[T6022]

I need some help with this table. The problem is to figure out why reduction potential are in this order.

1) Fe(H₂O)₆³⁺ + e^-  Fe(H₂O)₆²⁺    E°=0.77 V

2)Fe(CN)₆^3- + e^-  Fe(CN)₆^4-       E°=0.36 V

3)Fe(phen)₃³⁺ + e^-  Fe(phen)₃²⁺    E°=1.14 V


My hypothesis:

a) Fe³⁺ is harder than Fe²⁺, so it tends to bind hard ligand as H₂O and phen.
b) CN^- is hard, but it stabilizes low oxidation state (due to back-bonding in π*). Maybe for CN- the reduction potential is the lowest because the complex have high negative charge. So equilibrium favours reagent.
c) phen can't accept back-bonding because π-system is delocalized on carbons atoms. In theory this complex shoud have low potential because phen stabilizes high-oxidation state. But it isn't true.

This argument seems inapplicable to this problem. Can anyone help me out?