New complexanes. 31

Complexes of ethylenediamine-N,N'-dimalonic, ethylenediamine-N,N'-disuccinic, and ethylenediamine-N,N'-(α,α'-diglutaric) acids with the lanthanide ions La(III) with the exception of Pm were studied in aqueous solutions by potentiometry and electrophoresis on paper. Neutralization curves and the 'tren' methods were used in evaluating stability constants of the complexes for I = 0.10 (KNO3) and t = 20 0C. Electrophoresis on paper was employed in studying the charge of complex particles and in checking the complex composition. The formation of the ML complexes in the ratio of components of 1:1 was observed; the abundance of the complex forming in neutral or mild alkaline pH region also resulted in the formation of the ML2 complexes. The ML2 formation was most marked with EDDM yielding ML2 complexes with all lanthanides. On the other hand, EDDS and EDDG only formed ML2 complexes with heavier lanthanides, especially from Ho to Lu, whereas in the case of the first four (La-Nd) only complexes with a ratio of 1:1 were formed under the given experimental conditions. The formation of a higher ML2 complex was connected with the lower donor ability of the complexanes investigated and with the possibility of a higher coordination number of lanthanides. The formation of less soluble compounds in a mild acidic medium was characteristic of EDDM reacting with lanthanides. In the case of lanthane a compound of the composition H6La2L3.8H2O was isolated. (author)