Hydration Structure of SCN− in Concentrated Aqueous Sodium Thiocyanate Solutions

Time-of-flight (TOF) neutron-diffraction measurements for 10 mol% NaSC14N and NaSC15N solutions in D2O were carried out in order to investigate the hydration structure around the thiocyanate ion, SCN−. There are 1.8 ± 0.2 water molecules coordinated to SCN− with an intermolecular distance of r(N···D) = 2.16 ± 0.02 Å, suggesting that the hydrogen bond is formed between SCN− and the nearest-neighbor water molecules. It has also been indicated by pairing the neutron-diffraction and X-ray diffraction results that the angle between the molecular axis of SCN− and the hydrogen bond, ∠C–N··· H2O, is ca. 120° in 10 and 20 mol% NaSCN aqueous solutions. Furthermore, details concerning the local structure around Na+ in these concentrated solutions have been proposed based on the results of a least-squares fitting between the observed and structural model functions.