Ln = Nd or Yb) complexes self-assembled from the dihydroxylated Salophen ligand

Through self-assembly of the (OH)2-Salophen H4L (H4L=N, N′-bis(3-hydroxyl salicylidene)benzene-1,2-diamine) with LnCl3·6H2O (Ln=La, Nd, Yb, Er or Gd), series of [Ln4((OH)2-Salophen)4]-arrayed complexes [Ln4(H2L)2(L)2(EtOH)2] (Ln=La, 1; Ln=Nd, 2; Ln=Yb, 3; Ln=Er, 4 or Ln=Gd, 5) were obtained, respectively. The result of their photophysical properties shows that the strong and characteristic NIR luminescence for complexes 2–3 with emissive lifetimes in microsecond ranges is observed, and the sensitization arises from the excited state (1LC) of the (OH)2-Salophen ligand despite the luminescent quenching with OH-oscillators around the Ln3+ ions.

Substituent Effects on the Biological Properties of Zn-Salophen Complexes

The synthesis, characterization, and luminescent properties of a series of 5,5'-X-substituted salophen ligands, X = OCH3, Br, and NO2, and the corresponding Zn(II) complexes are reported here. Their biological activity has been analyzed and related to the different Lewis acid character of the complexes. In vitro studies (AFM and absorption and emission titrations) show that the strongest interaction with free plasmid DNA is observed for 5,5'-dinitro-substituted Zinc-salophen complex 3b. Semiempirical theoretical calculations together with redox potential measurements suggest that this might be interpreted as a direct consequence of this compound having the hardest Lewis acid character. Cellular uptake and cytotoxicity studies undertaken with these metal complexes show that they enter the cells but are not cytotoxic.

Salophen and salen oxo vanadium complexes as catalysts of sulfides oxidation with H2O2: Mechanistic insights

The application of V(V) catalysts in oxidation of sulfides with peroxides offers an efficient procedure, that is compatible with different functional groups, and leads to good yields and selectivities. However, the understanding of the factors affecting the reactivity of different catalysts is still far to be complete. An experimental and theoretical study on a series of V(V) complexes containing variously substituted salen and salophen ligands is reported with the aim to correlate the activity of the catalysts with the electronic character of the vanadium center. The results obtained indicate that steric factors play a major role in determining the outcome of the reaction, often overcoming the electronic effects. Theoretical results suggest the intervention in the catalytic cycle of an hydroperoxo vanadium species.

Direct observation of aluminium ions produced via pulsed laser ablation in liquid: a ‘turn-on’ fluorescence study

An Al metal plate was ablated by a pulsed Nd-YAG laser to produce nano-structured Al and gamma-Al(2)O(3) in deionized water without any surfactants or catalysts. In this study, direct evidence for the production of Al(3+) ions from the plasma plume is presented for the first time by characterizing the absorption and emission spectra of their [Al(salophen)](+) complex. Very interestingly, a remarkable increase in the fluorescence intensity was observed when the Al(3+) ions, produced via the pulsed laser ablation, complexed with the salophen ligand. This fluorescence 'turn-on' behaviour of [Al(salophen)](+) was investigated by DFT/TD-DFT calculations. Based on these results, mechanisms for the production of aluminium and alumina nanoparticles in the pulsed laser ablation in liquid (PLAL) process are proposed.

Ion-Pair Recognition by Metal - Salophen and Metal - Salen Complexes

The development of heteroditopic receptor systems that can simultaneously bind cationic and anionic species is one of the most challenging research topics in supramolecular chemistry, attracting the attention of a large number of research groups worldwide. Such an interest is due especially to the fact that the overall receptor–ion-pair complex is neutral and this can be advantageous in many situations, such as salt solubilization and extraction, and membrane-transport applications. Receptors designed for ion-pair complexation are molecules comprising well-known anion-binding motifs and familiar cation-binding sites. An important family of compounds that can use metal Lewis-acidic centres for anion recognition and that can be easily derivatized to introduce an additional binding site for the cation is metal–salophen and metal–salen complexes. This short review shows that the high versatility of salen and salophen ligands and of the corresponding metal complexes allows, through simple modifications of the basic skeleton, the obtention of highly efficient receptors for ion pairs.