Ba 2 [WO 3 F(IO 3 )][WO 3 F 2 ]: the first polar fluorinated tungsten iodate featuring a direct W-O-I bond.

The introduction of the transition metal cations with d 0 electron configurations and F in the iodate systems generates a new polar compound, Ba 2 [WO 3 F(IO 3 )][WO 3 F 2 ], which features the first example of a direct W-O-I bond in the structure. It exhibits excellent properties, including a large second harmonic generation response (∼3.5 × KH 2 PO 4 ), a wide visible and mid-infrared transparency region (0.28-10.74 μm), and a moderate birefringence of 0.061@532 nm.