Iodide-Iodates M₃[IO₃]₁₂·Ag₄I, M = Bi, Tb, with a Framework Structure and High Second-Harmonic Generation Optical Response

Single crystals of two new iodide-iodates, Bi 3 [IO 3 ] 12 ·Ag 4 I and Tb 3 [IO 3 ] 12 ·Ag 4 I, are synthesized in hydrothermal systems. The anionic parts in both iodide-iodates are characterized as a complex charged framework of isolated IO 3 umbrella-like groups and large Bi(Tb)–O polyhedra similar to those previously found in La 3 [IO 3 ] 12 [IO 3 ](Pb 3 O). Broad channels along the c- axis contain compensators: (Ag 3 I) 2+ umbrella-like groups and additional Ag + ions which form Ag 4 4+ tetrahedral clusters augmented with I – halogen. New iodates possess significantly higher second-order nonlinear optical characteristics compared to the previously known lead-containing compounds REE 3 [IO 3 ] 12 [IO 3 ](Pb 3 O), REE = La, Pr, Nd. The difference is related to the polar ordering of umbrella-like (Ag 3 I) 2+ groups in the channels in the new iodide-iodate. Additionally, planar-coordinated Ag atoms add three Ag atoms in umbrellas forming [Ag 4 I] 3+ polar clusters in the channels.