Actinium(III) oxalate is an inorganic compound of actinium and oxalic acid, with the formula Ac2(C2O4)3. The best-characterized form is the colorless decahydrate, Ac2(C2O4)3·10H2O.
Preparation Actinium(III) oxalate decahydrate can be prepared by precipitating a purified aqueous solution containing Ac3+ with oxalic acid:
2 Ac3+ + 3 H2C2O4 + 10 H2O → Ac2(C2O4)3·10H2O↓ + 6 H+
The compound is only sparingly soluble in water, which allows actinium to be precipitated as the oxalate from solution.
Structure and properties Actinium(III) oxalate decahydrate is a colorless crystalline solid. It is isomorphous with lanthanum oxalate decahydrate and crystallizes in the monoclinic crystal system. Powder diffraction measurements gave lattice parameters a = 11.26 Å, b = 9.97 Å, c = 10.65 Å and β = 111.3°, with two formula units per unit cell.
The calculated density from these crystallographic data is 2.68 g/cm3.
Only limited structural information is available for actinium compounds because of the element's intense radioactivity and scarcity. Actinium oxalate decahydrate is one of the few non-halide, non-chalcogenide Ac(III) compounds for which crystallographic data have been reported.
The structure has generally been considered analogous to that of lanthanum oxalate decahydrate, with nine-coordinate Ac3+ centres, although the available actinium data are based on powder diffraction rather than a full single-crystal structure determination.
Thermal decomposition Actinium oxalate can be converted to actinium(III) oxide by strong heating. In radiochemical preparations, ignition of actinium oxalate at about 1000–1100 °C has been used to obtain Ac2O3.
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