Electron Counting by Design: Antiferromagnetic Ribbons Double as Charge Reservoirs to Stabilize Hypervalent Selenium and Tellurium Chains
Year: 2026
Type: preprint
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.
Source: ChemRxiv
Language: English
Subfield: Atomic and Molecular Physics, and Optics
Field: Physics and Astronomy
Domain: Physical Sciences
Open Access status: green
OpenAlex ID: W7221765097