Synthesis and Characterization of f-Element Iodate Architectures with Variable Dimensionality, α- and β-Am(IO3)3

Two americium(III) iodates, β-Am(IO3)3 (I) and α-Am(IO3)3 (II), have been prepared from the aqueous reactions of AmIII with KIO4 at 180 °C and have been characterized by single-crystal X-ray diffraction, diffuse reflectance, and Raman spectroscopy. The α-form is consistent with the known structure type I of anhydrous lanthanide iodates. It consists of a three-dimensional network of pyramidal iodate groups bridging [AmO8] polyhedra where each of the americium ions are coordinated to eight iodate ligands. The β-form reveals a novel architecture that is unknown within the f-element iodate series. β-Am(IO3)3 exhibits a two-dimensional layered structure with nine-coordinate AmIII atoms. Three crystallographically unique pyramidal iodate anions link the Am atoms into corrugated sheets that interact with one another through intermolecular IO3 -···IO3 - interactions forming dimeric I2O10 units. One of these anions utilizes all three O atoms to simultaneously bridge three Am atoms. The other two iodate ligands bridge only two Am atoms and have one terminal O atom. In contrast to α-Am(IO3)3, where the [IO3] ligands are solely corner-sharing with [AmO8] polyhedra, a complex arrangement of corner- and edge-sharing μ2- and μ3-[IO3] pyramids can be found in β-Am(IO3)3. Crystallographic data: I, monoclinic, space group P21/n, a = 8.871(3) Å, b = 5.933(2) Å, c = 15.315(4) Å, β = 96.948(4)°, V = 800.1(4) Å3, Z = 4; II, monoclinic, space group P21/c, a = 7.243(2) Å, b = 8.538(3) Å, c = 13.513(5) Å, β = 100.123(6)°, V = 822.7(5) Å3, Z = 4.