Hexanuclear cluster

Other clusters listed in Table 19.4.2 have the property that their b value equals the number of edges of their M skeletons. 

For Os6 clusters the metal core rearrangement is accompanied by a change of the ligand positions but the number of metal-metal bonds is retained. Thus, the bridged-square pyramidal cluster [Os6(CO)i6(yU4-S)(/43-S)] (34) partially isomerizes upon heating to 125 °C to give a basket skeleton (also with ten Os Os bonds) in which the two sulfur atoms are in a /I3 mode (35).  

Although not strictly skeletal isomers, it is noteworthy that two conformational isomers of the cluster [Rh2(/z-AuPPh3)(/i-Cl)2(CNC8H9)4]2(PF6)2 are obtained in the solid state these easily recognizable by their color. For penta to heptanuclear chain clusters of type [Pt3M (//3-CR)L (] (M = Mo or W, R = Me or C6H4Me-4, and L = (/i-CMe), CO, cod, Cp or Cp ) several diastereoisomers have been observed. 

---

Figure 97 Hexanuclear cluster [(/i3-WSe4)2(Pd2)2(/r-dppm)2],2DMF.

The only non-octahedral hexanuclear cluster units are six-membered ring Rh6 (chair conformation, Figure 3), and open, non-planar zigzag chain Zr6, which are found respectively in Rh3S4 and Zr3Te (Rh-Rh 2.70 and 2.87 A Zr-Zr 3.01-3.15 A). In addition there are strong transannular interactions in the Rh6 ring (3.09 A), and weak contacts between the Zr6 chains.96,97... 

The first hexanuclear cluster obtained was for ruthenium, as the carbonyl-carbido RuflCfCO). This was prepared by heating Ru3(CO) 2 in... 

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. 

A few cluster complexes with fused triangles of molybdenum or tungsten have been reported. They are tetranuclear and hexanuclear cluster complexes, which may be viewed also as having fused incomplete cu-banes of M3E4. 

The three hexanuclear clusters are mixed valency complexes of two M(III) and four M(IV) centers, and the average oxidation state of the metal is +3.67. The number of cluster valence electrons is 14, which agrees with seven M—M bonds. Relatively short M-M distances for the intra- and intertriangles suggest that the clusters can be viewed as dimers of triangular clusters. Extension of the triangle condensation would lead to higher polymers. 

Over long periods, the hexanuclear cluster is light sensitive and it is best stored in the cold in the absence of light. It is soluble in polar solvents and slightly soluble in hydrocarbons, giving air-stable solutions. 

In the hexanuclear clusters the dominating shape is that of the octahedron, which is even able to dimerize as in Rhi2(CO)3Q (90). The few other structures are that of a trigonal prism as in Ptg(CO)i2 (60)] (22) and... 

C0gC(C0)i5 14), one case of a bicapped rhombus in Mo2Ni4(CO)i4 " 333), and one case of a bicapped tetrahedron in OSg(CO)jg [72] 284). The reasons for certain structures of hexanuclear clusters have been discussed in terms of several bonding approaches and will be treated in Chapter 2.3. 

Tetrameric silver clusters stabilized by internal ligands from NMe2 - and OMe-sub-stituted aryl groups seem to exist, too (272). Silver can also be incorporated into hexanuclear clusters of the type CUg Ag Ar4Br2 with = 0, 2, 4, 6 by reactions of [MAr]4 with MBr2 (M = Cu, Ag) in the corresponding ratio (256, 265, 272). 

The second class of hexanuclear clusters also contains an octahedron of metal atoms, but they are coordinated by twelve halide ligands along the edges (Fig. 16.64b). Niobium and tantalum form clusters of this type. Here the bonding situation is somewhat more complicated The metal atoms are surrounded by a very distorted square prism of (bur metal and four halogen atoms. Furthermore, these compounds are electron deficient in the same sense as the boranes—there are fewer pairs of electrons than orbitals to receive them and so fractional bond orders of are obtained. 

Unlike other dioximes, as for example the well-known DMG (Section 50.5.3.7.ii), camphorquinone dioxime, H2CQD, was found to coordinate with O and N atoms in the Ni(HCQD)2 complex which has square planar coordination (345).2504 The reaction of complex (345) with AgN03 in H20/Me0H solution gives a hexanuclear cluster of composition [Ni(HCQD)2Ag]3 (346).2505 Each hexanuclear molecule consists of three Ni(HCQD)2 anions... 

The hexanuclear cluster [Ni6(SEt),2] (25)" has a crown-like structure with a ring of six square-planar coordinated nickel ions and six -bridging ligands. 

---