RESUMEN
The application of two-photon excitation (TPE) in the study of light-responsive materials holds immense potential due to its deeper penetration and reduced photodamage. Despite these benefits, TPE has been underutilised in the investigation of the photoinduced spin crossover (SCO) phenomenon. Here, we employ TPE to delve into the out-of-equilibrium dynamics of a SCO FeII dimer of the form [FeII(HL)2]2(BF4)4·2MeCN (HL = 3,5-bis{6-(2,2'-bipyridyl)}pyrazole). Optical transient absorption (OTA) spectroscopy in solution proves that the same dynamics take place under both one-photon excitation (OPE) and TPE. The results show the emergence of the photoinduced high spin state in less than 2 ps and with a lifetime of 147 ns. Time-resolved photocrystallography (TRXRD) reveals a single molecular reorganisation within the first 500 ps following TPE. Additionally, variable temperature single crystal X-ray diffraction (VTSCXRD) and magnetic susceptibility measurements confirm that the thermal transition is silenced by the solvent. While the results of the OTA and TRXRD utilising TPE are intriguing, the high pump fluencies required to excite enough metal centres to the high spin state may impair its practical application. Nonetheless, this study sheds light on the potential of TPE for the investigation of the out-of-equilibrium dynamics of SCO complexes.
RESUMEN
Starting from the dinickel(II) dihydride complex [ML(Ni-H)2] (1M), where L3- is a bis(tridentate) pyrazolate-bridged bis(ß-diketiminato) ligand and M+ is Na+ or K+, a series of complexes [KLNi2(S2)] (2K), [MLNi2S] (3M), [LNi2(SMe)] (4), and [LNi2(SH)] (5) has been prepared. The µ-sulfido complexes 3M can be reversibly oxidized at E1/2 = -1.17 V (in THF; vs Fc+/Fc) to give [LNi2(Sâ¢)] (6) featuring a bridging S-radical. 6 has been comprehensively characterized, including by X-ray diffraction, SQUID magnetometry, EPR and XAS/XES spectroscopies, and DFT calculations. The pKa of the µ-hydrosulfido complex 5 in THF is 30.8 ± 0.4, which defines a S-H bond dissociation free energy (BDFE) of 75.1 ± 1.0 kcal mol-1. 6 reacts with H atom donors such as TEMPO-H and xanthene to give 5, while 5 reacts with 2,4,6-tri(tert-butyl)phenoxy radical in a reverse H atom transfer to generate 6. These findings provide the first full characterization of a genuine M-(µ-Sâ¢-)-M complex and provide insights into its proton-coupled electron transfer (PCET) reactivity, which is of interest in view of the prominence of M-(µ-SH/µ-S)-M units in biological systems and heterogeneous catalysis.
RESUMEN
The extraordinary advances in carbene (R1-C-R2) chemistry have been fuelled by strategies to stabilize the electronic singlet state via π interactions. In contrast, the lack of similarly efficient approaches to obtain authentic triplet carbenes with appreciable lifetimes beyond cryogenic temperatures hampers their exploitation in synthesis and catalysis. Transition-metal substitution represents a potential strategy, but metallocarbenes (M-C-R) usually represent high-lying excited electronic configurations of the well-established carbyne complexes (M≡C-R). Here we report the synthesis and characterization of triplet metallocarbenes (M-C-SiMe3, M = PdII, PtII) that are persistent beyond cryogenic conditions, and their selective reactivity towards carbene C-H insertion and carbonylation. Bond analysis reveals significant stabilization by spin-polarized push-pull interactions along both π-bonding planes, which fundamentally differs from bonding in push-pull singlet carbenes. This bonding model, thus, expands key strategies for stabilizing the open-shell carbene electromers and closes a conceptual gap towards carbyne complexes.
RESUMEN
A µ-oxo diiron complex, featuring the pyridine-2,6-dicarboxamide-based thiazoline-derived redox-active ligand, H2L (H2L = N2,N6-bis(4,5-dihydrothiazol-2-yl)pyridine-2,6-dicarboxamide), was synthesized and thoroughly characterized. [FeIII-(µ-O)-FeIII] showed electrocatalytic hydrogen evolution reaction activity in the presence of different organic acids of varying pKa values in dimethylformamide. Through electrochemical analysis, we found that [FeIII-(µ-O)-FeIII] is a precatalyst that undergoes concerted two-electron reduction to generate an active catalyst. Fourier transform infrared spectrum of reduced species and density functional theory (DFT) investigation indicate that the active catalyst contains a bridged hydroxo unit which serves as a local proton source for the Fe(III) hydride intermediate to release H2. We propose that in this active catalyst, the thiazolinium moiety acts as a proton-transferring group. Additionally, under sufficiently strong acidic conditions, bridged oxygen gets protonated before two-electron reduction. In the presence of exogenous acids of varying strengths, it displays electro-assisted catalytic response at a distinct applied potential. Stepwise electron-transfer and protonation reactions on the metal center and the ligand were studied through DFT to understand the thermodynamically favorable pathways. An ECEC or EECC mechanism is proposed depending on the acid strength and applied potential.
RESUMEN
The cleavage of C-S bonds represents a crucial step in fossil fuel refinement to remove organosulfur impurities. Efforts are required to identify alternatives that can replace the energy-intensive hydrodesulfurization process currently in use. In this context, we have developed a series of bis-thiolato-ligated CrIII complexes supported by the L2- ligand (L2- = 2,2'-bipyridine-6,6'-diyl(bis(1,1-diphenylethanethiolate), one of them displaying desulfurization of one thiolate of the ligand under reducing and acidic conditions at ambient temperature and atmospheric pressure. While only 5-coordinated complexes were previously isolated by reaction of L2- with 3d metal MIII ions, both 5- and 6-coordinated mononuclear complexes have been obtained in the case of CrIII, viz., [CrIIILCl], [CrIIILCl2]-, and [CrIIILCl(CH3CN)]. The investigation of the reactivity of [CrIIILCl(CH3CN)] under reducing conditions led to a dinuclear [CrIII2L2(µ-Cl)(µ-OH)] compound and, in the presence of protons, to the mononuclear CrIII complex [CrIII(LN2S)2]+, where LN2S- is the partially desulfurized form of L2-. A desulfurization mechanism has been proposed involving the release of H2S, as evidenced experimentally.
RESUMEN
Oxidation of [(ArBIG-bian)2-Yb2+(dme)] (1) (ArBIG-bian = 1,2-bis[(2,6-dibenzhydryl-4-methylphenyl)imino]acenaphthene; dme = 1,2-dimethoxyethane) by 0.5 equivalent of Me2NC(S)S-S(S)CNMe2 in dme at ambient temperature affords a mixture of two products, [(ArBIG-bian)2-Yb3+{SC(S)NMe2}1-(dme)] and [(ArBIG-bian)1-Yb2+{SC(S)NMe2}1-(dme)], which represent two redox-isomers (2a and 2b, respectively). Their ratio in solution depends on the solvent as well as on the temperature. In the solid state, a decrease of temperature (350 â 100 K) caused an electron transfer from the Yb2+ ion to the ArBIG-bian radical-anion in isomer 2b to afford isomer 2a. Accordingly, the ratio of isomers 2a and 2b changes from 1 : 1 (350 K) to 3 : 1 (100 K). In contrast, in the dimer [(dme)(dpp-bian)1-Yb2+(µ-Cl)2Yb3+(dpp-bian)2-(dme)] (dpp-bian = 1,2-bis[(2,6-diisopropylphenyl)imino]acenaphthene), which is the sole example of a lanthanide complex that reveals solid-state redox-isomerism (valence tautomerism) reported so far, the electron transfer from the Yb2+ ion to the dpp-bian radical-anion takes place at around 150 K and is completed within a temperature interval of ca. 7 K.
RESUMEN
Most 3d metal-based single-molecule magnets (SMMs) use N-ligands or ligands with even softer donors to impart a particular coordination geometry and increase the zero-field splitting parameter |D|, while complexes with hard O-donor ligands showing slow magnetization relaxation are rare. Here, we report that a diamagnetic NiII complex of a tetradentate ligand featuring two N-heterocyclic carbene and two alkoxide-O donors, [LO,ONi], can serve as a {O,O'}-chelating metalloligand to give a trinuclear complex [(LO,ONi)Co(LO,ONi)](OTf)2 (2) with an elongated tetrahedral {CoIIO4} core, D = -74.3 cm-1, and a spin reversal barrier Ueff = 86.9 cm-1 in the absence of an external dc field. The influence of diamagnetic NiII on the electronic structure of the {CoO4} unit in comparison to [Co(OPh)4]2- (A) has been probed with multireference ab initio calculations. These reveal a contrapolarizing effect of the NiII, which forms stronger metal-alkoxide bonds than the central CoII, inducing a change in ligand field splitting and a 5-fold increase in the magnetic anisotropy in 2 compared to A, with an easy magnetization axis along the Ni-Co-Ni vector. This demonstrates a strategy to enhance the SMM properties of 3d metal complexes with hard O-donors by modulating the ligand field character via the coordination of diamagnetic ions and the benefit of robust metalloligands in that regard.
RESUMEN
There has been much progress on mononuclear chromium(III) complexes featuring luminescence and photoredox activity, but dinuclear chromium(III) complexes have remained underexplored in these contexts until now. We identified a tridentate chelate ligand able to accommodate both meridional and facial coordination of chromium(III), to either access a mono- or a dinuclear chromium(III) complex depending on reaction conditions. This chelate ligand causes tetragonally distorted primary coordination spheres around chromium(III) in both complexes, entailing comparatively short excited-state lifetimes in the range of 400 to 800â ns in solution at room temperature and making photoluminescence essentially oxygen insensitive. The two chromium(III) ions in the dimer experience ferromagnetic exchange interactions that result in a high spin (S=3) ground state with a coupling constant of +9.3â cm-1. Photoinduced energy transfer from the luminescent ferromagnetically coupled dimer to an anthracene derivative results in sensitized triplet-triplet annihilation upconversion. Based on these proof-of-principle studies, dinuclear chromium(III) complexes seem attractive for the development of fundamentally new types of photophysics and photochemistry enabled by magnetic exchange interactions.
RESUMEN
Radicals of the lightest group 13 element, boron, are well established and observed in numerous forms. In contrast to boron, radical chemistry involving the heavier group 13 elements (aluminum, gallium, indium, and thallium) remains largely underexplored, primarily attributed to the formidable synthetic challenges associated with these elements. Herein, we report the synthesis and isolation of planar and twisted conformers of a doubly CAAC (cyclic alkyl(amino)carbene)-radical-substituted dialane. Extensive characterization through spectroscopic analyses and X-ray crystallography confirms their identity, while quantum chemical calculations support their open-shell nature and provide further insights into their electronic structures. The dialane-connected diradicals exhibit high susceptibility to oxidation, as evidenced by electrochemical measurements and reactions with o-chloranil and a variety of organic azides. This study opens a previously uncharted class of dialuminum systems to study, broadening the scope of diradical chemistry and its potential applications.
RESUMEN
Discrete spin crossover (SCO) tetranuclear cages are a unique class of materials that have potential use in next-generation molecular recognition and sensing. In this work, two new edge-bridged SCO FeII4L6 (L = 2,7-bis(((E)-pyridin-2-ylmethylene)amino)benzo[lmn] [3,8]phenanthroline-1,3,6,8(2H,7H)-tetraone) supramolecular cages with different counter anions: ClO4- (2) and CF3SO3- (3) were constructed via subcomponent self-assembly to investigate both solvent and anion influences on their magnetic properties and compare them to cage 1 with a BF4- anion. Pyridyl-hydrazone bidentate ligand scaffolds were employed to replace the 'classical' imidazole/thiazolyl-imine coordination units to induce SCO behaviour in these cages. 2 and 3 were structurally characterized by single-crystal X-ray diffraction analysis and electrospray ionization time-of-flight mass spectrometry. Magnetic susceptibilities of 1-3 and 1-3·desolvated indicate that the solvents' presence is in favor of the low-spin (LS) state. While different counter anions in 1-3·desolvated affect the spin-state configurations of the four FeII metal centers. According to the 57Fe Mössbauer spectral analysis, the spin-state distributions in 1-3 at 80 K are [2 high-spin (HS)-2LS], [1HS-3LS] and [2HS-2LS], respectively and density functional theory calculations were employed to investigate the reasons. These findings provide insights to regulate the spin-state versatility of SCO FeII cage systems in the solid state.
RESUMEN
Phosphorus-centered disbiradicals, in which the radical sites exist as individual spin doublets with weak spin-spin interaction have not been known so far. Starting from monoradicals of the type [â P(µ-NTer)2 P-R], we have now succeeded in linking two such monoradical phosphorus centers by appropriate choice of a linker. To this end, biradical [â P(µ-NTer)2 Pâ ] (1) was treated with 1,6-dibromohexane, affording the brominated species {Br[P(µ-NTer)]2 }2 C6 H12 (3). Subsequent reduction with KC8 led to the formation of the disbiradical {â [P(µ-NTer)]2 }2 C6 H12 (4) featuring a large distance between the radical phosphorus sites in the solid state and formally the highest biradical character observed in a P-centered biradical so far, approaching 100 %. EPR spectroscopy revealed a three-line signal in solution with a considerably larger exchange interaction than would be expected from the molecular structure of the single crystal. Quantum chemical calculations revealed a highly dynamic conformational space; thus, the two radical sites can approach each other with a much smaller distance in solution. Further reduction of 4 resulted in the formation of a potassium salt featuring the first structurally characterized P-centered distonic radical anion (5- ). Moreover, 4 could be used in small molecule activation.
RESUMEN
Four new pentadentate N5-donor ligands, [N-(1-methyl-2-imidazolyl)methyl-N-(2-pyridyl)-methyl-N-(bis-2-pyridylmethyl)-amine] (L1), [N-bis(1-methyl-2-imidazolyl)methyl-N-(bis-2-pyridylmethyl)amine] (L2), (N-(isoquinolin-3-ylmethyl)-1,1-di(pyridin-2-yl)-N-(pyridin-2-ylmethyl)methanamine (L3), and N,N-bis(isoquinolin-3-ylmethyl)-1,1-di(pyridin-2-yl)methanamine (L4), have been synthesized based on the N4Py ligand framework, where one or two pyridyl arms of the N4Py parent are replaced by (N-methyl)imidazolyl or N-(isoquinolin-3-ylmethyl) moieties. Using these four pentadentate ligands, the mononuclear complexes [FeII(CH3CN)(L1)]2+ (1a), [FeII(CH3CN)(L2)]2+ (2a), [FeII(CH3CN)(L3)]2+ (3a), and [FeII(CH3CN)(L4)]2+ (4a) have been synthesized and characterized. The half-wave potentials (E1/2) of the complexes become more positive in the order: 2a < 1a < 4a ≤ 3a ≤ [Fe(N4Py)(CH3CN)]2+. The order of redox potentials correlates well with the Fe-Namine distances observed by crystallography, which are 2a > 1a ≥ 4a > 3a ≥ [Fe(N4Py)(CH3CN)]2+. The corresponding ferryl complexes [FeIV(O)(L1)]2+ (1b), [FeIV(O)(L2)]2+ (2b), [FeIV(O)(L3)]2+ (3b), and [FeIV(O)(L4)]2+ (4b) were prepared by the reaction of the ferrous complexes with isopropyl 2-iodoxybenzoate (IBX ester) in acetonitrile. The greenish complexes 3b and 4b were also isolated in the solid state by the reaction of the ferrous complexes in CH3CN with ceric ammonium nitrate in water. Mössbauer spectroscopy and magnetic measurements (using superconducting quantum interference device) show that the four complexes 1b, 2b, 3b, and 4b are low-spin (S = 1) FeIVâO complexes. UV/vis spectra of the four FeIVâO complexes in acetonitrile show typical long-wavelength absorptions of around 700 nm, which are expected for FeIVâO complexes with N4Py-type ligands. The wavelengths of these absorptions decrease in the following order: 721 nm (2b) > 706 nm (1b) > 696 nm (4b) > 695 nm (3b) = 695 nm ([FeIV(O) (N4Py)]2+), indicating that the replacement of the pyridyl arms with (N-methyl) imidazolyl moieties makes L1 and L2 exert weaker ligand fields than the parent N4Py ligand, while the ligand field strengths of L3 and L4 are similar to the N4Py parent despite the replacement of the pyridyl arms with N-(isoquinolin-3-ylmethyl) moieties. Consequently, complexes 1b and 2b tend to be less stable than the parent [FeIV(O)(N4Py)]2+ complex: the half-life sequence at room temperature is 1.67 h (2b) < 16 h (1b) < 45 h (4b) < 63 h (3b) ≈ 60 h ([FeIV(O)(N4Py)]2+). Compared to the parent complex, 1b and 2b exhibit enhanced reactivity in both the oxidation of thioanisole in the oxygen atom transfer (OAT) reaction and the oxygenation of C-H bonds of aromatic and aliphatic substrates, presumed to occur via an oxygen rebound process. Furthermore, the second-order rate constants for hydrogen atom transfer (HAT) reactions affected by the ferryl complexes can be directly related to the C-H bond dissociation energies of a range of substrates that have been studied. Using either IBX ester or H2O2 as an oxidant, all four new FeII complexes display good performance in catalytic reactions involving both HAT and OAT reactions.
RESUMEN
A labile organoazide iron complex is reported. Under ambient conditions, the azide adduct is subject to a dissociation equilibrium in solution, yet also undergoes intramolecular C-H bond amination. Single-crystal irradiation of the azide at 80 K leads to partial N2-extrusion and formation of a putative imido iron intermediate, which was computationally identified as a highly covalent {FeNR}8 species.
RESUMEN
The structural evolution of spin crossover (SCO) complexes during their spin transition at equilibrium and out-of-equilibrium conditions needs to be understood to enable their successful utilisation in displays, actuators and memory components. In this study, diffraction techniques were employed to study the structural changes accompanying the temperature increase and the light irradiation of a defect [2 × 2] triiron(II) metallogrid of the form [FeII3LH2(HLH)2](BF4)4·4MeCN (FE3), LH = 3,5-bis{6-(2,2'-bipyridyl)}pyrazole. Although a multi-temperature crystallographic investigation on single crystals evidenced that the compound does not exhibit a thermal spin transition, the structural analysis of the defect grid suggests that the flexibility of the grid, provided by a metal-devoid vertex, leads to interesting characteristics that can be used for intermolecular cooperativity in related thermally responsive systems. Time-resolved photocrystallography results reveal that upon excitation with a ps laser pulse, the defect grid shows the first two steps of the out-of-equilibrium process, namely the photoinduced and elastic steps, occurring at the ps and ns time scales, respectively. Similar to a previously reported [2 × 2] tetrairon(II) metallogrid, FE3 exhibits a local distortion of the entire grid during the photoinduced step and a long-range distortion of the lattice during the elastic step. Although the lifetime of the pure photoinduced high spin (HS) state is longer in the tetranuclear grid than in the defect grid, suggesting that the global nuclearity plays a crucial role for the lifetime of the photoinduced species, the influence of the co-crystalising solvent on the lifetime of the photoinduced HS state remains unknown. This study sheds light on the out-of-equilibrium dynamics of a thermally silent defect triiron SCO metallogrid.
RESUMEN
For single-ion magnets (SIMs), understanding the effects of the local coordination environment and ligand field on magnetic anisotropy is key to controlling their magnetic properties. Here we present a series of tetracoordinate cobalt(ii) complexes of the general formula [FL2Co]X2 (where FL is a bidentate diamido ligand) whose electron-withdrawing -C6F5 substituents confer stability under ambient conditions. Depending on the cations X, these complexes adopt structures with greatly varying dihedral twist angle δ between the N-Co-N' chelate planes in the solid state (48.0 to 89.2°). AC and DC field magnetic susceptibility measurements show this to translate into very different magnetic properties, the axial zero-field splitting (ZFS) parameter D ranging from -69 cm-1 to -143 cm-1 with substantial or negligible rhombic component E, respectively. A close to orthogonal arrangement of the two N,N'-chelating σ- and π-donor ligands at the Co(ii) ion is found to raise the energy barrier for magnetic relaxation to above 400 K. Multireference ab initio methods were employed to describe the complexes' electronic structures, and the results were analyzed within the framework of ab initio ligand field theory to probe the nature of the metal-ligand bonding and spin-orbit coupling. A relationship between the energy gaps of the first few electronic transitions and the ZFS was established, and the ZFS was correlated with the dihedral angle δ as well as with the metal-ligand bonding variations, viz. the two angular overlap parameters eσ and eπs. These findings not only give rise to a Co(ii) SIM showing open hysteresis up to 3.5 K at a sweep rate of 30 Oe s-1, but they also provide design guidelines for Co(ii) complexes with favorable SIM signatures or even switchable magnetic relaxation properties.
RESUMEN
Two homoleptic Fe(II) complexes in different spin states bearing superbasic terpyridine derivatives as ligands are investigated to determine the relationship between spin state and electrochemical/spectroscopic behavior. Antiferromagnetic coupling between a ligand-centered radical and the high-spin metal center leads to an anodic shift of the first reduction potential and results in a species that shows mixed valency with a moderately intense intervalence-charge-transfer band. The differences afforded by the different spin states extend to the electrochemical reactivity of the complexes: while the low-spin species is a precatalyst for electrocatalytic CO2 reduction and leads to the preferential formation of CO with a Faradaic efficiency of 37%, the high-spin species only catalyzes proton reduction at a modest Faradaic efficiency of approximately 20%.
RESUMEN
A comprehensive understanding of the ligand field and its influence on the degeneracy and population of d-orbitals in a specific coordination environment are crucial for the rational design and enhancement of magnetic anisotropy of single-ion magnets (SIMs). Herein, we report the synthesis and comprehensive magnetic characterization of a highly anisotropic CoII SIM, [L2Co](TBA)2 (L is an N,N'-chelating oxanilido ligand), that is stable under ambient conditions. Dynamic magnetization measurements show that this SIM exhibits a large energy barrier to spin reversal U eff > 300 K and magnetic blocking up to 3.5 K, and the property is retained in a frozen solution. Low-temperature single-crystal synchrotron X-ray diffraction used to determine the experimental electron density gave access to Co d-orbital populations and a derived U eff, 261 cm-1, when the coupling between the d x 2 - y 2 and dxy orbitals is taken into account, in very good agreement with ab initio calculations and superconducting quantum interference device results. Powder and single-crystal polarized neutron diffraction (PNPD, PND) have been used to quantify the magnetic anisotropy via the atomic susceptibility tensor, revealing that the easy axis of magnetization is pointing along the N-Co-N' bisectors of the N,N'-chelating ligands (3.4° offset), close to the molecular axis, in good agreement with complete active space self-consistent field/N-electron valence perturbation theory to second order ab initio calculations. This study provides benchmarking for two methods, PNPD and single-crystal PND, on the same 3d SIM, and key benchmarking for current theoretical methods to determine local magnetic anisotropy parameters.
RESUMEN
Permethylation of the phenylene linker in a cationic ferrocenyl-phenylthioxanthylium dyad increases the amount of the diradical ferrocenium thioxanthyl radical valence tautomer and aids in supressing dimerization of the latter and of the one-electron reduced neutral radical.
RESUMEN
The rational design of 3d-metal-based single-molecule magnets (SMM) requires a fundamental understanding of their intrinsic electronic and structural properties and how they translate into experimentally observable features. Here, we determined the magnetic properties of the linear iron(I) silylamides K{crypt}[FeL2] and [KFeL2] (L = -N(Dipp)SiMe3; crypt = 4,7,13,16,21,24-Hexaoxa-1,10-diazabicyclo[8.8.8]hexacosan). For the former, slow-relaxation of the magnetization with a spin reversal barrier of Ueff = 152 cm-1 as well as a closed-waist magnetic hysteresis and magnetic blocking below 2.5 K are observed. For the more linear [KFeL2], in which the potassium cation is encapsulated by the aryl substituents of the amide ligands, the relaxation barrier and the blocking temperature increase to Ueff = 184 cm-1 and TB = 4.5 K, respectively. The increase is rationalized by a more pronounced axial anisotropy in [KFeL2] determined by dc-SQUID magnetometry. The effective relaxation barrier of [KFeL2] is in agreement with the energy spacing between the ground and first-excited magnetic states, as obtained by field-dependent IR-spectroscopy (178 cm-1), magnetic measurements (208 cm-1), as well as theoretical analysis (212 cm-1). In comparison with the literature, the results show that magnetic coercivity in linear iron(I) silylamides is driven by the degree of linearity in conjunction with steric encumbrance, whereas the ligand symmetry is a marginal factor.
RESUMEN
Although iron is a dream candidate to substitute noble metals in photoactive complexes, realization of emissive and photoactive iron compounds is demanding due to the fast deactivation of their charge-transfer states. Emissive iron compounds are scarce and dual emission has not been observed before. Here we report the FeIII complex [Fe(ImP)2][PF6] (HImP = 1,1'-(1,3-phenylene)bis(3-methyl-1-imidazol-2-ylidene)), showing a Janus-type dual emission from ligand-to-metal charge transfer (LMCT)- and metal-to-ligand charge transfer (MLCT)-dominated states. This behaviour is achieved by a ligand design that combines four N-heterocyclic carbenes with two cyclometalating aryl units. The low-lying π* levels of the cyclometalating units lead to energetically accessible MLCT states that cannot evolve into LMCT states. With a lifetime of 4.6 ns, the strongly reducing and oxidizing MLCT-dominated state can initiate electron transfer reactions, which could constitute a basis for future applications of iron in photoredox catalysis.