Investigation of structural relationships between racemic alkali and ammonium hydrogen tartrates and their chiral counterparts

Single crystals of racemic anhydrous alkali and ammonium hydrogen tartrates of the composition M(C4H5O6) with M = K, Rb, Cs, NH4 as well as MxM'(1-x)(C4H5O6) with {M = K, M' = Rb, x = 0.5}, {M = K, M' = NH4, x = 0.56} and {M = Rb, M' = NH4, x = 0.61} were obtained from the reaction of D,L-tartaric acid with the corresponding hydroxides MOH and / or M' OH. These compounds form an isostructural series (monoclinic, P2(1)/c, Z = 4). The structures consist of alternating tartrate anion layers and cation layers. Each tartrate layer is held together by a number of hydrogen bonds and contains exclusively either the D or the L-form of the tartrate. Structural analogies between these crystals and their chiral counterparts are investigated. The smilarity of cell parameters between racemic and chiral structures is shown to be a consequence of certain packing features that occur in both group