Polyhedral clusters

The structural principles and reaction chemistry of B-8 compounds have recently been reviewed. This includes not only electron-precise 4-, 5- and 6-membered heterocycles of the types described above, but also electron-deficient polyhedral clusters based on closo-. 

Fig. 12.2 (a) Polyhedral view of [MnCglAIgGe]. (b) Ball-and-stick view of the shell structure around the [MntglAIgGe] polyhedral cluster. The top and side views are along (001) and (no), respectively. In (c) a Mackay icosahedron in a-MnAI(Si) is oriented along the corresponding directions. 

L Monomeric and Polymeric Organic Analogs of Boron Cluster Systems The polyhedral clusters of boranes and carboranes are groups of cluster systems that are present ubiquitously in organoboron polymers. As in the case with the... 

So far, three types of i-QCs appear in the literature Mackay [17], Bergman [18], and Tsai types [19], which have been differentiated on the basis of the polyhedral cluster sequences observed in the respective 1/1 AC structures. These are commonly represented as shown in Fig. 2. An i-QC is concluded to be Mackay-type if its 1/1 AC contains a 54-atom multiply endohedral cluster ordered, from the center out, as a small icosahedron (12 atoms), a larger icosahedron (12), and an icosidodecahe-dron (30). This motif occurs in ACs that consist of transition metals and main-group elements on the right side of the periodic table such as Al-(Pd,Mn)-Si [17,20]. In... 

More often, polyhedral clusters with strong metal-metal (or metalloid-metalloid) bonding are the major structural motifs of classic Zintl phases. These are nominally salts composed of reduced p- (i.e., post-transition) elements that are usually inter-bonded into closed shell polyanions plus active metal cations, originally the alkali... 

Rules for counting the number of skeletal electrons provided by each vertex atom need to be established in order to determine the number of skeletal electrons in polygonal and polyhedral clusters of the post-transition elements. The rules discussed above for polyhedral boranes can be adapted to bare post-transition metal vertices as follows ... 

Bare group 13 metal vertices (e.g., Ga, In, Tl) provide, as noted above, only one skeletal electron each to polyhedral cluster structures. Thus it is not surprising that the bare metal cluster ions Enz (E = group 13 element) found in homonuclear alkali-metal/group 13 intermetallic phases [86-89] (mainly for In and Tl) have charges less negative than the — (n + 2) (i.e., z [Pg.21]

A metal atom cluster as defined by Cotton [1] is still a very broad term, because non-metal atoms can also be part of the cluster core. In this chapter mainly two types of metal atom clusters are presented the polyborane analogous polyhedral and the metalloid clusters E Rr of group 13 elements E. The structures and bonding of the polyhedral clusters with n < r are similar to those in the well-known polyboranes. 

We will first comment on metal-metal bonds (see Section 2.3.2) and then discuss (see Section 2.3.3) the polyhedral clusters [6], followed by the second central subject, the metalloid clusters in Section 2.3.4 (for recently published reviews see e.g., Refs. [7-11]). 

Multicenter bonding is the key to understanding carboranes. The series [CB H i and C2B H 2 (Schemes 3.2-44) contain mainly polyhedral clusters (trigonal bipyramids 15 and 39, octahedral [CBsHg]- and C2B4H6, icosahedra [CB11 H,2 and C2B10H12) which are three-dimensional a aromatics, however, the... 

Fig. 3.6-8. Polyhedral cluster frameworks in lithium phosphandiide chemistry. Compound 29 represents an electron-precise cluster, whereas 35 and 36 are electron-deficient,...

Concentric polyhedral clusters. Among the various contributions made by Corbett and co-workers to the different aspects of cluster science, special attention may be given to the investigations (preparation, structural description, electronic classification, etc.) carried out on phases containing multi-hedral, concentric polyhedral, clusters. 

Metal atoms have fewer valence electrons than orbitals available for bonding and in this they resemble boron. The consequences of this idea are examined and it is shown that many metals with electronegativities in the range 1.6-2.4 (B = 2.0) can subrogate boron atoms as vertices in polyhedral clusters. Such metalloboranes are often much more stable than the parent boranes or borane anions. Not only can metals mimic boron in known cluster geometries but the flexibility thus introduced can lead to novel and previously unsuspected cluster geometries. The construction of macropolyhedral clusters containing 17-20 vertices is also described. 

Ralph Rudolph made major contributions to our understanding of the structure and bonding of polyhedral cluster compounds and he had an abiding interest in developing a rationale which would enable the structure of individual compounds to be systematized and related to each other. He independently arrived at a method of counting skeletal electrons which is now generally referred to as Wade s Rules, and this has had a decisive influence on our general perceptions of polyhedral cluster compounds. Related to this was his preoccupation with the problem of heteroatoms such as sulfur, and the number of electrons which such atoms contribute to the heteroborane clusters. 

Some c/o o-Mbtallo-boranbs and -carboranes Containing at Least 1 Metal Atom in the n-VBRTEX Polyhedral Cluster... 

Reference to Tables II and III shows that cluster expansion reactions are in principle possible if neutral units such as BH, Fe(CO)3, Co(C5H5), or Ni(PR3)2 can be incorporated in an existing polyhedral cluster ... 

Refluxing Cjq with the metallacyclic carboranyliridium dihydride complex 13 in a toluene-acetonitrile mixture yields the complex 14, which contains two different polyhedral clusters as ligands (Scheme 7.7) [28]. The strong trans-influence of the o-bonded carborane ligand leads to a distortion of the iridacyclopropane moiety. The Ir-C bond trans to the carborane is significantly longer than the other Ir-C bond (2.229 vs. 2.162 A). This distortion can be utilized for the selective insertion... 

Eichhom BW, Haushalter RC, Pennington WT (1988) Synthesis and stracture of closo-SngCr (CO)3 the first member in a new class of polyhedral clusters. J Am Chem Soc 110 8704—... 

The geometries of metal carbonyl and metallocarborane cluster compounds have been systematized recently by a set of simple rules described collectively as the polyhedral skeletal electron pair theory (153, 218, 232). This approach originated from a perceptive analogy between isostructural metal carbonyl and borane polyhedral cluster molecules (232), and its applications have been widely discussed and reviewed (147, 153, 210, 218, 233, 234, 235, 240). In this review,... 

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