bis-Schiff Base Complexes Research Articles

Synthesis of a novel nanomagnetic N4 bis schiff base complex of copper(ii) as an efficient catalyst for click synthesis of tetrazoles.

In this study, we have prepared a novel bis-Schiff-base copper(ii) complex by modifying Fe3O4 with acetylacetone functionalities and subsequently forming a Schiff base with 2-picolylamine and CuCl2 through a template method. Immobilization of 2,4-pentanedione and its reaction with 2-picolylamine enabled the synthesis of 1,3-diketimines (HNacNac) as an anionic ligand. This unique design resulted in a tetradentate N4 coordination sphere for copper(ii) ion complexation. The resulting heterogeneous catalyst, [Fe3O4@Sil-Schiff-base-Cu(ii)], efficiently catalyzed the click condensation of diverse aryl nitriles with sodium azide to produce 5-substituted 1H-tetrazoles in high yields and selectivity. The catalyst demonstrated remarkable stability and recyclability without appreciable loss of catalytic activity, as confirmed by hot filtration and reusability studies.

Facile synthetic route of TiO2–ZnO heteronanostructure coated by oxovanadium (IV) bis-Schiff base complex as a potential effective homogeneous/heterogeneous catalysts for alcohols redox systems

Oxovanadium (IV) bis-Schiff base complex was synthesized by a facile complexation of 2 molar ratio of 2‑hydroxy-Schiff base ligand (HL) with 1 molar ratio of VO2+ ion giving mononuclear VOL2 complex with a square pyramidal geometry. The structure conformation of HL and its corresponding VOL2 complex was assigned within various spectroscopic tools (IR, UV–vis. Mass spectra), as well as the elemental analyses (EA). The deprotonated 4-OH group in VOL2 caused a successful coating of VOL2 on a mixed oxides of TiO2–ZnO nanoparticles awarding nanocomposite of TiO2–ZnO@VOL2. By applying alternative analytical techniques, the surface morphology and internal structure TiO2–ZnO@VOL2 nanocomposites were investigated compared to that of TiO2–ZnO, i.e. by XRD, FESEM, HR-TEM, EDS and IR spectra), and also with TGA and BET (adsorption–desorption isotherm).The catalytic effectiveness of both homogeneous and heterogeneous catalysts (VOL2 and TiO2–ZnO@VOL2) was examined in the productive oxygenation reactions of BA (benzyl alcohol) by an aqueous hydrogen peroxide under an aerobic environment to the chemo-selective product benzaldehyde (BZ), and benzoic acid (BO), as the overodixation product. Both VOL2 and TiO2-ZnO@VOL2 catalysts exhibited obvious classified action by 89% and 91% yielding amount of benzaldehyde after 4 h for reaction temperature 80 and 90 °C, respectively. The differentiation between them in the catalytic reactivity was depending on the heterogeneity and the effect of the coated TiO2–ZnO nanoparticles on the VOL2 catalytic potential. The kinetic parameter of the productive redox protocols for both catalyst was examined. Additionally, some other cyclic and acyclic alcohols were exhibited the productive redox protocol in the optimum control of both catalysts.

ZnO–TiO2 Nanoparticles Coated by the Dioxomolybdenum (VI) bis-Schiff Base Complex for Catalytic Oxidation of Sulfides

The oxygenation processes for the organic compounds have great applications in fine organic fabrications. To speed up progress in the industrialization of such oxidation systems, a monometallic dioxomolybdenum (VI) bis-Schiff base complex (MoO2L2) was synthesized through coordination of easily accessible 4-hydroxyiminophenol ligand (HL) with cis-MoO22+ ion in an octahedral geometry. The structural conformation of MoO2L2 and its coordinated ligand (HL) was determined using modern spectrophotometric tools. A heterogeneous catalyst (MoO2L2@ZnO–TiO2) was successfully prepared by immobilization of MoO2L2 on the surface of ZnO–TiO2 nanostructured particles through the deprotonation of 4-OH group in its coordinated ligand. Various analytical techniques were used to examine the surface morphology and internal structure features of ZnO–TiO2 and MoO2L2@ZnO–TiO2 nanocomposites. To study the catalytic efficiency of MoO2L2 and MoO2L2@ZnO–TiO2-based catalysts, they were employed in the oxygenation process of Ph2S (diphenyl sulfide) and MePhS (methylphenyl sulfide) using the most environmentally friendly oxidant (an aqueous H2O2) under an aerobic environment. A high degree of selectivity was observed for the productivity of diphenyl sulfoxide (Ph2SO) and methylphenyl sulfoxide (MePhSO), with some contamination of overoxidation side products (Ph2SO2 and MePhSO2). The catalytic oxidative ability was not observably superior for the heterogeneous coated catalyst by ZnO–TiO2 over its homogeneous one (MoO2L2) due to the less redox activity of ZnO and TiO2 nanoparticles in the catalytic cycles for the oxygen-transfer mechanism. Both catalysts were successfully recycled, in which the homogeneous catalyst sustained its high catalytic potential for up to three cycles, while the heterogeneous catalyst was able to be reused up to six times.

A study of mononuclear 3d transition metal bis-Schiff base complexes: Synthesis, characterization, and evaluation of their antibacterial activity

<p>In this study, we have outlined a conventional and user-friendly procedure for the production of <em>(E)-1-(((5-ethyl-1,3,4-thiadiazol-2-yl)imino)methyl)naphthalen-2-ol </em><em>(HL-1)</em> and <em>(E)-1-((thiazol-2-ylimino)methyl)-naphthalen-2-ol</em> (HL-2) by the reaction of heterocyclic amine, aldehyde in the presence of ethanol as a solvent and acid as the catalyst. The synthesis of new HL-1 and HL-2 may be accomplished with ease using this approach, which is also very efficient. In the presence of dipositive Co, Ni, and Cu metal complexation, HL-1 and HL-2 were carried out in the presence of metal: ligand (1:2). HL-1, HL-2, and metal complexes are characterized with the assistance of UV/visible, FT-IR, Mass, and <sup>1</sup>H NMR spectroscopy respectively. Furthermore, the ligands mentioned above (HL-1 and HL-2) and their metal complexes were tested for the antimicrobial study and showed an excellent inhibitory zone. These investigations indicated that HL1<strong>-</strong>Co (II), HL-1Cu (II), complexes and ligands HL-2Co (II), and HL-1Ni(II) had positive effects on <em>Escherichia coli</em> causing severe stomach cramps (Gram-negative- MTCC 1610) and positive impact on <em>Staphylococcus aureus</em> (Gram-positive MTCC<strong>-</strong>96) due to skin infections.</p>

Confining ultrafine ZnSe nanoparticles in N,Se-codoped carbon matrix using a direct solid state reaction approach for boosting sodium storage performance

Abstract As a most promising low-cost substitute for the current lithium-ion batteries technology, sodium-ion batteries (SIBs) have aroused particular attentions over the past few years. However, the performance of SIBs is still far from our expectations due to the lack of suitable electrode materials with excellent electrical conductivity, high energy density, long-term cycling stability, and high-rate performance. Herein, ultrafine ZnSe nanoparticles homogeneously confined within N,Se-codoped carbon matrix were constructed via a facile solid state reaction route. By directly using zinc acetate dihydrate, o-vanillin and o-phenylenediamine as starting raw materials, a self-assembly solid state reaction occurred to give rise to a bis-Schiff base complex with zinc (II) at room temperature. After subsequent calcination in the presence of selenium powder at elevated temperature, simultaneous carbonization and selenization took place, resulting to the in-situ formation of ultrafine ZnSe nanoparticles (∼6.5 nm) encapsulated in N,Se-codoped carbon matrix (named as ZnSe⊂NSeC). The unique ZnSe⊂NSeC hybrid demonstrated an impressive sodium storage performance in terms of long-term cycling stability (282 mA h g−1 of charging capacity after 500 cycles at 0.1 A g−1) and excellent rate capability (198 mA h g−1 of charging capacity at 5 A g−1). More importantly, a superb stable charging capacity of 238 mA h g−1 still maintained even after 1200 cycles at 1.0 A g−1. Such strategy may also be used to explore other nanocomposites to boost their energy storage performance.

Solid state reaction-enabled in situ construction of ultrafine CoS nanoparticles encapsulated within heteroatom-doped carbon scaffold for high performance sodium-ion batteries

Developing an efficient and reliable method for achieving high-yield and high-quality synthesis of transition metal sulfides combined with carbonaceous materials is highly desirable but still challenging. Herein, a very simple and cost-effective solid state reaction method for the fabrication of ultrafine CoS nanoparticles encapsulated within heteroatom-doped carbon scaffold is presented. By directly grinding cobalt acetate tetrahydrate, o-vanillin and o-phenylenediamine together with a molar ratio of 1:2:1 at ambient temperature in the presence of sulfur powder, a self-assembly solid state reaction took place to give rise to a bis-Schiff base complex with cobalt (II), which was evenly distributed in the sulfur powder surroundings. After subsequent annealing at elevated temperature, simultaneous carbonization and sulfidization occurred, resulting to the in-situ formation of ultrafine CoS nanoparticles (∼3.8 nm) encapsulated within an irregular N, S-codoped carbon scaffold (denoted as CoS⊂NSC). When evaluated as an anode material for sodium-ion batteries (SIBs), the CoS⊂NSC hybrid exhibits good cycling stability (305.6 mA h g−1 after 400 cycles at 100 mA g−1) and excellent rate capability (412.3 and 263.3 mA h g−1 at current densities of 200 and 5000 mA g−1, respectively), demonstrating exceptional electrochemical sodium storage performances. The findings in this work pave a novel way to synthesize the promising anode materials for high performance SIBs.

Facile synthesis, characterizations, and impedance spectroscopic features of Zn(II)-bis Schiff base complex films towards photoelectronic applications

Complexation of Zn2+ with pyridyl Schiff base (ZnL2) was synthesized. The ZnL2 was examined and characterized using the elemental analysis, NMR, IR, UV-Vis, and mass spectra. ZnL2 was formed within 1:2 molar ratios of metal ion to ligand, respectively, which is proven by continuous variation method. The thin films of ZnL2 are grown on the quartz substrates for optical measurements using thermal evaporation method. The absorbance, transmittance, and reflectance were measured using a spectrophotometric technique, from which many optical parameters were determined. The indirect allowed transition is the most probable transition and the optical energy gap is found to be 2.41 eV. Additionally, the ZnL2 was tested as a photosensitizer material in the thin film form grown onto single crystal of p-Si wafer to form a hybrid organic-inorganic Au/ZnL2/p-Si/Al heterostructure device for the first time. Many electrical aspects were studied for such device including impedance spectroscopic, dielectric constant, electric modulus, and electrical conductivity at various frequencies and under different illumination intensities. The high photosensitivity of Au/ZnL2/p-Si/Al heterojunction for low and high power intensity of light confirmed that the ZnL2 material is a promising candidate photosensitizer for photovoltaic applications.

Zinc bis-Schiff base complexes: Synthesis, structure, and application in ring-opening polymerization of rac-lactide

A series of bis-ligated zinc complexes supported by Schiff base ligands were successfully synthesized and characterized by 1H, 13C NMR, elemental analysis, and X-ray crystallography. These zinc complexes can be used as catalysts for the polymerization of rac-lactide in solution as well as in molten lactide. The results show that all catalysts exhibited high catalytic activity and obtained moderate heterotactic PLAs with the expected molecular weight. Complex 1 can catalyze the polymerization of rac-lactide under controllable conditions with living and immortal character in toluene solution. In addition, the steric hindrance and electronic effects has a great influence on the catalytic activity and selectivity of catalysts.

Synthesis, characterization and anticancer properties of (salicylaldiminato)platinum(II) complexes

Twelve new (salicylaldiminato)platinum(II) complexes have been prepared, characterized and examined for their in vitro cytotoxic properties against three human glioma cell lines LN18, LN405 and Hs683. Initial biotesting was done on platinum complexes 1–6, which display a wide range of physicochemical properties. Whereas introduction of aromatic rings in the complexes did not seem to have a significant impact on bioactivities, the length of the aliphatic group positively correlated with cytotoxicity in all cell lines. Complexes 2 and 3 were found to be particularly potent against LN18 cells as demonstrated by stronger cell growth inhibition when compared to cisplatin. These initial findings led us to develop an additional series of mono (salicylaldiminato)platinum(II) complexes 7–12, which were subjected to additional cytotoxicity studies but were less cytotoxic compared to the bis Schiff base complexes. These organometallic compounds could serve as interesting starting points for the development of novel therapeutic strategies to treat brain tumors.

Ferromagnetic interaction in iron(II)–bis-Schiff base complexes

The preparation and magnetic properties of three Fe(II)–bis-Schiff base complexes, [Fe 2(L1)2(4,4′-bpy)] · MeOH ( 1), [Fe(L2)(EtOH)] ( 2) and [Fe(L3)(MeOH)] ( 3) (L1 = N, N′-bis(2-hydroxy-1-naphthaldehyde)-1,2-phenylenediimine; L2 = N, N′-bis(salicylidene)-1,2-phenylenediamine; L3 = N, N′-bis(5-Cl-salicylidene)-1,2-phenylenediamine; 4,4′-bpy = 4,4′-bipyridine) are reported. X-ray single crystal structure analyses for 1– 3 reveal that 1 shows a dinuclear Fe(II)–bis-Schiff base complex bridged by 4,4′-bpy, while 2 and 3 show mononuclear structures. Molecular packing of 2 shows a uniform one-dimensional chain structure through hydrogen bonds and Fe⋯π interaction and that of 3 indicates significant π–π interaction to form a dimmer structure. The χT– T plots of 1– 3 show all ferromagnetic interaction at low temperature. The origin of the ferromagnetic interaction observed in 2 is tentatively ascribed to the dimer formation through Fe⋯π interaction at low temperature.

The effect of molecular packing on the occurrence of spin crossover phenomena in one-dimensional Fe(II)-bis-Schiff base complexes

Two new one-dimensional Fe(II)-bis-Schiff base complexes, [Fe(L1)(pyz)] · CH 2Cl 2 ( 1) and [Fe(L2)(pyz)] · 2CH 2Cl 2 ( 2) (H 2L1 = bis( O-vanillin)- O-phenylenediimine, H 2L2 = bis( O-vanillin)-2,3-naphthalenediimine, pyz = pyrazine) are reported with their crystal structures and magnetic property. Compound 1 shows a two-step SCO behavior while 2 shows HS at all the temperature range measured. Although the extension of aromatic moiety from benzene (L1) to naphthalene (L2) was introduced for the purpose of strengthening the cooperativity, it leads to the absence of SCO, due to the unanticipated π–π interaction, which leads to the longer Fe–N bond lengths and a weak ligand field around Fe(II) ion.

Studies on the Kinetics and Mechanism of Hydrolysis of p-nitrophenyl Picolinate (PNPP) by Unsymmetrical bis-Schiff Base Complexes with Aza-crown Ether or Morpholino Pendants

Two novel unsymmetrical bis-Schiff base manganese(III) and cobalt(II) complexes with benzo-10-aza-crown ether pendants (MnL1Cl, CoL1), and their analogoues with morpholino pendants (MnL2Cl, CoL2), have been synthesized and employed as models to mimic hydrolase in p-nitrophenyl picolinate (PNPP). The kinetics and the mechanism of PNPP hydrolysis catalyzed by these complexes were investigated. A kinetic mathematical model of PNPP cleavage catalyzed by these complexes was proposed. The effects of the complexes structure and reactive temperature on the rate of catalytic PNPP hydrolysis have been also examined. The results showed that the rate for the catalytic PNPP hydrolysis increased following the increase in pH of the buffer solution; four complexes exhibited high activity in the catalytic PNPP hydrolysis. Compared with the crown-free analogoues MnL2Cl and CoL2, the crowned Schiff base complexes (MnL1Cl, CoL1) exhibit a higher catalytic activity; the pseudo-first-order-rate (kobs) for the PNPP hydrolysis catalyzed by the complex MnL1Cl containing benzo-10-aza-crown ether is 1.04 × 103 that of spontaneous hydrolysis of PNPP at pH = 7.00, [S] = 2.0×10−4 mol dm−3.

Versatility of 2,6-diacetylpyridine (dap) hydrazones in stabilizing uncommon coordination geometries of Mn(ii): synthesis, spectroscopic, magnetic and structural characterization

Five seven- or eight-coordinate manganese complexes of hydrazone ligands have been prepared. Three seven-coordinate neutral Mn(II) complexes: [Mn(dapA2)]n (1), [Mn(dapB2)(H2O)2] (2), [Mn(dapS2)(H2O)2] (3) have been synthesized from the bis-Schiff bases of 2,6-diacetylpyridine: dap(AH)2, dap(BH)2 and dap(SH)2 (AH = anthraniloyl hydrazide, BH = benzoyl hydrazide, SH = salicyloyl hydrazide), respectively. Two eight-coordinate Mn(II) complexes: [Mn(dapS)2] (4) and [Mn(dapB)2].3H2O (5) have been synthesized from the mono-Schiff bases dapBH and dapSH, respectively. The complexes have been characterized by elemental analyses and by IR, UV-Vis., FAB mass, EI mass and EPR spectroscopy. The molecular structures of 1, 3.DMF and 4.DMF have been determined by single-crystal X-ray diffraction. The mono-Schiff bases are monoanionic and the bis-Schiff bases are dianionic. The octa-coordinated mono-Schiff base complex 4 adopts a dodecahedral geometry, while the hepta-coordinated bis-Schiff base complex 1 forms a one-dimensional linear polymeric chain. A weak antiferromagnetic exchange interaction (J=-0.15 cm(-1)) between the Mn(II) ions in is attributed to weak Mn...Mn interaction through the PhNH(2) moiety of the ligand, as indicated by extended-Hückel molecular orbital calculations. A good simulation of the EPR spectrum of a frozen solution (DMSO at 4 K) of compound 1 was obtained with g=2.0, D=0.1 cm(-1), E=0.01 cm(-1). The EPR spectrum of a powdered sample of compound 1 shows a large broadening of the signal, due in part, to the important zero-field splitting of the hepta-coordinated Mn(II) ion.

Synthesis, Characterization and Bioactivity of Bis-Schiff Base Complexes of Furoylpyrazolone

Synthesis, Characterization and Bioactivity of Bis-Schiff Base Complexes of Furoylpyrazolone

Synthesis and Structural Studies of Cxovanadium(V) Complexes of Semicarbazones

Abstract 1:1 and 1:2 mole ratio reactions of trichlorooxovanadium(V) with the sodium salt of semicarbazones derived from different heterocyclic aldehydes result in the formation of five- and six-coordinated oxovanadium(v) complexes, respectively. These have been isolated and characterised by elemental analysis, molecular weight determinations and conductance and magnetic measurements. Based on electronic, infrared and proton magnetic resonance spectral studies, distorted trigonal bipyramidal and octahedral geometries have been suggested for the mono- and bis-Schiff base complexes, respectively.

Niobium(V) and Tantalum(V) Derivatives of Schiff Bases Derived from β-Hydroxynaphthaldehyde and Acetylacetone with n-Hydroxy-alkylamines

Schiff base derivatives of niobium and tantalum of the types, M(OPri)3SB, M(OPri)(SB)2 and M(SB)2(SBH) have been synthesized by the reactions of the metal isopropoxides with the Schiff bases in 1:1, 1:2 and 1:3 molar ratios (where M=Nb or Ta, SBH⊖ and SB2⊖ represent the corresponding anions of the Schiff bases). Except the triisopropoxy acetylacetone-2-hydroxy-alkylimine derivatives of these metals which are distillable, all the remaining complexes decompose when an attempt is made to distil them. The triisopropoxy mono - Schiff base and the tris - Schiff base derivatives of these metals are essentially monomeric in boiling benzene and probably possess hexa- and octa-coordinated metal atoms, while the monoisopropoxy bis-Schiff base complexes show slight tendency of polymerization.