Mono-capped trigonal prismatic complexe

In a trigonal prismatic transition metal complex (16), in addition to the six a hybrids which form M-L bonds there are three non-bonding orbitals which include one pure d 2 and two e d-p hybrid non-bonding orbitals (see Table 3). As discussed above, it can be concluded that capping the square faces is preferred to the triangular faces in the mono- and bi-capped trigonal prismatic transition metal complexes because of the two d-p hybrid non-bonding orbitals which maximize their electron density towards the square faces. The existence of structures such as [Mo(CNR)gI] (mono-capped) [39] and ZrFf" (bicapped) [40] supports the conclusions above. 

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