Mercury(II) metal–organic coordination polymers with pyrazine derivatives

Abstract

Eight mercury coordination polymers of the three pyrazine ligands 2,6- and 2,5-dimethylpyrazine and pyrazine itself {2,5-dmpyr, 2,6-dmpyr, and pyr, respectively} were prepared from reactions with mercury(II) chloride, bromide, iodide and thiocyanate under thermal gradient conditions using the branched tube method and by simple solvent evaporation from the reactant mixtures. All eight compounds, namely [Hg(µ-pyr)(µ-Br)₂]_n (1), [Hg₂(µ-pyr)(µ-I)₂I₂]_n (2), [Hg(µ-pyr)(µ-SCN)₂]_n (3), [Hg₂(µ-2,5-dmpyr)(µ-Cl)₄]_n (4), [Hg₂(µ-2,5-dmpyr)(µ-Br)₄]_n (5), [Hg₂(µ-2,5-dmpyr)(µ-SCN)₂(SCN)₂]_n (6), [Hg(2,6-dmpyr)(µ-Br)₂]_n (7) and [Hg(µ-2,6-dmpyr)(µ-SCN)₂]_n (8), were structurally characterized by single-crystal X-ray diffraction. The results indicate that the substitution pattern of the pyrazine derivatives and the counter ions play important roles in the framework formation of the mercury(II) polymers and reveal that there are two general types of mercury(II) pyrazine derivatives: coordination complexes with HgX₂L stoichiometry with usually no holes, and (HgX₂)₂L complexes with one or two holes or vacant sites at the mercury atoms. X-Ray powder diffraction patterns and thermal properties of compounds 1–8 are discussed.