<p>Metal–halide complexes serve as key emissive centres in halide perovskites; however, precise control over their spatial organization through bottom-up assembly is challenging. Here we show that a crown-ether-assisted supramolecular assembly strategy can alternatingly connect metal–halide complexes and (crown ether@A)²⁺ (where ‘A’ is an alkaline earth metal cation) complexes into a one-dimensional molecular wire, which can then be packed into a hexagonal crystal structure. This process resulted in the creation of an (18C6@Ba)MnBr₄ single crystal with green emission, achieving over 80% photoluminescence quantum yield and a narrow full width at half maximum. In addition, the non-centrosymmetric crystal structure gave rise to strong nonlinear optical responses, including second-harmonic generation. This versatile supramolecular assembly approach could be generalized to create various [M(I)X₂]⁻, [M(I)X₃]²⁻, [M(II)X₄]²⁻ and [M(III)X₅]²⁻ molecular wires, broadening the potential for diverse emission colours and distinct optical properties. This strategy provides a general design principle for constructing supramolecular metal–halide building blocks with diverse optical functionalities.</p><p></p>