Abstract
Complexes of vanadium(IV) with aminopolycarboxylic acids, nitrilotriacetic (NTA), nitrilodiaceticpropionic (NDAP), nitrilodipropionicacetic (NDPA), and nitrilotripropionic (NTP) acids were studied by electromotrice force measurements [emf(H)] in 3.0 M KCl ionic medium at 25°C. Data analysis using the least-squares program LETAGROP, according to the general reaction p H+ + q VO2+ + r C3− ⇆ H p (VO) q C r p +2 q −3 r , indicates that the following complexes are formed (H3C ligands): NTA ([VOC]− and [OHVOC]2−); NDAP ([VOC]− and [OHVOC]2−); NDPA ([VOC]− and [OHVOC]2−); and NTP ([H2VOC]+, HVOC, [VOC]−, and [OHVOC]2−). The following order of coordination capacity NTA > NDAP > NDPA > NTP is suggested, based on values of stability constants and is attributed to the increase in propionic groups in the sequence. The study confirms that five-membered ring chelates are the most stable for VIV, like CuII, NiII, lanthanides, and other heavier elements.
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