Anionic Schiff Base Ligands Research Articles

Dinuclear zinc(II) acetate complexes derived from N,N',S-tridentate Schiff bases: synthesis, structural study and Hirshfeld surface analysis.

Three dinuclear zinc(II) acetate complexes of the general formula [Zn{Ln}(AcO)]2, namely, di-μ-acetato-κ4O:O'-bis[({2-[(pyridin-2-ylmethylidene)amino]phenyl}sulfanido-κ3N,N',S)zinc(II)], [Zn2(C12H9N2S)2(C2H3O2)2] (n= 1), 4, μ-acetato-1:2κ2O:O'-acetato-2κO-[μ-(2-{[1-(pyridin-2-yl)ethylidene]amino}phenyl)sulfanido-1κS:2κ3N,N',S][(2-{[1-(pyridin-2-yl)ethylidene]amino}phenyl)sulfanido-1κ3N,N',S]dizinc(II), [Zn2(C13H11N2S)2(C2H3O2)2] (n= 2), 5, and μ-acetato-1:2κ2O:O'-acetato-2κO-[μ-(2-{[phenyl(pyridin-2-yl)methylidene]amino}phenyl)sulfanido-1κS:2κ3N,N',S][(2-{[phenyl(pyridin-2-yl)methylidene]amino}phenyl)sulfanido-1κ3N,N',S]dizinc(II)-bis(2-aminophenyl) disulfide (2/1), [Zn2(C18H13N2S)2(C2H3O2)2]·0.5C12H12N2S2 (n= 3), 6·0.5(2-APS)2, were obtained from the reaction of 2-R-(pyridin-2-yl)benzothiazoline precursors (R= H, 1; R= Me, 2; R= Ph, 3) with zinc acetate dihydrate in a 1:1 ratio. All the complexes crystallized as dinuclear species and complex 6 cocrystallized with one molecule of bis(2-aminophenyl) disulfide (2-APS)2. The anionic Schiff base ligands {Ln}- displayed a κ2N,κS-tridentate coordination mode with the formation of two five-membered chelate rings. In 4, 5 and 6·0.5(2-APS)2, both ZnII ions are pentacoordinated and the coordination sphere of 4 was different with respect to those in 5 and 6·0.5(2-APS)2. For 4, the X-ray diffraction study showed a dinuclear complex containing two bridging acetate ligands linked to both ZnII ions. For 5 and 6·0.5(2-APS)2, the dinuclear complexes displayed one bridging acetate ligand linked to both ZnII ions, where the first ZnII ion includes a dative bond with one S atom from an adjacent anionic Schiff base {Ln}-, while the second ZnII ion is coordinated to one terminal acetate ligand. In each dinuclear complex, the geometry is the same for both ZnII metal centres. The local geometry of the ZnII cation in 4 is halfway between trigonal bipyramidal and square pyramidal local geometries; in 5 and 6, the local geometries are described as distorted square pyramidal. Hirshfeld surface analysis of 5 and 6 showed the predominance of H...H interactions, as well as the contribution of C-H...C, C-H...O and C-H...S noncovalent interactions to the cohesion of the crystalline network of the ZnII complexes.

Formation of Defect-Dicubane-Type NiII 2LnIII 2 (Ln = Tb, Er) Clusters: Crystal Structures and Modeling of the Magnetic Properties.

In the field of molecular nanoclusters, cubane and defect-dicubane, or butterfly structures, are typical examples of tetranuclear metal core architectures. In this work, a halogenated and anionic Schiff-base ligand (L2–) is utilized as it is predisposed to chelate within a cluster core to both 3d and 4f metal ions, in different binding configurations (H2L = 4-chloro-2-(2-hydroxy-3-methoxybenzyliden amino)phenol). The phenolate oxygen atoms of the deprotonated ligand can act in μ-O and μ3-O bridging binding modes for the intramolecular assembly of metal ions. Based on that, two tetranuclear and isostructural compounds [Ni2Tb2(L)4(NO3)2(DMF)2]·2CH3CN (1) and [Ni2Er2(L)4(NO3)2(DMF)2]·0.5CH3CN (2) were synthesized and structurally characterized. Magnetic susceptibility and magnetization data indicate the occurrence of dominant intramolecular ferromagnetic interactions between the spin centers. Particular emphasis is given to the theoretical description of the magnetic behavior, taking into account the Ln–Ni and Ni–Ni coupling paths and the magnetic anisotropy of the LnIII and NiII ions. The study is distinguished for its discussion of two distinct models, whereby model A relies on the uniaxial B20 Stevens term describing the lanthanide anisotropy and model B is based on point-charge model calculations. Importantly, the physical meaning of the obtained parameters for both models was critically scrutinized.

Formation of Tetranuclear Nickel(II) Complexes with Schiff-Bases: Crystal Structures and Magnetic Properties

The cubane-type structure is a typical representative of tetranuclear coordination compounds. In this work, two anionic Schiff-base ligands, (L1)2− and (L2)2−, each offering an O^N^O coordination pocket, ligate four NiII ions into a [Ni4O4] cubane core. The ligands are H2L1 = 2−[[(3-ethoxy-2−hydroxyphenyl) methylene]amino]benzenemethanol and H2L2 = 2−[[(5-fluoro-2−hydroxyphenyl)methylene]amino]benzenemethanol. In both compounds, [Ni4(L1)4(EtOH)4] (1) and [Ni4(L2)4(MeOH)4] (2), alkoxy oxygens of the ligands act in a bridging μ3-O binding mode. Magnetic susceptibility and magnetization data for compounds 1 and 2 are presented. The Ni–O–Ni bond angles of the cubane core determined from single crystal X-ray diffraction data play a key role for a magneto-structural correlation. Dominant intracube ferromagnetic behavior is observed, and the coupling parameters were determined for both compounds, leading to nonzero spin ground states in accordance with the broadly accepted bond angle guideline.

Two efficient ligand-assisted systems of two different ionic Schiff base ligands for palladium chloride catalyzed in Suzuki-Miyaura reaction

The bis- methyl imidazolium chloride-salophen Schiff base ligand as cationic Schiff base ligand (L1) was synthesized by the reaction of methyl imidazoliumsalicylaldehyde chloride (S1) and phenylendiamine. The phenylendiamine was also reacted by monosodium 5-sulfonatosalycilaldehyde (S2) to give the bis-sodium sulfonate-salophen Schiff base ligand (L2) as the anionic ligand. These two ligands were characterized by the 1H-NMR, 13C-NMR, IR, UV–visible and mass spectroscopy, as well as elemental analysis. The ligand assisted PdCl2 catalyst was investigated in the Suzuki-Miyaura reaction by using the L1 and L2 as cationic and anionic Schiff base ligands and different reaction conditions such as temperature, solvent and mol% of PdCl2 were optimized. The results revealed that the anionic ligand assistance had a better activity for the catalytic system of PdCl2 in Suzuki-Miyaura reaction. Two ionic Schiff base ligands (bis- methyl imidazolium chloride-salophen as cationic and bis-sodium solphonate-salophen as anionic Schiff base ligands) were synthesized. The ligand-assisted PdCl2 catalyst was investigated in the Suzuki-Miyaura reaction by using these ionic Schiff base ligands and the results revealed that the anionic ligand-assisted had a better activity for the catalytic system of PdCl2 in Suzuki-Miyaura reaction.

Half-sandwich Ruthenium(II) Schiff base complexes: Synthesis, characterization and effective catalysts for one-pot conversion of aldehydes to amides

Five new Schiff base ligands and conformationally rigid half-sandwich organo ruthenium(II) Schiff base complexes (1–5) with the general formula [Ru(η6‒p‒cymene)(Cl)(L1-5)] (where, L = mono anionic Schiff base ligands) have been synthesized from the reaction of [{(η6‒p‒cymene)RuCl}2(μ‒Cl)2] with a bidentate Schiff bases ligands. These ruthenium(II) Schiff base complexes were fully characterized by elemental analysis, FT‒IR, UV–Vis, 1H &13C NMR and mass spectroscopy studies. In chloroform solution, all the metal complexes exhibit characteristic metal to ligand charge transfer bands (MLCT) and emission bands in the visible region. The crystal structure of the complexes [Ru(η6‒p‒cymene)(Cl)(L1)] (1) and [Ru(η6‒p‒cymene)(Cl)(L3)] (3) were determined by single crystal X‒ray crystallography. The complexes exhibited good catalytic activity for aldehydes to amides by one-pot conversion process in the presence of NaHCO3/NH2OH·HCl.

Facile one-pot template synthesis of isotypic Co(II), Ni(II) and Cu(II) complexes of a Schiff base derived from glyoxylic acid and ethyl carbazate

Glyoxylic acid and ethyl carbazate condense in situ in the reaction medium and react with metal nitrates of Co, Ni or Cu to yield isostructural metal complexes with the general formula [M(gly-ec)2(H2O)2] (M = Co2+ (1), Ni2+ (2) and Cu2+ (3); Hgly-ec = ethoxycarbonyl-hydrazono-acetic acid). These products are elucidated through various physicochemical techniques including powder and single-crystal X-ray diffraction. X-ray crystallography of complexes 1 and 3 reveals that two anionic Schiff base ligands are coordinated to the metal ion via (N, O) bidentate chelation and situated trans to each other in equatorial positions and are nearly coplanar with the metal atom. The two coordinated water molecules occupy the trans axial positions, with a slightly distorted octahedral geometry. The thermal behavior of complexes 1–3 is studied in air and nitrogen atmosphere from 30 to 800 °C. In both mediums, all of the complexes show endothermic followed by exothermic decomposition to yield metal oxides as the end products at low temperature. Hence, these isotypic complexes may be used as solid-state precursors for the preparation of respective metal oxides due to their low temperatures of decomposition.

Crystal structure of bis-(2-{[(pyridin-2-yl)methyl-idene]amino}-benzoato-κ(3) N,N',O)cobalt(II) N,N-di-methyl-formamide sesquisolvate.

The title compound, [Co(C13H9N2O2)2]·1.5C3H7NO, is formed as a neutral Co(II) complex with di-methyl-formamide (DMF) solvent mol-ecules. The Co(II) atom has a distorted O2N4 octa-hedral coordination sphere defined by two tridentate anionic Schiff base ligands with the O atoms being cis. The coordination sphere around the Co(II) atom is geometrically different from that reported for the co-crystal [Co(C13H9N2O2)2]·AA·H2O (AA is anthranilic acid). One of the DMF solvent mol-ecules was modelled as being disordered about a crystallographic inversion centre with half-occupancy. The crystal structure is made up from alternating layers of complex mol-ecules and DMF mol-ecules parallel to (010). C-H⋯O hydrogen-bonding inter-actions between the complex mol-ecules and the solvent mol-ecules consolidate the crystal packing.

Bis{2-[(pyridin-2-yl)methyl-idene-amino]-benzoato-κ(3) N,N',O}chromium(III) nitrate monohydrate.

The title complex salt hydrate, [Cr(C13H9N2O2)2]NO3·H2O, comprises discrete cations, nitrate anions and solvent water mol­ecules. The CrIII atom is octa­hedrally coordinated by two anionic Schiff base ligands with the O atoms being cis. The two ligands differ significantly with dihedral angles between the pyridine and benzene rings of 4.8 (2) and 24.9 (2)°. The nitrate anion and solvent water mol­ecule were modelled as being disordered, with the major components having site-occupancy values of 0.856 (14) and 0.727 (16), respectively. The crystal is built of alternating layers of cations and of anions plus water mol­ecules, stacked along the c axis.

Synthesis, crystallographic characterization and catecholase activity of a monocopper(II) and a dimanganese(III) complex with an anionic Schiff base ligand

The mononuclear [CuII(HL)2] (1) and dinuclear [MnIII2(μ1,3-OAc)2L2] (2) [H2L=N-(2-hydroxypropyl)-3-methoxysalicylaldimine] compounds have been synthesized and characterized using microanalytical, spectroscopic and X-ray crystallographic results. Structural analysis reveals a bidentate chelation behavior of the monoanionic HL ligand, having a distorted square planar coordination environment around copper(II) with a CuN2O2 chromophore. In compound 2, each manganese(III) center has a distorted octahedral geometry, with an MnN2O4 chromophore bridged by two acetate ligands in a μ1,3 fashion. Variable-temperature magnetic susceptibility measurements of 2 indicate an antiferromagnetic interaction between the two manganese(III) centers. Both 1 and 2 behave as effective catalysts towards the oxidation of 3,5-di-tert-butylcatechol to its corresponding quinone with molecular oxygen in methanolic solution.

(Acetylacetonato-κ2O,O′)(2-bromo-4-chloro-6-{[2-(dimethylamino)ethylimino]methyl}phenolato-κ3N,N′,O)oxidovanadium(IV)

The VIV atom in the title complex, [V(C11H13BrClN2O)(C5H7O2)O], is six-coordinated by one phenolate O, one imino N and one amino N atom of the tridentate anionic Schiff base ligand, by one oxide O atom, and by two O atoms of an acetyl­acetonate anion, forming a distorted cis-VN2O4 octa­hedral coordination geometry. The deviation of the V atom from the plane defined by the three donor atoms of the Schiff base ligand and one O atom of the acetyl­acetone ligand towards the oxide O atom is 0.256 (2) Å.

N2O 주개 리간드와 테레프탈레이트를 포함하는 구리(II) 착물의 용매를 매개로 한 수소결합형 초분자 네트워크

일차원 수소결합형 배위고분자 <TEX>$[Cu^{II}(C_{13}H_{17}N_3OBr)(C_8H_5O_4)]{\cdot}2H_2O.CH_3OH$</TEX>을 합성하여 단결정 X-선 회절 연구로 특성을 규명하였다. 단량체 단위는 사각평면의 중심 <TEX>$Cu^{II}$</TEX>를 갖고 있다. 네개의 배위자리 중 세자리는 <TEX>$N_2O$</TEX>-주개 세트를 갖는 Schiff 염기형 리간드 (4-bromo-2-[(2-piperazin-1-yl-ethylimino)-methyl]-phenol)가 차지하고, 네 번째 자리는 옆에 있는 테레프탈레이트 단위의 산소 원자가 차지한다. 두개의 인접한 중성분자는 분자간 N-H---O 및 O-H---N 수소결합에 의해 연결되어 이합체 쌍을 형성한다. 각 이합체 쌍은 불연속적인 물 및 메탄올 분자에 의해 수소결합으로 다시 연결되어 일차원 초분자 네트워크를 형성한다. The title one-dimensional hydrogen-bonded coordination compound <TEX>$[Cu^{II}(C_{13}H_{17}N_3OBr)(C_8H_5O_4)</TEX><TEX>]</TEX><TEX>{\cdot}2H_2O.CH_3OH$</TEX> has been synthesized and characterized by single crystal X-ray diffraction study. The monomeric unit contains a square-planar <TEX>$Cu^{II}$</TEX> centre. The four coordination sites are occupied by a tridentate anionic Schiff base ligand (4-bromo-2-[(2-piperazin-1-yl-ethylimino)-methyl]-phenol) which furnishes an <TEX>$N_2O$</TEX>-donor set, with the fourth position being occupied by the oxygen atom of an adjacent terephthalate unit. Two adjacent neutral molecules are linked through intermolecular N-H---O and O-H---N hydrogen bonds and generate a dimeric pair. Each dimeric pair is connected with each other via discrete water and methanol molecules by hydrogen bonding to form a one-dimensional supramolecular network.

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

In the title salt, catena-poly[[[aquacopper(II)]-mu-3-(2-pyridylmethyleneamino)propanoato-kappa4N,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.

Mössbauer and infrared spectroscopic studies of some organotin(IV) schiff base complexes

Several organotin(IV) complexes with quadri- and terdentate anionic Schiff base ligands have been investigated in the solid state using 119Sn Mössbauer and IR spectroscopies, Mössbauer parameters derived from both zero-field and magnetically perturbed spectra suggest that the R2Sn(Salen)(R = Me, Et, Ph) and Me2Sn(Saldap-2OH) complexes have similarly distorted trans-octahedral structures. However, in Ph2Sn(HSaldap-2-O) the ligand appears to be only terdentate, leading to a penta-coordinate structure similar to those of the R2Sn(Sal-N-2-OC6H4) derivatives (R = Me, Ph). For Ph3Sn(Sal-N-2-OC6H4) the asymmetry parameter of the electric field gradient is close to unity, confirming a mer-octahedral configuration for this complex.