Crystal structure and Hirshfeld surface analysis of chiral <i>catena</i> -poly[ <scp>L</scp> -histidinediium [[diiodidocuprate(I)]-μ-iodido] monohydrate]

The title compound, {(C₆H₁₁N₃O₂)[CuI₃]·H₂O} _<i>n</i> or (l-HisH₂)CuI₃·H₂O (<b>1</b>), is a chiral organic-inorganic compound that crystallizes in the monoclinic <i>P</i>2₁ space group. The asymmetric unit of <b>1</b> consists of one diprotonated l-histidinium cation {4-[(2<i>S</i>)-2-aza-niumyl-2-carb-oxy-eth-yl]-1<i>H</i>-imidazol-3-ium}, one Cu⁺ cation, three iodide anions, and one co-crystallized water mol-ecule. The Cu⁺ cations is four-coordinated by iodide anions forming a [CuI₄] unit. Structural analysis of the [CuI₄] unit using the Baur, τ₄, and τ₄' indices reveals its slight deviation from ideal tetra-hedral geometry. Two iodide anions from each [CuI₄] unit bridge adjacent Cu⁺ centers, forming chiral left-handed helical [CuI₃] _<i>n</i> ^2<i>n</i>- polymeric chains. The biprotonated l-histidinium cations balance their negative charge and form N-H⋯I, O-H⋯I, and weak C-H⋯I hydrogen bonds with the [CuI₃] _<i>n</i> ^2<i>n</i>- chains. According to the Hirshfeld surface analysis, the main contributions to the crystal packing arise from H⋯I and H⋯O contacts, while C⋯I and N⋯I inter-actions indicate the presence of I⋯π contacts. The compound reported here represents the first example of a chiral <i>A</i> ₂Cu<i>X</i> ₃-type metal halide, which shows potential for second-harmonic generation, polarized blue-light emission, and other non-linear optical applications.