Carbide-containing clusters

Thus, Mo is present in the samples in the form of Mo-containing clusters localized in the iimer of ZSM-5 channels and surface M02C crystallites 2-10 nm in size. In addition, HRTM images show that free cavities are formed around the surface M02C particles, which is obviously connected to a partial zeolite decomposition and molybdenum carbide modification by aluminium. 

There are numerous /i4-carbide- and nitride-containing clusters examples from the iron-triad include [M4C(CO)i3] (M = Fe, and [M4N(CO)i2] (M = Fe,... 

Dudis, D. S. Corbett, J. D. (1987). Two Scandium Iodide Carbides Containing Dicarbon Units Within Scandium Clusters - Scgl C2 and Sc4lgC2. Synthesis, Structure and the Bonding of Dicarbon, Inorg. Chem. 26, 1933-1940. 

Electronic structure and chemical bonding in metal carbides containing C vacancies cluster and band models... 

The third control is by use of a fixed burnable poison. This consists of rods containing a mixture of aluminum oxide and boron carbide, included in the initial fuel loading using the vacant spaces in some of the fuel assembhes that do not have control clusters. The burnable poison is consumed during operation, causing a reactivity increase that helps counteract the drop owing to fuel consumption. It also reduces the need for excessive initial soluble boron. Other reactors use gadolinium as burnable poison, sometimes mixed with the fuel. 

Perspectives for fabrication of improved oxygen electrodes at a low cost have been offered by non-noble, transition metal catalysts, although their intrinsic catalytic activity and stability are lower in comparison with those of Pt and Pt-alloys. The vast majority of these materials comprise (1) macrocyclic metal transition complexes of the N4-type having Fe or Co as the central metal ion, i.e., porphyrins, phthalocyanines, and tetraazaannulenes [6-8] (2) transition metal carbides, nitrides, and oxides (e.g., FeCjc, TaOjcNy, MnOx) and (3) transition metal chalcogenide cluster compounds based on Chevrel phases, and Ru-based cluster/amorphous systems that contain chalcogen elements, mostly selenium. 

All these molecules contain 86 electrons associated with the valence shells of the 6 metal atoms (the core carbon atoms of the carbides are considered to contribute all their valence shell electrons to these clusters). In the hydride H2Rufl(CO)i8, for example, the metal atoms supply 48 electrons, the carbonyl ligands 36, and the hydrogen atoms 2. Formally, this hydride maj be regarded as derived from the anion [Ru(CO)3]g , which, in turn, can be shown to be formally related to the c(oso-borane anion RgHe " as follows (199, 200). 

D. africanus Fd III containing reactive [3Fe S] cluster, 38 138-144 definition, 38 117 ferredoxins, 38 126-128 ideal case, 38 124 problems, 38 118, 120-121 recent developments, 38 119-120 sensitivity, 38 125 techniques, 38 125-126 underuse, 38 118 useful features, 38 121-126 u.seful potential range, 38 122 voltammetric response, 38 121 voltammetry of adsorbed protein molecules, 38 122-123 Dysprosium carbides, 11 201 dibromide, 20 4 dichloride, 20 4 preparation of, 20 8 properties of, 20 16-18 di iodide, 20 4... 

Osmium (continued) carbide, 24 233 dianion, lA. Xil, 317-319 with phosphines and diphosphines, 30 191 protonation/deprotonation, 30 169 raft hexaosmium clusters, 30 180-182 reactions of condensation, 30 145 with hexafluoroacetone, 30 288 redox, 30 184-185 structural transformations, 30 203 sulfur-containing, synthesis of, 30 147 sulfur derivatives, 24 269, 300-310 synthesis... 

X-ray structure of the mesitylene derivative was reported shortly afterward.11 This represented the second structurally characterized cluster containing an interstitial atom [the structure of FesC(CO)i5 having already been established]12 and the first example of a cluster with a completely encapsulated carbide atom. At the time that the synthesis of 2 was first reported, another paper described the synthesis of a cluster also obtained from 3 when heated to 150°C in either benzene or cyclohexane. Based on an estimation of the mass of this compound from a differential vapor pressure measurement, the authors suggested that this compound corresponded to Ru6(CO)18.13 It was subsequently noted from a comparison of vco IR data and a structural determination that this compound was in fact 2. 

The carbide atom in 1 is located in the center of the square face such that it is partially exposed whereas the carbide atom in 2 is completely encapsulated by the six ruthenium atoms. From a spectroscopic viewpoint, carbide atoms are very distinctive and the earlier reviews have dealt with these aspects in detail.7 8 The IR spectrum of 1 contains peaks at 701 (s) and 670(m) cm 1, and 2 contains peaks at 717(sh), 703(s), 680(m), and 669(m) cm-1.22 I3C-NMR spectra of 1 and 2 do not appear to have been reported. This is probably due to the low yields in which these compounds were initially obtained at a time when, 3C-NMR was still not in widespread use in cluster chemistry. In general, the 13C-NMR resonance of carbide atoms ranges from 8 250 to 500. The high frequency resonances exhibited in 13C-NMR spectra reflect the different diamagnetic and paramagnetic effects experienced by a nucleus in such an unusual chemical environment.23... 

The thermolysis of the pentaruthenium cluster Ru5(ju,5-C2PPh2)(CO)i3(ju,-PPh2) 189 under varying conditions affords a number of products, including some containing a Ru5C cluster skeleton. The carbide atom is derived from... 

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