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Title: Tetra- and Heptametallic Ru(II),Rh(III) Supramolecular Hydrogen Production Photocatalysts

Supramolecular mixed metal complexes combining the trimetallic chromophore [{(bpy) 2Ru(dpp)} 2Ru(dpp)] 6+ (Ru 3) with [Rh(bpy)Cl 2] + or [RhCl 2] + catalytic fragments to form [{(bpy) 2Ru(dpp)} 2Ru(dpp)RhCl 2(bpy)](PF 6) 7 (Ru 3Rh) or [{(bpy) 2Ru(dpp)} 2Ru(dpp)] 2RhCl 2(PF 6) 13 (Ru 3RhRu 3) (bpy = 2,2'-bipyridine and dpp = 2,3-bis(2-pyridyl)pyrazine) catalyze the photochemical reduction of protons to H 2. This first example of a heptametallic Ru,Rh photocatalyst produces over 300 turnovers of H 2 upon photolysis of a solution of acetonitrile, water, triflic acid, and N,N-dimethylaniline as an electron donor. Conversely, the tetrametallic Ru 3Rh produces only 40 turnovers of H 2 due to differences in the excited state properties and nature of the catalysts upon reduction as ascertained from electrochemical data, transient absorption spectroscopy, and flash-quench experiments. And while the lowest unoccupied molecular orbital of Ru 3Rh is localized on a bridging ligand, it is Rh-centered in Ru 3RhRu 3 facilitating electron collection at Rh in the excited state and reductively quenched state. The Ru → Rh charge separated state of Ru 3RhRu 3 is endergonic with respect to the emissive Ru → dpp 3MLCT excited and cannot be formed by static electron transfer quenching of themore » 3MLCT state. Instead, a mechanism of subnanosecond charge separation from high lying states is proposed. Multiple reductions of Ru 3 and Ru 3Rh using sodium amalgam were carried out to compare UV–vis absorption spectra of reduced species and to evaluate the stability of highly reduced complexes. Furthermore, the Ru 3 and Ru 3Rh can be reduced by 10 and 13 electrons, respectively, to final states with all bridging ligands doubly reduced and all bpy ligands singly reduced.« less
ORCiD logo [1] ; ORCiD logo [1] ;  [2]
  1. Brookhaven National Lab. (BNL), Upton, NY (United States). Chemistry Division
  2. Brookhaven National Lab. (BNL), Upton, NY (United States). Chemistry Division; Virginia Polytechnic Inst. Blacksburg, VA (United States). Dept. of Chemistry
Publication Date:
Report Number(s):
BNL-114001-2017-JA; BNL-114146-2017-JA
Journal ID: ISSN 0002-7863; R&D Project: CO026; KC0304030; TRN: US1702325
Grant/Contract Number:
SC0012704; FG02-05ER15751
Accepted Manuscript
Journal Name:
Journal of the American Chemical Society
Additional Journal Information:
Journal Volume: 139; Journal Issue: 23; Journal ID: ISSN 0002-7863
American Chemical Society (ACS)
Research Org:
Brookhaven National Laboratory (BNL), Upton, NY (United States)
Sponsoring Org:
USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22)
Country of Publication:
United States
OSTI Identifier:
Alternate Identifier(s):
OSTI ID: 1376171