4 research outputs found
Assembly of Mn-Containing Unprecedented Selenotungstate Clusters with Photocatalytic H<sub>2</sub> Evolution Activity
The reaction of Na<sub>2</sub>WO<sub>4</sub> and Na<sub>2</sub>SeO<sub>3</sub> in the presence
of MnCl<sub>2</sub> under moderately
acidic conditions yielded two unprecedented tungstoselenites: dimeric
K<sub>2</sub>Na<sub>10</sub>[K<sub>2</sub>⊂{MnSe<sub>4</sub>W<sub>23</sub>O<sub>85</sub>(H<sub>2</sub>O)<sub>6</sub>}]·29H<sub>2</sub>O (<b>1</b>) and trimeric wheel-shaped K<sub>2</sub>Na<sub>10</sub>[K<sub>2</sub>⊂{Mn<sub>3</sub>Se<sub>7</sub>W<sub>39</sub>O<sub>131</sub>(OH)<sub>20</sub>(H<sub>2</sub>O)<sub>2</sub>}]·60H<sub>2</sub>O (<b>2</b>). The assemblies
of <b>1</b> and <b>2</b> are based upon the structure
directing effects of Se<sup>IV</sup> heteroatoms for generating diverse
well-defined vacancy selenotungstate precursors during the formation.
The polyoxoanion of <b>1</b> contains two novel Wells–Dawson-type-like
{Se<sub>2</sub>W<sub>11</sub>} fragments, which are constructed from
novel {SeW<sub>4</sub>} and {SeW<sub>7</sub>} species derived from
Wells–Dawson-type {α-Se<sub>2</sub>W<sub>14</sub>} fragments
and one disorder of Mn/W center. The polyoxoanion of <b>2</b> exhibits a crown-type structure composed of a [Se<sub>6</sub>W<sub>38</sub>O<sub>120</sub>(OH)<sub>18</sub>(H<sub>2</sub>O)<sub>2</sub>]<sup>6–</sup> “host” (abbreviated as {Se<sub>6</sub>W<sub>38</sub>}) encapsulating SeO<sub>3</sub><sup>2–</sup>-modified Mn/W and two K<sup>+</sup> “guests”. Remarkably,
the crown {Se<sub>6</sub>W<sub>38</sub>} shell remains a new type
of {Se<sub>2</sub>W<sub>12</sub>}-based trimeric aggregate in the
polyoxometalates chemistry. The two compounds were characterized by
single-crystal X-ray structure analysis, IR spectroscopy, thermogravimetric,
UV/vis spectroscopy, and ESI–MS. Moreover, their photocatalytic
H<sub>2</sub> evolution activity was also investigated
Side Group of Poly(3-alkylthiophene)s Controlled Dispersion of Single-Walled Carbon Nanotubes for Transparent Conducting Film
Controlled
dispersion of single-walled carbon nanotubes (SWCNTs) in common solvents
is a challenging issue, especially for the rising need of low cost
flexible transparent conducting films (TCFs). Utilizing conductive
polymer as surfactant to facilitate SWCNTs solubility is the most
successful pragmatic approach to such problem. Here, we show that
dispersion of SWCNT with polymer significantly relies on the length
of polymer side groups, which not only influences the diameter distribution
of SWCNTs in solution, also eventually affects their effective TCF
performance. Surfactants with longer side groups covering larger nanotube
surface area could induce adequate steric effect to stabilize the
wrapped SWCNTs against the nonspecific aggregation, as discerned by
the optical and microscopic measurements, also evidenced from the
resultant higher electrokinetic potential. This approach demonstrates
a facile route to fabricate large-area SWCNTs-TCFs exhibiting high
transmittance and high conductivity, with considerable uniformity
over 10 cm Ă— 10 cm
pH-Controlled and Sulfite Anion-Directed Assembly of a Family of Cerium(III)-Containing Polyoxotungstates Clusters
A versatile one-pot strategy was
employed to synthesize five ceriumÂ(III)-containing polyoxotungstate
nanoclusters through pH-controlled and sulfite anion-directed assembly:
[C<sub>2</sub>H<sub>8</sub>N]<sub>3</sub>Na<sub>7</sub>[Ce<sub>2</sub>(H<sub>2</sub>O)<sub>6</sub>W<sub>22</sub>O<sub>72</sub>(OH)<sub>4</sub>]·20H<sub>2</sub>O (<b>1</b>) at pH 5.0; [C<sub>2</sub>H<sub>8</sub>N]<sub>8</sub>Na<sub>16</sub>[Ce<sub>4</sub>(H<sub>2</sub>O)<sub>12</sub>W<sub>44</sub>O<sub>144</sub>(OH)<sub>12</sub>]·23H<sub>2</sub>O (<b>2</b>) at pH 4.5; [C<sub>2</sub>H<sub>8</sub>N]<sub>2</sub>Na<sub>4</sub>Ce<sub>2</sub>[Ce<sub>2</sub>(H<sub>2</sub>O)<sub>10</sub>W<sub>28</sub>O<sub>92</sub>(OH)<sub>2</sub>]·27H<sub>2</sub>O (<b>3</b>) at pH 2.8–3.3;
[C<sub>2</sub>H<sub>8</sub>N]<sub>2</sub>Na<sub>7</sub>[{α-SW<sub>7</sub>O<sub>28</sub>}Â{Ce<sub>2</sub>(H<sub>2</sub>O)<sub>6</sub>}Â(W<sub>3</sub>O<sub>6</sub>)Â{α-SW<sub>9</sub>O<sub>32</sub>}Â{α-SW<sub>9</sub>O<sub>31</sub>(OH)}]·18H<sub>2</sub>O (<b>4</b>) at pH 2.5; [C<sub>2</sub>H<sub>8</sub>N]<sub>2</sub>Na<sub>18</sub>[Ce<sub>2</sub>(H<sub>2</sub>O)<sub>9</sub>W<sub>36</sub>O<sub>110</sub>(OH)<sub>12</sub>]<sub>2</sub>·30H<sub>2</sub>O (<b>5</b>) at pH 1.5. These compounds were characterized
by single-crystal X-ray structure analysis, IR spectroscopy, thermogravimetric
(TG) analysis, X-ray photoelectron spectroscopy (XPS), and electrospray
ionization mass spectrometry (ESI-MS). Moreover, their electrochemical
properties were investigated. Single-crystal X-ray structure analysis
revealed that <b>1</b> and <b>2</b> were di- and tetra-ceriumÂ(III)-bridged
polyoxotungstates, constructed from two different types of lacunary
{W<sub>11</sub>} units. <b>3</b> composed of the well-known
ceriumÂ(III)-stabilized {W<sub>28</sub>} unit and organic amine–sodium–cerium
cations, was isolated in the pH range 2.8–3.3. In this reaction
system, the SO<sub>3</sub><sup>2–</sup> anion acted as a heteroanion
template at a lower pH 2.5. <b>4</b> was isolated by the combination
of ceriumÂ(III) centers and SO<sub>3</sub><sup>2–</sup> heteroanion
template, which is the first lanthanide-containing polyoxotungstates
with sulfur heteroatoms, and the 4f metal ceriumÂ(III) centers in <b>4</b> both have eight-coordinated modes and the SO<sub>3</sub><sup>2–</sup> heteroanion templates display ÎĽ<sub>7</sub> and ÎĽ<sub>9</sub> coordination modes. At a much lower pH 1.5,
the polyanion of <b>5</b> was obtained, two triangular-shaped
{W<sub>36</sub>} subunits were bridged by the ceriumÂ(III) ions, resulting
in the largest lanthanide-containing iso-polyoxotungstates known to
date
Assembly of Keggin-/Dawson-type Polyoxotungstate Clusters with Different Metal Units and SeO<sub>3</sub><sup>2–</sup> Heteroanion Templates
Using
a pH-dependent synthetic approach, the combination of different
simple metal salts or metal coordination complexes with SeO<sub>3</sub><sup>2–</sup> heteroanion templates was employed to synthesize
five distinct assemblies of Keggin-/Dawson-type tungstoselenites:
(C<sub>2</sub>H<sub>8</sub>N)<sub>10</sub>KNaÂ[(α-SeW<sub>9</sub>O<sub>34</sub>)Â{ZrÂ(H<sub>2</sub>O)}Â{WOÂ(H<sub>2</sub>O)}Â(WO<sub>2</sub>)Â(SeO<sub>3</sub>)Â{α-SeW<sub>8</sub>O<sub>31</sub>ZrÂ(H<sub>2</sub>O)}]<sub>2</sub>·14H<sub>2</sub>O (<b>1</b>) at pH = 1.3; (C<sub>2</sub>H<sub>8</sub>N)<sub>10</sub>KNa<sub>5</sub>Â[(Se<sub>2</sub>W<sub>18</sub>O<sub>60</sub>)<sub>2</sub>Â(ÎĽ<sub>2</sub>-O)<sub>4</sub>]·12H<sub>2</sub>O (<b>2</b>) at pH = 2.5; (C<sub>2</sub>H<sub>8</sub>N)<sub>4</sub>Na<sub>4</sub>Â[Se<sub>2</sub>W<sub>18</sub>O<sub>62</sub>Â(H<sub>2</sub>O)<sub>2</sub>]·13H<sub>2</sub>O (<b>3</b>) at pH = 3.6; (C<sub>2</sub>H<sub>8</sub>N)<sub>4</sub>ÂK<sub>3</sub>Na<sub>10</sub>Â[(α-SeW<sub>9</sub>O<sub>33</sub>)<sub>2</sub>Â{Ce<sub>2</sub>(CH<sub>3</sub>COO)Â(H<sub>2</sub>O)<sub>3</sub>W<sub>3</sub>O<sub>6</sub>}Â(α-Se<sub>2</sub>W<sub>14</sub>O<sub>52</sub>)]·26H<sub>2</sub>O (<b>4</b>) at pH = 4.5; K<sub>10</sub>Na<sub>5</sub>Â[(α-SeW<sub>9</sub>O<sub>33</sub>)<sub>2</sub>Â{Ce<sub>2</sub>(H<sub>2</sub>O)<sub>4</sub>W<sub>3</sub>O<sub>6</sub>}Â{α-Se<sub>2</sub>W<sub>14</sub>O<sub>51</sub>(OH)}]·24H<sub>2</sub>O (<b>5</b>) at pH = 4.5. All five compounds were characterized by single-crystal
X-ray structure analysis, IR spectroscopy, thermogravimetric, UV/vis
spectroscopy, and ESI-MS. Moreover, their electrochemical properties
were investigated. Keggin-type polyoxoanion of <b>1</b> remains
the first reported Zr-containing tungstoselenites based on {α-SeW<sub>9</sub>} building blocks. X-ray analysis revealed that the 4d metal
Zr centers have seven- and eight-coordinated modes, and SeO<sub>3</sub><sup>2–</sup> acts as the templates as well as the linkers.
With the increasing of the pH, Dawson-type polyoxoanions of <b>2</b> and <b>3</b> based on the first reported basic lacunary
{α-Se<sub>2</sub>W<sub>14</sub>} building blocks are obtained
by using 3d-4f metal coordination complexes. Polyoxoanions of <b>4</b> and <b>5</b> remain similar structures stabilized
by the 4f metal Ce centers at pH = 4.5 and that contain the basic Keggin-type
{α-SeW<sub>9</sub>} and Dawson-type {α-Se<sub>2</sub>W<sub>14</sub>} building blocks in <b>1</b>–<b>3</b> at the same time, presenting the mixed multiple lacunary building
blocks being combined into the single polyoxoanion architecture. Furthermore,
the density functional theory calculations have been performed on
polyoxoanions of <b>1</b> and <b>5</b> as the representatives
to investigate their electronic properties