Capping atom group

As an example, consider the reaction of the cobalt(m) complex of 7.8 with formaldehyde and nitromethane to give 7.9, the cobalt(m) complex of ligand 7.10 (Fig. 7-10). Notice that 7.8 is the same precursor that we needed for the synthesis of 7.7. In the new ligand, 7.10, the cap is formed from three molecules of formaldehyde and one of nitromethane, and the capping atom is now the carbon of the CN02 group derived from the nitromethane. 

The capping atoms in the hexa-, octa-, dodeca-, and octadecanuclear structures listed in Table III all have the same disposition i.e., they are attached to a /u,4-oxo group of the central cubane(s) to complete a tetrahedral coordination geometry about this site. This contrasts with the additional metal sites in the decanuclear cages, where they are attached to ixq-oxo groups which have octahedral geometries. 

The ability of encapsulated iron(II) ion to be oxidized to iron(III) ion drops in the series of capping atoms Ge > Sn > Sb > B. In C2-nonsymmetric clathrochelate complexes, the oxidation potentials are near average between the values for symmetric complexes with corresponding capping groups (Table 38). 

Cryptands are cyclic (mainly) polyether molecules with usually three chains linked at nitrogen caps at each end of the molecule (Figure 4.42), much like the sarcophagines but with a different capping atom and different donors. They can, depending on host cavity size, bind metal ions (alkali or alkaline earth ions preferred) or small molecules. A wide range of molecules of this family have been prepared. They can be effective in metal ion selection from a group of ions, useful in both analysis and separation of mixtures. They also help solubilize metal ions in aprotic solvents. 

Figure 23.28 presents a comparison of the UPS valence band spectra of DP7, for both the pristine molecule and the molecule interacting with Ca, Na, or Al atoms, and the DO VS for the corresponding tetradecaheptaene system as derived from LSD calculations. Since the tetradecaheptaene has no capping phenyl groups, only the upper part of the spectra are shown, and the contribution from the phenyl groups is omitted in the following discussion [61]. 

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