Hydrogen–hydrogen bonding: A stabilizing interaction in strained chelating rings of metal complexes in aqueous phase

Abstract

Two HH close contacts, classically associated with steric hindrance, were found to be H-H closed-shell bonding interactions which stabilize a zinc(II) complex with, by ca. 11 kcal/mol in aqueous phase.The strain energy of three 6-member rings (ca. 40 kcal/mol) is significantly offset by these interactions the presence of which is indicated by the presence of a bond path, an elevated delocalization index, and a lowering of the atomic energy of each hydrogen atom involved in an HH interaction by ~ 4-5 kcal/mol. The difference between relevant bond path angles and geometrical bond angles in the 6-member coordination rings correlates well with strain energy and formation constants. Unexpectedly, the bite angle N-Zn-O is found to be the least strained.

Physical Nature of Interactions in ZnIIComplexes with 2,2′-Bipyridyl: Quantum Theory of Atoms in Molecules (QTAIM), Interacting Quantum Atoms (IQA), Noncovalent Interactions (NCI), and Extended Transition State Coupled with Natural Orbitals for Chemical Valence (ETS-NOCV) Comparative Studies

“…It is important to note that Bader and co-workers interpreted close contacts CH--HC in some molecules as the bonding interactions, either from the calculated [29][30][31][32][33][34][35][36][37] or experimental 29,[38][39][40] electron density distributions, using the quantum theory of atoms in molecules (QTAIM). 41 The formation of H-H bonding interactions in simple molecules (like biphenyl, phenanthrene) was then challenged in the literature [42][43][44][45][46] and rebutted.…”

AIM analysis and the form of the bond-valence equation

“…Here, the bond order is posited to be based on the delocalization matrix and is approximately equal to the count of the electrons at a bond critical point. This idea has been developed for the case of strong bonding (Matta and Hernández-Trujillo 2003), and has been explored thoroughly for H … H bonding, where a similar relationship was observed (Cukrowski and Matta 2010). A similiar relationship has also been observed for biological molecules (Zhurova et al 2006).…”

Experimental study of electron density distribution in crystals of antimony(V) dicarboxylate complexes

“…The energies of these interactions (-0.63 kcal/mol in 1 and 2) insignificantly stabilize the plane structure of the carboxylate ligands. It should be noted that such stabilizing H…H interactions between ortho-hydrogen atoms take place in polynuclear aromatic organic molecules [37][38][39]. However, there is another point of view according to which such interactions not necessarily have to be of stabilizing character [40][41][42][43][44][45][46][47][48][49][50][51].…”