Retroracemization using new forms of Belokon's original ligand: intermediate NiII complexes of N-((2-[N-(S)-alkylprolylamino]phenyl)phenylmethylene)-(S)-phenylalanine (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)H(30)N(4)O(3))], (I), [N-(phenyl(2-[N-(S)-(3-picolyl)prolylamino]phenyl)methylene)-(S)-phenylalaninato]nickel(II) hemihydrate, [Ni(C(33)H(30)N(4)O(3))].0.5H(2)O, (II), and [N-((2-[N-(S)-ethylprolylamino]phenyl)phenylmethylene)-(S)-phenylalaninato]nickel(II), [Ni(C(29)H(29)N(3)O(3))], (III), the Ni(II) centres have approximate square-planar coordination geometries from N(3)O 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 N(3)O 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).