Structure of MgSO4 in Concentrated Aqueous Solutions by X-Ray Diffraction

Detailed time-and-space-averaged structure of MgSQ(4) in the concentrated aqueous solutions was investigated via X-ray diffraction with an X'pert Pro theta-theta diffractometer at 298 K, yielding structural function and radial distribution function(RDF). The developed KURVLR program was employed for the theoretical investigation in consideration of the ionic hydration and ion association. Multi-peaks Gaussian fitting method was applied to deconvolving the overlapping bands of Differential radial distribution function(DRDF). The calculation of the geometric model shows that octahedrally six-coordinated Mg(H2O)(6)(2+), with an Mg2+center dot center dot center dot O-w bond length of 0.201 nm dominates in the solutions. There exists contact ion-pair(CIP) in the more concentrated solution(1:18, H2O/salt molar ratio) with a coordination number of 0.8 and a characteristic Mg center dot center dot center dot S distance of 0.340 nm. The result indicates the hydrated SO(4)(2-)ion happens in the solution. The S...O-w bond distance was determined to be 0.382 nm with a coordination number of 13. The fraction of CIP increases significantly with the increasing concentration. The symmetry of the hydration structure of sulfate ion is lowered by forming complex with magnesium ion.