X-ray photoelectron spectra and structure of polynuclear nickel complexes

Mono- and binuclear nickel complexes of different stoichiometry have been studied by X-ray photoelectron spectroscopy (XPS). The Ni2p, Ni3p, and N1s X-ray photoelectron spectra have been examined, and the role of a ligand in their formation has been determined. As distinct from a low-spin Ni(II) complex, the Ni2p spectra of high-spin Ni(II) compounds show strong satellite lines. For high-spin Ni(II) complexes, which have unpaired 3d electrons, the Ni2p _1/2-Ni2p _3/2 spin-orbit splitting is larger than that for a low-spin Ni(II) compound. The presence or absence of the satellite structure has made it possible to classify these complexes with regard to their magnetic properties. The difference between the Ni2p _3/2 and N1s binding energies has made it possible to estimate the covalence of the metal-ligand bond. The XPS results are consistent with X-ray crystallography data.     

A Quantum Chemical Study of C<Subscript>60</Subscript>Cl<Subscript>30</Subscript>, C<Subscript>60</Subscript>(OH)<Subscript>30</Subscript> Molecules and Fe@C<Subscript>60</Subscript>(OH)<Subscript>30</Subscript> Endocomplex

(U)PBE0/cc-pVDZ method is used to study the structure of C₆₀Cl₃₀, C₆₀(OH)₃₀ molecules and Fe@C₆₀(OH)₃₀ endocomplex. The triplet state of the endocomplex is shown to be the lowest in energy among its four states corresponding to different spin multiplicities and positions of Fe nucleus within the fullerene cavity. This state is characterized by bonding between the iron atom and one of two benzenoid cycles of the carbon cage, six internuclear Fe–C distances (208 pm), and 1s²2s²2p⁶3s²3p⁶3d^7.24s^0.14p^0.3 electron configuration of iron with spin population of 2.36.     

X-Ray photoelectron spectra of iron trimethylacetate complexes

Bi-, tri-, and hexanuclear iron(II,III) trimethylacetate complexes were studied by X-ray photoelectron spectroscopy. The compounds differed in the number of Fe-O and Fe-N coordination bonds. The Fe 2p, Fe 3p, and N 1s X-ray photoelectron spectra were examined and the role of the ligand in their formation was elucidated. Based on the calculated multiplet splittings, numerous states were discerned in the Fe 2p spectra. This made it possible to reveal a correlation between the magnetic moment and some spectral parameters, such as the relative intensity and energy position of the satellites.     

Synthesis and redox characteristics of iron complexes with triphenylsubstituted corrols in the presence of argon and oxygen

para-Substituted iron meso-triphenylcorrole derivatives [Fe(ms-p-R-Ph)₃Cor] containing electron- donating (R = OMе) and electron-drawing (R = NO₂) groups in phenyl rings are synthesized and characterized by ¹H NMR, electronic absorption spectroscopy, and mass spectrometry. The effect of the nature of functional groups within iron complexes on the redox processes involving these complexes in water–alkaline solutions is analyzed. Electronic transitions in the ligand (E_red/ox = 0.820–0.850 V) and the metal (E_red/ox =–0.005 to–0.190 and–0.790 to–0.870 V for the Fe⁴⁺ ? Fe³⁺ and Fe³⁺ ? Fe²⁺ transitions, respectively) were found in the cyclic voltammograms. Iron in the synthesized complexes I–IV under the conditions under study exists in the +4 oxidation state. The activity of iron complexes in electroreduction of molecular oxygen significantly depends on the nature of a substituent, increases in the series: Fe(ms-p-NO₂Ph)₃Cor (II) < Fe(ms-p-MeOPh)₃Cor (I) < Fe(β-Br)₈(ms-Ph)₃Cor (IV) < Fe(ms-Ph)₃Cor (II) and is caused by the fact that low-energy redox electron transitions occur in the molecules. The electrocatalytic activity of iron corroles is much higher than that of metal porphyrins with a similar structure.     

Two novel dinuclear iron(III) complexes containing <Emphasis Type="Italic">μ</Emphasis>-oxo-di-<Emphasis Type="Italic">μ</Emphasis>-carboxylato motif

Two novel μ-oxo-di-μ-carboxylato-bridged iron(III) complexes of [Fe₂(bpea)₂(PhCO₂)₂(μ-O)] (ClO₄)₂·C₂H₅OH (1) and [Fe₂(bpma)₂(ClCH₂COO)₂(μ-O)](ClO₄)₂· H₂O (2) (bpea = N,N-bis(2-pyridylmethyl)ethylamine, bpma = N,N-bis(2-pyridylmethyl)methylamine), have been synthesized and determined by X-ray diffraction. Complex (1) crystallizes in the Orthorhombic space group P _nma with d(Fe···Fe) of 3.094 Å and average d(Fe–Ob_bridge) of 1.805 Å; Complex (2) crystallizes in the Monoclinic space group C ₂/c, with d(Fe···Fe) of 3.109 Å and average d(Fe–Ob_bridge) of 1.794 Å. The magnetic studies indicate a stronger antiferromagnetic interaction between iron(III) ions through μ-oxo-di-μ-carboxylato-bridge for complex (1), with J = ? 141.6 cm^?1.     

Kinetics and Mechanism of the Formation of (1,5)bis(2-hydroxybenzamido)3- azapentaneiron(III) and its Reactions with Thiocyanate,Azide, Acetate,Sulfur(IV) and Ascorbic Acid in Solution,and the Synthesis and Characterization of (nitrato)bis- (2-hydroxybenzamido)3-azapentaneiron(III). The Role of Phenol–amide–amine Coordination

The complexation of iron(III) with (1,5)bis(2-hydroxybenzamido)3-azapentane (H₂L) under varying [H⁺]_T (0.01–0.1 mol dm^?3) and [Fe^III]_T (3.0 × 10^?4–1.7 × 10^?2, [L]_T=(0.5 - 1.0) × 10^-4 mol dm^?3) (I=0.3 mol dm^?3, 10% v/v, MeOH  + H₂O, 25.0 °C) was reversible and displayed monophasic kinetics; the dominant path involved FeOH²⁺ and H₃L⁺. The mechanism is essentially a dissociative interchange (I_d) and dissociation of the aqua ligand from the encounter complex, [Fe(OH₂)₅OH²⁺, H₃L⁺] is rate-limiting. Equilibrium measurements indicated that the ligand binds iron(III) in a bidentate, tetradentate and pentadentate fashion under varying pH conditions. Iron(III) promoted deprotonation of the phenol moieties, and sec-NH ₂ ⁺ of the dien unit are in tune with this proposition. The octahedral coordination of [Fe(HL/L})(OH₂)]^2+/+ is further supported by the aqua ligand substitution by AcO^?, NCS^?, N ₃ ^- /N₃H, SO ₃ ^2- /HSO ₃ ^- . However, marked pK perturbation of the bound ascorbate in [Fe(L)(HAsc/Asc)]^0/? (ΔpK_{{[Fe(L)(HAsc)] ? HAsc?}}=6) is compelling evidence for chelation of HAsc^?/Asc^2? leading to unusual hepta coordination of iron(III) in the ascorbate complexes. Despite the multidentate nature of the ligand, its iron(III) complexes remain sensitive to reduction by S^IV and ascorbic acid. The complex (nitrato){(1,5)bis(2-hydroxybenzamido)3-azapentane}iron(III) has been synthesised and characterised by elemental analysis, i.r. and u.v.–vis spectral measurements. The room temperature magnetic moment (μ_eff=4.2 BM) conforms to the intermediate spin state of iron(III) (S=3/2) which is further supported by e.s.r. measurements (77 K, g=4.2, 8.1) and the ⁵⁷Fe Mössbauer spectrum (δ=0.41 mm s^?1; ΔE_Q=0.78 mm/s). The cyclic voltametry (MeOH, TEAP as background electrolyte) display only one quasi-reversible peak in the ?0.254 to ?0.4 V range (vs. SCE), the irreversibility being due to the formation of an iron(II) complex which dissociates under the experimental conditions.     

Synthesis,experimental and theoretical characterization,and antimicrobial studies of some Fe(II), Co(II), and Ni(II) complexes of 2-(4,6-dihydroxypyrimidin-2-ylamino)naphthalene-1,4-dione

The work reported the synthesis and characterisation of Fe²⁺, Co²⁺, and Ni²⁺ complexes of 2-(4,6-dihydroxypyrimidin-2-ylamino)naphthalene-1,4-dione (HL). The spectroscopic and elemental analysis results obtained were consistent with the adoption of the formulas, [ML₂] (M = Fe and Co) and [ML₂(H₂O)] (M = Ni) for the metal complexes. Electronic spectra and magnetic moments of the metal complexes corroborated octahedral geometry for Ni(II) complex and tetrahedral geometry for Fe(II) and Co(II) complexes. However, quantum-chemical calculations using density functional theory predicted trigonal bipyramidal geometry for Ni(II) complex and provided corroborative explanations for the structures of the other complexes. Conductance measurements in dimethylsulfoxide indicate that the complexes are non-electrolytes. The antimicrobial potential of the compounds was evaluated against Staphylococcus aureus, Pseudomonas aeruginosa, Escherichia coli, Bacillus cereus, Proteus mirabilis, Klebsiella oxytoca, Aspergillus niger, A. flavus, and Rhizopus stolonifer. The compounds gave moderate to good antimicrobial activity. However, the bacterial and fungal organisms were more susceptible to the cobalt complex and ligand respectively than the other compounds at concentration of 10 mg/mL. The compounds were also assessed for their antioxidant potential using 1, 1-diphenyl-2-picrylhydrazyl (DPPH) radical scavenging assay. The compounds displayed good DPPH radical scavenging activities. The nickel complex exhibited the best DPPH radical scavenging activity compared to the other compounds.     

Synthesis,structural and spectroscopic properties of asymmetric Schiff bases derived from 2,3-diaminopyridine

Two Schiff base derivatives, 4-(2-amino-3-pyridyliminomethyl)phenol (I) and 3-(2-amino-3-pyridyliminomethyl)nitrobenzene (II), were synthesised and characterised by spectroscopy. The structure of I was determined by single crystal X-ray diffraction studies. The asymmetric Schiff base derived from 2,3-diaminopyridine selectively recognise transition and heavy metal cations, and some anion. Ligands I and II form stable complexes with Cu²⁺, Zn²⁺, Pb²⁺, Al³⁺ whereas ligand I also binds F~ ions. The stoichiometry for the host: cation is 1: 1 and 2: 1. The addition of F~ ion in CH₃CN to ligand I causes a colour change of the solution from colourless to yellow. The binding behaviour of ligand I towards several ions was investigated using density functional theory calculations.     

Stepwise magnetic behavior of the liquid crystal iron(III) complex

EPR and Mössbauer spectroscopy is used to study a new liquid crystal complex of iron(III) with a Schiff base: 4,4′-dodecyloxybenzoyloxybenzoyl-4-oxysalicylidene-2-aminopyridine with a PF ₆ ^? counterion. It is shown that Fe(III) ions exist only in the high-spin (HS, S = 5/2) state. It is found that under the influence of temperature the system demonstrates the stepwise behavior of the product of the integrated intensity of EPR lines (I) and temperature (proportional to χ T, where χ is the magnetic susceptibility) with an inflection point at ～80 K. Above 80 K a new EPR spectrum is detected due to the excited S = 2 state and the formation of dimeric molecules (through oxygen bridges) with a strong intramolecular antiferromagnetic exchange interaction J ₁ = 162.1 cm^?1. Below 80 K iron(III) complexes are organized in 1D chains where the exchange value J ₂ = 2.1 cm^?1. At 80 K there is a structural phase transition in the system: the transition from a 1D chain organization of HS Fe(III) centers to dimeric molecules. Based on quantum chemical calculations a model of the binuclear iron(III) complex is proposed.     

Crystal structure,DFT study,antimicrobial properties and DNA cleavage potential and thermal behavior of some new mercury complexes

In this study, a new bidentate Schiff base ligand (L) entitled as N,N’-bis(dimethylaminocinnamaldehyde)-2,2-dimethyl-1,3-propanediamine and its mercury complexes were synthesized. The Schiff base ligand and its complexes were characterized using FT-IR, ¹H-, ¹³C-NMR spectroscopy, molar conductivity and electronic spectral study. Regarding physical and spectral data, the general formula for the complexes was suggested as HgLX₂ (L = Schiff base ligand and X = Cl^?, Br^?, I^?, SCN^?, N₃ ^?). For structural identification of these complexes, crystal structure of mercury iodide complex was analyzed as typical one. In the structure of this complex, Hg ion is surrounded by 2 iodide ions and 2 N atoms from the Schiff base ligand to form a four-coordinated mercury complex in triclinic system with space group of P ₁. Angular index (τ ₄) value was evaluated equal to 0.85, so the geometry around the mercury ion in this complex can be described as trigonal pyramid. A layered supramolecular structure for HgLI₂ complex is stabilized by C–H···I and C–H···π interactions in solid state. DFT study on the ligand and its complexes was also carried out, and then some calculated and experimental structural parameters of HgLI₂ were compared. Thermal behaviors of the titled compounds were investigated by thermogravimetric analyses. Furthermore, biological properties of the ligand and its complexes were examined against some Gram-negative and Gram-positive bacteria and also against 2 fungi. Finally, the interaction of the ligand and its complexes with DNA was investigated by electrophoresis method.     

Spectroscopic validation and biological screening of new iron(III) complexes with N,O donor ligands

Monometallic trivalent complexes of iron were synthesized by reaction between N, O type donor ligands (L) or (L′) and metal salt in a 1:2 (metal:ligand) molar ratio. Structure and composition of metal complexes were evaluated by elemental analysis, conductance measurements, magnetic moment measurements, and various spectroscopic studies viz. FTIR, UV–visible, and ESI–MS. Analytical and molar conductance data are consistent with the formulation of complexes as [Fe(L)₂X₂]·X and [Fe(L′)₂X₂]·X (where; L = Hydrazine carboxylic acid ethyl ester, L′ = Hydrazine carboxylic acid tert-butyl ester and X = Cl^?, Br^? or NO₃ ^?) due to their 1:1 electrolytic nature. IR spectral data revealed bi-dentate coordination behavior of ligands. An octahedral geometry may be assigned for metal complexes on the basis of electronic absorption data and magnetic moment parameters. The compounds were evaluated for their biological activity by in vitro antimicrobial screening against bacteria Staphylococcus aureus, Bacillus subtilis, Escherichia coli, and Salmonella typhi and fungi Candida parapsilosis and Saccharomyces cerevisiae. The results indicate that metal complexes exhibit more activity than free ligands against studied microbes.     

Thermochemical study of the complex formation of copper(II) and nickel(II) iminodiacetates with amino acids in aqueous solutions

The formation of mixed-ligand complexes in the M(II)–Ida–L systems (M = Cu, Ni, L = His, Orn, Lys), where Ida is the iminodiacetic acid residue, was studied by pH-metry, calorimetry, and spectrophotometry. The thermodynamic parameters (logK, Δ_rG⁰, Δ_rH, Δ_rS) of formation of the complexes were determined at 298.15 K and the ionic strength I = 0.5 (KNO₃). The most probable mode of coordination of the chelating agent and the amino acid in the mixed-ligand complexes was elucidated.     

EPR studies of covalent bonding and hyperfine coupling in the complexes of <Emphasis Type="Italic">ns</Emphasis><Superscript>1</Superscript> ions

Covalent bonding in the complexes containing ns ¹ ions of various metals was studied by EPR spectroscopy. Large series of octahedral, cubic, and cuboctahedral complexes of the ⁶⁷Zn⁺(4s ¹), ¹¹¹Cd⁺(5s ¹), ²⁰⁵Tl²⁺(6s ¹), and ²⁰⁷Pb³⁺(6s ¹) ions were analyzed in crystal structures like fluoroperovskite (KMgF₃), fluoroantiperovskite (LiBaF₃), fluorite (MF₂) (where M = Ca, Sr, and Ba), and alkali metal halides. The parameters of hyperfine couplings and ligand hyperfine couplings were interpreted with regard to bond covalence and spin polarization.     

Complexes of some tervalent metals with <Emphasis Type="Italic">N</Emphasis>-alkyl(benzyl)nitrozohydroxylamine derivatives

Twenty two new complexes of some tervalent metals (aluminum, chromium, iron, and lanthanides) with nitrozohydroxylamine N-alkyl(benzyl) derivatives ML₃^m · nH₂O, (m = 1?5) were synthesized and isolated in a crystalline state. The crystal and molecular structures of the iron(III) complex with N-(2-fluorobenzyl)-N-nitrozohydroxylamine were determined by X-ray diffraction. An octahedral coordination of the central ion and a bidentate chelating coordination of the organic ligand were established. The spectral criteria of coordination of nitrozohydroxylamine alkyl(benzyl) derivatives were determined, and the complexation processes in solutions were studied.     

Synthesis,crystal structure,and luminescent properties of silver complexes with 2-methylquinoline

The complexes [AgL₂(NO₃)] (I) and [AgL₂(CH₃SO₃)] · H₂O (II) (L is 2-methylquinoline, C₁₀H₉N) have been synthesized and structurally characterized by single-crystal X-ray diffraction. Crystals of I are monoclinic, space group P2₁/n, a = 9.296(1) Å, b = 13.495(1) Å, c = 14.931(1) Å, β = 95.06(1)°, V = 1865.8(3) ų, ρ_calc = 1.624 g/cm³, Z = 4. Crystals of II are monoclinic, space group P2₁/n, a = 13.147(1) Å, b = 11.767(1) Å, c = 13.814(1) Å, β = 96.06(1)°, V = 2124.3(3) ų, ρ_calc = 1.599 g/cm³, Z = 4. Compounds I and II are composed of discrete complexes of similar structure but with different orientation of the methyl groups of ligand L (trans and cis arrangement, respectively). Both anions, NO ₃ ^- and CH₃SO ₃ ^- function as a chelating weakly bound ligand for the Ag⁺ ion. The presence of water molecules in II is favorable for the formation of dimeric supramolecular moieties between the centrosymmetrically arranged Ag⁺ complexes with 2-methylquinoline. The luminescence spectra of solid complexes I and II showed a bathochromic shift as compared to the spectrum of L in acetonitrile. Complexes I and II have been characterized by ¹H and ¹³C{H} NMR spectra in CD₃CN.     

Synthesis,characterization, crystal structures,and antimicrobial activity of cobalt(II) and iron(III) complexes derived from N'-(2-hydroxybenzylidene)-3-methylbenzohydrazide

A new cobalt(II,III) complex, [Co^IIIL₂]₂[Co ₂ ^II (HL)₂(OH₂)₂(CH₃OH)₂] ? 2H₂O (I) and a new iron(III) complex, [Fe^III(HL)₂](NO₃) (II), where L^2– and HL^– are the dianionic and monoanionic form of N'-(2-hydroxybenzylidene)-3-methylbenzohydrazide, respectively, have been prepared and characterized by elemental analyses, infrared and UV-Vis spectroscopy and single-cyrstal X-ray diffraction (CIF files CCDC nos. 1417971 (I), 1417979 (II)). Complex I crystallizes in the monoclinic space group P2₁/n with unit cell dimensions a = 16.1665(9), b = 14.5692(8), c = 19.086(1) Å, β = 96.347(1)°, V = 4467.9(4) ų, Z = 2, R ₁ = 0.0521, and wR ₂ = 0.1411. Complex II crystallizes in the orthorhombic space group Pbcn with unit cell dimensions a = 12.475(1), b = 12.202(1), c = 18.859(2) Å, V = 2870.8(4) ų, Z = 4, R ₁ = 0.0796, and wR ₂ = 0.1981. The metal atoms in the complexes are in octahedral coordination. Crystals of the complexes are stabilized by hydrogen bonds. The efficiency of the aroylhydrazone and the two complexes was evaluated against B. subtilis, S. aureus, E. coli, P. fluorescence, C. albicans and A. niger, with the complexes demonstrating enhanced activity relatively to the free ligand.     

Crystal and molecular structure of guanidinium dicitratoferrate(II)

Synthesis and X-ray investigation of a (GunH)₂[Fe(Cit)₂] single crystal are described [a = 10.327(2) Å, b = 10.414(2) Å, c = 11.267(2) Å; β = 117.25(3)°, V = 1077.2(4) ų, P2₁/n, Z = 2, R(F) = 0,0239, 1196 reflections with I > 2σ(I )], where GunH is the guanidine cation (C(NH₂)₃)⁺, and Cit is the citric acid anion (C₆H₆O₇)^2?. The structure is composed of guanidinium cations and centrosymmetrical sym-cis-octahedral complex anions [Fe(Cit)₂]^2?. The Cit^2? anion acts as a cyclic tridentate ligand and forms condensed fiveand six-membered metal-containing cycles.     

Synthesis and crystal structures of the zinc(II) complexes with a tridentate Schiff base (1-pyridin-2-ylethylidene)pyridin-2-ylmethylamine

Two new isostructural zinc(II) complexes, [ZnCl₂(L)] (I) and [ZnBr₂(L)] (II), derived from the Schiff base ligand (1-pyridin-2-ylethylidene)pyridin-2-ylmethylamine (L), have been prepared and characterized by physicochemical methods and single-crystal X-ray crystallography. The crystal of I is monoclinic: space group P2₁/c, a = 11.699(3) Å, b = 8.460(2) Å, c = 14.766(3) Å, β = 99.686(3)°, V = 1440.6(6) ų, Z = 4. The crystal of II is monoclinic: space group P2₁/n, a = 8.166(2) Å, b = 15.153(3) Å, c = 11.966(2) Å, β = 96.964(2)°, V = 1469.7(5) ų, Z = 4. The geometry of the pentacoordinated zinc atoms in both complexes is best described as a square pyramid.     

Synthesis and characterization of half-sandwich ruthenium(II) complexes with N-alkyl pyridyl-imine ligands and their application in transfer hydrogenation of ketones

A series of new arene ruthenium(II) complexes were prepared by reaction of ruthenium(II) precursors of the general formula [(η⁶-arene)Ru(μ-Cl)Cl]₂ with N,N′-bidentate pyridyl-imine ligands to form complexes of the type [(η⁶-arene)RuCl(C₅H₄N-2-CH=N-R)]PF₆, with arene = C₆H₆, R = iso-propyl (1a), tert-butyl (1b), cyclohexyl (1c), cyclopentyl (1d) and n-butyl (1e); arene = p-cymene, R = iso-propyl (2a), tert-butyl (2b). The complexes were fully characterized by ¹H NMR and ¹³C NMR, UV–Vis and IR spectroscopies, elemental analyses, and the single-crystal X-ray structures of 2a and 2b have been determined. The single-crystal molecular structure revealed both compounds with a pseudo-octahedral geometry around the Ru(II) center, normally referred to as a piano stool conformation, with the pyridyl-imine as a bidentate N,N ligand. The activity of all complexes in the transfer hydrogenation of cyclohexanone in the presence of NaOH and iso-propanol is reported, the compounds showing turnover numbers of close to 1990 and high conversions. Complex 2b was also shown to be very effective for a range of aliphatic and cyclic ketones, giving conversions of up to 100 %.