Description:
<jats:p>Two isostructural Ni<jats:sup>II</jats:sup>compounds, bis{<jats:italic>N</jats:italic>-[1-(pyridin-2-yl-κ<jats:italic>N</jats:italic>)ethylidene]pyridine-4-carbohydrazonato-κ<jats:sup>2</jats:sup><jats:italic>N</jats:italic>′,<jats:italic>O</jats:italic>}nickel(II)–2,5-dichloroterephthalic acid (1/1), [Ni(C<jats:sub>13</jats:sub>H<jats:sub>11</jats:sub>N<jats:sub>4</jats:sub>O)<jats:sub>2</jats:sub>](C<jats:sub>8</jats:sub>H<jats:sub>4</jats:sub>Cl<jats:sub>2</jats:sub>O<jats:sub>4</jats:sub>), and bis{<jats:italic>N</jats:italic>-[1-(pyridin-2-yl-κ<jats:italic>N</jats:italic>)ethylidene]pyridine-4-carbohydrazonato-κ<jats:sup>2</jats:sup><jats:italic>N</jats:italic>′,<jats:italic>O</jats:italic>}nickel(II)–2,5-dibromoterephthalic acid (1/1), [Ni(C<jats:sub>13</jats:sub>H<jats:sub>11</jats:sub>N<jats:sub>4</jats:sub>O)<jats:sub>2</jats:sub>](C<jats:sub>8</jats:sub>H<jats:sub>4</jats:sub>Br<jats:sub>2</jats:sub>O<jats:sub>4</jats:sub>), were synthesized and their crystal structures determined. The pair of<jats:italic>N</jats:italic>,<jats:italic>N</jats:italic>′,<jats:italic>O</jats:italic>-tridentate<jats:italic>N</jats:italic>-[1-(pyridin-2-yl-κ<jats:italic>N</jats:italic>)ethyl]pyridine-4-carbohydrazonate<jats:italic>L</jats:italic>ligands result in a<jats:italic>cis</jats:italic>-NiO<jats:sub>2</jats:sub>N<jats:sub>4</jats:sub>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 (H<jats:sub>2</jats:sub>Cl<jats:sub>2</jats:sub>TPA,<jats:bold>1-Cl</jats:bold>) molecules form zigzag hydrogen-bonded chains with the [Ni(<jats:italic>L</jats:italic>)<jats:sub>2</jats:sub>] molecules, with the hydrogen-bond distances in<jats:bold>1-Br</jats:bold>slightly longer than those in<jats:bold>1-Cl</jats:bold>. The packing is consolidated by aromatic π–π stacking between the dicarboxylic acid molecules and terminal pyridine rings in [Ni(<jats:italic>L</jats:italic>)<jats:sub>2</jats:sub>] 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<jats:italic>L</jats:italic>and the C—O distances in the carboxyl groups show that<jats:bold>1-Cl</jats:bold>and<jats:bold>1-Br</jats:bold>are co-crystals rather than salts.</jats:p>