Systematic Study on Zirconium Chelidamates: From a Molecular Complex to a M-HOF and a MOF.

We report the synthesis and in-depth characterization of three zirconium chelidamates, a molecular complex (HCN)[Zr(HL)] (), a porous metal-containing hydrogen-bonded organic framework (M-HOF) [Zr(HO)(HL)]·HO (), and a metal-organic framework (MOF) (HCN)[Zr(HL)]· solvent (0 ≤ ≤ 1) () using chelidamic acid (HL, HCNO, 4-hydroxypyridine-2,6-dicarboxylic acid) as the ligand (HCN = dimethylammonium). High-throughput investigations of the system Zr/HL/HCl/DMF/HO were carried out, which resulted in highly crystalline compounds. The crystal structures of and were determined by single-crystal X-ray diffraction. Single-crystal three-dimensional (3D) electron diffraction and Rietveld refinements of powder X-ray diffraction (PXRD) data had to be used to elucidate the crystal structure of since only very small single crystals of about 500 nm in diameter could be obtained. In all structures, chelidamate ions act as anionic palindromic pincer ligands, and in , a coordinative bond is additionally formed by the aryloxy group. While dense packing of the molecular complexes is found in , hydrogen bonding of the molecular complexes in leads to a porous network that shows flexibility depending on the water content. The three-dimensional framework structure of the Zr-MOF contains a mononuclear inorganic building unit (IBU), which is very uncommon in Zr-MOF chemistry. The three compounds are stable in several organic solvents, and thermal decomposition starts above 280 °C. While the hydrogen-bonded framework is only porous toward water with a water uptake of almost 3.75 mol mol at / = 0.9, is porous against N, CO, methanol, ethanol, and water with a specific Brunauer-Emmett-Teller (BET) surface area of = 410 m g derived from the N adsorption isotherm. Stability upon water adsorption covering 10 cycles between 0.5% < / < 90% for is also demonstrated.