Fig. 1. Coordination-induced bond weakening (CIBW) motifs. (a) Traditional motif involving a reducing and Lewis acidic metal ion, (b) the multisite proton-coupled electron transfer motif evident in the oxygen-evolving complex of photosystem-II, (c) lack of weakening with typical AlIII ions, (d) the multisite proton-coupled electron transfer scheme reported here relying on redox non-innocence of the ligand. BD(F)EO-H values for Al-OH2 complexes were estimated using density-functional theory calculations.
The push for alternative renewable energy sources continues unabated. Several of these candidate materials involve forming energy reservoirs by using the chemical bonds in abundant molecules like water and ammonia. In order to achieve this objective, researchers must verify substances that can be used to weaken the robust (>100 kcal/mol) O-H and N-H bonds in order to achieve the proton-coupled electron transfer the underpins energy conservation.
The established method for this process is coordination-induced bond weakening via redox-active metals, i.e., metals that exhibit the classical behavior of a transition metal complex in a redox process involving oxidation or reduction of the metal, leaving the ligand unaffected. The optimal metal for this application due to its unrivaled ubiquity is aluminum. But coordination-induced bond weakening is considered problematic with Al due to its redox inertness.
Researchers from the University of Illinois Chicago and Brigham Young University gained an unprecedented understanding of coordination-induced weakening of the O-H and N-H bond through the use of aluminum with a redox non-innocent ligand to achieve significant levels of coordination-induced bond weakening. They characterized the result via x-ray crystallography studies of an oxygen-evolving complex of photosystem-II at the Advanced Crystallography facility of the NSF’s ChemMatCARS on Sector 15 of the Argonne National Laboratory Advanced Photon Source.
These results promise to inform the molecular design features of proton-coupled electron transfers, yielding a path to coordination-induced bond weakening and spurring the use of abundant but redox-inert metals for renewable energy materials through metal/ligand cooperativity.
See: Soumen Sinhababu1,3, Roushan Prakash Singh1,3, Maxim R. Radzhabov1, Jugal Kumawat2, Daniel H. Ess2, and Neal P. Mankad1*, “Coordination-induced O-H/N-H bond weakening by a redox non-innocent, aluminum-containing radical,” Nat. Commun. 15, 1315 (2024).
Author affiliations: 1University of Illinois Chicago, 2Brigham Young University
Correspondence: *npm@uic.edu
This material is based upon work supported by the U.S. Department of Energy (DOE), Office of Science, Office of Basic Energy Sciences under Award Number DE-SC0021055 to N.P.M and by the U.S. National Science Foundation with award CHE-2153215 to D.H.E. NSF’s ChemMatCARS is supported by the Divisions of Chemistry (CHE) and Materials Research (DMR), National Science Foundation, under grant number NSF/CHE-1834750. Use of the Advanced Photon Source, an Office of Science User Facility operated for the DOE Office of Science by Argonne National Laboratory, was supported by the DOE under Contract No. DE-AC02-06CH11357. Computational resources were provided by the Advanced Cyber Infrastructure for Education and Research (ACER) group at UIC and the Office of Research Computing at BYU.
For information about advanced crystallography at NSF’s ChemMatCARS contact:
Yu-Sheng Chen
(630) 252-0471
yushengchen@uchicago.edu