Dissolution/Reorganization toward the Destruction/Construction of Porous Cobalt(II)− and Nickel(II)−Carboxylate Coordination Polymers

The alkali-metal-cation-induced structural transformation of porous coordination polymers (CPs), {A2[M3(btec)2(H2O)4]}n (1, A = K, M = Co; 2, A = K, M = Ni; 3, A = Cs, M = Co; and 4, A = Cs, M = Ni; btec = benzene-1,2,4,5-tetracarboxylate), occurred via a unique dissolution/reorganization process in the presence of an alkali chloride (LiCl, NaCl) in water. Treatment of 1 or 2 in an aqueous solution of LiCl resulted in the formation of new metal−carboxylate species [Co2(btec)(H2O)10]·H2O (5·H2O) and {Li2[Ni3(btec)2(H2O)10]·3.5H2O}n (6·3.5H2O), respectively. When NaCl was used in place of LiCl under similar reaction conditions, similar dissolution/reorganization processes were observed. The cobalt species 1 and 3 were converted into the metal−carboxylate product [Na2Co(btec)(H2O)8]n (7), whereas the nickel−carboxylate frameworks 2 and 4 were transformed into {[Na4Ni2(btec)2(H2O)18]·3H2O}n (8·3H2O). Single-crystal X-ray diffraction analysis revealed that 5·H2O is a discrete molecule, which extends to a hydrogen-bonded 3D porous supramolecular network including tetrameric water aggregates. Compound 6·3.5H2O adopts a 3D polymeric structure with a novel (2,4,4)-connected net on the basis of a 4-connecting organic node of a btec ligand, a square-planar 4-connecting metallic trans-Ni(O2C)4(H2O)2 node, and a 2-connecting octahedral metallic trans-Ni(O2C)2(H2O)4 hinge. Compound 7 possesses a 3D polymeric structure comprised of two types of intercrossed (4,4)-layers, a [CoII(btec)]-based layer and a [NaI(btec)]-based layer, in a nearly perpendicular orientation (ca. 87°). Compound 8·3H2O adopted a 2D sheet network by utilizing heterometallic trinuclear clusters of Na2Ni(O2C)5(H2O)9 as secondary building units. Each sheet is hydrogen-bonded to neighboring units, giving a 3D supramolecular network. It is noteworthy that the dissolution/reorganization process demonstrates the cleavage and reformation of metal−carboxylate bonds, leading to a destruction/construction structural transformation of CPs.