Syntheses and crystal structures of catena-poly[[di-iodido-zinc(II)]-μ-2,3-di-methyl-pyrazine-κ2 N 1:N 4] and aqua-(2,3-di-methyl-pyrazine-κN)di-iodidozinc(II)-2,3-di-methyl-pyrazine-water (2/1/1).

The reaction of zinc iodide with 2,3-di-methyl-pyrazine (C6H8N2) in ethanol leads to the formation of [ZnI2(C6H8N2)] n (1), 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 (2) were serendipitiously obtained in a mixture with compound 1 as the major phase. The asymmetric unit of 1 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 c-axis direction in the uncommon space group P32. Within these chains, intra-chain C-H⋯I hydrogen bonding is observed. The asymmetric unit of 2 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.