Triangular clusters

The [Ms(/i3-E)(/t2-E)8Lg] (I), [ (/ - )(/ 2- 2) 8] (II), and [M3E5Lg] (III) types of cluster compounds (Fig. 29) are known, and because of the importance of triangular cluster units as building blocks of higher clusters, much effort has been put into the synthesis of such clusters. 

Some new compounds have been reported since the previous review 

No tellurium derivatives of M3E7X6-type compounds had been described until Fedin et al. reported the synthesis of Mo3Te10I10 from the reaction of molybdenum, tellurium, and iodine at 398°C for 48 hr in a sealed tube (119). The structure (Fig. 30) is composed of [Mo3(/t3-Te)(/x2- 

A compound with half of the u.3-Se replaced by fi3- has been obtained in the preceding reaction as another product (121). This is formulated as K2Mo3Se12 5O0 5 and is the first example of the Mo3 cluster compound with a /li3- ligand. The cluster is more closely packed than the ammonium salt because of the smaller size of potassium ion and the replacement of half the /n3-Se atoms by smaller oxygen atoms. 

Details of the MO analysis of [Mo3(/a3-S)2(ja2-S)3(PMe3)6] have been reported (125). The cluster unit Mo3S5 is the first member of the Chevrel cluster Mo3nS3n+2, and development of the chemistiy of this cluster complex is anticipated (Fig. 32). 

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The B3Hg ion (p. 166) is a triangular cluster of Cj (rather than C2 ) symmetry (see Fig. 6.15a) the bridging atoms are essentially in the B3 plane with Ht above and below. While it has been conventional to represent the cluster bonding in terms of two BHB and one B-B bond (Fig. 6.15b), recent high-level computations suggest the presence of a 3-centre BBB bond, as depicted approximately in Fig. 6.15c. 

In a localized picture, the electronic structure of Pr2ls [23] and also of Pr2Br5 [24] can be understood as if triangular clusters Pr3 contained one electron in a tricentric orbital. These triangles share common corners to chains Pr2/2Pri/i. ... 

It has been several decades since oxo-centered triruthenium-carboxylate complexes with triangular cluster frameworks of Ru3(p3-0)(p-00CR)6 (R = alkyl or aryl) were first isolated [1,2]. In the early 1970s, the first oxo-centered triruthenium complex was structurally characterized by Cotton through X-ray crystal structural determination [3]. Since then, oxo-centered trinuclear ruthenium-carboxylate cluster complexes with general formula [Ru30(00CR)6(L)2L ]n+ (R = aryl or alkyl, L and... 

Dinuclear Pt complexes of the type [ Pt(PR3) 2(p-S)2] are also known to serve as the good precursors to the trinuclear clusters. A series of triangular cluster cores M Pt2(p3-S)2 has been constructed therefrom (M = transition metals, main-group metals).50... 

If one applies the same procedure to Figure 1.10B, an iron-sulfur cluster often used as a model for those in biological systems, the same magic number of 60 would be obtained. Cluster magic numbers would occur as 48 e for a triangular clusters, 60 e for tetrahedral, 72 e for trigonal bipyramidal, 74 e for square pyramidal, 86 e for octahedral, 90 e for trigonal prisms, and 120 e for cubic structures. 

The parent structure of the anion-deficient fluorite structure phases is the cubic fluorite structure (Fig. 4.7). As in the case of the anion-excess fluorite-related phases, diffraction patterns from typical samples reveals that the defect structure is complex, and the true defect structure is still far from resolved for even the most studied materials. For example, in one of the best known of these, yttria-stabilized zirconia, early studies were interpreted as suggesting that the anions around vacancies were displaced along < 111 > to form local clusters, rather as in the Willis 2 2 2 cluster described in the previous section, Recently, the structure has been described in terms of anion modulation (Section 4.10). In addition, simulations indicate that oxygen vacancies prefer to be located as second nearest neighbors to Y3+ dopant ions, to form triangular clusters (Fig. 4.11). Note that these suggestions are not... 

For triangular clusters, for instance, this means 18 or 48 electrons. A classic example may be the Os3 triangular group in the carbonyl compound Os3(CO)12 in which 4 CO are connected to each Os (to each triangle vertex). Each Os atom contributes 8 valence electrons whereas the CO group acts as a 2-electron donor so ... 

If the site correlations are extended to triangular clusters, then... 

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. 

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