2D Chiral Ag(I) Complexes with A-π–<i>A</i>- and D-π–<i>A</i>-Type Dicarboxylic Acid Ligands: Presenting Significant Differences in Nonlinear Optical Responses

Three two-dimensional (2D) chiral Ag(I) complexes with formulas [Ag₄(L_<i>R</i>)₄(5-nipa)₂]<i>_n</i> (<b>1</b>), [Ag₄(L_<i>S</i>)₄(5-nipa)₂]<i>_n</i> (<b>2</b>), and {[Ag₄(L_<i>S</i>)₄(5-hipa)₂]·2H₂O}<i>_n</i> (<b>3</b>) were prepared through the reactions of Ag₂O with enantiopure <i>bis</i>-monodentate N-donors (L_<i>R</i>/L_<i>S</i>) and different dicarboxylic acids bearing A (acceptor)-π-<i>A</i>- and D (donor)-π-<i>A</i>-type structural features, where <i>L_R</i>/<i>L_S</i> = (-)/(+)-2-(4'-pyridyl)-4,5-pinene-pyridine, 5-H₂nipa = 5-nitroisophthalic acid, and 5-H₂hipa = 5-hydroxyisophthalic acid. A study of their nonlinear optical responses reveals that chiral <b>1</b> and <b>2</b> enantiomeric pairs with the A-π-<i>A</i>-type dicarboxylic acid ligand simultaneously display second- and third-harmonic generation (SHG and THG) responses, while chiral <b>3</b> containing the D-π-<i>A</i>-type dicarboxylic acid ligand only exhibits a very strong THG response. The THG intensity of <b>3</b> is 451 × α-SiO₂, being about 27 and 24 times larger than those of <b>1</b> and <b>2</b>, respectively.