The novel biphenyl-based ligand N,N′,N″,N″′-tetrakis(2,2′-bipyridin-6-ylmethyl)-4,4′-dimethyl-1,1′-biphenyl-2,2′,6,6′-tetramine (6) with 12 nitrogen donor atoms has been synthesized. Ligand 6 is able to host two metal ions in an octahedral coordination sphere. This was shown by the synthesis of the dinuclear iron(II) complex 5 ([Fe2(6)]4+). Furthermore, the corresponding mononuclear iron(II) complex 4 ([Fe(6)]2+), where one coordination site is free, was obtained. Both FeII complexes show spin-crossover behaviour, which was shown by 1H NMR spectroscopy and Evans' measurements. A comparison of the two complexes gives evidence of a sterically induced cooperative behaviour in the dinuclear complex 5.