Mononuclear single helices of lanthanum(III) and europium(III). Metal dependent diastereomeric excess

Abstract Using the 1:2 condensate of benzildihydrazone and 2-acetylpyridine as a tetradentate N donor ligand L, LaL(NO 3 ) 3 ( 1 ) and EuL(NO 3 ) 3 ( 2 ), which are pale yellow in colour, are synthesized. While single crystals of 1 could not be obtained, 2 crystallises as a monodichloromethane solvate, 2 ·CH 2 Cl 2 in the space group Cc with a  = 11.7099(5) A, b  = 16.4872(5) A, c  = 17.9224(6) A and β  = 104.048(4)°. From the X-ray crystal structure, 2 is found to be a rare example of monohelical complex of Eu(III). Complex 1 is diamagnetic. The magnetic moment of 2 at room temperature is 3.32 BM. Comparing the FT-IR spectra of 1 and 2 , it is concluded that 1 also is a mononuclear single helix. 1 H NMR reveals that both 1 and 2 are mixtures of two diastereomers. In the case of the La(III) complex ( 1 ), the diastereomeric excess is only 10% but in the Eu(III) complex 2 it is 80%. The occurrence of diastereomerism is explained by the chiralities of the helical motif and the type of pentakis chelates present in 1 and 2 .