A tetrahedral zinc(II) complex of N-(R)-1-phenylethylsalicylideneimine. Structural and circular dichroism spectral investigations on stereoselectivity

Abstract

The stereoselectivity of bis[N-(R)-1-phenylethylsalicylideneiminato]zinc(II) has been studied by means of single-crystal X-ray analysis and circular dichroism (c.d.) spectra. The complex crystallizes in space group P2₁2₁2₁ with a= 17.738(4), b= 29.632(9), c= 9.968(2)Å, and Z= 4. The unit cell is comprised of four units each containing two complex molecules (A and B). Each molecule adopts a nearly tetrahedral structure with two bidentate ligands; the dihedral angle defined by the two chelate rings is 81.7° for molecule A and 84.9° for molecule B. The absolute configuration along the pseudo-C₂ axis is Λ for both molecules. Based on the X-ray analysis it is suggested that intramolecular non-covalent interactions between the chiral N-substituent and the adjacent chelate ring give rise to stereoselectivity and the Λ configuration around the metal ion. The c.d. couplet (+and – signs) induced at the azomethine π–π* transition at around 27 000 cm^–1 is discussed with respect to the absolute configuration and in comparison with the spectra of related Schiff-base complexes.