Emergent dual functionality of water and reverse coordination of s-block metal ions in weakly solvating media

Water exhibits a wide range of anomalous properties, and various models have been proposed to elucidate its nature. In this study, we reexamine the diversity of water's behavior through the lens of solvating power and fundamental chemical interactions in solution. Electroanalytical and spectroscopic investigations in nonaqueous media reveal that s-block metal ions (Li⁺, Na⁺, Mg²⁺, Ca²⁺, etc.) possess an intrinsic ability to form both coordination-type (metal-centered species such as [MX _n ] ^m-) and "reverse coordination" complexes (anion-centered species represented by [M _n X] ^m+) with anions when the solvent's solvating power is sufficiently weak. These findings prompted a reconsideration of the role of trace water in nonaqueous systems, leading to a novel interpretation of the dual (or even multiple) nature of water. We propose that the cooperative hydrogen bond interactions within large-scale water assemblies enable bulk water to undergo reversible cleavage and regeneration of O-H bonds. The disruption of this hydrogen bond network-as observed in highly concentrated electrolyte solutions-markedly reduces the hydration power of water, giving rise to unusual chemical phenomena, such as a partial suppression of nitric acid dissociation and enhanced oxidizing ability.