Charge transfer in mixed-valence solids. Part VIII. Contribution of valence delocalisation to the ferromagnetism of Prussian Blue

Mayoh, Bryan; Day, P.

doi:10.1039/dt9760001483

Cited by 69 publications

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“…Here, we will discuss the origin of the magnetic interaction in the title complexes. The ferromagnetic ordering for n = 3 and 4 is considered to be established by the charge-transfer interaction between Fe II and Fe III , the same mechanism as in Fe [24,25] as shown in Fig-angular interactions in the 2-D plane [ Figure 10(a)]. In the case of the triangular lattice, the number of nearest neighbors of the Fe III (S = 5/2) site is 6.…”

Section: Discussionmentioning

confidence: 99%

Charge‐Transfer Phase Transition and Ferromagnetism of Iron Mixed‐Valence Complexes (n‐C_nH_2n+1)₄N[Fe^IIFe^III(dto)₃] (n = 3–6; dto = C₂O₂S₂)

et al. 2006

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The iron mixed‐valence complex, (n‐C3H7)4N[FeIIFeIII(dto)3] (dto = dithiooxalato) shows a charge‐transfer (CT) phase transition at TCT = 122.4 K. In the vicinity of TCT, the spin state changes from FeII (S = 2) – FeIII (S = 1/2) (high‐temperature phase: HTP) to FeII (S = 0) – FeIII (S = 5/2) (low‐temperature phase: LTP) accompanied by a charge transfer between FeII and FeIII. This complex also undergoes a ferromagnetic transition at 7 K in the LTP. In order to investigate the mechanism of the CT phase transition and the ferromagnetism, we have systematically synthesized (n‐CnH2n+1)4N[FeIIFeIII(dto)3] (n = 3–6), and have investigated their physical properties by magnetic susceptibility, powder X‐ray diffraction measurements, and ESR spectroscopy. The compounds (n‐CnH2n+1)4N[FeIIFeIII(dto)3] (n = 3–6) display ferromagnetic phase transitions at 7 K, 7 K (& 13 K), 19.5 K, and 22 K, respectively. For n = 3 and 4, the CT phase transitions take place at TCT ≈ 120 K and TCT ≈ 140 K, respectively. For n = 5 and 6, on the other hand, the CT phase transition does not occur, and the spin configuration of FeII (S = 2) and FeIII (S = 1/2) corresponding to the HTP for n = 3 and 4 is stable between 2 K and 300 K. The cation size of (n‐CnH2n+1)4N+ (n = 3–6) acts as an effective internal pressure which induces the CT phase transition and the ferromagnetic ordering in the [FeIIFeIII(dto)3]–∞ layer. We also discuss the mechanism of the CT phase transition and the ferromagnetism induced by the charge‐transfer interaction between FeII and FeIII. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006)

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Section: Discussionmentioning

confidence: 99%

Charge‐Transfer Phase Transition and Ferromagnetism of Iron Mixed‐Valence Complexes (n‐C_nH_2n+1)₄N[Fe^IIFe^III(dto)₃] (n = 3–6; dto = C₂O₂S₂)

et al. 2006

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“…Herein, the proposed approach to explain the origin of reversible changes on physical properties of PB films during the voltammetric scan is based on the covalentexchange model, 54 which is supported by the fact that changes in these films depend on the interaction between neighboring iron ions mediated by cyanide bonds. 55 The superexchange model could also be used. However, the system should be ferromagnetic for all Fe͑III͒ compositional fractions considering this last model.…”

Section: ͓2͔mentioning

confidence: 99%

Electronic Perspective on the Electrochemistry of Prussian Blue Films

Agrisuelas

Bueno

Ferreira

et al. 2009

J. Electrochem. Soc.

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The derivative of the voltabsommetric scans, together with previous nano-electrogravimetric and X-ray diffraction results, allow different electrochemical processes to be distinguished during the Prussian blue ͑PB͒ voltammetric scan. Potassium, proton, and hydrated proton counterions involved in PB electrochemistry are related here to the electrochemical reactions of specific Fe sites. Potassium counterions show two different sites for their insertion: one located in the crystalline framework and another in ferrocyanide vacancies. From the monitoring of electroactive Fe sites, the covalent-exchange model is suggested as one of the first approaches to explain the origin of the PB magnetic ordering observed at room temperature during voltammetric scanning. Systems that undergo reversible and controlled changes of their properties offer appealing perspectives for the fabrication of electronic switch devices. Thus, Prussian blue ͑PB͒-like materials have raised intense interest because of their electrochromic, ionexchange, ion-sensing, electrocatalytic, or photomagnetic properties, 1-5 because the PB Everitt's salt ͑ES͒ voltammetric scan is accompanied by reversible changes in these physicochemical properties.6-10 Likewise, they also display a wide range of important magnetic ͑e.g., room temperature magnetic ordering͒ and magnetooptical ͑e.g., ferromagnetism, photoinduced ͑de͒-magnetization͒ properties. [11][12][13][14] In particular, the PB electromagnetic properties can also be tailored by external conditions, such as the magnetic field, 15-17 light, 15,18,19 and by electrochemical methods. 18,[20][21][22][23][24] X-ray studies showed that the PB three-dimensional ͑3D͒ structure is face-centered cubic 25 with a general formula equal to Fe 4 ͓Fe͑CN͒ 6 ͔ 3 ·mH 2 O. Trivalent and divalent iron ions are in highand low-spin sites, Fe͑III͒ high-spin and Fe͑II͒ low-spin , respectively. 26Enclosed in this structure, high-and low-spin sites are both octahedral and surrounded by -NC and -CN units, respectively. Thus, the PB lattice is composed of repetitive units of Fe low-spin -CN-Fe high-spin in the three spatial directions. Nonetheless, 1 4 of low-spin Fe͑II͒ sites are missing and occupied by water molecules coordinated to Fe͑III͒ high-spin ions. The PB structure is completed with water molecules occupying interstitial positions. 27-29The above crystalline structure corresponds to the freshly deposited PB film following the electrochemical methodology described by Itaya et al. 22 and it is known as insoluble. The insoluble PB is electrochemically converted into the soluble PB by means of successive voltammetric cycles between the PB and ES forms 30,31 until a stable electrochemical response is achieved. 32 The soluble PB has been described as similar to the insoluble PB 3D structure. 33,34 Repetitive structural units of Fe low-spin -CN-Fe high-spin also compose its rigid framework, where 1 4 of the low-spin sites are missing. The position of the trivalent iron ions can be drawn as Fe͑II͒ low-spin -CN-Fe͑III͒ high-spin a...

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“…Of course, not only electrical but also magnetic properties are determined by the analogues of J and l. Prussian blue, perhaps the best-known mixed-valence solid, becomes magnetically ordered even though the high-spin Fe(III) ions are separated by 10 Å or more owing to a finite J and, remarkably, it is a ferromagnet (Ludi & Guedel 1973). In such a class 2 mixedvalence system, the ferromagnetic exchange is neatly explained in a HeitlerLondon formalism as being due to admixture of the intervalence excited configuration into the ground state (Mayoh & Day 1976). This presages much later work on molecular magnets.…”

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Mixed valence: origins and developments

Day

Hush

Clark

2007

Phil. Trans. R. Soc. A.

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142

109

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Mixed-valence compounds were recognized by chemists more than a century ago for their unusual colours and stoichiometries, but it was just 40 years ago that two seminal articles brought together the then available evidence. These articles laid the foundations for understanding the physical properties of such compounds and how the latter correlate with molecular and crystal structures. This introduction to a discussion meeting briefly surveys the history of mixed valence and sets in context contributions to the discussion describing current work in the field.

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Charge transfer in mixed-valence solids. Part VIII. Contribution of valence delocalisation to the ferromagnetism of Prussian Blue

Cited by 69 publications

References 0 publications

Charge‐Transfer Phase Transition and Ferromagnetism of Iron Mixed‐Valence Complexes (n‐C_nH_2n+1)₄N[Fe^IIFe^III(dto)₃] (n = 3–6; dto = C₂O₂S₂)

Charge‐Transfer Phase Transition and Ferromagnetism of Iron Mixed‐Valence Complexes (n‐C_nH_2n+1)₄N[Fe^IIFe^III(dto)₃] (n = 3–6; dto = C₂O₂S₂)

Electronic Perspective on the Electrochemistry of Prussian Blue Films

Mixed valence: origins and developments

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Charge transfer in mixed-valence solids. Part VIII. Contribution of valence delocalisation to the ferromagnetism of Prussian Blue

Cited by 69 publications

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Charge‐Transfer Phase Transition and Ferromagnetism of Iron Mixed‐Valence Complexes (n‐CnH2n+1)4N[FeIIFeIII(dto)3] (n = 3–6; dto = C2O2S2)

Charge‐Transfer Phase Transition and Ferromagnetism of Iron Mixed‐Valence Complexes (n‐CnH2n+1)4N[FeIIFeIII(dto)3] (n = 3–6; dto = C2O2S2)

Electronic Perspective on the Electrochemistry of Prussian Blue Films

Mixed valence: origins and developments

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Charge‐Transfer Phase Transition and Ferromagnetism of Iron Mixed‐Valence Complexes (n‐C_nH_2n+1)₄N[Fe^IIFe^III(dto)₃] (n = 3–6; dto = C₂O₂S₂)

Charge‐Transfer Phase Transition and Ferromagnetism of Iron Mixed‐Valence Complexes (n‐C_nH_2n+1)₄N[Fe^IIFe^III(dto)₃] (n = 3–6; dto = C₂O₂S₂)