Nitrogen Donor Atoms Research Articles

The Fluorescent Properties and Electronic Structure of Nd(111) Complexes with Carboxylic Acids

Mixed-ligand neodymium(III) complexes with carboxylic acids and nitrogen- and phosphorus-containing neutral ligands, which luminesce in the near-IR region, are studied by luminescence and X-ray photoelectron spectroscopies. It is found that coordination of neutral ligands through the nitrogen donor atom leads to an increase in the electron density at the neodymium(III) ion.

Antibacterial Screening of Nitrogen and Sulphur Donor Atom Containing Methylcarbamatethiosemicarbazone and Its Mn(II) and Co(II) Complexes: Synthesis, Spectroscopic Approach, Molecular Modeling

A series of Mn(II) and Co(II) complexes were obtained after the condensation of ligand methylcarbamatethiosemicarbazone (L) and corresponding metal salt. The ratio of metal salt to nitrogen and sulphur donor atom containing ligand was 1:2. The conventional condensation reaction was employed to synthesize the multi-donor ligand by refluxing methylcarbamate and thiosemicarbazide in 1:1 ratio. The mode of bonding and geometry of the synthesized complexes were confirmed by elemental analysis, magnetic susceptibility, molar conductance, IR, 1H-NMR, mass, electronic spectra, EPR and molecular modeling. The general composition ML2X2 is assigned to transition metal complexes, where M = Mn(II) and Co(II), L = methylcarbamatethiosemicarbazone and X = Cl−, CH3COO−. The non-electrolytic nature of metal complexes was confirmed by molar conductance. The spectral studies suggested six-coordinated geometry for the synthesized complexes. Molecular modeling of ligand and complexes was also done by using Gaussian. The bacterial activities of all the synthesized compounds were also evaluated against E. coli and S. aureus. Based on antimicrobial results, it was concluded that metal complexes exhibited higher inhibition potential than free Schiff’s base ligand.

Synthesis and Antibacterial Activity of Isatin Schiff Base Derivative with 3-Aminoacetophenone and its Ni(II), Co(II) Transition Metals Complexes

The (E)-3-(3-acetylphenylimino) indolin-2-one (Bidentate) ligand type [HL], has been prepared from Isatin and 3-aminoacetophenone in the presence of KOH. In general, the ligand contains oxygen (O) and nitrogen (N) donor atoms. The reaction of Isatin and 3-aminoacetophenon was carried out in ethanol by condensation reaction at 80°C with reflux for 4 h, to form [HL] ligand type. This ligand has been used to prepare NiII and CoII complexes in the ratio of 1:1 metal-ligand. All compounds have been characterized by spectroscopic methods (Fourier transform infrared and ultravioletvisible), C.H.N, thin-layer chromatography, mass spectrum, X-ray diffraction, magnetic moment, conductivity measurements and milting point, the synthesized ligand and its metal complexes have been tested for their antibacterial activity against Staphylococcus aureus and Bacillus subtilis using agar disc diffusion method. The ligand and its complexes showed significant activities against S. aureus and B. subtilis. Our study revealed the formation of four coordinate square planar complexes around NiII and CoII metal ions.

Synthesis and Characterization of Tetranuclear Metal Complexes with an Octadentate Azodye Ligand

An octadentate azodye ligand containing phenolic/ketonic oxygen and azo nitrogen donor atoms when complexed with divalent metal ions forms tetranuclear complexes of composition [M4LCl4(H2O)12] and [ $$ M_{4}^{/} $$ LCl4(H2O)4] where, M = CoII,CuII, NiII, MnII and M/ = Zn II,, CdII and LH4 = 4,4/-bis(2,4/-dihydroxy-5/-acylphenylazo)diphenylsulphone (BDHAPADPS). The metal complexes were characterised by analytical, magnetic moment, conductance, I.R., electronic spectra, thermal, ESI–MS, ESR, XRD, SEM and EDX. DFT calculations of the ligand and metal complexes have been made by GAUSSIAN 03 rev. A.01 programme package. The antibacterial study of the ligand and the complexes has been made using Gram positive and Gram negative bacteria.

Synthesis and physicochemical studies of cobalt(II), nickel(II) and copper(II) complexes with various Schiff bases containing oxygen and nitrogen donor atoms

Synthesis and physicochemical studies of cobalt(II), nickel(II) and copper(II) complexes with various Schiff bases containing oxygen and nitrogen donor atoms

Synthesis, Characterization and Thermal Study of Some Transition Metal Complexes Derived from Quinoxaline-2,3-Dione

The present paper describes the synthesis and structural studies of new transition metal complexes of cobalt(II), nickel(II), copper(II) and cadmium(II) with two bi dentate ligands derived from quinoxaline-2,3-dione. The two ligands were fully identified by elemental analyses, FT-IR, NMR and UV-Visible spectra. The metal complexes of Co(II), Ni(II), Cu(II) and Cd(II) were isolated in the solid state after reactions of their metal chlorides with the ligands in 2:1 mole ratio. The isolated solid metal complexes were characterized with the help of elemental analyses, NMR, FT-IR and UV-Visible spectra. As well as the thermal stability of the coordinated quinoxaline polymers were tested by TG-DSC analysis and it is found that cleavage of terminal moiety was investigated, the strong coordinated bonds between oxygen donor atoms in L1 while nitrogen donor atoms of quinoxaline ring in the L2 with the metal ions. Furthermore, the thermal stability of cobalt(II), nickel(II), copper(II) and Cd(II) complexes were screened by TG-DSC analysis and the results helped us in the investigation of the proposed structure of the prepared complexes in the formula [M(L)2Cl2].XH2O and [Cd(L)2]Cl2 where L= L1 and L2 ligands derived from quinoxaline-2,3-dione.

Influence of copper(II) ions on the noncovalent interactions between cytidine-5′-diphosphate or cytidine-5′-triphosphate and biogenic amines putrescine or spermidine

Potentiometric and NMR spectroscopic studies of the nucleotide (NucP)/polyamine (PA) system (where NucP = CDP, CTP, PA = putrescine or spermidine) revealed the formation of molecular complexes (NucP)(Hx+y)(PA) (where Hx+y = number of protons; x - from NucP and y - from PA). Their thermodynamic parameters were determined and the modes of their interactions were proposed. The main reaction centers were found to be the protonated amine groups of polyamine (positive centers) and phosphate groups of nucleotide (negative centers). The pH ranges in which the complex occurs correspond to those of amine protonation and -PO3x- group deprotonation, which unambiguously confirms the dipole-dipole type of interaction. In the pH range of total deprotonation of NHx+ groups from the polyamine, the molecular complexes disappear. The equilibrium and spectroscopic studies of the ternary systems Cu(II)/NucP/PA evidenced the formation of Cu(NucP)Hx+y(PA) type coordination compounds and Cu(NucP)⋯(PA)(Hx) type molecular complexes with polyamine in the outer coordination sphere. The main sites of metal ion bonding in the latter species are the phosphate groups of the nucleotide, while in the coordination compounds – besides the phosphate groups – also the donor nitrogen atoms from the polyamines. In this paper we have also quantitatively calculated the effect of metal ions on the formation of the molecular complexes.

Dioxidouranium isothiosemicarbazone coordination compounds: synthesis, characterization, crystal structure, and thermal behavior

Five uranium complexes with UO2L′(solv) formula (L′: prepared by condensation reaction between 2-hydroxyacetophenon S-pentyl isothiosemicarbazone (H2L) and 5-bromosalicylaldehyde (Sal); solv: ethanol (1), 2-propanol (2), 2-butanol (3), ethylene glycol (4), 1,2-propanediol (5)) were synthesized through template reactions between H2L, Sal, and UO2(CH3COO)2∙2H2O for 1 and recrystallization of 1 in appropriate solvents for the other complexes. The compounds are characterized by melting point, elemental analyses, FT-IR, 1H NMR, 13C NMR, TGA, and X-ray crystallography. Molecular structures of the obtained crystals, determined by X-ray diffraction analysis, showed that the complexes have distorted pentagonal bipyramidal geometry. In all complexes, the bianionic tetradentate ligand (N2O2) with phenolic oxygens (O3, O4), thioamidic and azomethine nitrogen donor atoms is coordinated to the metal center in equatorial positions and the solv molecules occupied the fifth equatorial site and finally linear UO2 is located in axial position. The thermal behavior of the complexes was studied with TGA and DTG data and the results revealed three weight loss stages. The Coats–Redfern method is used for all degradation steps to determine kinetic parameters.

New biologically active mixed-ligand Co(II) and Ni(II) complexes of enrofloxacin

New mixed-ligand Co(II) and Ni(II) complexes with enrofloxacin and 1,10-phenanthroline/8-hydroxyquinoline have been synthesized. The metal complexes have been characterized by elemental analyses, molar conductance, FT-IR, solid reflectance, magnetic moment, thermal analyses, X-ray powder diffraction (XRD) and SEM analysis. Conductance measurements indicate that all the complexes are non-electrolytes. Spectral IR data showed that the deprotonated enrofloxacin is bidentately bound to the metal ion through the pyridone oxygen and the carboxylated oxygen; 1,10-phenanthroline acts as neutral bidentate ligand coordinated through two nitrogen donor atoms, and the deprotonated 8-hydroxyquinoline is coordinated through nitrogen and oxygen donor atoms. The geometry of the complexes was elucidated with solid reflectance UV and magnetic moments. Thermal analysis recorded that TG/DTG/DSC experiments revealed the thermal stability of metal complexes and confirmed their compositions suggested by the analytical data. In addition to experimental data, a molecular modelling study has been performed to establish the optimized geometries of metal complexes. The XRD analysis of powders evidences the nanocrystalline nature of all complexes. The results are in agreement with molecular modelling data. SEM images revealed highly agglomerated particles with irregular shape with sizes in the micrometre range. The ligand and their metal complexes were screened for their antimicrobial activity against Escherichia coli 25922, Staphylococcus aureus 25923, Pseudomonas aeruginosa 27853 and Candida albicans 10231. The metal complexes were also investigated for their cytotoxicity using an in vitro assay.

Kinetic Studies of Oxidative Addition Reaction of Arylplatinum(II) Complex Containing 4,4′‐Bipyridine and Calculation of Activation Parameters

ABSTRACTNew complexes of arylplatinum(II) and arylplatinum(IV) containing a bridging ligand, 4,4′‐bipyridine, were synthesized by the reaction of starting material of platinum(II) including para‐tolyl groups,[(p‐MeC6H4)2Pt(SMe2)2], with the 4,4′‐bipyridine ligand in 1:1 molar stoichiometry. In the synthesized complexes, the ligand was bonded to the platinum center through the nitrogen donor atoms. To investigate the kinetic reaction of the platinum(II) complex with iodomethane (CH3‐I) as a reagent, the oxidative addition reaction of this reagent with Pt(II) was performed in dichloromethane and a Pt(IV) complex with the octahedral geometry was formed. The synthesized complexes have been characterized by different spectroscopic methods such as FT‐IR, 1H NMR, UV–vis, and elemental analysis. Moreover, the conductivity measurements showed nonelectrolyte characteristics for these complexes. The obtained data showed that the complexes have 1:1 metal‐to‐ligand molar ratio. Also, the oxidative addition reaction of CH3I with the arylplatinum(II) complex at different temperatures was used for obtaining kinetic parameters such as rate constants, activation energy, entropy, and enthalpy of activation using the Microsoft Excel solver. From the acquired data, an SN2 mechanism was suggested for the oxidative addition reaction.

Antimicrobial, antioxidant and DNA-binding studies of palladium(II) complexes with different chelate ligands containing nitrogen donor atoms

The antimicrobial and antioxidant activities, as well as the DNA-binding of four square-planar Pd(II) complexes, [Pd(terpy)Cl]+ (C1), [Pd(en)Cl2] (C2), [Pd(DMEAImiPr)Cl2] (C3) and [Pd(dach)Cl2] (C4) (terpy = 2,2?:6?,2??- -terpyridine, en = ethylenediamine, dach = trans-1,2-diaminocyclohexane and DMEAImiPr = N2-((1,3-dihydro-1,3-diisopropyl-4,5-dimethyl)-2H-imidazol-2- ylidene)-N1,N1-dimethyl-1,2-ethanediamine are reported. The antimicrobial activities of the Pd(II) complexes with the appropriate ligands were tested using the microdilution method against 18 strains of microorganisms, whereby the minimal inhibitory concentration (MIC) and the minimal microbicidal concentration (MMC) were determined. The antibiofilm activity of [Pd(terpy)Cl]+ and the corresponding ligand were determined on a formed biofilm. The intensity of antimicrobial activity varied depending on the type of microorganism and the tested compound. The C1 complex with the corresponding ligand demonstrated significantly greater overall antimicrobial activity than C2, C3 and C4. The antibacterial activity of the C1 complex was better than its antifungal activity that was overall greater than that of the positive control, fluconazole. The greatest sensitivity for C1 and L1 was with Penicillium italicum (MIC < 0.49 ?g mL-1) among the fungi, and with Proteus mirabilis ATCC 12453 (MIC = 0.98 ?g mL-1) among the tested bacteria. The tested compounds show low and moderate antibiofilm activity. The complexes showed weak antioxidant properties when tested using the DPPH (1,1-diphenyl-2- -picrylhydrazyl) method. The interaction of the metal complexes C1?C4 with calf thymus DNA (CT-DNA) was further examined by absorption (UV?Vis) and emission spectral studies (EthBr displacement studies). Overall, the investigated complexes exhibited good DNA interaction ability.

Synthesis, Spectroscopic, and DFT Studies of Some Platinum-Pyrazine Carboxamide Derivatives

Binary and ternary platinum(II) and platinum(IV) complexes were synthesized using heterocyclic ligands with nitrogen and oxygen donor atoms (2-pyrazinecarboxamide, pyridine, and bipyridine). The complexes were characterized by the analytical and spectroscopic tools such as elemental analysis, mass spectrometry, IR, and 1H NMR spectroscopy. The complexes showed different structural arrangements. The thermogravimetry analysis of some selected complexes were also investigated. Theoretical calculations based on accurate density functional theory (DFT) approximations were established to verify the optimized structures of the pyrazine carboxamide ligand and two complexes. The global chemical reactivity descriptors were estimated from the energy of the HOMO and LUMO orbitals.

Synthesis and characterization of α-diamine palladium complexes and insight into hybridization effects of nitrogen donor atoms on norbornene (co)polymerizations

Hybridization effects of nitrogen donor atoms showed that the α-diamine palladium catalyst more easily produced highly active Pd2+cations for norbornene (co)polymerization.

Tuning Structures and Properties for Developing Novel Chemical Tools toward Distinct Pathogenic Elements in Alzheimer's Disease.

Multiple pathogenic factors [e.g., amyloid-β (Aβ), metal ions, metal-bound Aβ (metal-Aβ), reactive oxygen species (ROS)] are found in the brain of patients with Alzheimer's disease (AD). In order to elucidate the roles of pathological elements in AD, chemical tools able to regulate their activities would be valuable. Due to the complicated link among multiple pathological factors, however, it has been challenging to invent such chemical tools. Herein, we report novel small molecules as chemical tools toward modulation of single or multiple target(s), designed via a rational structure-property-directed strategy. The chemical properties (e.g., oxidation potentials) of our molecules and their coverage of reactivities toward the pathological targets were successfully differentiated through a minor structural variation [i.e., replacement of one nitrogen (N) or sulfur (S) donor atom in the framework]. Among our compounds (1-3), 1 with the lowest oxidation potential is able to noticeably modify the aggregation of both metal-free Aβ and metal-Aβ, as well as scavenge free radicals. Compound 2 with the moderate oxidation potential significantly alters the aggregation of Cu(II)-Aβ42. The hardly oxidizable compound, 3, relative to 1 and 2, indicates no noticeable interactions with all pathogenic factors, including metal-free Aβ, metal-Aβ, and free radicals. Overall, our studies demonstrate that the design of small molecules as chemical tools able to control distinct pathological components could be achieved via fine-tuning of structures and properties.

Steric effects enforce double stereoselective N-coordination in twelve-membered binuclear palladium(II)-complexes containing chiral bridging aminoalkyl-phosphine ligands

The configuration of the ligand's N-substituent was found to determine the stoichiometry and strict stereoselectivity of N-coordination in twelve-membered palladium dimers 2a-b. The novel palladium(II)-complexes 2a-b have been synthesized in the reaction of [Pd(COD)Cl2] and optically pure (S,S)-pentane-2,4-diyl based aminoalkyl-phosphine ligands Ph2PCH(CH3)CH2CH(CH3)NHR 1a-b (R = (R)-α-phenylethyl 1a, R = (R)-α-(1-naphthyl)ethyl 1b) with stereogenic nitrogen atom, and studied by various 1D and 2D NMR techniques in solution and in the case of 2a by single-crystal X-ray diffraction. As an unprecedented case, ligands 1a-b were found to yield exclusively 12-membered cyclic dinuclear Pd(II)-complexes with stereospecific coordination of both of the donor nitrogen atoms. Formation of the 12-membered ring is shown to reduce the steric hindrance of the bulky substituents with respect to the six-membered ring.

An improved and one-pot procedure to the synthesis of symmetric amines by domino reactions of 5-methyl-1,3,4-thiadiazole-2-amine, a new nitrogen atom donor, and alkyl halides

A new one-pot method has been introduced in this work for the synthesis of symmetrical primary, secondary, and tertiary alkyl amines from alkyl halides and 5-methyl-1,3,4-thiadiazole-2-amine as a nitrogen-transfer reagent. In this method, all three types of amines have been successfully prepared after changing the ratio of substrates and base control. In addition to the introduction of a new nitrogen-transfer reagent, other important features of this work include normal atmospheric conditions and excellent yields under mild reaction conditions.

Synthesis, Structures, and Antibacterial Activities of Two Methanol Coordinated Zinc Complexes with Tetradentate Bis-Schiff Bases

Two methanol coordinated zinc(II) complexes, [Zn(L1)(MeOH)] (I) and [Zn(L2)(MeOH)] (II), where L1 and L2 are the dianionic form of N,N'-bis(5-fluorosalicylidene)ethane-1,2-diamine and N,N'-bis(5-fluorosalicylidene)propane-1,2-diamine, respectively, have been synthesized and characterized by physical chemical methods and single crystal X-ray diffraction (CIF files CCDC nos. 950907 (I) and 950908 (II)). Crystallographic data for I: triclinic, P $$\bar 1$$ , a = 8.8765(8), b = 9.6577(9), c = 10.5117(9) A, α = 114.590(2)°, β = 91.648(3)°, γ = 97.114(3)°, V = 809.87(13) A3, Z = 2, R 1 = 0.0307, wR 2 = 0.0698. Crystallographic data for II: orthorhombic, Pca21, a = 22.946(2), b = 7.6942(7), c = 9.6234(8) A, V = 1699.0(2) A3, Z = 4, R 1 = 0.0320, wR 2 = 0.0676. X-ray crystal structural study indicated that the coordination environment around each zinc(II) atom in the complexes is a five-coordinated distorted pyramid in which the apical position is occupied by a methanol oxygen atom, and the basal plane is defined by the nitrogen and oxygen donor atoms of the Schiff base ligand. The antibacterial activities of the complexes were assayed.

Reactivity of Fe and Ru Complexes of Picolyl-Substituted N-Heterocyclic Carbene Ligand: Diverse Coordination Modes and Small Molecule Binding.

Complexes [MClCp*(HL)] (1[Fe]/1[Ru]) (where HL = 1-mesityl-3-(pyridin-2-ylmethyl)imidazol-2-ylidene) were synthesized from the reaction of in situ generated HL ligand and [FeClCp*(TMEDA)] (where TMEDA is N,N,N',N'-tetramethylethylenediamine) or [RuClCp*]4, respectively. The deprotonation of 1[Fe]/1[Ru] with 1 equiv of LiHMDS led to cyclometalation through the o-Me of the mesityl group, forming [MCp*(L-κC,κC',κN)] 2[Fe]/2[Ru]. The coordinatively unsaturated compounds [MCp*(HL)]BPh4 3[Fe]/3[Ru] were prepared from 1[Fe]/1[Ru] and halide scavenger NaBPh4. Complex 3[Ru] showed agostic interactions between the o-Me group of the mesityl moiety and the metal center in solution and the solid state. When the vacant coordination site of 3[Fe]/3[Ru] is occupied by CO, the resulting [MCp*(CO)(HL)]BPh4 4[Fe]/4[Ru] can be deprotonated with 1 equiv of KHMDS at the pyridylic position to afford complexes [MCp*L'(CO)] 5[Fe]/5[Ru], where the L'- ligand chelates to the metal center through the nitrogen donor atom of the dearomatized pyridine ring and the carbene carbon. Complex 2[Fe] reacted rapidly with CO to afford the simple ligand substitution product [FeCp*(L-κC,κC')(CO)] 6[Fe], where the L- acts as a bidentate chelating ligand through the carbene carbon and benzylic carbon. Under the same condition, the reaction of 2[Ru] with CO forms [RuCp*L″(CO)] 7[Ru], where the L″- ligand (an isomer of L- and L'-) chelates to the metal center through the carbene carbon and a pyridyl carbon. Complexes 3[Fe]/3[Ru] reversibly bind dinitrogen to form [MCp*(HL)(N2)]BPh4 8[Fe]/8[Ru]. 3[Ru] reversibly binds dihydrogen to give [MCp*(H2)(HL)]BPh4 9[Ru], while no reaction was observed between 3[Fe] and H2. The reaction of 3[Ru] with dioxygen led to the isolation of a stable side-on O2 complex [RuCp*(HL)(O2)]BPh4 10[Ru], while the reaction of 3[Fe] with dioxygen led to an intractable mixture of products.

Coordinating Ability of the Iminophosphorane Group in ortho‐Carborane Derivatives

The coordinating ability of the nitrogen donor atom of C‐carboranyl iminophosphoranes was studied in different ligand systems. The analysis of organotin derivatives of the unsubstituted iminophosphorane I1 (SnMe3I1 and SnClMe2I1) and the comparison with the non‐carboranyl analog (SnClMe2I3), reveals the reduced donor capacity of the nitrogen atom due to the closo‐carborane group. To promote the coordination of this weak donor atom, new phosphine–iminophosphorane ligands (IP1 and IP2), with an extra –PPh2 group on the other cage carbon atom, were synthesized and structurally characterized. The analysis of the products formed by the reaction of these ligands with the metal precursor cis‐[PdCl2(PhCN)2] reveals that the phosphine group promotes the coordination of the iminophosphorane nitrogen atom, yielding (P, N) chelates. However, this coordination mode activates the closo‐carborane ligands towards deboronation, and the complexes evolve to the nido derivatives in response to the polar solvents. The activation is increased by the presence of extra donor groups, like in the tridentate ligand IP2, with an extra thioether group. The deboronation by coordination of (P, N) bidentate carboranyl ligands has never been reported, although it has been studied for other ligands, especially for chelating carboranyl diphosphines.

Experimental and DFT studies on the selective adsorption of Pb 2+ and Zn 2+ from aqueous solution by nitrogen-functionalized multiwalled carbon nanotubes

Abstract The ligand, 4′-(4-hydroxyphenyl)-2,2′:6′,2″-terpyridine, was bonded to multiwalled carbon nanotubes to afford nitrogen-functionalized carbon nanotubes (MWCNT-ttpy). This material was compared with acid-functionalized multiwalled carbon nanotubes (MWCNT-COOH) for the removal of Pb2+ and Zn2+ from aqueous solution. The comparison was conducted both experimentally and theoretically by means of batch adsorption experiments and density functional theory (DFT) analysis, respectively. The adsorption capacities (qe) of the adsorbents increased with increasing pH, contact time and adsorbent dose. The adsorption of Pb2+ and Zn2+ onto both sorbents was conducted at an optimum pH of 4.5 and 5.5, respectively. For both metal ions, better removal was observed with MWCNT-ttpy than with MWCNT-COOH. In the case of Pb2+, the Langmuir maximum adsorption capacity (qm) increased from 20.60 to 36.23 mg g−1, and for Zn2+, qm increased from 18.51 to 32.60 mg g−1, in going from MWCNT-COOH to MWCNT-ttpy, respectively. DFT analysis supports the experimental results showing a better coordination of Pb2+ to the nitrogen-donor atoms on MWCNT-ttpy than for Zn2+. The pseudo-second order kinetics model fitted both systems well, indicating a bimolecular interaction between the adsorbate cations and sorbents. The adsorption processes were endothermic in nature and spontaneous. DFT studies reveal that the metal-adsorbent interactions proceeded via a coordination/electrostatic mechanism between the nitrogen/oxygen donor atoms contained in the adsorbents and the metal ions. Desorption studies showed high desorption efficiencies, thereby demonstrating the suitability of the adsorbents for reuse. Thus, nitrogen-functionalized carbon nanotubes show promise as a good reusable adsorbent for the removal of Pb2+ and Zn2+ from wastewaters.