Vol 51, No 10 (2025)

To complete the studies of double complex compounds, (N-thiocyanato)chromates(III) of lanthanide complexes with pyridine-3-carboxylic acid, new compounds of the compositions [LnL₃(H₂O)₂][Cr(NCS)₆] · · nH₂O (Ln = Pr (I), n = 1.5; Sm (II), Gd (III), Tb (IV), n = 2; L = C₆H₅NO₂). The substances were studied by chemical analysis, IR spectroscopy, and PXRD (CCDC No. 2427051–2427054). In the crystal structures of complexes I–IV, the cation has a chain structure due to the bidentate-bridging function of pyridine-3-carboxylic (nicotinic) acid molecules. The coordination environment of the lanthanide atoms consists of eight oxygen atoms belonging to six nicotinic acid molecules and two coordinated H₂O molecules, located at the vertices of a distorted square antiprism. In the isolated [Cr(NCS)₆]^3– anions, the Cr coordination polyhedron consists of the N atoms of six thiocyanate ions and is close to a regular octahedron. In the structures of complexes I–IV, the space between polymeric cations is filled with complex anions and crystallization water molecules. Additionally, the structure is stabilized by intermolecular hydrogen bonds.

In the 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 X-ray diffraction in the range of 100–400 K (CCDC nos. 2429226–2429232 (I), 2429233–2429239 (II)). The complexes are isostructural and have an insular 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 surfaces were analyzed and a search for pseudoperiodicity in the crystal packings was carried out by 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.

A new scandium(III) 1,1,1-trifluorohexane-2,4-dionate complex [Sc(5Htfac)₃] was synthesized, purified, and characterized by elemental analysis, NMR spectroscopy, and mass spectrometry. Its structure was determined at 150 K by X-ray diffraction analysis (CCDC No. 2433044). The complex has a molecular structure in which the bidentate cyclic ligands are arranged according to the os-isomer. Shortened H…F interactions were identified in the structure. The thermal properties were studied by TGA and DSC, and the fusion temperature (309.3 ± 0.5 K), enthalpy (Δ_fusH°(T_fus) = 36.0 ± 1.4 kJ mol^–1), and entropy (Δ_fusS°(T_fus) = = 116.5 ± 4.5 J mol^–1 K^–1) of fusion were determined. The temperature dependence of the saturated vapor pressure was measured by the flow method (343–433 K) and the static method with a membrane null manometer (410–470 K). On this basis, the thermodynamic characteristics of evaporation at average and standard temperatures were calculated (Δ_vapH°(298.15 K) = 100.2 ± 1.3 kJ mol^–1, Δ_vapS°(298.15 K) = = 201.8 ± 2.8 J mol^–1 K^–1). From these data, the sublimation parameters of the complex were obtained (Δ_subH°(298.15 K) = 135.3 ± 1.9 kJ mol^–1, Δ_subS°(298.15 K) = 315.3 ± 5.4 J mol^–1 K^–1). The structure and thermal properties of [Sc(5HT_fac)₃] were compared with those of two scandium(III) β-diketonates bearing methyl and tert-butyl substituents in the ligand.