Effect of pH on the construction of lead coordination polymers by the diverse coordination modes of sulfonate functionalized imidazophenanthroline derivative ligand

Abstract

To determine the influence of reaction conditions on the formation of metal-organic frameworks(MOFs), three PbII-H3sfpip complexes {[Pb(Hsfpip)(H2O)3]·H2O}n (1), {[Pb2(Hsfpip)2(H2O)2]·H2O}n (2), [Pb2(Hsfpip)2(H2O)2]n (3) [H3sfpip=2-(2,4-disulfophenyl)imidazo(4,5-f)(1,10)-phenanthroline] have been synthesized under hydrothermal conditions and characterized by elemental analysis, IR and single crystal X-ray diffraction. The diverse structures of products show the marked sensitivity of the structural chemistry of the aromatic sulfonate ligand to synthetic conditions. Complex 1 is formed at pH 3.0, and displays a one-dimensional linear chain structure with Hsfpip2− group as a μ2–η2:η1 coordination mode. While at pH 5.0, a two-dimensional double layer structure of 2 is formed, in which Hsfpip2− group shows a μ4–η2:η1:η1:η1 coordination mode. The two-dimensional networks are further connected by hydrogen bonds to result in a three-dimensional supramolecular network. Furthermore a three-dimensional network of 3 is got by increasing pH to 6.5, in which Hsfpip2− group presents the unusual μ5–η2:η1:η1:η1:η1 coordination mode. The structural differences of three complexes give some insights into the effect of pH on the construction of coordination polymers. Additionally, the thermal stabilities and photoluminescence properties of 1–3 were also studied.