Redox flow batteries (RFBs) are regarded a promising technology for large-scale electricity energy storage to realize efficient utilization of intermittent renewable energy. Redox -active materials...

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Status and Prospects of Organic Redox Flow Batteries toward Sustainable Energy Storage

Morphology influences the functionality of covalent organic networks and determines potential applications. Here, we report for the first time the use of Zincke reaction to fabricate, under either solvothermal or microwave conditions, a viologen-linked covalent organic network in the form of hollow particles or nanosheets. The synthesized materials are stable in acidic, neutral, and basic aqueous solutions. Under basic conditions, the neutral network assumes radical cationic character without decomposing or changing structure. Solvent polarity and heating method determine product morphology. Depending upon solvent polarity, the resulting polymeric network forms either uniform self-templated hollow spheres (HS) or hollow tubes (HT). The spheres develop via an inside-out Ostwald ripening mechanism. Interestingly, microwave conditions and certain solvent polarities result in the formation of a robust covalent organic gel framework (COGF) that is organized in nanosheets stacked several layers thick. In the gel phase, the nanosheets are crystalline and form honeycomb lattices. The use of the Zincke reaction has previously been limited to the synthesis of small viologen molecules and conjugated viologen oligomers. Its application here expands the repertoire of tools for the fabrication of covalent organic networks (which are usually prepared by dynamic covalent chemistry) and for the synthesis of viologen-based materials. All three materials-HT, HS, and COGF-serve as efficient adsorbents of iodine due to the presence of the cationic viologen linker and, in the cases of HT and HS, permanent porosity.

Viologen-Based Conjugated Covalent Organic Networks via Zincke Reaction

A category of parallel π-stacking interaction, termed pancake bonding, is surveyed. The main characteristics are: the interaction occurs among radicals with highly delocalized π-electrons in their singly occupied molecular orbitals (SOMOs), the contact distances in the π-stacking direction are shorter than the typical van der Waals distances, and the stabilization obtained by the bonding combination of the SOMO orbitals leads to direct atom-to-atom overlap with strong orientational preferences. These atypical intermolecular interactions contain a component of electron sharing between the radicals that can be viewed as covalent-like. Pancake bonded dimers characteristically have low-lying singlet and triplet states and show characteristic interlayer vibrational modes. Pancake bonded aggregates serve as molecular components in many conducting and other functional organic materials. The role of van der Waals (vdW) interactions in pancake bonded dimers, chains, and other aggregates is different from closed shell vdW aggregates: here the Pauli repulsions reduce the attractive dispersion interaction significantly. Fluxionality between π- and σ-bonded aggregates often occur in the context of pancake bonding. Both experimental and computational aspects are reviewed.

Pancake Bonding: An Unusual Pi-Stacking Interaction.

The solvothermal reaction of Mn(ClO4)2, NaN3, and a rigid viologen-tethered tetracarboxylic acid (1,1′-bis(3,5-dicarboxyphenyl)-4,4′-bipyridinium chloride, [H4L]Cl2) led to a coordination polymer of formula [Mn4(L)(N3)6(H2O)2]n. X-ray analysis revealed a 3D coordination structure. The Mn(II) ions are connected by mixed azide and carboxylate bridges to give 2D layers, which are pillared by the viologen tether of the zwitterionic ligand. Magnetic analyses suggested that the compound features antiferromagnetism and field-induced metamagnetism. The compound also shows photochromic and photomagnetic properties. The long-range magnetic ordering is owed to the spin-canting structure of the Mn(II)-azide-carboxylate layer; the photochromism involves the formation of viologen radicals via photoinduced electron transfer, and the photomagnetism is related to the interactions between the metal ion and the photogenerated radicals. The study demonstrates a strategy for the design of new multifunctional materials with ph...

Magnetic and Photochromic Properties of a Manganese(II) Metal-Zwitterionic Coordination Polymer

To avoid crosstalk and suppress leakage currents in resistive random access memories (RRAMs), a resistive switch and a current rectifier (diode) are usually combined in series in a one diode–one resistor (1D–1R) RRAM. However, this complicates the design of next-generation RRAM, increases the footprint of devices and increases the operating voltage as the potential drops over two consecutive junctions1. Here, we report a molecular tunnel junction based on molecules that provide an unprecedented dual functionality of diode and variable resistor, resulting in a molecular-scale 1D–1R RRAM with a current rectification ratio of 2.5 × 104 and resistive on/off ratio of 6.7 × 103, and a low drive voltage of 0.89 V. The switching relies on dimerization of redox units, resulting in hybridization of molecular orbitals accompanied by directional ion migration. This electric-field-driven molecular switch operating in the tunnelling regime enables a class of molecular devices where multiple electronic functions are preprogrammed inside a single molecular layer with a thickness of only 2 nm. A multifunctional molecule acting both as diode and variable resistor is used to fabricate compact molecular switches with a thickness of 2 nm, good current rectification and resistive on/off ratio, and requiring a drive voltage as low as 0.89 V.

Electric-field-driven dual-functional molecular switches in tunnel junctions

Pi bonds between organic radicals have generated recent excitement as an orthogonal interaction for designing self-assembling architectures in water. Here, we provide the first a systematic investigation of the effect of the viologen cation radical structure on the strength and nature of the pimer bond. A striking and unexpected feature of the this pi bond is that the bond strength is unchanged by substitution with electron-donating groups or withdrawing groups or with increased conjugation. Furthermore, the interaction is undiminished by sterically bulky N-alkyl groups. Theoretical modelling indicates that strong dispersion forces dominate the interaction between the radicals, rationalizing the insensitivity of the bonding interaction to substituents: The stacking of polarizable pi radicals leads to attractive dispersion forces in excess of typical dispersion interactions of small molecules and helps overcome the Coulombic repulsion of bringing two cationic species into contact.

The Viologen Cation Radical Pimer: A Case of Dispersion-Driven Bonding.

https://lib.dr.iastate.edu/cgi/viewcontent.cgi?article=2048&context=chem_pubs

A radical spin on viologen polymers: organic spin crossover materials in water

A serendipitously discovered oxidative esterification reaction of cyclohexane hexacarboxylic acid with phosphorus pentachloride and phenols provides one-pot access to previously unknown aryl mellitic acid esters. The reaction features a solvent-free digestion and chromatography-free purifications and demonstrates the possibility of cyclohexane-to-benzene conversions under relatively mild, metal-free conditions.

https://lib.dr.iastate.edu/cgi/viewcontent.cgi?article=1146&context=chem_pubs

Access to aryl mellitic acid esters through a surprising oxidative esterification reaction.

The present invention provides bis(hydroxyalkyl)mercaptosuccinates of the formula: 
and derivatives thereof, where X 1 , X 2 , Z 1 , Z 2 , Y 1 , Y 2 , R a , R b , R 1 , and R 2 are those defined herein. The present invention also provides methods for producing and using the same.

Mark J. Juetten

Papers

The Viologen Cation Radical Pimer: A Case of Dispersion-Driven Bonding.

A radical spin on viologen polymers: organic spin crossover materials in water

Access to aryl mellitic acid esters through a surprising oxidative esterification reaction.

Bis-(hydroxyalkyl)mercaptosuccinates

Access to Aryl Mellitic Acid Esters Through a Surprising Oxidative Esterification Reaction.