Characterization of a delocalized mixed-valence bis-macrocyclic diiron compound

Spreer, Larry O.; Li, Aiping; MacQueen, David; Allan, Christian B.; Otvos, John W.; Calvin, Melvin; Frankel, Richard B.; Papaefthymiou, Georgia C.

doi:10.1021/ic00087a006

Cited by 33 publications

(22 citation statements)

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“…Previous bpmp complexes and trinuclear iron carboxylates consist of high-spin iron-() and -(), and intervalence transition (IT) bands are observed. Furthermore, dinuclear iron complexes composed of low-spin iron-() and -() have been reported by Spreer et al 18 and an intense near-infrared band due to an IT is observed. In contrast, diiron complexes with a nonadentate polypyridine ligand, which has a stronger ligand field than bpmp, have been synthesized by our group 19 and indicated no observable band due to an intervalence transition between a high-spin iron() and a low-spin iron().…”

mentioning

confidence: 86%

Crystal structures and Mössbauer spectra of mixed-valence dinuclear iron(II,III) complexes: detrapped valence states †

Manago¹,

Hayami²,

Oshio³

et al. 1999

J. Chem. Soc., Dalton Trans.

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mentioning

confidence: 86%

Crystal structures and Mössbauer spectra of mixed-valence dinuclear iron(II,III) complexes: detrapped valence states †

Manago¹,

Hayami²,

Oshio³

et al. 1999

J. Chem. Soc., Dalton Trans.

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“…The Lewis base of 1,4,8,11-tetraazacyclotetradecane (cyclam) was introduced to perovskite precursor solution as a ligand, which passivated defects spontaneously during the process of forming films via spin-coating without a subsequent anti-solvent process. Cyclam is one kind of ligand concerned widely in coordination chemistry because it can coordinate metal ions to form stable compounds. , In addition, as a delocalized system, cyclam has chemical properties that facilitate charge transportation . Thus, cyclam has multifunctional features that can combine both defect passivation and carrier recombination.…”

Section: Introductionmentioning

confidence: 97%

Novel Lewis Base Cyclam Self-Passivation of Perovskites without an Anti-Solvent Process for Efficient Light-Emitting Diodes

Han

Yuan

Fang

et al. 2020

ACS Appl. Mater. Interfaces

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Metal halide perovskites have been focused as a candidate applied as a promising luminescent material for next-generation high-quality lighting and high-definition display. However, as perovskite films formed, high density of defects would be produced in solution processing inevitably, leading to low exciton recombination efficiency in light-emitting diodes (LEDs). Herein, a facile and novel self-passivation strategy to inhibit defect formation in perovskite films for constructing high-performance LEDs is developed. For the first time, we introduce 1,4,8,11-tetraazacyclotetradecane (cyclam) in perovskite precursor solution, and it spontaneously passivates defect states of CsPbBr3-based perovskites by coaction between amine and uncoordinated lead ions during spin-coating without an anti-solvent process. Furthermore, as a delocalized system, cyclam also possesses chemical properties that facilitate exciton transportation. The proposed passivation strategy boosts the external quantum efficiency from 1.25% (control device) to 16.24% (cyclam-passivated device). Furthermore, defect passivation is also conductive to reduce LED degradation paths and improve device stability as the extrapolated lifetime (T 50) of LEDs at an initial brightness of 100 cd/m2 is increased from 0.9 to 127 h. These findings indicate that the introduction of cyclam is highly effective to enhance the performance of LEDs, and such a strategy in effectively reducing the defects could be also applied in other perovskite-based devices, such as lasers, solar cells, and photodetectors.

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“…The crystal structure shows the occurrence of a dehydrogenative oxidation of the ligand with formation of an imine bond between the aliphatic nitrogen in the side arm and the adjacent carbon close to the pyridine ring (Figure ). Relevant bond distances are included in Table , which show that the length of the bond between N4 and C9 is similar to that found in other Fe(II)-imine complexes. , The Fe–N bond lengths are typical of low spin (LS) Fe(II) complexes with ligands containing both aliphatic and pyridine donors. ,,, It is also interesting to note that the complex can be stored for long periods of time without any evidence of subsequent dehydrogenation processes affecting other carbon–nitrogen bonds, in contrast with literature examples showing more extensive dehydrogenation with formation of several imine bonds and even dimeric species resulting from coupling between two macrocyclic units. − …”

Section: Resultsmentioning

confidence: 61%

“…For those reasons, a deeper understanding of dehydrogenative oxidation processes in metal complexes and a way of controlling them would be desirable. The literature includes examples of dehydrogenative oxidation in iron complexes with a variety of ligands that range from simple open-chain aliphatic amines as en to macrocyclic amines as cyclam and related ligands. − Interestingly, there is a significant number of examples of oxidative dehydrogenations including complexes of ligands containing 2-(aminomethyl)pyridyl groups − because of the stability achieved by resonance in the product. Initial oxidation of the metal center is a common mechanistic proposal not only for the case of Fe(II) complexes ,− but also for other metals .…”

Section: Introductionmentioning

confidence: 99%

Iron(II) Complexes with Scorpiand-Like Macrocyclic Polyamines: Kinetico-Mechanistic Aspects of Complex Formation and Oxidative Dehydrogenation of Coordinated Amines

et al. 2017

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The Fe(II) coordination chemistry of a pyridinophane tren-derived scorpiand type ligand containing a pyridine ring in the pendant arm is explored by potentiometry, X-ray, NMR, and kinetics methods. Equilibrium studies in water show the formation of a stable [FeL] complex that converts to monoprotonated and monohydroxylated species when the pH is changed. A [Fe(HL)] complex containing an hexacoordinated dehydrogenated ligand has been isolated, and its crystal structure shows the formation of an imine bond involving the aliphatic nitrogen of the pendant arm. This complex is low spin Fe(II) both in the solid state and in solution, as revealed by the Fe-N bond lengths and by the NMR spectra, respectively. The formation rate of [Fe(HL)] in aqueous solutions containing Fe and L (1:1 molar ratio) is strongly dependent on the pH, the process being completed in times that range from months in acid solutions to hours in basic conditions. However, detailed kinetic studies show that those differences are caused, at least in part, by the effect of pH on the rate of formation of the unoxidized [FeL] complex. In this sense, the protonation of the donor atoms in the pendant arm of the scorpiand ligand leads to the formation of protonated species resistant to oxidative dehydrogenation. Complementary studies in acetonitrile solution indicate that the initial stage in the oxidative dehydrogenation process is the oxidation of the starting complex to form a [FeL] complex, which then undergoes disproportionation into [Fe(HL)] and [FeL]. Experiments starting with Fe(III) have allowed us to determine that disproportionation occurs with first order kinetics both in water and acetonitrile solutions. However, whereas a significant acceleration is observed in water when the pH is increased, no effect of the addition of acid or base on the rate of disproportionation is observed in acetonitrile. Oxidative dehydrogenation of the Fe(II) complex formed in experiments starting with an Fe(III) salt is slower than that occurring when an Fe(II) salt is used, an observation that can be explained in terms of the formation of two different Fe(III) complexes, one of them with a structure unable to evolve directly toward the product of oxidative dehydrogenation.

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Characterization of a delocalized mixed-valence bis-macrocyclic diiron compound

Cited by 33 publications

References 1 publication

Crystal structures and Mössbauer spectra of mixed-valence dinuclear iron(II,III) complexes: detrapped valence states †

Crystal structures and Mössbauer spectra of mixed-valence dinuclear iron(II,III) complexes: detrapped valence states †

Novel Lewis Base Cyclam Self-Passivation of Perovskites without an Anti-Solvent Process for Efficient Light-Emitting Diodes

Iron(II) Complexes with Scorpiand-Like Macrocyclic Polyamines: Kinetico-Mechanistic Aspects of Complex Formation and Oxidative Dehydrogenation of Coordinated Amines

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