Tetradentate Schiff Base Ligand Research Articles

Spectroscopic investigation, molecular structure, catalytic activity with computational studies of a novel Pd(II) complex incorporating unsymmetrical tetradentate Schiff base ligand

The treatment of an unsymmetrical tetradentate Schiff base ligand with Pd(OAc)2 salt yields novel palladium(II) Schiff base complex. The generated palladium(II) complex was characterized using elemental analysis (CHN) and different spectroscopic methods such as FT-IR and 1H NMR. Single crystal X-ray diffraction (SC-XRD) investigation has also been used to examine the crystal structure of the palladium complex. It is revealed from the SC-XRD study that the palladium ion in the complex is tetra-coordinated, inhabited by ONNO donor sites of the chelated ligand in a distorted square planar manner. The non-covalent interactions were explored by Hirshfeld surface analysis. The theoretical parameters calculated by DFT using the B3LYP/Def2-TZVP level of theory revealed that the theoretical conclusions matched the actual findings. For different aryl halides, the palladium(II) complex has exhibited excellent efficiency in the Suzuki-Miyaura cross-coupling reactions (SMCR), yielding biaryls in good to high yield.

Two different coordination modes of the Schiff base derived from ortho-vanillin and 2-(2-aminomethyl)pyridine in a mononuclear uranyl complex

This work describes the reaction of the potentially tetradentate Schiff-base ligand N-(2-pyridylmethy)-3-methoxysalicylaldimine (HL) with UO2(O2CMe)2·2H2O and UO2(NO3)2· 6H2O in MeOH in the absence or presence of an external base, respectively. The product from these reactions is the mononuclear complex [UO2(L)2] (1). Its structure has been determined by single-crystal, X-ray crystallography. The anionic ligand adopts two different coordination modes (1.1011, 1.1010; Harris notation) in the complex. The new compound was fully characterized by solid-state (IR, Raman and Photoluminescence spectroscopies) and solution (UV-Vis and 1H NMR spectra, conductivity measurements) techniques.

Synthesis, spectral characterization, and theoretical investigation of Ni(II) and Pd(II) complexes incorporating symmetrical tetradentate Schiff base ligand: Suzuki-Miyaura cross-coupling reaction using PdLSym

Synthesis, spectral characterization, and theoretical investigation of Ni(II) and Pd(II) complexes incorporating symmetrical tetradentate Schiff base ligand: Suzuki-Miyaura cross-coupling reaction using PdLSym

Synthesis, crystal structure, spectral characterization, catalytic studies and computational studies of Ni(II) and Pd(II) complexes of symmetrical tetradentate Schiff base ligand

In the current work, a symmetrical tetradentate Schiff base ligand (H2L) derived by the condensation of methoxy-salicylaldehyde with substituted phenylenediamine is used to prepare nickel (II) and palladium (II) complexes. The chemical structures of the synthesized compounds were investigated with the help of combustion analysis and spectrophotometrically using FT-IR and 1H NMR. H2L and its nickel (II) complex were obtained in pure crystalline form, and hence, these compounds were characterized by diffraction analysis. It was evident from single-crystal X-ray diffraction analysis (SC-XRD) that the ligand was doubly deprotonated (L−2 ) and coordinated with the Ni(II) ion via ONNO-donor sites, and a distorted square planar geometry was achieved. Interestingly, the complex also attaches a solvent molecule (DMF) through its electronegative O atom with the H atom of DMF through hydrogen bonding. The molecular structure of the synthesized compounds was further validated with the help of density functional theory (DFT) using the B3LYP/Def2-TZVP level of theory. Furthermore, the Pd(II) complex was tested for Suzuki–Miyaura cross-coupling reactions and the results showed better catalytic activity in mild conditions concerning the traditionally available catalysts.

Heterometallic iron(IV) μ-nitrido complexes supported by a tetradentate Schiff base ligand

A nitrido-bridged heterometallic iron(IV) chloride complex supported by a tetradentate Schiff base ligand has been synthesized and its chloride substitution reactions have been studied. Treatment of the Fe(II) Schiff base complex [Fe(Br4saloph)(py)] (H2Br4saloph = N,N’-bis(3,5-dibromosalicylidene)-1,2-phenylenediamine; py = pyridine) with the Ru(VI) nitride [Ru(N)Cl2(LOEt)] (1, LOEt− = [(η5-C5H5)Co{P(O)(OEt)2}3]−) afforded the μ-nitrido complex [(LOEt)(py)ClRu(μ-N)Fe(Br4saloph)Cl] (2-Cl). The short Fe-N(nitrido) [1.668(4) Å] and Ru-N(nitrido) [1.709(4) Å] distances and the roughly linear Fe-N-Ru linkage [172.9(3)o] in diamagnetic 2-Cl are indicative of the Fe(IV)=N=Ru(IV) bonding picture. Salt metathesis of 2-Cl with [Ag(CF3CO2)] and [Ag(ReO4)] afforded [{(LOEt)(py)ClRu(μ-N)Fe(Br4saloph)(CF3CO2)}⋅Ag(CF3CO2)] (2-CF3CO2⋅Ag(CF3CO2)) and [(LOEt)(py)ClRu(μ-N)Fe(Br4saloph)(ReO4)] (2-ReO4), respectively. Chloride abstraction of 2-Cl with TlPF6, followed by recrystallization in air led to isolation of the μ-oxo complex [{2}2(μ3-O)Tl](PF6)2 (3), which is paramagnetic with a magnetic moment of 2.0 μB. Complex 3 features a [Ru-N-Fe-O(Tl)-Fe-N-Ru]2+ unit, the Tl atom of which is coordinated to the μ-oxo ligand and the oxygen atoms of the Schiff base ligands. The Ru-N(nitrido) (av. 1.709 Å), Fe-N(nitrido) (av. 1.659 Å) and Fe-O(oxo) (av. 1.991 Å) distances in 3 are consistent with M = N double bonds and Fe-O single bonds, respectively. Treatment of 2-Cl with [Tl(SC6F5)] afforded the Fe(III)/Ru(IV) nitrido complex [(LOEt)(py)ClRu(μ-N)Fe(Br4saloph)] (4) that has a longer Fe-N(nitrido) distance [1.753(4) Å] than the Fe(IV) congener 2-Cl does. The crystal structures of complexes 2-Cl, 2-CF3CO2⋅Ag(CF3CO2), 2-ReO4, 3, and 4 have been determined.

Cover Feature: Versatile Activity of a Copper(II) Complex Bearing a N4‐Tetradentate Schiff Base Ligand with Reduced Oxygen Species (Eur. J. Inorg. Chem. 8/2022)

The Cover Feature shows the versatility of a copper complex formed with a N4-tetradentate Schiff-base ligand: it reacts with hydrogen peroxide and superoxide, and it catalyzes phenol oxidation. The complex scavenges superoxide by employing a Cu(II)/Cu(I) redox cycle for superoxide dismutase activity. In basic medium and at low temperature, it reacts with HO2− to form a stable end-on Cu(II)-hydroperoxide adduct, which either reacts with a second complex molecule to yield the redox products, through an intermediate peroxo-bridged dimer (catalase activity), or mediates phenol oxidation, through a ternary transition state (peroxidase activity), under suitable conditions. Kinetic, spectroscopic, and theoretical studies indicate that structural constraints imposed by the ligand distort the coordination geometry of the metal and control reactivity. More information can be found in the Research Article by S. R. Signorella and co-workers.

Synthesis, crystal structure, spectral characterization, theoretical and computational studies of Ni(II), Cu(II) and Zn(II) complexes incorporating Schiff base ligand derived from 4-(diethylamino)salicylaldehyde

Three new nickel(II), copper(II), and zinc(II) complexes were prepared by treating symmetrical tetradentate Schiff base ligand (H2L) with Ni(OAc)2·4H2O, Cu(OAc)2·H2O, and Zn(OAc)2·2H2O salts, respectively. The synthesized compounds were structurally characterized by elemental (CHN) and spectroscopic analysis like FT-IR and 1H NMR. Moreover, the crystal structure of the Ni(II) complex (NiL) has been determined by SC-XRD. The crystal structure investigation confirms that the metal ion is tetra coordinated by ONNO donor sites of ligand to acquire a square planar geometry, which is further compared with some related crystal structures by Cambridge structure database search. A Hirshfeld surface inspection was conducted for the sake of further investigation of the non-covalent interactions in NiL. An enrichment ratio is also calculated for the chemical species to determine the tendency of their interactions in the crystal packing. The theoretical values based on DFT using B3LYP/Def2-TZVP level of theory ensured that the expected consequences matched the experimental findings.

New Tetra-dentate Schiff Base Ligand N2O2 and Its Complexes with Some of Metal Ions: Preparation, Identification, and Studying Their Enzymatic and Biological Activities

In present work, new tetra-dentate ligand, titled 3,5-bis ((E)-5-Bromo-2-hydroxy benzylidene amino) benzoic acid (H3L), was prepared via an acid-catalyzed condensation process. New four metallic ligand complexes with Co(II), Ni(II), Cu(II) and Zn(II) ions, were also prepared from the refluxing of equivalent moles. Ligand's structure and its complexes; were confirmed by numerous characterization methods, including Ultraviolet-Visible, Infrared, Mass Spectrometer, 1H and 13C Nuclear Magnetic Resonance spectra, atomic absorption, magnetic moments, and molar conductivity measurements. The results of the spectroscopic analyzes proved that the prepared ligand acts as tetradentate bi-ionic ligand and it was bonded to the metal ions by two nitrogen atoms of the two azomethine groups and by two oxygen atoms of the two phenolic hydroxyl groups after losing their two protons. Octahedral structure proposed to all prepared complexes. The (anti-bacterial) and (anti-fungal) activities of these compound were screened against (E. coli, S. aureus, Klebsiella spp., S. epidermidis,), and (Candida albicans). The results indicated that these compounds have moderated inhibition behavior. The activity of the prepared compounds against Acetyl Choline Esterase Enzyme (AChE) have also studied and the obtained data indicated the presence of different inhibition behavior.

Synthesis, spectral characterization, antimicrobial evaluation and molecular docking studies on new metal complexes of novel Schiff base derived from 4,6-dihydroxy-1,3-phenylenediethanone

A new tetradentate Schiff base ligand was prepared from condensation of 4,6-dihydroxy-1,3-phenylenediethanone with ethane-1,2-diylbis(oxy)diethanamine. The ligand forms complexes in good yield. The Schiff base and its complexes were characterized by analytical (CHN elemental analyses, solubility, melting point, conductivity) measurements, spectral (IR, UV–vis, 1H NMR and MS) and magnetic measurements. The elemental analyses, Uv-vis spectra, and room temperature magnetic moment data and theoretically through density function theory were used as characterization techniques in supporting of further interpretation of the complexes structures. The results of elemental analyses, EI-mass and conductivity measurements confirmed the stoichiometry of the ligand and its complexes while the characteristic absorption bands and resonance peaks in IR and NMR spectra confirmed the formation of the ligand frameworks around the metal ions. The octahedral environment for complexes derived from Schiff base ligand have been confirmed based on results of electronic and diffused reflectance spectral studies and magnetic moment measurements. Detailed studies on the thermal properties of the Schiff base ligand and complexes were investigated by thermogravimetric technique. Moreover, the molecular docking into (PDB: 6NE0) was the DNA binding and supports the experimental finding and 6IY0 crystal structure of conserved hypothetical protein SAV0927 from Staphylococcus aureus subsp. aureus Mu50. The synthesized ligand and its complexes were tested for in vitro antimicrobial activity against Candida albicans, Aspergillus flavus, Bacillus subtilis, Escherichia coli, Pseudomonas aeruginosa and Staphylococcus aureus by using agar-well diffusion method. An enhancement in the antimicrobial activity due to metal chelation was observed.

Co(III), Ni(II) and Cu(II) complexes with a tetradentate Schiff base ligand: synthesis, characterization, electrochemical behavior, binding assessment and in vitro cytotoxicity

Two new Schiff base cobalt(III) ([Co(LH)Cl2], 1) and nickel(II) ([Ni(LH)ClO4], 2) complexes with a diimine-dioxime ligand, (4,9-diaza-3,10-diethyl-3,9-dodecadiene-2,11-dione bis oxime (LH2 )), were synthesized and characterized. The compounds were obtained in MeOH from corresponding metal salts and LH2 in molar ratio 1:1 and further characterized by mass spectrometry, IR spectroscopy, electrochemistry, and elemental analysis. Previously reported copper(II) analog ([Cu2(LH)2]·(ClO4)2, 3) was joined to 1 and 2, and the three metal analogs, 1–3, were further investigated in terms of their electrochemical behavior. Binding studies of the complexes with deoxyribonucleic acid (DNA) and human serum albumin (HSA) were carried out using both spectrophotometric and electrochemical methods. All three complexes exhibit binding affinity towards the DNA chain through intercalative interactions. The binding reaction with HSA showed for 1 and 3 decrease in the peak current obtained in the case of complexes before the addition of HSA, while the Ni complex–HSA possesses the same electroactivity as starting complex. The cytotoxicity of LH2 as well as its metal complexes, and cisplatin were evaluated on CT-26 mouse colon carcinoma and human LS174T cancer cell lines employing MTT assay. The copper(II) complex exhibited very promising anticancer activity compared with cisplatin.

Synthesis, Structural Characterization and Catalytic Activities of Palladium(II) Schiff base Complexes Containing Tetradentate N2O2 & N2S2 Donor Ligands

New family of palladium(II) tetradentate complexes of the general formula [Pd(L1-4)] (L1-L3; tetradentate N2O2 donors & L4; tetradentate N2S2 donors) have been synthesized by the reaction of Pd(OAc)2 with tetradentate Schiff base ligands. The palladium(II) complexes were fully characterized by analytical, spectral (FT-IR, UV-Vis, 1H-NMR & 13C-NMR) methods. Further, the new palladium(II) complexes were tested as catalyst for Suzuki-Miyaura and Sonogashira coupling reactions and exhibits very good catalytic activity.

Synthesis, crystal structure, quantum chemical calculations, electrochemistry and electro-catalytical properties as cytochrome P-450 model of tetradentate Mn(III)-Schiff base complex

The tetradentate Schiff base ligand has been obtained from condensation with mixing ethylenediamine and 2 mmoles of 5-methoxy-2-hydroxybenzaldehyde in absolute ethanol H2L. To the ethanolic solution was added manganese(II)acetatetetrahydrated and lithium chloride (LiCl) to obtain the tetradentate manganese(III) Schiff base complex [Mn(III)(Cl)L]. Theprepared compounds have been characterized by several spectroscopic techniques such as elemental analyses, FT-IR, UV–vis., 1H NMR and HRMS. In this paper, the X-ray diffraction (XRD) and the computational studies (DFT) of the ligand(H2L) with its manganese(III)-Schiff base complex [Mn(III)(Cl)L] are described and confirmed the given molecularstructures. The crystallographic studies have been utilized toelucidate the kinetics, selectivity and stereochemistry of thetransferred oxygen atomsto the substrate molecules when the considered complex is used as catalyst accordingthecytochrome P450 model. In addition, the density functional theory (DFT) calculation with B3LYP/6-31G(d,p) level isperformed to obtain the optimized geometries and electronic properties of the prepared compounds. The global reactivityparameters have also been calculated using the energies of frontier molecular orbitals suggesting that the ligand H2L is morestable than its Mn(III) complex. This may be due to the presence of hydrogen bonds in the ligand and the weaker energies ofcoordination bonds in the complex. The electrochemical behaviour of Mn(III)(Cl)L has been studied by cyclic voltammetryin acetonitrile solutions at room temperature. The resulting cyclic voltammogram shows Mn(III)/Mn(II) couple at E1/2= -0.62V with glassy carbon (GC) electrode. This redox couple is involved in the electrocatalytic cycle where themanganese(III) cation is successively mono-electronated until the formation of superoxo intermediates and then the oxospecies, respectively. These oxo forms, generated in situ, transfer their oxygen atoms to the substrate giving the oxidizedproduct. So, the chemical and electrochemical reactions, implicated in this electrocatalytical process, obey to the biomimeticoxidation reactions as those of monooxygenase enzymes (Cytochrome P450).

One-pot synthesis, characterization, optical studies and biological activities of a novel ultrasonically synthesized Schiff base ligand and its Ni(II) complex

A novel tetradentate Schiff base ligand, 3-((2-(-(1-(2-hydroxyphenyl)ethylidene)amino)ethyl)imino)-2-pentone and its Ni(II) complex have been synthesized by green chemical, ultrasonication method. The ligand and metal complex were characterized analytically and spectroscopically by elemental analysis, HRMS, IR, 1H NMR, 13C NMR, UV–vis absorption spectroscopy, molar conductance, and magnetic susceptibility measurements. Powder XRD analysis was done to show the crystalline nature of the samples. The surface morphology and size of both ligand and complex were monitored by SEM and TEM microscopic techniques. Based on the various physicochemical measurements and spectral analysis, Ni(II) complex is assigned to an octahedral geometry. The optical bandgap energy, fluorescence spectrum lifetime analyses and chromaticity studies were accomplished to encounter the possibilities of optical applications. The fluorescence nature of both ligand and complex was found to be in the visible range. Optical bandgap energy values fall in the range of semiconductor materials. The chromaticity studies give the CIE 1931 coordinates and colour correlation temperature values of the samples. The ligand and the Ni(II) complex were screened for biological activities such as antimicrobial, antioxidant, and larvicidal activities. The results implied that the Ni(II) complex shows better antimicrobial, antioxidant and larvicidal activities than the free ligand.

Synthesis, crystal structure, and DFT studies of a new phenoxo-bridged dinuclear zinc(II) Schiff base complex with two different geometries

A new dinuclear Zn(II) complex Zn2L(H2O)(NCS)2 (1) is synthesized by the reaction of the tetradentate Schiff base ligand N,N'-bis(5-bromosalicylidene)-1,3-diaminopropane (H2L) with Zn(OAc)2·2H2O in the presence of sodium thiocyanate. The ligand and complex 1 are characterized by microanalytical and spectroscopic techniques. The structure of the complex is established by single crystal X-ray diffraction studies. In the phenoxo-bridged zinc complex, one Zn atom is five-coordinated in a square-pyramidal geometry while another is four-coordinated in a tetrahedral geometry. To gain insight into the structural features of complex 1, DFT studies are performed. The calculations reveal a strong effect of the intermolecular interaction, namely the π—π stacking interaction, on the geometry of the complex.

Synthesis, spectral characterization, crystal structures, biological activities, theoretical calculations and substitution effect of salicylidene ligand on the nature of mono and dinuclear Zn(II) Schiff base complexes

Two new zinc(II) Schiff base complexes (Z1 and Z2) are prepared by treating ONNO tetradentate Schiff base ligands (H2L1 = [6,6′-((1E,1′E)-((2,2-dimethylpropane-1,3-diyl)bis(azanylylidene))bis(methanylylidene))bis(2-methoxyphenol)] and H2L2 = [2,2′-((1E,1′E)-((2,2-dimethylpropane-1,3-diyl)bis(azanylylidene))bis(methanylylidene))bis(4-methoxyphenol)]) with acetylacetonate salt of zinc. The synthesized Schiff base ligands and their respective zinc(II) complexes were characterized by elemental analysis (CHN) and various spectroscopic techniques like FT-IR and 1H NMR. The single crystal X-ray structures of Z1 and Z2 show the effect of salicylidene ligand on the nature of mono and dinuclear Zn(II) Schiff base complexes. In Z1 complex, a square pyramidal geometry is adapted by the complex, supported by the ONNO donor atoms of the tetradentate Schiff base and a coordinated water molecule. Structural analysis of Z2 complex revealed that the compound is a centrosymmetric dimer in which the five coordinated Zn(II) atoms are linked to the opposite metal center by making μ-phenoxo bridges through one of the phenolic oxygen atoms of Schiff base ligands. The nature of various kinds of non-covalent interactions present among the sample molecules was also investigated by using QTAIM and NCI calculations. The theoretical calculations were performed by DFT using the B3LYP/Def2-TZVP level of theory, which indicated that the intended outcomes are in compliance with the actual consequences. Furthermore, the antibacterial potential of the Schiff base ligands and their corresponding zinc complexes was measured by testing them against two Gram-positive (Staphylococcus aureus and Bacillus cereus) and two Gram-negative (Escherichia coli and Pseudomonas aeruginosa) bacterial strains. The agar well diffusion method and poisoned media technique were used for screening of bacterial and fungal species, respectively. According to the results of the zone of inhibition assessments, metal complexes have comparatively more inhibition potential relative to free ligands.

Pd(II) and Ni(II) complexes containing ONNO tetradentate Schiff base ligand: Synthesis, crystal structure, spectral characterization, theoretical studies, and use of PdL as an efficient homogeneous catalyst for Suzuki–Miyaura cross-coupling reaction

Two new palladium(II) and nickel(II) Schiff base complexes are prepared through the reaction of Pd(OAc)2 and Ni(OAc)2·4H2O with a tetradentate ONNO Schiff base, derived by condensing 4,5-dimethyl-1,2-phenylenediamine and 4-methoxysalicylaldehyde. The elemental analysis (CHN) and other spectroscopic techniques such as FT-IR and 1H NMR were used to characterize the synthesized ligand and its corresponding metal complexes. Moreover, the crystal structure of the Pd(II) complex was investigated by the single crystal X-ray diffraction analysis. The diffraction analysis explores a slightly distorted square planar geometry of the PdL complex due to the coordination with deprotonated phenolic O-atoms and N-atoms from azomethine chromophore. The DFT-based theoretical calculations which employed the B3LYP/Def2-TZVP level of theory explore that the theoretical results corresponded to the actual data obtained via spectroscopic characterization.

Synthesis, spectral characterization and antibacterial activity of transition metal (II) complexes of tetradentate Schiff base ligand

Nickel, zinc and cadmium complexes of a Schiff base derived from 4-nitro-o-phenylenediamine and 5-methoxysalicylaldehyde were synthesized and characterized using infrared, ultra violet, molar conductance measurements and nuclear magnetic resonance spectroscopy. Tetradentate schiff base complexes are widely used for the industrial purpose and also exhibit the wide range of biological activities. Hence the antibacterial activity of the Schiff base ligand and the metal complexes against some clinically important bacteria namely Escherichia coli, Proteus mirabilis, Streptococcus pneumoniae, Bacillus subtilis were investigated and the obtained results have shown that the complexes were possesses more antibacterial activity than the parent Schiff base ligand and hence could be potentially used in the preparation of anti bacterial agents.

Binuclear Zn(II) Schiff base complexes: Synthesis, spectral characterization, theoretical studies and antimicrobial investigations

Binuclear zinc(II) Schiff base complexes were synthesized through the reaction of ONNO tetradentate Schiff base ligands derived from the condensation of 2,2-dimethyl-1,3-propanediamine and 5-chlorosalicylaldehyde or 5-bromosalicylaldehyde with zinc acetylacetonate salt. The structures of synthesized products were explored spectroscopically through the FT-IR, 1H NMR and elemental analysis. Structural analysis of the complexes revealed that the compound is a centrosymmetric dimer in which the five coordinated Zn(II) atoms are linked to the opposite metal center by making μ-phenoxo bridges through one of the phenolic oxygen atoms of Schiff base ligands. The nature and types of non-covalent interactions present among the sample molecules were also investigated by using the quantum theory of atoms in molecules and non-covalent interactions calculations. The theoretical calculations, performed by density functional theory using the B3LYP/Def2-TZVP level of theory, direct that the intended outcomes are in compliance with the actual consequences. Furthermore, from antimicrobial screenings it was revealed that the zinc complexes are more active as compared to the ligands.

Structural Elucidation, Aggregation, and Dynamic Behaviour of N,N,N,N-Copper(I) Schiff Base Complexes in Solid and in Solution: A Combined NMR, X-ray Spectroscopic and Crystallographic Investigation.

A series of Cu(I) complexes of bidentate or tetradentate Schiff base ligands bearing either 1‐H‐imidazole or pyridine moieties were synthesized. The complexes were studied by a combination of NMR and X‐ray spectroscopic techniques. The differences between the imidazole‐ and pyridine‐based ligands were examined by 1H, 13C and 15N NMR spectroscopy. The magnitude of the 15Nimine coordination shifts was found to be strongly affected by the nature of the heterocycle in the complexes. These trends showed good correlation with the obtained Cu−Nimine bond lengths from single‐crystal X‐ray diffraction measurements. Variable‐temperature NMR experiments, in combination with diffusion ordered spectroscopy (DOSY) revealed that one of the complexes underwent a temperature‐dependent interconversion between a monomer, a dimer and a higher aggregate. The complexes bearing tetradentate imidazole ligands were further studied using Cu K‐edge XAS and VtC XES, where DFT‐assisted assignment of spectral features suggested that these complexes may form polynuclear oligomers in solid state. Additionally, the Cu(II) analogue of one of the complexes was incorporated into a metal‐organic framework (MOF) as a way to obtain discrete, mononuclear complexes in the solid state.

Zn(II) complexes containing O,N,N,O-donor Schiff base ligands: synthesis, crystal structures, spectral investigations, biological activities, theoretical calculations and substitution effect on structures

New zinc(II) Schiff base complexes (Z1 and Z2) were prepared through the treatment of ONNO tetradentate Schiff base ligands (H2L1 and H2L2 ) with zinc acetylacetonate. Elemental analysis (C, H and N) and other spectroscopic techniques such as FT-IR and 1H NMR were used to characterize the produced ligands and their associated Zn(II) complexes. The structure of Z1 was explored by single crystal X-ray diffraction analysis. The structural investigations of Z1 demonstrate that it exists in the form of a centrosymmetric dimer in which penta coordinated Zn(II) ions are inter connected via µ-phenoxo bridges from one of the phenolic oxygen atoms of each tetradentate Schiff base ligand to the opposite zinc(II) ions. The theoretical calculations, performed by DFT using the B3LYP/Def2-TZVP level of theory, directed that the intended outcomes are in compliance with the actual consequences. The nature and types of non-covalent interactions present among the sample molecules were also investigated by using QTAIM and NCI calculations. Furthermore, antimicrobial activities of the synthesized Schiff base ligands and their respective zinc(II) complexes were also examined against two Gram-positive (Staphylococcus aureus and Bacillus cereus) and two Gram-negative (Escherichia coli and Pseudomonas aeruginosa) bacteria, and two fungal species (Aspergillus brasiliensis and Candida albicans). The agar well diffusion method and poisoned media technique were used for the study of biological properties of bacterial and fungi species, respectively. According to assessments of inhibitory zones, metal chelates are found to be somewhat more efficient than free ligands.