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

Copper(II) silver(II) sulfate crystallizes in a monoclinic CuSO -related structure with P2 /n symmetry. This quasi-ternary compound features Ag(SO ) layers, while the remaining cationic sites may be occupied either completely or partially by Cu cations, corresponding to the formula of (Cu Ag )[Ag(SO ) ], x=0.6-1.0. CuAg(SO ) 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(SO ) layers, with the superexchange constant J of -11.1 meV. This renders CuAg(SO ) the rare representative of layered Ag -based antiferromagnets. Magnetic coupling is facilitated by the strong mixing of Ag d(x -y ) and O 2p states. Calculations show that M sites in MAg(SO ) can be occupied with other similar cations such as Zn , Cd , Ni , Co , and Mg .