4 research outputs found
Iodide-Iodates M<sub>3</sub>[IO<sub>3</sub>]<sub>12</sub>·Ag<sub>4</sub>I, M = Bi, Tb, with a Framework Structure and High Second-Harmonic Generation Optical Response
Single
crystals of two new iodide-iodates, Bi<sub>3</sub>[IO<sub>3</sub>]<sub>12</sub>·Ag<sub>4</sub>I and Tb<sub>3</sub>[IO<sub>3</sub>]<sub>12</sub>·Ag<sub>4</sub>I, are synthesized in hydrothermal
systems. The anionic parts in both iodide-iodates are characterized
as a complex charged framework of isolated IO<sub>3</sub> umbrella-like
groups and large BiÂ(Tb)–O polyhedra similar to those previously
found in La<sub>3</sub>[IO<sub>3</sub>]<sub>12</sub>Â[IO<sub>3</sub>]Â(Pb<sub>3</sub>O). Broad channels along the <i>c-</i>axis contain compensators: (Ag<sub>3</sub>I)<sup>2+</sup> umbrella-like
groups and additional Ag<sup>+</sup> ions which form Ag<sub>4</sub><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>3</sub>[IO<sub>3</sub>]<sub>12</sub>Â[IO<sub>3</sub>]Â(Pb<sub>3</sub>O), REE = La, Pr, Nd. The difference is related
to the polar ordering of umbrella-like (Ag<sub>3</sub>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>4</sub>I]<sup>3+</sup> polar clusters in the channels
Complex Structural Behavior of BiMn<sub>7</sub>O<sub>12</sub> Quadruple Perovskite
Structural properties
of a quadruple perovskite BiMn<sub>7</sub>O<sub>12</sub> were investigated
by laboratory and synchrotron X-ray powder diffraction between 10
and 650 K, single-crystal X-ray diffraction at room temperature, differential
scanning calorimetry (DSC), second-harmonic generation, and first-principles
calculations. Three structural transitions were found. Above <i>T</i><sub>1</sub> = 608 K, BiMn<sub>7</sub>O<sub>12</sub> crystallizes
in a parent cubic structure with space group <i>Im</i>3Ì….
Between 460 and 608 K, BiMn<sub>7</sub>O<sub>12</sub> adopts a monoclinic
symmetry with pseudo-orthorhombic metrics (denoted as <i>I</i>2/<i>m</i>(o)), and orbital order appears below <i>T</i><sub>1</sub>. Below <i>T</i><sub>2</sub> = 460
K, BiMn<sub>7</sub>O<sub>12</sub> is likely to exhibit a transition
to space group <i>Im</i>. Finally, below about <i>T</i><sub>3</sub> = 290 K, a triclinic distortion takes place to space
group <i>P</i>1. Structural analyses of BiMn<sub>7</sub>O<sub>12</sub> are very challenging because of severe twinning in
single crystals and anisotropic broadening and diffuse scattering
in powder. First-principles calculations confirm that noncentrosymmetric
structures are more stable than centrosymmetric ones. The energy difference
between the <i>Im</i> and <i>P</i>1 models is
very small, and this fact can explain why the <i>Im</i> to <i>P</i>1 transition is very gradual, and there are no DSC anomalies
associated with this transition. The structural behavior of BiMn<sub>7</sub>O<sub>12</sub> is in striking contrast with that of LaMn<sub>7</sub>O<sub>12</sub> and could be caused by effects of the Bi<sup>3+</sup> lone electron pair
Syntheses, Crystal Structures, and Nonlinear Optical Activity of Cs<sub>2</sub>Ba[AnO<sub>2</sub>(C<sub>2</sub>H<sub>5</sub>COO)<sub>3</sub>]<sub>4</sub> (An = U, Np, Pu) and Unprecedented Octanuclear Complex Units in KR<sub>2</sub>(H<sub>2</sub>O)<sub>8</sub>[UO<sub>2</sub>(C<sub>2</sub>H<sub>5</sub>COO)<sub>3</sub>]<sub>5</sub> (R = Sr, Ba)
X-ray diffraction
was applied to the elucidation of crystal structures of single crystals
of Cs<sub>2</sub>BaÂ[AnO<sub>2</sub>(C<sub>2</sub>H<sub>5</sub>COO)<sub>3</sub>]<sub>4</sub>, where An = UÂ(<b>I</b>), NpÂ(<b>II</b>), PuÂ(<b>III</b>), and KR<sub>2</sub>(H<sub>2</sub>O)<sub>8</sub>[UO<sub>2</sub>(C<sub>2</sub>H<sub>5</sub>COO)<sub>3</sub>]<sub>5</sub>, where R = SrÂ(<b>IV</b>), Ba (polymorphs <b>V-a</b> and <b>V</b><b>-</b><b>b</b>). FTIR
spectra were analyzed for the uranium-containing crystals <b>I</b>, <b>I</b><b>V</b>, and <b>V</b><b>-</b><b>b</b>. Isostructural cubic crystals <b>I</b>–<b>I</b><b>I</b><b>I</b> are constructed of typical mononuclear
anionic complex units [AnO<sub>2</sub>(C<sub>2</sub>H<sub>5</sub>COO)<sub>3</sub>]<sup>−</sup> and charge-balancing Cs and Ba cations.
Features of actinide contraction in the six U–Np–Pu
isostructural series known to date are analyzed. In crystal structures
of <b>IV</b> and <b>V</b> two typical complexes [UO<sub>2</sub>(C<sub>2</sub>H<sub>5</sub>COO)<sub>3</sub>]<sup>−</sup> bind with a hydrated Sr or Ba cation to form the rare trinuclear
neutral complex unit {<i>R</i>(H<sub>2</sub>O)<sub>4</sub>[UO<sub>2</sub>(C<sub>2</sub>H<sub>5</sub>COO)<sub>3</sub>]<sub>2</sub>}, where R = Sr, Ba. Two such trinuclear units and one typical mononuclear
unit further bind with a K cation to form the unprecedented octanuclear
neutral complex unit KÂ[UO<sub>2</sub>(C<sub>2</sub>H<sub>5</sub>COO)<sub>3</sub>]Â{RÂ(H<sub>2</sub>O)<sub>4</sub>[UO<sub>2</sub>(C<sub>2</sub>H<sub>5</sub>COO)<sub>3</sub>]<sub>2</sub>}<sub>2</sub>. As the derived
polynuclear complexes of uranyl ion with carboxylate ligands in the
crystal structures of <b>IV</b> and <b>V</b> are not the
first but are rare examples, the equilibrium between mono and polynuclear
complex units in aqueous solutions is discussed. The two polymorphic
modifications <b>V-a</b> and <b>V-b</b> were studied at
100 K and at room temperature, respectively. Peculiarities of noncovalent
interactions in crystal structures of the two polymorphs are revealed
using Voronoi–Dirichlet tessellation. The nonlinear optical
activity of noncentrosymmetric crystals <b>I</b> was estimated
by its ability for second harmonic generation
New Solid Electrolyte Na<sub>9</sub>Al(MoO<sub>4</sub>)<sub>6</sub>: Structure and Na<sup>+</sup> Ion Conductivity
Solid
electrolytes are important materials with a wide range of
technological applications. This work reports the crystal structure
and electrical properties of a new solid electrolyte Na<sub>9</sub>AlÂ(MoO<sub>4</sub>)<sub>6</sub>. The monoclinic Na<sub>9</sub>AlÂ(MoO<sub>4</sub>)<sub>6</sub> consists of isolated polyhedral [AlÂ(MoO<sub>4</sub>)<sub>6</sub>]<sup>9–</sup> clusters composed of a
central AlO<sub>6</sub> octahedron sharing vertices with six MoO<sub>4</sub> tetrahedra to form a three-dimensional framework. The AlO<sub>6</sub> octahedron also shares edges with one Na1O<sub>6</sub> octahedron
and two Na2O<sub>6</sub> octahedra. Na3–Na5 atoms are located
in the framework cavities. The structure is related to that of sodium
ion conductor II-Na<sub>3</sub>Fe<sub>2</sub>(AsO<sub>4</sub>)<sub>3</sub>. High-temperature conductivity measurements revealed that
the conductivity (σ) of Na<sub>9</sub>AlÂ(MoO<sub>4</sub>)<sub>6</sub> at 803 K equals 1.63 × 10<sup>–2</sup> S cm<sup>–1</sup>. The temperature behavior of the <sup>23</sup>Na
and <sup>27</sup>Al nuclear magnetic resonance spectra and the spin-lattice
relaxation rates of the <sup>23</sup>Na nuclei indicate the presence
of fast Na<sup>+</sup> ion diffusion in the studied compound. At <i>T</i><490 K, diffusion occurs by means of Na<sup>+</sup> ion
jumps exclusively through the sublattice of Na3–Na5 positions,
whereas Na1 and Na2 become involved in the diffusion processes (through
chemical exchange with the Na3–Na5 sublattice) only at higher
temperatures