Electrochemical, spectroscopic and magnetic properties of complexes of a new hemilabile non-innocent ligand and of different azobispyridines

In dieser Arbeit wurde gezeigt, wie geringe Änderungen in der Ligandenstruktur zu signifikanten Veränderungen der Eigenschaften von Komplexen führen können. Hierfür wurden Übergangsmetallkomplexe mit zwei Klassen nicht-unschuldiger Liganden untersucht: Ein neuer chinoider hemilabiler Ligand (QM) mit einer sterisch flexiblen S-Donorfunktion in Koordinationsverbindungen mit ausgewählten Übergangsmetallionen, und redoxaktive Bischelat-Azoverbindungen in Komplexen mit den {(bpy)2Ru}2+- oder {(acac)2Ru}-Komplexfragmenten. Im ersten Fall wurde eine leichtere und stabilere Koordination des S-Donoratoms durch die erhöhte Flexibilität von QMn im Vergleich zum rigideren Qy beobachtet. Die Redoxprozesse finden bei allen untersuchten Iminosemichinonat-Komplexen zumeist an den Liganden statt, allerdings kann aufgrund der vergleichbaren energetischen Lage der Grenzorbitale von chinoiden Liganden und Metallionen in Abhängigkeit vom Metall eine unterschiedlich starke Delokalisation hauptsächlich des LUMOs über Metall und Liganden beobachtet werden. Die im Vergleich zu Qy erleichterte und stabilere M-S-Bindung wurde mithilfe der homoleptischen Komplexe von CuII, NiII und CoIII gezeigt, ebenso der Einfluss geringer Änderungen der Koordination auf den Spinzustand ([Cu(QM)2]) und den Grad der Delokalisation der Grenzorbitale ([Ru(QM)2]). Im 3. Kapitel dieser Arbeit wurden ein- und zweikernige Ruthenium-Komplexe mit unterschiedlichen bisbidentaten Azoverbindungen untersucht. Mit dem {(bpy)2Ru}2+-Komplexfragment wurden einkernige, mit dem {(acac)2Ru}-Fragment ein- und zweikernige Verbindungen dargestellt. Bei den verwendeten Azoliganden handelt es sich um teilweise unveröffentlichte Derivate des 2,2‘-Azobispyridins abpy (e, f, h, i) und um die azoverbrückten Azole a, c sowie d. Bei den Einkernkomplexen ist eine Steuerung der elektrochemischen und spektroskopischen Eigenschaften durch die Variation der elektronischen Eigenschaften der Komplexkomponenten möglich. Durch den Wechsel der Coliganden von bpy zu acac- ist eine stärkere Änderung zu erreichen als durch Substitutionen am abpy, wodurch eine Feinabstimmung vorgenommen werden kann. Durch den Austausch der elektronenarmen Pyridingruppen durch elektronenreiche Azolsubstituenten werden Liganden erzeugt, die gleichzeitig gute akzeptive und donative Eigenschaften aufweisen, die Grenzorbitale sind über das gesamte Ligandengerüst delokalisiert. Die extrem niedrigen Reduktionspotentiale von a und d führen bei Verwendung des elektronenreichen {(acac)2Ru}-Fragments schon bei den Einkernkomplexen zur Reduktion des nicht-unschuldigen Liganden zur radikalanionischen Form (2a) bzw. zu einer ausgeprägten Delokalisation der Grenzorbitale über Metall und Azoligand (2d), was zeigt, dass auch die räumliche Lage der Grenzorbitale zwischen Ruthenium und Azoligand gezielt beeinflusst werden kann. Durch die Koordination eines zweiten Komplexfragments können die elektronischen Einflüsse der Substituenten durch den Einfluss der sterischen Effekte überlagert werden. So unterscheiden sich die Absorptionsmaxima gleicher Übergänge von meso- und rac-Form der Komplexe z.T. stärker als die von Verbindungen mit unterschiedlichen Brückenliganden. Bei 3e - 3i liegen z.B. die Absorptionsmaxima der intensiven MLCT/IVCT-Banden der rac- und meso-Form eines Komplexes um mindestens 10 nm auseinander (meso > rac) und die der gleichen Diastereome von Komplexen mit unterschiedlichen Brückenliganden um maximal 8 nm (zwischen 3er und 3fr). Die Stabilität der gemischtvalenten Formen wird durch die Substitution am abpy verändert und mit sinkender Pi-Akzeptivität des Brückenliganden größer . Eine Kombination aus elektronischen und sterischen Effekten führt bei den Zweikernkomplexen mit azolhaltigen Azoverbindungen zur zweifachen Reduktion des Brückenliganden und dem Auftreten von Gemischtvalenz in den Monoanionen.This thesis shows how small changes in the ligand structure can result in significant changes in the properties of coordination compounds. For this purpose transition metal complexes of two kinds of non-innocent ligands were investigated: a new quinonoid hemilabile ligand with a sterically flexible S-donor function in coordination compounds with selected transition metal ions and redox active bis-chelating azo compounds with the {(bpy)2Ru}2+ or {(acac)2Ru} complex fragments. In the first case, an easier and more stable coordination of the S-donor atom is established due to the increased flexibility of QMn compared to the more rigid Qy. In all iminosemiquinonate-complexes investigated the redox processes take place at the ligands, however, due to the comparable energies of the frontier orbitals of quinonoid ligands and metal ions, a variable degree of delocalisation over metal and ligands can be observed which concerns the LUMO most and is dependent on the metal. The easier and more stable M-S coordination as compared to Qy, was shown in the complexes of CuII, NiII and CoIII as well as the influence of small changes in the coordinationsphere on the spin state ([Cu(QM)2]) and the degree of delocalisation of the frontier orbitals ([Ru(QM)2]). In the third chapter of this thesis mono- and dinuclear ruthenium complexes with different bisbidentate azo compounds were investigated. With the {(bpy)2Ru}2+ fragment mononuclear complexes were synthesised, with the {(acac)2Ru} fragment mono- as well as dinuclear compounds. The azo used ligands are partly unpublished derivatives of 2,2'-azobispyridine abpy (e, f, h, i) as well as the azo-bridged azoles a, c and d. For the mononuclear compounds a control of the electrochemical and spectroscopic properties is possible by variation of the electronic properties of the complex components. By changing the coligands from bpy to acac- a larger modification can be achieved than by substitutions at the abpy, whereby fine-tuning can be undertaken. By replacement of the electron-poor pyridine groups by electron-rich azole substituents ligands are generated that exhibit good acceptive as well as good donative properties. Furthermore the frontier orbitals are delocalised over the whole ligand framework. The extremely low reduction potentials of a and d induce a reduction of the non-innocent ligand to its radical anionic form already in the native state of the mononuclear complexes if the electron-rich {(acac)2Ru} fragment is used (2a). In another complex a distinct delocalisation of the frontier orbitals over metal and ligand (2d) is observed, that shows that the spatial position of the frontier orbitals between ruthenium and azo ligand can be affected selectively. By coordination of a second complex fragment the electronic influences of the substituents may be overlain by steric effects. The absorption maxima of the same transitions in the meso and rac forms of the complexes are can differ more than in compounds with different bridging ligands. For 3e - 3i for example, the absorption maxima of the intense MLCT/IVCT bands of the corresponding rac and meso form are different by at least 10 nm (meso > rac) while the same diastereomers of complexes with different bridging ligands differ by about 8 nm at most (between 3er and 3fr). The stability of the mixed-valent form can be varied by substitution at the abpy and increases with decreasing pi-acceptivity of the bridging ligand . A combination of electronic and steric effects leads to a previously not observed twofold reduction of the bridging ligand for the dinuclear complexes with azole-containing azo compounds and to mixed-valence in the monoanions

A structurally characterised redox pair involving an indigo radical: indigo based redox activity in complexes with one or two [Ru(bpy)(2)] fragments

The reaction between indigo, H(2)Ind, and {Ru(bpy)(2)(EtOH)(2)}(2+) in EtOH/NaOH produced the compounds [Ru(bpy)(2)(mu-Ind)]ClO4 [1] ClO4, rac-{[Ru(bpy)(2)](2)(mu-Ind)}(ClO4)(2) [2](ClO4)(2), and meso-{[Ru(bpy)(2)](2)(mu-Ind)}(ClO4)(3) [2](ClO4)(3), which were structurally characterised, the latter as the first stable, isolable radical complex of indigo. The redox pair 2(2+)/2(3+) showed little structural difference, as confirmed using DFT calculations. The redox series 1(n) and 2(n) were investigated using voltammetry and spectroelectrochemistry (EPR, UV-vis-NIR). Remarkably, the EPR results for 1, 1(2+), 2(+) and 2(3+) revealed mostly ligand based spin in ruthenium(II) complexes of the indigo-derived radical ligands HInd(center dot 2-), HInd(center dot), Ind(center dot 3-) and Ind(center dot-), in agreement with the DFT calculated spin densities. The dominance of the frontier orbitals by the metalstabilised indigo chromophore was also confirmed via the TD-DFT based assignment of near-infrared absorptions as intra-indigo or ligand-to-ligand charge transfer transitions

Different manifestations of enhanced pi-acceptor ligation at every redox level of [Os(9-OP)L-2](n), n=2+, +, 0, - (9-OP-=9-oxidophenalenone and L = bpy or pap)

The title complexes were isolated as structurally characterised compounds [Os-II(9-OP)L-2]ClO4, L = 2,2'-bipyridine (bpy) or 2-phenylazopyridine (pap), and were compared with ruthenium analogues. A reversible one-electron oxidation and up to three reduction processes were observed by voltammetry (CV, DPV) and spectroelectrochemistry (UV-vis-NIR, partially EPR). Supporting calculations (DFT, TD-DFT) were used to assess the oxidation state combinations of the different redox active ligands and of the metal, revealing the effects of Os versus Ru exchange and of bpy versus pap acceptor ligation. Several unexpected consequences of these variations were observed for members of the new osmium-containing redox series. Remarkably, the EPR results exhibit a clear dichotomy between the complex ion [Os-III(9-OP-)( bpy)(2)](2+) and the radical species [Os-II(9-OP-)(pap)(2)](2+), which has not been similarly observed for the analogous [Ru-III(9-OP-)(L2)](2+) systems. This difference, unprecedented for 5d(n) systems, is attributed to the superior stabilisation of the Os-II state by the strongly pi-accepting pap ligands. The reduced forms [Os-II(9-OP-)(pap(-))(pap)] and [OsII(9-OP-)(pap(-))(2)](-) exhibit strong inter-ligand interactions, leading to spin isomers and electron hopping

Ruthenium nitrosyl complexes with 1,4,7-trithiacyclononane and 2,2 '-bipyridine (bpy) or 2-phenylazopyridine (pap) coligands. Electronic structure and reactivity aspects

The present article describes ruthenium nitrosyl complexes with the {RuNO}(6) and {RuNO}(7) notations in the selective molecular frameworks of [Ru(II)([9]aneS(3))(bpy)(NO(+))](3+) (4(3+)), [Ru(II)([9] aneS(3))(pap) (NO(+))](3+) (8(3+)) and [Ru(II)([9] aneS(3))(bpy)(NOS)](2+) (4(2+)), [Ru(II)([9]aneS(3))(pap)(NO center dot)](2+) (8(2+)) ([9] aneS(3) = 1,4,7-trithiacyclononane, bpy = 2,2'-bipyridine, pap = 2-phenylazopyridine), respectively. The nitrosyl complexes have been synthesized by following a stepwise synthetic procedure: {Ru(II)-Cl} -> {Ru(II)-CH(3)CN} -> {Ru(II)-NO(2)} -> {Ru(II)-NO(+)} -> {Ru(II)-NO(center dot)}. The single-crystal X-ray structure of 4(3+) and DFT optimised structures of 4(3+), 8(3+) and 4(2+), 8(2+) establish the localised linear and bent geometries for {Ru-NO(+)} and {Ru-NO(center dot)} complexes, respectively. The crystal structures and (1)H/(13)C NMR suggest the [333] conformation of the coordinated macrocyclic ligand ([9] aneS(3)) in the complexes. The difference in pi-accepting strength of the co-ligands, bpy in 4(3+) and pap in 8(3+) (bpy {Ru(I)-NO(+)}(minor). The electronic transitions of the complexes have been assigned based on the TD-DFT calculations on their DFT optimised structures. The estimated second-order rate constant (k, M(-1) s(-1)) of the reaction of the nucleophile, OH(-) with the electrophilic {Ru(II) NO(+)} for the bpy derivative (4(3+)) of 1.39 x 10(-1) is half of that determined for the pap derivative (8(3+)), 2.84 x 10(-1) in CH(3)CN at 298 K. The Ru-NO bond in 4(3+) or 8(3+) undergoes facile photolytic cleavage to form the corresponding solvent species {Ru(II)-CH(3)CN}, 2(2+) or 6(2+) with widely varying rate constant values, (k(NO), s(-1)) of 1.12 10(-1) (t(1/2) = 6.2 s) and 7.67 10(-3) (t(1/2) = 90.3 s), respectively. The photo-released NO can bind to the reduced myoglobin to yield the Mb-NO adduct

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

The doubly deprotonated form L2- of indigo=H2L 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 1(n) and 2(n), 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

1,5-Diamido-9,10-anthraquinone, a Centrosymmetric Redox-Active Bridge with Two Coupled beta-Ketiminato Chelate Functions: Symmetric and Asymmetric Diruthenium Complexes

The dinuclear complexes {(mu-H2L)[Ru(bpy)(2)](2)}(ClO4)(2) ([3] (ClO4)(2)), {(mu-H2L)[Ru(pap)(2)](2)}(ClO4)(2) ([4](ClO4)(2)), and the asymmetric [(bpy)(2)Ru(mu-H2L)Ru(pap)(2)]-(ClO4)(2) ([5](ClO4)(2)) were synthesized via the mononuclear species [Ru(H3L)(bpy)(2)]ClO4 ([1]ClO4) and [Ru(H3L)(pap)(2)]ClO4 ([2]ClO4), where H4L is the centrosymmetric 1,5-diamino-9,10-anthraquinone, bpy is 2,2'-bipyridine, and pap is 2-phenylazopyridine. Electrochemistry of the structurally characterized [1]ClO4, [2]ClO4, [3](ClO4)(2), [4](ClO4)(2), and [5] (ClO4)(2) reveals multistep oxidation and reduction processes, which were analyzed by electron paramagnetic resonance (EPR) of paramagnetic intermediates and by UV vis NIR spectro-electrochemistry. With support by time-dependent density functional theory (DFT) calculations the redox processes could be assigned. Significant results include the dimetal/bridging ligand mixed spin distribution in 3(3+) versus largely bridge-centered spin in 4(3+)-a result of the presence of Ru-II-stabilizig pap coligands. In addition to the metal/ligand alternative for electron transfer and spin location, the dinuclear systems allow for the observation of ligand/ligand and metal/metal site differentiation within the multistep redox series. DFT-supported EPR and NIR absorption spectroscopy of the latter case revealed class II mixed-valence behavior of the oxidized asymmetric system 5(3+) with about equal contributions from a radical bridge formulation. In comparison to the analogues with the deprotonated 1,4-diaminoanthraquinone isomer the centrosymmetric H2L2- bridge shows anodically shifted redox potentials and weaker electronic coupling between the chelate sites

Noninnocence of Indigo: Dehydroindigo Anions as Bridging Electron-Donor Ligands in Diruthenium Complexes

Complexes of singly or doubly deprotonated indigo (H₂Ind) with one or two [Ru­(pap)₂]²⁺ fragments (pap = 2-phenylazopyridine) have been characterized experimentally [molecular structure, voltammetry, electron paramagnetic resonance (EPR), and UV–vis–near-IR spectroelectrochemistry] and by time-dependent density functional theory calculations. The compound [Ru­(pap)₂(HInd^–)]­ClO₄ ([<b>1</b>]­ClO₄) was found to contain an intramolecular NH---O hydrogen bond, whereas [{Ru­(pap)₂}₂(μ-Ind^2–)]­(ClO₄)₂ ([<b>2</b>]­(ClO₄)₂), isolated as the meso diastereoisomer with near-IR absorptions at 1162 and 991 nm, contains two metals bridged at 6.354 Å distance by the bischelating indigo dianion. The spectroelectrochemical study of multiple reversible reduction and oxidation processes of <b>2</b>^<i>n</i> (<i>n</i> = 4+, 3+, 2+, 1+, 0, 1–, 2–, 3–, 4−) reveals the stepwise addition of electrons to the terminal π-accepting pap ligands, whereas the oxidations occur predominantly at the anionic indigo ligand, producing an EPR-identified indigo radical intermediate and revealing the suitability of deprotonated indigo as a σ- and π-donating bischelating bridge

Solar Cell Sensitizer Models [Ru(bpy-R)₂(NCS)₂] Probed by Spectroelectrochemistry

Complexes [Ru­(bpy-R)₂(NCS)₂], where R = H (<b>1</b>), 4,4′-(CO₂Et)₂ (<b>2</b>), 4,4′-(OMe)₂ (<b>3</b>), and 4,4′-Me₂ (<b>4</b>), were studied by spectroelectrochemistry in the UV–vis and IR regions and by in situ electron paramagnetic resonance (EPR). The experimental information obtained for the frontier orbitals as supported and ascertained by density functional theory (DFT) calculations for <b>1</b> is relevant for the productive excited state. In addition to the parent <b>1</b>, the ester complex <b>2</b> was chosen for its relationship to the carboxylate species involved for binding to TiO₂ in solar cells; the donor-substituted <b>3</b> and <b>4</b> allowed for better access to oxidized forms. Reflecting the metal-to-ligand (Ru → bpy) charge-transfer characteristics of the compounds, the electrochemical and EPR results for compounds <b>1</b>–<b>4</b> agree with previous notions of one metal-centered oxidation and several (bpy-R) ligand-centered reductions. The first one-electron reduction produces extensive IR absorption, including intraligand transitions and broad ligand-to-ligand intervalence charge-transfer transitions between the one-electron-reduced and unreduced bpy-R ligands. The electron addition to one remote bpy-R ligand does not significantly affect the N–C stretching frequency of the Ru^IINCS unit. Upon oxidation of Ru^II to Ru^III, however, the single N–C stretching band exhibits a splitting and a shift to lower energies. The DFT calculations serve to reproduce and understand these effects; they also suggest significant spin density on S for the oxidized form