The invention relates to a method for the preparation of platinum (II) complexes, in particular dicarboxylatoplatinum (II) complexes containing a neutral bidentate ligand, such as oxaliplatin. The method includes the step of reacting a bis-dicarboxylatoplatinate (II) species with a suitable neutral bidentate ligand to form a neutral dicarboxylatoplatinum (II) complex and, if necessary, recrystallising the product to form a pure dicarboxylatoplatinum (II) complex containing a neutral bidentate ligand. The invention also relates to a method for producing a bis-dicarboxylatoplatinate (II) species, and to new platinum (II) complexes that can be made by the method of the invention.