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

Two isostructural NiIIcompounds, bis{N-[1-(pyridin-2-yl-κN)ethylidene]pyridine-4-carbohydrazonato-κ2N′,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-κ2N′,O}nickel(II)–2,5-dibromoterephthalic acid (1/1), [Ni(C13H11N4O)2](C8H4Br2O4), were synthesized and their crystal structures determined. The pair ofN,N′,O-tridentateN-[1-(pyridin-2-yl-κN)ethyl]pyridine-4-carbohydrazonateLligands result in acis-NiO2N4octahedral 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 in1-Brslightly longer than those in1-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 inLand the C—O distances in the carboxyl groups show that1-Cland1-Brare co-crystals rather than salts.