Hexanuclear metal clusters

Penta- and hexanuclear clusters of the metals osmium and ruthenium coordinate with the same r ri ri - binding mode as the trinuclear clusters to CgQ. Such complexes are known for the clusters OsjC [75,76], RU5C [77-79], RugC [78], PtRu5C [77] and Rhg [80], In this collection of metal clusters rhenium plays a special role, because it forms a new fullerene-metal sandwich complex, where two C50 are bound to one cluster. 

Chemical Properties. Compound 2 is readily decarbonylated upon exposure to UV irradiation.5 Irradiated solutions of 2 readily yield addition products of sulfur containing small molecules such as COS, CS2, and H2S. In the absence of reagents it will form the hexanuclear compound Os6(CO)17(/r4-S)2. It reacts with other metal complexes to form higher nuclearity osmium clusters and heteronuclear metal cluster compounds.5,11,12... 

We discuss here two examples of vibronic effects in polynuclear highly symmetrical transition metal clusters. The existence of degenerate and quasi-degenerate molecular orbitals in their energy spectra results in the Jahn-Teller effect or in the vibronic mixing of different electronic states. We show that both quantum-chemical methods and model approaches can provide valuable information about these vibronic effects. In the case of the hexanuclear rhenium tri-anion, the Jahn-Teller effect is responsible for the experimentally observed tetragonal distortion of the cluster. The vibronic model of mixed-valence compounds allows to explain the nature of a transient in the photo-catalytic reaction of the decatungstate cluster. 

Fig. 62. Two views of H2Os6(CO)j8, a rare example of a non-octahedral hexanuclear metal cluster (Ref. 241). There was originally some suspicion that one of the H atoms might cap the basal square face of this cluster...

A logical extension of the synthesis of [Co6(CO)i5]2- from [Co(EtOH) J [Co(CO)4]2 has been successfully applied to the preparation of mixed-metal clusters. Thermal decomposition of [Ni(EtOII) J[Co (CO) 4]2 prepared in situ gives the red hexanuclear dianion [Ni2Co4(CO) n]2", through the following redox condensation and redistribution processes (44) ... 

J. C. Calabrese, L. F. Dahl, A. Cavalieri, P. Chini, G. Longoni, and S. Martinengo, Synthesis and Structure of a Hexanuclear Nickel Carbonyl Dianion, [Ni3(CO)3( j,2-CO)3]22, and Comparison with the [Pt3(CO)3(p2-CO)3]22 Dianion. An Unprecedented Case of a Metal Cluster System Possessing Different Metal Architectures for Congener Transition Metals, J. Am. Chem. Soc. 96, 2616-2618 (1974). 

T. F. Koetzle (1981). J. Am. Chem. Soc., 103, 1458-1466. An interstitial hydrogen atom in a hexanuclear metal cluster X-ray and neutron diffraction analysis of [(Ph3P)2N]"[HC06(CO),5r... 

In the chemistry of hexanuclear metal clusters the coexistence of mixed-charge cluster units within homo- and heteronuclear clusters is possible. The synthetic routes have been identified and include ... 

So far, only the hexanuclear clusters have been studied. What about different nuclearity clusters of other transition metal elements In other words, is it possible that a new chemistry within transition metal clusters has just started ... 

Hexanuclear main-group metal clusters which are composed of s metal ions can be luminescent, too (Fig. 5) [93], e. g.,... 

The trinudear metal carbonyl clusters [Fe3(CO)n] ", [197] [Ru3(CO)i2], [198] and [Os3(CO),2] [199] do not contain bridging ligands and the M-M distances are 4-8 % longer than in the corresponding bulk metals. On the other hand, tetranu-clear and hexanuclear metal clusters often show M-M distances which are very close to those of the metal crystals, but significant deviations have also been observed (Table 2-2). 

High-Valence Metal Clusters. Structural properties of selected hexanuclear high-valence cluster complexes are described in Table 2.5. A series of molybdenum and tantalum derivatives of type [(M6Y8)X6] and [(M6Ys)L8] (M = Mo or W X = halide or alkoxide Y = halide or other monovalent anion and L = neutral Lewis-base) are known. The structures of these species are like that of the anion [(Mo6Cl8)Cl6] illustrated in Fig. 2.19 in which the molybdenum atoms are in the vertex of an octahedron. Metal-metal distances of about... 

Most of the known high-valence metal cluster species belong to the tri and hexanuclear clusters discussed above. However, there are also some examples of... 

Table 2.6. Selected examples of hexanuclear metal clusters...

Fig. 2.25. Types of structures frequently adopted by hexanuclear metal clusters, (a) Octahedron (b) bicapped tetrahedron (c) capped square pyramid (d) edge-sharing bitetrahedron (e) trigonal-prism (f) six-atom-raft triangles (g) six-atom-raft rhomb (h), (i), and (j) edge-bridged bi-diminished bipyramidal or edge-bridged butterfly geometries...

In the case of carbonyl metal clusters, the presence of free carbon monoxide notoriously affects the reduction processes inducing condensations as well as degradation of the clusters species. Thus the reduction of the tetranuclear cobalt cluster 04(00)4 with lithium, sodium, or potassium in which the final product is the hexanuclear cluster [Co6(CO)i5] is an illustrative example of the complexity of such reactions. 

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