ANION INFLUENCE ON THE SOLUTION OPTICAL ACTIVITY (CPL) OF EUROPIUM NITRATE AND CHLORIDE COMPLEXES OF CHIRAL CROWN ETHERS.
The authors report the effects of differing methyl group position in a series of chiral methyl-substituted 18-crown-6 ethers (1)-(4) on the observed optical activity of complexes with europium(III) nirate and europium(III) chloride in 2,2,2-trifluoroethanol. The solution structure of the europium nitrate complex of (2) has been shown to be one with the europium centrally coordinated in the crown cavity with two bidentate nitrate anions coordinated on either side of the crown-europium 'plane'. Differences noted between the CPL of nitrate complexes of (4) and the other crowns are explained through changes in the orientation of the nitrate-europium chelate rings which cause a change in the configurational chirality of the lanthanide, as compared to the other nitrate complexes.
