AgPO2F2 and Ag9(PO2F2)14: the first Ag(i) and Ag(i)/Ag(ii) difluorophosphates with complex crystal structures

Abstract

The reaction of AgF₂ with P₂O₃F₄ yields a mixed valence Ag^I/Ag^II difluorophosphate salt with Ag^I₄Ag^II₅(PO₂F₂)₁₄ stoichiometry – the first Ag(II)–PO₂F₂ system known. This highly moisture sensitive brown solid is thermally stable up to 120 °C, which points at further feasible extension of the chemistry of Ag(II)–PO₂F₂ systems. The crystal structure shows a very complex bonding pattern, comprising of polymeric Ag^II₅(PO₂F₂)₁₄⁴⁻ anions and two types of Ag^I cations. One particular Ag^II site present in the crystal structure of Ag₉(PO₂F₂)₁₄ is the first known example of square pyramidal penta-coordinated Ag(II) in an oxo-ligand environment. Ag(I)PO₂F₂ – the product of the thermal decomposition of Ag₉(PO₂F₂)₁₄ – has also been characterized by thermal analysis, IR spectroscopy and X-ray powder diffraction. It has a complicated crystal structure as well, which consists of infinite 1D [Ag^IO_4/2] chains which are linked to more complex 3D structures via OPO bridges. The PO₂F₂⁻ anions bind to cations in both compounds as bidentate oxo-ligands. The terminal F atoms tend to point inside the van der Waals cavities in the crystal structure of both compounds. All important structural details of both title compounds were corroborated by DFT calculations.