N2O2 Donor Research Articles

Metal Center-Tuned Photocatalytic Carbon Dioxide Reduction for Frameworks with the Tetraphenylethene-Imidazole Ligand.

As heterogeneous photocatalysts that can effectively transform CO2 to CO, two MOFs with different metal centers, namely, [M(tipe)(H2O)2](ClO4)2·solvent (M = Ni named as Ni-MOF and M = Co referred to as Co-MOF), were synthesized by reactions of 1,1,2,2-tetrakis(4-(imidazole-1-yl)phenyl)ethene (tipe) with the corresponding metal perchlorate. Both Ni-MOF and Co-MOF have 3D structures, in which the metal centers have the same coordination environment with the N4O2 donor set. Driven by visible light, the CO production catalyzed by Co-MOF is 6734.1 μmol g-1 with 45.3% selectivity, and in contrast, Ni-MOF has 4601.3 μmol g-1 CO production with 97.6% selectivity in 5 h. Through photoelectrochemical characterization, DFT calculations, and in situ FT-IR measurements, the photocatalytic CO2 reduction process catalyzed by Ni-MOF and Co-MOF was investigated. The results show that the metal center of the MOF is crucial for photocatalytic CO2 reduction. This work offers an innovative approach for controlling the performance of photocatalytic CO2 reduction through tuning the metal centers of architectures.

Spectroscopic, anti-cancer, anti-bacterial and theoretical studies of new bivalent Schiff base complexes derived from 4-bromo-2,6-dichloroaniline

In this paper, four new mono-nuclear Ni(II), Pd(II), Pt(II) and Zn(II) complexes were prepared by using a bi-dentate Schiff base ligand, (E)-2-(((4-bromo-2,6-dichlorophenyl)imino)methyl)-5-chlorophenol (BrcOH), with bivalent ions in a methanol and distil water mixture as solvent in presence of NaOH as base. The structures of the prepared compounds were characterized by spectroscopic techniques (IR and 1H NMR), CHN analysis, and molar conductivity. The M(II) (Ni, Pd and Pt) ions are four-coordinated by a bi-dentate N2O2 donor ligand, forming square planar geometry, whereas the Zn(II) is coordinated as a tetrahedral geometry. The newly synthesized compounds, which include the Schiff base ligand and its complexes, underwent antibacterial screening against E. coli and S. aureus. The results demonstrated a remarkable and noteworthy biological activity of these compounds against these pathogenic bacterial strains. Different binding energies showed good correlation, with Pd showing the strongest binding. Small energy differences indicated high reactivity, with Ni and Pd complexes being the most reactive. Electrophilicity index exhibited electron-accepting properties, with Zn showing the highest reactivity. The dipole moments showed polarity and charge separation, with Pt having the highest polarity. We evaluated the pharmacokinetic properties (ADME) of a ligand and its metal complexes using the Swiss ADME website. The results of the in-silico prediction of physicochemical properties revealed that ten compounds in total adhered to Lipinski's rule.

Acid Mediated In‐Situ Catalytic Cleavage/Making of C=N Bonds in Bis‐Hydrazone Uranyl Complexes: Exploration of Photophysical, Electrochemical, Dye Sorption Properties and DFT Studies

AbstractTwo new uranium complexes [UO2L2(H2O)] (where L2=diacetyl bis‐isonicotinoyl hydrazone) complex 1, and [UO2(L1)2] (where L1=diacetylmonoxime isonicotinoylhydrazone) complex 2, have been synthesized by precisely adjusting the pH values of the reaction system. Complex 1 was formed in an acidic ethanolic solution (pH=3) through an in‐situ acid catalytic reaction of diacetylmonoxime isonicotinoylhydrazone and UO2(NO3)2.6H2O, while complex 2 was acquired in a neutral medium (pH=7) through self‐assembly of two ligands and one uranium (VI) metal centre. Both complexes were thoroughly characterized by elemental analysis, UV‐Visible spectroscopy, IR spectroscopy, NMR, TGA, cyclic voltammetry, and powder X‐ray diffraction. The studies indicate that the bis‐hydrazone in complex 1 is a dianionic tetradentate N2O2 donor, whereas in complex 2 it is a monoanionic tridendate N2O donor. The formation of complex 1 was further confirmed by a single‐crystal X‐ray diffraction study, which revealed the role of a water molecule in forming a pentagonal bipyramidal geometry of [UO2L2(H2O)]. Photophysical studies revealed that complexes 1 and 2 exhibited low band gap values of 2.07 and 2.12 eV, respectively, indicating their semiconducting nature. From the CV measurements, the higher negative potentials of the complexes 1 & 2 {1, −0.6 V and 2, −0.5 V vs. ferrocenium/ferrocene (Fc+/Fc)} in DMSO are assigned to the presence of {UO2}2+/{UO2}+ couple signifying their redox active nature. Dye adsorption studies show that both the complexes were able to remove 90 % of Methylene blue (MB) and Rhodamine B (RhB) from the solutions with the concentration of 10−5 M. The structural insights and electronic properties of Ligand HL1 and complex 1 were further explored by density functional theory (DFT) calculations.

An overview on copper based heterometallic complexes in combination with d10 metal ions derived from N2O2 donor di-Schiff base ligands

A good number of heterometallic complexes based on various Cu(II) bound “metalloligands” of N2O2 donor di-Schiff bases and some of their reduced counterpart along with group 12 metal ions have been synthesized and characterized by different research groups in the literature. This review focuses on an overview of the synthetic strategies, X-ray crystallographic structures and a few important properties of these complexes. These have been discussed in three major sub-classes: Cu(II)-Zn(II), Cu(II)-Cd(II) and Cu(II)-Hg(II) heterometallic complexes. Judicious combinations of carbonyls and di-amines in an easy and effective manner gives 14 selected di-Schiff base ligands (symmetrical and unsymmetrical) with particular shape, geometry and denticity that direct the synthesis of these metal complexes totally or preferentially towards di-, tri- or poly-nuclear entities. Moreover, owing to their ability to assemble three metal ions in close proximity, these resulting oxido-bridged flexible coordination clusters adapted to various other ligand functionalities with particular shape and sometimes unusual coordination modes with certain degree of control. Such unique structural aspect of this system is immensely important in inorganic synthesis. The inherent flexibility of the di-oxido bridged trinuclear coordination cluster led to produce isomeric linear and bent structures that usually depend upon various factors e.g. the nature of the Schiff base, anionic co-ligands, temperature, solvent etc. The structural aspects of resulting discrete and polymeric self-assemblies have enriched the coordination library that extended to develop numerous heterometallic systems with significant applications and new scopes

Theoretical and experimental demonstration of mononuclear Ni(II) and dinuclear Ni(III) complexes concerning their catalytic activity, DNA/ protein binding efficacy

The successful use of metal complexes in enzyme catalysis and biomedical applications boosts researchers to develop more and more metal-based compounds to inspect their said applications.In the present work one novel mononuclear Ni(II) [Ni(L1)2] (1) and one di nuclear Ni(III) complexes [Ni(L2)2(N3)2] (2) have been developed by utilizing N2O donor Schiff base ligand HL1 and N2O2 donor Schiff base ligand H2L2 respectively. The single crystal data analysis reveals that in complex 1 two deprotonated ligands coordinate to the Ni(II) forming a distorted octahedral geometry. The asymmetric unit of complex 2 comprises one deprotonated ligand (both the protons of phenolic –OH group were deprotonated), one azide anion, and one Ni(III). Two Ni(III) centers are connected via phenoxide bridging. Followed by the structural analysis the UV spectroscopic study is performed to understand the catecholase-like activity of the developed complexes by using 3,5-di-tertbutyl catechol (3,5-DTBC). The calculated turnover numbers (Kcat) for both complexes disclose the fact that complex2 is more susceptible to this catalytic process than 1. During the catalysis process, the production of Ni(II) in the case of complex2is favorable and this is the main factor to show its higher susceptibilitytowards the catalytic process. The biomedical applicability in terms of anticancer and antibacterial of complexes 1 and 2 is assessed by evaluating their interaction ability with DNA and HSA with the help of several spectroscopic approaches. The remarkably high complex-macromolecules binding constant values, obtained from electronic titration approve the binding efficacy of the target complexes (order ∼ 105). But if a tiny comparison is done then it is seen that complex 2 shows better DNA and HSA binding efficacy. The theoretical approach using molecular docking study fully validates the experimental findings.

Anti-Malarial and Multi-Bioactive Co (II), Cu (II) and Ni (II) Salen Complexes: Synthesis, Characterization and Computational Studies.

Herein, we report the anti-malarial, anti-bacterial and anti-inflammatory activities of the N2O2 donor tetradentate salen type ligand and its CoL, NiL, and CuL metal complexes. The synthesized compounds were characterized by various spectroscopic analytical methods. The in-vitro anti-malarial investigations revealed that the complex CuL exhibited equipotency with quinine drug having IC50 value 0.25 μg/mL. The compound L showed significant inhibition of bacterial spp. viz. E. Coli, P. Aeruginosa, and S. Aureus (MIC=12.5-50 μg/mL), while the compound CoL (MIC=12.5 μg/mL) exhibited potency against gram-positive bacteria. In the in-vitro anti-inflammatory study, the compound CuL displayed moderate activity than other tested compounds. The compound CuL showed the highest anti-malarial docking score with enzyme pLDH at -8.12 Kcal/mol. The DFT study also gives authentication of higher antimalarial activity of CuL due to high dipole moment. None of the potent compounds was found cytotoxic towards vero cell lines.

Cu(II)-Ln(III) (Ln = Gd, Tb and Dy) complexes of an unsymmetrical N2O3 donor ligand: field induced SMM behaviour of Cu(II)-Tb(III) complexes.

Three new hetero-metallic CuII-LnIII complexes [(CuL)Gd(NO3)3(CH3OH)]n (1), [(CuL)Tb(NO3)3(H2O)]·[CuL] (2) and [(CuL)Dy(NO3)3(H2O)]·[CuL] (3) have been synthesized using a mono-nuclear Cu(II) complex, [CuL], of an unsymmetrically di-condensed N2O3 donor Schiff base ligand, N-(3-methoxysalicylidene)-N-(salicylidene)-1,2-ethylenediamine (H2L). Single crystal X-ray crystallography revealed that complex 1 is a nitrate bridged 1D chain of dinuclear Cu(II)-Gd(III) units whereas in 2 and 3, the dinuclear Cu(II)-Ln(III) units are co-crystallized with a [CuL] unit. The Ln(III) centers are nine coordinated with the geometry of a spherical capped square antiprism for Gd and spherical tricapped trigonal prism for Tb and Dy. The geometry of the Cu(II) center is distorted octahedral for complex 1 and distorted square planar for complexes 2 and 3. Temperature-dependent molar magnetic susceptibility measurements in 1-3 revealed the presence of overall ferromagnetic coupling between the Cu(II) and Ln(III) centers. Notably, field induced single-molecule magnet behavior was witnessed in the Tb(III) derivative (2). The ab initio calculations indicated that upon application of an external magnetic field, the tunneling in the ground state of complex 2 gets reduced and thereby field-induced SMM behaviour is observed. Besides, in the case of complex 1, BS-DFT calculations were carried out to gain further insights into the magnetic exchange coupling interactions between the Cu(II) and Gd(III) centers.

Two Zn(II) complexes based on bis(benzimidazole) and different dicarboxylate anions: synthesis, structures, and fluorescent properties

Two new zinc(II) complexes, [Zn2(PBM)2(terephthalate)(formate)2] (1) and {[Zn(PBM)(fumarate)]∙H2O}n (2), were synthesized using 1,3-bis(1H-benzo[d]imidazol-2-yl)propane (PBM) and two different dicarboxylic acids under solvothermal conditions. Complexes 1 and 2 have been characterized by infrared spectroscopy, elemental analysis, and single-crystal X-ray diffraction analysis. The structural analysis showed that 1 was a binuclear structure and then formed a 3D supramolecular network structure through hydrogen bond and π-π conjugation, while 2 was a one-dimensional coordination polymer. In 1 and 2, the zinc ions were four-coordinate with an N2O2 donor set and a slightly distorted tetrahedral geometry. The solid-state fluorescence properties indicate that the fluorescence peaks belong to the π*-π transition of the ligand PBM, which has a significant red shift and enhancement with the order being 1 > 2 > PBM. The stronger fluorescence of the complexes than the ligand is due to the immobilization of the ligand through coordination, which reduces the energy loss of thermal vibration. The π∙∙∙π conjugation in 1 results in a stronger fluorescence of 1 than 2. Therefore, coordination and π∙∙∙π conjugation will affect the fluorescence of complexes.

Regulating effect of the halogen atoms on the cofacial dinuclear Schiff base complexes: Synthesis, spectroscopy, electrochemistry, and DFT calculations

The present study reports the synthesis and characterization of two new halogenated Schiff base copper (II) derivatives, namely [CuII2(3‐Cl‐Salmphen)2] (Cu‐Cl‐Salmphen) and [CuII2(3‐Br‐Salmphen)2] (Cu‐Br‐Salmphen), which were characterized by UV–Vis, FT‐IR, 1H‐NMR, and 13C‐NMR spectroscopy. Single crystal structural analysis revealed that each complex contains two crystallography independent, distorted copper centers, where each Cu center exhibits the same coordination environment with N2O2 donor atoms from two different ligands. To investigate the substitution effect of halogen atoms on the properties of the complexes, the non‐halogenated isomer [CuII2(H‐Salmphen)2] (Cu‐H‐Salmphen) was introduced for comparison. The differences between the halogenated and the non‐halogenated analogues were compared through spectroscopic, electrochemical, DFT, and TD‐DFT theoretical calculations. The optical experimental results indicated that the introduction of halogen atoms decreased the energy gap between the ground and excited states, leading to enhanced optical absorption capabilities of the compounds. Electrochemical tests showed that the halogenated analogues exhibited better electrochemical performance, and with the increase in an atomic number of the halogen atoms, the compounds displayed a gradual increase in cyclic voltammetry peak areas, diffusion coefficients, and conductivities. Theoretical calculations revealed that the introduction of halogen atoms simultaneously expanded the conjugated area of the molecules, decreased the HOMO‐LUMO energy levels of the complexes, and strengthened the intramolecular interactions. Furthermore, the potential mechanism of the tuning effect of halogen atoms on the charge transfer process was proposed.

Synthesis, structure, and mechanism of action of a unique mixed-ligand nickel (II)-complex of tetra-dentate phenol-based ligand with di-aquo co-ligands with significant pro-apoptotic and anti-metastatic effect against malignant human cancer cells

From the discovery of the anticancer activity of “cisplatin”, various type of numerous mononuclear platinum (II) complexes has been evaluated for antitumor activities, though therapeutic use is limited due to side effects and resistance. In this study, A unique mixed ligand mono nuclear octahedral Ni (II) complex [NiL(H2O)2].0·.5H2O (1) [H2L = N,Nʹ-dimethyl-N,Nʹ-bis (2-hydroxy-3,5-di methyl benzyl)-ethylenediamine] with tetra dentate phenol based ligand with N2O2 donor environment along with two labile water molecules was synthesised. The complex (1) is structurally characterized by spectroscopic tools including single-crystal X-ray diffractometer. Complex (1) crystallizes in monoclinic space group P21/n with a = 10.4871(17) Å, b = 20.860 (4) Å and c = 20.955(4) Å. The UV – visible spectra show two peaks around 507 nm and 367 nm due to spin-allowed 1A1g → 1A2g and 1A1g → 1B1g transitions respectively as expected for a square planar d8 system. Mixed ligand octahedral nickel (II) complex with facially coordinating tetra dentate phenol-based ligand (H2L) is in association with two water molecule as ancillary ligand. Two water molecules associated with coordination zone of nickel (II) centre is loosely bound. In this present study, we have evaluated the anti-cancer properties of Complex (1). We found that Complex (1) show potent cancer cell killing activity in case of poorly invasive mice and human cancer cell lines. Complex (1) trigger apoptosis chiefly via p53 dependent pathway. Complex (1) also inhibits cancer cell migration and epithelial to mesenchymal transition in case of metastatic breast cancer cells suggesting potent anti-cancer properties of complex (1).

An insight into the non-covalent Cl•••Cl interaction in the solid state structure of carboxylate bridged trinuclear mixed valence cobalt(III/II/III) complexes with tetradentate N2O2 donor reduced Schiff base ligands

Two mixed-valence trinuclear cobalt(III)-cobalt(II)-cobalt(III) complexes, [CoII{(μ-L1)(μ-OOCC6H5NO2)CoIII(N3)}2] (1) and [CoII{(μ-L2)(μ-OOCC6H4NO2CH3)CoIII(N3}2] (2) have been synthesized using two tetradentate N2O2 donor 'reduced Schiff base' ligands, H2L1 {2,2-dimethyl-1,3-propanediyl)bis(iminomethylene)bis(4-chlorophenol}, and H2L2{2-hydroxy-1,3-propanediyl)bis(iminomethylene)bis(4-chlorophenol}, and 3-nitrobenzoic benzoic acid or 4-methyl 3-nitrobenzoic benzoic acid as anionic co-ligands. The complexes have been characterized by spectroscopic measurements and their solid state structures have been determined by single crystal X-ray diffraction analysis. The trinuclear cobalt(III)-cobalt(II)-cobalt(III) skeleton of both the complexes are linear and centrosymmetric. Both the central cobalt(II) and terminal cobalt(III) of both the complexes are hexa-coordinated. DFT calculations have been used to analysed some supramolecular assemblies of the complex that have been observed in the solid state, specifically the Cl···Cl interactions that result in the creation of a stable 2D supramolecular assembly in the solid state. QTAIM and NCI Plot computational tools have been used to characterize the interactions. Thermo-gravimetric (TG) analysis was used to examine the thermal behaviour of both complexes. The redox behaviors of both the complexes were studied by using Cyclic Voltammetry (CV).

Syntheses, characterizations and crystal structures of two Ni(II) complexes [Ni2(neoc)4(H2O)(CO3)](NO3)2·3H2O and [Ni(bapa)2](NO3)2·H2O and magnetic properties of the carbonato complex

By the reaction of nickel(II) nitrate hexahydrate with 2,9-dimethyl-1,10-phenanthroline (neoc) and bis(3-aminopropyl)amine (bapa) two novel complexes were isolated, namely [Ni2(neoc)4(H2O)(CO3)](NO3)2·3H2O (1) and [Ni(bapa)2](NO3)2·H2O (2). Both structures are ionic and comprise hexacoordinated Ni(II) central atoms. Complex 1 is built up of dinuclear [Ni2(neoc)4(H2O)(CO3)]2+ complex cation, nitrate anions and water solvate molecules. The dinuclear complex cation is centrosymmetric and the two Ni(II) atoms are linked by a μ3-bridging-chelating carbonato ligand which, due to the presence of an inversion centre, exhibits two orientations with equal probability. The coordination sphere of Ni(II) atom is heteroleptic with an N4O2 donor set formed by two chelating neoc ligands and two O-donor atoms from bridging carbonato and aqua ligands. The carbonato ligand was formed by transformation of absorbed carbon dioxide from air (single crystals) or from dry ice (bulk sample). The crystal structure of 2 is formed by [Ni(bapa)2]2+ complex cation, nitrate anions and water solvate molecule. The coordination sphere of Ni(II) atom in 2 is homoleptic with N6 donor set. Both bapa ligands act as double chelating 3 N-donor ligands and are coordinated in mer-fashion. The study of the magnetic response of 1 in the temperature range 1.8–300 K revealed that the system can be considered as a system of antiferromagnetic S = 1 spin dimers with exchange interaction J/hc = -13.86 cm−1 (J/kB = -19.96 K) and axial single-ion anisotropy D/hc = -4.94 cm−1 (D/kB = -7.12 K). The experimental magnetic results were corroborated by ab initio and DFT calculations.

Designed synthesis and DFT study of R22(8) motifs in the solid state structures of trinuclear cobalt complexes of N2O2 donor Schiff bases using dicarboxylic acids as bridging co-ligands

Three trinuclear, linear, centrosymmetric, Co3 complexes, [Co{(μ-L1)(μ-Hsuc)Co(DMF)}2](ClO4)2 (1), [Co{(μ-L2)(μ-Hsuc)Co(DMF)}2](ClO4)2 (2) and [Co{(μ-L3)(μ- Hmal)Co(DMF)}2](ClO4)2 (3) have been synthesized using tetradentate N2O2 donor 'Schiff base' ligands, H2L1 {N,N'-bis(salicylidene)-1,3-diaminopropane}, H2L2{N,N'-bis(salicylidene)-2,2-dimethyl-1,3-diaminopropane}, H2L3 {N,N'-bis(5-chlorosalicylidene)-2,2-dimethyl-1,3-diaminopropane} and succinic acid (H2suc) or malonic acid (H2mal) as anionic co-ligands. The complexes have been characterized by spectroscopic measurements and their solid state structures have been determined by single crystal X-ray diffraction analysis. Some supra-molecular assemblies observed in the solid state of the complexes have been analysed using DFT calculations, in particular hydrogen bonding interactions. QTAIM computational tool has been used to characterize the interactions. Taking into consideration that each trinuclear complex is dicationic, the dimerization energy cannot be estimated using the supramolecular approach. Consequently, we have used the Lagrangian kinetic energy density (Gr) measured at the bond CPs that characterize the H-bonds to estimate the strength of the R22(8) motifs free from the pure Coulombic repulsion between the cations.

Formation of H-bonding networks in the solid state structure of a trinuclear cobalt(iii/ii/iii) complex with N2O2 donor Schiff base ligand and glutaric acid as bridging co-ligand: synthesis, structure and DFT study.

A trinuclear linear mixed-valence centrosymmetric cobalt(iii)-cobalt(ii)-cobalt(iii) complex, [CoII{(μ-L)(μ-Hglu)CoIII(OH2)}2](ClO4)2·6H2O has been synthesized during tetradentate N2O2 donor 'Schiff base' ligand, H2L {N,N'-bis(salicylidene)-1,3-diaminopropane} and glutaric acid (H2glu) as anionic co-ligand. The complex has been characterized by spectroscopic measurements and its solid state structure has been determined by single crystal X-ray diffraction analysis. The supra-molecular assembly formed by the hydrogen bonding interactions in the solid state of the complex has been analysed using DFT calculations.

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.

Application of a distinctly bent, trinuclear, end-to-end azide bridged, mixed valence cobalt(iii/ii/iii) complex in the fabrication of photosensitive Schottky barrier diodes.

A mixed-valence trinuclear cobalt(iii)-cobalt(ii)-cobalt(iii) complex, [(μ-1,3-N3)Co3L(N3)3]·MeOH has been synthesized using a tetradentate N2O2 donor 'reduced Schiff base' ligand, H2L {1,3-bis(2-hydroxybenzylamino)2,2-dimethylpropane} and azide as anionic co-ligand. The complex has been characterised by elemental analysis, IR, UV-vis spectroscopy and single-crystal X-ray diffraction studies etc. The cobalt(iii)-cobalt(ii)-cobalt(iii) skeleton in the complex is non-linear and non-centrosymmetric. The redox behavior of the complex was studied by using Cyclic Voltammetry (CV). The complex is found to be a semiconductor material as confirmed by determining the band gap of this complex by experimental as well as theoretical studies. The band gap in the solid state has been determined experimentally. The conductivity of the synthesized complex based device improves considerably in illumination conditions from the non-illuminated conditions. The complex has also been used to fabricate Schottky barrier diodes.

Synthesis, Crystal Structures, Photophysical Properties and Antibacterial Activities of Copper(II) Complex Derived from 4-Chloro-2-{[(2,6-dimethylphenyl)imino]methyl}phenol

A new asymmetrical Schiff base ligand, (E)-4-chloro-2-{[(2,6-dimethylphenyl)amino] methyl}phenol(HL), and its mononuclear Cu(Ⅱ) complex have been synthesized. The molecular structures and spectroscopic properties of the ligand and its complex were experimentally characterized by single crystal X-ray diffraction, elemental analysis, FT-IR, NMR and UV-Vis spectroscopic techniques. The analysis confirmed that the Cu atom in complex is generally four-coordinated by one imino N and one phenolic O atoms of a Schiff-base ligand adopting a trans-configuration of N2O2 donor atoms around the metal ion, forming a tetrahedral geometry. Density functional calculation is being carried out on both HL and copper(Ⅱ) complex to investigate changes in structural parameters, energies of the HOMO and LUMO. The results demonstrated that the HOMO and LUMO were effectively separated with the benzene ring of 2,6-dimethylbenzenamine as a donor unit and the benzene ring of 5-chlorosalicylaldehyde as an acceptor unit. The effective HOMO-LUMO separation helps to induce intramolecular charge transfer from the HOMO to the LUMO. The HOMO-LUMO energy gap become smaller when the Schiff base ligand coordinated with Cu(II) ion, most likely due to the interaction of the d-orbitals of copper(Ⅱ) with the HOMO and/or LUMO of the ligand. These theoretical calculations supported the experimentally observed results.The biological assay revealed that both Schiff base and the complex have different antimicrobial activity. The complex has the MIC value of 0.0781 mmol·L-1 against Escherichia coli.

Shift of the reduction potential of nickel(II) Schiff base complexes in the presence of redox innocent metal ions.

With the objective of gaining insight into the modulation of the reduction potential of the Ni(II/I) couple, we have synthesized two mononuclear nickel(II) complexes, NiLen (H2Len = N,N'-bis(3-methoxysalicylidene)-1,2-diamino-2-methylpropane) and NiLpn (H2Lpn = N,N'-bis(3-methoxysalicylidene)-1,3-diamino-2,2-dimethylpropane) of two N2O4 donor ligands and recorded their cyclic voltammograms. Both the nickel complexes show reversible reduction processes for the Ni(II/I) couple in acetonitrile solution but the reduction potential of NiLpn (E1/2 = -1.883 V) is 188 mV more positive than that of NiLen (E1/2 = -2.071 V). In the presence of redox inactive metal ions (Li+, Na+, K+, Mg2+, Ca2+ and Ba2+), the reduction potentials are shifted by 49-331 mV and 99-435 mV towards positive values compared to NiLen and NiLpn, respectively. The shift increases with the decrease of the pKa of the respective aqua-complexes of the metal ion but is poorly co-linear; however, better linearity is found when the shift of the mono- and bi-positive metal ion aqua complexes is plotted separately. Spectrophotometric titrations of these two nickel complexes with the guest metal ions in acetonitrile showed a well-anchored isosbestic point in all cases, confirming the adduct formation of NiLen and NiLpn with the metal ions. Structural analysis of single crystals, [(NiLen)Li(H2O)2]·ClO4 (1), [(NiLpn)Li(H2O)]·ClO4 (2), [(NiLpn)2Na]·BF4 (3) and [(NiLpn)2Ba(H2O)(ClO4)]·ClO4 (4), also corroborates the heterometallic adduct formation. The orbital energies of the optimised heterometallic adducts from which electron transfers originated were calculated in order to explain the observed reduction process. A strong linear connection between the calculated orbital energies and the experimental E1/2 values was observed. According to MEP and 2D vector field plots, the largest shift for divalent metal ions is most likely caused by the local electric field that they impose in addition to Lewis acidity.

Synthesis, Characterization, and Computational Studies on Gallium(III) and Iron(III) Complexes with a Pentadentate Macrocyclic bis-Phosphinate Chelator and Their Investigation As Molecular Scaffolds for 18F Binding.

With the aim of obtaining improved molecular scaffolds for 18F binding to use in PET imaging, gallium(III) and iron(III) complexes with a macrocyclic bis-phosphinate chelator have been synthesized and their properties, including their fluoride binding ability, investigated. Reaction of Bn-tacn (1-benzyl-1,4,7-triazacyclononane) with paraformaldehyde and PhP(OR)2 (R = Me or Et) in refluxing THF, followed by acid hydrolysis, yields the macrocyclic bis(phosphinic acid) derivative, H2(Bn-NODP) (1-benzyl-4,7-phenylphosphinic acid-1,4,7-triazacyclononane), which is isolated as its protonated form, H2(Bn-NODP)·2HCl·4H2O, at low pH (HClaq), its disodium salt, Na2(Bn-NODP)·5H2O at pH 12 (NaOHaq), or the neutral H2(Bn-NODP) under mildly basic conditions (Et3N). A crystal structure of H2(Bn-NODP)·2HCl·H2O confirmed the ligand's identity. The mononuclear [GaCl(Bn-NODP)] complex was prepared by treatment of either the HCl or sodium salt with Ga(NO3)3·9H2O or GaCl3, while treatment of H2(Bn-NODP)·2HCl·4H2O with FeCl3 in aqueous HCl gives [FeCl(Bn-NODP)]. The addition of 1 mol. equiv of aqueous KF to these chloro complexes readily forms the [MF(Bn-NODP)] analogues. Spectroscopic analysis on these complexes confirms pentadentate coordination of the doubly deprotonated (bis-phosphinate) macrocycle via its N3O2 donor set, with the halide ligand completing a distorted octahedral geometry; this is further confirmed through a crystal structure analysis on [GaF(Bn-NODP)]·4H2O. The complex adopts the geometric isomer in which the phosphinate arms are coordinated unsymmetrically (isomer 1) and with the stereochemistry of the three N atoms of the tacn ring in the RRS configuration, denoted (N)RRS, and the phosphinate groups in the RR stereochemistry, denoted (P)RR, (isomer 1/RR), together with its (N)SSR (P)SS enantiomer. The greater thermodynamic stability of isomer 1/RR over the other possible isomers is also indicated by density functional theory (DFT) calculations. Radiofluorination experiments on the [MCl(Bn-NODP)] complexes in partially aqueous MeCN/NaOAcaq (Ga) or EtOH (Ga or Fe; i.e. without buffer) with 18F- target water at 80 °C/10 min lead to high radiochemical incorporation (radiochemical yields 60-80% at 1 mg/mL, or ∼1.5 μM, concentration of the precursor). While the [Fe18F(n-NODP)] is unstable (loss of 18F-) in both H2O/EtOH and PBS/EtOH (PBS = phosphate buffered saline), the [Ga18F(Bn-NODP)] radioproduct shows excellent stability, RCP = 99% at t = 4 h (RCP = radiochemical purity) when formulated in 90%:10% H2O/EtOH and ca. 95% RCP over 4 h when formulated in 90%:10% PBS/EtOH. This indicates that the new "GaIII(Bn-NODP)" moiety is a considerably superior fluoride binding scaffold than the previously reported [Ga18F(Bn-NODA)] (Bn-NODA = 1-benzyl-4,7-dicarboxylate-1,4,7-triazacyclononane), which undergoes rapid and complete hydrolysis in PBS/EtOH (refer to Chem. Eur. J. 2015, 21, 4688-4694).

Hydrolytically Stable TiIV-Hydrazone-Based Metallodrugs: Protein Interaction and Anticancer Potential.

In this work, three titanium(IV) [TiIV(L1-3)2] (1-3) complexes have been reported using three different tridentate dibasic ONO donor hydrazone ligands, pyridine-4-carboxylic acid (3-ethoxy-2-hydroxybenzylidene)-hydrazide (H2L1), furan-2-carboxylic acid (3-ethoxy-2-hydroxybenzylidene)-hydrazide (H2L2), and thiophene-2-carboxylic acid (3-ethoxy-2-hydroxybenzylidene)-hydrazide (H2L3) tethered with heterocyclic moieties. Elemental analysis, FT-IR, UV-vis, NMR, HR-ESI-MS, and single-crystal X-ray analysis have been used to characterize H2L1-3 and 1-3. In solid structures of 1-3, two ligand molecules with N2O4 donor sets give distorted octahedral geometries to the metal center. The aqueous stability of 1-3 was investigated and well correlated to their perceived pharmacological results. During the investigation, all three complexes were found to be hydrolytically stable in a 90% DMSO-d6/10% D2O (v/v) medium up to 48 h. Furthermore, the interaction of 1-3 with bovine serum albumin (BSA) was tested using fluorescence and absorption techniques. The complexes showed static quenching with a biomolecular quenching constant of Kq ∼ 1013 proposing a high affinity of complexes for BSA. Finally, the anticancer potential of 1-3 was tested against HeLa, A549, and NIH-3T3 cell lines. Among all, 1 with an IC50 value of 11.6 ± 1.1 μM against HeLa cells was found to be the most cytotoxic in the series. Furthermore, it has been found that the compounds induce an apoptotic mode of cell death, which is confirmed by the live cell confocal microscopy and flow cytometry techniques.