This research was supported by the NSF Center for Chemical Innovation dedicated to Chemistry at the Space-Time Limit (CHE-1414466). Theoretical calculations were performed on the UCI Greenplanet cluster system (CHE-0840513). We thank P. El-Khoury for advice on DFT calculations. We have benefited from discussions with L. Jensen, X. Chen and P. Liu.

Reviewer information

Nature thanks Eric Le Ru and the other anonymous reviewer(s) for their contribution to the peer review of this work.