Alkali metal clusters stability

Khama, S. Dasgupta, S. Biradha, K. Bhattachaijee, M. Self-assembly of an alkali metal cluster stabilized by a new flexidentate metalloligand formation and structure of heterobimetalhc Na-Mo and Cs-Mo 2D networks. Eur. J. Inorg. Chem. 2005,5005. 

In coating fullerenes with alkali metals, the stability of the cluster seemed to be determined primarily by the electronic configuration. The units C qM and C7oMg, where M is any alkali metal, proved to be exceptionally stable cluster building blocks. Coating a fullerene with more than 7 alkali metal atoms led to an even-odd alternation in the mass spectra, inter-... 

It can be expected that solid bases could be successful for commercializing the alkylation of toluene with methanol as a route to styrene, or for selective alkene coupling. There is no doubt that achieving success in several important commercial processes will boost the field of solid base catalysis. Because it appears to be difficult to achieve superbasic organic resins, much more attention should be paid to enhancement of the base strengths of solid superbases. Further work should be done on supported alkali metals and mixed metal oxides. Development of new solid superbases will be improved by increasing our understanding of how alkali metal clusters (302-304) interact with supports and become stabilized. 

It was shown in Ref. [22] that the Q30 model correctly reproduces all magic numbers observed for alkali metal clusters up to N = 1500, using for the model parameters the values r = 0.038, A = 0.39. But there, these values were chosen more or less by trial and error, so as to fit the experimental data. With the renormalization of the energy expression described in the previous section, we now have a natural way for determining the deformation parameter r, which is connected with the cluster stability. 

The most intensively studied clusters are alkali-metal clusters [428 31], where the stability and the ionization energies have been measured as have the electronic spectra and their transition from localized molecular orbitals to delocalized band structure of solids [432, 433]. 

Whereas a negative value for A E(n) indicates that the process 2 M - M i + is energetically feasible, a positive value signals that the process M M , + M is less favorable than the reaction M +, M + M. When one plots the quantity A E(/i) against the cluster size n, the odd-even oscillations in the cluster stability become quite obvious (Fig. 2 4). For alkali metal clusters, the sharp maxima found at n = 2, 4, 6 and 8 indicate that clusters having odd numbers of atoms undergo fragmentation more easily than clusters with even nuclearity. [25, 91]... 

The IP s of several low nuclearity clusters have been computed by various methods with different degrees of success. As shown by the following examples, the trend in the IP s as a function of the cluster size strongly depends on the metal considered. For the alkali metal clusters Li and Na , odd-even oscillations have been observed, [112] whereby the higher IP s correspond to those clusters having closed shells and higher stability (n even). In general, however, the IP... 

For the alkali metal clusters in the solid state, only a small island of stability exists so far, and this is with the suboxides of the heavy alkali metals Rb and Cs [4] at relatively low temperatures. Similar compounds of the lighter metals and the higher homologues of oxygen do not exist. 

The structures of the alkali metal suboxides have been discussed in terms of bare metal clusters stabilized by interstitial oxygen atoms. Due to the direct M-M bonding between the clusters, the suboxides are metallic and show electrical properties [220] which are similar to the free alkali metals. 

Wang G, Cole RB. Solvation energy and gas-phase stability influences on alkali metal cluster ion formation in electrospray ionization mass spectrometry. Anal Chem. 1998 70 873 81. 

Alkali metal cluster formation presupposes that the element is in intermediate oxidation states between zero-valent and normal valence ones which are characteristic of metallic and salt-like species respectively. The chemistry of this class of compounds is therefore strongly associated with the stabilization of such states. 

Lower formal oxidation states are stabilized, however, by M-M bonding in ternary chalcogenides such as M MeQn, M4M6Q13 (M = alkali metal M = Re, Tc Q = S, Se) and the recently reported M gMeS. Their structures are all based on the face-capped, octahedral MeXg cluster unit found in Chevrel phases (p. 1018) and in the dihalides of Mo and W... 

What is the nature of the defects seen in the EPR spectra For alkali and alkali earth halogenides it is well known that irradiation with X-ray, neutrons, gamma-radiation, or electrons produce paramagnetic color centers (F-center) [109-111]. If these centers are created in large amounts, they can be stabilized by the formation of metal clusters as observed for MgCl2 films after prolonged electron radiation [106]. From the temperature dependence... 

Even the extremely electron-deficient alkali metals can form clusters when interstitial atoms contribute to their stabilization. Compounds of this kind are the alkali metal suboxides such as Rb902 it has two octahedra sharing a common face, and each is occupied by one O atom (Fig. 13.16). Flowever, the electron deficiency is so severe that metallic bonding is needed between the clusters. In a way, these compounds are metals, but not with single metal ions as in the pure metal Rb+e-, but with a constitution [Rb902]5+(e )5, essentially with ionic bonding in the cluster. 

With respect to the thermodynamic stability of metal clusters, there is a plethora of results which support the spherical Jellium model for the alkalis as well as for other metals, like copper. This appears to be the case for cluster reactivity, at least for etching reactions, where electronic structure dominates reactivity and minor anomalies are attributable to geometric influence. These cases, however, illustrate a situation where significant addition or diminution of valence electron density occurs via loss or gain of metal atoms. A small molecule, like carbon monoxide,... 

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