A novel two-dimensional metal-organic supramolecular framework including π-π stacking and hydrogen-bond interactions

[μ-N,N'-Bis(pyridin-3-yl)benzene-1,4-dicarboxamide-1:2κ(2)N:N']bis{[N,N'-bis(pyridin-3-yl)benzene-1,4-dicarboxamide-κN]diiodidomercury(II)}, [Hg2I4(C18H14N4O2)3], is an S-shaped dinuclear molecule, composed of two HgI2 units and three N,N'-bis(pyridin-3-yl)benzene-1,4-dicarboxamide (L) ligands. The central L ligand is centrosymmetric and coordinated to two Hg(II) cations via two pyridine N atoms, in a syn-syn conformation. The two terminal L ligands are monodentate, with one uncoordinated pyridine N atom, and each adopts a syn-anti conformation. The HgI2 units show highly distorted tetrahedral (sawhorse) geometry, as the Hg(II) centres lie only 0.34 (2) or 0.32 (2) Å from the planes defined by the I and pyridine N atoms. Supramolecular interactions, thermal stability and solid-state luminescence properties were also measured.