Osmium: Synthesis, Characterization and Applications
Сборник
| Язык |
Английский |
| Тип |
Сборник |
| ISBN |
978-1-63483-517-6 |
| Страниц |
155 |
Osmium, discovered in 1803, is a rare element with many physical and
chemical properties and is used in a variety of applications. In this book,
osmium is looked at as an emerging anthropic polluting traffic-related metal.
In the second chapter, homoleptic osmium cyanide complexes are explored,
particularly their synthesis and applications in molecular magnetism. The third chapter focuses on the synthesis and mixed-valence state of binuclear
osmocene derivatives. In the fourth and final chapter, photoneutron cross
sections on naturally present osmium isotopes are reviewed.
Chapter 1 Ŕ In the environmental field, and in the last decade, scientific
attention has addressed platinum group metals (PGMs) due to their increasing concentration in all the environmental matrices. This is due to the increasing use of these metals in several fields as for example production of industrial catalysts, anticancer drugs, jewels, even if in any case the cause of their growing concentrations in the environment is consequence of the compelling employment of autocatalytic converters. In fact the incorrect use "stop and go" of these converters, with consequent deterioration and abrasion, certainly implies a considerable release in the environment of airborne particulate matter at high PGMs concentration, which results to be the greatest, if not the only, source of contamination of the various environmental matrices, i.e., superficial water, soils, sediments, vegetables and so on. Really, after the first massive use of platinum, palladium and rhodium in the production of autocatalytic converters, there has been a gradual reduction of these PGMs with consequent growing use of iridium, ruthenium and, especially, osmium.
Indeed, in the last decade, and more and more frequently, osmium
together with iridium has been employed as alloying with platinum, palladium and rhodium in the manufacturing of autocatalytic converters in order to withstand high temperature and high wear. In fact, osmium in particular is
rarely used in its pure state, and it is instead considered an important alloying agent especially in high-wear applications, owing to its strong corrosion resistance even at very high temperatures.
Thus, this work intends to propose voltammetric methods for the osmium
determination at ultra-trace level concentration in environmental samples:
airborne particulate matter, superficial waters, soils/sediments, vegetables,
mussels, clams and algae. To better validate the proposed analytical
procedures, a critical comparison with spectroscopic measurements - electrothermal atomic absorption spectroscopy (ETŔAAS) because of its well established and tested robustness ŕ has been also carried out and discussed here, taking into account all the parameters of interest to set-up an analytical method, such as precision and trueness (that together give accuracy), limit of detection and quantification, selectivity and, especially, sensitivity.
Chapter 2 Ŕ In the past time the cyanometalate chemistry lived through an
unpredicted revival, driven by a large amount of publications reporting the use of these complexes as building blocks in design of discrete and extended systems with potential applications as molecular magnets, photo-switchable materials and memory storage devices. Cyano-bridged assemblies have provided a large number of materials with single-molecule magnet (SMM) and single-chain magnet (SCM) behavior. Among them, several ones based on hexacyanoferrate(III) heterometallic SMM clusters and SCMs were prepared and magnetically studied.
The octahedral [Fe(CN)6]3- anion represents an important orbitally-degenerate magnetic unit with unquenched orbital momentum; its incorporation in nanomagnets can potentially increase their magnetic anisotropy. However, anisotropy strength is sensitive to local polyhedron distortions in [FeIII(CN)6]3Ŕ. In this respect, its heavier counterpart, especially [OsIII(CN)6]3Ŕ, is more attractive anisotropic constituents due to a much stronger spin-orbit coupling energy and more diffuse magnetic orbitals resulting in larger magnetic spin coupling. There are only a few examples of the materials based on [OsIII(CN)6]3Ŕ, including the trigonal bipyramidal clusters [MII(tmphen)2]3 [OsIII(CN)6] (M = Fe, Ni, Mn), Prussian blue analogues MII3[OsIII(CN)6]2·nH2O (M = Co, Ni, Fe), three SMMs involving MnIII Schiff base complexes and the first osmium based SCM - (Ph4P)2[Mn(acacen)][Os(CN)6].
It has recently been shown that incorporation of [OsIII(CN)6]3Ŕ in MnIIIŔ
NCŔMIIIŔCNŔMnIII trinuclear complex considerably increases the SMM
energy spin-reversal barrier compared to that of the MnIII-NC-FeIII-CN-MnIII
cluster. This achievement opens new horizons for application of [OsIII(CN)6]3 in the design of magnetically bi-stable molecular systems. Therefore, development of facile, reliable and having high yield synthetic methods for the preparation of precursors and model compounds is highly demanded.
The research of cyanide compounds has been a subject of several reviews
over the years. Nevertheless, the scarce amount of information on homoleptic osmium cyanide complexes is astounding. Only cyanometallates(II) and (III) were structurally characterized to date despite the existence of higher oxidation states for osmium. Moreover, the homoleptic coordination compounds of Os comprise mainly hexaligated complexes, unlike its nearest neighbor, rhenium, which demonstrates coordination numbers from six to nine. In the chapter we review shortly the results on the osmium cyanides published pending 2006 and present the new data on the synthesis, properties and structure of cyanoosmates and their application in design of molecular nanomagnets. Recently we have developed a facile synthesis of the soluble in organic media paramagnetic (Cation)3[OsIII(CN)6] with different cations and pioneering preparation of (n-Bu4N)3[OsIV(CN)7]·0.5H2O, (Ph4P)2[OsIV(CN)6] and (n-Bu4N)[OsV(CN)6] complexes.
Chapter 3 Ŕ Facile preparation method of osmocene was developed.
Iodoosmocene(OcI), which is the first mono-halogenated osmocene, was
prepared by lithium-halogen-exchange reaction. Biosmocene(OcOc) was
synthesized by Ullmann coupling reaction of OcI. OcOc is the first and
simplest binuclear metallocene compound of osmium. Mixed-valence
biosmocenium salts [(C5H5)OsII(C5H4-C5H4)OsIV-X(C5H5)]Y(A; X=I, Y=I3, B1; X=Cl, Y=PF6, B2; X=Cl, Y=BF4, C; X=Br, Y=PF6) were obtained from oxidation reaction of OcOc by iodine, [(C5H5)2RuIV-Cl]PF6, [(C5H5)2RuIV-Cl]BF4 and [(C5H5)2RuIV-Br]PF6, respectively. The structures of these halogen adducts were determined by single crystal X-ray structural analysis. The valence states of biosmocenium salts were estimated as OsII-OsIV mixedvalence state in solid, while valence-detrapping was observed in solution state by variable-temperature 1H NMR spectroscopy. 1H NMR spectra showed that intramolecular electron exchange reaction accompanied by halogen migration occurs at higher temperature in solution. It was found that the activation energy of the reaction increased in the order, B1<C<A, and the tendency was explained by HSAB theory. OcI was also applied to cross-coupling reactions.
Ferrocenylosmocene(FcOc) was synthesized by Negishi coupling reaction of OcI and ferrocenylzinc chloride in 22 % yield. When FcOc was treated with I2, ferrocenylosmocenium-I triiodide[(C5H5)Fe(C5H4-C5H4)Os-I(C5H5)]I3(D) was obtained. The valence states of Fe center of FcOc and its oxidized sample were investigated by 57Fe Mössbauer spectroscopy. It was found that the valence state of D is FeII-OsIV at the temperature range of 78 - 298 K. Valence detrapping was not observed even in solution state by using variable temperature 1H NMR spectroscopy.
Chapter 4 Ŕ The nucleus is a bound system of protons and neutrons.
Different types of nucleon interactions are manifestly exposed in the properties of nuclei. The nucleus is a complex system which is affected by different aspects of the strong, electromagnetic, and weak interactions, and, therefore, different models are used for their description.