Systematic Helical Complexity Imparted by Chalcogen Atoms in Gallium Chalco-Iodide Tetrahelices

Low-dimensional inorganic crystals composed of main group elements manifest unique bonding motifs and exhibit strong axis-dependent properties. In particular, crystals possessing one-dimensional (1D) helical motifs have long been sought for their unique quantum states arising from their springlike, chiral order. However, the difficulty in experimentally realizing freestanding, all-inorganic helical materials has limited our physical understanding of their structure- and composition-dependent properties. Here, we present a new helical 1D van der Waals (vdW) crystal, GaTeI, to complete the 1D gallium chalco-iodide series. Using the completed Ga(S, Se, Te)I series, we demonstrate that the systematic stretching of the helical structure is driven by the rigid interchain interactions and the distortion of the tetrahedral building units along the chain, establishing the profound influence of the chalcogen site on the helical structure of exfoliable 1D vdW III-VI-VII crystals. Our results highlight how the nature of the chalcogen atom dictates the projected geometric cross section of the helical chains to form unusual and non-natural helical motifs, as well as the broad bandgap spectral window accessible in the series. These findings represent an experimentally accessible and modular class of helical structures that underscores how the fine-tuning of distinct constituent atoms could lead to new inorganic helical motifs.