Temperature-Dependent Supramolecular Isomeric Zn(II)-Metal–Organic Frameworks and Their Guest Exchange

A pair of three-dimensional metal–organic framework supramolecular isomers (1a and 2a) prepared from the solvothermal reactions of Zn(NO3)2·4H2O, 1,4-bis(4-pyridyl)piperazine (bpp), and 4,4′-oxybis(benzoic acid) (H2obc) in different temperatures was structurally elucidated, and a series of guest exchanges on these isomers were performed without the loss of single crystallinity. At 110 and 130 °C in DMF/H2O, an 8-fold [4 + 4] interpenetrated coordination polymer {[Zn(bpp)(obc)]·3H2O}n (1a) with sra topology and a self-penetrated coordination polymer {[Zn3(bpp)3(obc)3]·2DMF·4H2O}n (2a) with a new topology were isolated, respectively. In the guest-exchange experiments, water molecules in isomer 1a were displaced by acetone and ethylene glycol molecules, while dimethylformamide molecules in isomer 2a were replaced by acetone and ethylene glycol as well as bulkier diethylene glycol due to its larger void. Photoluminescence properties of two isomers and their guest-exchanged products were also measured and discussed.