Complexes of Pivaloyltrifluoroacetonates of Potassium and Rubidium with 18-Crown-6 Ether: Synthesis, Structure, Thermal Properties

In a search for volatile fluorinated compounds of potassium and rubidium, new complexes of the corresponding pivaloyltrifluoroacetonates (Ptac) with 18-crown-6 ether, [K(18C6)(Ptac)] (I) and [Rb(18C6)(Ptac)] (II), were synthesized. The compounds were characterized by elemental analysis, IR spectroscopy, and X-ray fluorescence analysis, and their structures were studied by single-crystal X-ray diffraction (SCXRD) in the range of 100–400 K (CCDC nos. 2429226–2429232 (I), 2429233–2429239 (II)). The complexes are isostructural and have an molecular mononuclear structure, with M…H and M…C contacts involving the tert-butyl group between fragments, forming chains. The thermal expansion tensors are elongated along this direction. X-ray diffraction analysis showed that the rubidium cation in such a complex can complete its coordination sphere with a solvent molecule (chloroform, CCDC no. 2429240 (IIs)). For I, II, and IIs, Hirshfeld surface were analyzed and a search for pseudoperiodicity in the crystal packings was carried out using the translational sublattice method. Thermogravimetric analysis showed that, unlike the initial pivaloyltrifluoroacetonates, complexes I and II are volatile and promising for testing in gas-phase processes of thin-film material deposition.