Silverland: the Realm of Compounds of Divalent Silver—and Why They are Interesting

Abstract

In this personal account, the author takes readers on the journey to "Silverland," i.e., the emerging field of electronic and magnetic materials based on divalent silver (Ag 2+ ). He blends historical background with the reasons which led him to become involved in this research, as well as to proposing (with Roald Hoffmann, 2001) that high-T C superconductivity might ultimately be observed in doped Ag 2+ fluorides. More recent experimental and theoretical findings related to novel compounds, and their electronic and magnetic structure, are presented.

New Ideas for Understanding the Structure and Magnetism in AgF2: Prediction of Ferroelasticity

“…Moreover, in oxides, [7,8] chlorides [9–11] and bromides [10,12,13] the Ag 2+ cation has been stabilized but only in the form of impurity. This handful of bulk materials have to be further dredged to find those that present an adequate layered AFM ground state [1–5] . Among these fluorides particular attention has been paid to the simple AgF 2 lattice, characterized by an unusually large oxidizing power [14] …”

“…The existence of high‐temperature (high‐Tc) superconductivity in some layered oxocuprates has stimulated research on transition metal compounds containing different d 9 ions. [ 1 , 2 , 3 , 4 ] In these cases, the search for superconductivity is guided by the presence of three key ingredients found in the high‐Tc cuprates, namely 1) a crystal lattice with layered structure, 2) the existence of elongated sixfold coordinated metal complexes often associated to the Jahn‐Teller (JT) effect, and 3) a strongly antiferromagnetic (AFM) ground state in each of the metal planes.…”

“…In this hunt for new d 9 ‐superconductors during the last two decades intense efforts[ 1 , 2 , 3 , 4 , 5 ] have been focused on the exploration of materials involving 4d 9 Ag 2+ cations. As this cation exhibits a higher electronegativity than Cu 2+ , [6] all known Ag 2+ compounds are fluorides.…”

“…As this cation exhibits a higher electronegativity than Cu 2+ , [6] all known Ag 2+ compounds are fluorides. Up to now one hundred stable Ag 2+ compounds, such as AgF 2 , Cs 2 AgF 4 or KAgF 3 ,[ 1 , 2 ] have been synthesized. Moreover, in oxides,[ 7 , 8 ] chlorides[ 9 , 10 , 11 ] and bromides[ 10 , 12 , 13 ] the Ag 2+ cation has been stabilized but only in the form of impurity.…”

“…This handful of bulk materials have to be further dredged to find those that present an adequate layered AFM ground state. [ 1 , 2 , 3 , 4 , 5 ] Among these fluorides particular attention has been paid to the simple AgF 2 lattice, characterized by an unusually large oxidizing power. [14] …”