Vibrational studies of tetrahalogenocuprates (II)
The compounds (R₄N)₂CuBrₙCℓ₄₋ₙ (R = CH₃, C₂H₅; n = 1 - 3) were studied by far infra-red spectroscopy. The results, in conjunction with the evidence of X-ray powder diffraction measurements we reported earlier, show that, within each series, the mixed bromochlorocuprates(II) are isomorphous with each other and with the corresponding compounds where n = 0, 4. There is also evidence of discrete CuBrₙCℓ₄₋ₙ²⁻ anions with flattened tetrahedral configurations. The assignment problems associated with the vibrational spectrum of caesium tetrachlorocuprate(II) were critically discussed. A unit cell analysis of the compound was performed with two primary objectives: (A) to interpret the vibrational spectrum; and (B) to develop a competent model force field for such study. The analysis produces a physically sensible set of force constants which supports one particular set of assignments. The potential force field developed in the unit cell analysis of Cs₂CuCℓ₄ was extended to the study of the vibrations of Cs₂ZnCℓ₄ crystal with encouraging results.
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