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

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: [Ag(2)(ptp)] (1), [Ag(2)(ppp)] (2), [Ag(3)(CH(3)CN)(pnp)(pnpH)] (3), and [Ag(3)(pcp)(pcpH)] (4) [ptp(2-) = pyro-3-thienylphosphonate, ppp(2-) = pyrophenylphosphonate, pnp(2-) = pyro-α-naphthylphosphonate, pcp(2-) = 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 Ag(4)O(P)(6) clusters linked by O-P-O units and AgAg 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 AgAg 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 CH(3)CN. 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.