Iodide-Iodates M3[IO3]12·Ag4I, M = Bi, Tb, with a Framework Structure and High Second-Harmonic Generation Optical Response
文摘
Single crystals of two new iodide-iodates, Bi<sub>3sub>[IO<sub>3sub>]<sub>12sub>·Ag<sub>4sub>I and Tb<sub>3sub>[IO<sub>3sub>]<sub>12sub>·Ag<sub>4sub>I, are synthesized in hydrothermal systems. The anionic parts in both iodide-iodates are characterized as a complex charged framework of isolated IO<sub>3sub> umbrella-like groups and large Bi(Tb)–O polyhedra similar to those previously found in La<sub>3sub>[IO<sub>3sub>]<sub>12sub>[IO<sub>3sub>](Pb<sub>3sub>O). Broad channels along the c-axis contain compensators: (Ag<sub>3sub>I)<sup>2+sup> umbrella-like groups and additional Ag<sup>+sup> ions which form Ag<sub>4sub><sup>4+sup> tetrahedral clusters augmented with I<sup>–sup> halogen. New iodates possess significantly higher second-order nonlinear optical characteristics compared to the previously known lead-containing compounds REE<sub>3sub>[IO<sub>3sub>]<sub>12sub>[IO<sub>3sub>](Pb<sub>3sub>O), REE = La, Pr, Nd. The difference is related to the polar ordering of umbrella-like (Ag<sub>3sub>I)<sup>2+sup> groups in the channels in the new iodide-iodate. Additionally, planar-coordinated Ag atoms add three Ag atoms in umbrellas forming [Ag<sub>4sub>I]<sup>3+sup> polar clusters in the channels.