Crystal engineering of metal-organic frameworks containing amide functionalities: Studies on network recognition, transformations, and exchange dynamics of guests and anions

The reactions of bis(pyridinecarboxamido)alkanes with copper(II) in the presence of various anions and solvent systems afforded several polymeric crystalline complexes with or without guest inclusion. The crystal structure analyses of these complexes reveal that the coordination networks observed here include open one-dimensional (1D) chains containing cavities and open (4,4)-networks with three types of packing modes, namely, mixed, offset-offset, and trigonal, doubly interpenetrated (4,4)-networks both in parallel and in perpendicular (diagonal/diagonal) modes and a three-dimensional pseudo-diamondoid (6(5)8-topology) network. The self-complementary amide groups of the ligands assembled these coordination networks into higher dimensional architectures via N-H center dot center dot center dot O hydrogen bonds. The exchange of counteranions from the polymeric crystalline complexes was found to trigger the network transformations. The 1D chain, which has rectangular cavities, was transformed into a pseudo-diamondoid network upon exchange of ClO4- with PF6- anions. The exchange of anions from two-dimensional (2D) open (4,4)-networks resulted in 2D-interpenetrated networks. It was found that the reverse exchange that is expected to result in open networks from interpenetrated networks is not allowed. The guest molecules included in these networks range from small molecules such as H2O, EtOH, and CHCl3 to big aromatic molecules such as nitrobenzene, toluene, anisole, p-xylene, benzonitrile, and naphthalene. The exchange of guest molecules in crystal-to-crystal fashion was also found to trigger the transformations in the mode of packing of 2D layers.