CsHfF 4 (IO 3 ): 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 4 (IO 3 ), was successfully designed and synthesized by integrating fluorinated hafnium-oxygen polyhedra (HfF 6 O 2 ) and IO 3 - anionic functional groups. Owing to the weak electronic effect of Hf 4+ and the bond-network-induced out-of-center distortion of the HfF 6 O 2 dodecahedra, CsHfF 4 (IO 3 ) achieves a good balance between a strong second-harmonic-generation effect (3.5 × KH 2 PO 4 ) and a rather large band gap (4.47 eV), which is the largest among the d 0 transition-metal iodates. In addition, CsHfF 4 (IO 3 ) 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 × AgGaS 2 ) 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.