Effect Of Axial Ligands Research Articles

Effect of Axial Ligands on the Oxidation State, Structure, and Electronic Configuration of Diruthenium Complexes. Synthesis and Characterization of Ru2(dpf)4Cl, Ru2(dpf)4(C⋮CC6H5), Ru2(dpf)4(C⋮CC6H5)2, and Ru2(dpf)4(CN)2 (dpf = N,N‘-Diphenylformamidinate)

The effect of axial ligands on the structure, oxidation state, and electronic configuration of two diruthenium(II,III) and two diruthenium(III,III) complexes is reported. The investigated compounds are represented by Ru2(dpf)4Cl (1), Ru2(dpf)4(C⋮CC6H5) (2), Ru2(dpf)4(C⋮CC6H5)2 (3), and Ru2(dpf)4(CN)2 (4), where dpf is the N,N‘-diphenylformamidinate ion. The chloro and mono(phenylacetylide) complexes, which contain a Ru25+ core, are paramagnetic and contain three unpaired electrons, while the bis(phenylacetylide) and bis(cyano) species, which contain a Ru26+ core, are diamagnetic. Compound 1, Ru2(dpf)4Cl, was prepared by heating Ru2(CH3COO)4Cl and excess molten N,N‘-diphenylformamidine (Hdpf) for 10 h at 130 °C under an argon atmosphere. Compound 2, Ru2(dpf)4(C⋮CC6H5), was prepared by reaction of purified Ru2(dpf)4Cl with LiC⋮CC6H5 (in a 1:5 ratio) in THF at room temperature (2 h). Compound 3, Ru2(dpf)4(C⋮CC6H5)2, was also obtained from Ru2(dpf)4Cl by using excess LiC⋮CC6H5. A related diruthenium(III,III) ...

Comparative study of Mössbauer spectra of iron(III) complexes of para-substituted tetraphenylporphyrins. Electronic effects of substituents and axial ligands

The Mossbauer spectra of high-spin iron(III) complexes of tetra-para-substituted derivatives of 5,10,15,20-tetraphenylporphyrin [FeL(X)](R = OMe, H, F or Cl; X = Cl, Br or I), have been compared with each other to clarify the electronic effects of the phenyl substituents and the axial ligands. They show a variety of patterns depending on the temperature: asymmetric broadening of the high-velocity line at higher temperatures, a symmetric doublet at a temperature Tr, and reversal in asymmetry below Tr. The temperature dependence results from the temperature-dependent spin–spin relaxation of high-spin iron(III) ion and the off-diagonal terms of the hyperfine operator, and reflects the ionic zero-field splitting. The reversal temperature, Tr, and the quadrupole splitting, ΔEQ, show two kinds of dependence on R. This is explained by considering the σ- and π-bonding characteristics of the porphyrins under the influence of the substituents. With a given R, the values of both Tr and ΔEQ increase in the order X = Cl < Br < I. This is interpreted as due to the predominantly ionic character of the bond between the halide and iron ions, except for R = OMe.

The Co−CH3 Bond in Imine/Oxime B12 Models. Influence of the Orientation and Donor Properties of the trans Ligand As Assessed by FT-Raman Spectroscopy

Near-IR FT-Raman spectroscopy was used to probe the properties of three types of methyl imine/oxime B(12) model compounds in CHCl(3) solution. These types differ in the nature of the 1,3-propanediyl chain and were selected to test the influence of electronic and steric effects on the Co-CH(3) stretching (nu(Co)(-)(CH)()3) frequency, a parameter related to Co-C bond strength. For the first type studied, [LCo((DO)(DOH)pn)CH(3)](0/+) ((DO)(DOH)pn = N(2),N(2)(')-propane-1,3-diylbis(2,3-butanedione 2-imine 3-oxime)), nu(Co)(-)(CH)()3 decreased from 505 to 455 cm(-)(1) with stronger electron-donating character of the trans axial ligand, L, in the order Cl(-), MeImd, Me(3)Bzm, 4-Me(2)Npy, py, 3,5-Me(2)PhS(-), PMe(3), and CD(3)(-). This series thus allows the first assessment of the effect of negative axial ligands on nu(Co)(-)(CH)()3; these ligands (L = Cl(-), 3,5-Me(2)PhS(-), CD(3)(-)) span the range of trans influence. The CH(3) bending (delta(CH3)) bands were observed at 1171, 1159, and 1150/1105 cm(-)(1), respectively. The decrease in C-H stretching frequencies (nu(CH)) of the axial methyl suggests that the C-H bond strength decreases in the order Cl(-) > 3,5-Me(2)PhS(-) > CD(3)(-). This result is consistent with the order of decreasing (13)C-(1)H NMR coupling constants obtained for the axial methyl group. The trend of lower nu(Co)(-)(CH)()3 and nu(CH) frequencies and lower axial methyl C-H coupling constant for stronger electron-donating trans axial ligands can be explained by changes in the electronic character of the Co-C bond. The symmetric CH(3)-Co-CH(3) mode (nu(CH)()3(-)(Co)(-)(CH)()3) for (CH(3))(2)Co((DO)(DOH)pn) was determined to be 456 cm(-)(1) (421 cm(-)(1) for (CD(3))(2)Co((DO)(DOH)pn). The L-Co-CH(3) bending mode (delta(L)(-)(Co)(-)(CH)()3) was detected for the first time for organocobalt B(12) models; this mode, which is important for force field calculations, occurs at 194 cm(-)(1) for ClCo((DO)(DOH)pn)CH(3) and at 186 cm(-)(1) for (CH(3))(2)Co((DO)(DOH)pn. The nu(Co)(-)(CH)()3 frequencies were all lower than those reported for the corresponding cobaloxime type LCo(DH)(2)CH(3) (DH = monoanion of dimethylglyoxime) models for planar N-donor L. This relationship is attributed to a steric effect of L in [LCo((DO)(DOH)pn)CH(3)](+). The puckered 1,3-propanediyl chain in [LCo((DO)(DOH)pn)CH(3)](+) forces the planar L ligands to adopt a different orientation compared to that in the cobaloxime models. The consequent steric interaction bends the equatorial ligand toward the methyl group (butterfly bending); this distortion leads to a longer Co-C bond. In a second imine/oxime type, a pyridyl ligand is connected to the 1,3-propanediyl chain and oriented so as to minimize butterfly bending. The nu(Co)(-)(CH)()3 frequency for this new lariat model was close to that of pyCo(DH)(2)CH(3). In a third type, a bulkier 2,2-dimethyl-1,3-propanediyl group replaces the 1,3-propanediyl chain. The nu(Co)(-)(CH)()3 bands for two complexes with L = Me(3)Bzm and py were 2-5 cm(-)(1) lower in frequency than those of the corresponding [L(Co((DO)(DOH)pn)CH(3)](+) complexes. The decrease in the axial nu(Co)(-)(CH)()3 frequencies is probably due to the steric effect of the equatorial ligand. Thus, the nu(Co)(-)(CH)()3 frequency can be useful for investigating both steric and electronic influences on the Co-C bond.

Effect of axial ligands on the spectroelectrochemical properties of zinc phthalocyanine films. In situ Raman and electroreflection spectra

Electroreflection and Raman spectra (in situ and ex situ) of zinc phthalocyanine (ZnPc) films (80 nm thick) have been studied. Raman spectra were resonantly and preresonantly enhanced. Both electroreflection and Raman experiments reveal the homogeneous inclusion of electrolyte anions upon oxidation of the film. The anions coordinate preferentially axial positions of the ZnPc molecule. This process is accompanied by an out-of-plane deformation of the phthalocyanine macrocycle, which results in the change of both electroreflection and Raman spectra. The ZnPc molecule remains deformed when the film is saturated with anions. The detailed analysis of new bands and altered intensities in the Raman spectrum indicates that the molecular symmetry point group changes from the D 4 h point group to C 2 v . The influence of ZnPc oxidation on the Raman excitation mechanism has been also studied. Effects of axial ligands on the molecular geometry have been studied by quantum chemical calculations for the ZnPc +, ZnPc +Cl − and ZnPc +(Cl −) 2 species using the unrestricted Hartree—Fock variant of the MNDO method. Calculation results show that the ZnPc molecule undergoes an out-of-plane deformation when one axial position is coordinated by the anion.

Effects of axial ligands on the electron transfer catalyzed by manganese tatrakis(pentafluorophenyl)porphyrin in poly(γ-methyl L-glutamate) membrane

Poly(γ-methyl L-glutamate) (PMLG) membrane containing manganese tetrakis(pentafluorophenyl)porphyrin1 Systematic name: Tetrakis(pentafluorophenyl)porphyrinatomanganese. (MnPFPP) has been studied for the transmembrane redox reaction between dithionite and ferricyanide in separated solutions. The effects of the ligand species, namely, OH−, Cl−, imidazole (Im), pyrazine (Pyz), triethylamine (TEA), and pyridine (Py), on the electron transfer rate in the membrane were examined. UV/VIS spectroscopy and sorption measurements confirm that these ligands are sorbed by the membrane from the external buffer solution and coordinate to MnPFPP. With the membrane containing 160 μmol · g−1 of MnPFPP, the apparent rate factor, estimated as the pseudo-first-order rate constant of the bleach of ferricyanide times membrane thickness, follows the order Im ≫ Cl− > Pyz > TEA, OH−, Py > 0, suggesting that Im, Cl− and Pyz are effective ligands for the electron transfer. Such a ligand-specific transfer stems from the electron-transferability of the ligands between MnPFPP's.

A Pronounced Axial Ligand Effect on the Reactivity of Oxoiron(IV) Porphyrin Cation Radicals

A Pronounced Axial Ligand Effect on the Reactivity of Oxoiron(IV) Porphyrin Cation Radicals

The effect of axial π-acceptor ligands in iron(III) porphyrinates. Characterization of the low-spin derivative [Fe(TPP)(4-CNPy)2]ClO4, a heme complex with an axial EPR spectrum.

The effect of axial π-acceptor ligands in iron(III) porphyrinates. Characterization of the low-spin derivative [Fe(TPP)(4-CNPy)2]ClO4, a heme complex with an axial EPR spectrum.

Polymeric complexed membranes used as oxygen carrier: Axial and in‐plane ligand effects

AbstractThe complex formation reaction of modified styrene–butadiene–styrene block copolymer (SBS‐g‐VP and ESBS) with cobalt Schiff base (CoS) in chloroform solution is studied. The coordination number and formation constant are determined by the Miller method. The polymeric complexed membranes (SBS‐g‐VP–CoS and ESBS–CoS and ESBS–CoS) are made by solution casting method. The kinetics of oxygen binding to polymeric complexed membranes (SBS‐g‐VP–CoS and ESBS–CoS) is studied and the equilibrium, association, and dissociation constants are determined. The effects of polymeric axial ligand and of the equatorial chelate group are discussed. © 1993 John Wiley &amp; Sons, Inc.

Preparation of Optically Active [1-(Methoxycarbonyl)ethyl]cobaloximes Coordinated with Various Axial Ligands and Their Photoracemization. Remarkable Steric Effect of Axial Ligand on the Co–C Bond Homolysis

Abstract Optically active [1-(methoxycarbonyl)ethyl]cobaloximes coordinated with various axial bases were prepared and their photoracemization rates were measured in a solution state. It was found that although the electronic effect of the axial ligand was negligible on the rate of photochemical Co–C bond homolysis, the steric bulkines accelerated the rate remarkably. These results had a similar tendency to those observed in a previously reported reaction wtih 1-cyanoethyl cobaloximes, though the degree of rate enhancement due to the steric bulkiness of the axial ligand was extremely enlarged. The reason is also discussed.

Axial ligand effects on the spin state and electrochemistry of iron porphyrins: An advanced laboratory experiment

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTAxial ligand effects on the spin state and electrochemistry of iron porphyrins: An advanced laboratory experimentDavid K. Geiger Cite this: J. Chem. Educ. 1991, 68, 4, 340Publication Date (Print):April 1, 1991Publication History Received3 August 2009Published online1 April 1991Published inissue 1 April 1991https://doi.org/10.1021/ed068p340RIGHTS & PERMISSIONSArticle Views906Altmetric-Citations2LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (2 MB) Get e-Alerts Get e-Alerts

Solid-state Photoracemization of Optically Active Alkyl Cobaloxime Complexes. Solid-state Specific Effect of Axial Ligand

Abstract Solid-state photoracemization of chiral alkyl cobaloxime complexes ocurred with the solid-state specific effect of the axial ligands (the first example of solid state photoracemization). The mechanism is also discussed.

Ab initio study of the photoelectron spectra and bonding in [Ru2(O2CH)4] and [Ru2(O2CH)4(NO)2]: the effect of axial ligands on metal-metal interactions

Ab initio calculations at the self-consistent field level have been carried out on [Ru2(O2CH)4] and [Ru2(O2CH)4(NO)2]. The ground-state configuration of [Ru2(O2CH)4] is predicted to be σ2π4δ2δ*2π*2 with the σ2π4δ2π*3δ* configuration being 15 kcal mol–1 higher in energy. The metal ionization energies of both molecules have been calculated by a configuration-interaction method and provide an interpretation of the experimental photoelectron spectra consistent with measured intensity changes using He I and He II radiation.

Synergistic effect of lipophilic carboxylic acids and heterocyclic axial ligands in alkene epoxidation by hydrogen peroxide catalysed by manganese(III) tetra-aryl porphyrins

The rate of alkene epoxidation promoted by 30% H2O2 and catalysed by MnIII tetra (2,6-dichlorophenyl)porphyrin is strongly enhanced by the addition of lipophilic carboxylic acids and lipophilic imidazole or pyridine axial ligands, in 1–8 : 1 and 1 : 1 molar ratios with respect to the porphyrin.

The Magnetic Properties of Copper(II) Alkanoate Adducts with Pyridine and Quinoline Analogues

Abstract Various copper(II) alkanoate adducts with pyridine and quinoline analogues have been prepared, and characterized by means of magnetic susceptibility and IR measurements. The effects of axial ligands on the magnetic moments are discussed on the basis of their basicities and steric requirements.

Voltammetry of some novel Fe(III) complexes with tetradentate ONNO ligands: The axial ligand effect

The electrochemistry of some novel Fe(III) complexes of the type Fe(L)Cl involving several tetradentate ligands based on the bis-condensation products of S-methylisothiosemicarbazide with two either identical or different aldehydes (salicylaldehyde, its derivatives, or 2-hydroxy-1-naphthaldehyde), was studied in DMF solutions at a GC electrode. All complexes undergo a two-step one-electron reduction which is usually complicated by chemical reactions. In solutions containing Cl − (either from the complex, or added as LiCl), the Cl −-DMF ligand exchange reaction takes place and is especially pronounced for the Fe(II) oxidation state. The stability of the chloride-containing complexes was discussed in detail in view of the coordinated ligand effect and the oxidation state of the central atom. Some relevant kinetic parameters are calculated.

A Systematic Investigation of the Effects of Axial Ligands and Peripheral Substituents on the Electronic Structures of Zinc(II) Tetraphenylporphyrin π-Cation Radicals: Electrochemical EPR and Spectroscopic Observation

Abstract A detailed study of the effect of axial ligand and peripheral substituent on the π-system of zinc(II) tetraphenylporphyrin π-cation radical has been made using an electrochemical EPR technique. It is confirmed from the EPR spectra that most of the anions and bases examined coordinate the radicals axially. The spin density on the nitrogen nuclei in the radicals increases with the polarizability of the axial ligand estimated from the optical spectra of the parent neutral complexes. For the fourteen complexes with different substituents on the phenyl groups examined here, there is a linear correlation between the Hammett substituent constant and the spin density. It is also shown that the para position of the phenyl group carries the spin density comparable to that of the ortho position, which indicates considerable conjugation between the porphyrin ring and the phenyl groups. In most cases, there exist two kinds of radical species which give rise to broad and sharp EPR spectra at low temperature. It is suggested that the difference in the motional states of the phenyl groups in the radicals is responsible for the different EPR spectra.

The effect of axial ligands on the heterogeneous rate constant for the redox reaction of [tetrakis(1-methyl-4-pyridinio) porphine]iron (III) ion in aqueous solution

The redox reactions of the [tetrakis(1-methyl-4-pyridinio)porphine]iron(III/II) (Fe(III or II)-TMPyP) ion were investigated in alkaline aqueous solution including CN t- ion by means of the cyclic voltammetry, in order to determine the effect of some axial ligands, ie H 2O, OH t- and CN t-, on the redox peak potentials Ep and the apparent heterogeneous transfer rate constant k′ s. The Ep values were considerably shifted anodically by the replacement of axial ligands by CN t-. The significant differences in the k′ s values were observed for the four Fe (III)- TMPyP species which have different combination of axial ligands. The plot of k′ s against the sum of Klopman's softness character of axial ligands is found to be linear.

ChemInform Abstract: Electrochemical Reactivity of Manganese(II) Porphyrins. Effects of Dioxygen, Benzoic Anhydride, and Axial Ligands.

AbstractCurrents for electrochemical reductions of Mn(III) porphyrins in oxygenated, aprotic media correspond to passage of between one and two electrons per porphyrin, depending on the experimental time scale, the axial base (Py, N‐methylimidazole) present, and the particular porphyrin (tetraphenyl‐, ‐mesityl‐, and ‐p‐methoxyphenylporphyrin).

ChemInform Abstract: Voltammetry of Zinc Tetraphenylporphyrin in Solution and in Polymer Films: The Effect of Axial Ligands.

Abstract Cyclic voltammetry at Pt electrodes is presented for the title compound in solution with added pyridine or polyvinylpyridine and (C6H5)3P and (C6H5)3As as the well, and in films formed on the electrode from polyvinylpyridine with the porphyrin incorporated by axial ligation. The axial ligands have only a small effect on the one electron reversible oxidaton of the porphyrin but after the second oxidation step, a slow reaction leads to a peripheral nucleophilic substitution whihc is reversed only at much more cathodic voltages (−0.1 V). The substituted form also displays a quasi-reversible reaction at a quite anodic potential (1.0 V) which is rendered unobservable by excess pyridine ligand.

Electrochemical reactivity of manganese(II) porphyrins. Effects of dioxygen, benzoic anhydride, and axial ligands

Electrochemical reactivity of manganese(II) porphyrins. Effects of dioxygen, benzoic anhydride, and axial ligands