Solvent-Mediated Reversible Structural Transformation of Mercury Iodide Coordination Polymers: Role of Halide Anions

Solvothermal reactions of HgX2 with 2,2′-(1,2-phenylene)-bis­(N-pyridin-3-yl)­acetamide, L, in ethanol afforded [Hg­(L)­X2] n (X = Cl, 1; Br, 2; I, 3), which are isostructural one-dimensional (1D) zigzag chains, while layering reactions of a ethanoic solution of L with a methanoic solution and an acetonitrile solution of HgI2, respectively, gave 1D helical chains [Hg­(L)­I2·MeOH] n , 4, and [Hg­(L)­I2·MeCN] n , 5. In marked contrast to 1 and 2, the iodide-containing 3 is able to exhibit reversible structural transformation with 4 and 5 by adsorption and desorption of methanol and acetonitrile, suggesting the importance of N–H---X and Hg---X interactions in the evaluation of structural transformation. Moreover, complexes 4 and 5 exhibit reversible crystal to crystal transformation triggered by solvent exchange. Complexes 3–5 represent a unique example that the solvents show a significant effect on folding and unfolding of the HgI2 single-stranded helical coordination polymers.