Introduction. The spin-ladder compounds of the ${\mathrm{BaFe}}_2{X}_3$ ($X$ = chalcogen) family may be viewed as dimensional reductions—along stripelike motifs—of the two-dimensional iron-based pnictide planes extensively studied since 2006. Remarkably, despite their reduced dimensionality, these materials retain the capacity for unconventional ground states, exemplified by the emergence of superconductivity in ${\mathrm{BaFe}}_2{\mathrm{Se}}_3$ under applied pressure beyond 10 GPa, following a structural phase transition at 4 GPa. Here, we report a comprehensive investigation combining high-resolution single-crystal x-ray diffraction, infrared spectroscopy, and ab initio calculations, which together elucidate the true crystallographic nature of this pressure-induced superconducting phase. While x-ray diffraction alone reveals a symmetry lowering from the widely accepted orthorhombic $Cmcm$ group to a monoclinic structure, it lacks sufficient sensitivity to resolve the precise space group. By integrating vibrational spectroscopy with density functional theory, we provide unambiguous evidence that the high-pressure phase is noncentrosymmetric, adopting the polar space group $P{2}_1$. These findings not only revise the structural assignment of ${\mathrm{BaFe}}_2{\mathrm{Se}}_3$ in its superconducting state, but also establish its noncentrosymmetric character—an essential ingredient for potential unconventional pairing mechanisms—thereby opening different perspectives on the interplay between lattice symmetry, dimensionality, and superconductivity in iron-based materials.

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• 1-dimensional spin chains
• Iron-based superconductors
• Crystallography
• Density functional theory
• Infrared spectroscopy