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

Two novel coordination polymers, namely, [Ca(NCP)(2)](infinity) (I) and [Sr(NCP)(2)](infinity), (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 pi-pi 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. (C) 2015 Elsevier Inc. All rights reserved.