Unexpectedly Complex Crystalline Phases in the MSO 3 F–Ag(SO 3 F) 2 Phase Diagram (M = Na, K, Rb, Cs)

A Unique Two-Dimensional Silver(II) Antiferromagnet Cu[Ag(SO4 )2 ] and Perspectives for Its Further Modifications

Copper(II) silver(II) sulfate crystallizes in a monoclinic CuSO4 -related structure with P21 /n symmetry. This quasi-ternary compound features Ag(SO4 )2 2- layers, while the remaining cationic sites may be occupied either completely or partially by Cu2+ cations, corresponding to the formula of (Cux Ag1-x )[Ag(SO4 )2 ], x=0.6-1.0. CuAg(SO4 )2 is antiferromagnetic with large negative Curie-Weiss temperature of -140 K and shows characteristic ordering phenomenon at 40.4 K. Density functional theory calculations reveal that the strongest superexchange interaction is a two-dimensional antiferromagnetic coupling within Ag(SO4 )2 2- layers, with the superexchange constant J2D of -11.1 meV. This renders CuAg(SO4 )2 the rare representative of layered Ag2+ -based antiferromagnets. Magnetic coupling is facilitated by the strong mixing of Ag d(x2 -y2 ) and O 2p states. Calculations show that M2+ sites in MAg(SO4 )2 can be occupied with other similar cations such as Zn2+ , Cd2+ , Ni2+ , Co2+ , and Mg2+ .

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

The reaction of AgF2 with P2O3F4 yields a mixed valence Ag(I)/Ag(II) difluorophosphate salt with AgAg(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(PO2F2)14(4-) 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(I)O4/2] 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.