A Neutral Borylene and its Conversion to a Radical by Selective Hydrogen Transfer.

A successful selective reduction of X2B-Tip (Tip = 1,3,5-iPr3-C6H2, X = I, Br) with KC8 and Mg metal, respectively, in the presence of a hybrid ligand (C6H4(PPh2)LSi) leads to a stable low-valent five-membered ring as a boryl radical [C6H4(PPh2)LSiBTip][Br] (1) and neutral borylene [C6H4(PPh2)LSiBTip] (2). Compound 2 reacts with 1,4-cyclohexadiene, resulting in hydrogen abstraction to afford the radical [C6H4(PPh2)LSiB(H)Tip] (3). Quantum chemical studies reveal that compound 1 is a B-centered radical, and compound 2 is a phosphane and silylene stabilized neutral borylene in a trigonal planar environment, whereas compound 3 is an amidinate-centered radical. Although compounds 1 and 2 are stabilized by hyperconjugation and π-conjugation, they display high H-abstraction energy and basicity, respectively.

Rhenium Tricarbonyl Complexes of Azodicarboxylate Ligands.

The excellent π-accepting azodicarboxylic esters adcOR (R = Et, iPr, tBu, Bn (CH2-C6H5) and Ph) and the piperidinyl amide derivative adcpip were used as bridging chelate ligands in dinuclear Re(CO)3 complexes [{Re(CO)3Cl}2(µ-adcOR)] and [{Re(CO)3Cl}2(µ-adcpip)]. From the adcpip ligand the mononuclear derivatives [Re(CO)3Cl(adcpip)] and [Re(CO)3(PPh3)(µ-adcpip)]Cl were also obtained. Optimised geometries from density functional theory (DFT) calculations show syn and anti isomers for the dinuclear fac-Re(CO)3 complexes at slightly different energies but they were not distinguishable from experimental IR or UV-Vis absorption spectroscopy. The electrochemistry of the adc complexes showed reduction potentials slightly below 0.0 V vs. the ferrocene/ferrocenium couple. Attempts to generate the radicals [{Re(CO)3Cl}2(µ-adcOR)]•- failed as they are inherently unstable, losing very probably first the Cl- coligand and then rapidly cleaving one [Re(CO)3] fragment. Consequently, we found signals in EPR very probably due to mononuclear radical complexes [Re(CO)3(solv)(adc)]•. The underlying Cl-→solvent exchange was modelled for the mononuclear [Re(CO)3Cl(adcpip)] using DFT calculations and showed a markedly enhanced Re-Cl labilisation for the reduced compared with the neutral complex. Both the easy reduction with potentials ranging roughly from -0.2 to -0.1 V for the adc ligands and the low-energy NIR absorptions in the 700 to 850 nm range place the adc ligands with their lowest-lying π* orbital being localised on the azo function, amongst comparable bridging chelate N^N coordinating ligands with low-lying π* orbitals of central azo, tetrazine or pyrazine functions. Comparative (TD)DFT-calculations on the Re(CO)3Cl complexes of the adcpip ligand using the quite established basis set and functionals M06-2X/def2TZVP/LANL2DZ/CPCM(THF) and the more advanced TPSSh/def2-TZVP(+def2-ECP for Re)/CPCMC(THF) for single-point calculations with BP86/def2-TZVP(+def2-ECP for Re)/CPCMC(THF) optimised geometries showed a markedly better agreement of the latter with the experimental XRD, IR and UV-Vis absorption data.

Excellent yield of a variety of silicon-boron radicals and their reactivity.

Herein we report stable silicon-boron radicals of composition LSi(NMe2)-B(Br)Tip (1), LSi(NMe2)-B(I)Tip (2) LSi(tBu)-B(I)Tip (3) [L = PhC(NtBu)2]. They were prepared in high yield using a one pot reaction of LSiR, X2BTip and KC8 in a 1 : 1 : 1 molar ratio (R = tBu, NMe2; X = Br, I). The reaction of the silicon-boron radical with Br2 and Se affords the dihalogenated compound LSi(tBu)-B(Br2)Tip (4) and oxidative addition product LSi(tBu)Se (5). All the compounds were characterized by single-crystal X-ray structural analysis, electron paramagnetic resonance (EPR) analysis, elemental analysis, multinuclear NMR spectroscopy, and mass spectrometry. Quantum chemical calculations show that the B-centered radicals 1-3 are stabilised by hyperconjugative interactions.

Diosmium compounds containing bis(imidazole)-p-quinone bridging ligands.

The doubly deprotonated bridging ligand L12- derived from 2,6-bis(2-pyridyl)-1,5-dihydro-1',4'-benzoquinono[2',3'-d:5',6'-d']diimidazole H2L1 forms coordination compounds with two bis(2,2'-bipyridine)osmium(II) complex fragments in anti ([1](ClO4)2) and syn configurations ([2](ClO4)2) of {(µ-L1)[Os(bpy)2]2}(ClO4)2, as evident from crystal structure analyses. Exchange of the metal-coordinating 2-pyridyl functions in the bridge through non-coordinating 4-tolyl substituents (L12- → L22-) leads to [3](ClO4)2 which involves chelation of the [Os(bpy)2]2+ groups through imidazole-N and carbonyl-O atoms of the central p-quinone function. In addition to identification, the compounds were subjected to electrochemical (CV, DPV) and spectroelectrochemical (UV-vis-NIR, EPR) analyses of electron transfer, the results being supported by results from TD-DFT calculations. Essential differences between [1n+]/[2n+] and [3n+] systems were found regarding variable but mostly metal centred oxidation, the two processes separated much more for [3n+]. The first reduction is bpy ([1+], [2+]) or quinone ligand centred ([3+]). Electronic structures and electron transfer behaviour are thus highly sensitive to differences of configuration and coordination.

Selective Route to Stable Silicon-Boron Radicals and Their Corresponding Cations.

Herein, we report on a facile and selective one-pot synthetic route to silicon-boron radicals. Reduction of Br2BTip (Tip = 2,4,6-iPrC6H2) with KC8 in the presence of LSi-R affords LSi(tBu)-B(Br)Tip (1) and LSi(N(TMS)2)-B(Br)Tip (2) [L = PhC(NtBu)2]. These first examples of silicon-boron isolated radical species feature spin density on the silicon and boron atoms. 1 and 2 exhibit extraordinary stability to high temperatures under inert conditions in solution and air stability in the solid state. Both radicals have been isolated and fully characterized by electron paramagnetic resonance spectroscopy, SQUID magnetometry, mass spectrometry, cyclic voltammetry, single-crystal X-ray structure analysis, and density functional theory calculations. Moreover, compound 1 exhibits one-electron transfer when treated with 1 equiv of AgSO3CF3 and [Ph3C]+[B(C6F5)4]-, respectively, resulting in the corresponding cations [LSi(tBu)-B(Br)Tip]+[CF3SO3]- (3) and [LSi(tBu)-B(Br)Tip]+[B(C6F5)4]- (4). Compounds 3 and 4 have been characterized with multinuclear NMR and mass spectrometry.

Variable electronic structure and spin distribution in bis(2,2'-bipyridine)-metal complexes (M = Ru or Os) of 4,5-dioxido- and 4,5-diimido-pyrene.

The odd-electron compounds [M(bpy)2(L1)](ClO4) M = Ru ([1](ClO4)) or Os ([2](ClO4)), and the even-electron species [M(bpy)2(H2L2)](ClO4)2, M = Ru ([3](ClO4)2) or Os ([4](ClO4)2) were obtained from pyrene-4,5-dione, L1, or 4,5-diaminopyrene, H4L2, and were characterised structurally, electrochemically and spectroscopically. Experimental and computational analysis (TD-DFT) revealed rather different electronic structures and spin distributions of the paramagnetic monocations 1+-4+. EPR investigations and electronic absorption studies exhibit increasing metal contributions to the singly occupied MO along the series 1+ < 3+ < 4+ < 2+, illustrated by g value and long-wavelength absorbance. In addition to variations of the metal (Ru,Os) and the donor atoms (O,NH) the extension of the π system of the semiquinone-type ligand has a large effect on the electronic structure of the paramagnetic cations.

The Indigo Isomer Epindolidione as a Redox-Active Bridging Ligand for Diruthenium Complexes.

Epindolidione (H2 L), a heteroatom-modified analogue of tetracene and a structural isomer of indigo, forms dinuclear complexes with [RuX2 ]2+ , X=bpy (2,2'-bipyridine, [1]2+ ) or pap (2-phenylazopyridine, [2]2+ ), in its doubly deprotonated bridging form µ-L2- . The dications in compounds meso-[1](ClO4 )2 and meso-[2](ClO4 )2 , [X2 Ru(µ-L)RuX2 ](ClO4 )2 , contain five-membered chelate rings N-C-C-O-RuII with π bridged metals at an intramolecular distance of 7.19 Å. Stepwise reversible oxidation and reduction is mainly ligand centered (oxidation: L2- ; reduction: X), as deduced from EPR of one-electron oxidized and reduced intermediates and from UV/Vis/NIR spectroelectrochemistry, supported by TD-DFT calculation results. The results for [1](ClO4 )2 and [2](ClO4 )2 are qualitatively similar to the ones observed with the deprotonated indigo-bridged isomers with their six-membered chelate ring structures, confirming the suitability of both π systems for molecular electronics applications, low-energy absorptions, and multiple electron transfers.

Structural and Oxidation State Alternatives in Platinum and Palladium Complexes of a Redox-Active Amidinato Ligand.

Reaction of [Pt(DMSO)2 Cl2 ] or [Pd(MeCN)2 Cl2 ] with the electron-rich LH=N,N'-bis(4-dimethylaminophenyl)ethanimidamide yielded mononuclear [PtL2 ] (1) but dinuclear [Pd2 L4 ] (2), a paddle-wheel complex. The neutral compounds were characterized through experiments (crystal structures, electrochemistry, UV-vis-NIR spectroscopy, magnetic resonance) and TD-DFT calculations as metal(II) species with noninnocent ligands L- . The reversibly accessible cations [PtL2 ]+ and [Pd2 L4 ]+ were also studied, the latter as [Pd2 L4 ][B{3,5-(CF3 )2 C6 H3 }4 ] single crystals. Experimental and computational investigations were directed at the elucidation of the electronic structures, establishing the correct oxidation states within the alternatives [PtII (L- )2 ] or [Pt. (L )2 ], [PtII (L0.5- )2 ]+ or [PtIII (L- )2 ]+ , [(PdII )2 (µ-L- )4 ] or [(Pd1.5 )2 (µ-L0.75- )4 ], and [(Pd2.5 )2 (µ-L- )4 ]+ or [(PdII )2 (µ-L0.75- )4 ]+ . In each case, the first alternative was shown to be most appropriate. Remarkable results include the preference of platinum for mononuclear planar [PtL2 ] with an N-Pt-N bite angle of 62.8(2)° in contrast to [Pd2 L4 ], and the dimetal (Pd2 4+ →Pd2 5+ ) instead of ligand (L- →L ) oxidation of the dinuclear palladium compound.

Three Bis-BODIPY Analogous Diruthenium Redox Series: Characterization and Electronic Structure Analysis.

The dianion derived from (2Z,6Z)-3,7-diphenyl-N2,N6-di(pyridin-2-yl)pyrrolo[2,3-f]indole-2,6(1H,5H)-diimine (H2 BL), a modified BODIPY ligand precursor, is shown to be capable of bridging two metal complex fragments RuL2 , L=2,4-pentanedionato (acac- ), 2,2'-bipyridine (bpy) or 2-phenylazopyridine (pap) in [Ru(acac)2 Ru(µ-BL)Ru(acac)2 ] (1/2), [Ru(bpy)2 Ru(µ-BL)Ru(bpy)2 ](ClO4 )2 ([3](ClO4 )2 ) and [Ru(pap)2 Ru(µ-BL)Ru(pap)2 ](ClO4 )2 ([4](ClO4 )2 ). The compounds, including a diastereoisomeric pair 1 (meso) and 2 (rac) were spectroscopically and structurally characterized. Reversible electron transfers as revealed by cyclic and differential pulse voltammetry allowed for an EPR and UV-vis-NIR spectroelectrochemical investigation of several neighboring charge states. Together with susceptibility measurements and TD-DFT calculations the assignment of oxidation states reveals that 1, 2 are diruthenium(III) species which can be oxidized or reduced by one electron whereas 32+ and 42+ contain ruthenium(II) and get reduced or oxidized mainly at the dianionic bridge (32+ ) or are reduced at the ancillary ligands pap (42+ ).

Fused N-Heterocyclic-Bridged Isomeric Diruthenium Complexes [(acac)2Ru(µ-DIPQD)Ru(acac)2]n, n = +2, + 1, 0, -1, -2.

π-Conjugated bridged isomeric diruthenium(II) complexes [(acac)2RuII(µ-DIPQD)RuII(acac)2], 1 (trans) and 2 (cis) (acac- = acetylacetonate, (8E,16E)-N8,N16-diphenylindeno[1,2-b]indeno[2',1':5,6]pyrazino[2,3-g]quinoxaline-8,16-diimine (trans-DIPQD), and (12E,16E)-N12,N16-diphenylindeno[1,2-b]indeno[1',2':5,6]pyrazino[2,3-g]quinoxaline-12,16-diimine (cis-DIPQD) were separated and structurally characterized. The structures of the rac (ΔΔ/ΛΛ) forms of 1 and 2 exhibit two units of {Ru(acac)2}, linked to adjacent pyrazine and imine nitrogen donors of the bridge (DIPQD) in trans and cis modes, with metal-metal separations of 9.050 and 6.330 Å, respectively. The packing diagrams of 1 and 2 revealed an intermolecular π···π stacking interaction (3.202-3.398 Å) involving the face-to-face arrangement of the aromatic rings of DIPQD in adjacent molecules and varying solid-state packing modes, slipped stacking in the former versus brick-layer stacking in the latter. The electronic forms associated with multiple reversible one-electron redox steps of 1 and 2 were addressed by DFT (MO composition, Mulliken spin density distribution), supported by EPR of intermediate paramagnetic states and by UV-vis-NIR spectroelectrochemistry in all redox states. The results reveal similar electronic forms along the redox series irrespective of their isomeric identities in 1 and 2, viz., primarily metal-based oxidations ([(acac)2RuII(µ-DIPQD)RuIII(acac)2]+, 1+/2+, S = 1/2; [(acac)2RuIII(µ-DIPQD)RuIII(acac)2]2+, 12+/22+, S = 1) and bridge-based reductions ([(acac)2RuII(µ-DIPQD•-)RuII(acac)2]-, 1•-/2•-, S = 1/2; [(acac)2RuII(µ-DIPQD2-)RuII(acac)2]2-, 12-/22-, S = 1). TD-DFT analysis of the electronic transitions in the complexes suggests bridge-targeted mixed metal/ligand-based multiple charge transfer transitions over the visible to NIR region in all redox states, while a weak band involving the radical bridge appeared in the long-wavelength region (∼2000 nm) in 1•-/2•-.

Chelate rings of different sizes with non-innocent ligands.

Redox-active unsaturated chelate ligands can be realised with different ring sizes of the resulting metallacycles. An overview is presented, starting from an exposition of non-innocent behaviour and chelate effects. A systematic approach is used to describe the most familiar situation, the metal complexes of 1,4-hetero-1,3-dienes in established forms (e.g. o-quinone, α-dithiolene, and α-diimine ligands) and with less common combinations of O, S, and N heteroatoms. The different steric and electronic conditions in six-membered chelate ring systems derived from the ß-diketonate structure will be discussed with examples of substituted and π extended ligands, including 9-oxidophenalenyl, formazanate, and anions derived from indigo or 9,10-anthraquinone. Four-membered chelate rings existing in at least two ligand-based oxidation states are available through steric and electronic stabilisation in amidinate or triazenide complexes. Three-membered and seven-membered chelate ring situations are discussed briefly as further alternatives.

Isolation of base stabilized fluoroborylene and its radical cation.

Herein, we report the synthesis and characterization of the metal free low valent fluoroborylene [(Me-cAAC)2BF] (1) stabilized by cyclic (alkyl)(amino) carbene (cAAC). The fluoroborylene 1 is obtained by the reductive defluorination of Me-cAAC:BF3 with 2.0 equivalents of KC8 in the presence of 1.0 equivalent of Me-cAAC. Due to its highly electron rich nature, 1 underwent one-electron oxidation with 1.0 equivalent of lithium tetrakis(pentafluorophenyl)borate [LiB(C6F5)4] to form the radical cation [(Me-cAAC)2BF]˙+[B(C6F5)4]- (2). DFT studies suggested that the lone pair of electrons is localized on the boron atom in 1, which explains its unprecedented reactivity. Both compounds 1 and 2 were characterized by X-ray crystallography. The radical cation 2 was studied by EPR spectroscopy.

Synthesis of cAAC stabilized biradical of "Me2Si" and "Me2SiCl" monoradical from Me2SiCl2 - an important feedstock material.

The cyclic alkyl(amino) carbene (cAAC) coordinated biradical of dimethylsilicon was isolated as (cAAC)2Me2Si (1), (cAAC = C(CH2)(CMe2)2N-2,6-i-Pr2C6H3), synthesized from the reduction of Me2SiCl2 using two equivalents of KC8 in the presence of two equivalents of cAAC. The reduction of Me2SiCl2 by one equivalent of KC8 in the presence of one equivalent of cAAC resulted in the stable dimethylsiliconchloride monoradical (cAAC)Me2SiCl (2).

Isolation of Transient Acyclic Germanium(I) Radicals Stabilized by Cyclic Alkyl(amino) Carbenes.

Despite the notable progress in the stabilization of main group radicals by NHCs and cAACs, no germanium radicals have been isolated so far due to synthetic challenges. Stabilization of neutral [:EIR]• (E = Si, Ge) radicals is an uphill task, as these reactive transient species are highly susceptible to dimerization. Herein, we report the synthesis of acyclic neutral germanium(I) radicals Cy-cAAC:GeN(SiMe3)Dip (1) and Me-cAAC:GeN(SiPh3)Mes (2) obtained by the reduction of [Ar(SiR3)NGeCl3] with KC8 in the presence of cAAC. Compounds 1 and 2 are well characterized by single crystal X-ray structural analysis, cyclic voltammetry, and EPR spectroscopy. Furthermore, the structure and bonding of compounds 1 and 2 have been investigated by theoretical methods.

Effect of positional isomerism on the spectroelectrochemical response of 3,6-bis(2-pyridyl)-diketopyrrolopyrrolate bridged bis(carbonylhydridoruthenium) compounds.

Reaction of 3,6-bis(2-pyridyl)-diketopyrrolopyrrole (H2-BPDPP) with two equivalents of [Ru(H)(CO)(Cl)(PPh3)3] in EtOH produced two symmetrical dinuclear isomers, (µ-BPDPP)[Ru(CO)H(PPh3)2]2, green 1 and blue 2, which could be separated chromatographically and characterised spectroscopically (1H and 31P NMR, IR, and UV-VIS). Isomeric forms of 1 and 2 were authenticated using their single crystal X-ray structures. In addition to the essentially planar bis-chelating bridge BPDPP2- and the mutually trans positioned axial PPh3 ligands in both complexes, compound 1 was established with the CO groups trans to the pyrrolate-N atoms, whereas 2 has the π acceptors CO and pyridine-N situated trans to each other. While the reduction of 1 and 2 proceeds irreversibly at negative potentials, the reversible oxidations at rather low potentials could be monitored by EPR and UV-VIS-NIR absorption measurements. Together with TD-DFT calculations, these results reveal that the primary electron transfers are largely confined to the BPDPP ligand. Despite the bridge centred processes, small differences between the isomers 10/+ and 20/+ were found, affecting e.g. the near infrared absorption of the radical cation species.

Mononuclear and Dinuclear Ruthenium Complexes of cis- and trans-Thioindigo: Geometrical and Electronic Structure Analyses.

The compounds [Ru(acac)2(L)] (1) and [Ru2(acac)4(µ-L)] (2) with acac- = acetylacetonato and L = thioindigo were characterized crystallographically with a cis-configurated L and O,O'-coordinated metal in 1 and with trans-configurated L and two S,O-coordinated bridged ruthenium centers for 2. The electronic structures of 1 and 2 were confirmed by spectroscopy and density functional theory calculations, suggesting considerable metal-to-ligand electron transfer resulting in the formation of the thioindigo radical anion and oxidized metal(s). UV-Vis-Near-IR and IR (spectro)electrochemistry was used to investigate charged forms 1 n ( n = 1+, 1-) and 2 n ( n = 1+, 1-, 2-), which reveal electron transfer activity of both the metal and the thioindigo ligand as well as sizable orbital mixing. An intense near-IR absorption is observed for 2- at 2180 nm. The remarkable ligand properties of thioindigo are being discussed in connection to related coordination compounds of indigo derivatives such as dehydroindigo and corresponding ("Nindigo") diimines.

Diruthenium Complexes of p-Benzoquinone-Imidazole Hybrid Ligands: Innocent or Noninnocent Behavior of the Quinone Moiety.

After double deprotonation, 2,6-diaryl-p-benzoquinonodiimidazoles (aryl=4-tolyl (I) or 2-pyridyl (II)) were shown to bridge two [Ru(bpy)2 ]2+ (bpy=2,2'-bipyridine) complex fragments through the imidazolate N and p-quinone O (I→12+ ) or through the imidazolate N and pyridyl N donor atoms (II→22+ ). Characterization by crystal structure analysis, 1 H/13 C NMR spectroscopy, cyclic and differential pulse voltammetry, and spectroelectrochemistry (UV/Vis/NIR, IR, EPR) in combination with TD-DFT calculations revealed surprisingly different electronic structures for redox systems 1n and 2n . Whereas 12+ is reduced to a radical complex with considerable semiquinone character, the reduction of 22+ with its exclusive N coordination exhibits little spin on the now redox-innocent quinone moiety, compared with the electron uptake by the pyridyl-imidazolate chelating site. The first of two close-lying oxidation processes occurs at the bridging heteroquinone ligand, whereas the second oxidation is partly (14+ ) or predominantly (24+ ) centered on the metal atoms.

At the Borderline between Metal-Metal Mixed Valency and a Radical Bridge Situation: Four Charge States of a Diruthenium Complex with a Redox-Active Bis( mer-tridentate) Ligand.

The complex ions [L3Ru(µ,η3:η3-BL)RuL3] n+ (1 n+, L3 = 4,4',4″-tri- tert-butyl-2,6,2',6″-terpyridine and H2BL2- = 1,2-bis(salicyloyl)hydrazide(2-)) were isolated with PF6- or ClO4- counterions ( n = 1) and as bis(hexafluorophosphate) ( n = 2). Structural, electrochemical, and spectroscopic characterization reveals the monocation as intermediate ( Kc = 108.2) in the three-step reversible redox system 10/+/2+/3+. The 1+ ion has the molecule-bridged (Ru- - -Ru 4.727 Å) ruthenium centers involved in five- and six-membered chelate rings, and it exhibits long-wavelength absorptions at λmax 2240, 1660, and 1530 nm (εmax = 1000, 3000, and 8000 M-1 cm-1, respectively), which would be compatible with a RuIIIRuII mixed-valent situation or with a coordinated radical ion bridge. In fact, EPR and DFT analysis of 1+ reveals that the spin is equally distributed over the ligand bridge and over both metals. The oxidized paramagnetic ions 12+ and 13+ have been studied by 1H NMR and EPR and by TD-DFT supported UV-vis-NIR and MIR (mid-IR) spectroelectrochemistry. The capacity of various kinds of bis( mer-tridentate) bridging ligands (π donors or π acceptors, cyclometalated or noncyclometalated) for mediating metal-metal interactions is discussed.

A Route to Base Coordinate Silicon Difluoride and the Silicon Trifluoride Radical.

Silicon difluoride (SiF2 ) is highly unstable at room temperature and condenses at this temperature rapidly to a polymeric material of unknown structure. Therefore, the isolation of a stable monomeric silicon difluoride species is a challenging task. The cyclic alkyl(amino) carbene (cAAC) coordinated silicon difluoride was isolated as (cAAC)2 SiF2 (2), synthesized from the reduction of cAAC-SiF4 (1) by using two equivalents of KC8 in the presence of one equivalent of cAAC. In the solid state, compound 2 is stable at room temperature for a long time under inert conditions. The reduction of compound 1 in the presence of one equivalent KC8 resulted in the first stable silicon trifluoride monoradical (cAAC)SiF3 (3).

Isomeric Diruthenium Complexes Bridged by Deprotonated Indigo in cis and trans Configuration.

The doubly deprotonated form L2- of indigo=H2 L can bind two [Ru(acac)2 ] complex fragments in the cis (1) and trans configuration (2), as evidenced from crystal structure analysis. While the latter type of N,O; N' ,O' coordination has been observed earlier, for example, with [Ru(bpy)2 ]2+ , leading to two equivalent six-membered ring chelates, the cis arrangement in 1 is observed here for the first time in a dinuclear complex, producing one five-membered ring chelate with N,N' coordination and one seven-membered chelate with O,O' coordination. The different structures of the isomers result in differing electrochemical and spectroelectrochemical (EPR, UV-Vis-NIR) responses for various accessible charge states 1n and 2n , n=-, 0, +, 2+. The associated electronic structures were analyzed by DFT (structures, spin density) and TD-DFT calculations (electronic transitions), revealing mainly metal-based reduction but largely indigo ligand-based oxidation of both neutral precursors.