![]() Such crystals have rarely been utilized as three dimensional objects 27. ![]() This fact has confined much of the ongoing research to applications that exploit the porosity of the molecular frameworks 25, 26. Although several works have shown that control over crystal size and shape can affect porosity 21, catalytic activity 22, and cellular uptake 23, to date, the majority of the efforts have been aimed at designing the crystal structures of MOFs 24. The synthesis of morphologically tailored metal-organic frameworks (MOFs) is still in its early stages 20. Interfacial synthesis 11, microemulsion 12, and template-assisted growth 13 are transversally used in colloidal chemistry to enhance the performance of both organic 14, 15 and inorganic materials 16, 17 such as drugs and functional nanoparticles 18, 19. Various parameters such as solvents and additives can control the evolution of crystal facets by selective surface interactions 8, 9, 10. However, unlike bio-crystallization, where crystal shaping is under cellular control, mastering of crystallization chemistry and kinetics is required for synthetic materials. The latter property is important for their efficacy for drug delivery and other therapeutic applications 6, 7. Among synthetic crystals, the shape of nanoparticles has been shown to affect optical properties 4, 5 and impact mechanical properties as well as cell membrane permeability 6. Sea urchins sculpt their spines by producing single crystals of calcite having a complex fenestrated morphology with smooth and curved surfaces 3. Single crystalline scaffolds having hierarchical architectures and curved features are widely used for structural purposes by many plants and animals (e.g., mollusks, corals, echinoderms, and algae) 1, 2. The shape-based relationship is manifested in both biological and synthetic systems. The properties and functionalities of crystals are strongly affected by their shape and structure. Our approach offers opportunities to generate a new class of crystals. This process reduces the concentration of the active metal salt. Sonication of the solvents generating radical species is essential for forming the multidomain single-crystals. The chiral crystals are formed from achiral components, and belong to a rare space group ( P622). Regardless of the different morphologies and growth mechanism, the crystallographic structures of the mono- and multidomain crystals are nearly identical. The monodomain crystals dissolve from the inner regions, while material is anisotropically added to their shell, resulting in hollow, single-crystals. These uniform objects are formed from unstable, monodomain crystals. We demonstrate the formation of metallo-organic single-crystals with a unique appearance: six-connected half-rods forming a hexagonal-like tube. Translating such feature to synthetic materials is a highly challenging process in crystal engineering. The coexistence of single-crystallinity with a multidomain morphology is a paradoxical phenomenon occurring in biomineralization.
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