Raman study of ferric nitrate crystalline hydrate and variably hydrated liquids

摘要

A Raman investigation on crystalline ferric nitrate enneahydrate (FNEH) has shown thatNO3minus;andFelpar;H2Orpar;63plus;ions are present in two distinct environments in the monoclinic unit cell of the crystal. In FNEH melt, it has been found thatNO3minus;and Fe3plus;ions form a complex in which water is also coordinated to the Fe3plus;ion. Raman evidence is presented which indicates thatNO3minus;ion in the nitrate complex is coordinated to the Fe3plus;ion in monodentate fashion, with an appreciable covalency in theFe3plus;sngbnd;ONO2minus;bond. The addition of water to FNEH melt causes dissociation of the nitrate complex. This complex almost ceases to exist when the water content of the melt is raised to 28 mole of water per mole of the salt. A weak polarized band at sim;407 cmminus;1in the Fe(NO3)3middot;xH2O system (xge; 28) has been attributed to the presence of the hydrolysis product of Fe3plus;ions. The effect of dilution and of temperature on this band has also been investigated. It is suggested that the hydrolysis product of the salt exists in the form of a polymeric species.