Raman and ab Initio Investigation of Aqueous Cu(I) Chloride Complexes from 25 to 80 degree C

Temperature-dependent Raman studies of aqueous copper(I) chloride complexes have been carried out up to 80 degree C, along with supporting ab initio calculations for the species [CuCl sub(n)(H sub(2)O) sub(m)] super(1-n), n = 0-4 and hydration numbers m = 0-6. Normalized reduced isotropic Raman spectra were obtained from perpendicular and parallel polarization measurements, with perchlorate anion, ClO sub(4) super(-), as an internal standard. Although the Raman spectra were not intense, spectra could be corrected by solvent baseline subtraction, to yield quantitative reduced molar scattering coefficients for the symmetric vibrational bands at 297 plus or minus 3 and 247 plus or minus 3 cm super(-1). The intensity variations of these bands with concentration and temperature provided strong evidence that these arise from the species [CuCl sub(2)] super(-) and [CuCl sub(3)] super(2-), respectively. The results from ab initio calculations using density functional theory predict similar relative peak positions and intensities for the totally symmetric Cu-Cl stretching bands of the species [CuCl sub(2)(H sub(2)O) sub(6)] super(-) and [CuCl sub(3)(H sub(2)O) sub(6)] super(2-), in which the water is coordinated to the chloride ions. A less intense Raman band at 350 plus or minus 10 cm super(-1) is attributed to the symmetric Cu-Cl stretching mode of hydrated species [CuCl(H sub(2)O)] super(0) with six waters of hydration. Temperature- and concentration-independent quantitative Raman molar scattering coefficients (S) are reported for the [CuCl sub(2)] super(-) and [CuCl sub(3)] super(2-)s pecies.