Self-assembly of silver(i) coordination polymers with novel layered open network structures based on a flexible double betaine ligand

Abstract

Three coordination polymers, [Ag₄(L¹)₂(NO₃)₄]·H₂O (1), [Ag(L¹)](BF₄)·2H₂O (2) and [Ag₂(L¹)(H₂O)](ClO₄)₂ (3), were obtained from self-assembly of AgX (X = NO₃⁻, BF₄⁻, or ClO₄⁻) with a new flexible double betaine L¹ (L¹ = 1,3-bis(pyridinio-4-carboxylato)propane). Single crystal X-ray diffraction studies for complexes 1–3 reveal layered open network structures containing novel cavities and channels. Complex 1 consists of an unprecedented rhombic tetrameric Ag₄O₂ subunit, in which a μ₃-η¹ coordination mode of the carboxylate group is found for the first time among silver(I) carboxylates. Complex 2 is constructed from a bis(carboxylate-O,O′)-bridged centrosymmetric dimeric subunit, in which the coordination sphere of each silver(I) atom is completed by a monodentate carboxylate group at each axial site. In complex 3, the [Ag₂(carboxylate-O,O′)₂] dimeric subunits are extended into a polymeric chain through the linkage of each metal centre to carboxylate groups of an adjacent dimer, and such infinite chains are extended into a plane wave-like layer structure by the cross-linkage of the molecular skeletons of the flexible double betaine ligands.