Porous Coordination Polymer with Flexibility Imparted by Coordinatively Changeable Lithium Ions on the Pore Surface.

Solvothermal reactions of equimolar zinc acetate, lithium acetate, and 1,3,5-benzenelricarboxylic acid (H3btc) in different mixed solvents yielded isostnictural three-dimensional frameworks [UZn(btc)()) - IG leG and IG denote coordinated and lattice guests, respectively; cG=(nmp)0.5(H2O)0.5, IG=(EtOH)0.5 (1a); cG=H2O, IG= EtOH (1b); nmp=N-methyl-2-pyrrolidone] with one-dimensional channels occupied by guest molecules and solvent-coordinated, extrusive Li+ ions. Thermogravimetry analyses and powder X-ray diffraction measurements revealed that both la and lb can lose all lattice and coordinated guests to torn', a desolvaled phase [LiZn(btc)] (MCF-27, 1) and almost retains the original framework structure. Gas adsorption measurements on 1 confirmed its permanent porosity but suggested a structural transformation horn 1a/1b 101.11 is noteworthy that only la can undergo a single-ctystal 10 single-crystal (SCSC) transformation into 1 upon desolvation. The crystal structure of 1 revealed that Ihe Li+ ions were retracted into the channel walls via complementary coordination to the carboxylate oxygen atoms in the framework rather than being exposed on the pore surface. Single-crystal X-ray diffraction analyses were also performed for N2- and CO2-loaded samples of 1, revealing that the framework remained unchanged when the gases were adsorbed. Although the gas molecules could not be modeled, the residue electrons inside the channels demonstrated that the retracted Li+ ions still behave as the primary interacting site for CO2 molecules. Nevertheless, solvent molecules such as H2O can readily compete with the framework oxygen atom to retrieve the extrusive Li+ ions, accompanying the reverse structural transformation, i.e., from 1 to 1a/1b. [ABSTRACT FROM AUTHOR]