11 research outputs found
Fluorescence Control of Boron Enaminoketonate Using a Rotaxane Shuttle
The effect of rotaxane shuttling on the fluorescence properties of a fluorophore was investigated by exploiting fluorophore-tethered [2]rotaxanes. A fluorescent boron enaminoketonate (BEK) moiety was introduced in a rotaxane via transformation of an isoxazole unit generated as a result of an end-capping reaction using a nitrile <i>N</i>-oxide. The rotaxane exhibited a red shift of the fluorescence maximum along with a remarkable enhancement of the fluorescence quantum yield through wheel translation to the fluorophore
Intercrystal Self-Assembly for the Design of High-Quality Nickel Molybdate Nanocrystals
Nanowire of nickel molybdate hydrate,
being recognized as an emerging supercapacitor material, was synthesized
from the intercrystal self-assembly process (commonly referred to
as oriented aggregation or attachment). The detailed lattice image
of a NiMoO<sub>4</sub>·0.75H<sub>2</sub>O nanowire and the intermediate
nanostructure before reaching the interplanar binding were successfully
captured by means of high-resolution transmission and scanning electron
microscopies. NiMoO<sub>4</sub>·0.75H<sub>2</sub>O possessed
highly crystalline surface and internal nanostructures
Monoclinic Ag<sub>2</sub>Mo<sub>2</sub>O<sub>7</sub> Nanowire: A New Ag–Mo–O Nanophotocatalyst Material
We report a template-free facile
technique that allows for the first ever synthesis of a <i>monoclinic</i> Ag<sub>2</sub>Mo<sub>2</sub>O<sub>7</sub> nanowire (m-Ag<sub>2</sub>Mo<sub>2</sub>O<sub>7</sub>-NW), using a commercially available MoO<sub>3</sub> particle. The nanowire possessed high crystallinity and structural
homogeneity and strongly suggested that the nanowire was grown through
an oriented aggregation mechanism in contrast to the case of a typical
solution-phase method. The corresponding bulky counterpart showed
no photoresponse; however, a complete structural transformation toward
a nanowire triggered activity for O<sub>2</sub> evolution in the presence
of Ag<sup>+</sup> as an electron acceptor under visible-light irradiation
New Series of Dinuclear Ruthenium(II) Complexes Synthesized Using Photoisomerization for Efficient Water Oxidation Catalysis
A new series of <i>proximal,proximal</i>-[Ru<sub>2</sub>(tpy)<sub>2</sub>(L)ÂXY]<sup><i>n</i>+</sup> (<i>p</i>,<i>p</i>-<b>Ru</b><sub><b>2</b></sub><b>XY</b>, tpy = 2,2′:6′,2″-terpyridine,
L = 5-phenyl-2,8-diÂ(2-pyridyl)-1,9,10-anthyridine, X and Y = other
coordination sites) were synthesized using photoisomerization of a
mononuclear complex. The <i>p</i>,<i>p</i><b>-Ru</b><sub><b>2</b></sub><b>XY</b> complexes undergo
unusual reversible bridge-exchange reactions to generate <i>p</i>,<i>p</i>-<b>Ru</b><sub><b>2</b></sub><b>(μ-Cl)</b>, <i>p</i>,<i>p</i>-<b>Ru</b><sub><b>2</b></sub><b>(μ-OH)</b>, and <i>p</i>,<i>p</i>-<b>Ru</b><sub><b>2</b></sub><b>(OH)Â(OH</b><sub><b>2</b></sub><b>)</b> with
μ-Cl, μ-OH, as well as hydroxo and aquo ligands at X and
Y sites of <i>p</i>,<i>p</i>-<b>Ru</b><sub><b>2</b></sub><b>XY</b>, respectively. The geometric
and electronic structures of these complexes were characterized based
on UV–vis and <sup>1</sup>H NMR spectra, X-ray crystallography,
and density functional theory (DFT) calculations. <sup>1</sup>H NMR
data showed <i>C</i><sub>2</sub> symmetry of <i>p</i>,<i>p</i>-<b>Ru</b><sub><b>2</b></sub><b>(OH)Â(OH</b><sub><b>2</b></sub>) with the distorted L chelate
and nonequivalence of two tpy ligands, in contrast to the <i>C</i><sub>2<i>v</i></sub> symmetry of <i>p</i>,<i>p</i>-<b>Ru</b><sub><b>2</b></sub><b>(μ-Cl)</b> and <i>p</i>,<i>p</i>-<b>Ru</b><sub><b>2</b></sub><b>(μ-OH)</b>. However,
irrespective of the lower symmetry, <i>p</i>,<i>p</i>-<b>Ru</b><sub><b>2</b></sub><b>(OH)Â(OH</b><sub><b>2</b></sub><b>)</b> is predominantly formed in neutral
and weakly basic conditions due to the specially stabilized core structure
by multiple hydrogen-bond interactions among aquo, hydroxo, and backbone
L ligands. The electrochemical data suggested that <i>p</i>,<i>p</i>-<b>Ru</b><sub><b>2</b></sub><b>(OH)Â(OH</b><sub><b>2</b></sub><b>)</b> (Ru<sup>II</sup>–OH:Ru<sup>II</sup>–OH<sub>2</sub>) is oxidized to
the Ru<sup>III</sup>–OH:Ru<sup>III</sup>–OH state at
0.64 V vs saturated calomel electrode (SCE) and further to Ru<sup>IV</sup>î—»O:Ru<sup>IV</sup>î—¸OH at 0.79 V by successive
1-proton-coupled 2-electron processes at pH 7.0. The cyclic voltammogram
data exhibited that the <i>p</i>,<i>p</i>-<b>Ru</b><sub><b>2</b></sub><b>(OH)Â(OH</b><sub><b>2</b></sub><b>)</b> complex works more efficiently for electrocatalytic
water oxidation, compared with a similar mononuclear complex <i>distal-</i>[RuÂ(tpy)Â(L)ÂOH<sub>2</sub>]<sup>2+</sup> (<i>d-</i><b>RuOH</b><sub><b>2</b></sub>) and <i>p</i>,<i>p</i>-<b>Ru</b><sub><b>2</b></sub><b>(μ-Cl)</b> and <i>p</i>,<i>p</i>-<b>Ru</b><sub><b>2</b></sub><b>(μ-OH)</b>, showing that the <i>p</i>,<i>p</i>-<b>Ru</b><sub><b>2</b></sub> core structure with aquo and hydroxo ligands
is important for efficient electrocatalytic water oxidation. Bulk
electrolysis of the <i>p</i>,<i>p</i>-<b>Ru</b><sub><b>2</b></sub><b>(OH)Â(OH</b><sub><b>2</b></sub><b>)</b> solution corroborated the electrocatalytic cycle involving
the Ru<sup>III</sup>–OH:Ru<sup>III</sup>–OH state species
as a resting state. The mechanistic insight into O–O bond formation
for O<sub>2</sub> production was provided by the isotope effect on
electrocatalytic water oxidation by <i>p,p</i>-<b>Ru</b><sub><b>2</b></sub><b>(OH)Â(OH</b><sub><b>2</b></sub><b>)</b> and <i>d-</i><b>RuOH</b><sub><b>2</b></sub> in H<sub>2</sub>O and D<sub>2</sub>O media
Light Energy Accumulation from Pyrene Derivative to Tris(bipyridine)ruthenium on Clay Surface
A novel
type of energy donor–acceptor system on a clay surface
has been prepared. The energy transfer between an energy-donating
cationic pyrene derivative (An-Py<sup>2+</sup>) and an energy-accepting
trisÂ(bipyridine)ruthenium complex (Ru<sup>2+</sup>) on the clay surface
was investigated using absorption, emission, and lifetime measurements.
An obvious energy transfer was observed, and one Ru<sup>2+</sup> molecule
quenched the emission from five molecules of An-Py<sup>2+</sup> with
an emission quenching efficiency of 85% on the clay surface. This
suggests that the light energies absorbed by five of the An-Py<sup>2+</sup> molecules were accumulated in the one Ru<sup>2+</sup> molecule.
Near-quantitative emission quenching was observed for stoichiometric
amounts of An-Py<sup>2+</sup> and Ru<sup>2+</sup>. The apparent quenching
rate constant is approximately 10<sup>17</sup> L mol<sup>–1</sup> s<sup>–1</sup>, and thus the quenching rate constant is 10<sup>7</sup>–10<sup>8</sup> times higher than the diffusion rate
constant in a homogeneous solution
Remarkable Stimulation of Emission Quenching on a Clay Surface
Tetra-cationic
pyrene derivative (Py<sup>4+</sup>) and trisÂ(bipyridine)ÂrutheniumÂ(II)
(Ru<sup>2+</sup>) were hybridized onto the surface of a synthesized
clay. We observed the remarkable stimulation of excited Py<sup>4+</sup> emission quenching on the clay surface, with a very large apparent
quenching rate constant (<i>k</i><sub>q</sub> = 7.4 ±
0.7 × 10<sup>15</sup> L mol<sup>–1</sup> s<sup>–1</sup>)
Hybridization between Periodic Mesoporous Organosilica and a Ru(II) Polypyridyl Complex with Phosphonic Acid Anchor Groups
A new
method for the hybridization of a rutheniumÂ(II) polypyridyl complex
([RuÂ(bpy)<sub>2</sub>((CH<sub>2</sub>PO<sub>3</sub>H<sub>2</sub>)<sub>2</sub>-bpy)]<sup>2+</sup> (<b>RuP</b><sub><b>2</b></sub><sup><b>2+</b></sup>: bpy =2,2′-bipyridine; (CH<sub>2</sub>PO<sub>3</sub>H<sub>2</sub>)<sub>2</sub>-bpy =2,2′-bipyridine-4,4′diÂ(metylphosphonic
acid)) with biphenylene-bearing periodic mesoporous organosilica <b>(Bp–PMO</b> made from 4,4′bisÂ(triethoxysilyl)Âbiphenyl
[(C<sub>2</sub>H<sub>5</sub>O)<sub>3</sub>Si-(C<sub>6</sub>H<sub>4</sub>)<sub>2</sub>-SiÂ(OC<sub>2</sub>H<sub>5</sub>)<sub>3</sub>]) was developed.
Efficient and secure fixation of the rutheniumÂ(II) complex with methylphosphonic
acid groups (<b>RuP</b><sub><b>2</b></sub><sup><b>2+</b></sup>) in the mesopores of <b>Bp–PMO</b> occurred.
This method introduced up to 660 μmol of <b>RuP</b><sub><b>2</b></sub><sup><b>2+</b></sup> in 1 g of <b>Bp–PMO</b>. Two modes of adsorption of <b>RuP</b><sub><b>2</b></sub><sup><b>2+</b></sup> in the mesopores of <b>Bp–PMO</b> were observed: one is caused by the chemical interaction between
the methylphosphonic acid groups of <b>RuP</b><sub><b>2</b></sub><sup><b>2+</b></sup> and the silicate moieties of <b>Bp–PMO</b> and the other is attributed to aggregation of
the <b>RuP</b><sub><b>2</b></sub><sup><b>2+</b></sup> complexes. In the case of the former mode, adsorbed <b>RuP</b><sub><b>2</b></sub><sup><b>2+</b></sup> (up to 80–100
μmol g<sup>–1</sup>) did not detach from <b>Bp–PMO</b> after washing with acetonitrile, dimethylformamide, or even water.
Emission from the excited biphenylene (Bp) units was quantitatively
quenched by the adsorbed <b>RuP</b><sub><b>2</b></sub><sup><b>2+</b></sup> molecules in cases where more than 60
μmol g<sup>–1</sup> of <b>RuP</b><sub><b>2</b></sub><sup><b>2+</b></sup> was adsorbed, and emission from <b>RuP</b><sub><b>2</b></sub><sup><b>2+</b></sup> was
observed. Quantitative emission measurements indicated that emission
from approximately 100 Bp units can be completely quenched by only
one <b>RuP</b><sub><b>2</b></sub><sup><b>2+</b></sup> molecule in the mesopore, and photons absorbed by approximately
400 Bp units are potentially accumulated in one <b>RuP</b><sub><b>2</b></sub><sup><b>2+</b></sup> molecule
Superior Inorganic Ion Cofactors of Tetraborate Species Attaining Highly Efficient Heterogeneous Electrocatalysis for Water Oxidation on Cobalt Oxyhydroxide Nanoparticles
A heterogeneous
catalyst incorporating an inorganic ion cofactor for electrochemical
water oxidation was exploited using a CoOÂ(OH) nanoparticle layer-deposited
electrode. The significant catalytic current for water oxidation was
generated in a Na<sub>2</sub>B<sub>4</sub>O<sub>7</sub> solution at
pH 9.4 when applying 0.94 V versus Ag/AgCl in contrast to no catalytic
current generation in the K<sub>2</sub>SO<sub>4</sub> solution at
the same pH. HB<sub>4</sub>O<sub>7</sub><sup>–</sup> and B<sub>4</sub>O<sub>7</sub><sup>2–</sup> ions were indicated to act
as key cofactors for the induced catalytic activity of the CoOÂ(OH)
layer. The Na<sub>2</sub>B<sub>4</sub>O<sub>7</sub> concentration
dependence of the catalytic current was analyzed based on a Michaelis–Menten-type
kinetics to provide an affinity constant of cofactors to the active
sites, <i>K</i><sub>m</sub> = 28 ± 3.6 mM, and the
maximum catalytic current density, <i>I</i><sub>max</sub> = 2.3 ± 0.13 mA cm<sup>–2</sup>. The <i>I</i><sub>max</sub> value of HB<sub>4</sub>O<sub>7</sub><sup>–</sup> and B<sub>4</sub>O<sub>7</sub><sup>2–</sup> ions was 1.4
times higher than that (1.3 mA cm<sup>–2</sup>) for the previously
reported case of CO<sub>3</sub><sup>2–</sup> ions. This could
be explained by the shorter-range proton transfer from the active
site to the proton-accepting cofactor because of the larger size and
more flexible conformation of HB<sub>4</sub>O<sub>7</sub><sup>–</sup> and B<sub>4</sub>O<sub>7</sub><sup>2–</sup> ions compared
with that of CO<sub>3</sub><sup>2–</sup> ions
Intercalation of a Surfactant with a Long Polyfluoroalkyl Chain into a Clay Mineral: Unique Orientation of Polyfluoroalkyl Groups in Clay Layers
Eight
novel polyfluorinated surfactants (C<sub><i>n</i></sub>F<sub>2<i>n</i>+1</sub>CONHÂ(CH<sub>2</sub>)<sub>2</sub> N<sup>+</sup>(CH<sub>3</sub>)<sub>2</sub>C<sub>16</sub>H<sub>33</sub> Br<sup>–</sup>; abbreviated as C<i>n</i>F–S,
where <i>n</i> = 1, 2, 3, 4, 5, 6, 8, 10) were synthesized
and their intercalation into cation-exchangeable clay was investigated.
All of the polyfluorinated surfactants intercalated in amounts exceeding
the cation exchange capacity (CEC) of the clay. The C4F–S and
C5F–S surfactants exhibited intercalation up to 480% of the
CEC as a saturated adsorption limit. On the basis of X-ray analysis,
C<i>n</i>F–S surfactants intercalated between clay
nanosheets to form a bilayer structure in which the surfactant molecules
tilt at an angle of ∼60° with respect to the clay surface.
The saturated adsorption limits and layer distances differed between
surfactants with short (<i>n</i> = 1, 2) and long (<i>n</i> = 3–10) perfluoroalkyl chains. For long-chain surfactants,
their saturated adsorption limits were independent of the perfluoroalkyl
chain length and the layer distances systematically increased with
increasing perfluoroalkyl chain length. These results suggest that
the microscopic orientation differed between the short and long chains.
X-ray analysis showed that the long-chain surfactants orient the perfluoroalkyl
chains at a tilt of 41 ± 5° with respect to the clay layer.
This value was in good agreement with polarized IR measurements of
42 ± 2° for this angle
Mechanistic Insight into Reversible Core Structural Changes of Dinuclear μ‑Hydroxoruthenium(II) Complexes with a 2,8-Di-2-pyridyl-1,9,10-anthyridine Backbone Prior to Water Oxidation Catalysis
<i>proximal,proximal</i>-(<i>p</i>,<i>p</i>)-[Ru<sup>II</sup><sub>2</sub>(tpy)<sub>2</sub>LXY]<sup><i>n</i>+</sup> (tpy = 2,2′;6′,2″-terpyridine, L = 5-phenyl-2,8-di-2-pyridyl-1,9,10-anthyridine,
and X and Y = other coordination sites) yields the structurally and
functionally unusual Ru<sup>II</sup>(μ-OH)ÂRu<sup>II</sup> core,
which is capable of catalyzing water oxidation with key water insertion
to the core (<i>Inorg. Chem.</i> <b>2015</b>, <i>54</i>, 7627). Herein, we studied a sequence of bridging-ligand
substitution among <i>p</i>,<i>p</i>-[Ru<sub>2</sub>(tpy)<sub>2</sub>LÂ(μ-Cl)]<sup>3+</sup> (<b>Ru</b><sub><b>2</b></sub><b>(μ-Cl)</b>), <i>p</i>,<i>p</i>-[Ru<sub>2</sub>(tpy)<sub>2</sub>LÂ(μ-OH)]<sup>3+</sup> (<b>Ru</b><sub><b>2</b></sub><b>(μ-OH)</b>), <i>p</i>,<i>p</i>-[Ru<sub>2</sub>(tpy)<sub>2</sub>LÂ(OH)Â(OH<sub>2</sub>)]<sup>3+</sup> (<b>Ru</b><sub><b>2</b></sub><b>(OH)Â(OH</b><sub><b>2</b></sub><b>)</b>), and <i>p</i>,<i>p</i>-[Ru<sub>2</sub>(tpy)<sub>2</sub>LÂ(OH)<sub>2</sub>]<sup>2+</sup> (<b>Ru</b><sub><b>2</b></sub><b>(OH)</b><sub><b>2</b></sub>) in aqueous solution. <b>Ru</b><sub><b>2</b></sub><b>(μ-Cl)</b> converted slowly (10<sup>–4</sup> s<sup>–1</sup>) to <b>Ru</b><sub><b>2</b></sub><b>(μ-OH)</b>, and further <b>Ru</b><sub><b>2</b></sub><b>(μ-OH)</b> converted very slowly (10<sup>–6</sup> s<sup>–1</sup>) to <b>Ru</b><sub><b>2</b></sub><b>(OH)Â(OH</b><sub><b>2</b></sub><b>)</b> by the
insertion of water to reach equilibrium at pH 8.5–12.3. On
the basis of density functional theory (DFT) calculations, <b>Ru</b><sub><b>2</b></sub><b>(OH)Â(OH</b><sub><b>2</b></sub><b>)</b> was predicted to be thermodynamically stable by 13.3
kJ mol<sup>–1</sup> in water compared to <b>Ru</b><sub><b>2</b></sub><b>(μ-OH)</b> because of the specially
stabilized core structure by multiple hydrogen-bonding interactions
involving aquo, hydroxo, and L backbone ligands. The observed rate
from <b>Ru</b><sub><b>2</b></sub><b>(μ-OH)</b> to <b>Ru</b><sub><b>2</b></sub><b>(OH)</b><sub><b>2</b></sub> by the insertion of an OH<sup>–</sup> ion increased linearly with an increase in the OH<sup>–</sup> concentration from 10 to 100 mM. The water insertion to the core
is very slow (∼10<sup>–6</sup> s<sup>–1</sup>) in aqueous solution at pH 8.5–12.3, whereas the insertion
of OH<sup>–</sup> ions is accelerated (10<sup>–5</sup>–10<sup>–4</sup> s<sup>–1</sup>) above pH 13.4
by 2 orders of magnitude. The kinetic data including activation parameters
suggest that the associative mechanism for the insertion of water
to the Ru<sup>II</sup>(μ-OH)ÂRu<sup>II</sup> core of <b>Ru</b><sub><b>2</b></sub><b>(μ-OH)</b> at pH 8.5–12.3
alters the interchange mechanism for the insertion of an OH<sup>–</sup> ion to the core above pH 13.4 because of relatively stronger nucleophilic
attack of OH<sup>–</sup> ions. The hypothesized <i>p</i>,<i>p</i>-[Ru<sub>2</sub>(tpy)<sub>2</sub>LÂ(μ-OH<sub>2</sub>)]<sup>4+</sup> and <i>p</i>,<i>p</i>-[Ru<sub>2</sub>(tpy)<sub>2</sub>LÂ(OH<sub>2</sub>)<sub>2</sub>]<sup>4+</sup> formed by protonation from <b>Ru</b><sub><b>2</b></sub><b>(μ-OH)</b> and <b>Ru</b><sub><b>2</b></sub><b>(OH)Â(OH</b><sub><b>2</b></sub><b>)</b> were
predicted to be unstable by 71.3 and 112.4 kJ mol<sup>–1</sup> compared to <b>Ru</b><sub><b>2</b></sub><b>(μ-OH)</b> and <b>Ru</b><sub><b>2</b></sub><b>(OH)Â(OH</b><sub><b>2</b></sub><b>)</b>, respectively. The reverse
reactions of <b>Ru</b><sub><b>2</b></sub><b>(μ-OH)</b>, <b>Ru</b><sub><b>2</b></sub><b>(OH)Â(OH</b><sub><b>2</b></sub><b>)</b>, and <b>Ru</b><sub><b>2</b></sub><b>(OH)</b><sub><b>2</b></sub> to <b>Ru</b><sub><b>2</b></sub><b>(μ-Cl)</b> below
pH 5 could be caused by lowering the core charge by protonation of
the μ-OH<sup>–</sup> or OH<sup>–</sup> ligand