Metal–organic frameworks (MOFs) containing redox active linkers have led to hybrid compounds exhibiting high electrical conductivity, which enables their use in applications in electronics and ...electrocatalysis. While many computational studies predict two-dimensional (2D) MOFs to be metallic, the majority of experiments show decreasing conductivity on cooling, indicative of a gap in the electronic band structure. To date, only a handful of MOFs have been reported that exhibit increased electrical conductivity upon cooling indicative of a metallic character, which highlights the need for a better understanding of the origin of the conductivity. A 2D MOF containing iron bis(dithiolene) motifs was recently reported to exhibit semiconducting behavior with record carrier mobility. Herein, we report that high crystallinity and the elimination of guest species results in an iron 2,3,6,7,10,11-tripheylenehexathiolate (THT) MOF, FeTHT, exhibiting a complex transition from semiconducting to metallic upon cooling, similar to what was shown for the analogous CoTHT. Remarkably, exposing the FeTHT to air significantly influences the semiconducting-to-metallic transition temperature (100 to 300 K) and ultimately results in a material showing metallic-like character at, and above, room temperature. This study indicates these materials can tolerate a substantial degree of doping that ultimately results in charge delocalization and metallic-like conductivity, an important step toward enabling their use in chemiresistive sensing and optoelectronics.
The reduction of CO2 into higher energy products such as carbon-based fuels and feedstocks is an attractive strategy for mitigating the continuous rise in CO2 emissions associated with the growing ...global energy demand. Rhenium tricarbonyl complexes bearing 2,2′-bipyridine (2,2′-bpy) ligands are well-established molecular electrocatalysts for the selective reduction of CO2 to CO. Construction of efficient devices for this electrochemical process requires the immobilization of electrocatalysts to electrode surfaces. To integrate Re(2,2′-bpy)(CO)3 fragments into a covalent organic framework (COF), Re(5,5′-diamine-2,2′-bpy)(CO)3Cl (1) was synthesized and electrochemically investigated. Complex 1 is an active and selective electrocatalyst for the reduction of CO2 to CO with excellent faradaic efficiency (99%). The presence of the amine substituents leads to a destabilization of the π* orbital of the 5,5′-diamine-2,2′-bpy ligand with respect to the metal center. Therefore, 1 requires more negative potentials (−2.47 V vs. Fc+/0) to reach the doubly reduced catalytically active species. DFT studies were conducted to understand the electronic structure of 1, and support the destabilizing effect of the amine substituents. The Re-2,2′-bpy fragments were successfully integrated into a COF containing 2,2′-bpy moieties (COF-2,2′-bpy) via a post-metallation synthetic route to generate COF-2,2′-bpy-Re. A composite of COF-2,2′-bpy-Re, carbon black, and polyvinylidene fluoride (PVDF) was readily immobilized onto glassy carbon electrodes and electrocatalytic CO2 reduction to CO was observed at −2.8 V vs. Fc0/+, with a faradaic efficiency of 81% for CO production.
Single-molecule one-dimensional topological insulator (1D TI) is a class of molecular wires that exhibit increasing conductance with wire length. This unique trend is due to the coupling between the ...two low-lying topological edge states of 1D TIs described by the Su–Schrieffer–Heeger model. In principle, this quantum phenomenon within 1D TIs can be utilized to achieve long-range gating in molecular conductors. Here, we study electron transport through a single-edge state of doubly oxidized oligophenylene bis(triarylamine) to understand the effect of the edge state coupling on conductance. We find that conductance is elevated by approximately 1 order of magnitude compared to a control molecule with the same conductance pathway. Density function theory calculations further support that the increase in conductance is due to the interaction between the edge states of 1D TIs. This work demonstrates a new gating paradigm in molecular electronics, while also providing a deeper understanding of how edge states interact and affect electron transport within 1D TIs.
The formation of carbon-carbon bonds with transition metal reagents serves as a cornerstone of organic synthesis. Here, we show that the reactivity of an otherwise kinetically inert transition metal ...complex can be induced by an external electric field to affect a coupling reaction. These results highlight the importance of electric field effects in reaction chemistry and offers a new strategy to modulate organometallic reactivity.
External electric fields can influence the reactivity of organometallic complexes in solution. This effect is demonstrated to induce carbon-carbon bond forming chemistry with a kinetically inert nickel complex at room temperature.
As social media platforms continue to grow in popularity, there is an increasing need for science outreach teams to bring STEM content to the virtual landscape. Here, we highlight the use of ...short-form videos on our TikTok channel@IvyLeagueScienceas a new way to approach science outreach. Through a combination of content production and data analytics, we were able to build an online platform with >150k followers, 3.6 million likes, and 18 million views. By bringing science to social media, we engage with students across the world, allowing them to experience science-based content. In this case study, we hope to encourage other scientific outreach teams to employ social media as a means of increasing visibility of scientists and STEM careers.
Correction for 'Electric-field-induced coupling of aryl iodides with a nickel(0) complex' by Nicholas M. Orchanian
et al.
,
Chem. Commun.
, 2022,
https://doi.org/10.1039/d2cc03671a
.
Coherent tunneling electron transport through molecular wires has been theoretically established as a temperature-independent process. Although several experimental studies have shown counter ...examples, robust models to describe this temperature dependence have not been thoroughly developed. Here, we demonstrate that dynamic molecular structures lead to temperature-dependent conductance within coherent tunneling regime. Using a custom-built variable-temperature scanning tunneling microscopy break-junction instrument, we find that oligonphenylenes exhibit clear temperature-dependent conductance. Our calculations reveal that thermally activated dihedral rotations allow these molecular wires to have a higher probability of being in a planar conformation. As the tunneling occurs primarily through π-orbitals, enhanced coplanarization substantially increases the time-averaged tunneling probability. These calculations are consistent with the observation that more rotational pivot points in longer molecular wires leads to larger temperature-dependence on conductance. These findings reveal that molecular conductance within coherent and off-resonant electron transport regimes can be controlled by manipulating dynamic molecular structure.
Here, we describe the synthesis of the hexameric macrocyclic aniline (MA6), which spontaneously assembles into coaxially conductive organic wires in its oxidized and acidified emeraldine salt (ES) ...form. Electrical measurements reveal that ES-MA6 exhibits high electrical conductivity (7.5 × 10–2 S·cm–1) and that this conductivity is acid–base responsive. Single-crystal X-ray crystallography reveals that ES-MA6 assembles into well-defined trimeric units that then stack into nanotubes with regular channels, providing a potential route to synthetic nanotubes that are leveraged for ion or small molecule transport. Ultraviolet–visible–near-infrared absorbance spectroscopy and electron paramagnetic spectroscopy showcase the interconversion between acidic (conductive) and basic (insulating) forms of these macrocycles and how charge carriers are formed through protonation, giving rise to the experimentally observed high electrical conductivity.
We advance the chemistry of apical chlorine substitution in the 2D superatomic semiconductor Re6Se8Cl2 to build functional and atomically precise monolayers on the surface of the 2D superatomic ...Re6Se8 substrate. We create a functional monolayer by installing surface (2,2′-bipyridine)-4-sulfide (Sbpy) groups that chelate to catalytically active metal complexes. Through this reaction chemistry, we can create monolayers where we can control the distribution of catalytic sites. As a demonstration, we create highly active electrocatalysts for the oxygen evolution reaction using monolayers of cobalt(acetylacetonate)2bipyridine. We can further produce a series of catalysts by incorporating organic spacers in the functional monolayers. The structure and flexibility of the surface linkers can affect the catalytic performance, possibly by tuning the coupling between the functional monolayer and the superatomic substrate. These studies establish that the Re6Se8 sheet behaves as a chemical pegboard: a surface amenable to geometrically and chemically well-defined modification to yield functional monolayers, in this case catalytically active, that are atomically precise. This is an effective method to generate diverse families of functional nanomaterials.
Synthesis and isolation of molecular building blocks of metal-organic frameworks (MOFs) can provide unique opportunities for characterization that would otherwise be inaccessible due to the ...heterogeneous nature of MOFs. Herein, we report a series of trinuclear cobalt complexes incorporating dithiolene ligands, triphenylene-2,3,6,7,10,11-hexathiolate (THT) (
1
3+
), and benzene hexathiolate (BHT) (
2
3+
), with 1,1,1,-tris(diphenylphosphinomethyl)ethane (triphos) employed as the capping ligand. Single crystal X-ray analyses of
1
3+
and
2
3+
display three five-coordinate cobalt centers bound to the triphos and dithiolene ligands in a distorted square pyramidal geometry. Cyclic voltammetry studies of
1
3+
and
2
3+
reveal three redox features associated with the formation of mixed valence states due to the sequential reduction of the redox-active metal centers (Co
III/II
). Using this electrochemical data, the comproportionality values were determined for
1
and
2
(log
K
c
= 1.4 and 1.5 for
1
, and 4.7 and 5.8 for
2
), suggesting strong resonance-stabilized coupling of the metal centers, with stronger electronic coupling observed for complex
2
compared to that for complex
1
. Cyclic voltammetry studies were also performed in solvents of varying polarity, whereupon the difference in the standard potentials (Δ
E
1/2
) for
1
and
2
was found to shift as a function of the polarity of the solvent, indicating a negative correlation between the dielectric constant of the electrochemical medium and the stability of the mixed valence species. Spectroelectrochemical studies of
in situ
generated multi-valent (MV) states of complexes
1
and
2
display characteristic NIR intervalence charge transfer (IVCT) bands, and analysis of the IVCT transitions for complex
2
suggests a weakly coupled class II multi-valent species and relatively large electronic coupling factors (1700 cm
−1
for the first multi-valent state of
2
2+
, and 1400 and 4000 cm
−1
for the second multi-valent state of
2
+
). Density functional theory (DFT) calculations indicate a significant deviation in relative energies of the frontier orbitals of complexes
1
3+
,
2
3+
, and
3
+
that contrasts those calculated for the analogous trinuclear cobalt dithiolene complexes employing pentamethylcyclopentadienyl (Cp*) as the capping ligand (
Co
3
Cp*
3
THT
and
Co
3
Cp*
3
BHT
, respectively), and may be a result of the cationic nature of complexes
1
3+
,
2
3+
, and
3
+
.
Synthesis and isolation of molecular building blocks of metal-organic frameworks (MOFs) can provide unique opportunities for characterization that would otherwise be inaccessible due to the heterogeneous nature of MOFs.
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