Three forms (cis-, trans-, /3-trans-) of [Pd(NH3)2CI2] were obtained as pure single-phase powder materials. Ab initio structure determinations using X-ray powder diffraction were carried out. The cis-Pd(NH3)2C12 [a = 6.3121(2), b = 6.4984 (2), c= 3.3886(1)A, ot = 96.604(4), /3=97.290(4), y= 104.691(2y ~, Z= 1, space group P1] and trans-Pd(NH3)2C12 [a = 6.5398 (3), b=6.8571 (4), c=6.3573 (3) A, t~ = 103.311 (5), 15 --102.454 (3), y = 100.609 (4) °, Z = 2, space group P1] phases have a typical layer-column structure, while /3-trans-Pd(NH3)2Cl 2 [a --8.1540 (2), b = 8.1482(2), c = 7.7945 (1)A, Z = 4, space group Pbca] is described as a parquet-like layer structure. Both trans phases demonstrate the order-disorder phenomenon. The possible ways of phase transitions are discussed. It is noted that the cis phase can transform into trans in the solid state without destroying the crystal body. Further transformation to /3-trans follows through a break up of the crystal body. The result was a fine yellow powder. Chemical analysis: Pd 50.50 (50.40), C1 33.41 (33.49)%. The trans compound could also be prepared by thermal transformation of cis-[Pd(NH3)2C12)] at --~523 K, but in this case the product is contaminated by other isomers. fl-trans-[Pd(NH3)2C12) ] was obtained by thermal transformation of trans-[Pd(NH3)2C12)]. The latter compound was heated in water at 363-368 K for 4h. The orange coloured product was washed and dried. Chemical analysis: Pd 50.45 (50.40), C1 33.40 (33.49)%. The trans isomer is insoluble in water.

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Phase formation in the NaF-KF-AlF3 system, in the vicinity of the K2NaAl3F12 composition, has been studied. The samples have been prepared by melting the starting components at 650 °C. A new phase has been revealed, which appeared to be a low-temperature form of the well-known K2NaAl3F12 ternary fluoride obtained by the hydrothermal synthesis method. The high-temperature form melts at 598 °C and is stable in a narrow temperature region of about 15 deg below the melting point. Thermal analysis, high temperature X-ray diffraction, IR-spectroscopy, X-ray fluorescence, and X-ray powder diffraction crystal structure analysis have been applied to study the composition, crystal structure, and thermal properties of the low-temperature phase. The crystal structure consists of trigonal-hexagonal two-dimensional (2D) grids built from the [AlF6] octahedra connected via vertices. The 2D grids have a specific wave-like conformation with a wavelength of 11.88 Å and an amplitude of 0.46 Å. There is a shift of the adjacent grids relative to each other. Because of this shift, the space between the grids changes. The shift leads to the formation of pores adapted to potassium and sodium ions. The reasons for the wave-like structure of layers are discussed. It is shown that the two polymorphic forms differ in the order of cation occupations.

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Crystal structures of [Pd(NH3)2X2] complexes, where X = Br or I, diamminediiodo-/-dibromopalladium(II), have been studied by X-ray powder diffraction. The series consists of five complexes: cis-[Pd(NH3)2Br2] (I) [a = 13.3202 (7), b = 12.7223 (6), c = 7.05854 (3) A, Z = 8, space group Pbca], trans-[Pd(NH3)2Br2] (II) [a = 6.7854 (3), b = 7.1057 (3), c = 6.6241 (2) A, alpha = 103.221 (3), beta = 102.514 (2), gamma = 100.386 (3) degrees, Z = 2, space group P1], beta-trans-[Pd(NH3)2Br2] (III) [a = 8.4315 (3), b = 8.4206 (3), c = 8.0916 (2) A, Z = 4, space group Pbca], cis-[Pd(NH3)2I2] (IV) [a = 13.9060 (8), b = 13.5035 (8), c = 7.5050 (4) A, Z = 8, space group Pbca], and beta-trans-[Pd(NH3)2I2] (V) [a = 8.8347 (5), b = 8.8410 (5), c = 8.6081 (2) A, Z = 4, space group Pbca]. Patterson synthesis and Rietveld refinement have been used for structural determination. Molecular structures with column- or parquet-type packing of flat complexes are characteristic of these substances. Corresponding cis- and beta-trans compounds are isostructural. The thermal transformations cis-->trans-->beta-trans (cis-->beta-trans in the case of iodine) are considered. Cl derivatives are also discussed. The transformations proceed irreversibly and are accompanied by decreasing specific volume. Owing to these features, they can be classified as chemical reactions. High-temperature X-ray powder diffraction was used to study the transformations in air. The set of data is consistent with a solid state transformation from cis to trans. According to this model, the columns of molecules remain intact during the process, and the transformation proceeds via the breaking of Pd...X and Pd...N intermolecular bonds. The powder diffraction data have been deposited in ICDD-JCPDS (45-0596, 46-0876, 46-0879, 47-1690, 48-1185).

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