Tin Flux, Crystal Structure, Magnetic Properties, Structural Relationships U Cr6P4 was prepared from a tin flux in two forms at low (a) and high (ß) temperatures (880 °C and 1000 °C), respectively. The crystal structures o f both m odifications were deter mined from single-crystal data. a-U C r6P4: P6m 2 (N o. 187), a = 698.5(3) pm, c = 350.8(1) pm, Z = 1, R = 0.052 for 18 variable parameters and 410 structure factors; /?-UCr6P4: Pmmn (N o. 59), a = 698.6(1) pm, b = 350.85(4) pm, c = 1196.1(2) pm, Z = 2, R = 0.047 for 21 variables and 656 structure factors. Although the lattice constants o f both m odifications are closely re lated, the two forms can be transformed into each other only by a very sluggish, reconstructive phase transformation. Nevertheless, both structures have very similar coordination polyhedra. The U atom s have 6 P neighbours in trigonal prismatic arrangement. H a lf o f the Cr atoms have tetrahedral, the other half square pyramidal P coordinations. As is typical for phosphides with high metal content, all metal atoms additionally have many metal neighbours. The P at oms are located in trigonal prisms o f metal atom s with two or three additional metal atoms outside the rectangular faces o f the prisms. Both m odifications o f UCr6P4 show relatively high, almost temperature independent paramagnetism, as is frequently observerd for intermetallic phases o f uranium.
The present status of research on condensed vanadic, molybdic, and tungstic acids is reviewed. Information about the structure and formation of polyanions can be obtained by X-ray analysis and from nuclear magnetic resonance, infrared, and Raman spectra, as well as from complex formation in aqueous solution. Salts of the polyacids can be prepared in organic solvents by hydrolysis of esters of the metal oxoacids.
Bei vorsichtiger Hydrolyse eines im organischen L6sungsmittel gelasten amphoteren Metallalkoxides in Gegenwart von Anhydrobasen oder Anhydrosauren entstehen Salze vonin der Regel mehrkernigen -Sffuren oder Basen. Die Reaktionen verlaufen ubersichtlicher als entsprechende Hydrolysen-und Kondensationsreaktionen im wHl3rigen Medium, weil das Wasser nur als Reagenz. nichr als Solvens fungiert. -Die Verwendung der Hydrolysenreaktionen fur analytische und praparative Zwecke, sowie ihre Bedeutung bei der Konstitutionsaufklhng von polykondensierten Ionen wird diskutiert.
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