On nickel–sulfate contacts and SO=4–H2O interactions in aqueous solutions

NiSO4 aqueous solutions are examined by x-ray diffraction. The peaks present in the G(r) correlation functions at about 2.05, 3.80, and 4.20 Å clearly indicate the existence of SO=4–H2O contacts and of two hydration shells around nickel. The absence of any peaks in the range 3.2–3.5 Å, indicates no quantitatively detectable inner sphere ion pairing between nickel and sulfate anion.