Hydrogen-Bond-Driven Synergistically Enhanced Hyperpolarizability: Chiral Coordination Polymers with Nonpolar Structures Exhibiting Unusually Strong Second-Harmonic Generation

Four chiral coordination polymers (CPs), M[(S,S)-C14H14N2O6] and M[(R,R)-C14H14N2O6] (M=Zn or Cd), have been exclusively synthesized in high yields with the aid of newly designed chiral ligand under hydrothermal condition. The CPs crystallizing in the orthorhombic nonpolar space group, C222(1), reveal three-dimensional framework structures composed of MO4 tetrahedra and the corresponding homochiral linkers. Powder second-harmonic generation (SHG) measurements indicate that the nonpolar CPs reveal very strong SHG efficiency of ca. 5-9 times that of KH2PO4 and exhibit type-I phase-matching behavior. Density functional theory calculations suggest that the unusually large SHG efficiency found from the nonpolar CPs should be attributable to the synergistic effect of polarizable metal cations and enhanced hyperpolarizability in the donor-acceptor system originating from the hydrogen bonding in the coordinated linkers.

Automated summary

Four chiral coordination polymers were synthesized with the aid of a newly designed chiral ligand under hydrothermal conditions. These polymers exhibit strong second-harmonic generation efficiency, which is attributed to the polarizable metal cations and synergistic effect in the donor-acceptor system.