Ag₂Cu₃Cr₂O₈(OH)₄: a new bidimensional silver–copper mixed-oxyhydroxide with in-plane ferromagnetic coupling

Abstract

AgCuCrO(OH), a new Ag-Cu-Cr-O layered mixed oxide, prepared by soft hydrothermal heterogeneous reactions, is reported. The new phase is an oxyhydroxide and presents a structure with alternating brucite-like Cu-O and Ag-O layers connected by individual chromate groups. The crystallographic structure has been solved and refined from high resolution powder X-ray diffraction data and is supported by density functional theory calculations, yielding a triclinic, space group P1[combining macron], a = 5.3329(1) Å, b = 5.3871(1) Å, c = 10.0735(1) Å, α = 80.476(1)°, β = 87.020(1)°, γ = 62.383(1)°. Bond valence sums suggest the formulation of AgCuCrO(OH), an electronic state fully supported by X-ray photoelectron spectroscopy (XPS) and Cr K-edge X-ray absorption near edge structure (XANES) measurements. AgCuCrO(OH) exhibits bidimensional Cu-O-Cu ferromagnetic correlations that are apparent at much higher temperatures than in other similar Cu-O layered structures, without coupling between Cu-O layers, which represents a unique case in the recent family of silver copper oxides. The role of Ag inducing bidimensionality in copper oxides is therefore expanded further with the presence of chromate anions. Ab initio calculations using density functional theory show that the electronic states involved originate mainly from Cu and OH orbitals, with minor contributions from Cr and the O atoms linking the Cr tetrahedra to the brucitic Cu-O layer, and almost no contribution from Ag. Further modeling of the in-plane magnetic interactions between Cu atoms suggests that the coupled magnetized stripes are responsible for the observed behavior. The results are discussed in relation with previous Ag-Cu mixed oxide phases where metallic behavior or ferro-antiferro transitions had been observed. The structure of this new Ag-Cu-O phase as compared with previous silver copper oxides supports the conclusion that the Ag-Cu layered ordering is favored under oxidizing conditions.

Delafossite Ag2CuMnO4 is a Novel Catalytic Material for Low‐Temperature Oxidation of CO and NH3

“…Such oxide as well as other delafossites might be prepared via the hydrothermal approach [3,4,24] . A particular feature of Ag 2 CuMnO 4 is the two‐dimensional ordering of silver and copper atoms, [4] which determines its unique magnetic properties in a similar way as for silver‐copper mixed‐oxyhydroxide Ag 2 Cu 3 Cr 2 O 8 (OH) 4 [25] . At the same time, the presence of cations with unfilled d‐sublevels (Cu 2+ and Mn 4+ ) might be responsible for improved redox properties of Ag 2 CuMnO 4 as potential catalytic material [24] .…”

Charge Delocalization, Oxidation States, and Silver Mobility in the Mixed Silver–Copper Oxide AgCuO2

“…Other members of this new family include AgCu 0.5 Mn 0.5 O 2 , 7 Rb 3 Ag 0.5 Cu 0.5 O 2 , 8 AgCu 3 V 4 O 12 , 9 and Ag 2 Cu 3 Cr 2 O 8 (OH) 4 . 10 AgCuO 2 exhibits a crednerite-type structure (C2/m) with alternating [CuO 2 ] ∞ and [Ag] ∞ layers parallel to the ab planes of the crystal, which are connected through Ag−O bonds (see Figure 1a). 4,6 Jansen and co-workers 6 noted that diamagnetic AgO contains two different Ag sites exhibiting linear and square planar coordinations.…”

“…), and a controversy followed concerning the electronic description of the system. Other members of this new family include AgCu 0.5 Mn 0.5 O 2 , Rb 3 Ag 0.5 Cu 0.5 O 2 , AgCu 3 V 4 O 12 , and Ag 2 Cu 3 Cr 2 O 8 (OH) 4 …”