Four hydrates of sodium lanthanum ethylenediamine‐tetraacetate have been isolated. Na[LaY],3H2O crystallizes at 50°, Na[LaY],8H2O at 35° and Na[LaY],9H2O at 25°. A hexahydrate, Na[LaY],6H2O, has also been obtained, but the conditions for its formation are not yet well established. The complexes of Ce, Pr, Nd and Sm appear so far to crystallize only as octahydrates, Na[RY],8H2O; they are isomorphous with Na[LaY],8H2O. The octahydrates are orthorhombic pyramidal and therefore piezoelectric. On heating, all the hydrates easily loose water; the anhydrous compounds are stable up to 350°. With exception for the lanthanum salt, our solubility data are in good agreement with the values published by Marsh.
The solubility diagrams of the system Na[La‐EDTA]–Na[Pr‐EDTA]–H2O (EDTA = ethylendiamine‐tetraacetate) have been established at 0°, 35° and 50°. A miscibility gap occurs a t 0° between the solid phases Na[(La, Pr)‐EDTA] 6 H2O and Na[(Pr, La)‐EDTA], 8H2O, and also at 50° between the latter and Na[(La, Pr)‐EDTA], 3H2O. At 35° however, a continuous series of mixed crystals Na[(La, Pr)‐EDTA], 8H2O appears as the solid phase in this system.
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