Coexistence of ion pairs and molecular associates in the nanoparticles of inorganic compounds

  • A. G. Grebenyuk O.O. Chuiko Institute of Surface Chemistry of National Academy of Sciences of Ukraine
Keywords: cluster, molecular associate, ion pair, prototropy, halotropy, structural transition in nanoparticles, quantum chemical simulation


The possibility of the existence of clusters of inorganic substances in the state of a molecular associate and a combination of ion pairs is analyzed. The main causes of the appearance of ionic pairs are considered: partial or complete transfer of an electron or electron pair from one molecule to another, transfer of a proton (prototropy) or halide ions (halotropy) between molecules, conversion of contact ionic pairs in microcrystals of salts into salts separated by solvation. The conditions of structural transitions between them are determined. The influence of nanoparticle sizes and temperature on the relative thermodynamic stability of these two forms of clusters is described.               The review covers a wide range of subjects: clusters formed by water molecules, hydrated molecules of oxygen and oxygen-free acids, inorganic bases (alkali metal and ammonia hydroxides) and salts; anhydrous and hydrated clusters containing simultaneously acid and base molecules; clusters of coordination compounds, and some other substances. The results are presented of quantum chemical calculations by Hartree-Fock (HF), electron density functional theory (DFT), coupled single, double and triple excitation (CCSD (T)) and second-order Möller-Plesset perturbation theory (MP2) methods of the spatial structure and energy characteristics of the models under consideration. The theoretical results are compared with the available experimental data.               It is revealed that dissociation of O–H bonds is possible in clusters formed by at least five water molecules and is a complex reaction controlled by the formation of hydrogen bonds, with two water molecules acting as promoters of the hydrolysis reaction where a synchronous displacement occurs of two protons, and the H3O+ and OH ions act simultaneously as hydrogen bond triple acceptors and triple donors. In clusters of hydrated inorganic acid molecules, both anoxic and oxygen-containing, including 3 to 5 water molecules, collective (i.e. concerted) proton transitions and ionic dissociation are possible. The ionic dissociation of alkali metal hydroxides and halides requires 3 to 7 water molecules in the cluster.               It has been shown that in clusters consisting of the same number of molecules of ammonia and hydrochloric acid (HCl)n•(NH3)n, the transition from the hydrogen bond to the ion pair occurs already at n = 2. Ionic coordination compounds can form oligomeric associates, where the distance between the cation and the anion depends on the coordination number of the cation and is intermediate between the values characteristic of the contact and separated ion pairs.


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How to Cite
Grebenyuk, A. G. (2019). Coexistence of ion pairs and molecular associates in the nanoparticles of inorganic compounds. Surface, (11(26), 344-371.
Theory of surface chemical structure and reactivity.