Abstract
Aqueous solutions of ScX 3 (X = Cl −, NO 3 −) contain, in the pH/D range of ca. 2–4, the species Sc(H 2O) 6 3+ [δ( 45Sc) = 0 ppm], Sc(H 2O) 5OH 2+ and Sc 2(H 2O) x(OH) 4 4+ (all in relatively fast exchange) and, if X = Cl −, an aqua—choroscandium complex in slow exchange with the other species. At pH > 4, a slowly exchanging hydroxo complex Sc 3(H 2O) y(OH) 5 4+ [δ( 45Sc) = +36 ppm] becomes predominant, 45Sc relaxation in the aqua/hydroxo system is exchange-dominated. For X = HCO 2 − and an intrinsic pH of 5.75, the main species present is a formiato complex [δ( 45Sc) = +32 ppm]. Complex formation has been observed in aqueous solutions containing scandium nitrate or scandium formiate [ c(Sc 3+) = 30 mmol/1] and the dipeptides H-val-ala-OH and H-glu-val-OH, and the tripeptide H-ala-val-leu-OH, and also in the scandium nitrate/ serine system. The δ( 45Sc) values for the complexes are +30 to +40 ppm [oxygen coordination: serine/ Sc(NO 3) 3, dipeptides/ScX 3] and ca. +70 ppm [oxygen and nitrogen coordination: H-ala-val-leu- OH/Sc(NO 3) 3].
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