Surface-confined metal–organic frameworks (2D MOFs) provide a versatile platform for studying low-dimensional coordination chemistry and tunable molecular architectures at atomic and molecular levels. Here, we investigate the self-assembly of 4,4-bipyridine and Fe on Au(111) and reveal a coverage-dependent phase behavior governed by metal–ligand coordination and surface availability. In the absence of Fe, 4,4-bipyridine forms a weakly substrate-coupled molecular network stabilized by intermolecular interactions. Fe coordination induces a sequence of distinct two-dimensional architectures, ranging from dense three-fold-coordinated tripod networks to open Kagome lattices composed of hexagonally arranged metal centers bridged by molecular linkers. Using scanning probe microscopy, low-energy electron diffraction, and density-functional theory calculations, we identify three thermodynamically stable phases with different coordination numbers, symmetries, and molecular densities. Transformations between these phases are reversible and controlled by the Fe-to-ligand ratio. These findings demonstrate how subtle control over coordination chemistry and surface coverage enables programmable structural transitions in two-dimensional metal–organic frameworks.
- Open Access
- Article
Reversible Structure Formation in 4,4-Bipyridine—Fe 2D Metal-Organic Frameworks on Au(111)
- Afra Gezmis 1,
- Simon Steinbach 1,
- Julien Steffen 2,
- Alisson Ceccatto 1,
- Isabela Tonon 3,
- Natalie Waleska-Wellnhofer 1,
- Abner de Siervo 3,
- Hans-Peter Steinrück 1,*
Author Information
Received: 27 Mar 2026 | Revised: 07 May 2026 | Accepted: 07 May 2026 | Published: 25 May 2026
Abstract
Graphical Abstract
Keywords
4,4-bipyridine | Fe | 2D MOF | structure transformation | STM | DFT
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