Kinetic studies on the formation of a cyanide-bridged adduct of two cationic metal complexes

Espenson, James H.; Bushey, William R.

doi:10.1021/ic50105a019

Cited by 17 publications

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“…In addition to structural features, there are prior reactivity observations that suggest a reasonable probability for the preferred Fe III −N−C−Cu I atom sequence in 10 and 11 . In the aquation reactions of [Cr(OH 2 ) 5 (CN)] 2+ and [Cr(OH 2 ) 5 (NC)] 2+ in the presence of Hg 2+ , the rate of reaction of the isocyano isomer is much faster because the formation of the [Cr−CN−Hg] 4+ intermediate and its linkage isomerization to [Cr−NC−Hg] 4+ are obviated . Reaction of the cyano complex [Cr(en) 2 (CN) 2 ] + with 1 equiv of Ag + induces linkage isomerization and the formation of the Cr−N−C−Ag bridge, as inferred from band shifts in absorption spectra …”

Section: Resultsmentioning

confidence: 99%

Molecular Heme−Cyanide−Copper Bridged Assemblies: Linkage Isomerism, Trends in ν_CN Values, and Relation to the Heme-a₃/Cu_B Site in Cyanide-Inhibited Heme−Copper Oxidases

1998

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Bovine heart cytochrome c oxidase and related heme copper oxidases are inhibited by cyanide, which binds at the binuclear heme-a(3)/Cu(B) site where dioxygen is reduced to water. To determine the mode of cyanide binding, heme-based binuclear complexes containing iron-cyanide-copper bridges in different oxidation states have been prepared by the reaction of [(py)(OEP)Fe(CN)] with Cu(II,I) precursors and structurally characterized by X-ray methods. Structures of two precursor complexes and two binuclear Cu(I)-CN-Cu(I) species are reported. The assembly [(py)(OEP)Fe-CN-Cu(Npy(3))](2+) has a nearly linear Fe(III)-CN-Cu(II) bridge containing low-spin Fe(III). The assemblies [(OEP)Fe-NC-Cu(MeNpy(2))](+) and [(OEP-CH(2)CN)Fe-NC-Cu(Npy(3))](+) exhibit the high-spin bridges Fe(III)-NC-Cu(I) and Fe(II)-NC-Cu(I), respectively. These are the first title bridges in these oxidation states. Bridge atom sequences are obtained from structural refinements of both linkage isomers; those for the reduced bridges are consistent with the soft-acid nature of Cu(I). Cyanide stretching frequencies respond to metal oxidation state and bridge geometry and, using data for solution and solid states, fall into the following ranges: Fe(III)-CN-Cu(II), 2120-2184 cm(-)(1) (11 examples); Fe(III)-NC-Cu(I), 2072-2100 cm(-)(1) (2 examples); Fe(II)-NC-Cu(I), 2099-2107 cm(-)(1) (1 example). These data are compared with nu(CN) values for the enzymes in different oxidation states. A nonlinear Fe(III)-CN-Cu(II) bridge (Cu-N-C = 150-160 degrees ) is consistent with the 2146-2152 cm(-)(1) range found for the fully oxidized enzymes. Bands that can be assigned with some certainty as Fe-CN vibrations in partially and fully reduced enzymes do not appear to correspond to Fe(III)-NC-Cu(I) and Fe(II)-NC-Cu(I) bridges but rather to Fe(II)-CN modes. The current work complements and extends our previous investigation (Scott and Holm, J. Am. Chem. Soc. 1994, 116, 11357) of linear and nonlinear Fe(III)-CN-Cu(II) bridges and is part of an investigation directed at providing a molecular basis of cyanide toxicity. (MeNpy(2) = bis(2-(2-pyridylethyl))methylamine; Npy(3) = tris(2-pyridylmethyl)amine; OEP = octaethylporphyrinate(2-), OEP-CH(2)CN = N-(cyanomethyl)octaethylporphyrinate(1-).)

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Section: Resultsmentioning

confidence: 99%

Molecular Heme−Cyanide−Copper Bridged Assemblies: Linkage Isomerism, Trends in ν_CN Values, and Relation to the Heme-a₃/Cu_B Site in Cyanide-Inhibited Heme−Copper Oxidases

1998

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“…The most detailed information about linkage isomerization induced by cyanometalation is for the Hg 2+ and Ag + metalates of cyano-Cr(III) complexes. , These appear to be fairly slow processes, with half-lives ranging from minutes for the pentaaquo complex 73 to many hours for cis -Cr(en) 2 (CN) 2 + . The isocyanide linkage isomers, Cr III −(NC - )−M n + , appear to dissociate relatively rapidly into Cr(III) hydrolysis products. − The Cr III −(CN - )−Ru II complexes discussed here are reasonably stable materials that can be reproducibly synthesized and characterized, and they show no spectroscopic signs of decomposition in deaerated solutions for periods of an hour or so. We have previously noted that CN - -stretching region of the IR spectrum is a good indication of the quality of the cyanoruthenate.…”

Section: Resultsmentioning

confidence: 99%

“…The most detailed information about linkage isomerization induced by cyanometalation is for the Hg 2+ and Ag + metalates of cyano-Cr(III) complexes. 73,74 These appear to be fairly slow processes, with half-lives ranging from minutes for the pentaaquo complex 73 to many hours for cis-Cr(en) 2 -(CN) 2 + . 74 The isocyanide linkage isomers, Cr III -(NC -)-M n+ , appear to dissociate relatively rapidly into Cr(III) hydrolysis products.…”

Section: Resultsmentioning

confidence: 99%

“…74 The isocyanide linkage isomers, Cr III -(NC -)-M n+ , appear to dissociate relatively rapidly into Cr(III) hydrolysis products. [72][73][74] The Cr III -(CN -)-Ru II complexes discussed here are reasonably stable materials that can be reproducibly synthesized and characterized, and they show no spectroscopic signs of decomposition in deaerated solutions for periods of an hour or so. We have previously noted that CN --stretching region of the IR spectrum is a good indication of the quality of the cyanoruthenate.…”

Section: Resultsmentioning

confidence: 99%

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Ground-State, Mode-Dependent Vibronic Coupling in Some Simple, Cyanide-Bridged Transition-Metal Donor−Acceptor Complexes

1999

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Patterns of the shifts in bridging cyanide-stretching frequencies have been examined in several fully saturated, &mgr;-cyano, bi- or trimetallic transition-metal donor-acceptor (D/A) complexes. An earlier (Watzky, M. A.; et al.Inorg. Chem. 1996, 35, 3463) inference that the bridging ligand nuclear and the D/A electronic coordinates are entangled is unequivocally demonstrated by the 32 cm(-)(l) lower frequency of nu(CN) for (NH(3))(5)Cr(CNRu(NH(3))(5))(4+) than for the cyanopentaamminechromium(III) parent. This contrasts to the 41 cm(-)(1) increase in nu(CN) upon ruthenation of (NH(3))(5)RhCN(2+). More complex behavior has been found for cis and trans trimetallic, donor-acceptor complexes. The symmetric combination of CN(-) stretching frequencies in trans-Cr(III)(MCL)(CNRu(II)(NH(3))(5))(2)(5+) complexes (MCL = a tetraazamacrocyclic ligand) shifts 100-140 cm(-)(1) to lower frequency, and the antisymmetric combination shifts less than about 30 cm(-)(1). This contrast in the shifts of the symmetric and the antisymmetric combinations of the CN stretches persists even in a trans complex with no center of symmetry. Two CN stretches have also been resolved in an analogous cis complex, and both shift to lower frequency by about 60 cm(-)(1). The net shift, summed over all the CN-stretching frequencies, is about the same for the bis-ruthenates of related dicyano complexes. A simple, symmetry-adapted perturbation theory treatment of the coupled vibrations is employed to deal with the opposing effects of the "kinematic" shifts (delta) of nu(CN) to higher frequency, expected in the absence of D/A coupling, and shifts ( f ) of nu(CN) to lower frequency that occur when D/A coupling is large. The Rh(III)- and Cr(III)-centered complexes correspond to different limits of this model: delta > f and delta < f, respectively. When referenced by means of this model to complexes with Rh(III) acceptors, the shifts in trimetallic complexes, summed over the symmetric and antisymmetric combinations of CN stretches, are about twice those of bimetallic complexes. Similarly referenced and summed over all bridging CN frequencies, the shifts of nu(CN) to lower energies are proportional to the oscillator strength of the electronic, donor-acceptor charge-transfer transition. The simplest interpretation of this correlation is that the donor-acceptor coupling in these systems is a function of the nuclear coordinates of the bridging ligand. This behavior of these complexes is semiquantitatively consistent with expectation for CN(-)-mediated vibronic (pseudo-Jahn-Teller) coupling of neighboring donors and acceptors, and the observed Ru(II)/CN(-) CT absorption parameters can be used in a simple, semiclassical vibronic model to predict shifts in nu(CN) that are in reasonable agreement with those observed.

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“…The intermediate dicyano product for CetMe3NBr and TX appears to undergo a linkage isomerization to the C-bound stable product. Such isomerizations are common for Cr(III) (Espenson and Bushey, 1971) where a CrNC2+ CrCN2+ occurs by a Cr-N cleavage, followed by a rotation to a transition state that is likely stabilized by bonding between the d orbitals of appropriate symmetry on the metal and the orbitals on CN-. It has been suggested (Awad and Badra, 1967) that a linkage isomerization occurs with metmyoglobin if the attacking agent is HCN, hence PFe + HCN ^PFe-NC + H+ and PFeNC -* PFeCN, whereas PFe + CN--» PFeCN, directly.…”

Section: Discussionmentioning

confidence: 99%

Hemin intercalated in micellar cetyltrimethylammonium bromide and Triton X-100. Kinetic, spectral, and equilibrium study with cyanide

Simplicio¹,

Schwenzer²

1973

Biochemistry

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Kinetic studies on the formation of a cyanide-bridged adduct of two cationic metal complexes

Cited by 17 publications

References 1 publication

Molecular Heme−Cyanide−Copper Bridged Assemblies: Linkage Isomerism, Trends in ν_CN Values, and Relation to the Heme-a₃/Cu_B Site in Cyanide-Inhibited Heme−Copper Oxidases

Molecular Heme−Cyanide−Copper Bridged Assemblies: Linkage Isomerism, Trends in ν_CN Values, and Relation to the Heme-a₃/Cu_B Site in Cyanide-Inhibited Heme−Copper Oxidases

Ground-State, Mode-Dependent Vibronic Coupling in Some Simple, Cyanide-Bridged Transition-Metal Donor−Acceptor Complexes

Hemin intercalated in micellar cetyltrimethylammonium bromide and Triton X-100. Kinetic, spectral, and equilibrium study with cyanide

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Kinetic studies on the formation of a cyanide-bridged adduct of two cationic metal complexes

Cited by 17 publications

References 1 publication

Molecular Heme−Cyanide−Copper Bridged Assemblies: Linkage Isomerism, Trends in νCN Values, and Relation to the Heme-a3/CuB Site in Cyanide-Inhibited Heme−Copper Oxidases

Molecular Heme−Cyanide−Copper Bridged Assemblies: Linkage Isomerism, Trends in νCN Values, and Relation to the Heme-a3/CuB Site in Cyanide-Inhibited Heme−Copper Oxidases

Ground-State, Mode-Dependent Vibronic Coupling in Some Simple, Cyanide-Bridged Transition-Metal Donor−Acceptor Complexes

Hemin intercalated in micellar cetyltrimethylammonium bromide and Triton X-100. Kinetic, spectral, and equilibrium study with cyanide

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Molecular Heme−Cyanide−Copper Bridged Assemblies: Linkage Isomerism, Trends in ν_CN Values, and Relation to the Heme-a₃/Cu_B Site in Cyanide-Inhibited Heme−Copper Oxidases

Molecular Heme−Cyanide−Copper Bridged Assemblies: Linkage Isomerism, Trends in ν_CN Values, and Relation to the Heme-a₃/Cu_B Site in Cyanide-Inhibited Heme−Copper Oxidases