Binuclear Systems Research Articles

The Structure of the D. gigas [NiFe] Hydrogenase and the Nature of the Hydrogenase Nickel Complex

Several surprises came to light in the recent single‐crystal X‐ray structural determination of a [NiFe] hydrogenase by Volbeda et al. For example, the Ni fraction of the enzyme clearly forms part of an unprecedented cysteine‐bridged heterometallic binuclear system. In retrospect, the feasibility of such a structural motif is evident from the known coordination chemistry of nickel thiolate complexes. But the mechanism of H2 oxidation by this NiFe(?) complex remains tantalizingly opaque and continues to challenge bioinorganic chemists.

Monte Carlo simulations of spin-crossover transitions using the two level model. II: Binuclear case

We show preliminary results of the Monte Carlo simulations on spin-crossover binuclear systems. The two-level Ising-like model was used with two interaction parameters: intermolecular (‘ferro’) and intramolecular (‘antiferro’). The obtained two step transitions are analysed in term of LS-LS, LS-HS HS-1HS populations.

Synthesis and solid-state structural characterization of N,N′-dicyclohexyldithiooxamide complexes of HgX2(X = SCN or Cl)

N,N′-Dicyclohexyldithiooxamide (H2L) reacted with HgX2(X = SCN or Cl) to form the novel mercury mixed-ligand complexes [Hg(H2L)(SCN)2]1, [HgCl2(H2L)]2 and [{HgCl2(H2L)}2]·EtOH 3. The crystal and molecular structures of 1 and 3 have been determined. Crystals of 1 are monoclinic, space group P21/n(no. 14), with a= 11.318(1), b= 17.727(2), c= 11.536(2)A, β= 109.08(2)° and Z= 4. Crystals of 3 are monoclinic, space group P21(no. 4), with a= 8.563(1), b= 21.414(3), c= 11.649(2)A, β= 103.58(2)° and Z= 2. The structures were each refined by a full-matrix least-squares procedure to R1 = 0.031 for 2218 reflections with F2 2.0σ(F2) for 1 and R1 = 0.047 (2374 reflections) for 3. Complex 1 is mononuclear with HgS4 units linked by short intermolecular S ⋯ S interactions. Complex 3 is a binuclear zwitterionic system with one S,S′-chelating H2L ligand bonded to a mercury atom and a second ligand acting in an unusual' conformation as a S,S′-bidentate bridging group between the ionic species HgS2Cl+ and HgCl3–. The two mercury atoms are separated at a non-interacting distance. The infrared spectra of the complexes in the range 650–200 cm–1 are discussed in the light of the known structures.

Properties of the mixed-valence binuclear complex ion, (NH 3) 5Ru III-NC-Os II(CN) 5] −

The mixed-valence ion, [(NH 3) 5Ru III-NC-Os II(CN) 5] −, was prepared in solution from [Ru(NH 3) 5H 2O] 3+ and [Os(CN) 6] 4− and was isolated as a potassium salt. A kinetic study of the formation reaction shows that a dissociative mechanism is operative, the process being rate-controlled by the loss of water from the Ru(III) moiety, as in related reactions with [Fe(CN) 6] 4− and [Ru(CN) 6] 4−. The binuclear ion shows a distinctive intervalence band, associated to charge transfer from Os(II) to Ru(III), at 830 nm (ϵ=3450 M −1 cm −1), with a noticeable asymmetry, probably associated to spin-orbit coupling. Shifts in the redox potentials at the metal centers on dimer formation are consistent with the Os(II)-Ru(III) formulation. By measuring solution Raman spectra in post-resonance conditions with respect to the IT band, activation of the bridging CN stretching, as well as of the terminal stretching modes, is observed; absolute distortion values for both of the modes can be calculated by applying a time-dependent analysis of the scattering problem. IR and Raman results of the solid samples are also presented. Theoretical models were applied to IT data, allowing an estimation of the delocalization parameter, α 2, and the electronic coupling parameter, H AB. The results are compared with other valence-trapped binuclear systems.

Charge-transfer states of bridged transition metal dimers: mono- vs binuclear copper azide systems with relevance to oxy-hemocyanin

The charge-transfer (CT) spectra of transition metal complexes show characteristic changes upon dimer formation. This study focuses on the (π nb )→Cu CT transitions of Cu azide systems which each split into two transitions if coordination to one copper center is replaced by bridging to two copper centers. In addition, a shift of the in-plane (π nb ) σ →Cu CT transitions of the azide systems to lower energy is observed in the dimer spectrum. This shift is ascribed to a strong antiferromagnetic interaction in the CT excited state which is due to coupling of one electron in the bridging orbital with one unpaired electron on a copper center

Hush theory in a copper mixed valence bioinorganic model generated photochemically

In the present study a copper mixed valence (MV) compound has been generated photochemically from the (CH 3COO) 2Cu(II)Cu(II)(OOCCH 3) 2 dimeric species in 95/5% (vol./vol.) methanol/acetic acid mixture as solvent. The MV species shows two intervalence (IT) bands at 19.6 and 10.4 kK and seven complex lines in the EPR spectra at room temperature. Although the two bands are IT bands in character, only the second (960 nm) could be related through the Hush and Hopfield theories to a thermal electron transfer process between the copper centers with kinetic parameters Δ G #=21.6 kJ mol −1 and k th=1.2×10 9 s −1 (Hush) or 4.0×10 11 s −1 (Hopfield) at 298 K and related to the change from (d x 2− y 2 ) 2Cu(I)(d x 2− y 2 )Cu(II) to (d x 2− y 2 ) 1Cu(II)(d x 2− y 2 ) 2Cu(I) electronic configuration ( D 4 h symmetry for each copper center). The electronic assignation of the more energetic band is also discussed. The value obtained for k th is in the range measured by EPR spectroscopy for other Cu(II)Cu(I) dimeric systems and provides evidence for the validity of the essence of the theoretical approach in copper binuclear systems although the value for the electronic coupling parameter is relatively high. The complex studied in this work has some characteristics in common with those of the type III copper observed in copper oxidases in its MV state such as: dimeric structure with tetragonal environment for the coppers, with oxygen perhaps as bridging ligand, EPR signal related to one unpaired electron interacting with both coppers and with k th values which compare well with some biological systems; so we believe it is a good bioinorganic model for type III copper in multicopper oxidases.

A binuclear manganese system with three isolated oxidation states: synthesis, structures, and properties of molecules with a Mn2(OR)2 bridge unit containing MnIIIMnIII, MnIIIMnII, and MnIIMnII

A binuclear manganese system with three isolated oxidation states: synthesis, structures, and properties of molecules with a Mn2(OR)2 bridge unit containing MnIIIMnIII, MnIIIMnII, and MnIIMnII

A binuclear non-heme iron oxo-transfer analog reaction system: observations and biological implications

A binuclear non-heme iron oxo-transfer analog reaction system: observations and biological implications

Ein neuer koordinationstyp bei acyclischen phosphaalkenen: F 3CPC(F)NMe 2 als (η 1-μ 2) 4e-donator

The chromium complex Cr(CO) 5[F 3CPC(F)NMe 2] ( 2) in chloroform solution is slowly transformed at room temperature to give the binuclear system [(CO) 5Cr] 2[F 3CPC(F)NMe 2] ( 3) besides the C-amino substituted phosphaalkene F 3CPC(F)NMe 2 ( 1). The yield of this process amounts to 21% within 6 months. The X-ray diffraction analysis of 3 reveals a so far unknown coordination mode of acyclic phosphaalkenes: 1 operates as (η 1-μ 2) 4e donor.

Binuclear copper(II) complexes of 1,4,7-trimethyl-1,4,7-triazacyclononane: synthesis, spectroscopy, and spin coupling across multiple-atom bridges of variable length (3.6–7.6 Å)

Thirteen new binuclear copper(II) complexes [LCu(µ-X)CuL]2+ with L = 1,4,7-trimethyl-1,4,7-triazacyclononane and X = 2Cl–, 2Br–, 2SCN–, C2O42–, (HN)2C2O22–, Cl2C6O42–, H2C6O42–, and 2CH3CO2– have been synthesized and characterized based on i.r., electronic, and e.s.r. spectroscopy and variable-temperature (100–300 K) magnetic susceptibility measurements. A varying range of magnetic interactions, no coupling, antiferromagnetic (2J=–460 cm–1), and ferromagnetic (J=+22 cm–1) coupling, has been observed between the copper(II) ions in these binuclear systems with variable metal–metal separation estimated to be in the range of 3.6–7.6 A. The interaction is more effective through a µ-oxamato bridge (2J=–460 cm–1) than through a µ-oxalato bridge (2J=–300 cm–1). A moderately strong antiferromagnetic interaction (2J=–60 cm–1) has been found for the Cl2C6O42-bridged compound, where the Cu ⋯ Cu separation is expected to be ≈ 7.6 A. The X-band e.s.r. spectra of the polycrystalline substances at 120 K indicate square-pyramidal geometry for the copper with a (dx2– y2)1 ground state. A mixed bridged compound (µ-1,1 -N3)(µ-OH), with a ferromagnetic interaction between the copper centres is also described. The difference in magnetic exchange interaction between the different copper(II) systems is discussed.

A binuclear mixed-valence ferromagnetic iron system with an S = 9/2 ground state and valence trapped and detrapped states

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTA binuclear mixed-valence ferromagnetic iron system with an S = 9/2 ground state and valence trapped and detrapped statesK. K. Surerus, E. Munck, B. S. Snyder, and R. H. HolmCite this: J. Am. Chem. Soc. 1989, 111, 14, 5501–5502Publication Date (Print):July 1, 1989Publication History Published online1 May 2002Published inissue 1 July 1989https://doi.org/10.1021/ja00196a086RIGHTS & PERMISSIONSArticle Views191Altmetric-Citations29LEARN 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 (274 KB) Get e-Alerts Get e-Alerts

Binuclear iron system ferromagnetic in three oxidation states: synthesis, structures, and electronic aspects of molecules with a Fe2(OR)2 bridge unit containing Fe(III,III), Fe(III,II), and Fe(II,II)

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTBinuclear iron system ferromagnetic in three oxidation states: synthesis, structures, and electronic aspects of molecules with a Fe2(OR)2 bridge unit containing Fe(III,III), Fe(III,II), and Fe(II,II)Barry S. Snyder, George S. Patterson, Andrew J. Abrahamson, and Richard H. HolmCite this: J. Am. Chem. Soc. 1989, 111, 14, 5214–5223Publication Date (Print):July 1, 1989Publication History Published online1 May 2002Published inissue 1 July 1989https://doi.org/10.1021/ja00196a031RIGHTS & PERMISSIONSArticle Views452Altmetric-Citations98LEARN 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 (1 MB) Get e-AlertsSupporting Info (1)»Supporting Information Supporting Information Get e-Alerts

Koordinationsambivalenz und fluktuierendes Verhalten bei ein- und zweikernigen Wolframpentacarbonyl-Komplexen des Pteridins und seiner Deazaderivate

The mono- and binuclear pentacarbonyltungsten complexes of highly ambidentate pteridine (1,3,5,8-tetraazanaphthalene), the parent heterocycle of the biochemically important pterins, and of its deaza derivatives 1,5-naphthyridien, 1,4,5- and 1,4,6-triazanaphthalene have been synthesized. Unambiguous identification of coordination sites was only possible by use of high resolution 1H NMR because the chemical shifts and spin-spin coupling constants are characteristically affected by W(CO) 5-coordination to neighbouring nitrogen centers. Fluxional behaviour with respect to the peri coordination sites was observed for the mononuclear complex of 1,4,5-triazanaphthalene and for the binuclear pteridine system, competition between the more basic pyridine or pyrimidine and the better π backdonating pyrazine N centers leads to various positions for the non-degenerate equilibria between linkage isomers. Cyclic voltammetry and solvent-dependent charge transfer absorption spectra of the complexes reveal low-lying π* levels which can become populated after chemical or electrochemical reduction, the spin distribution in the centrosym-metric binuclear complex of 1,5-naphthyridine anion radical has been fully characterized using ESR and results from molecular orbital calculations.

Complexes of platinum(II) containing 2,2′-bithiazoline and 2,2′-bipyrimidine as binucleating ligands

Dimethyl and diphenyl platinum(II) complexes containing binucleating α-diimine ligands BN (BN = 2,2′-bithiazoline and 2,2′-bipyrimidine) have been isolated and characterized. Electrophilic attack of mercuric chloride on the mononuclear compounds leads to binuclear systems of C 2 v symmetry, with the two chelating moieties of the ligands occupied by platinum and mercury, respectively. 1H NMR spectroscopy suggests a large transmission of electronic effects between the metals through the ligands.

Reactivity of bridging hydrocarbyl ligands in binuclear systems

Hydrocarbyl ligands bridging heteronuclear transition metal centres display a wide range of reactivity, especially with respect to the formation of carbon—hydrogen and carbon—carbon bonds. This article summarizes progress made in this area by Prof. F. G. A. Stone and coworkers at the University of Bristol.

A [MnIII2O(MeCO2)2(H2O)2(bipy)2]2+(bipy = 2,2′-bipyridine) unit with accessible co-ordination sites. Contribution to the modelling of the photosynthetic oxygen evolving centre

A new MnIII binuclear system with an oxo-bis(acetato) bridge and water co-ordinated to the Mn ions has been synthesized, crystallographically characterized, and its antiferromagnetic coupling measured (singlet–triplet gap 6·8 cm–1).

Ein- und zweikernige Bis(2,2′-bipyridyl)ruthenium-Komplexe mit N,O-Modelliganden für Dehydrogenase-Cofaktoren / Mono- and Binuclear Bis(2,2′-bipyridine)ruthenium Complexes with N,O-Ligands Modelling Dehydrogenase Cofactors

Abstract Coordination of substitutionally inert [Ru(bpy)2]2+ fragments (bpy: 2,2′-bipyridine) to the a-iminoketone chelate ligands pyrazine-2-dimethylcarboxamide (4) and 4,7-phenanthroline-5,6-dione (5) yields the complexes [(N,O-4)Ru(bpy)2]2⊕, [(O,O′-5⊖)Ru(bpy)2]⊕ and {(N,O; N′,O′-5)[Ru(bpy)2]2}4⊕ which exhibit a rich electrochemistry. The distinctly different electronic structures of the complexes are evident from the ESR behaviour of paramagnetic intermediates: N.O-coordinated complexes have the unpaired electron residing in the ligand n system upon reduction, albeit with g<2 for the binuclear complex of 5. The paramagnetic O,O′-coordinated mononuclear complex with 5 has its redox potentials shifted positively relative to that of the binuclear system. These results are particularly noteworthy because 4 and 5 can be regarded as model compounds for the flavin and methoxatin dehydrogenase cofactors.

Solvent reorganization in optical and thermal electron-transfer processes

Dielectric continuum models used to calculate the solvent reorganization energy in thermal and photochemical electron-transfer reactions are discussed. Expressions are derived for the reorganization energy for charge redistribution within a single ellipsoidal or spherical solvent cavity. The expressions for the ellipsoidal cavity model differ in important respects from those derived previously. The Marcus two-sphere and the ellipsoidal cavity model differ in important respects from those derived previously. The Marcus two-sphere and the ellipsoidal cavity models can satisfactorily predict the band maximum for the metal-to metal charge-transfer transition in a number of ion-paired and bridged binuclear systems, provided careful consideration is given to the cavity dimensions. In complexes containing 2,2'-bipyridine ligands the solvent can approach close to the charge centers by filling the space between the ligands: this results in a small effective radius and relatively large values for the solvent reorganization energy. On the other hand, in complexes containing ammine ligands the effective radius is increased due to the effects of dielectric saturation resulting from specific ligand interactions with the solvent. Despite the limitations of the two-sphere model the reorganization energies calculated are, in general, not very different from those obtained with the ellipsoidal cavity model.

ChemInform Abstract: Hydrogen Migration in Transition Metal Alkyne and Related Complexes.

AbstractZur Diskussion des Mechanismus werden die elektronischen und strukturellen Charakteristika der Umlagerungsreaktion eines 1‐Alkin‐Komplexes in einen Vinyliden‐Komplex über eine 1,2‐Wasserstoffverschiebung untersucht.

Hydrogen Migration in Transition Metal Alkyne and Related Complexes

AbstractThe electronic and structural characteristics of the reaction interconverting a l‐alkyne complex into a vinylidene via a 1,2 hydrogen shift are examined. In a mononuclear system, initial slippage of the alkyne to an η1 geometry is indicated. The subsequent step is shown to be analogous to the isomerization of a methylvinyl cation. We conclude that an alternative route involving a hydrido‐acetylide species will be of much higher energy. A concerted shift in binuclear and trinuclear systems is ruled out, based on the loss of a strong bonding interaction between the alkyne and the metallic piece, in the transition state. In trinuclear systems, a mechanism for the isomerization is suggested involving prior oxidative addition of the CH bond across a metal‐metal bond. The metallic piece in this case assists the transformation. The discussion is extended to other reactions featuring hydrogen shifts; these include the intramolecular formation of a binuclear vinylidene from a 1,2‐hydrido‐acetylide complex, the isomerization of a binuclear μ‐alkylidyne into a μ‐vinyl geometry and the transfer of a bridging hydrogen onto a capping hydrocarbon fragment in trinuclear cluster complexes.