Polydentate Schiff Base Ligand Research Articles

Homo and hetero-bridged dinuclear copper(II) complex: Synthesis, X-ray structure and catalytic N-arylation

Two new dinuclear Cu(II) Schiff base compounds were synthesized, structurally characterized and their catalytic efficacy in N-arylation reaction was studied. Reaction of CuCl2 with two different polydentate Schiff base ligands viz. H2L1 (H2L1 = 1-(N-ortho-hydroxyacetophenimine)-ethane-2-ol) and H2L2 (H2L2 = 2-methoxy-6-[(2-hydroxyethylimino)methyl]phenol) has afforded two new very different in structure complexes [Cu2(HL1)2(µ-Cl)2]·(H2O)3 (1) and [Cu2L2(HL2)(µ-Cl)Cl]2·(H2O) (2). Complexes 1 and 2 were characterized by single crystal X-ray diffraction, FT-IR, elemental analysis, UV/Vis spectroscopic and TG/DTA studies. Complex 1 featured a simple dichloro-bridged dinuclear moiety, whereas 2 a hetero-bridged (chloro and phenolic oxygen) dinuclear compound. Catalytic efficacy towards N-arylation reactions between aryl iodide with aryl amine catalyzed by complexes 1 and 2 under homogeneous condition had been studied. Both the catalysts exhibited excellent catalytic efficacy in DMSO medium.

Linear-shaped Ln and Ln clusters constructed by a polydentate Schiff base ligand and a β-diketone co-ligand: structures, fluorescence properties, magnetic refrigeration and single-molecule magnet behavior.

Herein, ten new linear-shaped LnIII4 and LnIII6 clusters, with the formula [Ln4(acac)6L2(CH3O)2(CH3OH)4]·xCH3OH (Ln = Nd (1), Sm (2), Eu (3), Gd (4), Tb (5), Dy (6), and Tm (8), Hacac = acetylacetone), [Ln6(acac)4L4(CH3O)6]·xCH3OH (Er (7) and Yb (9)), and [Lu4(acac)6L2(OH)2]·2CH2Cl2 (10), based on a polydentate Schiff base ligand, H2L, and a β-diketone co-ligand were successfully synthesized and structurally characterized. Single crystal X-ray diffraction measurements reveal that the structures of the clusters 1-6, 8 and 10 are very similar and their central Ln(iii) ions are linearly arranged Ln4; however, the clusters 7 and 9 possess a rare linearly arranged Ln6. The investigations on the solid-state fluorescence properties show that the clusters 2, 3, 5 and 6 display the characteristic lanthanum luminescence at room temperature. Magnetic studies reveal that weak antiferromagnetic interactions exist between adjacent Gd(iii) ions in cluster 4. More importantly, the cluster 4 exhibits significant MCE with the maximum -ΔSm value of 27.96 J kg-1 K-1 at 2.0 K and 7.0 T, whereas the cluster 6 displays a slow magnetic relaxation behavior under a zero dc field with the effective energy barrier ΔE/kB = 8.64 K and τ0 = 6.98 × 10-6 s.

Solvent-induced two Dy2 compounds with different structures showing distinct slow magnetization relaxation behaviors

Two new Dy2 compounds, namely, [Dy2(dbm)4(H2L)(CH3O)(CH3OH)] (1) and [Dy2(dbm)5(H2L)] (2) (dbm = dibenzoylmethane, H3L = (2E,N′E)-2-(hydroxyimino)-N′-(pyridin-2-ylmethylene)propanehydrazide, based a polydentate Schiff base ligand have been synthesized, structurally and magnetically characterized. The single-crystal X-ray diffraction researchshow that both compounds 1 and 2 are binuclear structures. The only difference is that two methanol molecules coordinated to Dy(III) ion in 1 instead of a dbm− coordinated to Dy(III) ion in 2. Magnetic property measurements indicate that they exhibit distinct slow magnetic relaxation behaviors (ΔE/kB = 0.87 K for 1 and ΔE/kB = 18.68 K for 2). This work revealed that the different solvent induced slight disparate structural and magnetic behaviors of two Dy2 compounds, which may provide an effective approach for tuning slow magnetization relaxation behaviors in polynuclear Ln-clusters.

Heptanuclear heterometallic Cu5Ln2(Ln = Gd, Tb) complexes: Synthesis, crystal structures, and magnetic properties studies

The reaction of Ln(NO3)3·6H2O (Ln = Gd, Tb) and Cu(O2CMe)2·H2O with the polydentate Schiff base ligand OHC10H7CHNC(C2H5)(CH2OH)2 (H3L) in Me2CO afforded the heptanuclear heterometallic complexes [Cu5Ln2(O2CMe)2(NO3)4(L)2(HL)2] (Ln = Gd (1), Tb (2)) which were characterized by single-crystal X-ray crystallography (1) and powder XRD measurements (2). Both complexes are isomorphous and consist of a central core {CuII5LnIII2(μ3-OR)6(μ3-O2CMe)2}8+ described as two distorted centrosymmetrically related cubane subunits, {CuII3LnIII(μ3-OR)3(μ3-O2CMe)}5+, with the common apex, Cu(1), residing on an inversion center. Peripheral ligation and bridging is provided by two triply and two doubly deprotonated Schiff base ligands, two μ3-acetates and four chelate nitrates. Magnetic susceptibility measurements revealed the presence of dominant ferromagnetic interactions for both complexes. The magnetocaloric effect of 1 was examined via isothermal magnetization measurements under various applied fields and the maximum entropy change was found equal to 15.7 J kg−1 K−1 at 2 K for ΔH = 5 T. Ac susceptibility measurements of 2 revealed slow magnetic relaxation process suggesting the presence of single-molecule magnet behavior.

Design, synthesis, and characterization of an Fe(ii)-polymer of a redox non-innocent, heteroatomic, polydentate Schiff's base ligand: negative differential resistance and memory behaviour

Complete characterization and memristive study of the electrochemically active, novel Fe(ii)-polymer of a fluorescence active conjugated, hexadentate ligand.

Structural variety of mono- and binuclear transition metal complexes of 3-[(2-hydroxy-benzylidene)-hydrazono]-1-(2-hydroxyphenyl)-butan-1-one: Synthesis, spectral, thermal, molecular modeling, antimicrobial and antitumor studies

A new polydentate Schiff base ligand and its metal complexes were synthesized and characterized by elemental analyses, IR, 1H NMR, electronic, ESR and mass spectra, conductivity and magnetic susceptibility measurements as well as thermal analyses. The free ligand was synthesized by condensation of o-acetoacetylphenol with salicylaldehyde hydrazone. The analytical and spectroscopic tools showed that the obtained complexes are mono- and binuclear complexes, which can be generally formulated as: [(L)M2X2(H2O)m]·nZ; M = Cr, Fe, Ni or Cu, X = OAc or NO3, m = 5 or nil and n = 3, 1.5 or 0.5 and Z = EtOH or H2O, [(H2L)2M(X)m].nH2O; M = Mn, Zn, or Cd, X = EtOH, H2O or nil, m = 2 or nil and n = 3.5 or 0, [(HL)2Co2]·0.5H2O and [(H2L)2UO2(H2O)]. The metal complexes displayed octahedral, tetrahedral and square-planar geometrical arrangements, while uranium complex displayed seven-coordinate. Kinetic parameters (Ea, A, ΔH, ΔS and ΔG) of the thermal decomposition stages have been evaluated using Coats–Redfern equations. The molecular structural parameters of the ligand and its metal complexes have been calculated and correlated with the experimental data such as IR. The antimicrobial activity of the ligand and its complexes was screened against some kinds of bacteria and fungi. The antitumor activity of the ligand and its Ni(II) and Cu(II) complexes was investigated against HepG2 cell line.

Synthesis, crystal structure and magnetic studies of linear and cubane-type tetranuclear Cu(II) complexes obtained by stoichiometric control of the reagents

Two new tetranuclear Cu(II) complexes, [Cu4(L)2(μ-OAc)2(CH3OH)2] (1) and [Cu4(HL)4(CH3OH)2] (2), were synthesized from the reaction of copper(II) acetate with a polydentate Schiff base ligand in different molar ratios in methanol solvent (H3L=2-{[(1E)-(5-bromo-2-hydroxyphenyl)methylene]amino}-2-methylpropane-1,3-diol). These complexes were characterized by elemental analysis, spectroscopic methods and single crystal X-ray analysis. Complex 1 is a linear tetranuclear Cu(II) complex while complex 2 has a cubane-like arrangement. The results show that the reaction of H3L with Cu(OAc)2·H2O in 1:2 molar ratios afforded complex 1 as sole product. By changing the molar ratios into 2:2 in the same reaction system, cubane-like tetranuclear copper(II) complex (complex 2) was isolated. Crystal structures of complexes indicate that part of the acetate anions remain coordinated to the Cu(II) ions when a higher amount of metal salt employees in the reaction. In this condition the ligand uses all of its donor atoms. When the reagents are added in equimolar ratio, all the acetate anions are replaced by ligand and one of the alcoholic donor groups of the ligand do not coordinate to the metal ion. The magnetic behavior of both compounds is closely related to their crystal structures showing antiferromagnetic couplings between nearest neighbors copper ions in 1 and both ferro and antiferromagnetic exchanges in the cubane like 2.

Manganese(IV) complex with a polydentate Schiff base ligand: synthesis, crystal structure, TDDFT calculation, electronic absorption and EPR spectral study

A six-coordinate Mn(IV) complex, [Mn(H2L)2] (1) [H4L = 2-methoxy-6-(tris(hydroxymethyl)methyliminomethyl)phenol], was synthesized and characterized by elemental analysis, single-crystal X-ray crystallography, FTIR, UV–Vis electronic absorption, and EPR spectroscopy. The single-crystal structural determination reveals that the complex crystallizes in tetragonal space group P41212 and the tridentate Schiff base ligands are arranged in mer configuration chelating manganese, which exhibits as slightly distorted octahedral coordination sphere with a N2O4 chromophore. Weak hydrogen bonding interactions of uncoordinated hydroxyl groups result in a 2-D supramolecular structure. The UV–Vis electronic absorption and IR spectral data of 1 have been compared with the results obtained by employing DFT and time-dependent density functional theory calculation using B3LYP, B3PW91, and MPW1PW91 functionals, with 6-31G (d-p) and LanL2MB basis sets. The results of these calculations are functional-dependent and, among those used, B3PW91 proved to better reproduce the experimental results.

Syntheses, crystal structures, and magnetic properties of a series of Fe2Ln complexes

A family of phenoxo-bridged heterometallic Schiff base trinuclear complexes, [Fe2LnL2(C3H7COO)(H2O)]·CH3OH·CH3CN·H2O (Ln = Sm, 1; Gd, 2; Tb, 3; Dy, 4) is reported. Those complexes were afforded by “one-pot” reaction of a polydentate Schiff base ligand 2-hydroxy-3-methoxy-phenylsalicylaldimine (H2L) with Fe(NO3)3·9H2O, Ln(NO3)3·6H2O and sodium butyrate (C3H7COONa) in a mixture of methanol and acetonitrile in the presence of triethylamine as a base. Single-crystal X-ray diffraction analysis reveals that the structures of the four complexes are isomorphic. In each complex, two anionic [FeL2]− units coordinate to the central lanthanide ion as a tetradentate ligand using its four phenoxo oxygens, forming a two-blade propeller-like molecular shape. Magnetic properties of 1–4 were investigated using variable temperature magnetic susceptibility, and weak ferromagnetic exchange between the FeIII and LnIII ions has been established for the Gd derivative. The Tb and Dy complexes show no evidence of slow relaxation behavior above 2.0 K.

Solvatochromic and application in dye-sensitized solar cells of sandwich-like Cd(II) complexes: supramolecular architectures based on N(1),N(3)-bis[(6-methoxypyridin-2-yl)methylene]benzene-1,3-diamine.

A novel polydentate Schiff base ligand N(1),N(3)-bis[(6-methoxypyridin-2-yl)methylene]benzene-1,3-diamine (L) and its two dinuclear sandwich-like complexes {[CdL(NO3)(H2O)]·NO3}2 (1) and {[CdL(CH3CN)(H2O)]·(ClO4)2·(CH3CN)2}2 (2) were synthesized. Both C-H∙∙∙O, C-H∙∙∙N and π-π non-covalent interactions had essential roles in constructing the resulting three-dimensional supramolecular networks. L emits a more intense blue-green fluorescence emission around 493 nm than in dilute solution, exhibiting stacking-induced emission properties. Complexes 1 and 2 exhibited the dual properties of exceptional solvatochromism and fluorescence quenching towards CH3OH molecules. As these compounds could overcome the absent absorption of ruthenium complex N719 in the low wavelength region of the visible spectrum, offset the competitive visible light absorption of I3(-) and reduce the charge recombination of injected electrons, the Schiff base ligand l and complexes 1 and 2 were used as co-sensitizers in combination with N719 to investigate their effect on enhancing the performance of dye-sensitized solar cells. A short circuit current density of 14.37 mA cm(-2), an open-circuit voltage of 0.71 V and a fill factor of 0.61 corresponding to an overall conversion efficiency of 6.17% under AM 1.5 G solar irradiation were achieved when 1 was used as a co-sensitizer, which are much higher than the results obtained for dye-sensitized solar cells sensitized by N719 alone (5.06%).

Coordination versatility of 1,5-bis(salicylidene)carbohydrazide in Ni(II) complexes

Versatile coordination behavior of a polydentate Schiff base ligand 1,5-bis(salicylidene)carbohydrazide (H3bsc) has been explored in Ni(II) complexes. [Ni(H3bsc)2](ClO4)2 (1)·H2O·3CH3CN is a bis chelate mononuclear complex of H3bsc in keto form, and [Ni4(H0.5bsc)2(O2CCMe3)3(CH3OH)4](2)·2H2O·2CH3OH is a tetranuclear complex of H3bsc with an unusual coordination. In 2, one phenolate group of the ligand coordinates in a monodentate way and the other coordinates in a μ2-bridging mode to the Ni(II) center. This unusual coordination mode of the ligand stabilizes the Ni(II) complex in a tetranuclear form where the carbonyl oxygen of the ligand exists in between keto and enol form of bond order 1.5. Thus, complex 2, represents an unprecedented coordination behavior of the Schiff base ligand derived from carbohydrazides. Studies of magnetic properties of 2 are reported which reveal antiferromagnetic interaction between four Ni(II) centers.

Formation of C C and C O bonds via solvothermal in situ metal–ligand reaction: Synthesis and crystal structures of two novel nickel(II) complexes supported by in situ generated polydentate Schiff base ligands

Under solvothermal conditions, complexes Ni(HL2) (1) and Ni(L3)center dot MeOH (2 center dot MeOH) (H(3)L2=N-(2-(2-hydroxybenzylideneamino)-1-(2-hydroxyphenyl)-2-(pyridin-2-yl)ethyl)picolinamide; H(2)L3=1-(pyridin-2-yl)prop-1-ene-1,2-diyl)bis(azan-1-yl-1-ylidene)bis((methan-1-yl-1-ylidene)diphenol) have been synthesized from the reaction of Ni(CH3COO)(2)center dot 4H(2)O with 2-((pyridin-2-ylmethyleneamino)methyl)phenol (HL1) at 70 and 90 degrees C, respectively. The complexes were characterized by X-ray single crystal diffraction, IR spectroscopy, and elemental analysis. The plausible mechanisms for the formation of H(3)L2 and H(3)L3 via solvothermal in situ metal-ligand reactions were proposed. (C) 2013 Elsevier B.V. All rights reserved.

Three dinuclear lanthanide(iii) compounds of a polydentate Schiff base ligand: Slow magnetic relaxation behaviour of the DyIII derivative

The initial employment of N1,N2,N3,N4-tri(3-methoxysalicylidene) triethylenetetraamine ligand (H3L, Scheme 1) in lanthanide coordination chemistry for single molecule magnets has yielded a new family of dinuclear LnIII2 compounds with the general formula of [Ln2(L)2]·nCH3CN (Ln = Gd (1), Tb (2) with n = 0, Ln = Dy (3) with n = 4). These three complexes have been structurally and magnetically characterized. The structural analyses reveal that they are isomorphous dinuclear complexes where the Ln2 entities were encapsulated by two polydentate Schiff base ligands. Variable-temperature magnetic susceptibility studies indicate the presence of dominant antiferromagnetic interactions in complexes 2 and 3, whereas complex 1 containing isotropic Gd ions allows the quantification of the antiferromagnetic interaction with JGd–Gd = −0.041 cm−1. Dynamic measurements reveal that 3 displays single-molecule magnet behaviour with an activation energy barrier Δ = 18.9 K and pre-exponential factor τ0 = 3.92 × 10−6 s, while 1 and 2 do not show any out-of-phase ac susceptibility signals.

Two d10-metal-organic frameworks based on polydentate Schiff-base ligand derived from biphenyl dihydrazide: Synthesis, crystal structure and luminescent properties

Two two-dimensional d10-metal-organic frameworks {[CdL2(NO3)2]·(H2O)6}n (1) and {[Zn2L4(NCS)4]·(H2O)4·(CH3OH)}n (2) have been synthesized and characterized by IR, elemental analyses, XRPD, TG technique and complete X-ray single crystal structure analyses, where L is bis(pyridin-3-ylmethylene)biphenyl-2,2′-dicarbohydrazide. The two polymers display similar 2D layer network containing tetranuclear metallacyclic ring units [MII4L4] (M=Cd (1) and Zn (2)) in the chair conformation, in which each ligand L acts as a bidentate bridging ligand to bind two metal centers through two terminal pyridyl N-donors. The solvent molecules were filled into the macrometallacyclic ring units through multiform hydrogen bonds. In addition, the CH⋯π interactions are found in the 2D networks and also play an important role in stabilizing the networks. The luminescent properties of 1 and 2 were investigated in the solid state at room temperature.

Synthesis, characterization, equilibrium study and biological activity of Cu(II), Ni(II) and Co(II) complexes of polydentate Schiff base ligand

Schiff base ligand, 1,4-bis[(2-hydroxybenzaldehyde)propyl]piperazine (BHPP), and its Cu(II), Ni(II) and Co(II) metal complexes were synthesized and characterized by elemental analysis, magnetic susceptibility, molar conductance and spectral (IR and UV–vis) studies. The ground state of BHPP ligand was investigated using the BUILDER module of MOE. Metal complexes are formed in the 1:1 (M:L) ratio as found from the elemental analysis and found to have the general formula [ML]·nH2O, where M=Co(II), Ni(II) and Cu(II), L=BHPP. In all the studied complexes, the (BHPP) ligand behaves as a hexadentate divalent anion with coordination involving the two azomethine nitrogen’s, the two nitrogen atoms of piperazine ring and the two deprotonated phenolic OH-groups. The magnetic and spectral data indicates octahedral geometry of metal(II) complexes. The ligand and their metal chelates have been screened for their antimicrobial activities using the disc diffusion method against the selected bacteria and fungi. They were found to be more active against Gram-positive than Gram-negative bacteria. Protonation constants of (BHPP) ligand and stability constants of its Cu2+, Co2+ and Ni2+ complexes were determined by potentiometric titration method in 50% DMSO–water solution at ionic strength of 0.1M sodium nitrate. It has been observed that the protonated Schiff base ligand (BHPP) have four protonation constants. The divalent metal ions Cu2+, Ni2+ and Co2+ form 1:1 complexes.

Synthesis, crystal structures and luminescent properties of two one-dimensional cadmium(II) coordination polymers generated from polydentate Schiff-base ligand

Two new one-dimensional coordination polymers {[CdL2(H2O)2](NO3)2(H2O)6}n (1) and {[CdLI2](H2O)(CH3OH)}n (2) have been synthesized and characterized by IR, elemental analysis, TG technique, XRPD and complete single crystal structure analyses, where L is bis(pyridin-4-ylmethylene)biphenyl-2,2′-dicarbohydrazide. The Cd(II) atom has a distorted octahedral coordination geometry with N4O2 donors from four ligands and two water molecules in 1 and a distorted tetrahedral coordination geometry with NOI2 donors from two ligands and two I− anions in 2, respectively. Polymer 1 shows a 1D framework structure containing bimetallic 42-membered quadrangular ring units. The adjacent 1D chains are interacted forming a 3D supramolecular network structure through multiform hydrogen bond interactions. In comparison with 1, polymer 2 is a new rampart-type chain and each chain is interacted with each other through hydrogen bond interactions to lead a 2D layer. The luminescent properties of the polymers 1 and 2 were investigated in the solid state at room temperature.

Polydentate Schiff Base Ligands and Their La(III) Complexes: Synthesis, Characterization, Antibacterial, Thermal, and Electrochemical Properties

We synthesized the Schiff base ligands H2L1–H2L4 and their La(III) complexes and characterized them by the analytical and spectroscopic methods. We investigated their electrochemical and antimicrobial activity properties. The electrochemical properties of the ligands H2L1–H2L4 and their La(III) complexes were studied at the different scan rates (100 and 200 mV), different pH ranges (), and in the different solvents. The electrooxidation of the Schiff base ligands involves a reversible transfer of two electrons and two protons in solutions of pH up to 5.5, in agreement with the one-step two-electron mechanism. In solutions of pH higher than 5.5, the process of electrooxidation reaction of the Schiff base ligands and their La(III) complexes follows an ECi mechanism. The antimicrobial activities of the ligands and their complexes were studied. The thermal properties of the metal complexes were studied under nitrogen atmosphere in the range of temperature 20–1000°C.

Two one-dimensional d10-metal coordination polymers based on polydentate Schiff-base ligand: Synthesis, crystal structure and luminescent properties

Two one-dimensional d10-metal coordination polymers {[AgL(H2O)]2[AgL(NO3)]2(NO3)2L(H2O)2}n (1) and [ZnLCl2]n (2) (L=N,N′-bis-(1-pyridin-4-yl-ethylidene)-hydrazine) have been synthesized and characterized by IR, elemental analysis, TG technique, XRPD and X-ray crystallography. Polymer 1 contains two types of 1D Ag-double-chain units. Ag(1)-double-chain unit is formed by linking two adjacent Ag(1)-L-chains through face-to-face π⋯π interactions, while Ag(2)-double-chain unit is formed through the combination of coordinating NO3− anions bridging interactions and π⋯π interactions between two adjacent Ag(2)-L-chains. Free ligands interact with the adjacent Ag(1)-double-chain units and Ag(2)-double-chain units to form a 3D supramolecular structure through multiform hydrogen bonds. For polymer 2, each ligand acts as a bis-monodentate bridging ligand to bind adjacent Zn(II) centers forming a one-dimensional chain structure. Furthermore, 1D chain is held together with its neighboring ones via CH⋯π interactions. The luminescent properties of the polymers 1 and 2 were investigated in the solid state at room temperature.

Hexanuclear Dysprosium(III) Compound Incorporating Vertex- and Edge-Sharing Dy3 Triangles Exhibiting Single-Molecule-Magnet Behavior

A unique hexanuclear dysprosium(III) compound with a new polydentate Schiff-base ligand shows complex slow relaxation of the magnetization most likely associated with the single-ion behavior of individual Dy(III) ions as well as the possible weak coupling between them.

Synthesis and structural characterization of a novel seven-coordinate cobalt(II) complex: 2,9-Bis(ethanolamine)-1,10-phenanthrolinechlorocobalt(II) chloride

Condensation reaction of 2,9-dicarboxaldehyde-1,10-phenanthroline with 2-aminoethanol followed by NaBH 4 reduction yielded the polydentate Schiff base ligand 2,9-bis(ethanolamine)-1,10-phenanthroline in its reduced form. This ligand was characterized by elemental analysis, LC–MS, IR, UV–Vis and NMR spectroscopy. Reaction of the reduced Schiff base ligand with aqueous solution of cobalt(II) chloride affords 2,9-bis(ethanolamine)-1,10-phenanthrolinechlorocobalt(II) chloride in high yield. Single crystals of the cobalt(II) complex were obtained from the crystallization in ethanol and its structure was elucidated by X-ray structural analysis. The cobalt(II) complex ion was found to be seven-coordinated in a pentagonal bipyramidal geometry, whereby cobalt(II) ion is surrounded by the six donor atoms in the ligand molecule and a chloride ion.