ABSORPTION SPECTRAL AND CIRCULAR DICHROIC STUDIES OF COMPLEXES OF HYDROXY ACIDS WITH PRAESEODYMIUM ION

Complexes of three types were characterized, according to the general pH range in which they were obtained, as acid, neutral, and alkaline complexes. All three could be obtained with many of the ligands. Spectra obtained could be attributed to effects of splitting both ground and excited states of the central metal ion. Each spectral transition apparently exhibited circular dichroism, so that a transition could be identified by either an absorption or dichroism component, as convenient. In the 430-510-mμ wavelength band, in which Pr(III) normally shows only three peaks of the 3P2,1,0 multiplet and also has a buried 1I6 transition, as many as 21 transitions could be recognized for the 1:1 alkaline tartrate complex. Correlation of the various spectra led to the following conclusions of chemical interest: acid complexes showed a sign of the CD defined by hydroxyl configuration at the α carbon ; neutral complexes showed a sign of CD correlated with the sign of the lactone rotation which in turn is correlated with the sign of the hydroxyl configuration at the γ carbon, where this is an asymmetric center. Further conclusion was that seven-membered rings would form where the internal levels of the ligand favored this, six-membered rings would also form readily where this was the available choice, and under certain conditions, five-membered rings could form. Ligand acids used were tartaric, lactic, erythronic, ribonic, arabonic, xylonic, gluconic, gulonic, mannonic, idonic, galactonic, glucoheptonic, saccharinic, pantoic, malic, and saccharic acids. © 1968, American Chemical Society. All rights reserved.