New isoformula iodates In(IO3)3 and Sm(IO3)3 with different crystal structures: Specific structural features of I5+ compounds

New iodates, namely, In(IO3)3 (space group R $$\bar 3$$ ) and Sm(IO3)3 (space group P21/a), are synthesized under hydrothermal conditions. The original crystal structure of the In(IO3)3 compound is determined without prior knowledge of the chemical formula. The Sm(IO3)3 compound is isostructural to the Gd(IO3)3 compound. The [IO4]3- tetrahedra with three short I-O bonds have an umbrella coordination, which is characteristic of pentavalent iodine, and form anionic radicals, such as a ring radical in the In(IO3)3 iodate, a triple helix in the isoformula compound Fe(IO3)3, a complex chain in the Sm(IO3)3 iodate, and a linear triortho group in the Sm(IO3)3·H2O compound. All radicals contain triortho groups. The structural differences are determined by different ionic radii and shapes of the coordination polyhedra of the cations (indium and iron octahedra and an eight-vertex samarium polyhedron).