Crystal structures of two nickel compounds comprising neutral NiII hydrazone complexes and dicarboxylic acids

Abstract

Two isostructural NiII compounds, bis{N-[1-(pyridin-2-yl-κN)ethylidene]pyridine-4-carbohydrazonato-κ2 N′,O}nickel(II)-2,5-dichloroterephthalic acid (1/1), [Ni(C13H11N4O)2](C8H4Cl2O4), and bis{N-[1-(pyridin-2-yl-κN)ethylidene]pyridine-4-carbohydrazonato-κ2 N′,O}nickel(II)-2,5-dibromoterephthalic acid (1/1), [Ni(C13H11N4O)2](C8H4Br2O4), were synthesized and their crystal structures determined. The pair of N,N′,O-tridentate N-[1-(pyridin-2-yl-κN)ethyl]pyridine-4-carbohydrazonate L ligands result in a cis-NiO2N4 octahedral coordination sphere for the metal ions. The asymmetric units consist of two half-molecules of the dicarboxylic acids, which are completed by crystallographic inversion symmetry. In the respective crystals, the 2,5-dichloroterephthalic acid (H2Cl2TPA, 1-Cl) molecules form zigzag hydrogen-bonded chains with the [Ni(L)2] molecules, with the hydrogen-bond distances in 1-Br slightly longer than those in 1-Cl. The packing is consolidated by aromatic π-π stacking between the dicarboxylic acid molecules and terminal pyridine rings in [Ni(L)2] and short halogen-halogen interactions are also observed. The qualitative prediction of the H-atom position from the C - N - C angles of the terminal pyridine rings in L and the C - O distances in the carboxyl groups show that 1-Cl and 1-Br are co-crystals rather than salts.