Rhenium octahedral clusters

Similarly, the octahedral cluster [RcgCfCOlig] " has been synthesized by the oxidation of [Re7C(CO)2i] with iodine, which leads to abstration of the capping rhenium unit (S76). 

Although less fully documented than osmium cluster chemistry, rhenium cluster chemistry has been subjected to many structural studies, including those on approximately 20 neutral or anionic carbonyls, particularly carbonyl hydrides [Rev(CO). H ] of nuclearities x = 2 to 6 (Fig. 7). In addition, some ten or more rhenium carbonyl carbides [Rev(CO)vH C] have been shown to contain a core carbon atom, usually occupying a central octahedral site. These systems offer scope not only to explore for rhenium the trends we have already shown for osmium, but also to study the effect on metal-metal distances (and so enthalpies) of such core carbon atoms, which formally donate all four of their valence shell electrons to the cluster bonding. To our knowledge only one rhenium carbonyl cluster compound, Re2(CO)io, has been subjected to calorimetric study to determine its enthalpy of formation. ... 

One of the stimuli for studying these complexes is their close relationship to the well-known Chevrel phases MMo Yg (Y = S, Se or Te). Accordingly, a noteworthy recent development is the discovery of octahedral rhenium-selenide clusters. The phase Re SegClj has been prepared by the high temperature reaction ( BOOK) of ReQj with mixtures of Re and Se. An X-ray crystal structure has shown the presence of the [RcgScg] core possessing Re—Re distances of 2.6 2.67 A. The presence of two terminal Re—Cl bonds tram to one another) inhibits interlayer linkages. ... 

In contrast to the synthetic accessibility of the above complexes using solution approaches, the synthesis of octahedral rhenium chalcogenide clusters requires the implementation of high temperature solid-state reactions, or the conversion of cluster-containing solids into soluble molecular species by the methods of cluster excision or dimensional reduction (see Section 7.2.2.1.8). While cluster excision has produced the mixed sulfide(selenide)-chloride clusters [Re6E4+ Clio 2 ] " ( = 1-3), the latter approach has led to the isolation of complexes with rhenium-chalcogenide cores [RegEgXg] - (E = S, Se X = C1, Br, I). 

Perrin, A., Leduc, L. Sergent, M. (1991). Halogen bridged RegLs units in octahedral cluster rhenium chalcohalides, Eur. J. Solid State Inorg. Chem. 28, 919-931. 

The number of d electrons in these types of clusters is usually shown by the superscript of the symbol denoting the number of skeletal atoms [Mj] [Ma] [M3]. Clusters containing more electrons are rarely formed. The only exceptions are [Moa] compounds. Rhenium(III) clusters, Re3Xg, and similar compounds possess twelve d electrons. In these cases the electronic structure is different the skeletal atoms form multiple metal-metal bonds. In the case of rhenium(III) compounds and for octahedral clusters, the M — M bonds can be satisfactorily described considering only interactions of d orbitals. ... 

Both compounds contain the carbide atom in an octahedral cavity. The hydride cluster is a simple octahedron with three terminal carbonyls on each rhenium atom. The heptanuclear cluster can instead be considered as the same octahedron in which the two hydrides are replaced by a [Re ( 0)3] fragment leading to a monocapped octahedral cluster. Both structures have seven skeletal dectron pairs. 

C. Perrin - Octahedral Clusters in Transition Element Chemistry, J. of Alloys and Compounds 10, 262-263,1997 A. Perrin, M. Sergent - Rhenium Clusters in Inorganic Chemistry Structures and Metal-Metal Bonding, New J. Chem. 12,337, 1988 A. Perrin, C. Perrin, M. Sergent - Octahedral Clusters in Mo" and Re " Chalcohalide Chemistry, J. Less Common Met. 137,241,1988 ... 

Figure 24.9 Cluster carbonyls of rhenium containing an encapsulated carbon atom, (a) Octahedral [HjReeC-(C0)i8] . (b) Monocapped octahedral [Re7C(CO)2i] . (c) tran -bicapped octahedral [RegC-(CO)24] . (d) and (e) isomers of [Re7HC(CO)2i] differing in the position of their /r-H atom.

Solid-state cluster chemistry is dominated by octahedral (M 5L8)L6 and (MsLi2)L units which are the focus of this paper. These two cluster types are different in the way the metal octahedral core is surrounded by the ligands. In (MsLg)L6-type clusters (Fig. 6.1a), typical for molybdenum and rhenium halides, chalcogenides, and chalcohalides, eight innei hgands (L ) cap the octahedron faces and six outer ligands (L ) are located in the apical positions [9]. For metals with a smaller number of valence electrons, the (M6L i2)L -type clusters... 

Rhenium is one of the oxophilic atoms effective for oxidation reactions. ReOx species are likely to have chemical interaction with various oxide supports and exhibit unique catalytic properties that cannot be observed on monomeric rhenium oxides. A new active six-membered octahedral Re cluster in zeolite pores (H-ZSM-5 [HZ]) is produced from inactive [Re04] monomers in situ under selective propene oxidation to acrolein (C3H6+02 - CH2=CHCH0+H20) in the presence of ammonia that is not involved in the reaction equation [16], The cluster is transformed back to the original inactive monomer in the absence ammonia. Note that coexistence of spectator NH3 is indispensable for the selective oxidation. 

Fig. 1. Ball-and-stick and ball representations of the octahedral rhenium cluster [Re6S8Cl6]4-. All sulfur atoms are inner ligands and all apical positions are occupied hy chlorine atoms.

The semiconductor-like rhenium telluride phase Re2Tes has been characterized by X-ray crystallography and shown to possess the usual octahedral Re6 core (r(Re—Re) = 2.67-2.72 A) within the structure [Re5Te8]Te5 Te, in which the [Re6Te8] clusters are linked via butterfly-like [Te Te —Te—Te 2] units.202... 

Mixed-metal clusters that contain rhenium, e.g. the phase Mol sRe4 5Se8, can also be prepared by direct reaction of the elements. They contain the octahedral (Mo,Re)6 cluster.203... 

The data in Table 4.3 correspond to a radius for the octahedrally coordinated carbon atom that Ues in the range 0.59-0.69 A. We noted earlier that the radius of the core carbon in osmium, rhenium, and rhodium clusters lie in the range 0.59-0.62 A. It appears likely that the enthalpy change ZE(M-C), needed to cleave the six M-C bonds in these molecular carbonyl clusters, will lie in the same range (239-306 kcal moT i.e., 38-51 kcal mol per MC link) that we have now calculated for the similarly coordinated carbon atoms in these extended lattice binary carbides MC or M2C. 

The alkali metal rhenium- and technetium chalcogenide clusters described in Section 5.6 are also octahedral.These clusters have M6Es units with eight face-capping anions on the octahedral faces in contrast to the niobium halide or oxide clusters. The A4M6S14 (A = alkali metal, M — Re, Tc), Cs6Rc6Si2, and... 

Much of the interest in clusters of this type arises from their structural similarity to the fundamental structural element of the superconducting Chevrel phases M MogEg (M = Pb, Sn, Cu, etc.) and more recently discovered rhenium halco halide phases. Although these solid-state compounds are known only for Mo and Re, molecular MgEgLg clusters of Zr, V, Cr, Mo, W, Re, Fe, and Co have been reported (Table 2). The lone examples of octahedral zirconium- and vanadium-chalcogenide clusters are unique in that they also possess interstitial O and S atoms, respectively. Evidence for interstitial FI atoms in the clusters [Cr6Eg(PEt3)g] (E = S, Se) has been presented. ... 

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