Honeycomb-shaped coordination polymers based on the self-assembly of long flexible ligands and alkaline-earth ions

• Two isomorphous and isostructural coordination polymers based on flexible ligand and two alkaline-earth metal salts have been synthesized and characterized.
• Structural analysis indicates that I and II are assembled into 3D porous honeycomb-shaped metal-organic frameworks.
• Both I and II display stronger fluorescence emissions and higher thermal stability.

Two novel coordination polymers, namely, [Ca(NCP)2]∞ (I) and [Sr(NCP)2]∞ (II) were synthesized under hydrothermal conditions based on 2-(4-carboxyphenyl)imidazo(4,5-f)-(1,10)phenanthroline (HNCP) and characterized by elemental analysis, infrared spectrometry, X-ray powder diffraction and single crystal X-ray diffraction. Findings indicate that I and II are isomorphous and isostructural, containing the unit of M(NCP−)4 (M=Ca(II) and Sr(II)), based on which to assemble into three-dimensional (3D) porous 4-fold interpenetration honeycomb-shaped neutral coordination polymers (CPs). Between the adjacent lamellar structures in I and II, there exist π–π interactions between the pyridine rings belonging to phenanthroline of NCP− which stabilize the frameworks. Both I and II display stronger fluorescence emissions as well as high thermal stability.

One-dimensional nanotubular channels with the cross dimension of 37.1959(20)×23.6141(11)Å2 in the three-dimensional honeycomb-shaped coordination network of II are observed. The topological analysis of II indicates that there exists a typical diamond framework possessing large adamantanoid cages, which containing four cyclohexane-shaped patterns in chair conformations.Figure optionsDownload as PowerPoint slide