Raman spectroscopic studies of scandium(III) hydration in aqueous solution- about the first hydration sphere of Sc(III) in solution

It has been shown conclusively that Sc(III) in aqueous perchlorate solution occurs as an hexaaqua cation. The weak, polarized Raman band assigned to t he v(1)(a(1g)) ScO6 mode of the hexaaqua-Sc(III) ion (T-h symmetry for the whole complex ion or O-h symmetry for the ScO6 unit) has been studied as a function of concentration and temperature. The isotropic scattering geometr y in R-format was employed in order to measure the true vibrational contrib ution of the band and account for the Boltzmann temperature factor B and th e wavenumber factor v. The v(1)(a(1g))ScO6 mode at 442 cm(-1) of the hexaaq ua-Sc(III) shifts only 3 cm(-1) to lower wavenumbers and broadens about 20 cm(-1) for a 60 degrees C temperature increase. The Raman spectroscopic dat a suggest that the hexaaqua Sc(III) ion is stable in perchlorate solution w ithin the temperature range measured. Besides the polarized component at 442 cm(-1), two weak depolarized modes a t 295 cm(-1) and 410 cm(-1) were measured in the Raman effect. These two mo des of the ScO6 unit were assigned to v(5)(f(2g)) and v(2)(e(g)) respective ly. The infrared active mode, v(3)(f(1u)), was measured to be at 460 cm(-1) . The wavenumber data confirm the centrosymmetry of the Sc(III)aqua-complex , in opposite to earlier Raman results. These findings are also in contrast to the results found in Sc-2(SO4)(3) so lutions, where sulfate replaces water in the first hydration sphere and for ms quite strong sulfate complexes. In ScCl3 solutions weak chloro-complex(e s) could be detected.