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(C 4 H 5 O 6 ) with M = K, Rb, Cs, NH 4 as well as M x M′ 1−x (C 4 H 5 O 6 ) with {M = K, M′ = Rb, x = 0.5}, {M = K, M′ = NH 4 , x = 0.56} and {M = Rb, M′ = NH 4 , 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, P 2 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 groups.