Reversible dehydration process in a novel three-dimensional covalent network based on pyrimidine-4,6-dionato bridging ligand

The novel metal-organic polymer Zn(μ-pmdt)(H₂O)]_n (1) (pmdt = pyrimidine-4,6-dionate) exhibits an extended three-dimensional network with two crystallographically independent pmdt bridging ligands, one zinc(II) atom and a coordinated water molecule. The Zn(II) atoms are located at the centre of a distorted ZnN₂OOw tetrahedral chromophore. One of the pmdt ligands acts as tetradentate bridge linking four metal centers, while the other pmdt ligand shows a bidentate coordination mode bridging two metal centers. The compound shows a reversible dehydration process, involving a coordinated water molecule, to lead an amorphous anhydrous phase. This transition has been characterized by thermogravimetric and variable-temperature X-ray powder diffraction techniques.