for the related compounds ([Ru(tbbpy)2(tpphz)PtX2](PF6)2 (X = Cl or I), a similar increase of HER activity is found when the chloride ligands are replaced by iodides. The authors assigned this increased activity to the higher electron density at the Pt center due to the large, easily polarized iodide ligands. To the best of our knowledge, this is the first time that ligand-tuning concepts have been demonstrated in POM-based HER catalysis.