Local charge accumulation at a trinuclear metal-organic nanostructure on a surface

Coordination chemistry relies on harnessing active metal sites within organic matrices. Polynuclear complexes — consisting of organic ligands bound to several metal atoms — are relevant due to their electronic and magnetic properties, and to their potential for functional reactivity pathways. However, their synthesis remains challenging, with few geometries and configurations that have been achieved. Here, we synthesize — via supramolecular chemistry on a noble metal surface — one-dimensional metal-organic nanostructures composed of terpyridine-based molecules coordinated with well-defined polynuclear iron clusters. Combining low-temperature scanning probe microscopy techniques, density functional theory and x-ray absorption spectroscopy, we demonstrate that the coordination motif consists of coplanar terpyridine groups linked via a quasi-linear tri-iron node with mixed positive valence and a metal–metal bond configuration. This unusual linkage is stabilized by local accumulation of electrons between cations, ligands and metal surface. This morphology, enabled by the bottom-up on-surface synthesis, yields an electronic structure that hints at a chemically active polynuclear metal center, paving the way for nanomaterials with novel catalytic and magnetic functionalities.