Chiral recognition among tris(diimine)-metal complexes, 6 -: Racemic compound formation versus conglomerate formation with [M(bpy)3](PF6)2 (M = Ni, Zn, Ru);: Molecular and crystal structures

modifications in molecular size and shape induced by variation of the central atom drastically alter the crystallization behaviour of the hexafluorophosphate salts of [M(bpy)(3)](2+). With M = Ru, racemic solutions crystallize as true racemates in the beta -type [P (3) over bar c1, a = 10.6453(5), c = 16.2987(9) Angstrom, Z = 2], while for M = Zn the racemic structure cannot be obtained, as spontaneous resolution {gamma -type [P3(1), a = 10.3873(5), c = 26.1309(16) Angstrom, Z = 3]} is the only crystallization path observed. For [Ni(bpy)(3)](PF6)(2), crystals of both structural types can be obtained concomitantly from the same crystallization batch. The gamma -phase is systematically twinned by merohedry. The dramatic and unpredictable change in the packing pattern of the very similar building blocks within this series arises from a delicate balance between the intermolecular forces. Distinct intermolecular interactions with different directionalities can be identified in the two structure types. Through careful analysis of the crystal and molecular structures, a trend with respect to molecular size and shape on going from [Ru(bpy)(3)](PF6)(2) to [Zn(bpy)(3)](PF6)(2) can be established. Even though one might speculate that increasing the size of the molecular cation should destabilize the beta -type structure relative to the gamma -type, no conclusive rationalization based solely on structural parameters can be given as regards why the relative order of the two local minima on the energy hypersurface should become inverted.