An X-ray diffraction study on concentrated aqueous calcium nitrate solutions at subzero temperatures
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文摘
X-ray scattering measurements on aqueous solutions of Ca(NO3)2 · R H2O with R = 6 and 12 have been performed over a temperature range of 258 - 298 K. The analysis of the X-ray data gave the coordination number of Ca2+ nearly seven with a Ca2+-O distance = 247 pm. It has been found that with decreasing temperature the hydration shells of Ca2+ and NO3− are significantly perturbed in the saturated solution (R = 6), accompanied by evolving of hydrogen bonded network in the water structure. Contact ion-pairs between Ca2+ and NO3− are present in both solutions, as also evidenced by Raman spectroscopy, the nitrate ion coordinating to Ca2+ in a monodentate fashion with a Ca2+ - N(NO3−) distance 300 - 310 pm.