CsHfF4(IO3): A Hafnium Iodate Exhibiting a Strong Second-Harmonic-Generation Effect and a Wide Band Gap Achieved by Mixed-Ligand Acentric Coordination

A new polar hafnium iodate, CsHfF4(IO3), was successfully designed and synthesized by integrating fluorinated hafnium–oxygen polyhedra (HfF6O2) and IO3– anionic functional groups. Owing to the weak electronic effect of Hf4+ and the bond-network-induced out-of-center distortion of the HfF6O2 dodecahedra, CsHfF4(IO3) achieves a good balance between a strong second-harmonic-generation effect (3.5 × KH2PO4) and a rather large band gap (4.47 eV), which is the largest among the d0 transition-metal iodates. In addition, CsHfF4(IO3) possesses a wide transparent region (0.27–9.9 μm), a large birefringence for phase-matching (0.161), and a high laser-induced damage threshold (55.41 MW cm–2, 26 × AgGaS2) and is nonhygroscopic. This work indicates that the integration of mixed-ligand acentric coordination polyhedra and functional groups containing lone electron pairs is an effective strategy for developing novel inorganic nonlinear-optical materials with balanced overall properties.