Rubidium oxalate
Rubidium oxalate is the oxalate salt of rubidium, with the chemical formula of Rb2C2O4. Preparation 

Rubidium carbonate and oxalic acid react to form rubidium oxalate:

Rubidium oxalate can also be obtained via the thermal decomposition of rubidium formate:

Properties 

Rubidium oxalate crystallizes as the monohydrate (COO)2Rb2 in the monoclinic crystal system. and is isomorphic to potassium oxalate monohydrate. Two modifications of the anhydrous form exist at room temperature: one modification is monoclinic and isotypic to caesium oxalate, the other is orthorhombic and isotypic to potassium oxalate. Freshly prepared anhydrous rubidium oxalate initially contains mainly the monoclinic phase, but this slowly transforms irreversibly into the orthorhombic modification. In 2004, two more high-temperature phases of rubidium oxalate were discovered. Crystal data of the different modifications of rubidium oxalate

The standard enthalpy of formation of the crystalline rubidium oxalate is 1325.0 ± 8.1 kJ/mol. The decomposition of rubidium oxalate with the release of carbon monoxide and subsequently carbon dioxide and oxygen takes place at 507–527 °C. In addition to the neutral rubidium oxalate, there is also a hydrogen oxalate with the formula RbH(COO)2, which is isomorphic to the corresponding potassium compound and forms monoclinic crystals, and an acidic tetraoxalate with the formula RbH3(COO)4, which exists as a dihydrate, has a density of 2.125 g/cm3 at 18 °C and a solubility of 21 g/L at 21 °C. Upon evaporation of a solution in hydrogen peroxide, rubidium oxalate forms a monoperhydrate of the composition (COO)2Rb2·H2O2, which forms monoclinic crystals that are relatively stable in air. Rubidium oxalate reacts with hydrogen fluoride to form a complex compound:

References 

Rubidium compounds
Oxalates