Lead(II) oxalate

Lead(II) oxalate is an organic compound with the formula PbC2O4. It is naturally found as a heavy white solid.

Preparation
This compound is commercially available. It may be prepared by the metathesis reaction between lead(II) nitrate and sodium oxalate:


 * Pb2+(aq) + C2O42&minus; → PbC2O4 (s)

A dihydrate may be formed with water solutions. But the dihydrate dehydrates in air:


 * (PbC2O4•2H2O (s) → (PbC2O4 (s) + 2H2O (g)

The trihydrate (PbC2O4•3H2O) can be made by reacting a solution of lead(II) carbonate in perchloric acid with oxalylhydroxamic acid.

Properties
As well as an anhydrous form, a monohydrate (PbC2O4•H2O), a dihydrate (PbC2O4•2H2O) and a trihydrate (PbC2O4•3H2O) are known. The dihydrate is from the orthorhombic crystal system, with space group Pnam (number 62), with unit cell dimensions: a = 9.053 Å b = 8.036 Å and c = 7.834 Å. The unit cell volume is 569.8 Å3 with four formula per cell, giving a density of 3.860 g/cm3

The trihydrate has triclinic crystals with space group P and unit cell dimensions and angles: a = 6.008 Å, b=6.671 Å, c=8.493 Å, α=74.70°, β=74.33°, and γ=80.98°. The unit cell volume is 314.41 Å3 with two formula per unit cell. Density is 3.69 g/cm3.

Solubility
Lead(II) oxalate is insoluble in water. Its solubility is increased in presence of excess oxalate anions, due to the formation of the Pb(C2O4)22&minus; complex ion.