Health & Environmental Research Online (HERO)


Print Feedback Export to File
2523146 
Journal Article 
Raman Spectroscopic Investigation of Speciation in MnSO4(aq) 
Rudolph, WW; Irmer, G 
2014 
Yes 
Journal of Solution Chemistry
ISSN: 0095-9782
EISSN: 1572-8927 
43 
3 
465-485 
WOS:000333156100004 
Raman spectroscopic measurements have been made on aqueous solutions of Mn(ClO4)(2), MnSO4, and (NH4)(2)SO4 in the terahertz frequency region (45-600 cm(-1)), in a few cases to higher wavenumbers of 4,200 cm(-1) and also down to low concentrations (0.0027 mol center dot L-1). In solutions of Mn(ClO4)(2) with water and heavy water, the hexahydrate species and its corresponding deuterate, [Mn(OH2)(6)](2+) and [Mn(OD2)(6)](2+), were characterized and weak, strongly polarized bands are observed at 354 and 338 cm(-1). These modes were assigned to nu (1)(MnO6) of the species [(Mn(OH2)(6)](2+) and [(Mn(OD2)(6)](2+), respectively. In MnSO4(aq) the nu (1)() mode at 980 cm(-1) broadens with increasing concentration and shifts to higher wavenumbers. At the same time, a band at 995 cm(-1) was detected and assigned to the bound sulfate of [MnOSO3], an inner-sphere complex (ISC). Confirmation of this assignment is provided by the simultaneous appearance of stretching bands of the Mn2+- bond of the complex at 216 cm(-1) and for the MnO5O* skeleton mode of [(H2O)(5)MnOSO3] at 321 cm(-1) that is visible as a weak component next to the symmetric stretching mode, nu (1)(MnO6), of the [Mn(OH2)(6)](2+)(aq) species at 354 cm(-1). The similarity of the nu (1)() Raman band profiles for MnSO4 in H2O and D2O is further strong evidence for formation of an ISC. After subtraction of the ISC component at 995 cm(-1), the nu (1)() band in MnSO4(aq) showed systematic differences from that in (NH4)(2)SO4(aq). This is consistent with a nu (1)() mode at 982.7 cm(-1) that can be assigned to the occurrence of outer-sphere complex ions (OSCs). These observations are shown to be in qualitative agreement with results derived from previous relaxation measurements. The band profile of the much weaker asymmetric S-O stretching modes, nu (3)(), shows asymmetry and was fitted with four band components {including nu (3)((aq))}. Quantitative Raman measurements showed that the formation of ISCs in MnSO4(aq) is comparable to that found in the similar MgSO4(aq) system. 
Raman spectroscopy; Terahertz frequency range; Mn2+ hexaaqua ion; Mn(ClO4)(2); MnSO4 solutions; Sulfato complexes; Outer-sphere complexes; Inner-sphere complexes of Mn2+