AgIISO4: A Genuine Sulfate of Divalent Silver with Anomalously Strong One-Dimensional Antiferromagnetic Interactions

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+ .

AgII -Mediated Electrocatalytic Ambient CH4 Functionalization Inspired by HSAB Theory

Although most class (b) transition metals have been studied in regard to CH₄ activation, divalent silver (Ag^II ), possibly owing to its reactive nature, is the only class (b) high-valent transition metal center that is not yet reported to exhibit reactivities towards CH₄ activation. We now report that electrochemically generated Ag^II metalloradical readily functionalizes CH₄ into methyl bisulfate (CH₃ OSO₃ H) at ambient conditions in 98 % H₂ SO₄ . Mechanistic investigation experimentally unveils a low activation energy of 13.1 kcal mol^-1 , a high pseudo-first-order rate constant of CH₄ activation up to 2.8×10³  h^-1 at room temperature and a CH₄ pressure of 85 psi, and two competing reaction pathways preferable towards CH₄ activation over solvent oxidation. Reaction kinetic data suggest a Faradaic efficiency exceeding 99 % beyond 180 psi CH₄ at room temperature for potential chemical production from widely distributed natural gas resources with minimal infrastructure reliance.

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

When exposed to air at ambient conditions, AgSO₄ slowly reacts with moisture, yielding AgSO₄ ⋅H₂ O. The crystal structure determination (powder data) shows that it may be described as [Ag(OH₂ )₂ ][Ag(SO₄ )₂ ], with some sulfate groups being shared between different Ag²⁺ cations, resembling in that way its Cu²⁺ analogue. [Ag(OH₂ )₂ ][Ag(SO₄ )₂ ], the first hydrate of a compound of Ag²⁺ , was extensively characterized using many physicochemical methods.

The role of terahertz polariton absorption in the characterization of crystalline iron sulfate hydrates

Solid-state density functional theory indicates that polariton absorption plays a central role in understanding the identifying terahertz-frequency spectral features of hydrated iron sulfate compounds.