Hetero-atomic clusters

Apart from gold-centred clusters, several hetero-atom clusters have been made [189]. The oxo-centred cluster has been used as a starting material in synthesis [190],... 

Hetero-atomic clusters, moreover, may be derived from the binary structures mainly through the introduction of late transition or earlier post-transition elements. Examples of ternary alloys containing such structures are the alkali metal salts of centred clusters In10Me10 (Me = Ni, Pd, Pt), Tl12 Me12- (Me = Mg, Zn, Cd, Hg), etc. The crystal structure of the phase Na T Cdi x)27 (0.24 < x < 0.33)... 

Figure2.6.5 [SngCr(CO) ], the first derivative of a deltahedral Zintl anion. The Cr(CO)3 fragment caps the open pseudo-square face of the original Sn cluster and does not donate electrons for cluster bonding. The hetero-atomic cluster is a closo-species according to both shape, a bicapped square antiprism, and electron count. The three empty d orbitals, xz, andyz ofCrfCO) overlap with the filled orbitals shown in Figure 2.6.4 and, therefore, the cluster behaves as a six-electron donating ligand...

Heteroatom fullerene-type clusters — The possibility of incorporation of hetero atoms into C clusters has excited the attention of both theoreticians and experimentalists since the earliest days of fullerene chemistry, particularly in view of the known stability and ubiquity of organic heterocycles. The structural relationship between Ceo and /3-rhombohedral boron has already been alluded to (p. 142). 

No. of thermal parameters refined (cluster hetero atoms treated anisotropically) 4,737... 

These reductive pathways are particularly suitable for making clusters that encapsulate hetero atoms, simply by introducing a suitable source of these atoms, such as CC14 for C, QCl for Q, H2S for S, or Ph3As for As. 

Rhodium also forms an unusually large number of clusters containing encapsulated hetero atoms as, for example, the [Rhn(S)2(CO)32]3 species whose skeletal structure is shown in Fig. 16-15, and a number that contain carbon atoms. It also forms both smaller, for example, Rh CO), and larger, for example, Rh H CO) clusters that have no encapsulated atoms. The Rh12 species has a very novel structure in which two Rl octahedra are linked together to form an Rh6 octahedron between them. Finally, rhodium also forms many mixed metal clusters, especially with plati-... 

The first extensive NMR studies of deltahedral Zintl ions were carried out by Rudolph and coworkers. Using Sn, Sn, and Pb NMR they were the first to show that the homo- and hetero-atomic nine-atom deltahedral clusters Sng, Pbg, Sng- Ge , and Sn9 j Pbj are fluxional in solution. The homo-atomic clusters exhibit single resonances while multiple signals were observed for the hetero-atomic species due to their different stoichiometries, with one signal per stoichiometry. In addition to this, all the clusters show single spin-spin couplings of the types Sn— Sn, Sn- ° Pb, and Sn— Pb. These observations indicate that, on the NMR timescale, all atoms of the cluster are equivalent by dynamic and... 

Our experiments show, unambigously, that a pure carbon film rich with sp linear chains can be formed by assembling carbon clusters at room temperature under ultra-high vacuum. Polyyne and polycumulene species are present and stabilized in all-carbon metastable structures without the need of hetero-atom terminal groups. Under He, N2, and H2 exposure the amount of sp species reduces exponentially with time depending upon the mass of the gas. For the investigated gases no chemical interactions have been observed. 

Another more recent development is the occurrence of clusters that are integral components of extended solid state structures. The Chevrel phases, already mentioned, are one example but there are numerous others, of which in some the clusters have a hetero atom in the center of the octahedron, e.g., Zr6NCli5. Recently, it has been shown that the individual clusters can often be extracted and dissolved in suitable solvents. 

As discussed in Sec. 1.28.3.1, the number of Ph3PAu(0) groups in the hetero-nuclear clusters of the type [M(CO)x(AuPPh3), ] is determined by the electronic demand of the transition metal M, that requires a stable 18 electron configuration. The cluster cation [Pt(dppe)(AuPPh3)4] + is an exception to this rule, since the central Pt atom only achieves 16 electrons by adding to the 10 d electrons of the Pt(0) atom the four electrons of the two Pt P bonds, and the two electrons of the... 

C2.1 Metal cluster complexes containing hetero-atom-substituted carbene ligands... 

Tabfe 2. Abundance maxima observed in hetero-atomic At,B clusters. The abundance maxima are characterised by the number of valence electrons in the cluster. Also given is the difference An% between the jellium background densities of A and B metals... 

Fullerene Ball-shaped cluster or cage of interconnected trigonal or sp carbon atoms. Derivatives include replacement of some carbons by hetero atoms, the presence of atoms inside the cluster/cage, and functionalization by reactions involving the formal double bonds connecting the carbons. 

Needle coke is derived mainly from clean i. e. lacking hetero atoms and solids) and highly aromatic (i.e. several condensed rings per cluster) feedstocks with a very low concentration of insolubles. Upon solidification a material with a distinctive streaked or flow-like macroscopic appearance is produced. Upon grinding the coke breaks up first into macroscopic needles and then, after further griruling, into micro-platelets. Sometimes the word acicular is used as a synonym for needle-like. 

Also, Te " and l produce [TeMo6024] and [Mo6024] and many more. These heteropolymolybdates(Vl), and heteropolytungstates(VI) (similar clusters) break up with OH but often not with H3O, and then can be made, e.g., by ion exchange, into strong acids, imlike the homopolymolybdates and homopolytungstates. Colorless hetero-atoms produce more-or-less yellow species. Similarly well known are homo- and heteropolymolybdates(V). 

We see that mai hetero-atoms occupy the unique vertices in these clusters with W3S4", but maity more are known to do so with Mo3S4. ... 

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