Tetradentate Schiff Base Ligand Research Articles

Synthesis and characterization of new Cr(III) complex with a tetradentate Schiff base ligand for polymer composite application

Synthesis and characterization of new Cr(III) complex with a tetradentate Schiff base ligand for polymer composite application

Well Defined Phosphine Free Ni-Catalyzed Dehydrogenation of Secondary Alcohols for the Synthesis of Ketones and Ketazines.

In this work, we unveil a novel synthesis of bench stable Ni (II) complexes supported by tetradentate Schiff-base ligands and the complexes were devoid of any phosphine or phosphine-based ligand. These Ni-complexes were successfully applied for the dehydrogenation of secondary alcohols for ketone and ketazine syntheses. Secondary alcohols with different functional groups were well tolerated during catalytic cycle. Moreover, we successfully extended this protocol for the synthesis of biologically significant ketones and ketazines. On the basis of various control experiments, probable reaction pathway was proposed and an acceptorless alcohol dehydrogenation mechanism was suggested.

Preparation and investigation of TbCrO3/montmorillonite-K10 nanocomposite electrode for electrochemical hydrogen storage application

The limited resources of fossil fuels and the increase in human’s demand for energy have made the use of alternative green energies like hydrogen very important. In this regard, achieving superior specific capacity and high-performance electrochemical hydrogen storage requires the structural design and development of highly active electrode material with cooperative influence of “spillover”, “redox”, and “physisorption” mechanisms. The aim of this report is to fabricate a binary TbCrO3/montmorillonite-K10 (TC/MMT) nanocomposite and to skillfully ensure its electrochemical ability for hydrogen storage in 2.0 M KOH electrolyte, for the first time. A facile sonochemical strategy was presented to successfully form uniform orthorhombic TC nanoparticles with varying tetradentate Schiff base ligands derived from salicylaldehyde and relative diamines as well as the molar ratio of H2Salbn to Tb3+. Characterization analyses displayed that the nucleation and growth process of TC samples can be well controlled by a molar ratio of H2Salbn:Tb3+ = 1:1 within the range of 17–72 nm. Furthermore, implementation of a well-organized MMT-based nanocomposite with various amounts of nano-TC perovskites was evaluated on the structural and electrochemical features. The greatly enhanced hydrogen storage capacity of TC/MMT nanocomposites was acquired as 734.3 mAh/g after 15 cycles, when 10.0 % of perovskite oxide is induced by MMT layers. Moreover, architecture of pristine TC and MMT electrodes possessed a 936.87 and 341.52 mAh/g discharge capacities at the same situation. These merits allow a promising potential application of the nanocomposite electrodes containing rare-earth chromite oxide and clay substrates in electrochemical energy-storage devices.

Development of mixed-ligand ruthenium complexes bearing phosphine and imine ligands for utilisation as catalysts in Suzuki-type C–C cross-coupling reactions

ABSTRACT Herein we report the development of two mixed-ligand ruthenium (II) complexes bearing phosphine and imine ligands, their thorough characterisation and their utilisation as homogeneous catalysts in Suzuki-type C–C cross-coupling reactions. Reactions of two tetradentate Schiff base ligands, derived from imidazole-2-carboxaldehyde and ethylenediamine (H2L1 ) or propylenediamine (H2L2 ), with [Ru(PPh3)3Cl2] in refluxing ethanol in the presence of NEt3 afforded two complexes of type [Ru(L1)(PPh3)2] and [Ru(L2)(PPh3)2], respectively. The solid-state structure of [Ru(L2)(PPh3)2] was determined by single crystal X-ray diffraction analysis. The molecular structure of [Ru(L1)(PPh3)2] was optimised by the DFT method. Electronic spectra of the complexes showed intense absorptions spanning over the visible and ultra-violet regions, the origin of which was probed with TDDFT calculations. Redox properties of the complexes were studied by cyclic voltammetry. These mixed-ligand ruthenium(II) complexes serve as efficient catalyst-precursors for Suzuki-type C–C cross-coupling reactions.

Photophysical Studies of a Zr(IV) Complex with Two Pyrrolide-Based Tetradentate Schiff Base Ligands.

The reaction of two equivalents of N,N'-bis(2-pyrrolylmethylidene)-1,2-phenylenediamine (H2bppda) with tetrabenzylzirconium provided the air- and moisture-stable eight-coordinate complex Zr(bppda)2. Temperature-dependent steady-state and time-resolved emission spectroscopy established weak photoluminescence (ΦPL = 0.4% at 293 K) by a combination of prompt fluorescence and thermally activated delayed fluorescence (TADF) upon visible light excitation at and around room temperature. TADF emission is strongly quenched by 3O2 and shows highly temperature-sensitive emission lifetimes of hundreds of microseconds. The lifetime of the lowest energy singlet excited state, S1, was established by transient absorption spectroscopy and shows rapid deactivation (τ = 142 ps) by prompt fluorescence and intersystem crossing to the triplet state, T1. Time-dependent density functional theory (TD-DFT) calculations predict moderate ligand-to-metal charge transfer (LMCT) contributions of 25-30% for the S1 and T1 states. A comparison of Zr(bppda)2 to related zirconium pyridine dipyrrolide complexes, Zr(PDP)2, revealed important electronic structure changes due to the eight-coordinate ligand environment in Zr(bppda)2, which were correlated to differences in the photophysical properties between the two compound classes.

Iron(II) spin crossover complexes of tetradentate Schiff-bases: tuning T1/2 by choice of formyl-heterocycle component.

Four new tetradentate Schiff-base ligands were prepared in situ from the 1 : 2 condensation of 1,3-diaminopropane and either 2-thiazolecarboxaldehyde (L2thiazole), 4-thiazolecarboxaldehyde (L4thiazole), 4-oxazolecarboxaldehyde (L4oxazole), or 5-bromopyridine-2-aldehyde (L5Br-pyridine), and complexed with [Fe(NCS)2(pyridine)4] to give four monometallic FeII complexes, [Fe(Lheterocycle)(NCS)2]. Structural characterisation shows the expected octahedral FeII centres in all cases, with Lheterocycle occupying the equatorial plane and the two thiocyanate ligands trans to each other, resulting in an N6 coordination sphere. Solid state magnetic measurements showed that the two complexes with the thiazole-based ligands exhibit the beginning of a spin transition above 300 K, with T1/2 = 350 K for [Fe(L4thiazole)(NCS)2] and 400 K for [Fe(L2thiazole)(NCS)2], whereas the 4-oxazole-based ligand gives [Fe(L4oxazole)(NCS)2] which remains high spin at all measured temperatures (50-400 K). Interestingly, [Fe(L5Br-pyridine)(NCS)2] crystallised as two solvent-free polymorphs: magnetic measurements on samples with both polymorphs present showed a two step SCO with an abrupt transition at T1/2 = 245 K assigned to the transition in polymorph A (as this was also seen in a sample of pure polymorph A), and a gradual transition at T1/2 = 304 K assigned to polymorph B. These findings show that the order of increasing ligand field strength for these heterocycles is 4-oxazole ≪ 5Br-pyridine < 4-thiazole < 2-thiazole.

Non-covalent interactions in molecular architectures and solvent-free catalytic activity towards CO2 fixation of mononuclear Co(III) complexes installed on modified Schiff base ligands.

A set of mononuclear cobalt(III) octahedral complexes {[Co(LH)(acac)] (Co-1H), [Co(LBr)(acac)] (Co-1Br), and [Co(LNO2)(acac)] (Co-1NO2)} were synthesized using new-generation N/O donors, maleonitrile-tethered, tetradentate heteroscorpionate half-reduced Schiff base ligands, 2-((E)-2-hydroxybenzylideneamino)-3-(pyridin-2-ylmethylamino)maleonitrile (H2LH), 2-((E)-(5-bromo-2-hydroxybenzylidene)amino)-3-((pyridin-2-ylmethyl)amino)maleonitrile (H2LBr), and 2-((E)-2-hydroxy-5-nitrobenzylideneamino)-3-(pyridin-2-ylmethylamino)maleonitrile (H2LNO2). All the compounds were well characterized spectroscopically and structurally. The non-covalent interactions present in the lattice of Co-complexes were studied in detail to explain the molecular architecture using the Hirshfeld surface (HS) analysis. The catalytic activity of CO2 fixation towards epoxides under mild and solvent-free conditions was demonstrated. The synthesized complexes are catalysts that are well-active towards the CO2 activation under ambient conditions, whereas most of the reported catalysts require harsh conditions.

Insight into the conformational selectivity of cobalt(iii) complexes with a tetradentate salen-type Schiff base ligand and their biorelevant catalysis: a combined experimental and theoretical study

A series of mononuclear CoIII complexes showing conformational selectivity (stepped vs. umbrella) and biomimetic catalytic activities are reported.

THE FIRST STRUCTURAL CHARACTERIZATION OF A NI(NCS)64– BRIDGED HOMOMETALLIC NI(II) CHAIN DERIVED FROM A N3O DONOR SCHIFF BASE LIGAND

Thiocyanate bridged homometallic Ni(II) chains have potential applications in areas such as molecular magnetism and spintronics due to their tunable magnetic properties. The magnetic properties of these chains are of particular interest and can lead to intriguing magnetic behaviors, such as antiferromagnetic or ferromagnetic interactions. In this context, we have successfully synthesized a Ni(NCS)64– bridge Ni(II) chain complex [Ni2(H2L)2(m1,3-NCS)2(NCS)4]n∙2nCH3CN (1), derived from a tetradentate N3O donor Schiff base ligand (HL). It has been thoroughly characterized by the help of elemental analysis and IR spectroscopy. Single crystal X-ray crystallography has confirmed the geometry of the chain complexes. Both Ni1 and Ni2 centers exhibit hexa-coordination with slightly distorted octahedral geometries, and their coordination environments differ significantly (NiN2O2S2 for Ni1 and NiN6 for Ni2). Within the solid-state structure of the complex, a noteworthy two-dimensional network of hydrogen bonding is observed. The present complex showing a unique example in the realm of single thiocyanato-bridged Ni(II) chains.

Unusual Ni⋯Ni interaction in Ni(ii) complexes as potential inhibitors for the development of new anti-SARS-CoV-2 Omicron drugs.

Two nickel(ii) coordination complexes [Ni(L)]2(1) and [Ni(L)]n(2) of a tetradentate Schiff base ligand (H2L) derived from 2-hydroxy-1-naphthaldehyde with ethylenediamine were synthesized, designed, and characterized via spectroscopic and single crystal XRD analyses. Both nickel(ii) complexes exhibited unusual Ni⋯Ni interactions and were fully characterized via single-crystal X-ray crystallography. Nickel(ii) complexes [Ni(L)]2(1) and [Ni(L)]n(2) crystallize in monoclinic and triclinic crystal systems with P21/c and P1̄ space groups, respectively, and revealed square planar geometry around each Ni(ii) ion. The structure of both the complexes have established the existence of a new kind of metal system containing nickel(ii)-nickel(ii) interactions with a square planar-like geometry about the nickel(ii) atoms. Both square planar Ni(ii) complexes were often stacked with relatively short Ni⋯Ni distances. The non-bonded Ni-Ni distance (Ni⋯Ni separation) seems to be 3.356 Å and 3.214 Å from the nickel atoms of [Ni(L)]2(1) and [Ni(L)]n(2), respectively. These distances are shorter than the sum of their van der Waals radii (4.80 Å) but longer than the sum of their covalent radii (2.50 Å), indicating that there is a Ni⋯Ni interaction but not a Ni-Ni bond. The discrete molecules are π-stacked and connected via weak intermolecular interactions (C-H⋯O and C-H⋯N). Cyclic voltammetry measurements were obtained for both the complexes, and their pharmacokinetic and chemoinformatics properties were also explored. Detailed structural analysis and non-covalent supramolecular interactions were investigated using single-crystal structure analysis and computational approaches. Both the unique structures show good inhibition performance for the Omicron spike proteins of the SARS CoV-2 virus. To gain insights into potential SARS-CoV-2 Omicron drugs and find inhibitors against the Omicron variants of SARS-CoV-2, we examined the molecular docking of the nickel(ii) complexes [Ni(L)]2(1) and [Ni(L)]n(2) with the SARS-CoV-2 Omicron spike protein (PDB ID: 7WK2 and 7WVO). A strong binding was predicted between Ni(ii) coordination complexes [Ni(L)]2(1) and [Ni(L)]n(2) with the SARS-CoV-2 Omicron variant receptor protein through the negative value of binding affinity. Molecular docking of Nil(ii) complexes [Ni(L)]2(1) and [Ni(L)]n(2) with a DNA duplex (PDB ID: 7D3T) and RNA (PDB ID: 7TDC) binding protein was also studied. Overall, this study suggests that Ni(ii) complexes can be considered as drug candidates against the Omicron variants of SARS-CoV-2.

IMPACT OF METAL SALTS ON COORDINATION CHEMISTRY OF NICKEL(II) WITH A N3O DONOR SCHIFF BASE LIGAND: SYNTHESIS, STRUCTURES AND HERSHFIELD SURFACE ANALYSIS

The key findings and significance of this report is the synthesis and characterization of two mononuclear nickel(II) complexes, [Ni(L)(val)].0.5MeOH (1) and [Ni(HL)2](ClO4)2 (2) derived from a tetradentate Schiff base ligand HL and two different nickel(II) salts. These complexes were thoroughly characterized using techniques such as elemental analysis, IR spectroscopy, single crystal X-ray diffraction, and Hirshfeld surface analysis. The results revealed distinct coordination modes of the ligands in the complexes, leading to different non-covalent interactions and packing arrangements in their crystal structures. Specifically, complex 1 exhibited tetradentate coordination in addition to the bidentate o-vanillinate ligand, while complex 2 featured tridentate coordination with the zwitterionic form of the ligand. Hirshfeld surface analysis provided insights into the relative contributions of various intermolecular interactions, highlighting the significance of hydrogen bonding, tetrel bonding, and other non-covalent interactions in stabilizing the crystal structures. In general, this study contributes to the differences in structural integrity on slide variation in metal salts and the understanding in depth of various non covalent interactions using Hirshfeld surface analysis tool.

Synthesis and characterization of Co (II), Ni (II) and Cu (II) complexes with unsymmetrical tetradentate Schiff base ligand

A novel series of cobalt (II), nickel (II) and copper (II) complexes of unsymmetrical Schiff base ligand 1-(2-hydroxynaphthalideneimino)-2-(5 methoxysalicylidene imino)-4 chlorobenzene-1,2-diamine was synthesised by condensation reaction of 1:1:1 molar ratio of 2-hydroxynaphthalene-1-carbaldehyde, 4-chlorobenzene -1,2-diamine and 5-methoxysalicyidehyde in alcoholic medium. The synthesised ligand and its metal complexes were characterised by elemental analysis, molar conductance measurements, magnetic susceptibility measurements, UV-Vis and infrared spectral data. The molar conductance of synthesised metal complexes in DMSO solution indicates their non-electrolytic nature. The analytical data show the general formula for the complexes to be [M(L)2] where L = Schiff base ligand and M = Co (II), Ni (II) and Cu (II). The spectral data and magnetic moment suggested that Schiff base behaves as a tetradentate ligand, coordinating through azomethine nitrogen and phenolic oxygen atoms to the metal ion. Magnetic susceptibility measurements, UV-Vis and infrared spectral data geometry of metal complexes were proposed to be square planar.

Biological evaluation, DFT, MEP, HOMO-LUMO analysis and ensemble docking studies of Zn(II) complexes of bidentate and tetradentate Schiff base ligands as antileukemia agents

Two Schiff base ligands and some related bidentate and tetradentate Zn(II) complexes were investigated for their biological activity profiles as anticancer agents by resazurin method against two leukemia cell lines. The results clearly evidenced the importance of the tetradentate structure and the presence of the metal ion on the cytotoxicity profile of these complexes. Noteworthy, they also showed an interesting selectivity index (SI; up to 15.1 for the complex [ZnL4(NO3)2] assessed on PBMC cells). The electronic behavior, stable geometries, MEP surfaces, and FMO analysis of the compounds were investigated employing density functional theory (DFT) at B3LYP level with LANL2DZ/6-311G(d,p) basic set. A comparison was made with the computational and experimental structural data of L2 and [ZnL2(NO3)2] compounds. Furthermore, ensemble docking studies were undertaken on a quadruplex-duplex (Q-D) DNA model to shed light on the interactions at molecular level of the complexes with the target. In silico ADME profiling was performed using the SwissADME program, which indicated their promising therapeutic applicability.

Exploring the antimicrobial, antioxidant and cytotoxic activities of organyltellurium (IV) complexes incorporating 2‐hydroxy‐1‐naphthaldehyde schiff base ligand: Synthesis, spectroscopic investigations and theoretical studies

In this study, Schiff base ligand 1,1′‐((propane‐1,3‐diylbis [azaneylylidene]) bis (methaneylylidene))bis (naphthalen‐2‐ol) based Organyltellurium (IV) complexes were synthesized with formulae C32H27ClN2O3Te (5a)\C31H25ClN2O3Te (5b)\C32H27ClN2O3Te (5c)\ C39H34N2O4Te (5d)\ C37H30N2O4Te (5e)\ C39H34N2O4Te (5f) for acquiring a potential therapeutic agent. The synthesized compounds were characterized by ultraviolet–visible (UV–Vis), FT‐IR, 1H‐NMR, 13C‐NMR, mass spectrometry, molar conductance, elemental analysis, powder X‐ray diffraction and EDAX, which states that the tetradentate Schiff base ligand (HNDP) coordinated via oxygen and nitrogen atom with tellurium giving hexa‐coordinated tellurium (IV) complexes. The thermal features of the ligand and complexes were studied using thermal (TGA and DTG) technique. The biochemical behavior of the Schiff base and its complexes was assessed by examining their reactivity against various microbial strains, DPPH free radicals as well as normal and cancer cells. The complex 5c exhibited the highest inhibition activity against bacterial strains while complex 5f showed the strongest inhibition activity against fungal strains. Complexes 5e and 5f displayed the most effective suppression of DPPH free radicals. The results of in vitro cytotoxicity study revealed that complex 5a demonstrated moderate cytotoxic effect on the L929 cell lines. Complex 5c displayed a significant cytotoxic effect on the PC3 cell line. Moreover, complex 5a, 5c and 5e exhibited the best cytotoxic activity against the Saos‐2 cell line. Additionally, the structural forms of synthesized compounds were elucidated by DFT study. Furthermore, pharmacokinetic ADMET properties were estimated for their drug similarity behavior. The results advocate that complexes can be utilized as biological drugs.

Synthesis, characterization and biological activity of a novel N1, N5-bis[2-hydroxyphenyl]-2-methyl-1,5-diaminopentane Schiff base: Effect of methylene spacers on biological activities

A novel ONNO donor tetradentate Schiff base ligand N,N'-bis[2- hydroxyphenyl]-2-methyl-1,5-diaminopentane (1) is synthesized and characterized by using 1H, 13C NMR spectroscopy and mass spectrometry. Biological studies on newly synthesized ligand are carried out and results are compared with the biological activities of known Schiff base ligands: N,N'-bis[{2- hydroxyphenyl }]-1,4-diaminobutane (2) and N,N'-bis[{2- hydroxyphenyl }]-1,3-diaminopropane (3). This comparative study highlights the effect of increasing methylene linkage on the biological activity of these ligands. The anti-microbial activities of all three ligands have been screened against two distinct gram-positive and gram-negative bacteria. In-vitro results of this comparative analysis are also supported by comprehensive molecular docking studies with DNA gyrase subunit B protein of gram-positive bacterium S. aureus and FabH–CoA complex of gram-negative bacterium E. coli. Experimental studies reveal that the spacer group plays a vital role in controlling the biological activities of the ligand. These findings are in good agreement with the theoretical findings. The study demonstrates that the biological activity of ligands is enhanced with increments in the number of spacers. Thus, the newly synthesized ligand (1) with the most extended spacer among the three showed the highest biological activity compared to other two ligands, similar to the popular drug Ciprofloxacin.

Synthesis, characterization, biomolecular interactions, molecular docking, and in vitro and in vivo anticancer activities of novel ruthenium(III) Schiff base complexes

In order to discover new anticancer drugs, novel ruthenium(III) complexes [Ru(L)Cl(H2O)], where L is tetradentate Schiff base bis(acetylacetone)ethylendiimine (acacen, 1), bis(benzoylacetone)ethylendiimine (bzacen, 2), (acetylacetone)(benzoylaceton)ethylendiimine (acacbzacen, 3), bis(acetylacetone)propylendiimine (acacpn, 4), bis(benzoylacetone)propylendiimine (bzacpn, 5) or (acetylacetone)(benzoylaceton)propylendiimine (acacbzacpn, 6), were synthesized. The complexes 1 – 6 were characterized by elemental analysis, molar conductometry, and by various spectroscopic techniques, such as UV–Vis, IR, EPR, and ESI-MS. Based on in vitro DNA/BSA experiments, complexes 2 (bzacen) and 5 (bzacpn) with two aromatic rings showed the highest DNA/BSA-activity, suggesting that the presence of the aromatic ring on the tetradentate Schiff base ligand contributes to increased activity. Moreover, these two compounds showed the highest cytotoxic effects toward human, A549 and murine LLC1 lung cancer cells. These complexes altered the ratio of anti- and pro-apoptotic molecules and induced apoptosis of A549 cells. Further, complexes 2 and 5 reduced the percentage of Mcl1 and Bcl2 expressing LLC1 cells, induced their apoptotic death and exerted an antiproliferative effect against LLC1. Finally, complex 5 reduced the volume of mouse primary heterotopic Lewis lung cancer, while complex 2 reduced the incidence and mean number of metastases per lung. Additionally, molecular docking with DNA revealed that the reduced number of aromatic rings or their absence causes lower intercalative properties of the complexes in order: 2 > 5 > 6 > 3 > 4 > 1. It was observed that conventional hydrogen bonds and hydrophobic interactions contribute to the stabilization of the structures of complex-DNA. A molecular docking study with BSA revealed a predominance of 1 – 6 in binding affinity to the active site III, a third D-shaped hydrophobic pocket within subdomain IB.

Design, synthesis, solid-state and solution structures, non linear optical and computational studies of copper(II) complexes supported by variously substituted enantiomerically pure push-pull tetradentate Schiff base ligands

The synthesis, spectroscopic and structural characterization, optical and electrochemical properties and theoretical studies of a family of four new copper(II) complexes supported by a ferrocene-containing N2O2-tetradentate chiral Schiff base ligand derived from enantiomerically pure (1R,2R)-(−)-1,2-diaminocyclohexane are reported. The push-pull Cu(II) complexes were prepared following a one-pot three-component reaction involving the chiral half-unit (1R,2R)-Fc-C(=O)CHC(CH3)NH-c-C6H10NH2, copper acetate monohydrate and the appropriately 3-R,5-R’-substituted salicylaldehyde derivative in a 1:1:1 ratio (Fc = ferrocenyl; 3: R=H, R’ = Cl; 4: R=H, R’ = Br; 5: R=R’ = F;6: R=R’ = NO2), and isolated in 65–97% yields as brown microcrystalline products. The characterization of the synthesized compounds were investigated through CHN elemental analysis, UV–vis, FT-IR, high-resolution mass spectrometry, and X-ray diffraction analysis in the case of the difluoro substituted complex 5 that was obtained in the form of single crystals. It crystallizes in the orthorhombic non-centrosymmetric space group P212121, with two (R,R)-(−)-chiral carbon atoms in the structure. The four-coordinate Cu(II) metal ion adopts a slightly distorted square planar geometry. Magnetic properties of powdered samples have been investigated (2-300 K) and found consistent with a single isolated copper(II) ion (s = 1/2). Cyclic voltammetry showed that the stronger the electron withdrawing effect of the 3,5-substituents, the more anodically shifted the oxidation potential (E1/2) of the ferrocenyl moiety, following the order: 5-Cl < 5-Br < 3,5-F2 < 3,5-(NO2)2. This trend is similar when considering the values of the second-order polarizabilities β of these compounds as measured using Harmonic Light Scattering (HLS) at 1.9 µm, confirming the increasing electron withdrawing effect evidenced by electrochemical studies as well as the conjugation between the electron donor ferrocenyl moiety and the different halogen or nitro substituents through the square planar copper Schiff base framework. Finally, DFT and TD-DFT calculations allow to rationalize the structure and properties of the complexes.

Solution Spin Crossover Versus Speciation Effects: A Cautionary Tale.

Two acyclic tetradentate Schiff base ligands, HLX-OH (X = H and Br), were synthesised by 2:1 condensation of either 2-pyridinecarboxaldehyde or 5-bromo-2-pyridinecarboxaldehyde and 1,3-diamino-2-propanol and then used to prepare six mononuclear complexes, [FeII(HLX-OH)(NCE)2], with three different NCE co-ligands (E = BH3, Se, and S). The apparent solution spin crossover switching temperature, T1/2, of these 6 complexes, determined by Evans method NMR studies, is tuned by several factors: (a) substituent X present at the 5 position of the pyridine ring of the ligand, (b) E present in the NCE co-ligand, (c) solvent employed (P'), and (d) potentially also by speciation effects. In CD3CN, for the pair of NCE = NCBH3 complexes, when X = H, the complex is practically LS (extrapolated T1/2 ∼624 K), whereas when X = Br, it is far lower (373 K), which implies a higher field strength when X = H than when it is Br. The same trend, X = H results in a higher apparent T1/2 than X = Br, is seen for the other two pairs of complexes, with E = Se (429 > 351 K, ΔT1/2 = 78 K) or S (361 > 342 K, ΔT1/2 = 19 K). For the family of three X = Br complexes, the change of E from BH3 (373 K) to Se (351 K) to S (342 K) leads to an overall ΔT1/2(apparent) = 31 K, whereas the decreases are far more pronounced in the X = H family (BH3 ∼624 > Se 429 > S 361 K). Changing the solvent used from CD3CN to (CD3)2CO and CD3NO2, for [FeII(HLBr-OH)(NCE)2] with either E = BH3 or S, revealed excellent, and very similar, positive linear correlations (R2 = 0.99) of increasing solvent polarity index P' (from 5 to 7) with increasing apparent T1/2 of the complex (E = BH3 gave T1/2 300 < 373 < 451 K , ΔT1/2 = 151 K; E = S gave T1/2 288 < 342 < 427 K, ΔT1/2 = 147 K). Several other solvent parameters were also correlated with the apparent T1/2 of these complexes (R2 = 0.74-0.96). Excellent linear correlations (R2 = 0.99) are also obtained with the coordination ability (aTM) of the three NCE co-ligands with the apparent T1/2 in both families of compounds, [FeII(HLX-OH)(NCE)2] where X = H or Br. The 15N NMR chemical shifts of the nitrogen atom in the three NCE co-ligands (direct measurement) show modest correlations (R2 = 0.74 for LH-OH family and 0.80 for LBr-OH family) with the apparent T1/2 values of the corresponding complexes.

Metal complexes derived from tetradentate Schiff base ligands: Synthesis, spectroscopic analysis, thermogravimetric degradation and antimicrobial activities

In the present study a series of compounds which consist of two novel Schiff base ligands (L1 and L2) and their cupper, nickel and cobalt complexes (L1-Cu, L1-Ni, L1-Co, L2-Cu, L2-Ni, L2-Co) were synthesized under argon atmosphere. 4-aminomethylpyridine and 4-aminoquinoline were used as primary amines for the syntheses of L1 and L2, respectively, 2,2′-[propane-1,3-diylbis(oxymethylene)]dibenzaldehyde was used as carbonyl compound for both L1 and L2. The structures of synthesized compounds determined by FT-IR, ESI-MS and 1HNMR spectroscopic techniques. TGA-DSC technique was used to determine the thermal decomposition of all synthesized compounds. L1, L1-Ni, L1-Co, L2, L2-Co began to decompose at 250 °C, L1-Cu and L2-Cu at 200 °C, L2-Ni at 300 °C. In vitro Antimicrobial activities of ligands and complexes have been evaluated against three Gram-positive, three Gram-negative bacteria and a fungus using the broth microdilution method. The synthesized compounds possessed the activity against all examined microorganisms having the minimum inhibitory concentration (MIC) values between 9.7 and 5000 μg/mL. L2 and L2-Co showed the best antibacterial activity against S. epidermidis and S. aureus with the low MIC value of 9.7 μg/mL.

Synthesis and Characterization of Tetradentate Schiff Base Ligand Containing 3,4-Diamino Benzophenone and Investigation of Complex Formation with Ni (II), Cu (II) and Co (II) metal ions

Compound that is a novel tetradentate Schiff base ligand [(3,4-bis(((E)-4-(diethylamino)-2-hydroxybenzylidene)amino)phenyl)(phenyl) methanone] (1), 4-(diethylamino) It was synthesized by the reaction of (3,4-diaminophenyl)(phenyl)methanone with -2-hydroxybenzaldehyde. Complex reactions with Co(II) (1a), Cu(II) (1b) and Ni(II) (1c) metals were prepared based on the obtained Schiff base ligand. The synthesized Schiff base and its Ni(II), Cu(II) and Co(II) complexes were featured using FT-IR, UV-vis, photoluminescence, mass and 1H and 13C-NMR spectroscopy. The characterization processes show that the tetradentate Schiff base compound coordinates with metal ions, oxygen of the hydroxyl group and nitrogen of the azomethine group.