Silver(i) pyrophosphonates: structural, photoluminescent and thermal expansion studies

Abstract

The solvothermal reactions of silver(I) salts with mono-organophosphonic acids, i.e.3-thienylphosphonic acid (3-TPA), phenylphosphonic acid (PPA), α-naphthylphosphonic acid (α-NPA) and cyclohexylphosphonic acid (CPA), yield four new silver(I) pyrophosphonates, namely: [Ag₂(ptp)] (1), [Ag₂(ppp)] (2), [Ag₃(CH₃CN)(pnp)(pnpH)] (3), and [Ag₃(pcp)(pcpH)] (4) [ptp²⁻ = pyro-3-thienylphosphonate, ppp²⁻ = pyrophenylphosphonate, pnp²⁻ = pyro-α-naphthylphosphonate, pcp²⁻ = pyrocyclohexylphosphoante]. In all cases, the pyrophosphonate ligands are generated in situ from their relative mono-organophosphonic acids, mediated by silver(I) ions. Single crystal structural determinations reveal that compounds 1 and 2 display two-dimensional layer architectures, while 3 and 4 show one-dimensional chain structures. Structure 1 can be best described as a layer made up of Ag₄O(P)₆ clusters linked by O–P–O units and Ag⋯Ag contacts, with the organic groups grafted on the two sides of the inorganic layer. A similar layer structure is found in 2 except that the Ag⋯Ag interactions are absent. Compound 3 shows a chain structure where the silver ions are bridged by the phosphonate oxygen atoms forming an infinite Ag–O(P) chain which is decorated by the pyrophosphonate ligand and CH₃CN. Compound 4 has another type of chain structure made up of Ag–O(P) with extensive Ag⋯Ag argentophilic interactions. Solid state photoluminescent properties and thermal expansion behaviors are also investigated.