d10-Metal coordination polymers based on analogue di(pyridyl)imidazole derivatives and 4,4′-oxydibenzoic acid: influence of flexible and angular characters of neutral ligands on structural diversity

Abstract

A series of mixed-ligand coordination complexes, namely [Zn(L¹)(oba)] (1), [Cd(L¹)(oba)] (2), [Zn₂(L²)(oba)₂]·8H₂O (3), [Cd₂(L²)(oba)₂]·2H₂O (4), [Zn₃(L³)(oba)₃] (5), [Cd₂(L³)(oba)₂]·(L³) (6), [Cd(L⁴)(oba)]·H₂O (7) and [Cd(L⁵)(oba)]·3H₂O (8), where L¹ = 2-(2-pyridyl)imidazole, L² = 1,4-bis[2-(2-pyridyl)imidazol-1-yl]butane, L³ = 1,4-bis[2-(2-pyridyl)imidazol-1-ylmethyl]benzene, L⁴ = 1,3-bis[2-(2-pyridyl)imidazol-1-ylmethyl]benzene, L⁵ = 1,2-bis[2-(2-pyridyl)imidazol-1-ylmethyl]benzene and H₂oba = 4,4′-oxydibenzoic acid, have been synthesized under hydrothermal conditions. Their structures have been determined by single crystal X-ray diffraction analyses and further characterized by elemental analyses, IR spectra, and thermogravimetric (TG) analyses. In compounds 1 and 2, oba²⁻, L¹ ligand and Zn^II or Cd^II ions assemble to form the parallel chains or parallel sheets which are linked by the weak hydrogen bonding and π⋯π stacking interactions to give the 2D supramolecular sheet or 3D supramolecular net, respectively. For 3, L² ligands connect [Zn(oba)] chains to generate a unusual (10,3)-b topological structure which is the first example for eight-fold interpenetrating framework based on the (10,3)-b net. In 4, L² ligands link [Cd(oba)] double-chains to give a 2D sheet which is assembled by π⋯π stacking interactions to obtain a 3D supramolecular net. In 5, L³ ligands link Zn^II ions from α-Po net formed by Zn^II ions and oba²⁻ anions to show a novel 3D 8-connected self-penetrating framework with the unreported (4¹⁶·6¹¹·8) topological structure. In 6, the double-chains constructed by Cd^II and oba²⁻ anions are linked by one kind of L³ ligand to form a layer-like structure which is assembled by π⋯π stacking interactions to show a 3D supramolecular structure. In 7, oba²⁻ anions coordinate to Cd^II cations to form chains which are connected by L⁴ to form a four-fold interpenetrating diamond network. In 8, the weak hydrogen bonding and π⋯π stacking interactions connect the [Cd(L⁵)(oba)] chains to give a 2D supramolecular sheet. By careful inspections of the structures of 1–8, we believe that the different flexible and angular neutral ligands, coordination geometries of metal centers and weak interactions (hydrogen bonds and π⋯π stacking interactions) are crucial factors for the formation of the different structures. The photoluminescent properties of 1–8 have been studied in the solid state at room temperature.