Unconventional Mixed‐Valent Complexes of Ruthenium and Osmium

Kaim, Wolfgang; Lahiri, Goutam Kumar

doi:10.1002/anie.200602737

Cited by 345 publications

(245 citation statements)

References 186 publications

(121 reference statements)

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“…Similar anisotropy has also been observed in many other Ru and Os complexes [24]. It is, therefore, natural to consider Ru and oxalate to realize the Kitaev interaction, as the first candidate.…”

Section: Fig 1 (Color Online) (A)supporting

confidence: 73%

Designing Kitaev Spin Liquids in Metal-Organic Frameworks

2017

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Kitaev's honeycomb lattice spin model is a remarkable exactly solvable model, which has a particular type of spin liquid (Kitaev spin liquid) as the ground state. Although its possible realization in iridates and α-RuCl3 has been vigorously discussed recently, these materials have substantial non-Kitaev direct exchange interactions and do not have a spin liquid ground state. We propose metal-organic frameworks (MOFs) with Ru 3+ (or Os 3+ ) forming the honeycomb lattice as promising candidates for a more ideal realization of Kitaev-type spin models where the direct exchange interaction is strongly suppressed. The great flexibility of MOFs allows generalization to other three-dimensional lattices, for potential realization of a variety of spin liquids such as a Weyl spin liquid.PhySH: Frustrated magnetism, Spin liquid, Quantum spin liquid, Organic compoundsIntroduction. -Quantum spin liquids, purported exotic states of quantum magnets where long-range magnetic orders are destroyed by quantum fluctuations, have been a central subject in quantum magnetism [1]. As an important theoretical breakthrough, Kitaev constructed a spin-1/2 model on the honeycomb lattice [2] with Ising interactions between spin components depending on bond orientations. Its exact solution demonstrates many intriguing properties such as fractionalized anyonic excitations. This model was later generalized to other lattices, including three-dimensional ones, still retaining the exact solvability [3]. In this paper, we call this type of model including various generalizations as Kitaev model, and its ground states as Kitaev spin liquids. Jackeli and Khaliullin [4] discovered that the "Kitaev interaction", namely bond-dependent Ising couplings, can be realized in a (111) honeycomb layer of iridates, i.e. the A 2 IrO 3 (A = Na, Li) structure, by the superexchange interaction through the oxygen ions due to the strong spin-orbit coupling of Ir 4+ in the Mott insulator limit (see also Ref.[5] for the itinerant limit).However, unfortunately, it turned out that iridates and related inorganic compounds, such as α-RuCl 3 [6], exhibit a conventional magnetic order at low enough temperatures and do not have a true spin liquid ground state. This is due to the non-Kitaev interactions, such as antiferromagnetic Heisenberg interaction, mainly coming from the direct exchange interaction between the metal ions [7]. While their finite-temperature properties still reflect the proximity to the Kitaev model [8] and thus are of great interest, the current situation calls for a more ideal realization of the Kitaev model in real materials, so that they exhibit spin liquid ground states.In this Letter, we propose such a possible realization of the Kitaev model in metal-organic frameworks (MOFs), crystalline materials consisting of metal ions and bridging organic ligands. Although MOF is a central subject in modern complex chemistry, MOFs have not attracted much attention in the context of magnetism. This is

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Section: Fig 1 (Color Online) (A)supporting

confidence: 73%

Designing Kitaev Spin Liquids in Metal-Organic Frameworks

2017

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“…As can be seen from the DFT-calculated MO diagram (see above), the fact that the Me Tpmd ligand might show "non-innocent ligand" [50] behaviour, owing to the energetic destabilisation of the carbanions has to be kept in mind. Since the carbanionic moieties are very close in energy to the metal-centred frontier orbitals, redox processes, which are commonly assumed to be metal-centred [Eqn.…”

mentioning

confidence: 99%

Syntheses, Structures and Electronic Properties of Zwitterionic Iron(II) and Cobalt(II) Complexes Featuring Ambidentate Tris(pyrazolyl)methanide Ligands

Kuzu

Krummenacher

Hewitt

et al. 2009

Chemistry A European J

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By deprotonation of the corresponding tris(pyrazolyl)methane ((Me)Tpm) precursor complexes [M((Me)Tpm)(2)][(OTf)(2)] (1 and 2), the zwitterionic tris(pyrazolyl)methanide iron(II) (3) and cobalt(II) (4) "sandwich" complexes of the general formula [M((Me)Tpmd)(2)] are easily accessible. The structurally characterised complexes 3 and 4 are the first such homoleptic 3d transition metal species to feature two "naked", outward pointing pyramidal carbanions. Density functional theory calculations show metal-centred HOMOs and LUMOs with the destabilised carbanion orbitals in the energy region of the filled transition-metal-centred frontier orbitals. The electronic structures of these complexes have been investigated in detail by various spectroscopic techniques such as NMR, EPR, SQUID, Mössbauer, etc. Both complexes adopt a high-spin (HS) configuration at room temperature in solution and in the solid state. A thermally induced high-spin to low-spin (HS-LS) transition is observed for the iron(II) complex 3. The HS-LS transition temperature of 3 in solution differs from that in the solid state, which in turn strongly depends on the amount of solvent molecules in the crystal lattice. Electrochemical studies on the corresponding cobalt(II) complex 4 provide evidence for a HS-Co(II) <==> LS-Co(III) transition upon oxidation, which was confirmed by preliminary synthetic oxidation reactions. Overall, it can be concluded that the related kappa(3)N-donor ligands tris(pyrazolyl)hydroborates (Tp(R)) and (R)Tpmd ligands have similar bonding properties and that the metal cations experience more or less the same ligand environment.

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“…[4][5][6][7][8][9][10][11][12][13] In addition, mixed-valence complexes have attracted a lot of attention due to the interest in the synthesis of the so-called molecular wires. These materials can be defined as "a molecule between two reservoirs of electrons" or "a molecule that conducts electrical current between two electrodes", according to Kirczenow 14 and Ratner, 15 respectively.…”

Section: Introductionmentioning

confidence: 99%

“…As a consequence, the synthesis and characterization of several linear systems based on coordination complexes have been reported lately. 10,[17][18][19] Focusing on the production of molecular wires, many synthetic approaches have tried to prepare oligonuclear transition metal complexes with different degrees of electronic coupling between their constituents; hence, their design relies on the known properties of binuclear complexes.…”

Section: Introductionmentioning

confidence: 99%

Mixed-valence state of symmetric diruthenium complexes: synthesis, characterization, and electron transfer investigation

Pinheiro¹,

Paulo²,

Abreu³

et al. 2012

Dalton Trans.

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Complexes of the type {[( pyS)Ru(NH 3 ) 4 ] 2 -μ-L}n , where pyS = 4-mercaptopyridine, L = 4,4′-dithiodipyridine ( pySSpy), pyrazine ( pz) and 1,4-dicyanobenzene (DCB), and n = +4 and +5 for fully reduced and mixed-valence complexes, respectively, were synthesized and characterized. Electrochemical data showed that there is electron communication between the metal centers with comproportionation constants of 33.2, 1.30 × 10 8 and 5.56 × 10 5 for L = pySSpy, pz and DCB, respectively. It was also observed that the electronic coupling between the metal centers is affected by the π-back-bonding interaction toward the pyS ligand. Raman spectroscopy showed a dependence of the intensity of the vibrational modes on the exciting radiations giving support to the assignments of the electronic transitions. The degree of electron communication between the metal centers through the bridging ligands suggests that these systems can be molecular wire materials.

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Unconventional Mixed‐Valent Complexes of Ruthenium and Osmium

Cited by 345 publications

References 186 publications

Designing Kitaev Spin Liquids in Metal-Organic Frameworks

Designing Kitaev Spin Liquids in Metal-Organic Frameworks

Syntheses, Structures and Electronic Properties of Zwitterionic Iron(II) and Cobalt(II) Complexes Featuring Ambidentate Tris(pyrazolyl)methanide Ligands

Mixed-valence state of symmetric diruthenium complexes: synthesis, characterization, and electron transfer investigation

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