Stabilization of Strongly Reduced Fe(I) Single Atom Species Coordinated in a 2D Self-Assembled Metal–Organic Network

Stabilization of low-valent iron centers in atomically defined coordination environments remains a major challenge in the design of reactive metal–organic materials. Here, we report the rational stabilization of Fe(I)-N4 single sites in a graphene-supported, two-dimensional metal–organic network assembled from FeTPyP tectons and Co coordination nodes. We find that nitrogen tetra-coordination in this specific bidimensional metal–organic network allows the stabilization of iron in the +1 oxidation state. Using state-of-the-art experimental techniques, complemented by theoretical calculations, we reveal that Co coordination induces charge redistribution across the network and reduces the porphyrinic Fe center from Fe(II) toward Fe(I). The latter species is highly reactive: even in ultra-high vacuum, residual oxygen-containing species oxidize the Fe center. O2 activation occurs instead at near-ambient pressure, yielding the common Fe(II) species, as supported by dedicated theoretical models. These results demonstrate a coordination-network strategy to stabilize Fe(I) centers, which are believed to play a relevant role in a number of key reactions, including the biological synthesis of ammonia from N2.