The Au13 cluster carries a charge of +3, and during dimer formation, there should be electrostatic repulsion between the Au13 units as well as between the Fe 2+ ions. However, the stability constant (β) for the complexation between Fe 2+ and Tpy, Fe 2+ + 2Tpy ⇄ [Fe(Tpy)2], is large (β = 10 20.9 M -2 ), indicating that complex formation is thermodynamically favorable. This large stability constant likely contributes to the efficient formation of dimers through complexation despite electrostatic repulsion. This