Polyion Covalency: Exotic Species from the Unexplored World of Electrostatically Shielded Molecular Ion Chemistry

Abstract

Standard quantum chemical methods have been employed to describe a variety of kinetically stable polyionic molecular species that are trapped in appreciable potential wells by chemical bonding forces, despite powerful electrostatic opposition that challenges conventional chemical detection and characterization. The studied species are covalent or dative analogs of “anti‐electrostatic” hydrogen‐bonded (AEHB) species, all illustrating how short‐range quantum covalency can overcome the powerful “shielding” opposition of long‐range electrostatic forces to form highly charged molecular species, analogous to known neutral or singly ionic counterparts. Computational predictions of representative structural, spectroscopic, and NBO‐based electronic signatures of multiply charged analogs of common neutral species (CH3CH3, CO2, FeCO) are provided to suggest the unique material properties characteristic of this shielded domain of polyionic chemical phenomena.

Protonated nucleobases are not fully ionized in their chloride salt crystals and form metastable base pairs further stabilized by the surrounding anions

“…10). Analogous observations made for other kinds of same-charge dimers, not for nucleobases, are present in the literature (Gamrad et al, 2015;Weinhold, 2017Weinhold, , 2018Alkorta et al, 2016;Grimme & Djukic, 2011;Shokri et al, 2013;Mata et al, 2015).…”

Intermolecular Interactions in Ionic Crystals of Nucleobase Chlorides—Combining Topological Analysis of Electron Densities with Energies of Electrostatic Interactions

“…. C + ) and anion-anion (A − ...A − ) aggregation by hydrogen bond interactions in the solid state despite ionic repulsion [10][11][12][13][14][15][16][17][18][19][20][21][22][23][24][25][26]. To elaborate on this, Braga and co-workers [17,20,25,27] studied the ionic crystal structure of hydrogen oxalate, KHC 2 O 4 , alkali hydrogen squarate salts and alkali metal croconate salts, and introduced a concept called Coulombic compression "arising from attractive next-neighbour A − .…”

Switching from Negative-Cooperativity to No-Cooperativity in the Binding of Ion-Pair Dimers by a Bis(calix[4]pyrrole) Macrocycle

“…It is also known that in nonpolar solvents, calix [4]pyrrole receptors bind MTOA•Cl with higher affinity than the TBA counterparts. 18,32,33 This is due to the better fit of the methyl group of the MTOA + cation in the shallow and electron-rich cup opposite to the bound anion in comparison to the alkyl groups of TBA.…”

“…17 The goal of this latter research aims at mimicking nature and gaining insights on how it copes with concurrently binding anions in close proximity, i.e., anion channels, synthesis of ATP, DNA, RNA, etc. In this vein, dimers of polyatomic anions have been investigated "in silico" 18,19 and experimentally stabilized by noncovalent binding using synthetic receptors, both in solution and the solid state. 20−23 Calix [4]pyrroles are effective heteroditopic receptors for the complexation of ion-pairs in nonpolar solvents.…”