The K-hydroxyisobutyrate and lactate ions arc known to form stable soluble complexes with the lanthanidcs. CHOPPIN ANI) CHOPOORIAN~ reported vulucs of the stability constants for the first 3 complexes of 9 lanthanidc elements and yttrium. However, their, as well as other, investigations on the same subjectze3 provided eviclcnce that the isobutyratc ancl lactate anions form unincgative tctra-ligand complexes with the lanthanitles.
It was also shown by EIXKHAUT cl al.4 that other cu-hydroxycarboxylatc lignnds as mcthylcthyl-and methylpropyl glycolatc form analogous complexes of the type ML4-(M = trivalent lanthanide ion; I, = organic ligand).
In the work described here, the determination of the 4 stability constants of the lanthanidcs and yttrium has been performed potentiometrically, using a glass-calo-me1 electrode system and the CN_VIN -WILSOS titration rncthod~, while CHOPPIN AND CHOPOORIAN used quinhydronc electrodes and FIIONAEUS' titration tcchnique0. The calculation of R, the average number of L-bound to MS+, has been carried out by a modification of the method used by CALVIN ANI) WILSON~ for MO+ and con~plcxes ML2. [L-) has been calculated from the apparent clissociation constant of the acid'. The stability constants arc derived graphically from corresponding fl and [L-] values by B J ERRUM'S llalf-+I mctllodfl, FHoNAEus'~ and PouLsEN's" extrapolation methods, and by means of a computer program, using the IBM 1620 digital compu-ter4* 10. 3> Lactic acid, analytical grade from BDH, was dcclimcrizecl by completely neutralizing with soclium hydroxide and then removing the sodium ions with a DOWCX 50 column in the hydrogen form. The lactic acid used gave a negative dimer test. Other reagents were the same as in a previous invcstigation4. A@arcttlrs and firocedwe A Radiometer PH M-4C potentiometer with a G 202 33 glass electrode and a K IOO f~rld.
C/ri)rr. AC/cl.