Reversible single-crystal to single-crystal transformations in a Hg(II) derivative. 1D-polymeric chain <=>2D-networking as a function of temperature.

Reactions of HgX(2) (X = Cl(-), Br(-), l(-)) with the ligand hep-H (hep-H = 2-(2-hydroxyethyl)pyridine) in methanol at 298 K result in 1D-polymeric chains of [(X)Hg(mu-X)(2)(hep-H)](infinity), 1-3, respectively, where hep-H binds to the Hg(ii) ions in a monodentate fashion exclusively with the pyridine nitrogen donor and the suitably ortho-positioned -(CH(2))(2)OH group of hep-H remains pendant. The packing diagrams of 1-3 exhibit extensive intramolecular and intermolecular hydrogen bonding interactions leading to hydrogen bonded 2D network arrangement in each case. Though the single crystal of either 2 (X = Br) or 3 (X = I) loses crystallinity upon heating, the single crystal of 1 selectively transforms to a 2D-polymeric network, 4 on heating at 383 K for 1.5 h. The polymeric 4 consists of central dimeric [Hg(mu(3)-Cl)(hep-H)Cl](2) units, which are covalently linked with the upper and lower layers of [-(mu-Cl)(2)-Hg-(mu-Cl)(2)-Hg(mu-Cl)(2)-](n). The packing diagram of 4 reveals the presence of O-H-Cl and C-H-Cl hydrogen bonding interactions which in effect yields hydrogen bonded 3D-network. Remarkably, the single crystals of 4 convert back to the single crystals of parent 1 on standing at 298 K for three days.