Unusual and unprecedented multipathway electrochemical mechanisms for a new class of supramolecular Ru/Rh bimetallic photocatalysts have been uncovered. The near isoenergetic Rh(dσ*) and bridging ligand(π*) molecular orbitals and a rate of halide loss that occurs on the cyclic voltammetry timescale provide a series of closely related complexes which display four different electrochemical mechanisms. A single complex displays two concurrent electrochemical pathways in marked contrast to all previously studied cis-[Rh(NN)(2)X(2)] motifs.

What is the most significant result of this study?The work presented in this paper uncovers new redox pathways for metal complexes. Electron-transfer or redox reactions are critical to many areas of chemical research, as well as to the functioning of biological systems; thus, uncovering new redox pathways has a wide ranging impact. Unprecedented redox properties of Rh complexes are discovered in this study. The Ru II /Rh III complexes undergo a number of different, concurrent electrochemical reduction mechanisms. The competing reduction pathways give rise to peak currents that do not correspond to integer values for the number of electrons transferred, presenting a very unusual result for single molecular systems not reacting with a substrate. In addition, Rh II complexes are prepared with unusual stability in marked contrast to the wide array of Rh II complexes prone to rapid disproportionation. What aspects of this project do you find most exciting?Uncovering unexpected reactivity of Ru II /Rh III complexes after several decades of studying related metal complexes highlights the challenges that still exist in molecular design. Development of molecular machines for the conversion of light or electrical energy into chemical energy is a challenging and exciting field. The systems we study apply these molecular devices to solar energy conversion applicable in water splitting and artificial photosynthesis. The assembly of supramolecules built from individual subunits that each performs a simple task leading to the overall molecular device accomplishing a complex function is a promising field of study with limitless applications and much new chemistry to explore. To think about molecules as atomic scale machines is an important view of chemistry. The new reactivity of reduced Rh complexes uncovered in this study will provide insight into the mechanism of water reduction by metal complexes. Uncovering the factors that impact partitioning of the analyte along the competing reductive pathways will allow for control of catalyst speciation in the catalytic cycle and development of more active catalysts for solar energy harvesting and conversion. What other topics are you working on at the moment?The Brewer group at Virginia Tech is exploring other areas of research including other areas of solar energy conversion, NSF sponsored research in the development of structurally diverse supramolecules with unusual reactivity with biomolecules, the development of new drugs to treat cancer, polymer-supported supramolecules for light to energy conversion, and light cycled materials that are self-sterilizing. We have had a number of outstanding collaborations including with Prof. Invited for the cover of this issue are researchers from the Department of Chemistry at Virginia Tech featuring work on electrochemical properties of photochemical molecular devices for solar hydrogen production. The image highlights the complexity of the redox chemistry of the studied supramolecules, detailing speciation following reduction. Mr. Skye King a...

Multiple electrochemical pathways…︁ for a new class of supramolecular Ru/Rh bimetallic photocatalysts have been uncovered. The unusual redox chemistry of these species highlights the complexity of possible pathways operative in the photochemical reduction of H2O to H2 by these Ru/Rh systems. Halide loss competes with Rh reduction and in the presence of H2O additional species are possible for each RhII or RhI species observed herein, due to protonation of the Rh center or possible oxidative addition of H2O to the RhI center. See the Communication by K. J. Brewer et al. on for more details.