Asymmetric Schiff Base Ligand Research Articles

Syntheses and conversions of dinuclear cadmium(ii) compounds containing N2O/N2O2 donor tridentate/tetradentate asymmetrical Schiff base ligands

Through different synthetic strategies, four dinuclear cadmium(II) complexes containing N2O/N2O2 donor tridentate/tetradentate asymmetrical Schiff base ligands have been synthesized and characterized. The two complexes [Cd(L1)(μ2-Cl)(CH3OH)]2 (1) and [Cd(L2)Cl]2·CH3OH (2) are constructed, respectively, from self-assembly of a Cd2+ ion with two asymmetrical Schiff base ligands, namely 2-((2-(dimethylamino)ethylimino)methyl)phenol (HL1) and 2-((2-(dimethylamino)ethylimino)methyl)-6-methoxyphenol (HL2). However, via single-crystal to single-crystal structural transformations driven by temperature, the other two corresponding compounds [Cd(L1)Cl]2 (1a) (1 → 1a) and [Cd(L2)Cl]2 (2a) (2 → 2a), with N2O2Cl and N2O3Cl donors, respectively, can be obtained. Obviously, the synthetic strategies presented in the text provide very effective methods for constructing the dinuclear CdII compounds with N2O/N2O2 donor tridentate/tetradentate asymmetrical Schiff base ligands. Meanwhile, the strong fluorescence emission of 1 and 2 makes them potentially useful photoactive materials.

Pseudo‐Octahedral Schiff Base Nickel(II) Complexes: Does Single Oxidation Always Lead to the Nickel(III) Valence Tautomer?

AbstractWith the aim of establishing correlations between the ligand structure and the oxidation site in nickel complexes from Schiff base ligands, five ligands and their nickel complexes have been synthesized. The prototypical asymmetric Schiff base ligand HL1 contains both phenol and pyridine pendant arms with a pivotal imine nitrogen atom. Ligands HL2–5 differ from HL1 by either their phenolate para substituent, the hybridization of the pivotal nitrogen atom, and/or the N‐donor properties of the pyridine moiety. The five complexes [Ni(L1–5)2] are obtained by treating the corresponding ligands with 0.5 equiv. of Ni(OAc)2·4H2O in the presence of NEt3. X‐ray crystal‐structure diffraction studies as well as DFT calculations reveal that [Ni(L1–5)2] involves a high‐spin nickel(II) ion within a pseudo‐octahedral geometry. The two ligands are arranged in a meridional fashion when the pivotal nitrogen atom is an imine {as in [Ni(L1–2)2] and [Ni(L4–5)2]}, while the fac isomer is preferred in [Ni(L3)2] (amino pivotal nitrogen atom). [Ni(L1)2] is characterized by an oxidation potential at –0.17 V vs. Fc+/Fc. The one‐electron‐oxidized species [Ni(L1)2]+ exhibits an EPR signal at g = 2.21 attributed to a phenoxyl radical that is antiferromagnetically coupled to a high‐spin NiII ion. [Ni(L2)2] differs from [Ni(L1)2] by the phenolate para substituent (a tert‐butyl instead of the methoxyl group) and exhibits an oxidation potential that is ca. 0.16 V higher. Compared to [Ni(L1)2]+ the cation [Ni(L2)2]+ exhibits a SOMO that is more localized on the metal atom. The EPR and electrochemical signatures of [Ni(L3)2]+ are similar to those of [Ni(L1)2]+, thus showing that an imino to amino substitution compensates for a methoxy to tert‐butyl one. Replacement of the pyridine by a quinoline group in [Ni(L4–5)2] makes the complexes slightly harder to oxidize. The EPR signatures of the cations [Ni(L4–5)2]+ are roughly similar to those of the pyridine analogs [Ni(L1–2)2]+. The oxidation site is thus not significantly affected by changes in the N‐donor properties of the terminal imino nitrogen atom.(© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008)

Copper(II) complexes of symmetrical and unsymmetrical tetradentate Schiff base ligands incorporating 1-benzoylacetone: Synthesis, crystal structures and electrochemical behavior

Three new copper(II) complexes [CuL 1] 2(ClO 4) 2 ( 1), [CuL 2]ClO 4 ( 2) and [CuL 3] ( 3) with three Schiff base ligands [HL 1 = 1-phenyl-3-{3-[(pyridin-2-ylmethylene)-amino]-propylimino}-butan-1-one, HL 2 = 1-phenyl-3-[3-(1-pyridin-2-yl-ethylideneamino)-propylimino]-butan-1-one and H 2L 3 = 3-[3-(1-methyl-3-oxo-3-phenyl-propylideneamino)-propylimino]-1-phenyl-butan-1-one] have been synthesized and structurally characterized by X-ray crystallography. The mono-negative tetradentate asymmetric Schiff base ligands (L 1) − and (L 2) − are chelated in complexes 1 and 2 to form square planar copper(II) complexes. In complex 1, the two units are associated weakly through ketonic oxygen of benzoylacetone fragment to form the dimeric entity. The square planar geometry of complex 3 is unusually distorted towards tetrahedral one. All three complexes exhibit reversible cyclic voltammetric responses in acetonitrile solution corresponding to the Cu II/Cu I redox process. The E 1/2 (−0.47 V versus SCE) of 3 shows significant anodic shift due to the tetrahedral distortion around Cu(II) compare to that of 1 and 2 (−0.82 and −0.87 V versus SCE, respectively).

(1-{(E)-2-[(2E,3Z)-4-Oxidopent-3-en-2-ylideneamino]ethyliminomethyl}naphthalen-2-olato)manganese(II) methanol solvate

In the title compound, [Mn(C18H18N2O2)]·CH3OH, the Mn atom is coordinated by two N atoms and two O atoms from the asymmetrical Schiff base ligand 1-[2-(4-oxidopent-3-en-2-ylidene­amino)ethyl­imino­meth­yl]naphthalen-2-olate in an approximately square-planar configuration. There is an O—H⋯O hydrogen-bond inter­action between the complex and the methanol solvent mol­ecule.

Novel Dinuclear Uranyl Complexes with Asymmetric Schiff Base Ligands: Synthesis, Structural Characterization, Reactivity, and Extraction Studies

The reaction of uranyl nitrate with asymmetric [3O, N] Schiff base ligands in the presence of base yields dinuclear uranyl complexes, [UO2(HL1)]2.DMF (1), [UO2(HL2)]2.2DMF.H2O (2), and [UO2(HL3)]2.2DMF (3) with 3-(2-hydroxybenzylideneamino)propane-1,2-diol (H3L1), 4-((2,3-dihydroxypropylimino)methyl)benzene-1,3-diol (H3L2), and 3-(3,5-di-tert-butyl-2-hydroxybenzylideneamino)propane-1,2-diol (H3L3), respectively. All complexes exhibit a symmetric U2O2 core featuring a distorted pentagonal bipyramidal geometry around each uranyl center. The hydroxyl groups on the ligands are attached to the uranyl ion in chelating, bridging, and coordinate covalent bonds. Distortion in the backbone is more pronounced in 1, where the phenyl groups are on the same side of the planar U2O2 core. The phenyl groups are present on the opposite side of U2O2 core in 2 and 3 due to electronic and steric effects. A similar hydrogen-bonding pattern is observed in the solid-state structures of 1 and 3 with terminal hydroxyl groups and DMF molecules, resulting in discrete molecules. Free aryl hydroxyl groups and water molecules in 2 give rise to a two-dimensional network with water molecules in the channels of an extended corrugated sheet structure. Compound 1 in the presence of excess Ag(NO3) yields {[(UO2)(NO3)(C6H4OCOO)](NH(CH2CH3)3)}2 (4), where the geometry around the uranyl center is hexagonal bipyrimidal. Two-phase extraction studies of uranium from aqueous media employing H3L3 indicate 99% reduction of uranyl ion at higher pH.

Interaction of Mn(acac)3 with Asymmetrical Schiff Base Ligands containing an Amido Group

AbstractInteraction of asymmetrical Schiff base ligands H3Ln [where H3Ln are substituted 3–aza–4–(2–hydroxyphenyl)–N– (2–hydroxyphenyl)but–3–enamide] with Mn(acac)3 (acac = acetylacetonate) has been investigated. Two different type of manganese(III) complexes have been obtained depending on the nature of the substituents on the ligand. We have found that ligands containing donor substituents drives to the formation of two different kinds of complexes from the same reaction: Mn(Ln)(H2O)x (1a–5a) and [Mn(HLn)(acac)](H2O)y (1b–5b) (where Ln and HLn signify the ligand in its trianionic and dianionic form, respectively). However, when the substituents are electron withdrawing or poor donor only compounds of the type [Mn(HLn)(acac)](H2O)y (6–10) are obtained. All these compounds have been characterized by elemental analyses, IR and 1H NMR spectroscopy, FAB mass spectrometry, magnetic measurements and molar conductivities. The electrochemical behaviour of these complexes has also been studied.

A new route to the asymmetric Schiff base ligands. The ligand exchange in [Mo(CN)3O(salhy)]2? ion. Kinetics and mechanism

The kinetics of the ligand exchange in (PPh4)2[Mo(CN)3O(salhy)]. 6H2O (Hsalhy = salicylaldehyde hydrazone) by a solvent molecule and by 2,2′-bipyridine (bpy) have been studied in EtOH. For the ligand exchange by a solvent molecule the pseudo-first order rate constant equals kobs = 3.2 (±0.2) × 10−3 s−1 (t=25 °C), ΔH‡=67 (± 7) kJ mol−1, ΔS‡=−75 (±23) J mol−1 K−1, while for the exchange by a bpy molecule kobs=3.5 (±0.2) × 10−3 s−1 (t=25 °C), ΔH‡=56 (±7) KJ mol−1, ΔS‡ = −104 (±8) J mol−1 K−1. It was found, that all reactions proceed via the same mechanism which involves the chelate ring opening cis to the Mo=O bond. The mechanism of the reaction was proposed and was proved by the synthesis of (PPh4)2[Mo(CN)3O(N-pic)]. 2.5H2O (N-pic denotes that the nitrogen of picolinic acid is trans to Mo=O) by ligand exchange in EtOH, while in aqueous solution the O-pic analogue is formed exclusively.

Synthesis and spectroscopic characterization of new adducts of diorganotin(IV) dichlorides with an asymmetric schiff base ligand

The novel schiff base adducts of tin(IV), [SnMe2Cl2(H2cdsalen)] and [SnPh2Cl2(H2cdsalen)2] have been synthesized by reaction of SnR2Cl2 (R=Me, Ph) with methyl 2-[2-(salicylideneamino)ethylamino]cyclopent-1-ene-1-dithiocarboxylate (H2cdsalen). The new products were characterized by elemental analysis, IR, 1H NMR and 119Sn NMR spectroscopies. Spectroscopic data suggest that in both complexes the ligand is coordinated through oxygen. The phenolic hydrogen within the free ligand was transferred to the imine nitrogen atom due to the coordination of oxygen with tin after the complex formation.

Preparation and Characterization of Novel Asymmetrical Schiff-Base Ligands Derived from 2-methyl-7-formyl-8-hydroxyquinoline and their Metal Complexes

Two novel asymmetrical Schiff-base ligands, H2L1 and H2L2, were prepared by reacting two half-unit Schiff-base compounds with 2-methyl-7-formyl-8-hydroxyquinoline. The two half-unit Schiff-base compounds were initially prepared by condensing dimedone with either ethylenediamine or p-phenylenediamine, respectively. Both ligands are dibasic and contain two sets of NO coordinating sites. Twelve metal complexes were obtained by reacting both ligands with Cu(II), Ni(II), Co(II), Mn(II), Fe(III), VO(IV) cations. The ligands and their metal complexes were characterized by elemental analysis, IR, UV-Vis, ESR and mass spectra, also magnetic moments of the complexes were determined. Visible spectra of the complexes indicated distorted octahedral geometries around the metal cations. ESR spectra indicated mononuclear and dinuclear structures of the complexes of ligands H2L1 and H2L2, respectively. Magnetic moments of the complexes were rather low compared with those expected for octahedral geometries and indicated polymeric linkage of the metal complex molecules within their crystal lattices. The insolubility of the metal complexes in most organic solvents support the polymeric structures.

A HIGH YIELD ROUTE TO NOVEL MANGANESE(III) COMPLEXES

Neutral manganese(III) complexes have been prepared, with high yield and purity, by a modification of the Boucher synthesis, using asymmetrical Schiff base ligands. These ligands [H3-amsal = 3-aza-4-(2-hydroxyphenyl)-N-(2-hydroxyphenyl)but-3-enamide], mcorpo-rating hard donor atoms, are derived from the condensation of an amine precursor containing an amide group and substituted salicylaldehydes. The complexes are found to be of the form MnIII (amsal-R)(H2O) n (n=0.5,3) and have been characterised by various methods. Data point to octahedral geometry at the manganese atom.

Synthesis, characterization and antimicrobial activity of cobalt(II), nickel(II)and copper(II) complexes with new asymmetrical Schiff base ligands derived from 7-formyanil-substituted diamine-sulphoxine and acetylacetone

Asymmetric 7-formyanil-substituted-imino-4-(4-methyl-2-butanone)-8-hydroxyquinoline-5-sulphonic acid (Schiff bases), react with CoII, NiII and CuII ions to give 1:2, 1:1 and 2:1 complexes as established by conductometric titrations in 1:1 DMF:H2O. The complexes were investigated by elemental analyses, molecular weight determinations, molar conductance, magnetic moments, thermal analysis, i.r., u.v.–vis. and e.s.r. spectra. The complexes have an octahedral crystal structure and general formula [ML·(OH2)2], where MII = Co, Ni and Cu, and L = Na[7—X—HL], (—X— = (CH2)2, (CH2)3, p-C6H4, o-C6H4). Antimicrobial activity of these new ligands and their transition metal complexes has been screened in vitro on common fungi and bacteria.

Copper(II) Complexes with Asymmetrical Schiff Base Ligands Derived from 2‐Acetylpyrazine

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A direct route to obtain manganese(III) complexes with a new class of asymmetrical Schiff base ligands

A new class of asymmetrically substituted Schiff base ligands has been synthesised incorporating hard amido donor atoms. The single crystal X-ray structure of one of these ligands, H3-amsal, has been determined [H3-amsal=3-aza-4-(2-hydroxyphenyl)-N-(2-hydroxyphenyl)but-3-enamide]. The structure reveals the ligand to be suitable for use as an equatorially co-ordinating ligand in octahedral complexes. A new route to obtaining manganese(III) complexes of these ligands, with high yield and purity, has been designed. Complexes of the form MnIII(amsal-R)(H2O)n (n=1–4) have been prepared by the electrochemical oxidation of a manganese anode in an acetonitrile solution of the ligands. The compounds have been characterised by elemental analyses, IR and 1H NMR spectroscopies, FAB mass spectrometry, magnetic measurements, ΛM and cyclic voltammetry.

Novel Asymmetric Tetradentate Schiff Base Ligands Derived from 6-Metwia-Formyl4-Hydroxy-2-(1H)-Quinolone and Their Metal Complexes

Novel asymmetric, tetradentate, dibasic Schiff base ligands were synthesized by the condensation of the half-unit Schiff base ligand 3-[o-aminophenyliminomethyl]-4-hydroxy-6-methyl-2-(1H)-quinolone with acetylacetone and salicylaldehyde. Cu(II), Ni(II), UO2 (VI) and Fe(III) complexes of both ligands were prepared using different salts in the case of Cu(II) and Ni(II) cations The structures of the ligands and the complexes were elucidated by chemical analyses, IR, UV-visible, mass spectra and magnetic moment measurements. Both Cu(II) and Ni(II) cations are initially coordinated to the N2O2 coordinating sites of the ligands The Cu(II) complexes were either square-planar mononuclear compounds, [LCu]. xH2O, or dinuclear compounds, [LCu2(OAc)2], where both square-planar and octahedral geometries exist in the same complex molecule, while the Ni(II) complexes were either diamagnetic square-planar or paramagnetic compounds where both octahedral and square-planar geometries do exist, indicating their anomalous behaviour. Both UO2(VI) and Fe(III) cations are initially coordinated to the outer O-O atoms of the ligand molecule(s) The uranyl complex of the ligand H2La is coordinated to two ligand molecules while that of ligand H2Lb is coordinated to only one ligand molecule and to a bidentate acetate group. TheFe(III) complexes are dinuclear where each Fe(III) cation is linked to orlly one ligand molecule and the two Fe(III) cations are bridged through two chlorine atoms. The geometry of the uranyl complexes are pentagonal bipyramidal while the Fe(III) complexes are octahedral.

Bis{2-[(3-aminopropyl)iminomethyl]-4,6-dinitrophenolato-O,N,N'}nickel(II)

The title compound, [Ni(C10H11N4O5)2], contains asymmetric Schiff-base ligands. The coordination sphere around Ni atom is a distorted octahedron, with an average Ni—O distance of 2.072 (2) Å and Ni—N distances ranging from 2.059 (2) to 2.084 (3) Å. Bond angles at the Ni atom have values between 83.80 (9) and 96.93 (9)°. The structure is stabilized through an intermolecular hydrogen-bonding network.

Structural and spectroscopic characterization of dioxovanadium(V) complexes with asymmetric Schiff base ligands

A wide range of asymmetric Schiff base ligands containing primary amine functions can be prepared in one step and in high yield by the reaction of VO(OEt) 3 with salicylaldehyde and the appropriate diamine. The resulting VO 2 L complexes contain tridentate ligands with phenolate, imine, and amine coordination to the dioxovanadium(V) complex ion. An X-ray structure of one compound ([VO 2 (1,2-pnSAL), 5A, where 1,2-pnSAL=1(N-salicylideneamina)-2-aminopropane) demonstrates that it is a dimer in the solid state with a V 2 O 4 score

Preparation and Properties of Metal Complexes with New Asymmetric Pentadentate Schiff Base Ligands

Abstract Two new asymmetric pentadentate tribasic Schiff bases with a N2O3, donor set were prepared which contain two adjacent coordinating compartments capable of coordinating two similar or dissimilar metal cations. Mononuclear complexes were obtained which react with metal cations to produce homo- or hctero-, bi- or tri-nuclear complexes. The structures of the complexes were inferred from chemical analyses, electronic and IR spectra and by conductance and magnetic measurements. Both Ni(II) and Cu(II) coordinate either to mixed nitrogen and oxygen or oxygen and chlorine donating atoms while UO2+ 2 coordinates to oxygen atoms only.

Stereochemical rigidity and geometrical isomerism in nine-co-ordinate complexes of Th IV and U IV in aqueous solution

The 1H n.m.r. spectra, in adqueous solution at room temperature, of tris-complexes of ThIV and UIV with an asymmetric tridentate Schiff base ligand show the presence of two isomers, which are assigned to the symmetric and asymmetric forms of a tricapped trigonal prism.