Anion Influence on the Structures of a Series of Copper(II) Metal−Organic Frameworks

The main aim of the work herein presented is to investigate the influence of different anions on the overall structure
of a series of metal−organic frameworks. The reactions between CuCl2, Cu(OAc)2, and CuSO4 and the two
bipyridylurea ligands L1 and L2 [L1 = 1,3-bis(pyridin-4-ylmethyl)urea; L2 = 1,3-bis(pyridin-3-ylmethyl)urea; see
Scheme in paper] have been carried out and the crystal structure of five of the resulting metal−organic assemblies
determined. These crystal structures have shown that the geometry and size of the corresponding anions together
with their coordinating and hydrogen-bonding properties are essential in determining the final structures of the
assemblies. Particularly interesting, because of their potential as nanoporous materials, are the assemblies obtained
from the reaction between each of the two ligands (L1 and L2) and CuCl2, which yield noninterpenetrating 2D
metal−organic layers made of squares of ca. 15 × 15 Å. These layers stack on top of each other, producing infinite
3D channels filled with solvent molecules. The thermal stabilities of the five metal−organic frameworks prepared
have been studied by means of thermogravimetric analysis. Preliminary X-ray powder diffraction studies of one of
these metal−organic frameworks indicate that upon heating the assembly changes to a different crystalline structure.
Interestingly, the original structure reforms upon exposure of this sample to traces of water.