[Ag(OH2 )2 ][Ag(SO4 )2 ]: A Hydrate of a Silver(II) Salt

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+ .

Crystal structures of [SbF6]− salts of di- and tetrahydrated Ag +, tetrahydrated Pd2 + and hexahydrated Cd2 + cations

The [Ag(H2O)2]SbF6, is triclinic, P1̅ (No. 2), with a=6.6419(3) Å, b=7.6327(3) Å, c=11.1338(3) Å, α=95.492(3)°, β=96.994(3)°, γ=113.535(4)°, V=507.13(4) Å3 at 150 K, and Z=3. There are two crystallographically non-equivalent Ag+ cations. The Ag1 is coordinated by two water molecules with Ag–OH2 distances equal to 2.271(2) Å forming in that way a discrete linear [Ag(H2O)2]+ cation. Additionaly, it forms two short Ag···F contacts (2.630(2) Å), resulting in AgO2F2 plaquette, and four long ones (2×3.001(2) Å and 2×3.095(2) Å) with fluorine atoms located below and above the AgO2F2 plaquette. The H2O molecules bridge Ag2 atoms into {–[Ag(μ-OH2)2]–}n infinite chains, with Ag–O distances of 2.367(2)–2.466(2) Å. The [Pd(H2O)4](SbF6)2·4H2O is monoclinic, P2 1 /a (No.14), with a=8.172(2) Å, b=13.202(3) Å, c=8.188(3) Å, β=115.10(1)o, V=799.9(4) Å3 at 200 K, and Z=2. Its crystal structure can be described as an alternation of layers of [Pd(H2O)4]2+ cations (interconnected by H2O molecules) and [SbF6]− anions. It represents the first example where [Pd(H2O)4]2+ has been structurally determined in the solid state. Four oxygen atoms provided by H2O molecules are in almost ideal square-planar arrangement with Pd–O bond lengths 2×2.004(5) Å and 2×2.022(6) Å. The [Cd(H2O)6](SbF6)2, is orthorhombic, Pnnm (No.58), with a=5.5331(2) Å, b=14.5206(4) Å, c=8.9051(3) Å, V=715.47(4) Å3 at 200 K, and Z=2. It consists of [Cd(H2O)6]2+ cations and [SbF6]− anions.