[M(rac-N-benzyl Asp)(H2O)] (M = Co, Ni): Noncentrosymmetric Coordination Polymeric Chains with Racemic Chiral Ligands

The hydrothermal reaction of fumaric acid, benzylamine, and metal salts yielded M­[(rac-N-benzyl-Asp)­(H2O)] (M = Co, Ni), 1 and 2, and Ni­[(rac-N-benzyl-Asp)­(H2O)3]·H2O 3. Under mild hydrothermal conditions, Michael addition of benzylamine to fumaric acid led to the formation of a racemic mixture of N-benzyl aspartic acid enantiomers. The noncentrosymmetric structures of 1 and 2 consist of one-dimensional polymeric chains in which metal cations are bridged by d- and l-N-benzyl aspartate anions alternating along the chain. The centrosymmetric structure of 3 is composed of discrete Ni­[(rac-N-benzyl-Asp)­(H2O)3] units that are connected by hydrogen bonds into layers. The single layers are homochiral but are hydrogen bonded to similar homochiral layers that contain the N-benzyl aspartate with the opposite handedness. Compounds 1 and 2 showed second harmonic generation (SHG), and their magnetic and thermodynamic properties are described.