Incidental Polymorphism, Non-Isomorphic and Isomorphic Substitution in Calcium-Valine Coordination Polymers

Five coordination polymers with the stoichiometry CaX2(valine)2(H2O)2 (X = Cl, Br) were obtained from the corresponding calcium halides and either racemic and enantiopure valine. In all cases the zwitterionic amino acid is exclusively O coordinated and the halides act as counteranions for the resulting one-dimensional cationic chains. The enantiopure chloride shows dimorphism; both forms differ in connectivity from the bromide. In contrast to this structural variability for L-valine, the derivatives of the racemic amino acid are isomorphous.