New interpenetrated copper coordination polymer frameworks having porous properties

Abstract

Two new 3-fold interpenetrated 3D microporous metal-organic coordination polymers (MOCPs) of Cu(II), [Cu₃(bipy)_1.5(2,6-ndc)₃]_n (1) and {[Cu(bpe)_0.5(2,6-ndc)]·0.5H₂O}_n (2) (bipy = 4,4′-bipyridine; bpe = 1,2-bis(4-pyridyl)ethane; and 2,6-ndc = 2,6-naphthalenedicarboxylate), have been synthesized using a mixed-ligand system and structurally characterized by single-crystal X-ray diffraction study. Room-temperature reaction of Cu(II) with bipy and 2,6-ndc affords 1, whereas reaction with bpe and 2,6-ndc yields 2. Structure determination reveals that in both cases, a 2D square grid made by Cu(II) and 2,6-ndc with the aid of Cu₂(CO₂)₄ paddlewheel building block is connected by bipy (1) or bpe (2) organic pillar results 3D Α-polonium type frameworks. Framework 1 is rigid and robust without any guest molecules, whereas 2 is flexible, realized by the guest induced structural transformations. Both the frameworks show high thermal stability. Framework 1 and dehydrated form of 2, i.e 2′ contains 16.6% and 21.4% void space, respectively and Langmuir surface area calculated from nitrogen adsorption study for 1 and 2′ is 113.0 and 337.5 m²/g, respectively. Both the frameworks can store approximately 1 wt % of molecular hydrogen at 77 K and 15 bar, in particular, the density of adsorbed hydrogen in 1 is one of the highest reported so far in porous MOCPs. Compounds 1 and 2′ can also store 11.0 and 13.2 wt % carbon dioxide at 195 K.