Proton conduction
is vital for living systems to execute various
physiological activities. The understanding of its mechanism is also
essential for the development of state-of-the-art applications, including
fuel-cell technology. We herein present a bottom-up strategy, that
is, the self-assembly of
Cage-1
and
-2
with
an identical chemical composition but distinct structural features
to provide two different supramolecular conductors that are ideal
for the mechanistic study.
Cage-1
with a larger cavity
size and more H-bonding anchors self-assembled into a crystalline
phase with more proton hopping pathways formed by H-bonding networks,
where the proton conduction proceeded via the Grotthuss mechanism.
Small cavity-sized
Cage-2
with less H-bonding anchors
formed the crystalline phase with loose channels filled with discrete
H-bonding clusters, therefore allowing for the translational diffusion
of protons, that is, vehicle mechanism. As a result, the former exhibited
a proton conductivity of 1.59 × 10
–4
S/cm at
303 K under a relative humidity of 48%, approximately 200-fold higher
compared to that of the latter. Ab initio molecular dynamics simulations
revealed distinct H-bonding dynamics in
Cage-1
and
-2
, which provided further insights into potential proton
diffusion mechanisms. This work therefore provides valuable guidelines
for the rational design and search of novel proton-conducting materials.
Polymorphism control of metal-organic frameworks is highly desired for elucidating structure-property relationships, but remains an empirical process and is usually done in a trial-and-error approach. We adopted the rarely used actinide cation Th 4 + and a ditopic linker to construct a series of thorium-organic frameworks (TOFs) with a range of polymorphs. The extraordinary coordination versatility of Th 4 + cations and clusters, coupled with synthetic modulation, gives five distinct phases, wherein the highest degree of interpenetration (threefold) and porosity (75.9 %) of TOFs have been achieved. Notably, the O atom on the capping site of the nine-coordinated Th 4 + cation can function as a bridging unit to interconnect neighboring secondary building units (SBUs), affording topologies that are undocumented for other tetravalent-metal-containing MOFs. Furthermore, for the first time HCOOH has been demonstrated as a bridging unit of SBUs to further induce structural complexity. The resulting TOFs exhibit considerably different adsorption behaviors toward organic dyes, thus suggesting that TOFs represent an exceptional and promising platform for structure-property relationship study.
Mapped electron density and ab initio modelling reveal how H-atom position and molecular environment tune short hydrogen bond characteristics and properties.
We developed a very efficient and expandable divergent approach initiated by a direct electrophilic borylation at phenyl rings to synthesize a series of double heterohelicenes. Their πextended structures with pristine zigzag nitrogen (N)−boron (B)− nitrogen (N) edges offer them substantial physical properties and strong double hydrogen-bond donating capability. The isolated (P,P) and (M,M) enantiomers exhibit circularly polarized luminescence in response to hydrogen-bonding interactions.
Naphthalimide based ligands have received significant attention for their ability to act as secondary building units (SBUs) for metal-containing network structures. The potentially bridging 1,2,4-triazole containing N- (1,2,4-triazolyl
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