Wiberg index values

Theoretical data supported quite well the vibrational IR and RAIRS data and allowed an interpretation of the energetic process of the complex-surface interaction. The variation observed in the Wiberg index values for the metal-ligand coordination bond suggests an important tc electronic redistribution around the cation by surface effect Table 14.7. 

Table 14.7. Selected Wiberg index values for different interactions...

The most relevant data of the adsorbate-substrate interaction, listed in Table 14.8, indicate that the Ni complex-colloidal Ag interaction is the most stable in the series. The Wiberg index values of the free complexes and the adsorbate-substrate adduct in Table 14.9, point to an electronic energy redistribution by interaction effect, being the most influenced bonds those directly involved in the metal coordination site. 

Table 14.9. INDO/1 Wiberg index values for selected bonds of the free complexes and the adsorbate-suhsirate adducts.(See Figure 14.10)...

The most relevant Wiberg index values for the isolated and the macrocycle-cluster interaction systems are displayed in Table 14.11. 

Hydrochloric acid is able to react with a hydroxyl-free silica surface without a barrier, with formation of hydroxyl groups and weakly bonded chlorine (Fig. 5( 1)). The distance between chlorine and silicon for the system under study is 2.417 A, compared to the experimental value of 2.017 A and calculated value 2.054 A for SiCU. The formal charge on chlorine for the system under study is -0.754 e, compared with -0.354 e for SiCU- The Wiberg index (bond order) for the chlorine-silicon bond for the system under study is 0.3231, compared to a value of 0.8468 for SiCU- A similar phenomenon is presented for systems like water and hydrochloric acid/water (Fig. 5(2)). These data show that the chlorine atom is bonded to the silica cluster mainly as an ion, and it is possible to understand the system under study as an ion-pair, which may dissociate into ions. As a result the chatted particles will be repelled electrostatically. 

The Wiberg-bond index (BO) [25] is calculated as sum of the quadratic non-diagonal elements of the density matrix between two atoms. This is done in the NAO-basis. The index has always positive values, therefore one cannot differentiate between bonding and antibonding character of the interaction between the two atoms. 

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