NH 4 IO 2 F 2 and (NH 4 ) 3 (IO 2 F 2 ) 3 ·H 2 O: A Series of Ammonium-Containing Fluoroiodates with Wide Band Gaps.

A series of ammonium-containing fluoroiodates, NH 4 IO 2 F 2 and (NH 4 ) 3 (IO 2 F 2 ) 3 ·H 2 O, with isolated [IO 2 F 2 ] units have been fabricated by a fluorine-oxygen substitution strategy from NH 4 IO 3 . The two compounds crystallize in the orthorhombic system, but in different space groups, noncentrosymmetric Pca 2 1 for NH 4 IO 2 F 2 and centrosymmetric Pnma for (NH 4 ) 3 (IO 2 F 2 ) 3 ·H 2 O, and show wide band gaps of 4.53 eV for (NH 4 IO 2 F 2 ) and 4.55 eV for ((NH 4 ) 3 (IO 2 F 2 ) 3 ·H 2 O). In addition, NH 4 IO 2 F 2 exhibits a 1.2 × KDP second harmonic generation response, a short ultraviolet cutoff edge in iodates, and a good crystal growth habit. The crystal of NH 4 IO 2 F 2 with a size of 11 × 5 × 2 mm 3 was obtained by the aqueous solution method. The results enrich the structural diversity of iodate and supply a greater understanding of the design of new functional materials based on the fluoroiodates.