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

## TL;DR

Scientists used electron diffraction to determine the crystal structures of a new semiconductor material made from a topochemical reaction.

## Contribution

A novel method combining nanoscale electron diffraction tomography and DFT calculations reveals the structures of two intergrown Cu(Sb2S3)Cl polytypes.

## Key findings

- Orthorhombic and monoclinic forms of Cu(Sb2S3)Cl have similar layers but differ in stacking.
- DFT calculations confirm the stability of the orthorhombic form and metastability of the monoclinic form.
- The material forms from leaching AlCl3 from a layered precursor.

## Abstract

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.

The new layered semiconductor Cu(Sb2S3)Cl can only be obtained by leaching of AlCl3 from the
precursor compound Cu(Sb2S3)[AlCl4]. The topochemical reaction results in poorly crystalline flakes.
Manual three-dimensional electron diffraction tomography on the nanoscale
allowed to determine the crystal structures of two intergrown and
twinned polytypes. Quantum chemical calculations reveal that one of
them is stable, while the other is metastable.