Cluster isomers

The authors of this work did not consider I-IV as cluster compounds nor did they view II and IV as cluster isomers. Let us see if we can relate the observed chemistry to cluster isomerization albeit one in which the forward (C apart to C adjacent) and reverse (C adjacent to C apart) have similar barriers. That is, an effective alkyne metathesis catalyst cannot have any species in the catalytic cycle of high stability (Bunz, 2005). 

Of particular interest are the predicted magnetic moments and the question of whether or not isomers of transition metal clusters can be separated using inhomogeneous magnetic fields. To date, cluster isomers have only been detected via their different chemical reactivity (70-73). One would expect abnormally large magnetic moments for the Ih clusters if they had unusually high density of states at the Fermi level, as has been postulated for aluminum (74)-... 

Relative stabilities of small carbon cluster isomers... 

The examples presented illustrate three points already presented in Sections 2 and 3. The formation of a cluster structure containing specified transition metal and main group atoms depends on (1) the skeletal electron count, (2) the identity of the elements chosen, and (3) the number and type of ligands on the cluster atoms. In addition, the following dramatically shows the wide variety of cluster isomers and stoichiometries that remain to be discovered. 

Two non-interconvertible metallacyclopentadienyl cluster isomers [WRe2(yU-H)-Cp (CO)9 CHCH(C6H8) ] were obtained by heating a solution of the vinylacety-lide complex [WRe2Cp (CO)9 C=C(C6H9) ] to reflux in toluene, under hydrogen. Structural analysis revealed that one isomer has a triangular backbone with a metal-metal double bond, which supposes a total electron number of 46, whereas the other has a bent chain of metal atoms (TEC 50). 

Figure 21.2. Schematic outline of the apparatus used for the measurement of cluster velocities (a) and typical cluster intensity profiles for different nozzle tube temperatures (b). The broken lines indicate the shift of the maxima of the intensity profiles with increasing nozzle tube temperature for the two different cluster isomers.

Evidence for Neutral Silicon Cluster Isomers from Calorimetric Studies... 

Collision Cross-Sections and Shape of Neutral Silicon Cluster Isomers... 

From the observed broadening of the cluster intensity profiles in the velocity slip experiments one cannot determine how many isomers each of the assumed two isomer classes contains. However, it is possible to extract from the broadening of the cluster intensity profiles the ratio of all isomers having a more compact, spherical shape to all of the isomers having a less compact, elongated shape. From the areas of the two gaussians in Figure 21.2 (b) one obtains the temperature-dependent intensity ratio of the two silicon cluster isomers, which is the intensity of the spherical isomers divided by the intensity of the non-spherical isomers. 

In the second application of selective ionization, we select not different rigid cluster isomers but differentiate between rigid and fluxional cluster subpopulations of... 

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