Coordination chemistry relies on harnessing active metal sites within organic matrices. Polynuclear complexes-where organic ligands bind to several metal atoms-are relevant due to their electronic/magnetic properties and potential for functional reactivity pathways. However, their synthesis remains challenging; few geometries and configurations have been achieved. Here, we synthesise-via supramolecular chemistry on a noble metal surface-one-dimensional metal-organic nanostructures composed of terpyridine (tpy)-based molecules coordinated with well-defined polynuclear iron clusters. Combining low-temperature scanning probe microscopy and density functional theory, we demonstrate that the coordination motif consists of coplanar tpy's linked via a quasi-linear tri-iron node in a mixed (positive-)valence metal-metal bond configuration. This unusual linkage is stabilised by local accumulation of electrons between cations, ligand and surface. The latter, enabled by bottom-up on-surface synthesis, yields an electronic structure that hints at a chemically active polynuclear metal centre, paving the way for nanomaterials with novel catalytic/magnetic functionalities.

ARC Centre of Excellence in Future Low Energy Electronics Technologies Monash University 19 Rainforest Walk Clayton 3800 Australia

Australian Synchrotron 800 Blackburn Road Clayton Victoria 3168 Australia

Department of Chemistry University of British Columbia 2036 Main Mall Vancouver British Columbia Canada V6T 1Z1

Department of Physics and Astronomy University of British Columbia 6224 Agricultural Road Vancouver British Columbia Canada V6T 1Z1

Institute of Physics of the CAS Cukrovarnicka 10 Prague 16200 Czech Republic

Monash Centre for Atomically Thin Materials Monash University 20 Research Way Clayton 3800 Australia

RCPTM Palacky University Šlechtitelů 27 783 71 Olomouc Czech Republic

School of Physics and Astronomy Monash University 19 Rainforest Walk Clayton 3800 Australia

Stewart Blusson Quantum Matter Institute University of British Columbia 2355 East Mall Vancouver British Columbia Canada V6T 1Z4

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