Crystal structures and circular dichroism of {2,2′-[(1S,2S)-1,2-di­phenyl­ethane-1,2-diylbis(nitrilophenyl­methanylyl­idene)]diphenolato}nickel(II) and its ethanol solvate

A chiral nickel(II) Schiff base complex derived from 2-hy­droxy­benzo­phenone and (1S,2S)-1,2-di­phenyl­ethyl­enedi­amine shows a λ conformation of the central di­amine chelate ring. The substituents on the C=N carbon atoms significantly affect the circular dichroism spectra.

The title compound, [Ni(C₄₀H₃₀N₂O₂)] (1), with an optically active Schiff base ligand derived from 2-hy­droxy­benzo­phenone and (1S,2S)-1,2-di­phenyl­ethyl­enedi­amine, was crystallized as the solvent-free and ethanol solvate forms (1 and 1·2C₂H₅OH). In both structures, the two phenyl groups on the stereogenic centers of the O,N,N,O-tetra­dentate ligand are axially oriented, and the conformation of the central di­amine chelate ring is λ. The circular dichroism (CD) spectra of 1 and the analogous nickel(II) complex [Ni(C₃₀H₂₆N₂O₂)] (2) in solution show partially similar patterns in the 350–450 nm range, but are mirror images in the longer wavelength region (450–650 nm). In the latter region, the sign of CD for these complexes is sensitive to the substituents on the C=N carbon atoms (phenyl for 1 and methyl for 2) rather than the di­amine chelate ring conformation.