In[IO3](OH)2 – New member of hydrous and anhydrous iodate family with indium

•Syntheses in mild hydrothermal conditions new iodate hydrate In(IO3)(OH)2 and crystal structure determination.•Structural-chemical relation in the row of hydrous In iodates depending on the degree of protonation.•Crucial role of ionic radii of alkali metals on block {In[IO3]6}3− condensation in anhydrous In-iodates.•Confirmation of structure-properties relation in iodates with similar octahedral chains to asymmetric bonds.

A new indium iodate hydrate In[IO3](OH)2 was synthesized by the hydrothermal methods. Single crystal X-ray diffraction revealed centrosymmetric Pnma space group. [IO3]-groups have typical umbrella-like configuration: iodine atom and three oxygens with I–O distances ∼1.8 Å. In-octahedra have 4 equatorial OH-groups and 2 apical O-atoms of 2 [IO3]-groups and are connected into the layers via OH-groups. It is found that indium iodate family without any other metals is a regular row of compounds: anhydrous In[IO3]3, one hydrated In[IO3]2(OH)·H2O, new two hydrated In[IO3](OH)2 and “end member” represented by three hydrated hydroxide In(OH)3. Chemical relations are parallel to the structural: In-octahedral framework in In-hydroxide, In-octahedral layer as a fragment of the framework, In-octahedral chain as a fragment of the layer, isolated In-octahedra as a fragment of the chain with no In-octahedral condensation via vertices but only via [IO3]-groups in anhydrous In-iodate. If alkali metals are introduced in anhydrous In-iodates, their influence is different. Large metals as K, Rb, Cs hinder condensation of {In[IO3]6}3− blocks which are isolated in the structures whereas smaller Li, Na metals allows condensation up to bands {In[IO3]4}1−∞. Octahedral chains selected in hydrated In-iodates are similar to chains in nonlinear optical compound TiO[IO3]2. The reasons of polarity or non-polarity and possible elements substitutions promising for properties are discussed.

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