Search for: All records

Catalytic water oxidation is an important process for the development of clean energy solutions and energy storage. Despite the significant number of reports on active catalysts, systematic control of the catalytic activity remains elusive. In this study, descriptors are explored that can be correlated with catalytic activity. [Ru(tpy)(pic)₂(H₂O)](NO₃)₂and [Ru(EtO‐tpy)(pic)₂(H₂O)](NO₃)₂(where tpy=2,2′ : 6′,2“‐terpyridine, EtO‐tpy=4′‐(ethoxy)‐2,2′:6′,2”‐terpyridine, pic=4‐picoline) are synthesized and characterized by NMR, UV/Vis, EPR, resonance Raman, and X‐ray absorption spectroscopy, and electrochemical analysis. Addition of the ethoxy group increases the catalytic activity in chemically driven and photocatalytic water oxidation. Thus, the effect of the electron‐donating group known for the [Ru(tpy)(bpy)(H₂O)]²⁺family is transferable to architectures with a tpy ligandtransto the Ru‐oxo unit. Under catalytic conditions, [Ru(EtO‐tpy)(pic)₂(H₂O)](NO₃)₂displays new spectroscopic signals tentatively assigned to a peroxo intermediate. Reaction pathways were analyzed by using DFT calculations. [Ru(EtO‐tpy)(pic)₂(H₂O)](NO₃)₂is found to be one of the most active catalysts functioning by a water nucleophilic attack mechanism.

 

A mononuclear nonheme manganese(IV)–oxo complex binding the Ce⁴⁺ion, [(dpaq)Mn^IV(O)]⁺–Ce⁴⁺(1‐Ce⁴⁺), was synthesized by reacting [(dpaq)Mn^III(OH)]⁺(2) with cerium ammonium nitrate (CAN).1‐Ce⁴⁺was characterized using various spectroscopic techniques, such as UV/Vis, EPR, CSI‐MS, resonance Raman, XANES, and EXAFS, showing an Mn−O bond distance of 1.69 Å with a resonance Raman band at 675 cm⁻¹. Electron‐transfer and oxygen atom transfer reactivities of1‐Ce⁴⁺were found to be greater than those of Mn^IV(O) intermediates binding redox‐inactive metal ions (1‐Mⁿ⁺). This study reports the first example of a redox‐active Ce⁴⁺ion‐bound Mn^IV‐oxo complex and its spectroscopic characterization and chemical properties.

 

Linear free−energy scaling relationships (LFESRs) and regression analysis may predict the catalytic performance of heterogeneous and recently, homogenous water oxidation catalysts (WOCs). This study analyses thirteen homogeneous Ru−based catalysts—some, the most active catalysts studied: the Ru(tpy−R)(QC) and Ru(tpy−R)(4−pic)2 complexes, where tpy is 2,2’;6’,2”terpyridine, QC is 8−quinolinecarboxylate and 4−pic is 4−picoline. Typical relationships studied among heterogenous catalysts cannot be applied to homogeneous catalysts. The selected group of structurally similar catalysts with impressive catalytic activity deserves closer computational and statistical analysis of multiple reaction step energetics correlating with measured catalytic activity. We report general methods of LFESR analysis yield insufficiently robust relationships between descriptor variables. However, volcano−plot−based analysis grounded in Sabatier’s principle reveals ideal relative energies of the RuIV = O and RuIV−OH intermediates and optimal changes in free energies of water nucleophilic attack on RuV = O. A narrow range of RuIV−OH to RuV = O redox potentials corresponding with the highest catalytic activities suggests facile access to the catalytically competent high−valent RuV = O state, often inaccessible from RuIV = O. Our work incorporates experimental oxygen evolution rates into approaches of LFESR and Sabatier−principle−based analysis, identifying a narrow yet fertile energetic landscape to bountiful oxygen evolution activity, leading to future rational design.