Syntheses and crystal structures of <i>catena</i> -poly[[diiodidozinc(II)]-μ-2,3-dimethylpyrazine-κ ² <i>N</i> ¹ : <i>N</i> ⁴ ] and aqua(2,3-dimethylpyrazine-κ <i>N</i> )diiodidozinc(II)–2,3-dimethylpyrazine–water (2/

The reaction of zinc iodide with 2,3-di-methyl-pyrazine (C₆H₈N₂) in ethanol leads to the formation of [ZnI₂(C₆H₈N₂)] _<i>n</i> (<b>1</b>), that according to powder X-ray diffraction was obtained as a pure phase. When the same reaction was performed in a mixture of ethanol and water as solvent, a few crystals of [ZnI₂(C₆H₈N₂)(H₂O)]·0.5C₆H₈N₂·0.5H₂O (<b>2</b>) were serendipitiously obtained in a mixture with compound <b>1</b> as the major phase. The asymmetric unit of <b>1</b> consists of one zinc cation, two crystallographically independent iodide anions and one 2,3-di-methyl-pyrazine ligand all of them located in general positions. In the extended structure, the Zn cations are tetra-hedrally coordinated by two iodide anions and two symmetry-related 2,3-di-methyl-pyrazine ligands and are linked by bridging 2,3-di-methyl-pyrazine ligands into helical chains that proceed along the <i>c</i>-axis direction in the uncommon space group <i>P</i>3₂. Within these chains, intra-chain C-H⋯I hydrogen bonding is observed. The asymmetric unit of <b>2</b> consists of two crystallographically independent [ZnI₂(C₆H₈N₂)(H₂O)] complexes as well as one water mol-ecule and one none-coordinating 2,3-di-methyl-pyrazine ligand. In the complexes, the Zn cations are tetra-hedrally coordinated by two iodide anions, one 2,3-di-methyl-pyrazine ligand and one water mol-ecule. These complexes are packed in such a way that cavities are formed, which are filled by water and 2,3-di-methyl-pyrazine solvate mol-ecules that are hydrogen bonded to each other.