The new ligand L has been prepared by appending three 2,2′-bipyridine molecules to a tren (tris(2-aminoethyl)amine) unit. It binds a Fe²⁺ cation with its three bipyridines, imparting to it an octahedral co-ordination. The obtained [FeL]²⁺ molecular cation has a closed shape, whose nature has been ascertained by X-ray diffraction studies on the complex [Fe(HL)][PF₆]₃. The tren unit can thus be described as one half of a bis-tren cage. The kinetic inertness of the complex between Fe²⁺ and the three bipyridines has been verified: in the pH 2–12 range the [Fe^II(bipyR)₃] unit is stable and plays only an architectural role. According to this it has been possible to determine the protonation and complexation constants (in the presence of 1 equivalent of Cu²⁺) of the tren fragment, which is in fact able to interact with protons and metal cations, behaving as a tight and rigid half of a bis-tren ligand. High percentages (70–100%) of the [FeLH_n]^(n + 2)+ species can be found in sharp pH ranges, while, in the presence of 1 equivalent of Cu²⁺, the metal-containing species [FeCu(HL)]⁵⁺, [FeCuL]⁴⁺, [FeCuL(OH)]³⁺ and [FeCuL(OH)₂]²⁺ exist in the pH 2–12 range, each one prevailing in distinct pH intervals, reaching high percentages (70–100%). The variation of the spectral and electrochemical properties of the [Fe(bipyR)₃] fragment have been studied as a function of pH, and related with the protonation degree or complexation of the tren unit.