Chiral zero-dimensional hybrid organic–inorganic metal halides based on nipecotic acid and tetrabromocuprate

Abstract

Chiral hybrid organic–inorganic metal halides combining chirality from organic components and optoelectronic properties from the inorganic moieties have attracted considerable interest from the academic community. The field is still in its early stages, especially for low-dimensional (0D, 1D) chiral hybrid organic–inorganic metal halides. Here, we report chiral zero-dimensional metal halides based on chiral nipecotic acid (NA) and tetrabromocuprate. Chiral hybrid organic–inorganic metal halides, [S-NA]₂[CuBr₄] and [R-NA]₂[CuBr₄], were synthesized from chiral NA and copper salt via the slow solution evaporation method at room temperature. The obtained crystals were characterized by X-ray diffraction, X-ray photoelectron spectroscopy, scanning electron microscopy and energy spectroscopy, Raman spectroscopy, UV-vis spectroscopy, circular dichroism (CD), thermogravimetry (TG) analysis, and differential scanning calorimetry (DSC). The single crystals were in the orthorhombic system of the chiral non-centrosymmetric space group C222₁. These chiral metal halides exhibit typical zero-dimensional (0D) structures. One unit cell contains two chiral NA cations and one tetrabromocuprate ([CuBr₄]²⁻) anion. The organic cations and inorganic anions are alternately arranged and integrated by N–H–Br hydrogen bonds. [S-NA]₂[CuBr₄] and [R-NA]₂[CuBr₄] exhibited strong CD signals with opposite values, indicating that these two hybrid organic–inorganic metal halides are enantiomers. The crystal metal halides demonstrate high thermal stability. This work provides a new strategy for designing chiral hybrid organic–inorganic metal halides in low dimensions from various biologically chiral amino acids.