Ligands that include a numerical prefix in the name use the prefixes bis for 2, tris for 3, or tetrakis for 4 to indicate their number.
If the complex ion is an anion, we drop the ending of the metal name and add –ate.
In the given coordination compound, Co is the cobalt metal, C2O42− are the ligands named as oxalato.
The charge on [Co(C2O4)3] is −3 and oxalate is having charge of −2.
X+3(−2)=−3X=+3
Hence, the IUPAC name of the compound K3[Co(C2O4)3] is Potassium trioxalatocobaltate(III).