Coordination compounds with the general formula trans-[M(18-crown-6)(C5HO2F6)2] as structural-thermochemical analogs. The complexes trans-[Pb(18-crown-6)(C5HO2F6)2] and trans-[Ba(18-crown-6)(C5HO2F6)2]

The molecular geometries of the complexes trans-M(18-crown-6)(C₅HO₂F₆)₂] (where M = Ca, Sr, Ba (I), Zn, Cd, Sn, Pb (II), Fe, Co, Eu, and Yb) were modeled by the molecular mechanics method with fixed R(M-O) distances. The shielding degrees of the central metal atom in these complexes were calculated and the number and types of possible intermolecular contacts between their molecules in the structure were determined. The intermolecular interactions involve identical fragments (atoms) of the ligands: the CF₃ groups of the hexafluoroacetylacetonate ligands and the methylene fragments of the crown ether. Previously unknown complex II and complex I were synthesized according to an original procedure. The structure and thermochemical properties (including sublimation by the Knudsen method) of complex II were studied. As in complex I, the metal cation in complex II is in the cavity of the macrocycle of the crown ether; the hexafluoroacetylacetonate ligands are trans relative to that cation. The presumed similarity of complexes I and II in thermochemical characteristics was confirmed experimentally. Both the complexes melt in close temperature intervals and sublime at the same temperature (～10^?2 mm Hg) without decomposition. The enthalpies of sublimation of complexes I and II, as well as the entropy contributions to their volatilities, are equal to within the experimental error.