Two novel lead(ii) carboxyphosphonates with a layered and a 3D framework structure: syntheses, crystal structures, reversible dehydration/hydration, and luminescence properties

Abstract

Two novel lead(II) carboxyphosphonates with a layered and a 3D framework structure, namely, [Pb₂Cl₃(H₂L)]·H₂O (1) and [Pb₂(HL)(HBTC)] (2) (H₃L = H₂O₃PCH₂–NC₅H₉–COOH, H₃BTC = 1,3,5-benzenetricarboxylic acid), have been synthesized under hydrothermal conditions and structurally characterized. For compound 1, the interconnection of Pb(1)O₂Cl₃, Pb(2)O₂Cl₃, and CPO₃ polyhedra via corner- and edge-sharing forms a 1D chain. The adjacent chains connect with each other by sharing the chloride anion, thereby generating a 2D layered structure in the ab-plane. The lattice water molecules are located between adjacent layers. Compound 2 exhibits a 3D pillared-layered structure. The Pb(1)O₅, Pb(2)O₅, and CPO₃ polyhedra are interconnected into a 1D double chain via corner- and edge-sharing, which is further linked to adjacent chains through carboxyphosphonate ligands to form a 2D double layer structure. Neighboring double layers are bridged through the second linkers HBTC²⁻, leading to a 3D pillared-layered structure with a 1D channel system along the a-axis. An interesting feature of compound 1 is the presence of the dehydration/hydration properties. It is worth noting that compound 2 can be stable up to a high temperature. The luminescent properties of compounds 1 and 2 have also been studied.