Reversible single-crystal to single-crystal transformations in a Hg(ii) derivative. 1D-polymeric chain ⇌ 2D-networking as a function of temperature

Abstract

Reactions of HgX₂ (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(μ-X)₂(hep-H)]_∞, 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 –(CH₂)₂OH 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(μ₃-Cl)(hep-H)Cl]₂ units, which are covalently linked with the upper and lower layers of [–(μ-Cl)₂–Hg–(μ-Cl)₂–Hg(μ-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.