Crystal engineering of mixed-ligand frameworks: Ligand-directed assembly and structural diversity

Four new coordination networks based on dipyridyl linkages 2,6-(N ,N ′-di(4-pyridyl)amino)pyridine (dpap) or 1,3-bis(4-pyridyl)propane (bpp) and different dicarboxylates have been synthesized and structurally characterized. Using dpap to react with two different dicarboxylates, maleic acid (H2mal) and 4,4′-sulfonyldibenzoate (H2sdba), respectively, two different two-dimensional (2D) coordination polymers of Cd(II), [Cd(dpap)(mal)]n (1) and {[Cd(dpap)(sdba)] · 2H2O}n (2) were obtained. Compound 1 features a 42-membered bimetallic macrocyclic structural motif which is extended by mal groups to form a 2D network. In the case of 2, two different layers can be achieved depending on the conformation of sdba. The layer has a (8210) net topology with Cd as nodes and dpap, sdba bridges as the connectors. The overall structure of {[Mn(dpap)(sdba)] · 1.5H2O}n (3) similar to that of 2 despite the presence of different metal ions. When dpap was replaced by bpp to react with Co(NO3)2 · 6H2O, another 1D coordination polymer, {[Co(bpp)(H2O)4] · sdba}n(4) was constructed. The 1D chains join sdba to make an overall 3D supramolecular architecture by hydrogen-bonding interactions (View the MathML sourceR24 (22),View the MathML sourceR24 (12)). The Cd coordination polymers exhibit strong solid-state luminescence emission at room temperature. Thermal stability of these crystalline materials has been explored by thermogravimetric analysis of mass loss.