Theoretical study of the structures of [M(18C6)](HFA)2 complexes (M = Ba,Sr, Pb,Cd, Mn; 18C6 = 18-crown-6; HFA = hexafluoroacetylacetonate anion)

The structures of the M(18C6)]²⁺ cations (M = Ba, Sr, Pb, Cd, Mn) and their salts M(18C6)](HFA)₂ and M(18C6)](NO₃)₂ have been calculated by the density functional theory method (in the B3LYP/6-311++G** + LanL2Dz approximation). Upon geometry optimization, the gas-phase structures of compounds of different composition have been calculated; for them, the strength of binding of the central cation to the crown ether (18C6) and the degree of structural similarity have been evaluated. The structure of the NH₄(18C6)]⁺ cation identified in a practical synthesis has also been considered. For metal cations acting as a central atom, NH ₄ ⁺ and M(18C6)]²⁺ complex cations, as well as for intermediate and ultimate products M(18C6)](NO₃)₂ and M(18C6)](HFA)₂ (M = Ba, Sr, Pb, Cd, Mn), the electronic chemical potential and Pearson hardness, which enables the consideration of the propensity of various reagents to interact with each other in terms of the empirical HSAB principle (hard with hard and soft with soft), have been evaluated. Comparison of the estimates with the properties of the synthesized compounds with M = Ba, Sr, and Pb makes it possible to preliminarily verify the applicability of this principle to the systems under consideration and predict some properties of isostructural analogues important in the search for methods of synthesis of M(18C6)](HFA)₂, where M = Cd and Mn. The possibility of establishing a correlation between the electron density of the system, stability, and hydrolytic activity of complexes has been shown.