The Paradox of Hydrogen-Bonded Anion–Anion Aggregates in Oxoanions: A Fundamental Electrostatic Problem Explained in Terms of Electrophilic···Nucleophilic Interactions

Abstract

A theoretical study of anionic complexes formed by two partly deprotonated oxoacids joined by hydrogen bonds has been carried out at the MP2 computational level. In spite of the ionic repulsion, local energy minima are found both in the gas phase and in aqueous solution. Electrostatic potential and electron density topologies, and the comparison with neutral complexes formed by oxoacids, reveal that the ionization has no significant effect on the properties of the hydrogen bonds. The stability of the complexes in the gas phase is explained by attractive forces localized in a volume situated in the hydrogen bond and defined as the electrostatic attraction region (EAR) and determined by the topological analyses of the electron density and the electrostatic potential, and by the electric field lines. In solution, the strong anionic repulsion is mostly screened by the effect of the surrounding polar solvent, which only leads to a weak destabilizing interaction in the hydrogen bond region and finally favors the overall stability of the complexes. The anion−anion complexes have been compared with the corresponding neutral ones (as salts or protonated forms), showing that EAR remains unchanged along the series.

Quantum Crystallography: Current Developments and Future Perspectives

“…Hence, the study of the topological critical points (CP) of r 2 1 r ðÞhas indicated that charge concentration (CC) and charge depletion (CD) sites found in the valence shell of atoms are drivingg eometric preferences of molecules in the solid state. [214] Furthermore, the intersection of the gradient vector fields of 1 r ðÞ and V r ðÞ has shown to help to understand the counterintuitive assembling of anion-anion and cation-cation aggregates, [215][216][217][218] pointing out the regions of space that are involved in local attractive electrostatic interactions in hydrogen [219] and halogen [212] bonding. [212,213] Thus, in the polyiodide chains of the crystal structure of tyrosinium polyiodide hydrate (Figure 10 b), iodines are distinguished from iodides by the type of CPs found in their interactions with surrounding atoms.…”

Ion Pairing and Co‐facial Stacking Drive High‐Fidelity Bisulfate Assembly with Cyanostar Macrocyclic Hosts

“…The class of bonding between these two anions has been discussed and led to the consideration of anti ‐electrostatic hydrogen bonding . Classified as strong hydrogen bonds, they may also display features of multi‐center covalent bonding between anion radicals .…”

Hydrogen‐ and Halogen‐Bonds between Ions of like Charges: Are They Anti‐Electrostatic in Nature?

“…Based on current understanding, the electrostatic attraction between the electron‐deprived hydrogen and the electron‐rich center on D plays the key role in H‐bonding, while the charge‐transfer (CT) from D to the antibonding σ* orbital of H–A (i.e., n D →σ* H‐A ), which brings about covalence, is also important and largely responsible for the directionality of the hydrogen bond . While many new types of strong and unconventional H‐bonds have been identified and recognized, some initially unexpected forms of H‐bonding, such as the B – H···π hydrogen bond, or the hydrogen bond between positively charged phosphorus and hydrogen atoms, or even hydrogen bonds between ions of like charge, have also been experimentally observed. These recent and novel studies enrich the categories of H‐bonds, and call for a more profound and comprehensive theoretical treatment of H‐bonding.…”

“…Our interest here lies is in the H‐bonding between H‐donor and ‐acceptor of like charges, such as the recent experimentally observed OH···P H‐bonding . The existence of such a complex seemingly violates the electrostatic paradigm of H‐bonding, as ions of like charges must be mutually repulsive.…”