Trinuclear clusters, oxides

Tungsten pentachlofide [13470-13-8], WCl, mp 243°C, bp 275.6°C, is a black, crystalline, deHquescent soHd. It is only slightly soluble in carbon disulfide and decomposes in water to the blue oxide, 200 2. Magnetic properties suggest that tungsten pentachlofide may contain trinuclear clusters in the soHd state, but this stmcture has not been defined. Tungsten pentachlofide may be prepared by the reduction of the hexachloride with red phosphoms (9). 

The complexity of the low temperature MCD spectra of the oxidized and reduced trinuclear cluster shows the multiplicity of the predominantly S — Fe charge transfer transitions that contribute to the absorption envelope. While MCD spectroscopy provides a method of resolving the electronic transitions, assignment cannot be attempted without detailed knowledge of the electronic structure. However, the complexity of the low temperature MCD spectra is useful in that it furnishes a discriminating method for determining the type and redox state of protein bound iron-sulfur clusters. Each well characterized type of iron-sulfur cluster, i.e. [2Fe-2S], [3Fe-4S], and [4Fe-4S], has been shown to have a characteristic low temperature MCD spectrum in each paramagnetic redox state (1)... 

Ceruloplasmin is involved in copper storage and transport as well as in iron mobilisation and oxidation. Among the blue oxidases it is unique since it contains, in addition to the usual motif of a type 1 combined with the trinuclear cluster, two other type 1 coppers. Electron transfer occurs, however, only between five of the six copper ions since one of the type 1 centres is not catalytically relevant due to its too high redox potential. The redox potentials of the centres were determined and possible electron transfer pathways among the copper sites were discussed.101... 

There are three important routes to the formation of the mercury-transition metal bond (a) displacement of halogen or pseudohalogen from mercury(II) salts with carbonyl metallate anions (b) reaction of a halo-phenylmercury compound with a transition metal hydride and (c) oxidative addition of a mercury halide to neutral zero valent metals.1 We report here the syntheses of three compounds containing three-centre, two-electron, mercury-ruthenium bonds utilizing trinuclear cluster anions and mercury(II) halides.2-4... 

Some proteins contain more than one copper site, and are therefore among the most complicated and least understood of all. The active site known as type 4 is usually composed of a type 2 and a type 3 active site, together forming a trinuclear cluster. In some cases, such proteins also contain at least one type 1 site and are in this case termed multicopper oxidases, or blue oxidases [3], Representatives of this class are laccase (polyphenol oxidase) [7-9], ascorbate oxidase (Figure 5.Id) [10], and ceruloplasmin [11], which catalyze a range of organic oxidation reactions. 

Our relatively innocent venture into the chemistry of molybdenum oxide systems has led to the discovery of a whole new class of ternary oxide compounds dominated in their structural features by strong metal-metal interactions. Interest in the question of whether the trinuclear clusters in the well known compound Zn.Mo 0 (10, 11) could accept more than 6 electrons in the metal-... 

Numerous trinuclear cluster compounds are formed by molybdenum, and to a lesser but significant extent by tungsten and niobium. Four principal types are known, and their structures are shown schematically in Fig. 16-22. In all of these the M—M bond orders are in the range % to 1. For molybdenum particularly, there are numerous mixed oxides in which the type of structure shown in Fig. 16-22(b) figures prominently. 

It is in this oxidation state that the known chemistry of the two elements is most different. For rhenium di- and trinuclear cluster species predominate (Section 18-D-5), whereas for Tc there are only a few Tc and no Tc3+ complexes. Mononuclear Tc3+ species do occur. The only simple [MXJ3- complex known for either element is the [Tc(NCS)6]3 ion, but the mer-MCl3(PR3)3, MCl3py3, and [MX2(LL)2]+ complexes with X = halide, NCS , or MeS" and LL a diphosphine or diarsine are important.41 Some of these complexes can be reduced with retention of structure in the II and even I oxidation states.42... 

The metal framework of trinuclear clusters capped by one or two bridging groups is more robust toward oxidation or reduction. The mixed-metal clusters [FeCo2(CO)9(/t-E)] (65) (E = S, Se, or PR) reduce in successive one-electron steps, first to a somewhat persistent anion radical [E = S, r,/2 = 60 seconds 142)) at mild potentials (E = S, = -0.24 V vs Ag/AgCl), and then to a very unstable dianion 142, 143). 

Doubly bridged trinuclear clusters may be oxidized or reduced, but the stability of the one-electron product depends on the identity of the bridging group and on the terminal ligands bonded to the metals. The iron complex [Fe3(CO)2(/u-S)(/Li-SR)Cp3], the structure of which has not been fully defined, oxidizes reversibly in two one-electron steps. The monocation was synthesized by iodine oxidation of the neutral species but apparently decomposes to [ Fe(CO)( i-SR)Cp 2] (Section III,E) 148). 

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