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.     

Komplexbildung der späten 3d-Elemente mit Arensulfonyl-thioharnstoffen,Arensulfonylmonothio- und Arensulfonyl-dithiocarbamidsäureestern

Complex Formation of the Late 3d-Elements with Arenesulfonylthioureas, Arenesulfonyl-monothio-, and Arenesulfonyldithiocarbamic Acid Esters Arenesulfonylthioureas (SPT-H, SAT-H, SMT-H), arenesulfonylmonothio-, and arenesulfonyldithiocarbamic acid esters (STCO-H, STCS-H) form neutral 1,2-chelates with copper(II), nickel(II), and cobalt(II), but not with iron(II) and manganese(II). Basing on the ESCA data, ESR and VIS spectra differences of the structure are proved: Four-membered rings (coordination of the sulfonamide function by nitrogen) are present in the copper(II) chelates, but six-membered ones (coordination of the sulfonamide function by one oxygen atom of the sulfonyl group) in the nickel(II) chelates. In the case of the complexes Co(SPT)₂, Co(SAT)₂, and Co(SMT)₂ both types of structure are realized by the formation of a high-spin and a low-spin isomer. The bonding behaviour of the ligands in the new complexes is discussed and in this connection both the IR spectra of SAT-H and its complexes and the selectivity of the copper(II) extraction from acidic solutions by the ligands STCO-H and STCS-H are explained.     

Complexes of cobalt(II) halides with 2-(1<Emphasis Type="Italic">H</Emphasis>-pyrazol-1-yl)-4(3<Emphasis Type="Italic">H</Emphasis>)-pyrimidinone

The electronic structures of complexes of cobalt(II) halides with 2-(1H-pyrazol-1-yl)-4(3H)-pyrimidinone have been studied by X-ray photoelectron spectroscopy. The Co2p _3/2 lines of cobalt atoms, N1s lines of nitrogen atoms, and O1s lines of oxygen atoms in the X-ray photoelectron spectra have been analyzed. Based on these data for the free and coordinated ligands, the atoms of the ligand coordinated to the central metal atom are determined. The coordinated organic compound serves as an electron-donating ligand. The results obtained are consistent with IR and UV-Vis spectroscopic data.     

Synthesis and characterization of cobalt(III) tetraaza macrocyclic complexes containing chloro and azido ligands

The complexes [Co(L)Cl₂]Cl · 4H₂O (1) and [Co(L)(N₃)₂]N₃ · 2H₂O (2) (L = 3,14-dimethyl-2,6,13,17-tetraazatricyclo [14,4,0^1.18,0^7.12]docosane) have been synthesized, and structurally characterized by X-ray crystallography, spectroscopy and cyclic voltammetry. The crystal structure of (1) is centrosymmetric and the cobalt(III) atom has an axially elongated octahedral geometry with four nitrogen atoms of the macrocycle and two chloride ligands. The cobalt(III) ion in (2) is coordinated to four nitrogen atoms from the macrocycle, and two azide ligands in an octahedral environment, which forms the 1D polymer through hydrogen bonding contacts involving the cation, azide anion and solvent water molecules. Electronic spectra of the complexes also exhibit a low-spin octahedral environment. Cyclic voltammetry of the complexes undergoes a one-electron wave corresponding to Co(III)/Co(II) processes. The electronic spectra and electrochemical behaviors of the complexes are significantly affected by the nature of the axial ligands.     

Complexation between nickel(II), cobalt(III) and hydrazones derived from pyridoxal 5′-phosphate and hydrazides of 2-,3-,4-pyridinecarboxylic acids in aqueous solution

abstract

The present work reports on stoichiometry, apparent stability constants of biologically relevant complexes of nickel(II), cobalt(III) with hydrazones derived from pyridoxal 5′-phosphate and hydrazides of 2-,3-,4-pyridinecarboxylic acids at pH 7.4, T?=?25.0?°C, I?=?0.25 determined using UV-Vis spectroscopy. The thermodynamic constants of some complexes formation (NiL, NiL₂, NiL₂H) were estimated. Cobalt(II) ion was found to be oxidized to cobalt(III). Co(II) and Co(III) form low-spin state complexes. Hydrazones binding ability (pL_0.5) in the medium mimicking biological ones towards Ni(II) and Co(III) was estimated.     

Study of the electronic structure of polynuclear cobalt trimethylacetate complexes by Co3<Emphasis Type="Italic">s</Emphasis> and Co3<Emphasis Type="Italic">p</Emphasis> X-ray photoelectron spectroscopy

The electronic structure of mono-, hexa-, and nonanuclear cobalt trimethylacetate complexes was studied by XPS. The Co3s- and Co3p X-ray photoelectron spectra of the complexes were recorded. The Co3p spectrum of bivalent cobalt was calculated in the isolated-ion intermediate-coupling approximation. Spectrum analysis showed that the [Co(N-Phobsqdi)2(η′-N-Ph-opda)(OOCCMe₃)] complex is a strong-field complex with Co(III) in the diamagnetic state; the [Co(dipy)₂(OOCCMe₃)₂], [Co(dipyam)(OOCCMe₃)₂], and [Co₉(μ₃-OH)₆(μ-OOCCMe₃)₁₂(OCMe₂)₄] are high-spin weak-field Co(II) complexes; and the [Co₆(μ₄-O)₂(OOCCMe₃)₁₀(THF)₄] complex contains both the Co(II) and Co(III) atoms. The energy position of major Co3s- and Co3p spectral maxima were found to be sensitive to the nature of the nearest environment of cobalt atoms. The data correlate well with X-ray crystallographic data.     

Synthesis,characterization, and electrochemical studies of Co(II,III) dithiocarbamate complexes

Cobalt(II) complexes of N-methyl phenyl, 1-phenylpiperazyl, and morpholinyl dithiocarbamates have been synthesized and characterized by UV–Visible, FTIR, ¹H-, ¹³C-NMR, and mass spectrometry. The spectroscopic data indicated that two ligands coordinated in bidentate chelating to the metal ion to form four-coordinate cobalt(II) complexes (1–3), which was confirmed by mass analysis (TOF MS ES⁺) of the complexes with m/z [M]⁺ = 450.98, 382.94, and 382.94 for 1, 2, and 3, respectively. Single crystal analysis of 2A and 3A show centrosymmetric mononuclear cobalt(III) bonded to three dithiocarbamate ligands forming a distorted octahedral geometry, indicating the cobalt(II) undergoes aerial oxidation to cobalt(III) during recrystallization. In addition, 2A crystallized with one solvated molecule of toluene. The redox behaviors of the complexes were studied by cyclic and square wave voltammetry in dichloromethane; the result revealed a metal centered redox process consisting of a one-electron quasi-reversible process assigned to Co(III)/Co(IV) oxidation and a corresponding Co(IV)/Co(III) reduction. Randles–Sevcik plots (anodic peak current versus the square root of the scan rate (I_p,a versus ν^1/2)) for the redox couples revealed diffusion-controlled behavior.     

New quadridentate ONNS ligands and their metal complexes

Summary Two new quadridentate sulphur-nitrogen chelating agents have been prepared and characterized. These ligands yield stable complexes of general formulae, M(ONNS)·xH₂O (M=Ni, Cu, Zn, Cd, Pd and Pt; ONNS^–2=ligand dianion; x=0, 1 or 2) and M(ONNS)X (M=Co or Fe; X=Cl or AcO). The nicke(II) complexes are diamagnetic and squareplanar. Based on magnetic and spectral data a square-planar structure is also assigned to the copper(II) complexes. The iron(III) complexes, Fe(ONNS)Cl are high-spin and five-coordinate. Magnetic and spectral evidence support an octahedral structure for the cobalt(III) complex, Co(ONNS)OAc.     

Synthesis and characterization of mixed ligand complexes of cobalt(II) with some nitrogen and sulfur donors

Mixed ligand complexes of Co(II) with nitrogen and sulfur donors, Co(OPD)(S–S) · 2H₂O and Co(OPD)(S–S)L₂ [OPD = o-phenylenediamine; S–S = 1,1-dicyanoethylene-2,2-dithiolate (i-MNT^2?) or 1-cyano-1-carboethoxyethylene-2,2-dithiolate (CED^2?); L = pyridine (py), α-picoline (α-pic), β-picoline (β-pic), or γ-picoline (γ-pic)], have been isolated and characterized by analytical data, molar conductance, magnetic susceptibility, electronic, and infrared spectral studies. The molar conductance data reveal non-electrolytes in DMF. Magnetic moment values suggest low-spin and high-spin complexes. The electronic spectral studies suggest distorted octahedral stereochemistry around Co(II) in these complexes. Infrared spectral studies suggest bidentate chelating behavior of i-MNT^2?, CED^2?, or OPD while other ligands are unidentate in their complexes.     

Korrelation zwischen Mössbauer-Isomerieverschiebungen und ESCA-Bindungsenergien

Correlation between Mössbauer Isomer Shifts and ESCA Binding Energies The correlation between core-electron binding energies and Mössbauer isomer shifts is investigated and discussed for low-spin pentacyanoferrates(II), high-spin iron(III) compounds and high-spin iron(II) halides. The Fe2p_3/2 binding energies of the investigated pentacyano ferrates(II) increase with decreasing isomer shifts as a consequence of the increasing π acid strengths of the sixth ligands. In contrast, the electron binding energies in high spin iron(III) compounds and iron(II) halides increase with increasing isomer shifts. This correlation is caused by the σ donor properties and the electronegativity of the ligands.     

XPS study of the electronic structure of binuclear 3d transition metal pivalate complexes

Binuclear pivalate complexes of 3d transition metals (manganese, iron, cobalt, and nickel) with the same ligand environment and a lantern structure have been studied by X-ray photoelectron spectroscopy. The M2p, M3s, C1s, O1s, and N1s X-ray photoelectron spectra have been examined. A redistribution of electron density in the OCO group has been revealed. It has been shown that the theory fits the experimental data on the energy separation between the high- and low-spin components in the M3s spectra and between the spin doublet components in the M2p spectra. It has been demonstrated that the iron, cobalt, and nickel complexes are paramagnetic at room temperature, whereas the manganese complex exhibits antiferromagnetic properties. There is a correlation between the size of the 3d subshell of the transition metal atom and the M-O and M-N bond lengths.     

Oxygenation of p-nitrophenylhydrazones with Co(II)-schiff base complexes

$\text{p}$-Nitrophenylhydrazones, unsusceptible to autoxidation, are readily oxygenated in the presence of a five-coordinate cobalt(II)-Schiff base complex, Co(II)(MeOSalen) (Py) leading to quantitative formation of novel 1-($\text{p}$-nitrophenylazo)-1-peroxy Co(III) complexes 2, which were isolated as crystals. A plausible mechanism involving hydrogen abstraction by Co(III)(O₂^?.) from the substrate followed by formation of a substrate anion Co(III) complex intermediate is proposed.     

Spin-State Variations of Iron(III) Complexes with Tetracarbene Macrocycles

Starting from their six-coordinate iron(II) precursor complexes [L^8RFe(MeCN)]²⁺, a series of iron(III) complexes of the known macrocyclic tetracarbene ligand L^8H and its new octamethylated derivative L^8Me, both providing four imidazol-2-yliden donors, were synthesized. Several five- and six-coordinate iron(III) complexes with different axial ligands (Cl⁻, OTf⁻, MeCN) were structurally characterized by X-ray diffraction and analyzed in detail with respect to their spin state variations, using a bouquet of spectroscopic methods (NMR, UV/Vis, EPR, and ⁵⁷Fe Mößbauer). Depending on the axial ligands, either low-spin (S=1/2) or intermediate-spin (S=3/2) states were observed, whereas high-spin (S=5/2) states were inaccessible because of the extremely strong in-plane σ-donor character of the macrocyclic tetracarbene ligands. These findings are reminiscent of the spin state patterns of topologically related ferric porphyrin complexes. The ring conformations and dynamics of the macrocyclic tetracarbene ligands in their iron(II), iron(III) and μ-oxo diiron(III) complexes were also studied.     

Some transition metal complexes of new terdentate ligands: Bis[2-(diphenylphosphino)ethyl]benzylamine and bis[2-(diphenylarsino)ethyl)benzylamine

Complexes of the terdentate ligands bis[2-diphenylphosphino)ethyl]benzylamine (DPBA) and bis[2-(diphenylarsino)ethyl]benzylamine (DABA) with Co(II), Ni(II), Pd(II), Pt(II), Rh(III), Ir(III), Rh(I) and Ir(I) are reported. The ligand DPBA reacts with Co(II) ion to form two types of complexes: a high-spin, paramagnetic, tetrahedral Co(II) complex of composition [CoCl(DPBA)]Cl and a low-spin, paramagnetic, square-planar complex of composition [CoBr(DPBA)]B(C₆H₅)₄. The reaction of DPBA with Ni(II) ion in methanol yields low-spin, diamagnetic, square-planar complexes of type [NiX(DPBA)]Y [X = Cl, Br or I; Y = Cl or B(C₆H₅)₄]. Four-coordinate, square-planar, cationic complexes of type [MY(L⁺[M = Pd(II), Pt(II), Rh(I) or Ir(I); Y = Cl or P(C₆H₅)₃; L = DPBA or DABA], were obtained on reaction of L with various starting materials containing these metal ions. Reaction of DPBA and DABA with rhodium and iridium trichlorides gave octahedral, neutral complexes of general formula [MCl₃(L)] (M = Rh or Ir, L = DPBA or DABA). All the complexes were characterized on the basis of their elemental analysis, molarconductance data, magnetic susceptibilities, electronic spectra, IR spectral measurements, and¹H and³¹P-{¹H} NMR spectral data.     

Dioxygen activation with a cytochrome P450 model. Characterization and electrochemical study of new unsymmetrical tetradentate Schiff-base complexes with iron(III) and cobalt(II)

Salicylaldehyde or 5-bromosalicylaldehyde react with 2,3-diaminophenol to give two unsymmetrical Schiff-bases H₂L¹, H₂L², respectively. With Fe(III) and Co(II), these ligands lead to four complexes: Fe(III)ClL¹, Fe(III)ClL², Co(II)L¹, Co(II)L². The structures of these complexes were determined by mass spectroscopy, infrared and electronic spectra. Cyclic voltammetry in dimethylformamide (DMF) showed irreversible waves for both ligands. In the same experimental conditions, Fe(III)ClL¹ exhibited a reversible redox couple Fe(III)/Fe(II) while the three other complexes showed quasi-reversible systems. The behavior of some of these complexes in the presence of dioxygen and the comparison with cytochrome P450 are described.     

Combining Open-Shell Verdazyl Environment and Co(II) Spin-Crossover: Spinmerism in Cobalt Oxoverdazyl Compound

The spin states of a Co(II) oxoverdazyl compound are investigated by means of wavefunction-based calculations. Within a ca. 233 K energy window, the ground state and excited states display a structure-sensitive admixture of low-spin S_M=1/2 in a dominant high-spin S_M=3/2 Co(II) ion as indicated by the localized molecular orbitals. The puzzling spin zoology that results from the coupling between open-shell radical ligands and a spin-crossover metal ion gives rise to this unusual scenario, which extends the views in molecular magnetism. In agreement with experimental observation, the low-energy spectroscopy is very sensitive to deformations of the coordination sphere, and a growing admixture of Co(II) low-spin is evidenced from the calculations. In analogy with mesomerism that accounts for charge delocalization, entanglement combines different local spin states to generate a given total spin multiplicity, a spinmerism phenomenon.     

Spin-crossover in cobalt(II) compounds containing terpyridine and its derivatives

In this review article we discuss the unique and novel magnetic properties for the cobalt(II) compounds with a variety of terpy derivatives including substituents at the 4-position. These are also compared with the unsubstituted terpy cobalt(II) complex. Since the first SCO cobalt(II) complex with terpy ligand was reported, this system has been widely studied. SCO cobalt(II) complexes possessing terpy or OH-terpy ligand reveal incomplete or gradual SCO behavior. The pyterpy-appended cobalt(II) complex shows SCO depending on the guest molecules involved. Cobalt(II) complexes with long-alkylated terpy ligands, [Co(Cn-terpy)₂](BF₄)₂ (n = 16, 14 and 12) have been synthesized and some were characterized by single crystal X-ray analysis. Furthermore, variable-temperature magnetic susceptibility indicated that the non-solvated compounds [Co(Cn-terpy)₂](BF₄)₂ (n = 16, 14 and 12) exhibit “reverse spin transition” phenomenon with wide thermal hysteresis around room temperature. In addition, the solvated compound [Co(C12-terpy)₂](BF₄)₂·EtOH·0.5H₂O shows “re-entrant SCO” behavior. The long alkyl chains in SCO cobalt(II) complexes can lead to novel physical properties resulting from a synergetic effect between SCO and response of the flexibility toward external stimuli.     

Synthesis, characterization, electrochemical studies, and antibacterial activities of cobalt(III) complexes with Salpn-Tipe Schiff base ligands. Crystal structure of trans-[CoIII(L1)(Py)2]ClO4

The synthesis, characterization, spectroscopic and electrochemical properties of trans-[Co^III(L¹)(Py)₂]ClO₄ (I) and trans-[Co^III(L²)(Py)₂]ClO₄ (II) complexes, where H₂L¹ = N,N′-bis(5-chloro-2-hydroxybenzylidene)-1,3-propylenediamine and H₂L² = N,N′-bis(5-bromo-2-hydroxybenzylidene)-1,3-propylenediamine, have been investigated. Both complexes have been characterized by elemental analysis, FT-IR, UV-Vis, and ¹H NMR spectroscopy. The crystal structure of I has been determined by X-ray diffraction. The coordination geometry around cobalt(III) ion is best described as a distorted octahedron. The electrochemical studies of these complexes revealed that the first reduction process corresponding to Co(III/II) is electrochemically irreversible accompanied by dissociation of the axial Co-N(Py) bonds. The in vitro antimicrobial activity of the Schiff bse ligands and their corrsponding complexes have been tested against human pathogenic bacterias such as Staphylococcus aureus, Bacillus subtilis, Pseudomonas aeruginosa, and Escherichia coli. The cobalt(III) complexes showed lower antimicrobial activity than the free Schiff base ligands.     

Quantum chemical calculations of the isomer shift in iron(II) complexes of 1,2,4-triazoles with a 1 A 1 ⇔ 5 T 2 spin transition

DFT calculations have been performed to determine the isomer shift for a series of iron(II) clusters with nitrogen-containing ligands which serve as models of coordination units in Fe(II) complexes with 1,2,4-triazoles possessing a ¹ A ₁ ? ⁵ T ₂ spin transition. Good agreement has been found between the theoretical and experimental values of the isomer shift for both low-and high-spin phases. Our calculations confirmed the hypothesis about relationship between the experimentally observed differences in the isomer shift for the low-spin phases of the complexes and variations of the Fe-N mean bond length.     

Polymerization of acrylate monomers with MAO activated iron(II) and cobalt(II) complexes bearing tri- and tetradentate nitrogen ligands

Octahedral iron(II) and cobalt(II) based complexes, [N,N′-di(quinoline-2-methylene)-1,2-phenylenediimine]MCl₂, and [N,N′-di(quinoline-2-methylene)diiminocyclohexane]MCl₂ (M = Co and Fe), bearing tetradentate diimino nitrogen ligands were prepared and used in tert-butylacrylate (t-BA) polymerization after activation with methylaluminoxane (MAO). In general, polyacrylates with high molar mass and narrow molar mass distribution (MMD ≈ 2) were obtained. In order to understand the influence of the ligand on the polymerization process, polymerization behaviour of the hexacoordinated complexes was compared to pentacoordinated iron(II) and cobalt(II) complexes, 2,6-bis[1-(cyclohexylimido)ethyl]pyridine MCl₂ (M = Co and Fe), bearing tridentate diimine nitrogen ligands as well as to free iron(II) chloride. The ability of the MAO activated hexacoordinated complexes to polymerize methylacrylate (MA) and methyl methacrylate (MMA) was also considered, but reduced activities as well as lower molar mass polymers were obtained than in the experiments with t-BA.