Host–Guest Symmetry and Charge Matching in Glycine-Templated Metal Sulfate–Oxalates Obtained by a Solvent-Free Method

Two metal sulfate–oxalates, (Hgly)₂·Zn(SO₄)(C₂O₄) (1) and Hgly·In(SO₄)(C₂O₄)(gly) (2), were prepared under solvent-free conditions, where gly = glycine. They have similar layered structures despite the fact that aliovalent metal ions are used as structural nodes. Notably, glycine molecules play dual roles as a protonated cation and a zwitterionic ligand in compound 2. The two compounds display moderate second-harmonic-generation (SHG) responses, confirming their noncentrosymmetric structures. Theoretical calculations were performed to reveal the origin of their SHG responses.