Molecular-mechanics and -dynamics simulations of trivalent europium complexes of calix[4]arene derivatives and a bislariat diazacrown ether

Molecular‐mechanics (MM) and molecular‐dynamics (MD) simulations (in MeOH) were performed on Eu3⁺ complexes of two derivatized calix[4]arenes (2b and 2d) and a bislariat diazacrown ether (3). The Quanta/CHARMm Lennard‐Jones parameters of Ca2⁺ proved suitable as a model for the Lennard‐Jones parameters of Eu3⁺. The radial distribution function (RDF) of Eu3⁺ … MeOH (O) agrees well with experimental data. The MD of 2b · Eu3⁺ showed that the phenolic oxygens cannot compete with the solvent, although they are preorganized. Three molecules of MeOH are within the first coordination shell. The MD of 2d · Eu3⁺ showed two transitions. After the first the Eu3⁺ was coordinated by one molecule of MeOH and after the second by three molecules of MeOH. The pyridine ring was not involved in coordination to Eu3⁺, which explained the measured lifetimes and derived coordination shells in methanol. The calculations on 3 · Eu3⁺ revealed that the conformation with the pendant arms in an anti configuration is unlikely to exist in solution, whereas the syn form calculated by MM rearranged to a structure with two molecules of MeOH in the first coordination sphere. This is consistent with experimental data, which show that the two dominant species in methanol solution have two molecules of MeOH coordinated to the Eu3⁺. All calculations were performed with the Quanta/CHARMm package.