An Anthracene-Based Metal-Organic Framework for Selective Photo-Reduction of Carbon Dioxide to Formic Acid Coupled with Water Oxidation.

A Zr-based metal-organic framework has been synthesized and employed as a catalyst for photochemical carbon dioxide reduction coupled with water oxidation. The catalyst shows significant carbon dioxide reduction property with concomitant water oxidation. The catalyst has broad visible light as well as UV light absorption property, which is further confirmed from electronic absorption spectroscopy. Formic acid was the only reduced product from carbon dioxide with a turn-over frequency (TOF) of 0.69 h-1 in addition to oxygen, which was produced with a TOF of 0.54 h-1 . No external photosensitizer is used and the ligand itself acts as the light harvester. The efficient and selective photochemical carbon dioxide reduction to formic acid with concomitant water oxidation using Zr-based MOF as catalyst is thus demonstrated here.

Electrocatalytic Reduction of CO2 to Acetic Acid by a Molecular Manganese Corrole Complex.

The controlled electrochemical reduction of carbon dioxide to value added chemicals is an important strategy in terms of renewable energy technologies. Therefore, the development of efficient and stable catalysts in an aqueous environment is of great importance. In this context, we focused on synthesizing and studying a molecular MnIII -corrole complex, which is modified on the three meso-positions with polyethylene glycol moieties for direct and selective production of acetic acid from CO2 . Electrochemical reduction of MnIII leads to an electroactive MnII species, which binds CO2 and stabilizes the reduced intermediates. This catalyst allows to electrochemically reduce CO2 to acetic acid in a moderate acidic aqueous medium (pH 6) with a selectivity of 63 % and a turn over frequency (TOF) of 8.25 h-1 , when immobilized on a carbon paper (CP) electrode. In terms of high selectivity towards acetate, we propose the formation and reduction of an oxalate type intermediate, stabilized at the MnIII -corrole center.

Electrochemical organic reactions: A tutorial review.

Although the core of electrochemistry involves simple oxidation and reduction reactions, it can be complicated in real electrochemical organic reactions. The principles used in electrochemical reactions have been derived using physical organic chemistry, which drives other organic/inorganic reactions. This review mainly comprises two themes: the first discusses the factors that help optimize an electrochemical reaction, including electrodes, supporting electrolytes, and electrochemical cell design, and the second outlines studies conducted in the field over a period of 10 years. Electrochemical reactions can be used as a versatile tool for synthetically important reactions by modifying the constant electrolysis current.

Direct realization of an Operando Systems Chemistry Algorithm (OSCAL) for powering nanomotors.

Systems chemistry focuses on emergent properties in a complex matter. To design and demonstrate such emergent properties like autonomous motion in nanomotors as an output of an Operando Systems Chemistry Algorithm (OSCAL), we employ a 2-component system comprising porous organic frameworks (POFs) and soft-oxometalates (SOMs). The OSCAL governs the motion of the nanocarpets by the coding and reading of information in an assembly/disassembly cascade switched on by a chemical stimulus. Assembly algorithm docks SOMs into the pores of the POFs of the nanocarpet leading to the encoding of supramolecular structural information in the SOM-POF hybrid nanocarpet. Input of a chemical fuel to the system induces a catalytic reaction producing propellant gases and switches on the disassembly of SOMs that are concomitantly released from the pores of the SOM-POF nanocarpets producing a ballast in the system as a read-out of the coded information acquired in the supramolecular assembly. The OSCAL governs the motion of the nanocarpets in steps. The assembly/disassembly of SOM-POFs, releasing SOMs from the pores of SOM-POFs induced by a catalytic reaction triggered by a chemical stimulus coupled with the evolution of gas are the input. The output is the autonomous linear motion of the SOM-POF nanocarpets resulting from the read-out of the input information. This work thus manifests the operation of a designed Systems Chemistry algorithm which sets supramolecularly assembled SOM-POF nanocarpets into autonomous ballistic motion.

Self-Assembly and Cascade Catalysis by a Soft-Oxometalate (SOM) System.

Cascade catalysis has gained importance due to its various applications. In this work, cascade catalysis was performed using a self-assembled soft-oxometalate (SOM) as a model system. At first, we synthesized an oxometalate (OM) hybrid with a polymerizable organic cation, namely tetrakis(4-aminophenyl)methane, and an OM, K8[SiW11O39]. The hybrid in turn was converted into SOM in water, DMSO mixture, and characterized by different techniques, ranging from electron microscopy to DLS. The SOM state is endowed with the ability to polymerize the aniline based counter ions associated with it in the presence of UV-light. This polymerization is possible due to the presence of photocatalytic OMs (oxometalates) in the SOMs. The polymer-SOM hybrid in cascade oxidizes selectively aniline to nitrobenzene and nitrite to nitrate owing to the residual oxidizing property of the OM constituents in it. This is the first example of cascade catalysis in SOM chemistry.

Molecular cobalt corrole complex for the heterogeneous electrocatalytic reduction of carbon dioxide.

Electrochemical conversion of CO2 to alcohols is one of the most challenging methods of conversion and storage of electrical energy in the form of high-energy fuels. The challenge lies in the catalyst design to enable its real-life implementation. Herein, we demonstrate the synthesis and characterization of a cobalt(III) triphenylphosphine corrole complex, which contains three polyethylene glycol residues attached at the meso-phenyl groups. Electron-donation and therefore reduction of the cobalt from cobalt(III) to cobalt(I) is accompanied by removal of the axial ligand, thus resulting in a square-planar cobalt(I) complex. The cobalt(I) as an electron-rich supernucleophilic d8-configurated metal centre, where two electrons occupy and fill up the antibonding dz2 orbital. This orbital possesses high affinity towards electrophiles, allowing for such electronically configurated metals reactions with carbon dioxide. Herein, we report the potential dependent heterogeneous electroreduction of CO2 to ethanol or methanol of an immobilized cobalt A3-corrole catalyst system. In moderately acidic aqueous medium (pH = 6.0), the cobalt corrole modified carbon paper electrode exhibits a Faradaic Efficiency (FE%) of 48 % towards ethanol production.

pH-induced phase transition and crystallization of soft-oxometalates (SOMs) into polyoxometalates (POMs): a study on crystallization from colloids.

In this work, we demonstrate a simple approach for growing 1D (one-dimensional) inorganic chains of K(C6H16N)3Mo8O26·H2O polyoxometalates (POMs) from its colloidal soft-oxometalate (SOM) phase through the variation of pH. The structure is composed mainly of a 1D inorganic chain with a ß-Mo8O264- binding node linked using K+ via Mo-O-K linkages, which results in a cuboctahedral geometry for the K+ ions. Crystal structure and Hirshfeld surface studies reveal the role of triethylammonium cations in restricting the growth of the 1D chain into 2D/3D (two-/three-dimensional) structures. During the nucleation process from the heterogeneous SOM phase, some of the intermolecular interactions in the dispersion phase are retained in the crystal structure, which was evidenced from residual O...O interactions. The crystallization of the species from its colloidal form as a function of pH was studied by the use of Raman spectroscopy and it was found that the increase in volume fraction of the ß-Mo8O264- species in the crystallizing colloidal mixture with the decrease in pH is responsible for the nucleation. This was monitored by time-dependent DLS (dynamic light scattering) measurement and zeta-potential studies, revealing the co-existence of both the crystal and the colloidal forms at pH 3-2. This brings us to the conclusion that in the crystallization of POMs, the colloidal SOM phase precedes the crystalline POM phase which occurs via a phase transition. This work could open up avenues for the study of POM formation from the stand-point of colloidal chemistry and SOMs.

Softoxometalate [{K6.5Cu(OH)8.5(H2O)7.5}0.5@{K3PW12O40}]n (n = 1348-2024) as an Efficient Inorganic Material for CO2 Reduction with Concomitant Water Oxidation.

An immediate challenge for chemists is to devise different methods to trap chemical energy using light by reduction of carbon dioxide to a transportable fuel. To reach this goal the major obstacle lies in finding a suitable material that is abundant and possesses catalytic power to effect such reduction reaction and perform this reduction reaction without using any external photosensitizer. Here we report for the first time a softoxometalate based on a {[K6.5Cu(OH)8.5(H2O)7.5]0.5[K3PW12O40]} metal oxide framework which is stable in reaction conditions that effectively performs photochemical CO2 reduction reaction in water with a very high turnover number of 613 and TOF of 47.15 h-1. We observe that during this reaction water gets oxidized to oxygen, while the electrons released directly go to CO2 reducing it to formic acid. A detailed account of the characterization of the catalyst along with that of products of this reaction is reported.