Temperature-Dependent Guest-Driven Single-Crystal-to-Single-Crystal Ligand Exchange in a Two-Fold Interpenetrated CdII Grid Network

摘要

A doubly interpenetrated square-grid coordination polymer {[Cd-ACHTUNGTRENUNG(ImBNN)_2ACHTUNGTRENUNG(CF_3SO_3)_2]guest}_n (1) (guest=C_7H_8 and ImBNN=2,5-bisACHTUNGTRENUNG[4’- (imidazol-1-yl)phenyl]-3,4-diaza-2,4- hexadiene) that contains cavities able to accommodate toluene guest molecules has been assembled by the reaction of the Schiff base ligand ImBNN and CdACHTUNGTRENUNG(CF_3SO_3)_2. The framework 1 shows dynamism in either temperaturedependent expansion and shrinkage or cooperatively temperature-dependent guest-driven ligand exchange at the metal center. Studies of guest removal/ uptake by heating in a vacuum, cooling in air, and then heating in toluene at reflux have revealed a series of singlecrystal- to-single-crystal structural transformations: complex 1 lost toluene guests and captured water molecules to give guest-free 1b via a proposed metastable phase 1a, and 1b could readsorb toluene guests to give 1’, which represents a restored 1. These structural changes establish an indirect recoverable process that involves ligand exchange in the coordination sphere and guest exchange in the cavity accompanied by the cleavage/formation of Cd-O bonds and CF_3SO_3- anion-shifting. In contrast, direct heating of 1 in theabsence of a vacuum resulted in thermostable 1c, confirmed by X-ray powder diffraction as a new phase that could not be converted back into 1 and that had lost the ability of readsorbing toluene guests.