Electron Diffraction Tomography on Two-Phase Nanolamellae of Topochemically Synthesized Cu(Sb₂S₃)Cl

The dark red semiconductor Cu(Sb₂S₃)Cl was obtained by leaching the layered precursor Cu(Sb₂S₃)[AlCl₄] in a 0.1 M aqueous HCl solution. The selective extraction of AlCl₃ yielded a mica-like lamellar product of poor crystallinity. Misalignment of lamellae down to the nanoscale prevented structure determination by conventional single-crystal X-ray diffraction, but a combination of transmission electron microscopy, selected area electron diffraction, and selected area electron precession diffraction tomography on a nanoscale spot with largely ordered crystalline lamellae revealed the crystal structures of two intergrown modifications. Orthorhombic o-Cu(Sb₂S₃)Cl and monoclinic m-Cu(Sb₂S₃)Cl have similar layers to the precursor and differ only in the stacking of the layers. These consist of uncharged Sb₂S₃ strands, whose sulfide ions, together with chloride ions, coordinate the copper(I) cations. Only one chloride ion remained from the [AlCl₄]^- group. DFT calculations confirm the structure solution for the orthorhombic form and suggest that the monoclinic structure is metastable against transformation to o-Cu(Sb₂S₃)Cl.