Retroracemization using new forms of Belokon's original ligand:: intermediate NiII complexes of N-({2-[N-(S)-alkylprolylamino]-phenyl}phenylmethylene)-(S)-phenyl-alanine (alkyl is 2-picolyl, 3-picolyl or ethyl)

In the title compounds, [N-(phenyl{2-[N-(S)-(2-picolyl)prolylamino]phenyl}methylene)-(S)-phenylalaninato]nickel(II), [Ni(C-33 H30N4O3)], (I), [N-(phenyl{2-[N-(S)-(3-picolyl)prolylamino]phenyl}methylene)-(S)-phenylalaninato]nickel(II) hemihydrate, [Ni(C33H30N4O3)] . 0.5H(2)O, (II), and [N-({2-[N-(S)ethylprolylamino]phenyl}phenylmethylene)-(S)-phenylala- ninato]nickel(II), [Ni(C29H29N3O3)], (III), the Ni-II centres have approximate square-planar coordination geometries from N3O donor sets. The picolyl N atoms in (I) and (II) are too remote from the metal centres to interact significantly, but the metal coordination geometries experience tetrahedral distortion and/or displacement of the metal centre from the N3O plane. These are linked to conformational differences between the ligands of the symmetry-independent complexes (Z' = 2), which in turn are related to molecular packing. In (III), where a less sterically demanding ethyl group replaces the picolyl substituents, there are none of the distortions or displacements seen in (I) and (II).