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PreprintCC BY-NC-NDChemRxiv

Surface-Confined Steric Frustration Directs One-Dimensional BisNHC Assembly

  • Keita Tanaka1,2,3,4
  • Jong-Guk Ahn5,6
  • Rafael B Jaculbia5,6
  • Kensuke Kimura1,2
  • Howon Kim5,6
  • Kuniyuki Miwa1,2,5,6
  • Hyunseob Lim3,4,5,6
  • Hiroshi Imada1,2,3,4,5,6
  • Zhaomin Hou7,2
  • Kenta Amemiya8,9
  • Yousoo Kim1,2,3,4,5,6,10
10 affiliations
  1. 1Surface and Interface Laboratory
  2. 2RIKEN
  3. 3Department of Chemistry
  4. 4Gwangju Institute of Science and Technology (GIST)
  5. 5Center for Quantum Conversion Research
  6. 6Institute for Basic Science (IBS)
  7. 7Organometallic Chemistry Laboratory
  8. 8Institute of Materials Structure Science (IMSS)
  9. 9High Energy Accelerator Research Organization (KEK)
  10. 10The University of Tokyo
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Abstract

Sterically demanding ligands are widely used to control coordination geometry and stabilize otherwise inaccessible metal complexes, yet how steric repulsion influences metal–ligand coordination and periodic molecular assembly under surface confinement remains underexplored. Here, we show that a tert -butyl-substituted bis(N-heterocyclic carbene) (bisNHC) assembles into a one-dimensional metal-organic lattice. Steric constraints give rise to an asymmetric NHC–adatom–NHC arrangement, generating dipolar bisNHC–adatom units whose dipole-dipole interactions contribute to their organization into periodic chains. The lattice decomposes upon mild annealing, showing that direct deposition of the free bisNHC is essential for preserving this coordination motif. Despite chemisorption through metal adatoms, the lattice exhibits reduced electronic coupling to the substrate. It also defines sterically protected cavities for individual metal atoms. Lanthanide atoms accommodated within these cavities show higher-energy spin-flip excitations and enhanced positive-bias stability compared with graphene-supported atoms. These findings demonstrate that steric congestion under surface confinement can prevent conventional covalent chain formation without precluding periodic metal–organic assembly. This approach offers a strategy for constructing ordered molecular architectures with tailored coordination sites for individual metal atoms.

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Cite

BibTeXRIS
BibTeX
@misc{tanaka2026surfaceconfined,
  title = {{Surface-Confined Steric Frustration Directs One-Dimensional BisNHC Assembly}},
  author = {Keita Tanaka and Jong-Guk Ahn and Rafael B Jaculbia and Kensuke Kimura and Howon Kim and Kuniyuki Miwa and Hyunseob Lim and Hiroshi Imada and Zhaomin Hou and Kenta Amemiya and Yousoo Kim},
  howpublished = {ChemRxiv},
  year = {2026},
  month = oct,
  doi = {10.26434/chemrxiv.15000158/v2},
  url = {https://chemrxiv.org/doi/full/10.26434/chemrxiv.15000158/v2},
  note = {CC BY-NC-ND},
}
RIS
TY  - UNPB
TI  - Surface-Confined Steric Frustration Directs One-Dimensional BisNHC Assembly
AU  - Keita Tanaka
AU  - Jong-Guk Ahn
AU  - Rafael B Jaculbia
AU  - Kensuke Kimura
AU  - Howon Kim
AU  - Kuniyuki Miwa
AU  - Hyunseob Lim
AU  - Hiroshi Imada
AU  - Zhaomin Hou
AU  - Kenta Amemiya
AU  - Yousoo Kim
PY  - 2026
DA  - 2026/10/16
PB  - ChemRxiv
DO  - 10.26434/chemrxiv.15000158/v2
UR  - https://chemrxiv.org/doi/full/10.26434/chemrxiv.15000158/v2
AB  - Sterically demanding ligands are widely used to control coordination geometry and stabilize otherwise inaccessible metal complexes, yet how steric repulsion influences metal–ligand coordination and periodic molecular assembly under surface confinement remains underexplored. Here, we show that a tert -butyl-substituted bis(N-heterocyclic carbene) (bisNHC) assembles into a one-dimensional metal-organic lattice. Steric constraints give rise to an asymmetric NHC–adatom–NHC arrangement, generating dipolar bisNHC–adatom units whose dipole-dipole interactions contribute to their organization into periodic chains. The lattice decomposes upon mild annealing, showing that direct deposition of the free bisNHC is essential for preserving this coordination motif. Despite chemisorption through metal adatoms, the lattice exhibits reduced electronic coupling to the substrate. It also defines sterically protected cavities for individual metal atoms. Lanthanide atoms accommodated within these cavities show higher-energy spin-flip excitations and enhanced positive-bias stability compared with graphene-supported atoms. These findings demonstrate that steric congestion under surface confinement can prevent conventional covalent chain formation without precluding periodic metal–organic assembly. This approach offers a strategy for constructing ordered molecular architectures with tailored coordination sites for individual metal atoms.
ER  -