K 3 V 2 O 3 F 4 (IO 3 ) 3 : a high-performance SHG crystal containing both five and six-coordinated V 5+ cations.

The combination of d 0 transition metal oxofluorides with iodate anions helps to synthesize polar crystals. Herein, a novel polar crystal, K 3 V 2 O 3 F 4 (IO 3 ) 3 , which is the first metal vanadium iodate with two types of V 5+ -centered polyhedra (VO 4 F 2 octahedron and VO 3 F 2 trigonal bipyramid), has been prepared hydrothermally. It crystallizes in the polar space group of Cmc 2 1 and its structure displays an unprecedented 0D [V 2 O 3 F 4 (IO 3 ) 3 ] 3- anion, which is composed of Λ-shaped cis -[VO 2 F 2 (IO 3 ) 2 ] 3- and [VO 2 F 2 (IO 3 )] 2- anions interconnected via the corner-sharing of one oxo anion. The synergy gained from the VO 4 F 2 , VO 3 F 2 and IO 3 groups resulted in K 3 V 2 O 3 F 4 (IO 3 ) 3 exhibiting both a strong second-harmonic generation (SHG) response (1.3 × KTiOPO 4 ) under 2050 nm laser irradiation and a large birefringence (0.158 @ 2050 nm). This study provides a facile route for designing SHG materials by assembling various vanadium oxide-fluoride motifs and iodate anions into one compound.