CsHfF(IO): 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, CsHfF(IO), was successfully designed and synthesized by integrating fluorinated hafnium-oxygen polyhedra (HfFO) and IO anionic functional groups. Owing to the weak electronic effect of Hf and the bond-network-induced out-of-center distortion of the HfFO dodecahedra, CsHfF(IO) achieves a good balance between a strong second-harmonic-generation effect (3.5 × KHPO) and a rather large band gap (4.47 eV), which is the largest among the d transition-metal iodates. In addition, CsHfF(IO) 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, 26 × AgGaS) 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.