Formation constants of mixed ligand complexes of UO<img src='http://www.niscair.res.in/jinfo/twoplustwo.gif' border=0> and Th⁴⁺ with complexones and oxygen donor ligands

Abstract

Formation Constants (log K<img src="http://www.niscair.res.in/jinfo/equation108.gif" alt="" border="0" />) of the mixed complexes of the type MAL, where M = UO + or Th⁴⁺ , A= iminodiacetate (IMDA), nitrilotriacetate (NTA), 2-hydroxyethylethylenediaminetriacetate (HEDTA), ethylenediaminetetracetate (EDTA), 1,2- diaminocyclohexanetetraacetate (CDT A) or diethylenetriaminepentaacetate (DTPA), and L=catechol (cat), 4-methylcatechol (m-cat), tiron (tir), 2,3-dihydroxynaphthalene (DHN) or chromotropic acid salt (CS), have been determined potentiometrically by the Irving-Rossotti approach at 25°C and at an ionic strength, <em>I = </em>0.2 (mol dm^-3, KNO₃). The observed trends in solution stabilities arc (i) Th⁴⁺ > UO<img src="http://www.niscair.res.in/jinfo/twoplustwo.gif" alt="" border="0" />, (ii) CS > tir > DHN > m-cat > cat, and (iii) IMDA > NTA > HEDTA > EDTA > CDTA > DTPA with respect to the metal ions, secondary ligands (L) and primary Iigands (A), respectively. The <img src='http://www.niscair.res.in/jinfo/delta.gif' border=0>log<em>K </em>values are negative. The formation constnats log <em>K</em> <img src="http://www.niscair.res.in/jinfo/equation109.gif" alt="" border="0" /> and log <em>K <img src="http://www.niscair.res.in/jinfo/equation163.gif" alt="" border="0" /></em> have also been determined and compared with the log <em>K</em><img src="http://www.niscair.res.in/jinfo/equation108.gif" alt="" border="0" /> values.