Structural diversity of Zn(II)/Cd(II) coordination polymers constructed from mixed ligand systems of conformationally flexible azo functionalized bis-imidazolate and dicarboxylates

Abstract

Six coordination polymers based on a conformationally flexible azo functionalized bis-imidazolate ligand bis(3-imidazol-1-ylphenyl)-diazene (L) with diverse conformations, namely, {[ZnL(tp)]·2H2O}n (1), [ZnL(ndc)]n (2), {[ZnL(ip)]·DMF}n (3), [Cd(L)0.5(tp)]n (4), {[CdL(ndc)]·0.625DMF}n (5) and [CdL(ip)]n (6), have been synthesized under solvothermal conditions with the aid of three different dicarboxylic acid ligands (H2tp=terephthalic acid, H2ndc=naphthalene-1,4-dicarboxylic acid, H2ip=isophthalic acid). Complexes 1–3 exhibit 2D+2D→3D polycatenation or 2D→2D interpenetration of (4, 4) sheets with metal ions as 4-connected nodes and ligands as linkers, while the layers are interpenetrated in different ways. Complex 4 possesses an unprecedented self-penetrating framework with a uninodal 8-connected with (416.55.67) topology based on infinite rod-shaped secondary building units (SBUs). Complex 5 displays a 3D 6-connected self-penetrated rob topology constructed from binuclear Cd(II) SBUs. Complex 6 features non-interpenetrated sql topology built on binuclear Cd(II) SBUs. The effects of the conformations of the L ligand, coordination modes of the dicarboxylic acids and metal ions on the diverse structures have been discussed. The thermal stability and luminescent properties of the CPs are also investigated.