Four one-dimensional (1D) mercury(II) halide coordination polymers have been synthesized by using a semi-rigid N-donor ligand, 2,2'-(1,4-phenylene)-bis(N-(pyridin-3-yl)acetamide) (1,4-pbpa). While [Hg(1,4-pbpa)Cl₂·CH₃OH]n, 1, forms a sinusoidal chain, the complexes [Hg(1,4-pbpa)X₂]n (X = Cl, 2; Br, 3; I, 4) are helical. The sinusoidal 1 undergoes reversible structural transformation with helical 2 upon removal and uptake of CH₃OH, which was accompanied with the conformation adjustment of the 1,4-pbpa ligand from trans anti-anti to trans syn-anti. Pyridyl ring rotation of the 1,4-pbpa ligand that results in the change of the ligand conformation is proposed for the initiation of the structural transformation.
Keywords: bis-pyridyl-bis-amide; coordination polymer; mercury halide; structural transformation.