Polydentate Schiff Base Ligand Research Articles

Synthesis and Characterization of CuO and NiO Nanoparticles Derived from Schiff Base Complexes

This study reports the synthesizes of such as copper oxide (CuO) and nickel oxide (NiO) nanoparticles (NPs) by thermal decompositions of Schiff base complexes and their physical characterization. A polydentate Schiff base ligand, (E)-2-(((2-chlorobenzyl)imino)methyl)phenol (CIMP), was synthesized by condensing 2-chlorobenzylamine and 2-hydroxybenzaldehyde. The ligand was identified by melting point, FT-IR, UV-Vis, and (1H and 13C NMR) spectroscopy. Cu(II) and Ni(II) complexes were prepared by reacting CIMP with the corresponding molar ratio in a 1:1 (metal: ligand). The complexes (Com1 and Com2) were characterized by melting point, FT-IR, and UV-Vis spectroscopy. The FT-IR spectra of the (Com1 and Com2) showed that the deprotonated CIMP ligand coordinated to the Ni(II) and Cu(II) metal ions through the azomethine nitrogen, aryl chloride, chlorine, and phenolic oxygen atoms. To determine the crystalline structure of the synthesized products, X-ray powder diffraction (XRD) and scanning electron microscopy (SEM) techniques were employed. The formation of copper oxide and nickel oxide as the new products was confirmed by XRD analysis. SEM imaging revealed the uniform and spherical morphology of the nanoparticles, which exhibited a remarkably narrow size distribution with an average diameter of 20 to 22 nm, highlighting their exceptional precision.

Important application value of injectable hydrogels loaded with omeprazole Schiff base complex in the treatment of pancreatitis

Abstract In this study, a novel Ho(iii) coordination complex with the chemical composition of [Ho6(acac)4L4(CH3O)6]·xCH3OH (1) has been prepared via using a polydentate Schiff base ligand N′-(2,3-dihydroxybenzylidene) picolinohydrazide (H2L) and a β-diketone (Hacac = acetylacetone) co-ligand, and then successfully loaded with drug omeprazole. Hyaluronic acid, a natural polysaccharide with good biocompatibility, was used as raw material to prepare drug carriers that can be injected into hydrogels based on chemical synthesis method. The internal microstructure of the hydrogel was observed by scanning electron microscope, which showed a good three-dimensional connected porous structure. After the synthesis of the hydrogel, the value of their application in the treatment of pancreatitis was evaluated and the related mechanisms were explored at the same time.

Synthesis, structural elucidation, Hirshfeld surface analysis and cytotoxicity studies of homometallic dinuclear Cu(II), Ni(II) and Zn(II) Schiff base complexes derived from m-phenylenediamine

A polydentate Schiff base ligand, L was synthesized via condensation reaction between o-vanillin (OVan) and trimethyl-m-phenylenediamine [(Me)MPD]. Its Cu(II), Ni(II), and Zn(II) dinuclear complexes were prepared through complexation with corresponding acetate salts. The compounds were characterized via CHN elemental analyzer, molar conductivity, magnetic susceptibility, TGA, IR, 1H and 13C NMR. The crystal structure of the ligand, L and zinc(II) complex, Zn2L2 were elucidated by using single crystal x-ray diffraction. The crystal structure of Zn2L2 showed that the two Zn(II) metal atoms serve as bridges between the two units of the ligand through ONNO donor atoms leading to the formation of a centrosymmetric cyclic dinuclear complex. Based on the single x-ray crystallography, the zinc atoms exhibit a distorted tetrahedral geometry. Hirshfeld surface analysis was performed to determine the intermolecular interactions in the crystal structures. From this analysis, it revealed that H···H interaction for L (55%) and Zn2L2 (62.7%) was the dominant intermolecular interaction in the total area of Hirshfeld surface. The ν(CN) and ν(CO) peaks in IR spectra of the ligand L appeared at 1615 cm−1 and 1255 cm−1, respectively. The peaks shifted to lower and higher frequency by Δν of 4–12 cm−1 in the complexes. The new peaks assignable to ν(MN) and ν(MO) were observed at 514–562 cm−1 and 422–436 cm−1, respectively, indicating the coordination of the metal centers to the azomethine N and phenolic O. The Cu(II) and Ni(II) complexes are paramagnetic with μeff of 1.90 and 2.89 B.M., respectively. The thermal gravimetric analysis revealed the presence of three lattice water molecules in Cu(II) complex. The cytotoxicity studies of all compounds were carried out against colon cancer cell lines (HCT116). The parent ligand was found to be less cytotoxic than its metal complexes. Cu(II) showed the highest activity with IC50 of 0.73 ± 0.21 μM, better than the standard 5-FU.

Interaction of metal ions with Schiff bases having N2O2 donor sites: Perspectives on synthesis, structural features, and applications

Metal Schiff base complexes are versatile platforms for the development of potential catalysts, potent biomaterials, or luminescent compounds. Transition metals possess a diverse array of properties that can be manipulated to yield promising candidates for the future in various industrial applications. Metal Schiff base complexes represent a class of compounds that have become a field of immense interest because of their intriguing chemical and physical properties and their wide range of applications in several scientific fields. The reaction of transition metal elements with a polydentate Schiff base ligand to form metal complexes offers a good platform for combining the chemical, electronic, magnetic, optical, and redox properties of metal complexes with those of the organic materials, generating new functional materials with useful mechanical, catalytic, thermal and chemical, optoelectronic, structural and magnetic properties. The transition metal complexes can often mimic biological sites; they are, therefore, of great interest as enzyme models. This review discusses the structural features of metal complexes of the first series of transition metals with Schiff bases as ligands having N2O2 coordination sites. Further perspectives concerning the synthesis, structural aspects, characterization, and applications are presented.

Construction of three novel Ln3 compounds using multidentate Schiff base ligand: Crystal structures, fluorescence properties, and biological activities

Three new trinuclear lantharide-based compounds: [Ln3(dbm)5(L)2(CH3OH)]·CH2Cl2 (LnIII = Nd(1), Sm(2), and Tb(3), dbm− = diphthaloylmethae) have been synthesized via the solvothermal method by using a polydentate Schiff base ligand (H2L = (E)-6-(hydroxymethyl)-N'-((6-methoxypyridin-2-yl)methylene)picolinohydrazide) reacting with Ln(dbm)3·2H2O. X-ray diffraction study reveals that all compounds 1–3 belong to monoclinic crystal system with space group C2/c, and compounds 1–3 are isostructural and possess a broken-line Ln3 core. The solid-state luminescence properties measurements indicate that compound 3 displays the characteristic lanthanide luminescence at room temperature. Moreover, photoluminescence properties study show that 1 and 2 display typical NIR luminescence of Nd(III) and Sm(III) ions at room temperature. Furthermore, biological activities research reveals that compounds 1–3 have greater antibacterial activity than the ligand H2L and Ln(dbm)3·2H2O (LnIII = Nd (1), Sm (2), and Tb (3)). The interaction between compounds 1–3 and calf thymus DNA was studied and the results revealed that the compounds were mainly intercalated with calf thymus DNA.

Two tetranuclear Tb(III)-based clusters: Crystal structures and effectively catalyze the cycloaddition of CO2 with epoxides

Two new and interesting tetranuclear Tb(III)-based clusters [Tb4(NO3)2(acac)4(HL)2(CH3OH)2]·2(CH3CN)] (1) and [Tb4(NO3)2(acac)4(L)2(CH3CH2OH)2] (2) (H4L1 = 2-(hydroxymethyl)-2-(((2-hydroxynaphthalen-1-yl)methylene)amino)propane-1,3-diol); H3L2 = 2-(((2-hydroxynaphthalen-1-yl)methylene)amino)-2-methylpropane-1,3-diol; and Hacac = acetylacetone) have been successfully synthesized by using two polydentate Schiff base ligands (H3L2 and H4L1). The crystal structures, fluorescent properties, magnetic properties and catalytic properties of the two clusters 1 and 2 have been systematically studied. Interestingly, both clusters 1 and 2 can catalyze the cycloaddition of CO2 with epoxides with high efficiency under mild conditions; and cluster 1 as a catalyst could be reused at least three times without obvious loss of catalytic performance.

A tetranuclear Er(III)-based cluster with bifunctional properties: Efficient conversion of CO2 and slow magnetic relaxation behavior

A new Er4 cluster [Er4(NO3)2(acac)4(L)2(CH3OH)2]·2CH3CN (1) (H4L = (E)-2-(hydroxymethyl)-2-(((2-hydroxynaphthalen-1-yl)methylene)amino)propane-1,3-diol, and Hacac = acetylacetone) were synthesized by employing a polydentate Schiff-base ligand (H4L) and a β-diketonate co-ligand and further characterized structurally. Alternating current (ac) magnetic susceptibility measurements indicated that cluster 1 shows slow relaxation of magnetization behavior. More importantly, cluster 1 shows high catalytic activity of the cycloaddition reaction of CO2 and epichlorohydrin under mild conditions; and cluster 1 as heterogenous catalyst can be reused at least three times without any obvious loss in catalytic activity. It is worth mentioning that cluster 1 is a rare bifunctional Ln(III)-based material for both molecular based magnetic material and heterogenous catalyst.

New Low-Dimensional Organic–Inorganic Lead Halide Hybrid Systems Directed by Imidazo[1,5-a]pyridinium-Based Cation or Imines: Synthesis, Structures, Non-Covalent Interactions and Optical Properties

The organic–inorganic lead halide hybrids comprising semiconducting perovskite components and organic modules have proven to be promising candidates for optoelectronic applications. The modulation of the inorganic components as optical centres by diverse organic cationic templates is under intense investigation. Herein, we successfully prepared new one-dimensional lead halide hybrid perovskites [L1]2n[Pb2Cl6]n∞·nH2O (1) and [PbBr2(L2)]n∞·0.5nH2O (2), and the dimeric complex [PbBr2(L3)]2 (3) in water media. In 1, 2-(2-hydroxyethyl)-2H-imidazo[1,5-a]pyridinium cation [L1]+ resulted from the oxidative condensation–cyclization between formaldehyde, ethanolamine and 2-pyridinecarbaldehyde (2-PCA); the polydentate Schiff base ligands L2 and L3 formed in the in situ condensation of 2-PCA and ethanolamine or ethylenediamine, respectively. The lead chloride hybrid 1 contains the previously unreported type of a [Pb2Cl6]∞ double chain constructed from three-edge- and five-edge-sharing PbCl6 octahedra, and cations forming π-bonded stacks aligned along the inorganic wires. In the crystal of 2, pairs of the double-side organically decorated [PbBr2(L2)]∞ chains built of corner-sharing PbBr3N2O octahedra arrange hydrophilic channels to host water molecules. In the solid state, the identically stacked dimers of 3 form columns parallel to the ab plane with the Pb2Br4 moieties in the column being strictly coplanar. Hirshfeld surface analysis was used to rationalize the packing patterns through hydrogen bonds of O−H···O/Cl and C−H···O/Cl types with the involvement of OH groups of [L1]+, L2 and water molecules in 1 and 2, as well as C–H∙∙∙Br hydrogen bonding in 2 and 3. The QTAIM analysis of non-covalent interactions in 1–3 was performed. According to the analysis of the solid-state UV–visible reflectance spectra by a Tauc plot, the optical band gap values of 1, 2 and 3 as direct gap semiconductors were estimated to be 3.36, 3.13 and 2.96 eV, respectively.

Four Ln2 compounds constructed by a polydentate Schiff base ligand: Gd2 compound displaying large magnetocaloric effect and Dy2 compound showing single-molecule magnet behavior

Four new acyloxy bridged LnIII2 compounds [Ln2(L)2(acac)2(EtOH)2] (Ln(III) = Gd (1), Tb (2), Dy (3), and Ho (4), Hacac = acetylacetone, and H2L = pyridine-2-carboxylic acid (3-ethoxy-2-hydroxy-benzylidene)-hydrazide) have been prepared by a polydentate Schiff base ligand under solvothermal condition. The single-crystal X-ray structure study reveals that 1–4 are isostructural and contain a parallelogram Ln2O2 core. Magnetic study reveals that antiferromagnetic interaction exists in compound 1. More importantly, compound 1 displays well cryogenic magnetic refrigeration property (−ΔSm = 28.2 J kg−1 K−1, T = 2.0 K and ΔH = 70 kOe); while compound 3 exhibits evident single-molecule magnet behavior under zero-field condition (ΔE/kB = 26.8 K, τ0 = 1.05 × 10−7 s).

Formation of a macrocycle from dichlorodimethylsilane and a pyridoxalimine Schiff base ligand

The reaction of dichlorodimethylsilane with a polydentate Schiff base ligand derived from pyridoxal and 2-ethanolamine yielded the macrocyclic silicon compound (8E,22E)-4,4,12,18,18,26-hexamethyl-3,5,17,19-tetraoxa-8,13,22,27-tetraaza-4,18-disilatricyclo[22.4.0.010,15]octacosa-1(24),8,10,12,14,22,25,27-octaene-11,25-diol, C24H36N4O6Si2. The asymmetric unit contains the half macrocycle with an intramolecular O—H...N hydrogen bond between the imine nitrogen atom and a neighbouring oxygen atom. The crystal structure is dominated by C—H...O and C—H...π interactions, which form a high ordered molecular network.

Molecular assemblies from linear-shaped Ln4 clusters to Ln8 clusters using different β-diketonates: disparate magnetocaloric effects and single-molecule magnet behaviours.

A series of tetranuclear lanthanide-based clusters [Ln4(dbm)6(L)2(CH3OH)4]·2CH3OH (Ln(III) = Gd (1), Dy (2), and Ho (3); H3L = 2-[(2-(hydroxyimino)propanehydrazide)methyl]-2,3-dihydroxybenzaldehyde, Hdbm = dibenzoylmethane) and octanuclear lanthanide-based clusters [Ln8(HL)10(CH3O)4(CH3OH)2]·6CH3OH (Ln(III) = Gd (4), Dy (5)) were assembled using a polydentate Schiff-base ligand H3L and two different β-diketone salts via a solvothermal method, and their structures and magnetic properties have been characterized. Interestingly, β-diketones play an important role in assembling and affecting the structures of Ln4 to Ln8 clusters. This is the first use of β-diketone to affect the structures of polynuclear Ln(III)-based clusters from linear-shaped Ln4 clusters to Ln8 clusters. Magnetic studies revealed that antiferromagnetic interactions exist in clusters 1-Gd4 and 4-Gd8. More importantly, clusters 1-Gd4 and 4-Gd8 display significant cryogenic magnetic refrigeration properties (-ΔSm = 24.88 J kg-1 K-1 for 1-Gd4 and -ΔSm = 32.52 J kg-1 K-1 for 4-Gd8); the results show that cluster 4-Gd8 exhibits a larger magnetocaloric effect than 1-Gd4. Cluster 2-Dy4 shows remarkable single-molecule magnet (SMM) behavior (ΔE/kB = 67.5 K and τ0 = 3.06 × 10-7 s) under a zero dc field, and 5-Dy8 exhibits a field-induced SMM-like behavior (ΔE/kB = 39.83 K and τ0 = 2.12 × 10-7 s) under a 5000 Oe dc field.

Heterometallic Complexes Containing the NiII-LnIII-NiII Moiety—Structures and Magnetic Properties

This review summarizes the structural characteristics and magnetic properties of trinuclear complexes containing the NiII-LnIII-NiII moiety and also oligonuclear complexes and coordination polymers containing the same trinuclear moiety. The ligands used are mainly polydentate Schiff base ligands and reduced Schiff base ligands and, in some cases, oximato, β-diketonato, pyridyl ketone ligands and others. The compounds reported are restricted to those containing one, two and three oxygen atoms as bridges between the metal ions; examples of carboxylato and oximato bridging are also included due to structural similarity. The magnetic properties of the complexes range from ferro- to antiferromagnetic depending on the nature of the lanthanide ion.

Synthesis, crystal structures, magnetic and magnetocaloric studies of heterometallic enneanuclear {Cu7Gd2} complexes

The reaction of Gd(NO3)3·6H2O and [Cu2(piv)4(pivH)2] with the polydentate Schiff base ligands o-OH-C10H6-CH = NC(R)(CH2OH)2 (R = CH3, H3L1; R = C2H5, H3L2) in MeOH afforded the enneanuclear heterometallic complexes [Cu7Gd2(L1)4(HL1)2(piv)4(H2O)(MeOH)3] (1) and [Cu7Gd2(L2)4(HL2)2(piv)4(MeOH)5] (2). Crystallographic studies revealed that both complexes are isostructural and consist of a central core {Cu7Gd2(μ3-Oalkoxo)6(μ2-Oalkoxo)4(μ2-Opivalato)2}8+. Peripheral ligation and bridging are provided by four triply and two doubly deprotonated Schiff base ligands, two μ3-pivalates, two chelate pivalates, and terminal aqua and/or MeOH molecules. Magnetic susceptibility measurements revealed the presence of dominant ferromagnetic intramolecular interactions in both complexes. The magnetocaloric effect of 1 and 2 was examined via isothermal magnetization measurements under various applied fields and the maximum entropy change was found equal to 13.3 and 12.1 Jkg-1K−1 for 1 and 2, respectively, at 2 K for ΔH = 5 T.

Magnetic refrigeration property and slow magnetic relaxation behavior of five dinuclear Ln(III)-based compounds

In this work, a series of dinuclear Ln(III)-based compounds with the molecular form [Ln2(L)2(dbm)2(H2O)2]·nCH3OH (Ln(III) = Eu (1), Gd (2), Tb (3), Dy (4) and Ho (5), Hdbm = 1,3-diphenyl-1,3-propanedione and H2L = 2-[(1E)-{[(pyridin-2-yl)formamido]imino}methyl]benzoic acid) have been successfully synthesized using a polydentate Schiff base ligand (H2L) and reacting it with the β-diketone salts Ln(dbm)3·2H2O. The crystal structures and magnetic properties of the five Ln2 compounds have been completely studied. The crystal structure studies reveal that compounds 1–5 are isostructural and show a dinuclear structure with a parallelogram Ln2O2 core. The magnetic research suggests that the Gd2 compound shows a cryogenic magnetic refrigeration property with magnetic entropy (−ΔSm) = 23.2 J K−1 kg−1 (T = 2.0 K and ΔH = 7.0 T), while the Dy2 compound exhibits slow magnetic relaxation behavior.

Structure, fluorescence properties and slow magnetic relaxation of Dy2 and Tb4 clusters

Two new Ln(III)-based clusters, namely [Dy2(acac)2(HL)2(H2O)2] (1) and [Tb4(L)4(CH3OH)4]•3CH3OH•H2O (2) (H3L = 2-hydroxy-N'-[(1E)-(8-hydroxyquinolin-2-yl)methylidene]benzohydrazide, and Hacac = acetylacetone), were successfully synthesized by employing a polydentate Schiff base ligand (H3L) under solvothermal conditions. The structures and magnetic properties of clusters 1 and 2 have been systematacially investigated. Single crystal X-ray diffraction indicates that cluster 1 is a dinuclear structure, whereas cluster 2 displays a novel Tb4 tetrahedral arrangement. Magnetic studies reveal that cluster 1 exhibits single-molecule magnets (SMMs) behavior under zero dc filed (ΔE/kB = 48.1 K, and τ0 = 3.63 × 10−7 s), while no SMM behavior was observed in cluster 2.

Crystal structure and single-molecule magnet behavior of a novel tetranuclear Dy(III)-based cluster

By using a polydentate Schiff base ligand (H3L), in this paper, a new Dy(III)-based cluster, namely [Dy4(HL)4(CH3O)4]·4CH3OH (1), was successfully obtained and further characterized by single-crystal X-ray diffraction. The crystal structure measurement suggests that cluster 1 crystallizes in the monoclinic space group C2/c and the four center Dy(III) ions of cluster 1 displays a tetrahedral arrangement. The magnetic study reveals that cluster 1 shows remarkable single-molecule magnet (SMM) behavior under zero dc filed (ΔE/kB = 54.6 K, and τ0 = 6.43 × 10−7 s).

A novel tetranuclear Gd(III)-based cluster showing larger magnetic refrigeration property

A novel tetranuclear Gd(III)-based cluster, namely [Gd4(HL)4(CH3O)4] •3CH3OH (1), has been successfully synthesized by using a polydentate Schiff base ligand (H3L) reacted with Gd(acac)3•2H2O. The crystal structure and magnetic property of cluster 1 have been completely studied. Crystal structure study reveals that cluster 1 is a tetranuclear compound and the four center Gd(III) ions display a tetrahedral arrangement. The magnetic research suggests that cluster 1 shows cryogenic magnetic refrigeration property with a larger magnetic entropy (−ΔSm = 30.42 J K−1 kg−1, T = 2.0 K and ΔH = 7.0 T).

Preparation, characterization of some transition metal complexes of hydrazone derivatives and their antibacterial and antioxidant activities

A new series of metal complexes of Pd(II), Cd(II) and Cu(II, I) of polydentate Schiff base ligand (H2L), namely ((Z)-2-(phenylamino)-N'-(thiophen-2-ylmethylene) acetohydrazide) have been prepared. The ligand and its metal complexes have been characterized based on various physicochemical studies as elemental analyses, molar conductance, spectral (UV–Vis, MS, IR, 1H NMR, 13C NMR and XRD), magnetic moment measurements and thermal studies (TG, DTG). In the view of previous studies, the ligand (H2L) acts as polydentate one and coordinates with metal ions to form all metal complexes. The kinetic and thermodynamic parameters of decomposition process (ΔG, ΔH, ΔS) were calculated. The possible structures of the metal complexes have been computed using the molecular mechanic calculations using the hyper chem. 8.03 molecular modeling program. The calculations are performed to obtain the optimized molecular geometry. The antibacterial study of the selected compounds was assayed against two pathogenic bacteria. Moreover, the complexes (Cu II, I), Cd(II), Pd(II)) and the ligand revealed excellent antioxidant properties and could be useful in fighting the free radicals which occur in close connection with cancerous cells. It was remarkable that the two complexes (Cu II, I) demonstrated stronger antioxidant effects than their parent compounds. It is clear that the new complexes are good active compounds for use in a variety of applications.

Structures and magnetic properties of novel Ln(iii)-based pentanuclear clusters: magnetic refrigeration and single-molecule magnet behavior

The Gd5 cluster displays significant magnetic refrigeration properties, whereas the Dy5 cluster exhibits remarkable SMM behavior. Clusters 2, 4, and 5 display the characteristic lanthanum luminescence.

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.