β‐Ag₃RuO₄, a Ruthenate(V) Featuring Spin Tetramers on a Two‐Dimensional Trigonal Lattice

Abstract

Open-shell solids exhibit a plethora of intriguing physical phenomena that arise from a complex interplay of charge, spin, orbital, and spin-state degrees of freedom. Comprehending these phenomena is an indispensable prerequisite for developing improved functional materials. This type of understanding can be achieved, on the one hand, by experimental and theoretical investigations into known systems, or by synthesizing new solids displaying unprecedented structural and/or electronic features. β-Ag3 RuO4 may serve as such a model system because it possesses a remarkable anionic structure, consisting of tetrameric polyoxoanions (Ru4 O16 )(12-) , and is an embedded fragment of a 2D trigonal MO2 lattice. The notorious frustration of antiferromagnetic (AF) exchange couplings on such lattices is thus lifted, and instead strong AF occurs within the oligomeric anion, where only one exchange path remains frustrated among the relevant six. The strong magnetic anisotropy of the [Ru4 O16 ](12-) ion, and the effectively orbital nature of its net magnetic moment, implies that this anion may reveal the properties of a single-molecule magnet if well-diluted in a diamagnetic matrix.

Antiferromagnetism in the van der Waals layered spin-lozenge semiconductor CrTe3

“…The interpretation of the magnetic data as arising from 2D correlations is consistent with the layered nature of the crystal structure of CrTe 3 ; however, since the CrTe 3 layers themselves are made up of Cr 4 Te 16 units containing tetramers of Cr, a zero-dimensional or molecular magnetism viewpoint can also be considered. Magnetism associated with lozenge shaped tetramers formed by spin- 3 2 magnetic ions like those found in CrTe 3 has been studied in several systems [59][60][61][62], by assuming magnetically isolated tetramers with intra-tetramer interactions described by J 1 and J 2 defined in Fig. 1a.…”

Expanding the Rich Crystal Chemistry of Ruthenium(V) Oxides via the Discovery of BaRu2O6, Ba5Ru4O15, Ba2Ru3O10, and Sr2Ru3O9(OH) by pH-Controlled Hydrothermal Synthesis

“…Although we limited this report to the Ba and Sr alkaline earth ruthenates we have in parallel demonstrated the feasibility to obtain, by varying the reacting pH, other Ca/Ru compositions besides the single one Ca2--xRu2O7 solely reported by Hiley et al 10 . Interestingly, we should recall a similar strategy has previously led to the synthesis of silver based ruthenate phase 12,13 . Thus obvious future investigations could aim in replacing alkaline earth by alkali ions or ruthenium itself by other elements of practical interest, namely Mn.…”

“…Following this work several other ruthenium (+V) phases were obtained using the same chemical trick. 11,12,13 Surprisingly, none of these studies went into a deep understanding of the reacting paths by which these new phases were formed. Progress in this direction, however, cannot be uncoupled from a deeper appreciation of the means by which the reduction and precipitation steps are affected by various physico--chemical parameters.…”

Synthesis, crystal and magnetic structure of the spin-chain compound Ag2RuO4

“…Utilizing high-oxygen-pressure and hydrothermal synthesis techniques, we started to explore Ag 2 O/RuO x systems, which has resulted in the discovery of several silver ruthenates. Among them, AgRuO 3 shows strong antiferromagnetic exchange coupling on a [RuO 3 ] honeycomb lattice [38], α-Ag 3 RuO 4 forms a 1D polyoxoanion of edge-sharing octahedra [39], while the β polymorph features an oligomeric oxoanion [40]. The latter representative is kind of exceptional in as much it is closely related to the sodium analog, containing the same tetrameric oxoanion [41][42][43], showing frustrated-magnetic exchange coupling within the tetrameric spin cluster [40,43].…”