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 ]·(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 μmol g -1 h -1 and functions well also with unpurified air as the feeding gas. Experimental and theoretical studies show that the active [Zn 2+ -(N≡N) - -Zn 2+ ] sites can promote the formation of NH 3 and the detachment of the NH 3 formed creates unsaturated [Zn 2+ ···Zn + ] intermediates, which in turn can be refilled by external N 2 sequestration and fast intermolecular electron migration. The [Zn 2+ ···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.