Halide containing clusters

PPha, pyridine) organic groups (olefines, aromatic derivatives) and also form other derivatives, e.g. halides, hydrides, sulphides, metal cluster compounds Compounds containing clusters of metal atoms linked together by covalent (or co-ordinate) bands, metaldehyde, (C2H40) ( = 4 or 6). A solid crystalline substance, sublimes without melting at I12 1I5" C stable when pure it is readily formed when elhanal is left in the presence of a catalyst at low temperatures, but has unpredictable stability and will revert to the monomer, ft is used for slug control and as a fuel. 

Of course, the chemistry of zirconium cluster phases has been well described and reviewed in the literature [1-4]. Apart from a very few examples, mostly in the binary halides, almost all reduced zirconium halides contain octahedra of zirconium atoms centred on an interstitial atom Z. Several possible and experimentally realized Z include H, Be-N, K, Al-P, and the transition metals Mn-Ni. All these compounds have the general formula Ax"[(Zr6Z)Xi2X[J], with a " = alkali or alkaline earth metal cation, X=C1 Br or I, X =inner edge-bridging halide [5], X =outer exo-bonded halide, and 0[Pg.61]

The dependence of rate constants for approach to equilibrium for reaction of the mixed oxide-sulfide complex [Mo3((i3-S)((i-0)3(H20)9] 1+ with thiocyanate has been analyzed into formation and aquation contributions. These reactions involve positions trans to p-oxo groups, mechanisms are dissociative (391). Kinetic and thermodynamic studies on reaction of [Mo3MS4(H20)io]4+ (M = Ni, Pd) with CO have yielded rate constants for reaction with CO. These were put into context with substitution by halide and thiocyanate for the nickel-containing cluster (392). A review of the chemistry of [Mo3S4(H20)9]4+ and related clusters contains some information on substitution in mixed metal derivatives [Mo3MS4(H20)re]4+ (M = Cr, Fe, Ni, Cu, Pd) (393). There are a few asides of mechanistic relevance in a review of synthetic Mo-Fe-S clusters and their relevance to nitrogenase (394). 

Several compounds with network structures which contain S2 units can be prepared by high-temperature reactions (250-700 °C). An example of a reaction of a metal halide with sulfur and S2C12 is shown in equation (7). The conditions under which these S2 -containing cluster compounds are formed illustrate their high stability. 

Hydride-containing clusters can be prepared under very mild conditions by reacting ZrCl4 and various amounts of HSnBu3 followed by addition of phosphines or halide salts52 (phosphonium or ammonium) as shown in Fig. 18-A-8. 

Hydride-containing clusters can be prepared nnder very mild conditions by reacting ZrCLi and varions amounts of HSnBus followed by the addition of phosphines or halide salts (phosphoninm or ammoninm) (equation 12). ... 

This chloro-containing cluster also failed to react with nitrogen despite the fact that all of the metal ions are formally divalent. These observations provide further support to the conclusion that halide ions, by coordinating the samarium atoms, prevent the reaction of the cluster with nitrogen from occurring. 

Some sub-halides contain extended structural motifs, which are derived from the extended structures of the cluster-forming element itself. The one- and two-dimensional structures of the bismuth sub-bromides and sub-iodides BiuLi,... 

With the smaller, harder rare earth elements (Gd through Lu), such compounds have never been seen, except for scandium where scandium-defrcient hexagonal perovskites, ASc Xs (A = Rb, Cs X = Cl, Br, I), have been observed. These are discussed together with the perovskite-type halides of R = Sm, Eu, Dy, Tm, Yb below. All other complex hahdes with reduced rare earth metals contain clusters and are discussed in Rare Earth Metal Cluster Complexes. 

The synthesis of compounds of the lanthanides containing cluster complexes follows in general the same routes as described in The Divalent State in Solid Rare Earth Metal Halides, the conproportionation route and the metallothermic reduction route, for example... 

Burkholderia cepacia strain 2CBS is able to degrade ort/jo-halogenated benzoates by dioxygenation to catechol with the elimination of halide and decarboxylation. The enzyme contains a ferredoxin-and a Rieske-type [2Fe-2S] center. These could be distinguished on the basis of their EPR spectra, and the results were compared with those for other [2Fe-2S] clusters (Riedel et al. 1995). 

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