Solution studies of vanadium(IV) complexes with nitrilotriacetic acid (NTA) and other aminopolycarboxylic acids (NDAP, NDPA, and NTP)

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.