Andreas Ludi

Structure, Reactivity, Spectra, and Redox Properties of Cobalt(III) Hexaamines

Publisher Summary This chapter discusses the effect of structural properties of cobalt (III) hexa-amines on their other properties. The chapter discusses complexes ranging from cobalt hexa-ammine, to complexes composed of three secondary and three tertiary amine donors. The chapter discusses only those coordination compounds, having a complete CoN 6 core, thus excluding the enormous number of CoN 6 - x L x complexes. Ammonia and organic amines with an aliphatic skeleton are described in the chapter. The chapter discusses complexes, containing just one kind of ligand—that is, homoleptic complexes. Structural properties and their relationship to kinetic stability (toward hydrolysis and racemization), electronic structure, reduction potentials, and electron transfer processes are explained in this chapter. The standard preparative procedure for the Co(III)–amine complexes consist of the reaction of an aqueous or alcoholic solution of a Co(II) salt with the free base of the amine. Oxidation in the solution is achieved by air, oxygen, H 2 0 2 , or other oxidants. In this chapter, the term molecular mechanics describes a method used frequently to predict structures and relative energies of related complexes (usually isomers). The method involves summing the potential energy of all the interatomic interactions in terms of bond deformation, valence angle deformation, torsion angle deformation, and nonbonded interactions. The chapter discusses the effects of structure on the other properties of the amine complexes predominantly in terms of the steric effects.

Electronic spectra of M(bipy)2+3 complexions (M = Fe, Ru and Os)

Abstract Linearly polarized absorption spectra of the complex ions M(bipy) 2+ 3 (M = Fe, Ru, Os) have been determined, together with the CD of the corresponding optical isomers at low temperature. The visible electronic spectra have been assigned to spin-allowed and spin-forbidden charge transfer as well as ligand-localized singlet to triplet transitions. The structure of the intense visible absorption band is due to two electronic transitions.

The Creutz-Taube complex revisited

Les structures cristallines obtenues par rayons X et spectres Mossbauer ont ete enregistres pour 3 complexes binucleaires du type [(NH 3 ) 5 Ru(pyz)Ru(NH 3 ) 5 ] n+ avec n=4, 5, 6 et pyz=pyrazine. Pas plus la structure que les spectres Mossbauer ne peuvent etre decrits comme une moyenne des especes oxydees (n=6) et reduites (n=4). Spectres RPE, electroniques IR et Raman

Ring opening metathesis polymerization of bicyclo [2.2.1] hept-2-ene (2-norbornene) and exo,exo-5,6-bis (methoxycarbonyl)-7-oxabicyclo [2.2.1]hept-2-ene using Ru(II) and Ru(III) complexes: Polymerization kinetics and ruthenium content in polymers

Abstract Bicyclo [2.2.1]hept-2-ene (2-norbornene, 1) and exo,exo-5,6-bis (methoxycarbonyl)-7-oxabicyclo [2.2.1]hept-2-ene (2) were polymerized with the Ru complexes [Ru(H2O)6]tos2, [Ru(II)(η6-benzene) (H2O)3]tos2 (to=p-toluenesulfonate) and RuCl3·3H2O. It is shown that the aqueous ROMP with these catalysts is not a living polymerization, since molecular weights are almost independent of the polymerization time and of the monomer to catalyst ratio. Molecular weight distributions are broad, typically more than 1.5–2. Yields depend strongly on both the monomer and the catalyst concentration, are difficult to reproduce and seldom reach values above 80–90%. These observations are explained by the proposed reaction mechanism, with a slow and sensitive initiation step followed by a fast propagation and termination by occlusion or blocking of the catalyst within the polymer. It was not possible to reduce the Ru content in these polymers below a certain level (250–300 ppm), which corresponds to ca. one Ru atom per polymer chain. Therefore complete recycling of the catalyst solutions is not possible due to catalyst depletion.

A modified synthesis of ruthenium(II) hexaaqua salts

Abstract An efficient preparation of ruthenium aqua ions starts from the hydrated dioxide. Oxidation by periodate produces ruthenium tetroxide which is reduced by metallic lead to [Ru(H2O)6]2+. Ion exchange and crystallization affords pure [Ru(H2O)6](tos)2 (tos = p-toluenesulphonate) in 70–80% yield.

Determination of the location and effective angular size of solar flares with a 210 GHz multibeam radiometer

We report on the study and successful application of an improved measurement method for solar flares at millimeter wavelengths. A 210 GHz multibeam receiver for the observation of solar bursts was installed in the KOSMA 3 m telescope on the Gornergrat. It consists of three radiometer channels, with a fourth beam synthesised from the other three. The four inter- secting beams allow measurements of source locations with arcsecond resolution and, for the first time, also the determination of the effective source size at short millimeter waves. The typical sensitivity of <1.5 sfu allows also the detection of weak flares at millisecond time resolution. In this paper we present the instrument and the numerical method for the determination of the source flux density, position and effective size, as well as simulations to asses the validity of the method. First observational results were obtained for the GOES X17.2 flare on October 28, 2003. The event reached a peak flux density of 11 000 sfu at 210 GHz and exhibited a slowly varying, time-extended emission from an extended source (effective diameter ≈ 60 arcsec), as well as a short-lived component from a compact source (<10 arcsec) originating from a different location.

Structure parameters for temperature and humidity from simultaneous eddy-covariance and scintillometer measurements

Line-averaged values of the structure parameters of temperature and humidity, CT2 and Cq2, were estimated from simultaneous measurements with an optical and a microwave scintillometer over a path of 4.7 km length at the Meteorological Observatory Lindenberg during the LITFASS-2003 experiment. By cross-correlating the detected signals of the two scintillometers, the temperature-humidity structure parameter, CTq, and the temperature-humidity correlation, rTq, were also derived directly from the measurements. Comparison with corresponding values obtained from local measurements with an eddy-covariance system on a meteorological tower show a consistent behaviour in time (with some exceptions especially for Cq2 and rTq during nighttime). The deviations are of a magnitude between 20 % and 35 % of the typical daytime values of the structure parameters.

Thermal- and photoinduced ring-opening metathesis polymerization (ROMP)/(PROMP): an efficient tool in polymer chemistry

Abstract Properties and applications of newly developed homogeneous ring-opening metathesis polymerization catalysts as well as photoinduced ring-opening metathesis polymerization catalysts are discussed. It is shown that simple alkyl complexes, e.g. [W(NPh)(CH 2 SiMe 3 ) 3 Cl] as well as [Ru(arene) 2 ] 2+ or [Ru(NC–R) 6 ] 2+ complexes act as one-component Photo-ROMP initiators. Catalysts with good thermal latency are described for both classes. High quantum yields are observed for the photochemically induced solvation of Ru(II) complexes. Polymer structure and kinetic aspects of the reaction are consistent with [Ru(solvent) 6 ] 2+ acting as the catalytically active species. The mechanism of aqueous ROMP with Ru(II) salts is discussed, which differs considerably from the classical ROMP reaction with Schrock-type catalysts in the sense that it is a chain reaction and not a living polymerization. Homo- and copolymers using exo-oxa-norbornene-carboximide ester derivatives were prepared with the ROMP technology and used, inter alia, to formulate very sensitive positive tone high-resolution microresists.

Synthesis and properties of the binuclear complexes and

The binuclear complexes (NC5FeLM(NH3)5 (L = 4,4′bipyridine, M =Ru, Rh) were prepared by the rapid reaction between M(NH3)5L3+ and Fe(CN)5OH3−2. The compound Na[(NC)5FeL′Ru(NH3)5] (L′ = pyrazine) was prepared by the reaction between Fe(CN)5NH3−3 and ru(NH3)5L2+. Oxidation of Na[(NC)5FeL′Ru(NH3)5] with cerium(IV) or peroxydisulfate yielded (NC)5FeL′Ru(NH3)5. The reaction between Fe(CN)5NH3−3 and Rh(NH3)5L′3+ produced (NC)5FeL′Rh(NH3)5. Cobalt analogs of the FeRu complexes were prepared by reaction of Co(CN)5OH3−2 with Ru(NH3)5L2+ and Ru(NH3)5LL′2+. The compounds were characterized by solid state spectroscopic measurements (KBr pellets) in the visible, near infrared, and infrared regions. The wavelengths of the maxima of the metal to ligand charge transfer bands, cyanide stretching bands and ammonia deformation bands of the title compounds, and comparisons with the corresponding bands of their rhodium and cobalt analogs, are used to assign a valence-trapped formulation with localized iron(II) and ruthenium(III) oxidation states to the title com[ounds

Luminescence of cesium dicyanoaurate(I). Evidence for extended Au(I)Au(I) interactions in two dimensions

The luminescence of microcrystalline samples of Cs[Au(CN)2] is reported and ascribed to planar AuAu interactions. Low-temperature measurements from 1.6 to 100 K of the luminescence decay rate of Cs[Au(CN)2] for the band centered at 458 nm reveal the presence of at least two emitting levels separated by 46 cm−1. A simple orbital model is proposed to account for the luminescence, and spin—orbit coupling is invoked to explain the splitting of the two lowest states. The analogies and differences between this luminescence and that observed for salts of Pt(CN)42− are briefly discussed.