Mechanism of ionic recognition by polymer-supported reagents: immobilized tetramethylmalonamide and the complexation of lanthanide ions.
The mechanism of ionic recognition by polymer-supported reagents is probed with cross-linked polystyrene modified with tetramethylmalonamide (TMMA) ligands. The substrates are lanthanide ions in 0.001-8 M HCl and HNO(3) solutions. The results fall into three regions of acid concentration: low, mid, and high. In HCl, distribution coefficients are low in 0.001 to 2 M, increase in 4 and 6 M, and then decrease in 8 M HCl. In the low-acid region, the metal ion remains with its waters of hydration and does not coordinate to the carbonyl oxygens. As the acid concentration exceeds 2 M, protonation of the amide occurs to form an iminium moiety, electrostatically attracting the anionic lanthanide complex through ion-exchange and releasing waters of hydration. At high acid concentration, the apparent affinity decreases due to competition by the large excess of chloride ions for the ion-exchange sites. The affinity sequence in 6 M HCl is Tb > Dy > Eu > Gd > Ho > Sm > Er > Tm > Yb > Lu > Nd > Ce > La. The TMMA-Ln interaction is due to recognition since there is a point of maximum affinity across the series rather than a monotonic trend. The trends are comparable in HNO(3). A comparison of the distribution coefficients at the maxima (6 M HCl and 4 M HNO(3)) shows nitrate to have greater values than chloride due to a hydration effect, as also indicated by results from H(2)SO(4).
Yang
Yijia
Y
Department of Chemistry, Hunter College of the City University of New York, 695 Park Avenue, New York, New York 10065, USA.
Alexandratos
Spiro D
SD
D000577:Amides / Q000737:chemistry*; D007202:Indicators and Reagents / Q000737:chemistry*; D007477:Ions / Q000737:chemistry; D028581:Lanthanoid Series Elements / Q000737:chemistry*; D008024:Ligands; D009942:Organometallic Compounds / Q000138:chemical synthesis / Q000737:chemistry*; D011145:Polyvinyls / Q000737:chemistry*
D000577:Amides; D007202:Indicators and Reagents; D007477:Ions; D028581:Lanthanoid Series Elements; D008024:Ligands; D009942:Organometallic Compounds; D011145:Polyvinyls; C080604:polyvinylbenzyl chloride