Coordination polymer based on Cu(ii), Co(ii) and 4,4′-bipyridine-2,6,2′,6′-tetracarboxylate: synthesis, structure and adsorption properties

Abstract

4,4′-Bipyridine-2,6,2′,6′-tetracarboxylic acid H₄L·3H₂O, (1) and its copper(II) and cobalt (II) coordination polymers [Cu₂L(H₂O)₄]²_n (2) and {[Co(H₂O)₆]·[Co₃L₂(H₂O)₂]·10H₂O}³_n (3) have been hydrothermally synthesized. Compound 1 packs into a crystal viaH-bonds. Complex 2 is a 2D coordination grid, in which Cu is in an elongated octahedral constructed by a mer-geometry pyridyl-2,6-dicarboxylate, one bridging carboxylate oxygen and two water molecules. The L⁴⁻ is central symmetrical. Each pyridyl-2,6-dicarboxylate chelete to Cu(II) and one carboxylate bridge Cu(II) ions in a 1,1-fashion. The 2D coordination polymer links to adjacent layers viaH-bonds. Complex 3 is a metal–organic framework with 11.6 × 10.5 Å rectangular channels. All Co(II) ions are located in an octahedral coordination environment. The rectangular channels are composed of Co²⁺-L⁴⁻ walls and the walls are linked through carboxylate oxygen atoms and Co(II) ions. Co(H₂O)₆²⁺ as counter ions fill in porous channel. The removal of water molecules from 3 at 210 °C or higher affords the porous material [Co₄L₂]_n, which can adsorb 16 (36%) methanol or 9 (32%) ethanol in the vapour phase. The porosity of 3 is higher than reported 4,4′-bipyridine-2,6,2′,6′- tetracarboxylate complexes. The framework of 3 remains but the crystallinity is lost upon removal of the H₂O molecules. The dehydrated framework of 3 partially recovery crystallinity after it adsorbs H₂O, CH₃OH and C₂H₅OH. The methanol in the framework can be replaced by H₂O reversibly.