8 research outputs found
Polar Noncentrosymmetric ZnMoSb<sub>2</sub>O<sub>7</sub> and Nonpolar Centrosymmetric CdMoSb<sub>4</sub>O<sub>10</sub>: d<sup>10</sup> Transition Metal Size Effect Influencing the Stoichiometry and the Centricity
Two
new quaternary molybdenumÂ(VI) antimonyÂ(III) oxides, ZnMoSb<sub>2</sub>O<sub>7</sub> and CdMoSb<sub>4</sub>O<sub>10</sub>, have been
synthesized in phase-pure form. The title compounds consist of highly
polarizable cations, i.e., d<sup>0</sup> (Mo<sup>6+</sup>) and d<sup>10</sup> (Zn<sup>2+</sup> or Cd<sup>2+</sup>), and lone-pair cations
(Sb<sup>3+</sup>). ZnMoSb<sub>2</sub>O<sub>7</sub> exhibits a three-dimensional
framework with ZnO<sub>4</sub>, MoO<sub>4</sub>, and SbO<sub>4</sub> polyhedra in the polar space group <i>P</i>2<sub>1</sub>, whereas CdMoSb<sub>4</sub>O<sub>10</sub> exhibits one-dimensional
tubule structures with CdO<sub>6</sub>, MoO<sub>4</sub>, and SbO<sub>3</sub> polyhedra in the space group <i>P</i>2<sub>1</sub>/<i>m</i>. Several synthetic efforts suggest that the the
dissimilar radii of Zn<sup>2+</sup> and Cd<sup>2+</sup> that can accommodate
polyhedra of Sb<sup>3+</sup> cations influence the stoichiometry as
well as the centricity for the reported materials. Spectroscopic,
thermal, and elemental analyses are reported along with dipole moment
calculations. Nonlinear optical properties and their structural origin
are examined for polar ZnMoSb<sub>2</sub>O<sub>7</sub> as well
A Polar Titanium–Organic Chain with a Very Large Second-Harmonic-Generation Response
A noncentrosymmetric
(NCS) titanium–organic compound, [H<sub>2</sub>NÂ(CH<sub>3</sub>)<sub>2</sub>]ÂTiOÂ{[NC<sub>5</sub>H<sub>3</sub>(CO<sub>2</sub>)<sub>2</sub>]Â[NC<sub>5</sub>H<sub>4</sub>(CO<sub>2</sub>)]} (CAUMOF-18),
has been synthesized by a solvothermal reaction. The aligned unidimensional
polar chain structure of CAUMOF-18 consisting of corner-shared distorted
TiO<sub>5</sub>N<sub>2</sub> pentagonal bipyramids is attributed to
strong hydrogen-bonding and π–π interactions. CAUMOF-18
reveals a very strong second-harmonic-generation efficiency of 400
times that of α-SiO<sub>2</sub> and is phase-matchable (type
I). Water-molecule-driven reversible centricity conversion and topotactic
transformation to TiO<sub>2</sub> microrods for CAUMOF-18 are also
presented
Variable Asymmetric Chains in Transition Metal Oxyfluorides: Structure–Second-Harmonic-Generation Property Relationships
Four
novel transition metal oxyfluorides, [ZnÂ(pz)<sub>3</sub>]Â[MoO<sub>2</sub>F<sub>4</sub>]·0.1H<sub>2</sub>O (<b>1</b>), [ZnÂ(pz)<sub>2</sub>F<sub>2</sub>]Â[ZnÂ(pz)<sub>3</sub>]<sub>2</sub>[WO<sub>2</sub>F<sub>4</sub>]<sub>2</sub> (<b>2</b>), [CdÂ(pz)<sub>4</sub>]Â[CdÂ(pz)<sub>4</sub>(H<sub>2</sub>O)]Â[MoO<sub>2</sub>F<sub>4</sub>]<sub>2</sub>·0.625H<sub>2</sub>O (<b>3</b>), and [ZnÂ(mpz)<sub>3</sub>]<sub>2</sub>[MoO<sub>2</sub>F<sub>4</sub>]<sub>2</sub> (<b>4</b>) (pz = pyrazole; mpz = 3-methyl pyrazole) have been synthesized.
Compounds <b>1</b> and <b>4</b> contain helical chains.
Compound <b>2</b> accommodates zigzag chains, and compound <b>3</b> has quasi-one-dimensional linear chains. The variable chain
structures are found to be attributable to the different structure-directing
anionic groups and hydrogen bonding interactions. Compound <b>4</b> crystallized in the noncentrosymmetric (NCS) polar space group, <i>Pna</i>2<sub>1</sub>, is nonphase-matchable (Type I), and reveals
a moderate second-harmonic-generation (SHG) efficiency (10 ×
α-SiO<sub>2</sub>). The observed SHG efficiency of compound <b>4</b> is due to the small net polarization occurring from the
arrangement of ZnN<sub>3</sub>F<sub>2</sub> trigonal bipyramids. Spectroscopic
and thermal characterizations along with calculations for the title
materials are reported
Li<sub>6</sub>M(SeO<sub>3</sub>)<sub>4</sub> (M = Co, Ni, and Cd) and Li<sub>2</sub>Zn(SeO<sub>3</sub>)<sub>2</sub>: Selenites with Late Transition-Metal Cations
A series of lithium
metal selenites, Li<sub>6</sub>MÂ(SeO<sub>3</sub>)<sub>4</sub> (M =
Co, Ni, and Cd) and Li<sub>2</sub>ZnÂ(SeO<sub>3</sub>)<sub>2</sub>,
were synthesized by hydrothermal and solid-state reactions. Li<sub>6</sub>MÂ(SeO<sub>3</sub>)<sub>4</sub> is composed of Li<sup>+</sup> cations, MO<sub>6</sub> octahedra, and SeO<sub>3</sub> polyhedra,
while Li<sub>2</sub>ZnÂ(SeO<sub>3</sub>)<sub>2</sub> consists of Li<sup>+</sup>, ZnÂ(Li)ÂO<sub>4</sub> tetrahedra, and SeO<sub>3</sub> polyhedra.
Isostructural Li<sub>6</sub>CoÂ(SeO<sub>3</sub>)<sub>4</sub> and Li<sub>6</sub>NiÂ(SeO<sub>3</sub>)<sub>4</sub> crystallize in the rhombohedral
space group <i>R</i>3Ì…, forming a three-dimensional
distorted cubic lattice. Li<sub>2</sub>ZnÂ(SeO<sub>3</sub>)<sub>2</sub> crystallizes in the orthorhombic space group <i>Pbam</i> and reveals a layered structure in the <i>bc</i> plane.
Li<sub>6</sub>CdÂ(SeO<sub>3</sub>)<sub>4</sub> revealing a unidimensional
structure crystallizes in the polar non-centrosymmetric space group <i>C</i>2, attributed to the parallel alignment of distorted CdO<sub>6</sub> octahedra. The direct-current magnetic susceptibility measurements
unveil that Li<sub>6</sub>CoÂ(SeO<sub>3</sub>)<sub>4</sub> is a canted
antiferromagnet with <i>T</i><sub>N</sub> = 25 K, while
Li<sub>6</sub>NiÂ(SeO<sub>3</sub>)<sub>4</sub> undergoes an antiferromagnetic
transition at <i>T</i><sub>N</sub> = 54 K, having a negligible
canted moment. The weak ferromagnetism observed in Li<sub>6</sub>CoÂ(SeO<sub>3</sub>)<sub>4</sub> indicates the significance of spin–orbit
coupling, bringing about anisotropic exchange interactions. Li<sub>6</sub>CdÂ(SeO<sub>3</sub>)<sub>4</sub> reveals a second harmonic
generation (SHG) efficiency of 10 × α-SiO<sub>2</sub>.
Dipole moment calculations on Li<sub>6</sub>CdÂ(SeO<sub>3</sub>)<sub>4</sub> indicate that the cooperative interaction of CdO<sub>6</sub> and SeO<sub>3</sub> is responsible for the observed SHG properties.
Band gaps of the compounds are enlarged as atomic number increases.
The effect of late transition-metal cations with different coordination
numbers on the framework structures and the subsequent physical properties
will be also discussed
Influence of Thermally Activated Solid-State Crystal-to-Crystal Structural Transformation on the Thermoelectric Properties of the Ca<sub>5–<i>x</i></sub>Yb<sub><i>x</i></sub>Al<sub>2</sub>Sb<sub>6</sub> (1.0 ≤ <i>x</i> ≤ 5.0) System
The solid-solution Zintl compounds
with the mixed cations of Ca<sup>2+</sup>and Yb<sup>2+</sup> in the
Ca<sub>5–<i>x</i></sub>Yb<sub><i>x</i></sub>Al<sub>2</sub>Sb<sub>6</sub> (1.0 ≤ <i>x</i> ≤
5.0) system have been
synthesized by high-temperature solid-state reactions. Two slightly
different crystal structures of the Ba<sub>5</sub>Al<sub>2</sub>Bi<sub>6</sub>-type and Ca<sub>5</sub>Ga<sub>2</sub>Sb<sub>6</sub>-type
phases have been characterized for seven compounds with 2.5 ≤ <i>x</i> ≤ 5.0 and three compounds with 1.0 ≤ <i>x</i> ≤ 2.0, respectively, by both powder and single-crystal
X-ray diffraction analyses. The two title phases adopt the orthorhombic
space group <i>Pbam</i> (<i>Z</i> = 2, <i>oP</i>26) with seven independent asymmetric atomic sites and
share certain structural similarities, including infinite one-dimensional
[Al<sub>2</sub>Sb<sub>8</sub>] double chains and isolated space-filling
Ca<sup>2+</sup>/Yb<sup>2+</sup> cations. Interestingly, we reveal
the crystal-to-crystal solid-state structural transformation of the
Yb-rich compound Ca<sub>1.5</sub>Yb<sub>3.5</sub>Al<sub>2</sub>Sb<sub>6</sub> from the Ba<sub>5</sub>Al<sub>2</sub>Bi<sub>6</sub>-type
to the Ca<sub>5</sub>Ga<sub>2</sub>Sb<sub>6</sub>-type phase through
the postannealing process, which can be rationalized as the phase
transition from the kinetically more stable structure to the thermodynamically
more stable crystal structure on the basis of theoretical calculations.
Discrepancies of the local coordination geometries of the anionic
[Al<sub>2</sub>Sb<sub>8</sub>] units and the geometrical arrangements
of structural building moieties in the two distinct phases provoke
the different electrical properties of metallic and semiconducting
conduction, respectively, for the Ba<sub>5</sub>Al<sub>2</sub>Bi<sub>6</sub>-type and Ca<sub>5</sub>Ga<sub>2</sub>Sb<sub>6</sub>-type
phases. Density of states and crystal orbital Hamilton population
analyses based on tight-binding linear muffin-tin orbital calculations
prove that the band-gap opening in the Ca<sub>5</sub>Ga<sub>2</sub>Sb<sub>6</sub>-type phase should mainly be attributed to an extended
bond distance of the bridging Sb–Sb in the [Al<sub>2</sub>Sb<sub>8</sub>] unit. A series of thermoelectric (TE) property measurements
indicates that the phase transition via the postannealing process
eventually results in an enhancement of the TE performance of Yb-rich
Ca<sub>1.5</sub>Yb<sub>3.5</sub>Al<sub>2</sub>Sb<sub>6</sub>
Photoconversion Mechanisms and the Origin of Second-Harmonic Generation in Metal Iodates with Wide Transparency, NaLn(IO<sub>3</sub>)<sub>4</sub> (Ln = La, Ce, Sm, and Eu) and NaLa(IO<sub>3</sub>)<sub>4</sub>:Ln<sup>3+</sup> (Ln = Sm and Eu)
Four
new metal iodates, namely, NaLnÂ(IO<sub>3</sub>)<sub>4</sub> (Ln =
La, Ce, Sm, and Eu), and a series of NaLaÂ(IO<sub>3</sub>)<sub>4</sub>:Ln<sup>3+</sup> (Ln = Sm and Eu) solid solutions were synthesized
through hydrothermal reactions. The structures of the title compounds
are similar to that of NaYÂ(IO<sub>3</sub>)<sub>4</sub> crystallizing
in the acentric monoclinic space group <i>Cc</i>. The iodate
materials reveal layered structures composed of LnO<sub>8</sub> square
antiprisms and IO<sub>3</sub> polyhedra, in which each layer is connected
by the I···O interactions. NaLaÂ(IO<sub>3</sub>)<sub>4</sub> suggests a great potential as a matrix for optical source
attributed to its acentricity and broad transparency from visible
to mid-IR region. The photoluminescence properties depending on the
concentration of Sm<sup>3+</sup> reveal that NaLaÂ(IO<sub>3</sub>)<sub>4</sub>:Sm<sup>3+</sup> undergoes a self-quenching relaxation over
7 mol % of Sm<sup>3+</sup> by dipole–quadrupole interactions.
Attributable to the asymmetric coordination environment of Ln<sup>3+</sup>, stronger electric dipole transitions compared to magnetic
dipole transitions were observed for both compounds. In addition,
the materials exhibit strong second-harmonic generation (SHG) responses
and are type I phase-matchable. The structural origin of the SHG properties
for the reported iodates is elucidated
Syntheses, Structures, and Characterization of Quaternary Tellurites, Li<sub>3</sub>MTe<sub>4</sub>O<sub>11</sub> (M = Al, Ga, and Fe)
Three
new quaternary lithium metal tellurites, Li<sub>3</sub>MTe<sub>4</sub>O<sub>11</sub> (M = Al, Ga, and Fe), have been synthesized through
hydrothermal and solid-state reactions by heating a mixture of LiOH·H<sub>2</sub>O, TeO<sub>2</sub>, and M<sub>2</sub>O<sub>3</sub>. The structures
of the title compounds have been determined by single-crystal and
powder X-ray diffraction. Li<sub>3</sub>MTe<sub>4</sub>O<sub>11</sub> reveal three-dimensional (3D) frameworks that consist of MO<sub>6</sub> octahedra, TeO<sub>3</sub> trigonal pyramids, and TeO<sub>4</sub> polyhedra. The variable coordination mode of Te<sup>4+</sup> within the framework leads to the formation of 1D channels that
host Li<sup>+</sup> cations on both tetrahedral and octahedral sites.
The bulk and grain boundary Li<sup>+</sup> ion conductivities for
a Li<sub>3</sub>FeTe<sub>4</sub>O<sub>11</sub> pellet in open air
are estimated to be 1.0 × 10<sup>–4</sup> and 2.7 ×
10<sup>–6</sup> S cm<sup>–1</sup>, respectively, at
room temperature from the impedance profile analysis. A lower activation
energy of 19.9 kJ mol<sup>–1</sup> is obtained for the system,
which is similar to that of Li<sub>10</sub>GeP<sub>2</sub>S<sub>12</sub> (24 kJ mol<sup>–1</sup>). Detailed characterizations such
as thermal, spectroscopic, and magnetic properties for the reported
materials are also reported
Li<sub>13</sub>Mn(SeO<sub>3</sub>)<sub>8</sub>: Lithium-Rich Transition Metal Selenite Containing Jahn–Teller Distortive Cations
A novel lithium-rich
transition metal selenite, Li<sub>13</sub>MnÂ(SeO<sub>3</sub>)<sub>8</sub>, that is composed of a Jahn–Teller distortive cation,
Mn<sup>3+</sup>, in the high spin d<sup>4</sup> state, and a second-order
Jahn–Teller (SOJT) distortive lone pair cation, Se<sup>4+</sup>, has been synthesized via hydrothermal and high temperature solid
state reactions. The selenite is classified as a molecular compound
consisting of MnO<sub>6</sub> octahedra, SeO<sub>3</sub> trigonal
pyramids, and Li<sup>+</sup> cations. Considering the Li–O
interactions, the structure of Li<sub>13</sub>MnÂ(SeO<sub>3</sub>)<sub>8</sub> may be described as a pseudo-three-dimensional framework
as well. The title compound is thermally stable up to 500 °C
and starts decomposing above the temperature attributable to the volatilization
of SeO<sub>2</sub>. While the MnO<sub>6</sub> octahedra in Li<sub>13</sub>MnÂ(SeO<sub>3</sub>)<sub>8</sub> exhibit six identical Mn–O
bond distances at room temperature due to the dynamic Jahn–Teller
effect, a clear elongation of two Mn–O bonds along a specific
direction is observed at 100 K. A series of isostructural selenites
with different transition metals, i.e., Li<sub>13</sub>MÂ(SeO<sub>3</sub>)<sub>8</sub> (M = Sc, Cr, and Fe), have been also successfully obtained
in phase pure forms using similar synthetic methods. Magnetic properties,
spectroscopic characterizations, and local dipole moments calculations
for all the synthesized selenites are presented