The thermal behaviour of solvates in the LiCI(MgCl2, AlCl3) water-1,4-dioxane systems

Abstract

The thermal behaviour of the solvates and mixed solvates in the LiCI(MgC12, A1Cla)-water-1,4-dioxane systems was investigated by means of DTA measurements of the melting behaviour and by quasi-isothermal and quasi-isobaric investigations of the thermal decomposition processes.The compounds melt incongruently. The positions of the melting points and the processes of thermal decomposition confirm the assumption that 1,4-dioxane is bonded in the first coordination sphere in the mixed solvate of lithium, but in the cases of magnesium and aluminium chloride it is bonded via hydrogen-bonds and not directly to the cations. Only for the lithium and magnesium compounds does the decomposition of the anhydrous solvates result in anhydrous chlorides.At 298.15 K, LiCI, MgCI 2 and A1C13 form the salt hydrates LiCI-H20 , MgC12 9 6H20 and A1Cl a 9 6H20 in aqueous solution. Moreover, in the presoace of 1,4-dioxane (C4H802) the solvates and mixed solvates LiCI.H20.C4HsO2, LiC1. C4H80 2 [1], MgC12 9 6H20" C4H80 2 , MgCl 2 " 2C4HaO 2[2], A1CI3 "9H20" 3C4HaO 2 and AIC13 9 2C4HAO2 [3] can be obtained.From the point of view of coordination chemistry, the incorporation of 1,4-dioxane in the solvates is interesting because this can be coordinated as a bridging ligand between the aquo complexes of the cations, as well as directly to the cation.As a continuation of our thermoanalytical investigations of solid-phase solvates in the salt-water-organic component systems, this paper is intended to demonstrate the influence of 1,4-dioxane on the solvate structure and the coordination of the solvents to the different cations, through an investigation of their thermal behaviour.Detailed results ofthermoanalytical investigations are available only for the pure salt hydrates [4][5][6][7]. As concerns the solvates and mixed solvates, the data published John Wiley & Sons, Limited, Chichester Akad~miai Kiadt, Budapest