Clusters rhenium

The chemistry of pure rhenium clusters 273, 332 is confined in this context mainly to the hydrides. Two new preparations of H3Re3(CO)i2 were described 204, 234, the structure of which is like that of [JO] 394, and H Re lCO) of structure [7] was obtained from Re2(CO)jo and KOMe 17. ... 

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.

Polynuclear clusters fill the gap between mononuclear and extended solid transition metal vibronic systems. The applications of the theory of vibronic interaction allow to describe physical and chemical properties of these systems, sometimes directly linked to their application. The Jahn-Teller distortion found for the rhenium clusters defines the architecture of hybrid inorganic-organic materials and, as a result, their electric and magnetic properties. The application of the vibronic theory to the decatungstate cluster elucidates the details of its reactivity in the photocatalytic reaction. The modern DFT methods give a key to the calculations of key parameters of the vibronic theory. In future, we will assist at the combination of these methods with phenomenological approaches leading to the description of vibronic effects in physical and chemical properties of polynuclear clusters from first principles. 

Similar conclusions have been drawn from a study of the hydrogenolysis and isomerization of cyclopropane over catalysts made up of supported rhenium clusters of differing nuclearity.29 The hydrogenolysis of cyclopropane was found to take place only over those catalysts having at least a Re3 nuclearity while the hydrogenation of propene, an isomerization product of cyclopropane, took place on Re I species (Eqn. 3.1). 

Figure 24.12 Rhenium clusters [Re ChR ] arrows indicate vacant coordination sites where further ligands can be attached.

Augustine and Sachtler, on reduction, rhenium oxides migrate over the support surface and become reduced in contact with a prereduced platinum particle. In this way, each platinum particle can generate a mixed platinum-rhenium cluster that has the beneficial effects of bimetallic catalysts on selectivity and stability. 

Re(CO)3(/t-OCH3)3Re(CO)3] (64) whereas decreasing pressure favoured production of rhenium clusters of higher nuclearity with mixed (/t-oxo)- and (/r-methanolato) bridges. The presence of 1.33 equivalent of base per metal atom in the clusters 44 and 44b facilitates subsequent reactions, that demand base. The reaction of 44 with (HCsMes), for example, resulted in the quantitative formation of 45 [79], In the case of the trinuclear rhenium cluster 44b, reaction with the caibene precursor 1,1 -methylene-bis(3-methyl-1 //-imidazolium)-diiodide yielded the corresponding mononuclear Re(I) complex (65) with the bidentate caibene ligand (see Scheme 14) [80]. 

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. ... 

Another feature of the bond enthalpy data for rhenium clusters is that they show a very wide range of values of S (Re Re)/5 ib, the enthalpy per notional 2c2e metal metal bond present - the value varies from 45 to 85 kJmol , underlining the unsatisfactory nature of associating bond enthalpies with skeletal bond pairs. 

E2.3 Rhenium clusters in inorganic chemistry structures and metal-metal bonding... 

The planar tetranuclear rhenium cluster has been crystallographically shown to possess >2 symmetry with a 1,3 Re-Re bond (92). Thus, it was proposed (94) that [Ir2(CO)4X4]22 is also planar. Due to the eight out-ofplane ligands (CO and halide), close intermolecular Ir-Ir interaction is unlikely, thus not explaining the observed electrical properties, vide infra. 

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