Features of the structure of oxynitridophosphates K3MIII(PO3)3N (MI = Al, Ga)

Немає доступних мініатюр
Zatovsky, Igor V.
Ogorodnyk, Ivan V.
Baumer, Vyacheslav N.
Zhilyak, Ivan D.
Horda, Ruslana V.
Strutynska, Nataliya Yu.
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Crystals of trispotassium aluminum (or gallium) nitride tris(phosphate) were prepared by the self-flux’s method. All the metal cations and the N atom occupy special positions with site symmetry 3, while the P and O atoms are situated in general positions. The three-dimensional framework of these oxynitridophosphates is built up [Al(or Ga)O6] octahedra linked together via [(PO3)3N] groups (formed from three PO3N tetrahedra sharing an N vertex). The coordination environment of potassium atoms shows three types of polyhedral K1O9, K2O9N and K3O9N. An unusual tetradentate type of coordination of two potassium atoms with the [(PO3)3N]6- anion is observed.
Synthesis and characterization For the synthesis of (I) and (II), KH2PO4, K4P2O7·10H2O, urea, Al2O3 or Ga2O3 (all analytically or extra pure grade) were used as initial reagents. The sequence of preparation procedure was as follows: (1) phosphates KPO3 and K4P2O7 were prepared by calcining KH2PO4 and K4P2O7·10H2O at 600C, respectively; (2) a mixture of 20.07 g KPO3, 13.21 g K4P2O7 and 30.03 g urea (molar ratio K:P = 1:1.32, urea:P = 2:1) ground in an agate mortar, was heated to complete degassing full outgassing at 350C in a porcelain dish. The resulting solid was reground and heated to homogeneous liquid at 750C and then frozen by pouring the melt onto a copper sheet to form glass. The glass was crushed using a mill and a powder with a particle size of less than 125 µm was separated. According to chemical analysis, the prepared glass has the composition K1.32PO2.43N0.50; (3) a mixture of 10 g glass (K1.32PO2.43N0.50) and powders 0.3 g Al2O3 or 0.7 g Ga2O3 were placed into porcelain crucibles and heated up to 770C and then cooled to 650C at a rate of 25 /h. After cooling to room temperature, the colorless tetrahedral crystals of (I) or (II) were washed with deionized water. Elemental analysis indicated the presence of K, Al (or Ga), P and N in the atomic ratio 3:1:3:1. The grows of well shaped crystals of both reported compounds, suitable for single crystal XRD, was one of the tasks of the investigation. So we applied a similar way we used before for sodium-containing compounds. A method to preparation of crystalline nitrogen-containing phosphates by the self-fluxes was proposed by us earlier (Zatovsky et al., 2006). Thermal decomposition of urea is multistage and leads to the formation of C3N4 (Wang et al., 2017). The initial MI-P-O-N (MI = alkali metal) melt can be obtained by reacting of urea with alkali metal phosphates, when a mixture of phosphates and C3N4 interact. In addition, changing the ratio of phosphate:C3N4 (or phosphate:urea) and the nature of the alkali metal affects the composition of the resulting melt. In our case, the molar ratio of K:P was 1:1.32 (a mixture of KPO3 and K4P2O7 in this proportion has the lowest melting point close to 613°C), and the quantitative value of urea:P was set 2:1. As a result, glass of a composition K1.32PO2.43N0.50 was prepared.
Ключові слова
In this work, we report the flux-growth synthesis, structural characterization and FTIR spectra for K-containing oxynitridophosphates K3Al(PO3)3N (I) and K3Ga(PO3)3N (II).
Бібліографічний опис
Zatovsky, I.V., Ogorodnyk, I.V., Baumer, V.N., Zhilyak, I.D., Horda, R.V. & Strutynska, N.Y. (2021). Structural features of the oxidonitridophosphates K3MIII(PO3)3N ( MIII = Al, Ga). Acta Cryst. E 77, https://doi.org/10.1107/S2056989021011336.