Two new multidentate ligands, H3L1 and H4L2, possessing bipyridine–phenol repetitive units were designed so that the multi-metal complexation could produce a single-helical structure in a pre-programmed fashion. The ligands were synthesized by successive palladium-catalyzed coupling reactions. The complexation of H3L1 with zinc(II) and nickel(II) acetate afforded [L1Zn2(OAc)] and [(L1)2Ni4](OAc)2, respectively. Each of the ligand moieties in these complexes formed a one-turn single helix. The zinc(II) complex [L1Zn2(OAc)] underwent a helix compression–extension motion in solution. The complexation of the H3L1ligand with iron(III) chloride gave a dinuclear complex [(HL1)2Fe2Cl2] with a non-helical dimeric structure. The longer ligand H4L2 afforded a trinuclear complex [L2Zn3(OAc)2] with a 1.5-turn single-helical structure upon complexation with zinc(II) acetate. The reaction of the H4L2ligand with cobalt(II) acetate under aerobic conditions gave a mixed valence complex [L2Co3(OAc)3(OMe)], which had two trivalent and one divalent cobalt ions. The structural features of the trinuclear complexes significantly depended on the metals; [L2Co3(OAc)3(OMe)] had a helical pitch of 7.6 Å, which was almost twice that of [L2Zn3(OAc)2] (4.0 Å).
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