Thorium tetranitrate hydrates

The enthalpy of solution of the tetrahydrate in 35OH2O was reported without details by Ferraro et al. [1956FER/KAT] as -(32.01 + 1.70) kJ-moF, the imcertainty being that estimated by this review. 

As in the case of the dissolution of the anhydrous thorium nitrate in water by the same authors, these results caimot be used as such for the determination of the enthalpy of formation of the compound, due to the lack of experimental data on the enthalpies of formation of the thorium nitrate complexes. This is also the case for the enthalpy of solution of the pentahydrate in water to reach the same final concentration, also given by the same authors as (Th(N03)4-5H20, cr, 298.15 K) = 

Morss and McCue [1976MOR/MCC] measured the enthalpy of solution of high purity Th(N03)4-5H20(cr) in 0.01 M HCIO4 at 293.15, 298.15, and 308.15 K. At infinite dilution, and after a small correction for hydrolysis, the value (Th(N03)4-5H20, cr, 298.15 K) = -(19.807+0.250) kJ-mol was reported. The uncertainty in this value is estimated by the present review. 

The enthalpy of formation of the tetrahydrate can be calculated from this value, together with the difference between the enthalpies of solution of the pentahydrate and the tetrahydrate in 350 mol H2O by [1956FER/1CAT], -(17.16 0.40) kJ-mof, and the partial molar enthalpy of formation of water in the resulting solution. There are insufficient data to calculate the latter precisely, but in such a dilute solution (co. 0.15 m) it will differ very little from Aj//° (H2O, 1, 298.15 K), so we have taken Af/7ni(H20, partial, 298.15 K) = -(285.83 + 1.0) kJ-mof with increased uncertainty limits. This gives 

The heat capacity of the pentahydrate has been measured by Cheda et al. [1976CHEAVES]. Their results, 

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Thorium tetranitrate hydrates and oxide nitrate hydrates reported to-date are listed in Table 18 with the anhydrous compounds and the presently known peroxide nitrate hydrate and hydroxide nitrate hydrates. The pre-1950 literature is discussed in Thorium 1955,... 

Several thorium tetranitrate hydrates are described in the literature, Th(N03)4-xH20 (x=12, 6, 5.5, 4, 3, 2, 1). Those most readily obtained by crystallisation from aqueous media are Th(N03)4 5H20 and Th(N03)4-4H20. The pre-1950 accounts of the preparation of the various phases are discussed in Thorium 1955, pp. 243/4 (see also [1 to 3]). The present discussion is confined to more recent publications and, for convenience, the different hydrates are dealt with in a single section. 

An alternative route to Th(N03)4-5H20 involves dissolution of reagent grade thorium tetranitrate hydrate in ether followed by removal of the insoluble hydrolysed material to allow crystallisation of the pentahydrate by evaporation of the solvent [11, 12, 40]. 

The preparation of thorium tetranitrate hydrates on the industrial scale is described in references [14 to 17] for earlier reports see Thorium 1955, pp. 244/5. 

Unit Cell Dimensions for Thorium Tetranitrate Hydrates. 

The solubility of Th(N03)4 5H20 in ether-diluent mixtures has been reported by Vdovenko et al. [84] the results, obtained by contacting the solid nitrate with the appropriate non-aqueous phase, are shown in Table 31. Earlier information on the solubilities of thorium tetranitrate hydrates in non-aqueous media will be found in Thorium 1955, pp. 249/51. 

Infrared spectral data have also been reported for solutions of thorium tetranitrate hydrates in solvents such as acetone [5 to 7], diethyl ether [3,7], dioxane, acetonitrile and dimethylform-amide [7], methylisobutylketone, dibutyl carbitol" and tributylphosphate [8] and tri-n-octyl-phosphine oxide [9]. The results indicate the presence of co-ordinated nitrate groups. 

The infrared spectrum recorded by Ferraro, Walker [8] for anhydrous thorium tetranitrate is compared in Table 19 with those reported at the same time for the tetra- and penta-hydrate (see also [3] for information on Th(N03)4). The ultraviolet spectrum of a diethyl ether solution of the anhydrous tetranitrate (illustrated in [1]) is quite different from those of the hydrates. 

Ferraro et al. [1] showed that only the penta- and tetra-hydrate could be obtained from the Th(N03)4-HN03-H20 system (Fig. 23). The composition for co-existence of the penta- and tetra-hydrate was reported as 17.70 wt% water - 28.67 wt% thorium tetranitrate and that for the tetrahydrate and an unidentified anhydrous phase 5.10 wt% water-21.13 wt% thorium tetranitrate. They postulated that phases such as Th(N03)6 6H20 and Th(N03)4 5.5H20 were actually the pentahydrate X-ray powder studies confirmed [2] that Th(N03)4 5.5H20 [3] exhibited the same diffraction pattern as Th(N03)4 5H20 [2, 4]. 

The compound Th(N03)4 2.67(CH3)3P0, which has been shown by a full structure determination to be [Th(N03)3(C3H9P0)4]2[Th(N03)6] (see p. 112), is obtained by evaporation of an ethanol solution containing trimethylphosphine oxide (4.5 mmol) and hydrated thorium tetranitrate (1.5 mmol) followed by recrystallisation of the initial product from a 1 2 methyl-cyanide-methanol mixture [18]. The hexamethylphosphoramide (= hmpa) analogue [Th(N03)3-(hmpa)4]2[Th(N03)6l forms on addition of 2-methylbutane to an acetone solution of Th(N03)4 5H2O containing hexamethylphosporamide [19]. 

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