The structure of metallo-supramolecular polyelectrolytes in solution and on surfaces

Abstract

Metal ion induced self-assembly of the rigid ligand 1,4-bis(2,2′:6′,2″-terpyridine-4′-yl)benzene (1) with Fe(II), Co(II), Ni(II) and Zn(II) acetate in aqueous solution results in extended, rigid-rod like metallosupramolecular coordination polyelectrolytes (MEPE-1). Under the current experimental conditions the molar masses range from 1000 g mol−1 up to 500 000 g mol−1. The molar mass depends on concentration, stoichiometry, metal-ion and time. In addition, we present viscosity measurements, small angle neutron scattering and AFM data. We introduce a protocol to precisely control the stoichiometry during self-assembly using conductometry. The protocol can be used with different terpyridine ligands and the above-mentioned metal ions and is of paramount importance to obtain meaningful and reproducible results. As a control experiment we studied the mononuclear 4′-(phenyl)-2,2′:6′,2″-terpyridine (3) complex with Ni(II) and Zn(II) and the flexible ligand 1,3-bis[4′-oxa(2,2′:6′,2″-terpyridinyl)]propane (2) with Ni(II) acetate (Ni-MEPE-2). This ligand does not form extended macro-assemblies but likely ring-like structures with 3 to 4 repeat units. Through spin-coating of Ni-MEPE-1 on a solid surface we can image the MEPEs in real space by AFM. SANS measurements of Fe-MEPE-1 verify the extended rigid-rod type structure of the MEPEs in aqueous solution.