Abstract
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 tpyʼs 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.
Highlights
Coordination chemistry relies on harnessing active metal sites within organic matrices
Polynuclear complexes are of special interest, since magnetic[6] and electronic interactions between metal atoms in close proximity can give rise to useful properties, with multiple active metal centres potentially enhancing the catalytic processes in comparison to mononuclear systems[7,8,9]
Using a combination of low-temperature scanning tunnelling microscopy (STM) and spectroscopy (STS), non-contact atomic force microscopy, local contact potential difference (LCPD) measurements, density functional theory (DFT), and ncAFM image simulations, we directly demonstrate that the metal–ligand coordination motif consists of flat, coplanar tpys linked via a quasi-linear tri-iron cluster
Summary
Coordination chemistry relies on harnessing active metal sites within organic matrices. Combining low-temperature scanning probe microscopy and density functional theory, we demonstrate that the coordination motif consists of coplanar tpys 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. On-surface supramolecular chemistry13—a bottom-up approach driven by noncovalent intermolecular interactions and metal–ligand bonding on a surface—allows for the design of selfassembled, atomically precise metal-organic nanomaterials, with morphologies, properties and functionalities that can differ dramatically from those obtained via conventional synthetic chemistry Such approaches can provide an alternative for synthesising functional complexes with polynuclear metal sites. The surface, via its structural symmetry and chemical reactivity, can further provide a means of control over atomicscale morphology and electronic/chemical properties These methods have recently allowed for the synthesis of lowdimensional metal-organic systems with di-nuclear coordination metal centres (e.g., di-iron complexes with promising catalytic[15] and magnetic[16] properties). Our results position onsurface supramolecular chemistry as a pathway to synthesise functional multinuclear coordination nodes from bottom-up, with configurations and properties that would not be feasible via conventional synthetic chemistry approaches without a surface
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