Unbalanced racemates: solid state solutions containing enantiomeric pairs crystallizing in Sohncke space groups with (L:D) ratios other than (1:1) – illustrated with crystals of a Co(III) coordination compound

Abstract

Abstract Herein we describe materials of composition [Co(NH3)4(X-leucinato)]I2·H2O in which the amino acid ligand is either L or D, and in which (a) while in pure enantiomorphic form (L), crystallizes in a Sohncke space group with Z′ = 2.0; but, whose packing closely resembles that of its racemate. Such substances are labeled a Racemic Mimic; and (b) crystals in which the L:D ratio of the amino acid ligand in the asymmetric unit is (71:29), which interestingly crystallize in the same space group and cell constants as those of the former. Moreover, the packing behavior is essentially the same in both—the difference being that the (1:1) species is fully ordered, while that with L:D (71:29) ratio has a partially disordered propyl chain. The (71:29) species we describe herein as an Unbalanced Racemate.