Electrochemical Behaviour of the Fe(CO)3NO⊖ Ion (original) (raw)
Journal of Organometallic Chemistry, 2001
A mechanism is proposed for the electrochemical reduction of [Fe(h 5-C 6 H 7)(CO) 3 ][PF 6 ] based on cyclic voltammetry and simulation techniques. In [NBu 4 ][X]/CH 3 CN (X=BF 4 or ClO 4) but not in [NBu 4 ][BF 4 ]/CH 2 Cl 2 , a rapid equilibrium prior to the electron transfer process is identified between [Fe(h 5-C 6 H 7)(CO) 3 ][PF 6 ] and a species formulated as [Fe(h 3-C 6 H 7)(CO) 3 (NCMe)] +. The formation of the species under equilibrium involves solvent coordination and h 5 to h 3 ring slippage of the cyclohexadienyl ligand as the response of the system to the high electron count. Electrochemical electron transfer to [Fe(h 3-C 6 H 7)(CO) 3 (NCMe)] + affords a highly reactive 19-electron intermediate exhibiting chemical reactivity (ECE mechanism) that leads to the formation of dimer-type species. A 'father-son' type mechanism is proposed for the formation of the products of the electrochemical reduction of [Fe(h 5-C 6 H 7)(CO) 3 ][PF 6 ]. All the species involved in the mechanism were analysed by theoretical means and are proposed on the basis of calculations made with the B3LYP HF/DFT hybrid functional.
Journal of Organometallic Chemistry, 2001
The structure of [Fe(h 5 -C 5 H 5 )(h 5 -C 5 H 4 CH NNHC 5 H 4 N)]·HCl (1·HCl) has been solved to R= 0.05 and is described. The parent compound has been shown to act as a ligand for a range of M 2 + cations in the form 1MCl 2 (where M =Cd 2 + , Cu 2 + , Zn 2 + , Sn 2 + , Pd 2 + and Fe 2 + ). 57 Fe Mö ssbauer spectroscopy has been used to probe the ferrocenyl iron electronic environments to give a ligand's eye view of the metal bonding. Two compounds of the formula [1M(H 2 O) 4 ][PF 6 ] 2 where M = Fe 2 + or Zn 2 + were also prepared. The ferrocenyl quadrupole splittings of these two compounds were much smaller than those of the corresponding chloride. The change is explained in terms of the electric field experienced by the ferrocenyl iron atoms. In the chloride complexes the field from the M 2 + is compensated by the chloride anions, whereas in the two [PF 6 ] − salts the charge on the M 2 + is not compensated in the first coordination sphere. The ferrocenyl iron is thus directly exposed to the M 2 + charge and it is the effect of this that gives rise to the small quadrupole splitting value. This is the first time such a field effect has been observed on a ferrocenyl iron by Mö ssbauer spectroscopy. The coordination geometry of the inorganic iron(II) environment is also elucidated as tetrahedral in 1MCl 2 and distorted octahedral in [LM(H 2 O) 4 ][PF 6 ] 2 .
On the [Fe(H2O)5XO]2+ (XC, N, O) complex ions via density functional theory
Journal of Molecular Structure: THEOCHEM, 2005
The coordination of XO (XaC, N, O) to metal iron is important in biochemistry. In this paper, the properties of spin ground states for [Fe(H 2 O) 5 XO] 2C are studied via UB3LYP method. The spin ground states for [Fe(H 2 O) 5 CO] 2C , [Fe(H 2 O) 5 NO)] 2C , and Fe(H 2 O) 5 O 2 ] 2 are determined to be SZ2, 3/2, and 1, respectively. Both the Fe-CO bond in [Fe(H 2 O) 5 CO] 2C and Fe-NO bond in [Fe(H 2 O) 5 NO] 2C are linear. The Fe-O-O bond in [Fe(H 2 O) 5 O 2 ] 2C is bent. The order of the Fe-X distances is Fe-N!Fe-C!Fe-O, and that of net charge on XO ligands is O 2 !CO!NO. To determine the characteristics of the central Fe, the Fe I (H 2 O) 6 C , Fe II (H 2 O) 6 2C , and Fe III (H 2 O) 6 3C ions are employed as references. Results indicate that the [Fe(H 2 O) 5 CO] 2C (SZ2), [Fe(H 2 O) 5 NO] 2C (SZ3/2), and Fe(H 2 O) 5 O 2 ] 2C (SZ1) are best described by Fe II (SZ2) coupled to CO (SZ0), NO (SZ1/2), and O 2 (SZ1), respectively. The determined atomic net charges of Fe are robust even when the XO ligands undergo internal rotation. These results can be used as references models in understanding the bindings between XO and metal iron.
Electrochimica Acta, 2014
An innovative study on the electrochemical behaviour of mixed d metal-iron containing Wells-Dawson sandwich-type complexes [(FeOH 2 ) 2 M 2 (X 2 W 15 O 56 ) 2 ] 14− and [(MOH 2 ) 2 Fe 2 (X 2 W 15 O 56 ) 2 ] 14− (with M = Cr III , Mn II , Mn III , Co II , Ni II , Cu II or Zn II and X = P V or As V ) was carried out. These complexes have a four-centre equatorial metal cluster constituted of two Fe atoms and two atoms of another metal. The Fe III centres are either in an external position, [(FeOH 2 ) 2 M 2 ], or in an internal position, [M 2 (OH 2 ) 2 Fe 2 ]. Experimental methods (cyclic voltammetry and controlled potential coulometry) and theoretical calculations (density functional theory) allowed us to determine and analyse the redox potential values associated with the reduction of the Fe III centres in these species. The influence of the position of the Fe III centres, the nature of the metal centre M and the electron density distribution in the tetranuclear cluster (either [(FeOH 2 ) 2 M 2 ] or [(MOH 2 ) 2 Fe 2 ]) have been studied and rationalised in order to account for the observed behaviours. The data suggest that the most stable isomers are those where Fe III centres are internally-located, [(MOH 2 ) 2 Fe 2 ]. Consequently, their reduction is more difficult than those having externally-located Fe III isomers, [(FeOH 2 ) 2 M 2 ]. Some experimental results revealed a few exceptions to this rule which have not been rationalised yet.
Voltammetry of Dissolved Iron(III)-Nitrilotriacetate-Hydroxide System in Water Solution
Electroanalysis, 2005
The investigation of the dissolved iron(III) -nitrilotriacetate -hydroxide system in the water solution (I = 0.1 mol L -1 in NaClO 4 ; pH = 8.0±0.1) using differential pulse cathodic votammetry, cyclic voltammetry, and sampled direct current (d.c.) polarography, was carried out on a static mercury drop electrode (SMDE). The dissolved iron(III) ion concentrations varied from 2.68×10 -6 to 6×10 -4 mol L -1 and nitrilotriacetate concentrations were 1×10 -4 and 5×10 -4 mol L -1 . By deconvoluting of the overlapped reduction voltammetric peaks using Fourier transformation, four relatively stable, dissolved iron(III) complex species were characterized, as follows: [Fe(NTA) 2 ] 3-, mixed ligand complexes [FeOHNTA]and [Fe(OH) 2 NTA] 2-, showing a one-electron quasireversible reduction, and binuclear diiron(III) complex [NTAFeOFeNTA] 2-, detected above 4×10 -4 mol L -1 of the added iron(III) ions, showing a one-electron irreversible reduction character. The calculations with the constants from the literature were done and compared with the potential shifts of the voltammetric peaks. Fitting was obtained by changing the following literature constants: log β 2 ([Fe(NTA) 2 ] 3-) from 24 to 27.2, log β 1 ([FeNTA] -) from 8.9 to 9.2, log β 2 ([Fe(NTA) 2 ] 4-) from 11.89 to 15.7 and log β 2 ([Fe(OH) 2 NTA] 3-) from 15.63 to 19. The determination of the electrochemical parameters of the mixed ligand complex [FeOHNTA] -, such as: transfer coefficient (α), rate constant (k s ) and formal potential (E o ') was done using a sampled d.c.
Dalton transactions (Cambridge, England : 2003), 2015
In this paper we study the influence of substituting one CO ligand in [Fe2(CO)6{μ-(SCH2)2(Ph)P[double bond, length as m-dash]O}] () by better σ-donor L ligands affording [Fe2(CO)5(L){μ-(SCH2)2(Ph)P[double bond, length as m-dash]O}] {L = PPh3 () and P(OEt)3 ()} in relation to the steric interactions and the voltammetric behavior. Cyclic voltammetric investigations under N2 and CO showed remarkable differences in the electrochemical behaviour of complexes and : (i) Complex tends to expel PPh3 upon reduction whereas complex exhibits chemical reversibility and (ii) Under CO, complex reacts with CO affording a new compound , which shows a reversible wave at E1/2 ∼ -0.9 V (vs. ferrocenium/ferrocene couple). The presence of CO assists the formation of after electrochemically induced loss of PPh3 during the voltammetric experiment of . Using DFT calculations we provide an explanation for the difference in stabilities between the Fe-PPh3 and Fe-P(OEt)3 bonds.
Journal of Molecular Spectroscopy, 2002
In this contribution, we report density functional theory calculations on the transition metal complex (η 5 -C 5 H 5 )Fe(CO) 2 Cl and its fragments in differently charged states (anionic, neutral, cationic). The results are compared to literature data. The work is motivated by the long-term objective of a charge reversal or "NeNePo" (negative-neutral-positive) experiment (Wolf, Sommerer, Rutz, Schreiber, Leisner, Wöste, and Berry, Phys. Rev. Lett. 74, 4177-4180 (1995)). The calculated data explain results from preliminary mass spectroscopical experiments on anions. The calculations show that the complex could be well suited for a successful "NeNePo" experiment. C 2002 Elsevier Science 58
Inorganic Chemistry, 1996
The influence of the solvent on the structure and IR spectrum of the [Fe(CN) 5 NO] 2ion is investigated by using gradient corrected density functional theory. IR spectra are also measured on different solvents and the results obtained are compared with the predicted ones. We have treated the solvent effects with a continuum model, based on the Onsager's reaction field approach; in order to mimic strong specific interactions, calculations were also performed on the complex protonated at the cyanide trans to the nitrosyl group. The reaction field calculations predict only qualitatively the most important observed trends, e.g., the shifts in the nitrosyl stretching wavenumber, but fail in accounting quantitatively for the differences between the spectra in water and acetonitrile. The possible role of specific interactions is consistently accounted for by interpreting the experimental shifts of the NO stretching wavenumber ν(NO), as well as the visible absorption energies, when changing the Lewis acidity of the solvent, as measured by the Gutmann's acceptor number. Ligand population analysis was performed to relate the solvent effects with the σ donor and π acceptor behavior of cyanide and nitrosyl ligands. The significance of ν(NO) shifts as a result of changes in the medium is discussed in view of the physiological relevance of transition-metal nitrosyl chemistry.
Organometallics, 1992
The oxidative electrochemical behavior of 18 mono-and bimetallic complexes in which (q5-C5H5)Fe(C0), (Fp) groups are u-bound to arene and azine rings has been determined by cyclic voltammetry (CH2C12, n-ByNPF6, Pt electrodes) and is described. The oxidation potentials and reversibilities of these compounds are found to be very dependent on the structures of the aromatic ligands. In particular, it was found that the addition of fluorine substituents increased both the oxidation potentials and chemical reversibilities for the aryl complexes, as did the substitution of a nitrogen atom for a C-X group in the aromatic ring. For the bimetallic arene-bridged complexes, the perhydro derivatives (Le. 1,3-and 1,4-C6H4Fp2) show low chemical reversibilities, while the fluorinated bimetallics (i.e. 1,3-and 1,4CP4Fp2) are reversibly oxidized in two sequential one-electron steps with separation between their first and second oxidations (Le. AEl12 = p'+1/+2of 280 and 200 mV for the para-and meta-substituted complexes, respectively. This is indicative of substantial long-range metal-metal electronic coupling in these compounds. The first oxidations for these complexes are much more chemically and electrochemically reversible than are the second oxidations, which are accompanied by complex electrode/electrolyte interactions. For the azine complexes, we find that those species having the Fp substituents ortho to a nitrogen atom are irreversibly oxidized at scan rates of up to 10 V s-l, while the para-substituted halopyridine complexes show excellent chemical reversibilities. The X-ray crystal structures of the title complexes CpFe(C0)&P5, (C1,H$$eO2; a = 6.993 (2) A, b = 12.774 (4) A, c = 13.649 (3) A, V = 1219 A3; orthorhombic; &ma; 2 = 4), 4-CpFe-(CO)2-C$4N, (C12H6F4FeN02; a = 6.948 (1) A, b = 12.828 (1) A, c = 13.000 1) A, V = 1159 A3; orthorhombic; 4 B = 107.822 (7)O, V = 901 $i3, monochc; P2,/c; 2 = 2) have been determined. In each m e , the CpFe(CO), group is oriented such that ita mirror plane (complexes 6 and 10) or pseudo mirror plane (complex 3) is perpendicular to the arene or azine ring rather than parallel to it 88 predicted by molecular orbital arguments. It is suggested that these unexpected orientations minimize unfavorable steric interactions between the o-fluorine substituents on the aromatic groups and the H atoms on the C5H5 group of Fp.
Electrochemical behavior of iron(III) complexes with aminohydroxamic acids
Polyhedron, 2002
The electrochemical reduction of various aminohydroxamate complexes of iron(III), such as alanine-, serine-, lysine-, histidineand glutamo-g-hydroxamate, has been investigated in aqueous solution by cyclic voltammetry on hanging mercury drop electrodes to determine the mechanism involved in the electron transfer processes. In all the studied cases the iron(III) complexes, with the exception of histidinehydroxamate, have been found to undergo reversible reductions followed by irreversible chemical reactions (EC mechanism). Rate constants for the irreversible dissociation of iron(II) complexes were calculated. The typical quasi-reversible pattern for the reduction of histidinehydroxamate was attributed to the different coordination mode. The observed differences in redox potentials between the investigated complexes suggest that the electronic effect of the substituent on the carbonyl group, involved in the coordination to the iron center, may modify the donor properties of the oxygen atoms of the hydroxamate moiety. The potentials determined at physiological pH are in the range of biological reducing agents, which makes these compounds potential siderophore models. #
Journal of the American Chemical Society, 1996
Oxidation of [FeCp*(η 1 -dtc)(CO) 2 ], 1 (Cp* ) η 5 -C 5 Me 5 , dtc ) S 2 CNMe 2 ), or [FeCp*(η 2 -dtc)(CO)], 2, using [Fe III Cp 2 ] + X -(X -) PF 6 -or BF 4 -, Cp ) η 5 -C 5 H 5 ) in THF cleanly gives [Fe III Cp*(η 2 -dtc)(CO)] + X -, 2 + X -, as microcrystalline green, thermally stable, but substitution labile, salts. The substitution of CO in 2 + PF 6 -by various solvents (CH 2 Cl 2 , THF, CH 3 COCH 3 , CH 3 CN) (visible spectroscopy) follows pseudo-first-order kinetics but shows clearly the influence of the incoming solvent ligand on the substitution rate and, hence, is in good agreement with an associative mechanism. Displacement of the labile solvent ligand in these complexes by a phosphine results in the 17-electron (17e) cations [Fe III Cp*(η 2 -dtc)(L)] + PF 6 -, L ) PPh 3 (7 + PF 6 -) or η 1 -dppe (8 + PF 6 -). The same reaction in the presence of the anionic ligands CN -, SCN -, and Claffords the corresponding neutral 17e Fe III complexes (respectively compounds 11, 13, and 14). All these 17e complexes were characterized by IR, ESR, and Mössbauer spectroscopies and elemental analysis. The cations were reduced to isostructural neutral Fe II complexes using 1 equiv of [Fe I Cp(C 6 Me 6 )] in THF or oxidized to the robust green 18e Fe IV complex [Fe IV (η 5 -C 5 Me 5 )(η 2 -S 2 CNMe 2 ) 2 ] + -PF 6 -, 9 + PF 6 -, using Na + dtc -‚2H 2 O. [Fe IV (η 5 -C 5 (CH 2 C 6 H 5 ) 5 )(η 2 -S 2 CNMe 2 ) 2 ] + PF 6 -, 16 + PF 6 -, was structurally characterized, and the dihapto mode of coordination of both dtc ligands was established. The 19e Fe III species 9 was shown to be an intermediate which further reduced H 2 O. It could be alternatively synthesized by reduction of the 18e precursor 9 + PF 6 -using 1 equiv of [Fe I Cp(C 6 Me 6 )] or by addition of anhydrous Na + dtcto 3 + PF 6 -in MeCN at -40°C. The 19e complex 9 showed an ESR spectrum indicating an axial symmetry (two g values) in contrast with the ESR spectra of all the 17e species (2 + -14) which show three g values characteristic of a rhombic distortion (for instance, the very close model 13). The Mössbauer doublet of 9 very slowly evolved to the new doublet of the thermally stable 17e complex 9′. In MeCN solution, the transformation of the blue complex 9 to the purple 17e complex 9′ was much more rapid (above -40°C) as indicated by the rhombic spectrum of 9′ in frozen solution and by low-temperature 13 C NMR. In toluene, however, the 19e complex 9 showed a remarkable stability up to room temperature, which allowed recording of the 13 C spectrum in d 8 -toluene. MO calculations have been performed on models for the 17e and 19e bis-dtc Fe III complexes. They suggest that the 17e species should have some significant sulfur spin density. The 19e species is found to have its odd electron occupying an antibonding metal-centered orbital. The cyclic voltammogram of 9 + PF 6 -under continuous scanning for the monoelectronic reduction and the two monoelectronic reductions showed the decrease of the waves of 9 + PF 6 -and the concomitant increase of those due to the partially decoordinated dtc complexes formed upon reduction. This permits an interpretation of the CV in terms of a triple-square scheme involving 9 +/0/-, 9′ +/0/-, and solvent (DMF) adducts in 18-and 19e states. † URA No. 35. ‡ URA No. 71. Present address: Laboratoire d'Optique et de Magnétisme, URA No. 1531, Université de Versailles,
Organometallics, 2001
A theoretical study of the structural versatility of the di-iron carbonylate, [Fe 2 (CO) 8 ] 2-, and of its adducts with electrophiles is presented. The geometries of three energy minima and four transition states of [Fe 2 (CO) 8 ] 2have been characterized, and the relative energies of several alternative structures have been evaluated. The calculated vibrational spectra in the Fe-Fe and the CtO stretching regions are discussed for the three isomers, and a good correlation between the Fe-Fe stretching force constant and the Fe-Fe bond distance is found for both theoretical and experimental data. The effect of the orientation of the terminal ligands on the Fe-Fe bond and the rearrangement of such ligands by the formation of adducts with electrophiles are also addressed. a Abbreviations: im) N-methylimidazole; lut) N-methyllutidinium; py) pyridine.