Crystal structures of two nickel compounds comprising neutral Ni hydrazone complexes and di-carb-oxy-lic acids.

Two isostructural Ni compounds, bis-{-[1-(pyridin-2-yl-κ)eth-ylidene]pyridine-4-carbohydrazonato-κ',}nickel(II)-2,5-di-chloro-terephthalic acid (1/1), Ni(CHNO), and bis-{-[1-(pyridin-2-yl-κ)eth-ylidene]pyridine-4-carbohydrazonato-κ',}nickel(II)-2,5-di-bromo-terephthalic acid (1/1), Ni(CHNO), were synthesized and their crystal structures determined. The pair of ,',-tridentate -[1-(pyridin-2-yl-κ)eth-yl]pyridine-4-carbohydrazonate ligands result in a -NiON octa-hedral coordination sphere for the metal ions. The asymmetric units consist of two half-mol-ecules of the di-carb-oxy-lic acids, which are completed by crystallographic inversion symmetry. In the respective crystals, the 2,5-di-chloro-terephthalic acid (HClTPA, ) mol-ecules form zigzag hydrogen-bonded chains with the [Ni()] mol-ecules, with the hydrogen-bond distances in slightly longer than those in . The packing is consolidated by aromatic π-π stacking between the di-carb-oxy-lic acid mol-ecules and terminal pyridine rings in [Ni()] and short halogen-halogen inter-actions are also observed. The qualitative prediction of the H-atom position from the C-N-C angles of the terminal pyridine rings in and the C-O distances in the carboxyl groups show that and are co-crystals rather than salts.