K₅NaZr₄F₂₂(H₂O)₂: A Hydrated Zirconium Fluoride with a Second-Harmonic Generation Effect and a Short Ultraviolet Cutoff Edge Induced by Cosubstitution with Heterovalent Cations

The development of nonlinear optical (NLO) crystal materials with short ultraviolet cutoff edges is of great significance to laser applications and industrial development. Based on acentric AE-M-F22 (Sr5Zr3F22 (1), Ca5Zr3F22 (2), and Ca5Hf3F22 (3), with AE = alkaline earth metal and M = Zr, Hf), a novel hydrated zirconium-based fluoride, K5NaZr4F22(H2O)2 (4), was obtained through a cosubstitution strategy involving mixed alkali metal cations. K5NaZr4F22(H2O)2 crystallizes in the C2 space group and presents a unique three-dimensional {[Zr4F22(H2O)2]6-}∞ anion framework composed of hydrogen-bonded {[Zr4F23(H2O)2]7-}∞ chains. 1-4 exhibit phase-matched second-harmonic generation (SHG) responses and short ultraviolet cutoff edges. This work has brought about a novel structure of zirconium fluoride and enriched the family of NLO zirconium/hafnium fluorides.