The chiral helical structure of a copper(II) complex with a tridentate Schiff base ligand

In the title salt, catena‐poly[[[aquacopper(II)]‐μ‐3‐(2‐pyridylmethyleneamino)propanoato‐κ⁴N,N′,O:O′] perchlorate], {[Cu(C₉H₉N₂O₂)(H₂O)]ClO₄}_n, the monomeric unit contains a square‐based pyramidal Cu^II centre. The four basal positions are occupied by a tridentate anionic Schiff base ligand which furnishes an NNO‐donor set, with the fourth basal position being occupied by an O‐donor atom from the carboxylate group of an adjacent Schiff base ligand. The coordination sphere is completed by a water molecule at the apical position. Interestingly, each carboxylate group in the ligand forms a syn–anti‐configured bridge between two Cu^II centres, leading to left‐handed chiral helicity. The framework also exhibits O—H...O hydrogen bonds involving the water molecules and an O atom of the perchlorate anion.     

A novel trinuclear nickel(II) complex with a Schiff base derived from m-phenylenediamine and diacetyl monoxime

Summary A tetradentate Schiff base derived from diacetyl monoxime and m-phenylenediamine (H₂mphdao₂) reacts in MeOH with NiI₂ to form the trinuclear complex Ni₃(mphdao₂)₂I₂, which was characterized by elemental and thermal analyses, and i.r. and u.v.-vis. spectroscopies. The magnetic properties have been investigated in the 4.2–300 K range.     

Cooperative self-assembly of a macrocyclic Schiff base complex

A metal template approach affords in high yield a tetra-Zn(salphen) macrocycle (3) which shows strong and cooperative self-assembly mediated by the formation of Zn(salphen) dimer units held together via μ(2)-phenoxo interactions. A cooperative binding mode for the tetranuclear Zn(4) macrocycle 3 is supported by comparison of UV-vis and fluorescence titration data recorded for 3 when compared with respective mononuclear and dinuclear Zn(salphen) model compounds. UV-vis dilution experiments carried out for Zn(4) macrocycle 3 and its Pd(4) analogue 4, as well as comparative TEM studies involving the same tetranuclear macrocycles further support the strong assembly behavior of 3. This self-assembly seems to be primarily dictated by its ability to form multiple, self-assembled dimeric [Zn(salphen)](2) units.     

Uranyl stabilized Schiff base complex

Uranyl Schiff base complex [(UO(2))(2)(Salpro)(OH)(Solvent)(2)] (1) in the presence of excess of ethylenediamine (EDA) does not undergo nucleophilic addition (hydrolysis) and substitution (transamination) reactions due to an extended chelation [2N, 3O + OH] by the flexible backbone.     

Design of end-on cyanato bridged trinuclear Cu(II) Schiff base complex with salen type Schiff base ligand: synthesis,structural investigation and DFT study

One ONNO-donor tetradentate Schiff base ligand LH₂ was derived from the condensation of salicylaldehyde and 1,3-diaminopropane and reacted with Cu(NO₃)₂·6H₂O and NaNCO to yield one trinuclear complex with molecular formula [Cu₃L₂(µ_1,1-NCO)₂]. The synthesized complex was characterized by IR, UV–vis spectroscopy, and electrochemical analysis. Single-crystal X-ray diffraction study explores that the two terminal copper atoms adopt square pyramidal geometry, whereas the central copper atom situated at the inversion center is surrounded by four phenoxo oxygens and two end-on cyanato anions to adopt an octahedral geometry. The ONNO-tetradentate Schiff base ligand coordinates with the copper(II) ion via two oxygen atoms of the phenoxo-group and two nitrogen atoms from the imine moiety. A theoretical density functional theory (DFT) calculation was also carried out to supplement the experimental results. All the DFT calculations were done in gas phase.     

Heterogeneous copper-free Sonogashira coupling reaction catalyzed by a reusable palladium Schiff base complex in water

Heterogeneous Sonogashira coupling of terminal alkynes with aryl halides was studied over a polymer-supported macrocyclic Schiff base palladium complex. The cross-coupling reaction proceeded smoothly by adding a piperidine in water medium. The catalyst exhibited effective catalytic activities to afford the corresponding products in good to excellent yields under copper-free conditions. Furthermore, the catalyst could be easily recovered and reused for several times without a significant loss of its activity.     

An unprecedented Cu–Schiff base complex existing as two different trinuclear units with strong antiferromagnetic couplings

A new tetradentate N₂O₂ donor Schiff base ligand [OHC₆H₄CHNCH₂CH₂CH(CH₂CH₃)NCHC₆H₄OH = H₂L ] was obtained by 1:2 condensation of 1,3-diaminopentane with salicylaldehyde and has been used to synthesise an unusual copper(II) complex whose asymmetric unit presents two structurally different almost linear trinuclear units [Cu₃(μ-L)₂(ClO₄)₂] [Cu₃(μ-L)₂(H₂O)(ClO₄)₂] (1). The ligand and the complex were characterised by elemental analysis, FT-IR, ¹H NMR and UV–Vis spectroscopy in addition electrochemical and single crystal X-ray diffraction studies were performed for the complex. The magnetic properties of 1 reveal the presence of strong intra-trimer (J₁ = −202(3) cm⁻¹ and J₂ = −233(3) cm⁻¹) as well as very weak inter-trimer (zJ′ = −0.11(1) cm⁻¹) antiferromagnetic interactions.     

Synthesis and near infrared luminescence of a tetrametallic Zn2Yb2 architecture from a trinuclear Zn3L2 Schiff base complex

Near infrared luminescence is observed in tetrametallic [Zn2Yb2L2(mu-OH)2Cl4].2MeCN which is obtained from the Zn3 Schiff-base complex [Zn3L2(NO3)2].MeOH, (H2L =N,N'-bis(5-bromo-3-methoxysalicylidene)propylene-1,3-diamine).     

Stepwise substitution of oxo-centered,trinuclear chromium(III) carboxylates with Schiff base

Oxo-centered, trinuclear, mixed-ligand complexes of chromium(III) have been synthesized by stepwise substitutions of acetate ions of [Cr₃O(OOCMe)₄(OOCR)₃] · 3MeOH (1) and the isolated products of the type [Cr₃O(OOCMe)₂ (SB)(OOCR)₃]PF₆ · 3MeOH (2), [Cr₃O(OOCMe)(SB)₂(OOCR)₃]PF₆ · 3MeOH (3) and [Cr₃O(SB)₃(OOCR)₃]PF₆ · 3MeOH (4) [where R = C₁₃H₂₇ and HSB = C₆H₄(OH)CHNC₆H₄Cl] have been characterized by a full battery of complementary physico–chemical methods including spectral (infrared, electronic, FAB mass and powder XRD) studies, elemental and thermogravimetric analyses, molar conductance and magnetic susceptibility measurements. The infrared spectra suggest the bridging nature of both carboxylate and Schiff base anions along with ν _asym(Cr₃O) vibrations in the complexes. The trinuclear nature of the complexes has been assessed from FAB mass data. Electronic spectra and magnetic moment values were consistent with chromium(III) ion present in an octahedral environment which was supported by their powder X-ray diffraction data. Cyclic voltammetric data of complex (4) indicate a reversible oxidation wave and an irreversible reduction wave in the range − 1.2–0.6 V. The decomposition pathway of all the complexes has been discussed on the basis of thermogravimetric analysis data. Conductance data indicate the monocationic nature of the complexes and their plausible structure has been established on the basis of above physico–chemical studies.     

Magnetic properties and structure of a CuDy heterodinuclear Schiff base complex

The crystal structure of a new heterodinuclear lanthanide complex, L²Cu(Me₂CO)Dy(NO₃)₃ (L²=N,N′-bis(2-hydroxy-3-methoxy-benzylidene)-ethylenediamine) has determined and the magnetic properties of the complex investigated. (C₁₈H₁₈N₂O₄)Cu(C₃H₆O)Dy(NO₃)₃, monoclinic, space group P2₁/c, with a=9.875(2), b=18.870(7), c=15.675(8) Å, β=95.45(3)°, V=2908(2) Å³, Z=4. The structure consists of ordered dinuclear units with Cu^II and Dy^III ions bridged by two phenolato oxygen atoms of the Schiff base ligand. The Cu^II ion has a square-pyramidal geometry involving the basal N₂O₂ donor atoms of the Schiff base ligands and one oxygen atom of the acetone molecule at the apex position. The Dy^III ion is decacoordinated by the four oxygen atoms of L² and six oxygen atoms from the three bidentate nitrate ions. The Cu?Dy separation is 3.461(2) Å. The χT versus T plots, χ being the molar magnetic susceptibility per Cu^IIDy^III unit and T the temperature, has been measured in the 4.5-300 K temperature range. The magnetic properties of the compound are dominated by the crystal field effect on the Dy^III site, masking the magnetic interaction between the paramagnetic centers.     

Synthesis and crystal structure of an unexpected anionic trinuclear cobalt(III) complex with ferrocenyl-containing tridentate ONO donor Schiff base ligands

The tridentate ONO-donor Schiff base ligand derived from the condensation of 1-ferrocenyl-1,3-butanedione and 2-aminophenol, generated in situ and treated further with potassium tert-butoxide, reacted in THF with Co(NO₃)₂·6H₂O in the presence of pyridine to afford the ionic complex [{(η⁵-C₅H₅)Fe(η⁵-C₅H₄)-C(O)CH=C(CH₃)N-C₆H₄-2-O}₂Co(III)]^-[K(HOCH₂CH₃)₂]⁺ (1, 50% yield). Compound 1 was characterized by elemental analysis, FT-IR, and multidimensional ¹H and ¹³C NMR spectroscopy. Single-crystal X-ray diffraction reveals that the two metalloligands are meridionally coordinated to a Co(III) ion that adopts a slightly distorted octahedral geometry. The doubly solvated potassium counter-ion is asymmetrically positioned with respect to the two metalloligands. Such an arrangement allows the observation by ¹H NMR of restricted rotation of the ferrocenyl units and the splitting of both carbonyl and imine carbons, thus suggesting that the structure observed in the solid state is retained in solution. Complex 1 exhibits in its cyclic voltammetry curve two anodic reversible waves attributed to the oxidation of Co(III)-phenolates into Co(III)-phenoxyl radical and that of the ferrocenyl fragment into its ferrocenium counterpart.     

Synthesis and physico-chemical characterization of a Schiff base and its zinc complex

Research on Chemical Intermediates - In the present studies, a Schiff base ligand and complex were synthesized by condensation reaction of 2-hydroxy-1-napthaldehyde and 4-methyl-1,3-phenyldiamine....     

Crystal structure of indium(III) Schiff base complex

The title compound [In(C₂₂H₃₀N₄O₄)]Cl (I) bis[(N-salicylidene-N′-(2-hydroxyethyl)ethyleneediamine) indium(III) chloride is prepared, and its crystal structure is determined by single crystal X-ray diffraction at room temperature. The complex crystallizes in the monoclinic space group P2₁/n, a = 9.9704(6) ?, b = 24.9554(15) ?, c = 10.5707(6) ?, β = 116.46(2)°, V = 2354.6(2), Z = 4. The X-ray analysis reveals that the In^III ion is surrounded by four nitrogen and two oxygen atoms from two ligands leading to a distorted octahedral geometry. The molecule has the form of tongs at a junction point with the metal. Five membered rings adopt envelope conformation. In the crystal structure, the molecules are linked via N-H...Cl, O-H...O, O-H...Cl, and C-H...Cl intermolecular interactions. The structure is further stabilized by C-H...π (arene) interactions.     

Polymerization of isoprene catalyzed by neodymium heterocyclic Schiff base complex

Neodymium-based heterocyclic Schiff base complex was prepared and applied for the coordination polymerization of isoprene. This complex polymerized isoprene to afford products featuring high cis-1,4 stereospecificity （ca. 95%） and high molecular weight （ca, 10^5） in the presence of the triisobutyl aluminium （AliBu3） as cocatalyst, The microstructure of obtained polyisoprene was investigated by FTIR, 1^H NMR. Two different kinds of active centers in the catalyst system were examined by GPC method.     

Magnetic and spectroscopic properties of gadolinium tripodal Schiff base complex

Gadolinium(III) tripodal Schiff base (tris(((5-chlorosalicylidene)amino)ethyl)amine) complex has been obtained and investigated by infrared spectroscopy (IR), magnetic susceptibility, and electron paramagnetic resonance (EPR) methods. Comparison of IR bands in ligand and gadolinium complex confirmed the formation of the gadolinium complex and allowed to propose its structure. Both electron ionization and electron spray molecular spectroscopy spectra confirmed the [1:1] proportion of a ligand to metal in gadolinium tripodal Schiff base complex sample. IR spectroscopy and TG–DTA excluded the presence of water molecule in the metal coordination sphere. X-ray powder analysis applying Fullprof computer program has shown that the investigated sample was monophase with the monoclinic symmetry of the unit cell having the lattice constants: a = 10.028(4) Å, b = 13.282(5) Å, c = 21.20(1) Å and β = 101.58(4)°. Space group P21/c, Z = 4. EPR spectra of the complex have been registered in the 4–300 K temperature range. Each spectrum has been fitted using EPR–NMR computer program and the values of the spin-Hamiltonian parameters at each temperature have been calculated. Temperature dependence of the integrated intensity of the EPR spectrum allowed revealing the magnetic interactions in the spin system of this compound. Comparison of the temperature dependence of dc magnetic susceptibility (χ) and EPR susceptibility (χ_EPR) showed significant differences between these quantities due to the presence of short-lived clusters with a non-magnetic ground state.     

A one‐dimensional coordination polymer based on a di‐Schiff base supported trinuclear CuII subunit

A novel one‐dimensional Cu^II coordination polymer, catena‐poly[bis(μ₄‐3‐{[2‐(3‐hydroxy‐2‐oxidobenzylidene)hydrazinylidene]methyl}benzene‐1,2‐diolato)dimethanoltricopper(II)], [Cu₃(C₁₄H₁₀N₂O₄)₂(CH₃OH)₂]_n, (I), was constructed with a di‐Schiff base supported centrosymmetric trinuclear Cu^II subunit. In the subunit, two peripheral symmetry‐related Cu^II cations have square‐pyramidal CuNO₄ geometry and the central third Cu^II cation lies on an inversion centre with octahedral CuN₂O₄ geometry. In (I), each partially deprotonated di‐Schiff base 3‐{[2‐(3‐hydroxy‐2‐oxidobenzylidene)hydrazinylidene]methyl}benzene‐1,2‐diolate ligand (Hbcaz³⁻) acts as a heptadentate ligand to bind the Cu^II centres into chains along the a axis. A centrosymmetric Cu₂O₂ unit containing an asymmetrically bridging O atom, being axial at one Cu atom and equatorial at the other Cu atom, links the trinuclear Cu^II subunit into a one‐dimensional chain, which is reinforced by intramolecular phenol–methanol O—H...O and methanol–phenolate O—H...O hydrogen bonds. Interchain π–π stacking interactions between pyrocatechol units, with a distance of 3.5251 (18) Å, contribute to the stability of the crystal packing.     

Asymmetric sulfoxidation of prochiral sulfides using aminoalcohol derived chiral C3-symmetric trinuclear vanadium Schiff base complexes

A series of trimeric variants of the efficient and well known Bolm’s chiral vanadium salen catalysts are reported. These C₃-symmetric trinuclear chiral Schiff bases were synthesized by condensing a variety of trialdehydes with optically active aminoalcohols. The catalytic activity of the chiral vanadium complexes of these ligands was investigated for the enantioselective oxidation of prochiral sulfides using hydrogen peroxide as an oxidant. The procedure afforded the corresponding sulfoxide in good yield and the enantioselectivities were comparable to those obtained with the mononuclear complexes.