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Alkali-lead clusters

Reactions of Cp TiF3 with alkali metals and their fluorides lead to a variety of reduced titanium alkali metal clusters containing Ti-F bonds.433-435 (CsH4SiMe3)TiF3 has been reduced with Zn and Mn to give tetranuclear Ti(m) clusters, which are converted to (G5H4SiMe3)2TiF2 by oxidative fluorination with AgF.352... [Pg.400]

Excess electrons in clusters also exhibit the above structural characteristics as well as Other quantum mechanical effects that arise when the electron wavelength is comparable to the cluster diameter. Path integral studies of an excess electrons in alkali halide clusters have established the existence of internal cavity structures and of extended surface states. Dissociative attachment, leading to the formation of an isolated alkali atom, and structural isomerization have also been observed. Similar calculations have demonstrated the prevalence of surface states in water clusters. " Representative structures are shown in Figure 5. [Pg.2026]

The polyhedral boranes and carboranes discussed above may be regarded as boron clusters in which the single external orbital of each vertex atom helps to bind an external hydrogen or other monovalent atom or group. Post-transition main group elements are known to form clusters without external ligands bound to the vertex atoms. Such species are called bare metal clusters for convenience. Anionic bare metal clusters were first observed by Zintl and co-workers in the 1930s [2-5], The first evidence for anionic clusters of post-transition metals such as tin, lead, antimony, and bismuth was obtained by potentiometric titrations with alkali metals in liquid ammonia. Consequently, such anionic post-transition metal clusters are often called Zintl phases. [Pg.17]

When it comes to metal-rich compounds of the alkaline earth and alkali metals with their pronounced valence electron deficiencies it is no surprise that both principles play a dominant role. In addition, there is no capability for bonding of a ligand shell around the cluster cores. The discrete and condensed clusters of group 1 and 2 metals therefore are bare, a fact which leads to extended inter-cluster bonding and results in electronic delocalization and metallic properties for all known compounds. [Pg.247]

R = H or Si are generated. An increase in the surface basicity (molar ratio Na2C03 or K2C03 0s = 10-20 1) leads to anionic [Os(CO)3(OR)2UOR) " (R = H or Si= m > 1) species up to [Os(CO)3(OH)3]". The low reactivity of this latter species explains why low yields of carbonyl clusters are obtained when adding to the siUca surface a stronger base such as an alkali hydroxide instead of an alkali carbonate [14, 60]. [Pg.664]

The crystal structures of numerous organolithium compounds and complexes with 0—Li bonds are now available (2-5). Table IV lists a number of these species, as well as two derivatives of heavier alkali metals. As with the C—Li derivatives just discussed (Tables II and III), clustered (ROLi) tetramers and hexamers, as well as ring dimers, are prevalent. Note that (OLi)2,3 ring systems also are pseudoplanar (Fig. 21a). However, extensive stacking leading to polymers will only occur if the substituents on 0 are small and if polar ligands are absent. Otherwise, limited (double) stacks or unstacked rings form. [Pg.88]

Particle irradiation effects in halides and especially in alkali halides have been intensively studied. One reason is that salt mines can be used to store radioactive waste. Alkali halides in thermal equilibrium are Schottky-type disordered materials. Defects in NaCl which form under electron bombardment at low temperature are neutral anion vacancies (Vx) and a corresponding number of anion interstitials (Xf). Even at liquid nitrogen temperature, these primary radiation defects are still somewhat mobile. Thus, they can either recombine (Xf+Vx = Xx) or form clusters. First, clusters will form according to /i-Xf = X j. Also, Xf and Xf j may be trapped at impurities. Later, vacancies will cluster as well. If X is trapped by a vacancy pair [VA Vx] (which is, in other words, an empty site of a lattice molecule, i.e., the smallest possible pore ) we have the smallest possible halogen molecule bubble . Further clustering of these defects may lead to dislocation loops. In contrast, aggregates of only anion vacancies are equivalent to small metal colloid particles. [Pg.320]


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