Temperature-dependent guest-driven single-crystal-to-single-crystal ligand exchange in a two-fold interpenetrated Cd(II) grid network.

A doubly interpenetrated square-grid coordination polymer {[Cd(ImBNN)(2)(CF(3)SO(3))(2)])guest}(n) (1) (guest = C(7)H(8) and ImBNN = 2,5-bis[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 Cd(CF(3)SO(3))(2). The framework 1 shows dynamism in either temperature-dependent 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 single-crystal-to-single-crystal structural transformations: complex 1 lost toluene guests and captured water molecules to give guest-free 1 b via a proposed metastable phase 1 a, and 1 b 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(3)SO(3)(-) anion-shifting. In contrast, direct heating of 1 in the absence of a vacuum resulted in thermostable 1 c, 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.