Interplay between Isomerization and Spin Crossover in 1D Fe-Indigo Coordination Polymers on Ag substrates

Abstract

Spin-crossover (SCO) compounds offer a route to switchable molecular functionality in reduced dimensions. However, one-dimensional (1D) SCO chains, which offer the possibility to study ligand fields other than the paradigmatic octahedral field, remain comparatively little studied. Here, we use first-principles density functional theory (DFT+U) to investigate Fe-indigo coordination-polymer chains synthesized experimentally on Ag(111) and Ag(100) substrates. These display a rich interplay between changes in ligand field (isomerization) and spin crossover. On-surface isomerization on Ag(111) interconverts (N,O)-chelated \textit{trans} configuration and (N,N)-/(O,O)-chelated \textit{cis} configurations at the Fe centers. The lowest-energy \textit{trans} and \textit{cis} solutions on Ag(111) have different spin configurations over the interval 0.66<U<3.00~eV. At the reference value U=1~eV, the preferred \textit{trans} solution is the mixed LS--LS--HS configuration, whereas the preferred \textit{cis} solution is LS--LS--LS. The experimentally observed preference for \textit{cis} chains on Ag(111) and \textit{trans} chains on Ag(100) is reproduced for the range 0.88<U<3.75~eV. To interpret these results, toy models and spin-resolved Fe 3d projected densities of states are used, while freestanding-chain calculations reveal a strain-sensitive LS--HS competition. These results provide a microscopic explanation for isomerization-controlled spin-state switching in a 1D coordination polymer.

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BibTeX RIS

BibTeX

@misc{chakraborty2026interplay,
  title = {{Interplay between Isomerization and Spin Crossover in 1D Fe-Indigo Coordination Polymers on Ag substrates}},
  author = {Ritam Chakraborty and Hongxiang Xu and Biao Yang and Harshdeep Singh Chhabra and Joachim Reichert and Johannes V. Barth and Anthoula C. Papageorgiou and Shobhana Narasimhan},
  howpublished = {arXiv},
  year = {2026},
  month = sep,
  doi = {10.48550/arxiv.2609.03041},
  eprint = {2609.03041},
  archivePrefix = {arXiv},
  url = {https://arxiv.org/abs/2609.03041},
}

RIS

TY  - UNPB
TI  - Interplay between Isomerization and Spin Crossover in 1D Fe-Indigo Coordination Polymers on Ag substrates
AU  - Ritam Chakraborty
AU  - Hongxiang Xu
AU  - Biao Yang
AU  - Harshdeep Singh Chhabra
AU  - Joachim Reichert
AU  - Johannes V. Barth
AU  - Anthoula C. Papageorgiou
AU  - Shobhana Narasimhan
PY  - 2026
DA  - 2026/09/02
PB  - arXiv
DO  - 10.48550/arxiv.2609.03041
UR  - https://arxiv.org/abs/2609.03041
AB  - Spin-crossover (SCO) compounds offer a route to switchable molecular functionality in reduced dimensions. However, one-dimensional (1D) SCO chains, which offer the possibility to study ligand fields other than the paradigmatic octahedral field, remain comparatively little studied. Here, we use first-principles density functional theory (DFT+U) to investigate Fe-indigo coordination-polymer chains synthesized experimentally on Ag(111) and Ag(100) substrates. These display a rich interplay between changes in ligand field (isomerization) and spin crossover. On-surface isomerization on Ag(111) interconverts (N,O)-chelated \textit{trans} configuration and (N,N)-/(O,O)-chelated \textit{cis} configurations at the Fe centers. The lowest-energy \textit{trans} and \textit{cis} solutions on Ag(111) have different spin configurations over the interval 0.66<U<3.00~eV. At the reference value U=1~eV, the preferred \textit{trans} solution is the mixed LS--LS--HS configuration, whereas the preferred \textit{cis} solution is LS--LS--LS. The experimentally observed preference for \textit{cis} chains on Ag(111) and \textit{trans} chains on Ag(100) is reproduced for the range 0.88<U<3.75~eV. To interpret these results, toy models and spin-resolved Fe 3d projected densities of states are used, while freestanding-chain calculations reveal a strain-sensitive LS--HS competition. These results provide a microscopic explanation for isomerization-controlled spin-state switching in a 1D coordination polymer.
ER  -

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