The molecular structure and crystal-packing mode of the enantiopure chiral building blocks Delta-[Ru(bpy)(2)(py)(2)][(+)-O,O'-dibenzoyl-D-tartrate]. 12H(2)O (I) and Lambda-[Ru(bpy)(2)(py)(2)][(-)-O,O'-dibenzoyl-L-tartarate]. 12H(2)O (II) have been determined by single-crystal X-ray diffraction data. This study proposes a model of how the L- and D-dibenzoyltartrate anions recognize the chirality of the hydrophobic [Ru(bpy)(2)(py)(2)](2+) complex. The monoclinic unit cell contains four complex cations, four tartrate anions, and 48 water molecules. Since there are no possibilities to form hydrogen bonds between the cations and anions, chiral recognition is due to crystal packing. Two benzoyl rings of two different tartrate anions are gripping the two bpy-planes of the Ru-complex. Further a third benzoyl ring from a tartrate anion is packed between the two pyridine rings, favoring one enantiomeric form to crystallize from aqueous solution. Crystal structure data for I at 153 K: a = 15.342(3) Angstrom. b = 19.200(4) Angstrom, c = 18.872(4) Angstrom, beta = 104.841(3)degrees, monoclinic space group C-2, R-1 = 0.0239 (I > 2 sigma (I). R-2 = 0.0606, Flack parameter = 0.0115 (with esd 0.0166). For II at 293 K: a = 15.376(4) Angstrom, b = 19.388(11) Angstrom, c = 19.085(7) Angstrom, beta = 105.11(2)degrees, monoclinic space group C121, R-1 = 0.0686 (I > 2 sigma (I), R-2 = 0,1819, Flack parameter = -0.0100 (with esd 0.0521).