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PreprintCC BY-NC-NDChemRxiv

Electron Counting by Design: Antiferromagnetic Ribbons Double as Charge Reservoirs to Stabilize Hypervalent Selenium and Tellurium Chains

6 affiliations
  1. 1Department of Chemistry and Biochemistry
  2. 2Baylor University
  3. 3Materials Science Center
  4. 4National Laboratory of the Rockies
  5. 5Department of Chemistry
  6. 6North Carolina State University

Abstract

Linear chains of hypervalently bonded chalcogen atoms are attractive building blocks for topological materials, but they almost always dimerize or modulate, and the few known examples are confined to actinide compounds. Here we show that Se, mixed Se/Te, and Te chains that are equidistant in their extended crystal structures are stabilized in a new Ibam structure type, Ba 2 Cu 2−x Fe 1+x Se 5−y Te y (y = 0 to 3.2), by combining a low reaction temperature (750 °C), aliovalent Cu/Fe mixing, and a geometric matching between the chains and ribbons of edge-sharing (Cu/Fe)Se 4 tetrahedra. Single-crystal X-ray diffraction at 100 and 300 K shows no superstructure for any composition, whereas the displacement parameters reveal static displacements of the Se atoms along the chain (0.17 Å rms) that decrease with Te substitution and vanish for the Te chain. The ribbons order antiferromagnetically at 132–151 K without a net moment, and the Curie constants show that the Fe(II)/Fe(III) ratio adjusts to place a charge of −0.8 to −1.3 on each chain Se atom, bracketing the value of −1 that is optimal for hypervalent bonding. Electronic structure calculations show steep chain bands and a chain bond index that is independent of the Cu/Fe ratio, and a magnetic symmetry analysis shows that the chain-band crossings persist as fourfold Dirac points in the antiferromagnetic state, about 0.4 eV below the Fermi level. Aliovalent cation mixing thus provides a chemical handle on the electron count of hypervalent chalcogen chains.

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BibTeX
@misc{jana2026electron,
  title = {{Electron Counting by Design: Antiferromagnetic Ribbons Double as Charge Reservoirs to Stabilize Hypervalent Selenium and Tellurium Chains}},
  author = {Subhendu Jana and E.A. Chirantha Edirisinghe and Ian Leahy and Milena Jovanovic and Rebecca W. Smaha and Paul A. Maggard},
  howpublished = {ChemRxiv},
  year = {2026},
  month = oct,
  doi = {10.26434/chemrxiv.15010438/v1},
  url = {https://chemrxiv.org/doi/full/10.26434/chemrxiv.15010438/v1},
  note = {CC BY-NC-ND},
}
RIS
TY  - UNPB
TI  - Electron Counting by Design: Antiferromagnetic Ribbons Double as Charge Reservoirs to Stabilize Hypervalent Selenium and Tellurium Chains
AU  - Subhendu Jana
AU  - E.A. Chirantha Edirisinghe
AU  - Ian Leahy
AU  - Milena Jovanovic
AU  - Rebecca W. Smaha
AU  - Paul A. Maggard
PY  - 2026
DA  - 2026/10/14
PB  - ChemRxiv
DO  - 10.26434/chemrxiv.15010438/v1
UR  - https://chemrxiv.org/doi/full/10.26434/chemrxiv.15010438/v1
AB  - Linear chains of hypervalently bonded chalcogen atoms are attractive building blocks for topological materials, but they almost always dimerize or modulate, and the few known examples are confined to actinide compounds. Here we show that Se, mixed Se/Te, and Te chains that are equidistant in their extended crystal structures are stabilized in a new Ibam structure type, Ba 2 Cu 2−x Fe 1+x Se 5−y Te y (y = 0 to 3.2), by combining a low reaction temperature (750 °C), aliovalent Cu/Fe mixing, and a geometric matching between the chains and ribbons of edge-sharing (Cu/Fe)Se 4 tetrahedra. Single-crystal X-ray diffraction at 100 and 300 K shows no superstructure for any composition, whereas the displacement parameters reveal static displacements of the Se atoms along the chain (0.17 Å rms) that decrease with Te substitution and vanish for the Te chain. The ribbons order antiferromagnetically at 132–151 K without a net moment, and the Curie constants show that the Fe(II)/Fe(III) ratio adjusts to place a charge of −0.8 to −1.3 on each chain Se atom, bracketing the value of −1 that is optimal for hypervalent bonding. Electronic structure calculations show steep chain bands and a chain bond index that is independent of the Cu/Fe ratio, and a magnetic symmetry analysis shows that the chain-band crossings persist as fourfold Dirac points in the antiferromagnetic state, about 0.4 eV below the Fermi level. Aliovalent cation mixing thus provides a chemical handle on the electron count of hypervalent chalcogen chains.
ER  -