Alkali Metal Cation (K+, Cs+) Induced Dissolution/Reorganization of Porous Metal Carboxylate Coordination Networks in Water

Porous metal-organic coordination networks (MOCNs) {A(2)[M-3(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) with nearly identical structural features were hydrothermally prepared. These compounds adopt (4,8)-connected scu nets but exhibit subtle differences in the topology of the final three-dimensional architectures. Compound 1 has a regular net with the largest solvent void (21.1 %), while the nets of the other three (2-4) are slightly distorted from a regular shape and have malformed pores with smaller solvent voids (5.4-11.4%). Likely, the different supramolecular environments among 1-4 subtly depend on the eight-connected binodal cubical vertices/four-connected square-planar connectivity between the trimetallic clusters and the btec ligands. Cobalt species 3 dissolved in an aqueous solution of KCl, and then reorganized to form 1 at ambient temperature. Interestingly, under similar conditions, 1 dissolved and then was regenerated to give the same structure. Nickel species 2 and 4 also underwent a dissolution/reorganization process in an aqueous solution of KCl to afford new metal-carboxylate product {K-2[Ni-3(btec)(2)(H2O)(4)]}(n) (2'). This compound forms a (4,8)-connected scu net with regular pores, which is isostructural and isomorphous with 1. and is a supramolecular isomer of 2. Similarly, in an aqueous solution of CsCl, 1-4 were converted to ID zigzag chain structures {Cs-2[M(btec)(H2O)(4)]}(n) (5, M=Co; 6, M=Ni) that enlarged to hydrogen-bonded 3D porous supramolecular networks. Remarkable, reversible alkali metal cation induced structural transformations between I and 5 occurred via dissolution/reorganization processes. Thermogravimetric analyses showed that these metal-carboxylate species have high thermal stability (T>300 degrees C).