KBi(IO3)3(OH) and NaBi(IO3)4: from the centrosymmetric chain to a noncentrosymmetric double layer

Two new alkali–metal bismuth iodates KBi(IO3)3(OH) (1) and NaBi(IO3)4 (2) have been synthesized by a hydrothermal method via tuning of alkali–metal ions. Compound 1 crystallizes in the space group P and features a [Bi(IO3)3(OH)]n chain with eight-membered Bi–O–I–O–Bi–O–I–O rings. The [Bi(IO3)3(OH)]n chain consists of paddlewheel-like dimeric Bi2(OH)2(IO3)4 units linked by IO3 pairs. Compound 2 in the polar space group Cc features a [Bi(IO3)4]− double layer with Bi4I4 eight-membered rings (8-MRs). NaBi(IO3)4 exhibits a strong second harmonic generation (SHG) response of ∼5.0 × KDP (KH2PO4) and a wide transmittance window (0.4–12 μm), and structure analyses and theoretical calculations reveal that polarization results mainly from the proper alignment of the IO3 groups. The calculated electronic structure based on the DFT method indicates that the BiOn and IO3 groups dominate their optical properties.