On the Complex Chemistry of the Tervalent Rare Earth Ions. II. The Acetate Systems of Praseodymium, Samarium, Dysprosium, Holmium, Erbium, and Ytterbium.

Six rare earth acetate systems were examined potentiometrically and one extinctiometrically. The complexity and stability constants are listed. All measurements were performed in perchlorate medium of ionic strength 2 M at 20 C. The extinctiometnic investigation of the Er/sup 3+/-Ac/sup -/ system shows that the rormation of the acetate complexes is accompanied by the appearance of new peaks close to the original ansorption bands at about 380 m mu and 525 M mu . The new peaks, one at every band, have a somewhat shorter wavelength than the original peaks. The agreement between the potentiometrically and the extinctiometrically obtained complexity constants is good. The stability constant of the first comp1ex, bt, increases with the atomic number from La to Sm. Then it decreases for Gd and Dy and remains approximately constant for Dy, Ho, Er, and Yb. To begin with, b/sub 2/ and b/sub 3/ also increase with the atomic number of the rare earth. For the heaviest rare earths, however, b/sub 2/ and b/ sub 3/ decrease slightly. The heavier rare earths (Gd-Yb) seem to form polynuclear complexes which, however, are rather weak. (auth)