# Caesium oxalate

Caesium oxalate (standard IUPAC spelling), or dicesium oxalate, or cesium oxalate (American spelling) is a chemical compound with the chemical formula Cs$_2$C$_2$O$_4$. It is a caesium salt of oxalic acid. It consists of caesium cations Cs$^+$ and oxalate anions C$_2$O2−4.

## Preparation

Caesium oxalate can be prepared by passing carbon monoxide and carbon dioxide over caesium carbonate at 380 °C:
    Cs$_2$CO$_3$ + CO → Cs$_2$C$_2$O$_4$
Other alkali carbonates do not undergo transformation to oxalate.
Caesium carbonate can react with oxalic acid in aqueous solution to give caesium oxalate.
    Cs$_2$CO$_3$ + H$_2$C$_2$O$_4$·2H$_2$O → Cs$_2$C$_2$O$_4$·H$_2$O + CO$_2$ + 2 H$_2$O

## Chemical Reactions

Caesium oxalate can be reduced back into caesium carbonate and carbon monoxide by thermal decomposition.
    Cs$_2$C$_2$O$_4$ → Cs$_2$CO$_3$ + CO

## Double salts

Compounds that contain caesium and another element in addition to the oxalate anion are double salts of caesium and oxalate. The oxalate may form a complex with a metal that can make a salt with caesium.
Examples include:
| name | formula | properties |
| caesium bis(oxalato)oxotitanate(IV) trihydrate | Cs$_4$[TiO(C$_2$O$_4$)$_2$]$_2$·3H$_2$O | |
| caesium oxalatooxovanadate(IV) | Cs$_2$[VO(C$_2$O$_4$)$_2$] | |
| caesium tris(oxalato) ferrate(III) dihydrate | Cs$_3$[Fe(C$_2$O$_4$)$_3$]·2H$_2$O | |
| caesium bis(oxalato) cobaltate(II) tetrahydrate | Cs$_2$[Co(C$_2$O$_4$)$_2$]·4H$_2$O | |
| caesium bis(oxalato)nickelate(III) tetrahydrate | Cs[Ni(C$_2$O$_4$)$_2$]·4H$_2$O | |
| caesium tris(oxalato)germanate(IV) | Cs$_2$[Ge(C$_2$O$_4$)$_3$] | |
| caesium yttrium(III) oxalate monohydrate | CsY(C$_2$O$_4$)$_2$·H$_2$O | monoclinic a = 8.979, b = 6.2299, c = 8.103 Å, β = 90.05° V = 453.3 Å$^3$, space group P2/n |
| caesium (diaquo)bis(oxalato)oxoniobate(V) dihydrate | Cs[NbO(C$_2$O$_4$)$_2$(H$_2$O)$_2$]·2H$_2$O | |
| | Cs$_2$[NH$_4$]$_2$[Mo$_3$O$_8$(C$_2$O$_4$)$_3$] | |
| tetracaesium dilanthanum(III) oxalate octahydrate | Cs$_4$La$_2$(C$_2$O$_4$)$_5$·8H$_2$O | |
| tetracaesium dipraseodymium(III) oxalate octahydrate | Cs$_4$Pr$_2$(C$_2$O$_4$)$_5$·8H$_2$O | |
| caesium neodymium(III) oxalate hexahydrate | CsNd(C$_2$O$_4$)$_2$·6H$_2$O | |
| caesium samarium(III) oxalate hexahydrate | CsSm(C$_2$O$_4$)$_2$·6H$_2$O | |
| caesium dysprosium(III) oxalate hydrate | CsDy(C$_2$O$_4$)$_2$·?H$_2$O | |
| caesium gadolinium(III) oxalate sesquihydrate | CsGd(C$_2$O$_4$)$_2$·1.5H$_2$O | |
| caesium terbium(III) oxalate sesquihydrate | CsTb(C$_2$O$_4$)$_2$·1.5H$_2$O | |
| caesium dysprosium(III) oxalate sesquihydrate | CsDy(C$_2$O$_4$)$_2$·1.5H$_2$O | |
| caesium holmium(III) oxalate sesquihydrate | CsHo(C$_2$O$_4$)$_2$·1.5H$_2$O | |
| caesium ytterbium(III) oxalate sesquihydrate | CsYb(C$_2$O$_4$)$_2$·1.5H$_2$O | |
| caesium lutetium(III) oxalate sesquihydrate | CsLu(C$_2$O$_4$)$_2$·1.5H$_2$O | |
| dicaesium dioxotungsten(VI) oxalate | Cs$_2$[WO$_2$](C$_2$O$_4$)$_2$ | |
| dicaesium dioxotungsten(VI) difluoride monooxalate | Cs$_2$[WO$_2$]F$_2$(C$_2$O$_4$) | |
| caesium tris(oxalato)rhenate(III) | Cs$_3$[Re(C$_2$O$_4$)$_3$] | |
| dicaesium uranyl monooxalate monosulfate dihydrate | Cs$_2$[UO$_2$](C$_2$O$_4$)(SO$_4$)·2H$_2$O | |
| ammonium caesium uranyl monooxalate monosulfate dihydrate | [NH$_4$]Cs[UO$_2$](C$_2$O$_4$)(SO$_4$)·2H$_2$O | |
| caesium dioxoneptunium(VI) oxalate hydrate | Cs[NpO$_2$]C$_2$O$_4$·nH$_2$O | |
Mixed anion compounds containing caesium, oxalate and another anion also exist, such as the uranyl sulfate above, and caesium bis(oxalato)borate (CsBOB) (Cs[B(C$_2$O$_4$)$_2$]).