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, Bi3[IO3]12·Ag4I and Tb3[IO3]12·Ag4I, are synthesized in hydrothermal systems. The anionic parts in both iodide-iodates are characterized as a complex charged framework of isolated IO3 umbrella-like groups and large Bi­(Tb)–O polyhedra similar to those previously found in La3[IO3]12­[IO3]­(Pb3O). Broad channels along the c-axis contain compensators: (Ag3I)2+ umbrella-like groups and additional Ag+ ions which form Ag44+ tetrahedral clusters augmented with I– halogen. New iodates possess significantly higher second-order nonlinear optical characteristics compared to the previously known lead-containing compounds REE3[IO3]12­[IO3]­(Pb3O), REE = La, Pr, Nd. The difference is related to the polar ordering of umbrella-like (Ag3I)2+ groups in the channels in the new iodide-iodate. Additionally, planar-coordinated Ag atoms add three Ag atoms in umbrellas forming [Ag4I]3+ polar clusters in the channels.两种新型碘-碘酸盐单晶Bi₃[IO₃]₁₂·Ag₄I与Tb₃[IO₃]₁₂·Ag₄I通过水热（hydrothermal）体系合成。两种碘-碘酸盐的阴离子部分均由孤立的伞形IO₃基团与大尺寸铋（铽）-氧多面体构成复杂带电骨架，该骨架结构与此前在La₃[IO₃]₁₂[IO₃](Pb₃O)中发现的结构类似。沿c轴方向存在宽通道，通道内的电荷补偿剂为(Ag₃I)²+伞形基团与额外的Ag⁺离子，后者与I⁻卤素结合形成Ag₄⁴+四面体团簇。与已知含铅化合物REE₃[IO₃]₁₂[IO₃](Pb₃O)（其中REE=La、Pr、Nd）相比，新型碘-碘酸盐具有显著更高的二阶非线性光学（second-order nonlinear optical）性能。该性能差异与新型碘-碘酸盐通道内(Ag₃I)²+伞形基团的极性有序排列相关。此外，平面配位（planar-coordinated）的Ag原子与伞形结构中的三个Ag原子结合，在通道内形成[Ag₄I]³+极性团簇。