The complex Δ, Λ-[Ru(bipy)2(L-ala)]ClO4·0.5H2O contains both Δ,L and Λ,L diastereoisomeric cations in the one crystalline form. The crystals are monoclinic, space group C2, with a = 32.816 ± 0.004, b = 11.961 ± 0.002, c = 12.368 ± 0.011 Å, β = 94.92 ± 0.04° and Z = 8. The structure was refined by block-matrix least-squares methods to R = 0.041 for 3078 non-zero reflexions. A pseudo c-glide operation relates the two diastereoisomers. The two Ru atoms are each octahedral with small differences in the coordination spheres of the two metals. The bipyridine and L-alanine molecules are all bidentate. Bond dimensions are: RuNbipy 2.001(8)-2.123(8) Å, RuNamine 2.071(11) and 2.130(11) Å, RuO 2.061(7) and 2.095(7) Å, NbipyRuNbipy average 78.6(7)° and NamineRuO average 79.3(4)°. In the Λ,L isomer the amino acid ring is puckered, whereas in the Δ,L form this ring is closely planar. An analysis of interatomic contact distances and bond-rotational distortions in the cations shows that the Δ,L isomer due to a steric interaction between the methyl-group of the amino acid and one of the bipyridine rings in that isomer. This observation is related to previously reported chiral discriminations observed for such species. A detailed analysis of angular distortions in the bipyridine groups has been performed. The water molecules lie on crystallographic two-fold axes and hydrogen bond symmetry related uncoordinated carboxylic oxygen atoms. The amine protons appear to be involved in weak interactions with the perchlorate oxygen atoms, the latter showing some degree of disorder.