Photocatalytic nitrogen fixation under an ambient atmosphere using a porous coordination polymer with bridging dinitrogen anions

The design of highly electron-active and stable heterogeneous catalysts for the ambient nitrogen reduction reaction is challenging due to the inertness of the N-2 molecule. Here, we report the synthesis of a zinc-based coordination polymer that features bridging dinitrogen anionic ligands, {[Zn(L)(N-2)(0.5)(TCNQ-TCNQ)(0.5)]center dot(TCNQ)(0.5)}(n) (L is tetra(isoquinolin-6-yl)tetrathiafulvalene and TCNQ is tetracyanoquinodimethane), and show that it is an efficient photocatalyst for nitrogen fixation under an ambient atmosphere. It exhibits an ammonia conversion rate of 140 mu mol g(-1) h(-1) and functions well also with unpurified air as the feeding gas. Experimental and theoretical studies show that the active [Zn2+-(N & EQUIV;N)(-)-Zn2+] sites can promote the formation of NH3 and the detachment of the NH3 formed creates unsaturated [Zn2+center dot center dot center dot Zn+] intermediates, which in turn can be refilled by external N-2 sequestration and fast intermolecular electron migration. The [Zn2+center dot center dot center dot Zn+] intermediates stabilized by the sandwiched cage-like donor-acceptor-donor framework can sustain continuous catalytic cycles. This work presents an example of a molecular active site embedded within a coordination polymer for nitrogen fixation under mild conditions.

Automated summary

We report the synthesis of a zinc-based coordination polymer that contains bridging dinitrogen anionic ligands, which shows high efficiency as a photocatalyst for nitrogen fixation under ambient conditions. Experimental and theoretical studies reveal that the active sites in the polymer promote the formation of NH3 and sustain continuous catalytic cycles. This work presents an example of a molecular active site embedded within a coordination polymer for mild nitrogen fixation.