Synthesis of a New Copper-Azobenzene Dicarboxylate Framework in the Form of Hierarchical Bulk Solids and Thin Films without and with Patterning

Reaction of copper(II) acetate with azobenzene-4,4′-dicarboxylic acid results in the formation of a metal–organic framework with the unexpected stoichiometry of Cu(II):ligand of 2:1. The bulk synthesis results in microspheres assembled from either nanobricks or nanoflakes, depending on the ratio of the reactants in solution. While the former behaves like a bulk solid with clear reflections in the X-ray and electron diffraction experiments, the latter obviously is dominated by surface effects, with a significant fraction of slightly expanded elemental cells and a significantly increased outer surface area. The material could also be deposited on a variety of surfaces using a stepwise layer-by-layer growth, permitting the observation of the changes in composition at each of the deposition steps. The orientation of the crystallites could be influenced by the choice of surface functionalities and their order. When the surfaces became chemically patterned, in this case by microcontact printing (μCP), the deposits could be localized, with the nucleation/growth rate being the determining factor for the preferred growth sites.