Vibrational spectroscopic properties of botallackite-structure basic copper halides

Mid-infrared (4000–400 cm−1) absorption and Raman (4000–95 cm−1) spectra of the series of geometrically frustrated materials, botallackite-structure basic copper halides, α-Cu2(OH)3Cl and α-Cu2(OH)3Br polycrystalline samples were first, to the best of our knowledge, measured, respectively, to study the corresponding relationship between their vibrational spectral properties and crystal microstructures. Through the comparative analysis to the four spectra, the authors have definitely assigned or tentatively suggested the vibrational modes of hydroxyl groups in the trimeric hydrogen bond environment (OH)3 Cl/Br, and atomic units O–Cu–O, Cu–O and Cl/Br–Cu–Cl/Br, etc. These results can be propitious to the low temperature spectral property of α-Cu2(OH)3Cl and α-Cu2(OH)3Br which must help to understand the underlying physics of their exotic geometric frustration phenomena at low temperatures.