Correction to: Nature https://doi.org/10.1038/s41586-018-0154-7, published online 30 May 2018.
In Fig. 1 of this Letter, owing to an error during the production process, there should have been two nitrogen (N) atoms at the 1,3-positions of all the blue chemical structures (next to the oxygen atoms), rather than one at the 2-position. The figure has been corrected online, and the original incorrect figure is shown as Supplementary Information to this Amendment, for transparency.
Supplementary information is available for this Amendment at https://doi.org/10.1038/s41586-018-0297-6