Untersuchungen an Tetranatrium-cyclo-tetraphosphat(V) und seinen Hydraten

A reinvestigation of the system (NaPo₃)₄/H₂O has been carried out. Besides the already known tetra-hydrate and anhydrous form, a mono-hydrate in the temperature range 100–120°C exists. Single crystals were obtained by crystallization from aqueous solutions containing higher alcohols (e.g. ethyleneglycol) at ～115°C. The crystal structure was solved by X-ray methods (orthorhombic;P2₁2₁2₁;a=1365.4(2),b=1 347.5(3),c=629.1(3)pm;Z=4; 2774 diffractometer data;R=0.053). The cyclic anions exhibit point symmetryD _2d with all terminal oxygens in eclipsed conformation. With respect to the (NaPO₃)₄-part of structure, mono-hydrate and anhydrous forms are isostructural; lattice parameters of the latter area=1 380.8(2),b=1 363.3(2),c=602.7(2) pm. The transition mono-hydrate to anhydrous form occurs topochemically and is reversible.