9 research outputs found
Covalent Organic Frameworks as Porous Pigments for Photocatalytic Metal-Free C–H Borylation
Covalent organic frameworks (COFs) are highly promising
as heterogeneous
photocatalysts due to their tunable structures and optoelectronic
properties. Though COFs have been used as heterogeneous photocatalysts,
they have mainly been employed in water splitting, carbon dioxide
reduction, and hydrogen evolution reactions. A few examples in organic
synthesis using metal-anchored COF photocatalysts were reported. Herein,
we report highly stable β-keto-enamine-based COFs as photocatalysts
for metal-free C–B bond formation reactions. Three different
COFs have been availed for this purpose. Their photocatalysis performances
have been monitored for 12 different substrates, like quinolines,
pyridines, and pyrimidines. All the COFs showcase moderate-to-high
yields (up to 96%) depending upon the substrate’s molecular
functionality. High crystallinity, a large surface area, a low band
gap, and a suitable band position result in the highest catalytic
activity of TpAzo COF. The thorough mechanistic investigation further
highlights the crucial role of light-harvesting capacity, charge separation
efficiency, and current density during catalysis. The light absorbance
capacity of the COF plays a critical role during catalysis as yields
are maximized near the COF’s absorption maxima. The high photostability
of the as-synthesized COFs offers their reusability for several (>5)
catalytic cycles
Porosity Prediction through Hydrogen Bonding in Covalent Organic Frameworks
Easy and bulk-scale
syntheses of two-dimensional (2D) covalent
organic frameworks (COFs) represent an enduring challenge in material
science. Concomitantly, the most critical aspect is to precisely control
the porosity and crystallinity of these robust structures. Disparate
complementary approaches such as solvothermal synthesis have emerged
recently and are fueled in part by the usage of different modulators
and acids that have enriched the COF library. Yet, the fundamental
understanding of the integral processes of 2D COF assembly, including
their growth from nucleating sites and the origin of periodicity,
is an intriguing chemical question that needs to be answered. To address
these cardinal questions, a green and easy-to-perform approach of
COF formation has been delineated involving acid-diamine salt precursors.
The role of hydrogen bonding [<i>d</i><sub>av</sub>(N<sub>amine</sub>–H···O<sub>acid</sub>); <i>d</i><sub>av</sub> signifies the average N<sub>amine</sub>–H···O<sub>acid</sub> distances, i.e., the average distance from the H atom
of the amine to the O atom of the acid] present in the acid-diamine
salts in improving the COFs’ crystallinity and porosity has
further been decoded by thorough crystallographic analyses of the
salt molecules. What is particularly noteworthy is that we have established
the hydrogen-bonding distances <i>d</i><sub>av</sub>(N<sub>amine</sub>–H···O<sub>acid</sub>) in the acid-diamine
salts that are pivotal in maintaining the reversibility of the reaction,
which mainly facilitates highly crystalline and porous COF formation.
Moreover, this reactant-structure to the product-quality relationship
has further been utilized for the synthesis of highly crystalline
and porous COFs that are unattainable by other synthetic means
Porosity Prediction through Hydrogen Bonding in Covalent Organic Frameworks
Easy and bulk-scale
syntheses of two-dimensional (2D) covalent
organic frameworks (COFs) represent an enduring challenge in material
science. Concomitantly, the most critical aspect is to precisely control
the porosity and crystallinity of these robust structures. Disparate
complementary approaches such as solvothermal synthesis have emerged
recently and are fueled in part by the usage of different modulators
and acids that have enriched the COF library. Yet, the fundamental
understanding of the integral processes of 2D COF assembly, including
their growth from nucleating sites and the origin of periodicity,
is an intriguing chemical question that needs to be answered. To address
these cardinal questions, a green and easy-to-perform approach of
COF formation has been delineated involving acid-diamine salt precursors.
The role of hydrogen bonding [<i>d</i><sub>av</sub>(N<sub>amine</sub>–H···O<sub>acid</sub>); <i>d</i><sub>av</sub> signifies the average N<sub>amine</sub>–H···O<sub>acid</sub> distances, i.e., the average distance from the H atom
of the amine to the O atom of the acid] present in the acid-diamine
salts in improving the COFs’ crystallinity and porosity has
further been decoded by thorough crystallographic analyses of the
salt molecules. What is particularly noteworthy is that we have established
the hydrogen-bonding distances <i>d</i><sub>av</sub>(N<sub>amine</sub>–H···O<sub>acid</sub>) in the acid-diamine
salts that are pivotal in maintaining the reversibility of the reaction,
which mainly facilitates highly crystalline and porous COF formation.
Moreover, this reactant-structure to the product-quality relationship
has further been utilized for the synthesis of highly crystalline
and porous COFs that are unattainable by other synthetic means
Porosity Prediction through Hydrogen Bonding in Covalent Organic Frameworks
Easy and bulk-scale
syntheses of two-dimensional (2D) covalent
organic frameworks (COFs) represent an enduring challenge in material
science. Concomitantly, the most critical aspect is to precisely control
the porosity and crystallinity of these robust structures. Disparate
complementary approaches such as solvothermal synthesis have emerged
recently and are fueled in part by the usage of different modulators
and acids that have enriched the COF library. Yet, the fundamental
understanding of the integral processes of 2D COF assembly, including
their growth from nucleating sites and the origin of periodicity,
is an intriguing chemical question that needs to be answered. To address
these cardinal questions, a green and easy-to-perform approach of
COF formation has been delineated involving acid-diamine salt precursors.
The role of hydrogen bonding [<i>d</i><sub>av</sub>(N<sub>amine</sub>–H···O<sub>acid</sub>); <i>d</i><sub>av</sub> signifies the average N<sub>amine</sub>–H···O<sub>acid</sub> distances, i.e., the average distance from the H atom
of the amine to the O atom of the acid] present in the acid-diamine
salts in improving the COFs’ crystallinity and porosity has
further been decoded by thorough crystallographic analyses of the
salt molecules. What is particularly noteworthy is that we have established
the hydrogen-bonding distances <i>d</i><sub>av</sub>(N<sub>amine</sub>–H···O<sub>acid</sub>) in the acid-diamine
salts that are pivotal in maintaining the reversibility of the reaction,
which mainly facilitates highly crystalline and porous COF formation.
Moreover, this reactant-structure to the product-quality relationship
has further been utilized for the synthesis of highly crystalline
and porous COFs that are unattainable by other synthetic means
Porosity Prediction through Hydrogen Bonding in Covalent Organic Frameworks
Easy and bulk-scale
syntheses of two-dimensional (2D) covalent
organic frameworks (COFs) represent an enduring challenge in material
science. Concomitantly, the most critical aspect is to precisely control
the porosity and crystallinity of these robust structures. Disparate
complementary approaches such as solvothermal synthesis have emerged
recently and are fueled in part by the usage of different modulators
and acids that have enriched the COF library. Yet, the fundamental
understanding of the integral processes of 2D COF assembly, including
their growth from nucleating sites and the origin of periodicity,
is an intriguing chemical question that needs to be answered. To address
these cardinal questions, a green and easy-to-perform approach of
COF formation has been delineated involving acid-diamine salt precursors.
The role of hydrogen bonding [<i>d</i><sub>av</sub>(N<sub>amine</sub>–H···O<sub>acid</sub>); <i>d</i><sub>av</sub> signifies the average N<sub>amine</sub>–H···O<sub>acid</sub> distances, i.e., the average distance from the H atom
of the amine to the O atom of the acid] present in the acid-diamine
salts in improving the COFs’ crystallinity and porosity has
further been decoded by thorough crystallographic analyses of the
salt molecules. What is particularly noteworthy is that we have established
the hydrogen-bonding distances <i>d</i><sub>av</sub>(N<sub>amine</sub>–H···O<sub>acid</sub>) in the acid-diamine
salts that are pivotal in maintaining the reversibility of the reaction,
which mainly facilitates highly crystalline and porous COF formation.
Moreover, this reactant-structure to the product-quality relationship
has further been utilized for the synthesis of highly crystalline
and porous COFs that are unattainable by other synthetic means
Access to Silicon(II)– and Germanium(II)–Indium Compounds
Despite
the remarkable ability of N-heterocyclic silylene to act
as a Lewis base and form stable Lewis adducts with group 13 elements
such as boron, aluminum, and gallium, there has been no such comparable
investigation with indium and the realization of a stable silylene–indium
complex has still remained elusive. Similarly, a germylene–indium
complex is also presently unknown. We describe herein the reactions
of [PhC(N<i>t</i>Bu)<sub>2</sub>SiN(SiMe<sub>3</sub>)<sub>2</sub>] (<b>1</b>) and [PhC(N<i>t</i>Bu)<sub>2</sub>GeN(SiMe<sub>3</sub>)<sub>2</sub>] (<b>4</b>) with InCl<sub>3</sub> and InBr<sub>3</sub> that have resulted in the first silylene–indium
complexes, [PhC(N<i>t</i>Bu)<sub>2</sub>Si{N(SiMe<sub>3</sub>)<sub>2</sub>}→InCl<sub>3</sub>] (<b>2</b>) and [PhC(N<i>t</i>Bu)<sub>2</sub>Si{N(SiMe<sub>3</sub>)<sub>2</sub>}→InBr<sub>3</sub>] (<b>3</b>), as well as the first germylene–indium
complexes, [PhC(N<i>t</i>Bu)<sub>2</sub>Ge{N(SiMe<sub>3</sub>)<sub>2</sub>}→InCl<sub>3</sub>] (<b>5</b>) and [PhC(N<i>t</i>Bu)<sub>2</sub>Ge{N(SiMe<sub>3</sub>)<sub>2</sub>}→InBr<sub>3</sub>] (<b>6</b>). The solid-state structures of all species
have been validated by single-crystal X-ray diffraction studies. Note
that <b>5</b> and <b>6</b> are the first structurally
characterized organometallic compounds that feature a Ge–In
single bond (apart from the compounds in Zintl phases). Theoretical
calculations reveal that the Si(II)→In bonds in <b>2</b> and <b>3</b> and the Ge(II)→In bonds in <b>5</b> and <b>6</b> are dative bonds
Multistimuli-Responsive Interconvertible Low-Molecular Weight Metallohydrogels and the in Situ Entrapment of CdS Quantum Dots Therein
Two
low molecular weight metallohydrogels (ZALA and CALA) have
been synthesized from an amino-acid-based ligand precursor (LA) and
two different metal salts [zinc acetate dihydrate (ZA) and cadmium
acetate dihydrate (CA), respectively. These two hydrogels show a unique
chemically stimulated interconversion to each other via a reversible
gel–sol–gel pathway. This programmable gel–sol
reversible system satisfies logic operations of a basic Boolean logic
(INHIBIT) gate. Also, these hydrogels can be degraded into different
MOF phases at room temperature spontaneously or in the presence of
chloride and bromide salts (NaCl and NaBr.). CdS quantum dots can
be grown inside the CALA gel matrix (CdS@CALA) in the presence of
small amount of Na<sub>2</sub>S. This CdS doped gel exhibits time
dependent tunable emission (white to yellow to orange) as a consequence
of a slow agglomeration process of the entrapped quantum dots inside
the gel matrix. This luminescence property also reflects the corresponding
gel derived MOFs (obtained either by self-degradation of CdS@CALA
or via anion induction) as well. This, to the best of our knowledge,
is probably the simplest way to make a CdS quantum dot based composite
material where CdS is entrapped within the gel and the gel-derived
MOF matrix
A Covalent Organic Framework for Cooperative Water Oxidation
The future of water-derived hydrogen as the “sustainable
energy source” straightaway bets on the success of the sluggish
oxygen-generating half-reaction. The endeavor to emulate the natural
photosystem II for efficient water oxidation has been extended across
the spectrum of organic and inorganic combinations. However, the achievement
has so far been restricted to homogeneous catalysts rather than their
pristine heterogeneous forms. The poor structural understanding and
control over the mechanistic pathway often impede the overall development.
Herein, we have synthesized a highly crystalline covalent organic
framework (COF) for chemical and photochemical water oxidation. The
interpenetrated structure assures the catalyst stability, as the catalyst’s
performance remains unaltered after several cycles. This COF exhibits
the highest ever accomplished catalytic activity for such an organometallic
crystalline solid-state material where the rate of oxygen evolution
is as high as ∼26,000 μmol L–1 s–1 (second-order rate constant k ≈
1650 μmol L s–1 g–2). The
catalyst also proves its exceptional activity (k ≈
1600 μmol L s–1 g–2) during
light-driven water oxidation under very dilute conditions. The cooperative
interaction between metal centers in the crystalline network offers
20–30-fold superior activity during chemical as well as photocatalytic
water oxidation as compared to its amorphous polymeric counterpart
Constructing Ultraporous Covalent Organic Frameworks in Seconds via an Organic Terracotta Process
Research
on covalent organic frameworks (COFs) has recently gathered
significant momentum by the virtue of their predictive design, controllable
porosity, and long-range ordering. However, the lack of solvent-free
and easy-to-perform synthesis processes appears to be the bottleneck
toward their greener fabrication, thereby limiting their possible
potential applications. To alleviate such shortcomings, we demonstrate
a simple route toward the rapid synthesis of highly crystalline and
ultraporous COFs in seconds using a novel salt-mediated crystallization
approach. A high degree of synthetic control in interlayer stacking
and layer planarity renders an ordered network with a surface area
as high as 3000 m<sup>2</sup> g<sup>–1</sup>. Further, this
approach has been extrapolated for the continuous synthesis of COFs
by means of a twin screw extruder and <i>in situ</i> processes
of COFs into different shapes mimicking the ancient terracotta process.
Finally, the regular COF beads are shown to outperform the leading
zeolites in water sorption performance, with notably facile regeneration
ability and structural integrity