Cluster structure transformation

Room temperature deposition of silver on Pd(lOO) produces a rather sharp Ag/Pd interface [62]. The interaction with a palladium surface induces a shift of Ag 3d core levels to lower binding energies (up to 0.7 eV) while the Pd 3d level BE, is virtually unchanged. In the same time silver deposition alters the palladium valence band already at small silver coverage. Annealing of the Ag/Pd system at 520 K induces inter-diffusion of Ag and Pd atoms at all silver coverage. In the case when silver multilayer was deposited on the palladium surface, the layered silver transforms into a clustered structure slightly enriched with Pd atoms. A hybridization of the localized Pd 4d level and the silver sp-band produces virtual bound state at 2eV below the Fermi level. 

Fig. 10. Illustration of the similarity between the cluster structure of 3 and the closest packing in A1 metal Rotation of the upper ring of I by 30° leads to a structure II, which can then easily be transformed into a section of the closest packing of A1 metal by shifting in the layer of the page by...

The proposed Re6 cluster (8) with terminal and bridged-oxygen atoms acts as a catalytic site for selective propene oxidation under a mixture of propene, Oz and NH3. When the Re6 catalyst is treated with propene and Oz at 673 K, the cluster is transformed back to the inactive [Re04] monomers (7), reversibly. This is the reason why the catalytic activity is lost in the absence of ammonia (Table 8.5). Note that NH3, which is not involved in the reaction equation for the acrolein formation (C3H6+02->CH2=CHCH0+H20) is a prerequisite for the catalytic reaction as it produces the active cluster structure under the catalytic reaction conditions. 

The carbonyl cluster Rh,5(CO)i,5 was initially stable as such on the completely dehydroxylated alumina surface. But as soon as hydroxyl groups were generated (e.g., by adding traces of water) it decomposed to give various surface transformations. First, the cluster structure was dismpted, with breakage of the core cluster frame, into (Al-0-)(Al-0H)Rh (C0)2, Rh > monoatomic species sigma and n-bonded to the oxygens atoms of the alumina surface, with formation of molecular... 

In this section, we discuss the high performance of the Rejo cluster/HZSM-5 catalyst, its active structure and dynamic structural transformation during the selechve catalysis, and the reaction mechanism for direct phenol synthesis from benzene and O2 on this novel catalyst [73, 107]. Detailed characterization and determination of active Re species have been conducted by XRD, Al solid-state MAS NMR, conventional XAFS and in situ time-resolved energy dispersive XAFS, which revealed the origin and prospects of high phenol selectivity on the novel Re/HZSM-5 catalyst [73]. 

Osmium (continued) carbide, 24 233 dianion, lA. Xil, 317-319 with phosphines and diphosphines, 30 191 protonation/deprotonation, 30 169 raft hexaosmium clusters, 30 180-182 reactions of condensation, 30 145 with hexafluoroacetone, 30 288 redox, 30 184-185 structural transformations, 30 203 sulfur-containing, synthesis of, 30 147 sulfur derivatives, 24 269, 300-310 synthesis... 

Nido Clusters (2n + 4 Systems). Many closo boranes and heteroboranes add two electrons and undeigo a concomitant structural transformation from a deltahedron to a deltahedral fragment. For instance, closo-2,6-C2B9H1 l [17764-89-0], (2n + 2 = 24e ), is readily reduced to... 

If instead of a mild Lewis base such as THF a strong Lewis base such as pyridine is used in the reaction between copper acetate and dtbp-H, one obtains yet another type of one-dimensional polymeric phosphate (Chart 16).36c Recrystallization of this water-bridged polymer in a DMSO/ THF/CH3OH mixture results in the transformation of the polymer to a more stable tetranuclear copper cluster [Cu4-(u3-OH)2(dtbp)e(py)2] in about 60% yield (Figure 3). This observation demonstrates that even simple recrystallization can bring about an interesting structural transformation at room temperature in such materials. 

Figure 8.5 Representative structures of the X( B12 (-co, -ico) clusters, and the structures of B( B6 clusters. The initial and optimized structures are depicted. The number markings added to boron atoms are consistent before and after optimization. The H< , Cr< , and Mn B,2-co clusters and the Be< and B B12 clusters form structure (c). Meanwhile, the V , Cr< , Mn< , Fe< , and Co( B12-ico clusters have structure (d). The B B6 cluster undergoes great distortion and gains total energy. The optimized B B6 cluster should be called a B7 cluster without the octahedral structure. The arrow represents the transformation of the cluster structure.

Catalytic molecular surface species may undergo drastic changes in their structure in the presence of reactants. For example, polymeric clusters may transform into highly distorted monomeric species. A crystalline phase may become mobile at its Tammann temperature, as shown by Raman spectroscopy, and it may spread over oxide supports driven by the reduction of the overall surface free energy. Reactive environments trigger many structural transformations, exemplified by particle sintering, dispersion of bulk phases, segregation of surface species into bulk phases, and solid-state reactions between supported oxides and supports. 

Figure 2-9. The structure of coupled-cluster similarity-transformed Hamiltonian for coupled-cluster singles and doubles...

Scheme 23. Structural transformations of some M5 clusters upon addition of nucleophiles.

Catalytic Activity of Pt4 Clusters towEird the Hydration of Acetonitrile Trinuclear Platinum(II) Cluster Complexes A. Synthesis—Cluster Core Transformation Structures of Triangular Cluster Complexes Mechanism of the Cluster Core Transformation Reaction from Square-Planar to Triangular Type EHMO Study Solution Behavior 195pt NMR Spectra of Pts Clusters IV. Concluding Remarks References... 

Skapski et al. reported the structure of 1 in 1976, but the chemistry was not been studied in detail until the regioselective lability of the coordinated acetates was reported by our research group in 1989 (29). Since then, many derivatives of 1, including trinuclear Pt(II) clusters, have been synthesized and their chemistries have been investigated. In this article, the chemistry of Pt 4 clusters are reviewed along with Pt 3 clusters, which are derived from the cluster core transformation of 1. 

One way to see that a transition is discontinuous is to detect a coexistence of two phases, in this case the orientationally ordered and disordered phases, in a temperature interval. This is revealed by time variation of the potential energy of the cluster. In the temperamre region of phase coexistence, each cluster dynamically transforms between the phases, and its potential energy fluctuates around two different mean values (Fig. 4). In an ensemble of clusters, the coexistence of different phases is observable insofar as a fraction of the clusters (e.g., in a beam [17]) can exhibit the structure of one phase, while another fraction takes on the stmcture of another phase. 

To describe the thermodynamics and kinetics of clusters with due regard for the multiplicity of the structure states (SS) of these nuclei, it is necessary to introduce the SS sets. The mutual transformations of clusters by atom attach ment or detachment, or by atom rearrangements are possible. It means that the SS set may be ordered to form a space. Then, it is possible to consider the nucleation of noncrystalline nuclei (clusters) as a diffusion process in an extended space of cluster structure states (CSS), which is, in fact, the join of hierarchy of ultrametric subspaces. The kinetic criterion of glass transition can be formulated as a condition of the overwhelming transformation of a liquid into a noncrystalline amorphous solid. 

As a further substantiation of the intrinsic limits of the welfare regime approach, alone or first within the continental cluster, France has embarked on this consistent structural transformation of its social protection both on the side of funding (the significant increase of the funding by tax and special new contributions to the state budget) and on the labour market side (reductions of social contributions for employers). This has resulted in a rather clear strategy to liberalise the system, mainly stressing the demand side of the labour market, and less importantly the supply-side and individual incentives. From the current evaluation studies, the... 

---