Potassium Tetraiodatoiodate(III) Iodate(V): A Nonlinear Optical Crystal with Exceptional Second‐Harmonic Generation and Full‐Wavelength Phase Matching

The development of nonlinear optical materials with large nonlinear optical susceptibilities, wide transmission ranges, and comprehensive full‐wavelength phase matching capabilities remains a significant challenge. In this study, we synthesized a novel potassium tetraiodatoiodate(III) iodate(V) via an in situ reduction and complexation reaction. The resulting compound, K2[IIII(IVO3)4]IVO3, exhibits exceptional second harmonic generation responses (21.6KH2PO4 at 1064 nm, 1.0KTiOPO4 at 2050 nm), a wide transparency range from the visible to the mid‐infrared wavelengths (0.37–6.05 μm and 7.03–13.40 μm), and a high birefringence (0.358 at 543 nm) to achieve full‐wavelength phase matching. These properties are primarily ascribed to the synergistic substantial hyperpolarizability and polarizability anisotropy exhibited by the [IIII(IVO3)4]− complex ions, which comprise square‐planar coordinated trivalent iodine and optimally arranged iodate ligands. This study demonstrates the pivotal role of nonmetallic cation centered coordination entities in influencing linear and nonlinear optical properties, a discovery that has significant implications for the development of innovative inorganic functional materials.