Ab initio X-ray powder diffraction structural analyses from laboratory data have been widely employed in the characterization of coordination polymers not affording single crystals of suitable quality to undergo conventional structural determinations. This is particularly true for coordination polymers built upon strong ligand-to-metal bonds, as those formed by anionic, nitrogen-based heterocycles - pyrazolates, imidazolates, pyrimidinolates and more complex moieties derived therefrom. More than one hundred species belonging to this class have been structurally characterized in the last three decades, affording key, otherwise inaccessible stereochemical and supramolecolar features. This contribution summarizes our most recent experience in the XRPD structural characterization of pyrazolato-based coordination polymers, devoting a special consideration to the methodologies and tricks which allowed us to juxtapose the structural description of these materials to their physico-chemical and, above all, functional properties.

Structures of [Cd(C2H8N2)Cl2]n(1) and [Cd(C2H8N2)Br2]n(2) were solved from powder diffraction data. Compound (1) crystallizes in the space group Pbam (No. 55), a = 9.9021(7) Å, b = 7.8186(6) Å, c = 4.0705(3) Å, V = 315.13(3) Å3, Z = 2. (2) is isostructural: space group Pbam (No. 55), a = 10.405(2) Å, b = 7.8634(8) Å, c = 4.2079(5) Å, V = 344.28(6) Å3, Z = 2. The investigated compounds are examples of two-dimensional hybrid coordination polymers, in which neighboring metal centers are bridged via both organic and inorganic moieties: ethylenediamine molecules and halide anions. Both crystal structures were solved ab initio from powder data using direct methods.