Spin-crossover cobalt(III) complexes: steric and electronic control of spin state

Klaeui, W.; Eberspach, W.; Guetlich, P.

doi:10.1021/ic00271a004

Cited by 97 publications

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“…This provides evidence for the cobalt oxide samples having an average +3 cobalt oxidation state (determined from the edge position) and a near‐octahedral coordination geometry that is bound to six oxo ligands (determined from the pre‐edge region) . The Co III centres have a low‐spin electronic configuration,, as evident by the occurrence of only one pre‐edge peak, which corresponds to the 1s→e g (3d orbital) transition to the 2 E final state . There are no inflections or differences in the XANES data that may indicate contamination with a secondary phase (for example, a small loading of Co 3 (PO 4 ) 2 in the CoO x (8.6 %P) sample).…”

Section: Results and Analysissupporting

confidence: 86%

Engineering Disorder into Heterogenite‐Like Cobalt Oxides by Phosphate Doping: Implications for the Design of Water‐Oxidation Catalysts

et al. 2016

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Amongst the most promising materials designed to catalyse water oxidation from earth‐abundant materials are the metal oxides. Despite the success of these materials, understanding the relationship of structure to function has been very challenging. It has been noted that many metal oxide water‐oxidation catalysts function best in a proton‐accepting electrolyte, such as a borate or phosphate buffer. However, these same electrolytes are known to significantly affect the metal oxide structures by imparting a level of “disorder” or “molecular nature” to the materials. The most well‐known case is that of Nocera's Co–Pi catalyst (Pi: inorganic phosphorus). In this study, we have synthesised a series of “heterogenite‐like” cobalt oxides with different levels of phosphate doping (0–9 %P). Our synthetic method enables us to make “bulk materials”, the structural properties of which (as observed by X‐ray absorption spectroscopy and transmission electron microscopy) mimic those observed directly on electrode surfaces. The changes made to the bulk phases were directly correlated with the reactivity for water‐oxidation catalysis and the ability of the CoOx materials to act as sacrificial oxidants. The most disordered materials were most reactive for sacrificial oxidation but were less effective as water‐oxidation catalysts. These results help us understand how disorder changes the thermodynamic stability of metal oxides and how this impacts on efficiency for water oxidation.

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Section: Results and Analysissupporting

confidence: 86%

Engineering Disorder into Heterogenite‐Like Cobalt Oxides by Phosphate Doping: Implications for the Design of Water‐Oxidation Catalysts

et al. 2016

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“…ε LS and ε HS describe the molar extinction coefficients of the pure low‐spin (LS) and high‐spin (HS) states at this wavelength. The ideal solution model for the mole fraction of molecules in the high‐spin state is described by [Equation ]:

γ_{normalHS} = \frac{1}{1 + \exp (Δ H / R T - Δ S / R)}

…”

Section: Resultsmentioning

confidence: 99%

Spin State Variations and Spin‐Crossover in Diiron(II) Complexes of Bis(pentadentate) Pyrazolate‐Based Ligands

Schober

Demeshko

Meyer

2018

Zeitschrift anorg allge chemie

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Compartmental pyrazolato‐bridged ligands [LPy]− and [LIm]−, each providing two {N5} binding sites but differing in the terminal N‐donors (pyridine vs. imidazole), were used to prepare a set of diferrous complexes; the ligand HLIm is new and its synthesis is reported. Complexes [LPyFe2(MeCN)2](OTf)3, (1OTf), [LPyFe2(MeCN)2](BF4)3 (1BF4), [LImFe{Fe(MeCN)}](OTf)3 (2OTf), and [LImFe{Fe(MeCN)}](BF4)3 (2BF4) were characterized by single‐crystal X‐ray diffraction, revealing a MeCN coligand at both (1OTf, 1BF4) or at only one (2OTf, 2BF4) of the two accessible Fe coordination sites that are directed into the bimetallic cleft. Magnetic measurements (SQUID) and 57Fe Mößbauer spectroscopy indicate low‐spin states for the six‐coordinate FeII ions in 1OTf and 1BF4 that are based on [LPy]−, but two high‐spin FeII ions in 2BF4 that is based on [LIm]−, in agreement with structural data. Complex 2OTf shows abrupt spin‐crossover (SCO) from a mixed high‐spin/low‐spin to an all high‐spin state at T½ = 264 K, which appears to be correlated with the Fe–N≡C(Me) bonding angle. SCO, though gradual, is observed for 2OTf also in solution (T½ = 273 K in MeCN, 248 K in EtCN), which was studied by Mössbauer spectroscopy of frozen solution samples, variable temperature UV/Vis spectroscopy and SQUID magnetometry; the latter methods consistently gave thermodynamic parameters ΔH = 24.2 kJ·mol–1, ΔS = 89 J·mol–1·K–1 for the SCO of 2OTf in MeCN, and ΔH = 19.1 kJ·mol–1, ΔS = 77 J·mol–1·K–1 in EtCN.

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“…The comparison of the three curves shows that the change in the peripheral R group on the ligand has only a weak influence on the transition temperature. The temperature dependence of these chemical shifts can be modelled to extract the thermodynamic parameters of the Boltzmann spin equilibrium by using the following equation:

δ_{o b s}^{T} \times T = δ_{L S} \times T + \frac{c}{{1 + \exp [\frac{Δ H^{°}}{R} (\frac{1}{T} - \frac{1}{T 1 / 2})]}}

where δ obs T is the experimental chemical shift and δ LS/dia is the chemical shift in the diamagnetic state. The values extracted from these fits are given in Table .…”

Section: Resultsmentioning

confidence: 99%

Solution and Solid‐State Study of the Spin‐Crossover [Fe^II(R‐bik)₃](BF₄)₂ Complexes (R = Me, Et, Vinyl)

Tewary

Garnier

et al. 2017

Eur J Inorg Chem

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Overall these experiments give coherent results with T1/2 located between 320 and 335 K, a narrow range in comparison to the solid-state. DFT calculations allowed rationalizing the differences in the magnetic differences. The molecular orbital and spin density calculations reveal that the presence of the C=O group between the imidazolyl units in the ligands of 1-3 leads to an extended aromatic system, an effective -acceptor effect, stabilizing a LS state and reducing the LS-HS gap in comparison to 4.

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Spin-crossover cobalt(III) complexes: steric and electronic control of spin state

Cited by 97 publications

References 0 publications

Engineering Disorder into Heterogenite‐Like Cobalt Oxides by Phosphate Doping: Implications for the Design of Water‐Oxidation Catalysts

Engineering Disorder into Heterogenite‐Like Cobalt Oxides by Phosphate Doping: Implications for the Design of Water‐Oxidation Catalysts

Spin State Variations and Spin‐Crossover in Diiron(II) Complexes of Bis(pentadentate) Pyrazolate‐Based Ligands

Solution and Solid‐State Study of the Spin‐Crossover [Fe^II(R‐bik)₃](BF₄)₂ Complexes (R = Me, Et, Vinyl)

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Spin-crossover cobalt(III) complexes: steric and electronic control of spin state

Cited by 97 publications

References 0 publications

Engineering Disorder into Heterogenite‐Like Cobalt Oxides by Phosphate Doping: Implications for the Design of Water‐Oxidation Catalysts

Engineering Disorder into Heterogenite‐Like Cobalt Oxides by Phosphate Doping: Implications for the Design of Water‐Oxidation Catalysts

Spin State Variations and Spin‐Crossover in Diiron(II) Complexes of Bis(pentadentate) Pyrazolate‐Based Ligands

Solution and Solid‐State Study of the Spin‐Crossover [FeII(R‐bik)3](BF4)2 Complexes (R = Me, Et, Vinyl)

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Solution and Solid‐State Study of the Spin‐Crossover [Fe^II(R‐bik)₃](BF₄)₂ Complexes (R = Me, Et, Vinyl)