Dihydrogen bonds hydrogen bond energy

Since hydrogen and dihydrogen bonds have comparable energies and directionality, their combination also holds interest for crystal engineers. 

Nevertheless, the data in Table 3.5 reveal an important difference between classical hydrogen bonding and dihydrogen bonds. In fact, since in O- - -H conventional bonds the electrostatic component is followed by charge transfer energy while the polarization contribntion iipL is very small, classical hydrogen bonds can be formulated as... 

TABLE 3.5. Energy Components (kcal/mol) for the Simplest Hydrogen- and Dihydrogen-Bonded Complexes ... 

Bonding energies are similar for classical hydrogen bonds and dihydrogen bonds. 

In the first report on the beryllinm dihydrogen-bonded complex, pnblished in 1996 [5], the H-Be-H- H-N(H3)+ system was located at an energy minimnm of the potential energy surface calcnlated at the MP2/6-311-H-G level. By analogy with classical hydrogen bonds, this dihydrogen complex can be said to be charge-assisted. 

One of the important aspect of the use of dihydrogen bonds as driving forces in molecular associations is their cooperativity or anticooperativity when increasing the number of H- H contacts in the self-association of molecular systems leads to additional energy, calculated on the basis of one dihydrogen bond, or vice versa. As we have shown in Chapter 2, classical hydrogen bonds can be highly cooperative, due to their mutual polarization [5]. 

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