What is Common for Dihydrogen Bond and H…σ Interaction—Theoretical Analysis and Experimental Evidences

Abstract

Two types of the hydrogen bond are described and compared here; the A–H…H–B dihydrogen bond and the A–H…σ interaction. In a case of the dihydrogen bond the H…H contact between the hydrogen atoms characterized by the opposite charges is observed; i.e. between the protonic (A)H and hydridic (B)H hydrogens. For the A–H…σ hydrogen bond the A–H proton donating bond interacts with the σ-electrons of the molecular hydrogen. These interactions are topologically different since for DHB the bond path linking the attractors of H-atoms with the corresponding bond critical point is observed. For the A–H…σ interaction the bond path between the (A)H-atom attractor and the bond critical point of the H–H bond of the molecular hydrogen is observed. Both types of the hydrogen bond are characterized by the significant σ → σ* orbital-orbital interaction, σBH → σAH* in a case of DHB and σHH → σAH* for A–H…σ. There are also evidences that A–H…H–B and A–H…σ may be classified as the hydrogen bonds. The examples of complexes characterized by the mentioned above types of the hydrogen bond are analyzed in this chapter, the theoretical as well as experimental examples are presented.