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 (R24 (22),R24 (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.

Graphical abstractFour new coordination networks based on dipyridyl linking units 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. Two polymers of Cd(II), [Cd(dpap)(mal)]n (1) and {[Cd(dpap)(sdba)] · 2H2O}n (2) exhibit different topology due to different dicarboxylate anions. The overall structure of {Mn(dpap)(sdba) · 1.5H2O}n (3) is 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. These results evidently indicate that the nature of ligands and dicarboxylates are significant in the construction of the structures, which are also well regulated by the metal centers.Figure optionsDownload full-size imageDownload as PowerPoint slide