Enantioselective Resolutions and Circular Dichroism Studies of Lanthanide-Containing Keggin-Type [Ln(PW11O39)2]11- Polyoxometalates

Enantiopure crystals of K1.3Na3.2H6.5[L-Pr(PW11O39)(2)]center dot 8.3L-proline center dot 21.5H(2)O (1), K1.3Na3.2H6.5[D-Pr(PW11O39)(2)]center dot 8.3D-proline center dot 17H(2)O (2), and K1.3Na3.2H6.5[L-Er(PW11O39)(2)]center dot 8.3L-proline center dot 22.5 H2O (3) were successfully obtained by using L- and D-proline (pro) as chiral auxiliary agents. In these crystals, L- and D-[Ln (PW11O39)(2)](11-) anions are attached by two L- and D-pro molecules, respectively, through a O center dot center dot center dot N hydrogen-bonding interaction between the square-antirismatic LnO(8) center and amino-N atoms. The L- and D-[Pr(PW11O39)(2)](11-) anions in aqueous solutions exhibited a couple of mirror-imaged CD spectra due to H-3(4/2)-> P-3(0,1,2) and D-1(2) transitions in the stereogenic Pr3+ center. Chirality inductions by L- and D-pro from a racemic solution of [Er(PW11O39)(2)](11-) was demonstrated by means of CD spectroscopy.