Structure, Spectroscopic Properties, and Reversible Solid-to-Solid Reactions of Metal Complexes of 5-Nitro-pyrimidin-2-olate

In searching for coordination polymers containing the highly polarized 5-nitro-pyrimidin-2-olate ligand (NP), a number
of species containing 3d transition metals have been prepared and characterized, namely Co(NP)2(H2O)4, [Co(NP)2]n, Ni(NP)2(H2O)4, [Ni(NP)2]x, and [Zn(NP)2]n. Their structures have been determined by X-ray powder diffraction
methods. The hydrated compounds contain mononuclear M(NP)2(H2O)4 units interconnected by means of a three-dimensional (3D) network of hydrogen bonds. The homoleptic species, at variance from the already known metal(II) pyrimidin-2-olate ones, crystallize as two-dimensional (2D) slabs, where the metal coordination is of the MN3O
kind. The electron-withdrawing nitro group, never bound to the metal ion, is likely to influence the observed
stereochemistry through steric and dipolar effects within the crystal lattice. The thermal, spectroscopic, and magnetic
properties of these species are presented. The M(NP)2(H2O)4/[M(NP)2]x,n systems interconvert reversibly upon
dehydration/rehydration processes.