Single shapes

The basis of the single-bead concept is the use of single-shaped bodies as the catalytic material of interest. These particles may in principle be of any shape, but usually spherical particles are applied. In accordance with approaches known from CombiChem, such spherical particles are called beads, although they fulfill veiy different functions in comparison to their application in combinatorial setups... 

How many different cluster structures can you devise for the molecular formula Os6(CO)2i You should be able generate more than a single shape. Four shapes are known for six-atom metal clusters with the same electron count as this cluster. 

In practice, it is often sufficient to consider a single shape group type for a specified type of truncation. Then, one may also consider each separate piece of the MIDCO s obtained in the truncation process as a separate entity with its own shape group. An example for such a modified (a,b)-map has been calculated for the allyl alcohol molecule. 

Presumably, this effect makes it difficult to assert that a single shape is universally explanatory. If ammonia engages in a reaction under conditions where it has a trigonal bipyramidal shape, than we probably could not say it reacts in a certain way because it has the shape of a trigonal pyramid. Chemists routinely appeal to shape to explain how a molecule reacts.Some shape might be explanatory in every explanation, but the shape will be different in different explanations. 

Fig. 3. Ljjj absorption spectra of Sm in trivalent Sm Oj (lower spectrum) and in mixed valent SmB (upper spectrum). The absorption maxima in both compounds are observed at identical ener es. SmB, however, exhibits a significant shoulder at about — 8eV displaced from the maximum of the trivalent absorption line (adapted from Vainshtein et aL (1965a)). The second absorption line indicates the presence of divalent Sm in SmB ( = 2.65 0.05). The valence number v is obtained from a weighted superposition d two single-shaped Lm absorption spectra disjdaced by 8eV (Vainshtein et al-1965b).

The complete catenoid is thus not suitable for variations of form like the unduloid, but constitutes a single shape, like the sphere and the cylinder. 

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