Coordination cavities

Eujii Y, Matsutani K, Kikuchi K. Formation of a specific coordination cavity for a chiral amino-acid by template synthesis of a polymer Schiff-base cobalt(III) complex. Chem Commun 1985 415-417. 

This equation provides a way to estimate the molecular cavity volume for any system but the shape of the cavity has also to be defined. Constant coordinate cavities such as the sphere or the ellipsoid are obviously not appropriate for most systems and they have been almost definitively abandoned in favor of molecular-shaped cavities. The majority of current continuum methods, and MPE as well, use van der Waals-type molecular surfaces. Atomic radii are in general larger than standard Bondi radii so that the obtained surface is close to the so-called solvent-excluding surface [64,65], Consistent with the expression for the volume given above, the order of magnitude of atomic radii should be... 

The sizes of the coordination cavities are illustrated by the following data ... 

FIGURE 10.3.1 The twist of the 12-coordinate cavity in ReOj to form two octahedra sharing faces, as found in LiReO and Li ReO (From Ref. 4, J. Solid State Chem., 42 (1982) 251. 1982 Elsevier). 

Considering a crystallographic model of the a-TiCl3 surface, Cossee noticed that the layers basic plane was not parallel to it but formed an angle of about 55° that situation creates a non-equivalence between the 2 vicinal coordination positions located in a coordination cavity and very strong steric compression around one of them (Fig. 11). As a consequence ... 

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