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

Abstract

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