Properties Of Cp Research Articles

Luminescent ligand-to-metal charge-transfer excited states based on pentamethylcyclopentadienyl complexes of tantalum

Understanding of the photochemistry and photophysics of complexes with metal-to-ligand charge-transfer (MLCT) excited states has developed rapidly, evolving to the point that application to energy conversion processes is now a predominant focus. This success can be traced directly to an understanding of the photophysics and photochemistry of complexes of the type M (bpy){sub 3}{sup n+ } (M is Ru, n is 2; M is Os, n is 2; M is Ir, n is 3) and M(bpy){sub 2}L{sub 2}{sup 2+} (M is Ru and Os, and L can be a variety of neutral 2-electron donor ligands), which has reached a level of sophistication so that design of chemically stable photosensitizers with prescribed excited-state lifetimes and redox potentials can be realized by synthetic manipulation of the coordination sphere. Despite this success, there exists a whole class of complexes whose excited-state properties has been largely ignored-those containing ligand-to-metal charge transfer (LMCT) excited states. Early examples of photochemical reactions from LMCT excited states are found in the classical series Co {sub III} (NH{sub 3}){sub 5}X{sup 2}, where charge transfer from halide to Co(III) results in photoreduction to Co(II) and the formation of halide radicals. To discover new LMCT excited states, complexes which contain oxidizablemore » donor ligands coordinated to early or middle transition metal of d{sup 0} like Ta(V) were investigated. Reported are the excited-state properties of the complex Cp*TaCl{sub 4} and the derivative Cp*TaCl{sub 3}(OO) (where OO is a bidentate oxygen donor such a a corboxylic or sulfonic acid) which exhibit long-lived luminescence in fluid solution and can have quantum efficiencies for emission of up to 16% (at 23 degrees C). For each complex, the photophysical parameters are included.« less

Organometallic nitrosyl chemistry. 53. Synthesis, characterization, and properties of 16-electron Cp*M(NO)(aryl)2 (M = molybdenum, tungsten) complexes

Organometallic nitrosyl chemistry. 53. Synthesis, characterization, and properties of 16-electron Cp*M(NO)(aryl)2 (M = molybdenum, tungsten) complexes

ChemInform Abstract: η2 Coordination of Si‐H σ Bonds to Transition Metals

Publisher Summary This chapter discusses the η 2 coordination of Si–H σ bonds to transition metals. The first complexes of type Cp(OC) 2 Mn(H)SiR 3 (R = Ph, C1) were prepared by Jetz and Graham by the photochemical reaction of Cp(OC) 3 Mn with the corresponding silanes HSiR 3 . From the very beginning, it was realized that some properties of the complexes CP(OC) 2 Mn(H)SiR 3 are different from those of other hydrido silyl complexes and that the silane moiety was bonded in an unusual way. The first structural evidence for an Si–H interaction in complexes of the type Cp(OC) 2 Mn(H)SiR 3 was obtained for the SiPh 3 derivative. On the basis of the structural data, the two CO ligands in the dicarbonyl complexes would be expected to be inequivalent. Photoelectron (PE) spectra provide direct and quantitative information on the electron distribution within a compound. Recent investigation of the PE spectra of a number of MeCp(OC) 2 Mn(H)SiR 3 derivatives confirmed the theoretical results. Both the chemical behavior and crystal structure of Cp(OC) 2 Re(H)SiPh 3 indicate that, contrary to the corresponding manganese complexes, there is no metal–hydrogen–silicon three-center bond.

Reversible electron-transfer properties of the titanium(II) organometallic species (Cp)2Ti(bpy)

The electrochemical and spectroelectrochemical properties of (Cp){sub 2}Ti(bpy) in tetrahydrofuran (THF) with tetrabutylammonium perchlorate (TBAP) as supporting electrolyte are presented. This formal Ti(II) species exhibits four reversible electron-transfer reactions on the cyclic voltammetric time scale.

Topological excitations and phase transition hierarchy in strongly correlated electronic systems

The ground state structure and topological properties of CP' field with finite action and a fractional charge are considered in 2+1 system of strongly correlated particles. It is concluded that a holon and a spinon are different states of an anyon. To describe the phase structure of the antiferromagnetic Heisenberg model with the Chern-Simons term I introduce the lattice loop model mapped into discrete Gaussian Zp model of an effective spin with frustrations. At low temperatures there is an electric charge Bose condensate, in the intermediate temperature region there exists a Coulomb phase with long-range interactions and at high temperatures there is a confinement phase of topological charges (magnetic charge Bose condensate) and phases of oblique confinement of dyons.

A model of the surface and catalytic activity of supported bimetallic Fe- and Co-containing complexes in CO+H 2, synthesis reactions

The catalytic properties of the complexes Cp(CO) 2Fe-Co(CO) 4 ( I), Cp(CO) 2Fe-Fe(CO) 2Cp ( II) and Ph 2Co 2(CO) 6 ( III), and of Fe(CO) 5 + Co 2(CO) 8 ( IV), Fe(CO) 5 ( V) and Co 2(CO) 8 ( VI) carbonyls supported on γAl 2O 5 in the CO hydrogenation reaction at atmospheric pressure and 220–280 °C have been studied. The ratios of Fe and Co metallic and ionic forms formed by interaction of the complexes with the support before and during the catalytic reaction were measured by means of Mössbauer spectroscopy and magnetic susceptibility. It was found that catalysts prepared from complex I exhibited both the high catalytic activity characteristic of catalyst III and the high selectivity in olefin production typical of catalyst II. In contrast, although the catalysts produced from a mixture of carbonyls ( IV) showed quite high activity comparable with that of sample VI, they exhibited a very low selectivity towards olefins. Mössbauer and magnetic susceptibility data showed that a Fe/Co-intermetallic phase was formed as a result of the interaction of complex I with γ-Al 2O 3, while such a phase was not present in catalysts derived from the mixture of carbonyls ( IV). Samples I and II are characterized by higher Fe 2+/Fe 3+ ratios relative to that in sample IV where oxidation of Fe 2+ to Fe 3+ took place under the reaction conditions. The mechanism of formation of metallic and ionic form on the catalyst surface is discussed.

On the novel H 2-activating iron-sulfur center of the “Fe-only” hydrogenases

The two hydrogenases (I and II) of the anaerobic N2-fixing bacterium Clostridium pasteurianum (Cp) and the hydrogenases of the anaerobes Megasphaera elsdenii (Me) and Desulfovibrio vulgaris (strain Hildenborough, Dv), contain iron-sulfur clusters but not nickel. They are the most active hydrogenases known. All four enzymes in their reduced states give rise to EPR signals typical of [4Fe-4S]1+ clusters but exhibit novel EPR signals in their oxidized states. For example, Cp hydrogenase I exhibits a sharp rhombic EPR signal when oxidized under mild conditions but the enzyme is inactivated by over-oxidation and then exhibits an axial EPR signal. A similar axial signal is observed from mildly oxidized hydrogenase I after treatment with CO. EPR, Mössbauer and ENDOR spectroscopy indicate that the EPR signals from the oxidized enzyme and its CO derivative arise from a novel spin-coupled Fe center. Low temperature magnetic circular dichroism (MCD) studies reveal that an EPR-silent Fe-S cluster with S greater than 1/2 is also present in oxidized hydrogenase I. From a study of all spectroscopic properties of Cp, Dv, and Me hydrogenases, it is concluded that the H2-activating site of all four is a novel Fe-S cluster with S greater than 0 and integer, which in the oxidized state is exchange-coupled to a S = 1/2 species. The data are most consistent with the S = 1/2 species being a low spin Fe(III) center. The H2-activating site is susceptible to oxidative rearrangements to yield both active and inactive states of the enzyme. We discuss the possible implications of these finding to methods of enzyme oxidation and purification procedures currently used for hydrogenases.

Darstellung und Struktur einiger η5 -Cyclopentadienyldicarbonyleisenbismut-Verbindungen Cp(CO)2 FeBiX2 mit fünffach koordiniertem Bismutatom/Synthesis and Structure of Some η5 -Cyclopentadienyldicarbonylironbismuth Compounds Cp(CO)2 FeBiX2 with Five-Coordinated Bismuth Atoms

Abstract The synthesis and the spectroscopic properties of the title compounds Cp(CO)2FeBiX2 (with X = SC(S)NEt 2 and SC(S)OMe) are described. The crystal structure of Cp(CO)2FeBi[SC(S)NEt2]2 was investigated by an X-ray analysis.

Properties of general classical CP n−1 solutions

The general classical solutions with finite action of the CP n−1 model are displayed. Various properties of the solutions such as topological charge, action, Bäcklund-like transformations and stability are discussed.

Formation of (η3‐methallyl) and (η4‐butadiene) ligands from (η1‐2‐buten‐1‐yl) coordinated to group IVB metals

AbstractThe synthesis and some properties of the novel triallyl compounds Cp*M(CH2CHCHCH3)3 (Cp*=η5‐C5(CH3)5; M=Ti, Zr or Hf ) and the butadiene‐methallyl compounds Cp*M(η4‐butadiene) (η3‐methallyl) therefrom are reported. The compounds are very reactive towards carbon monoxide and other small molecules.

On the interaction of cyclopentadienyltitanium(IV) chlorides with lithium aluminium hydride

The interactions in the systems Cp 2TiCl 2/LiAlH 4 and CpTiCl 3/LiAlH 4 have been studied by calorimetric titration and EPR techniques. There are four steps to each of these reactions corresponding to the following Cp 2TiCl 2 (CpTiCl 3) to LiAlH 4 ratios: 2/1 (reduction of titanium(IV) to titanium(III) and formation of trinuclear complexes Cp 2TiH 2AlCl 2 · Cp 2TiCl or Cp(Cl)TiH 2AlCl 2 · CpTiCl 2), 1/1 (formation of dimers [Cp 2TiH 2AlH(Cl)] 2 or [Cp(Cl)TiH 2AlH(Cl)] 2), 1/1.5 (replacement of a terminal chloro atom in the dimers and formation of (Cp 2TiH 2) 2Al 2H 3Cl or (Cp(Cl)TiH 2) 2Al 2H 3Cl), and 1/2 (replacement of the remaining terminal chloro atom, dissociation of dimers and formation of unstable triple complexes Cp 2TiH 2AlH 2 · AlH 3 or Cp(Cl)TiH 2AlH 2 · AlH 3). The catalytic properties of the system Cp 2TiCl/LiAlH 4 in the hydrogenation of cyclohexene and hex-1-ene are described.