Metal iodates are a class of hot scientific topic due to their further application as excellent second-order nonlinear optical (NLO) materials. The previous studies for combining iodate units with V-centered polyhedra have resulted in over 20 types of structures, but the metal vanadium iodate with three-dimensional (3D)  anionic network has not been reported.

In a recent study published in Angewandte Chemie International Edition, the research group led by Prof. MAO Jianggao at Fujian Institute of Research on the Structure of Matter (FJIRSM) of the Chinese Academy of Sciences reported that the low molar ratio of IO₃/V (about 1:1) led to the first alkali-metal vanadium iodate fluoride, CsVO₂F(IO₃), with an unprecedented 3D [VO₂F(IO₃)]^- anionic framework.

The 3D [VO₂F(IO₃)]^- is constructed from 0D Λ-shaped [VO₃F(IO₃)₂]^4- clusters. Firstly, the 0D clusters are inter-linked into 1D [VO₂F(IO₃)₂]^3- chains, via corner-sharing of axial oxo anions and antiparallelly arranging “up” and “down” along c-direction. Then, the bridging of iodate groups connects 1D chains forming 3D [VO₂F(IO₃)]^- framework.

The 3D [VO₂F(IO₃)]^- framework has very strong structural polarization. Hence, CsVO₂F(IO₃) exhibits the outstanding second-harmonic generation (SHG) performance (1.1 x KTP @2.05 μm), and high laser-induced damage threshold (LIDT) of 107.9 MWcm^-2, which show that CsVO₂F(IO₃) is a promising SHG material.

Importantly, such design strategy, properly assembling 0D Λ-shaped polyanions into the high-dimensional anionic network, could be a facile and effective route for exploring new SHG materials.

A scheme showing the building of 3D [VO₂F(IO₃)]^- framework. (Image by Prof. MAO’s group)