Varying the Interpentacene Electronic Coupling to Tune Singlet Fission - Papadopoulos, Ilias; Zirzlmeier, Johannes; Hetzer, Constantin; Bae, Youn J.; Krzyaniak, Matthew D.; Wasielewski, Michael R.; Clark, Timothy; Tykwinski, Rik; Guldi, Dirk Michael (Journal of the American Chemical Society, 2019)
We have designed and used four different spacers, denoted A-D, to connect two pentacenes and to probe the impact of intramolecular forces on the modulation of pentacene-pentacene interactions and, in turn, on the key steps in singlet fission (SF), that is, the 1 (S 1 S 0 )-to- 1 (T 1 T 1 ) as well as 1 (T 1 T 1 )-to- 5 (T 1 T 1 ) transitions by means of transient absorption and electron paramagnetic resonance measurements. In terms of the 1 (S 1 S 0 )-to- 1 (T 1 T 1 ) transition, a superexchange mechanism, that is, coupling to a higher-lying CT state to generate a virtual intermediate, enables rapid SF in A-D. Sizeable electronic coupling in A and B opens, on one hand, an additional pathway, that is, the population of a real intermediate, and changes, on the other hand, the mechanism to that of hopping. In turn, A and B feature much higher 1 (T 1 T 1 ) quantum yields than C and D, with a maximum value of 162% for A. In terms of the 1 (T 1 T 1 )-to- 5 (T 1 T 1 ) transition, the sizable electronic coupling in A and B is counterproductive, and C and D give rise to higher 5 (T 1 T 1 )-to-(T 1 + T 1 ) quantum yields than A and B, with a maximum value of 85% for D.
CRIS-Team Scopus Importer:2019-05-02

Verkapselung von apfelwickler-granuloseviren für eine nachhaltige biotechnische schädlingsbekämpfung - Scheurer, Andreas; et al. (Chemie Ingenieur Technik, 2010)

Verkapselung von Apfelwickler-Granuloviren für eine nachhaltige biotechnische Schädlingsbekämpfung - Pemsel, Matthias; Schwab, Stefan; Scheurer, Andreas; Freitag, Detlef; Schatz, Robert; Schlücker, Eberhard (Chemie Ingenieur Technik, 2009)

Visible light induced reversible extrusion of nitric oxide from a ruthenium(II) nitrosyl complex: a facile delivery of nitric oxide. - Heinemann, Frank Wilhelm; et al. (Journal of the American Chemical Society, 2005)
The new ruthenium compound [Ru(NO)(pysiS4)]Br (3) (pysiS4 = 2,6-bis(3-triphenylsilyl-2-sulfanylphenylthiomethyl)pyridine), containing sterically bulky SiPh3 groups ortho to the thiolate donors, has been synthesized. In solution, 3 releases NO efficiently on exposure to visible light (lambda >/= 455 nm) at room temperature to afford [Ru(Br)(pysiS4)] (4). Treatment of 4 with NO yielded exclusively 3 without any metal-bound side reaction.

Visible-Light Photocatalysis by Two-Center Surface Coordination Complexes with Titania as Ligand - Kisch, Horst (wiley, 2023)
Treating an aqueous suspension of titania with H2 [PtCl6] or RhX3 (X = Cl, Br) affords halogenometalate complexes of composition Cln M–O–TiO2 M = Pt: n = 4, M = Rh, n = 3. In these, titania can be viewed as a semiconducting “ligand” bound via oxygen to a platinum(IV) or rhodium(III) center. The quasi-Fermi level of electrons in this ligand is shifted anodically by 0.2–0.3 V as compared to the free “ligand.” In the case of the platinum complex visible-light irradiation results in a platinum-centered excitation followed by homolytic Pt–Cl bond cleavage and electron injection of Pt(III) into the titania conduction band. Thus, the reducing and oxidizing surface centers can be described as a trapped electron, i.e. a Ti(III) site, and a loosely bound chlorine atom. In the case of the rhodium surface complex, the excitation is of rhodium-to-titanium charge-transfer type resulting in a Ti(III) center and a Rh(IV) species. These two-center hybrid metal complexes photocatalyze the aerobic visible-light mineralization of halocarbons, atrazine and inactivate bacteria and fungi. They are active even in diffuse indoor daylight.
CRIS-Team Scopus Importer:2023-09-08
Keywords: Chloroplatinate(IV); Detoxification; Flatband potential; Halogenorhodate(III); Photocatalysis; Surface complex; Titanium dioxide; Visible light

Wanzlick's equilibrium in tri- and tetraaminoolefins - Messelberger, Julian; Kumar, Manoj; Goodner, Stephen Joseph; Munz, Dominik (Organic Chemistry Frontiers, 2021)
The dissociation mechanism of electron-rich olefins into their parent carbenes has been a controversial topic since Wanzlick's pioneering work. Herein, we present a combined synthetic and computational study on the formation (dissociation, respectively) of hetero- and homo-carbene dimers derived from benzimidazolin-2-ylidenes (benzNHCs), imidazolidin-2-ylidenes (saNHC), and cyclic (alkyl) (amino) carbenes (CAACs) through sublimation (in vacuo) as well as in condensed phase. We quantify the effect of proton catalysis and report that even triaminoolefins dissociate to their free carbenes, yet only under proton catalysis. Accordingly, we report how the judicious choice of the base (KOtBu vs. KHMDS) and solvent (hexane/benzene vs. THF) allows N,N '-dimethylbenzimidazolin-2-ylidene to be obtained quantitatively as a metastable, kinetic product. This free carbene had been previously reported to dimerize directly to the olefin-dimer, which is the thermodynamic product.
CRIS-Team WoS Importer:2021-11-05

Water exchange on seven-coordinate Mn(II) complexes with macrocyclic pentadentate ligands: Insight in the mechanism of Mn(II) SOD mimetics - Dees, Anne; Zahl, Achim; Puchta, Ralph; van Eikema Hommes, Nico; Heinemann, Frank Wilhelm; Ivanovic-Burmazovic, Ivana (Inorganic Chemistry, 2007)
Seven-coordinate manganese(II) complexes [Mn(L)(HO) ], where L represents an equatorial pentadentate macrocyclic ligand with five nitrogen donor atoms, were studied with regard to their acid-base properties, water-exchange rate constants, and corresponding activation parameters (ΔH, ΔS, and ΔV). Three of the studied complexes without imine bonds in the macrocyclic ligand are proven superoxide dismutase (SOD) mimetics. Their water-exchange parameters were compared with those of the imino groups containing complex [Mn(L1)(Cl)] (dichloro-2,13-dimethyl-3,6,9,12,18- pentaazabicyclo[12.3.1]-octadeca-1(18),2,12,14,16-pentaenemanganese(II)), which does not show SOD activity. In addition the X-ray crystal structure of a new complex, dichloro-2,6-bis[1-(2-(N-methylamino)-ethylimino)ethyl]pyridine- manganese(II) [Mn(L2)(Cl)], which is the acyclic analog of [Mn(L1)(Cl)], is reported. Stability constants of the complexes and the pK values of the ligands were measured by potentiometric titration. The titrations of [Mn(L1)(HO)] and [Mn(L2)(HO)] led to complicated species distribution curves because of their ligands containing imine bonds. Water exchange was measured by temperature- and pressure-dependent O NMR techniques. In addition to the measurements on [Mn(EDTA)(HO)] and its derivatives, this is the only study of water exchange on seven-coordinate manganese complexes. The water exchange rate constants vary between 1.6 × 10 s and 5.8 × 10 s at 25°C and are mainly controlled by the π-acceptor abilities of the ligands. The exchange rate constant of the diaqua-1,4,7,10,13- pentaazacyclopentadecanemanganese(II) [Mn([15]aneN)(H O)] complex seems to be even higher but could not be exactly determined. On the basis of the obtained activation parameters, the exchange mechanism of the studied seven-coordinate manganese(II) complexes follows a dissociative pathway (I mechanism). DFT calculations (UB3LYP/LANL2DZp) were performed to obtain the energy required for the dissociation of the coordinated water molecule, that is, the energy difference between the starting seven-coordinate complex and a six-coordinate intermediate. The results have been discussed in terms of the catalytic mechanism of the proven SOD mimetics. © 2007 American Chemical Society.

Water exchange rates and mechanisms in tetrahedral [Be(H2O)(4)](2+) and [Li(H2O)(4)](+) complexes using DFT methods and cluster-continuum models - Regueiro-Figueroa, Martín; Esteban-Gomez, David; Pujales Paradela, Rosa; Caneda-Martínez, Laura; de Blas, Andrés; Platas-Iglesias, Carlos (International Journal of Quantum Chemistry, 2016)
The water exchange reactions in aquated Li+ and Be2+ ions were investigated with density functional theory calculations performed using the [Li(H2O)(4)](+)14H(2)O and [Be(H2O)(4)](2+)8H(2)O systems and a cluster-continuum approach. A range of commonly used functionals predict water exchange rates several orders of magnitude lower than the experimental ones. This effect is attributed to the overstabilization of coordination number four by these functionals with respect to the five-coordinated transition states responsible for the associative (A) or associative interchange (I-a) water exchange mechanisms. However, the M06 and M062X functionals provide results in good agreement with the experimental data: M062X/TZVP calculations yield a concerted I-a mechanism for the water exchange in [Be(H2O)(4)](2+)8H(2)O that gives an average residence time of water molecules in the first coordination sphere of 260 s. For [Li(H2O)(4)](+)14H(2)O the water exchange reaction is predicted to follow an A mechanism with a residence time of inner-sphere water molecules of 25 ps.
Keywords: berylium; density functional calculations; lithium; water exchange

Water exchange reactivity and stability of cobalt polyoxometalates under catalytically relevant pH conditions: Insight into water oxidation catalysis - Lieb, Dominik; Zahl, Achim; Wilson, Elizabeth Frances; Streb, Carsten; Nye, Leanne; Meyer, Karsten; Ivanovic-Burmazovic, Ivana (Inorganic Chemistry, 2011)
Water exchange on a molecular, purely inorganic cobalt-based water oxidation catalyst, [Co (H O) (α-P W O ) ] (1), in the catalytically relevant pH region (pH 6-10) is studied using O-NMR spectroscopy and ultrahigh-resolution electrospray ionization mass spectrometry. The results are compared with those of the inactive [Co (H O) Si W O ] (2), which is stable in the same pH region. The results obtained provide mechanistic details of the elementary reaction step related to the water oxidation on homogeneous metal oxide catalysts under catalytically relevant conditions. It is shown that the structural integrity of 1 and 2 is maintained, no deprotonation of the aqua ligands on the Co(II) centers occurs, and the water exchange does not undergo any mechanistic changeover at the catalytic pH conditions. We have demonstrated that the water exchange process is influenced by the cluster environment surrounding the water binding sites and is fast enough to not be rate-limiting for the water oxidation catalysis. © 2011 American Chemical Society.

Water soluble Eu(III) complexes of macrocyclic triamide ligands: Structure, stability, luminescence and redox properties - Pujales Paradela, Rosa; et al. (Inorganica Chimica Acta, 2019)
Two macrocyclic triamide octadentate chelator scaffolds L-1 and L-2 were synthesized, characterized by several spectroscopic techniques, and their pK(a) values were determined by potentiometric titration. Using these ligands, two water soluble paramagnetic Eu(III) complexes, [EuL1(OH2)](NO3)(3)center dot H2O (EuL1) and [EuL2(OH2)](NO3)(3)center dot H2O (EuL2) were synthesized and characterized in the solid state and in solution. Single crystal X ray diffraction measurement of [EuL1(OH2)](NO3)(3)center dot H2O (EuL1) reveals octadentate binding of the ligand to Eu(III) and ninth coordination being completed by an oxygen atom of a solvent molecule (H2O). X-ray diffraction data of [EuL2(OH2)](NO3)(3)center dot H2O (EuL2) were severely disordered and hence its chloride analogue [EuL2(DMF)]Cl-3 center dot H2OMeOH (EuL2-Cl) was synthesized and characterized using single-crystal X-ray diffraction measurements. The crystal data of [EuL2(DMF)](Cl)(3)center dot H2OMeOH (EuL2-Cl) reveal octadentate binding of the ligand to Eu(III), with the ninth coordination being completed by an oxygen atom of a solvent molecule (DMF). Luminescence measurements confirm the presence of a water molecule coordinated to Eu(III) in aqueous solution. The stability of the Eu(III) complexes was investigated using spectrophotometric molar ratio method. Cyclic voltammetry studies obtained from aqueous solutions of the Eu(III) complexes show reversible one electron reduction processes at the glassy carbon electrode with E-1/2 = -0.799 V and -0.777 V (versus Ag/AgCl) for the complexes of L-1 and L-2.
Keywords: Eu(III) macrocyclic complexes; X-Ray; Luminescence; Redox properties; pKa & stability constant; DFT calculation

Weak M-H center dot center dot center dot H-C and M-Cl center dot center dot center dot H-C interactions in orthometalated iridium and rhodium complexes - Huang, L. Y.; Aulwurm, Uwe; Heinemann, Frank Wilhelm; Knock, F.; Kisch, Horst (Chemistry - A European Journal, 1998)
Four different types of intramolecular MX ... C interactions have been observed in a series of five, structurally very similar, orthometalated iridium(III) and rhodium(III) complexes. For X=H and M=Ir or Rh, two-center or three-center interactions with MH ... HC distances of 1.80 - 1.83 (M = Ir) or 2.00 -2.20 Angstrom (M = Rh) were observed. For X=Cl the MCl ... HC distances of the three-center arrangement (M = Ir) were in the range of 2.38-2.60 Angstrom, while values of 2.41-2.89 Angstrom were found for the four-center geometry (M = Rh), These weak interactions open new perspectives for the mechanism of cyclometalations.
Keywords: azo compounds; hydrogen bonds; iridium; metalations; rhodium

Weak M - H ··· H - C and M - Cl ··· H - C interactions in orthometalated iridium and rhodium complexes - Heinemann, Frank Wilhelm; et al. (Chemistry - A European Journal, 1998)
Keywords: Hydrogen bonds; Azo compounds; Metalations; Iridium; Rhodium

Well-defined molecular uranium(iii) chloride complexes - la Pierre, Henry Storms; Heinemann, Frank Wilhelm; Meyer, Karsten (Chemical Communications, 2014)
The first anhydrous molecular complexes of uranium(iii) chloride, soluble in polar aprotic solvents, are reported, including the structures of the dimeric [UCl(py)] and the trimetallic [UCl(py) (μ-Cl)U(py)(μ-Cl)UCl (py)]. © 2014 the Partner Organisations.

Werner-Type Complexes of Uranium(III) and (IV) - Riedhammer, Judith; Aguilar-Calderón, J. Rolando; Miehlich, Matthias; Halter, Dominik; Munz, Dominik; Heinemann, Frank Wilhelm; Fortier, Skye; Meyer, Karsten; Mindiola, Daniel (Inorganic Chemistry, 2020)
Transmetalation of the β-diketiminate salt [M][MenacnacPh] (M+ = Na or K; MenacnacPh- = PhNC(CH3)2CH-) with UI3(THF)4 resulted in the formation of the homoleptic, octahedral complex [U(MenacnacPh)3] (1). Green colored 1 was fully characterized by a solid-state X-ray diffraction analysis and a combination of UV/vis/NIR, NMR, and EPR spectroscopic studies as well as solid-state SQUID magnetization studies and density functional theory calculations. Electrochemical studies of 1 revealed this species to possess two anodic waves for the U(III/IV) and U(IV/V) redox couples, with the former being chemically accessible. Using mild oxidants, such as [CoCp2][PF6] or [FeCp2][AlOC(CF3)34], yields the discrete salts [1][A] (A = PF6-, AlOC(CF3)34-), whereas the anion exchange of [1][PF6] with NaBPh4 yields [1][BPh4].
CRIS-Team Scopus Importer:2020-02-28

Wheel-Shaped Icosanuclear Homo- and Heterometallic Complexes of Ni II, Co II, and Cu II ions supported by unsymmetrical aminoalcohol ligands - Scheurer, Andreas; et al. (Inorganic Chemistry, 2012)

When the packaging becomes organic! Wenn die verpackung bio wird! - Collin, Daniela; Wintzheimer, Susanne; Schwaiger, Johannes; Amberg-Schwab, Sabine (Farbe und Lack, 2015)

X-Ray Crystallography of Tetracycline, Doxycycline and Sancycline - Heinemann, Frank Wilhelm; Leypold, Clemens; Roman, Cyprian R.; Schmitt, Matthias O.; Schneider, Siegfried (Journal of Chemical Crystallography, 2013)
Although the packing of the three title compounds in the respective crystals is different, the geometries of the molecular framework are nearly the same as the one shown for the sancycline cation. A comparison of experimentally determined bond lengths with calculated Wiberg-Bond orders provides evidence that only one tautomer is present in the crystal..
Keywords: Molecular and crystal structures; Tetracycline; Doxycycline; Sancycline; Wiberg-bond order

X-ray Spectroscopic and Theoretical Investigation on the Ferric Star Molecule - Takács, A.; Neumann, M.; Postnikov, A.; Sperner, Stefan; Scheurer, Andreas; Saalfrank, Rolf (New Trends In Advanced Materials, 2005)

X-ray structure analysis and DFT study of a chiral (salen)MnIII complex toward understanding of inversion of enantioselection in epoxidation catalysts - Scheurer, Andreas; et al. (Journal of Coordination Chemistry, 2010)
Keywords: Conformation analysis; (Salen)manganese(III) complex; N; O ligand; Density functional calculations; X-ray diffraction

X-ray structure and theoretical studies on a palladium(II) Schiff base complex - Akbari, Alireza; Ahmadi, Mehdi; Takjoo, Reza; Heinemann, Frank Wilhelm (Journal of Coordination Chemistry, 2013)
Treatment of N,N-bis(salicylidene)-1,2-cyclohexanediamine (H2L) with PdCl2 in the presence of triethylamine afforded [Pd(N2O2)]. Recrystallization in chloroform and acetonitrile (1:1) gave suitable crystals for X-ray crystallography. The solid-state structure shows that the environment around palladium is square planar. The structural parameters of the molecule obtained by density functional theory (DFT) calculation in the gas phase and by X-ray diffraction are compared. The Pd(II) Schiff base complex adopts planar geometry by DFT calculation. The coordination site structural parameters, which are obtained from geometry optimization calculation, are close to those from X-ray crystallographic data. The spectral properties such as vibrational frequencies, chemical shifts, electronic excitation and the natural bond orbital analyses of Pd(Salen) are calculated, analyzed and compared with experimental data.
Keywords: Palladium(II) complex; Crystal structure; Schiff base; DFT calculation

Zur Struktur und Konstitution von Dichloro(tetraalkylcyclobutadien)platin(II)-Komplexen - Steinborn, Dirk; Gerisch, M.; Heinemann, Frank Wilhelm; Scholz, Judith; Schenzel, K. (Zeitschrift für Anorganische und Allgemeine Chemie, 1995)

π-Stacking attraction vs. electrostatic repulsion: competing supramolecular interactions in a tpphz-bridged Ru(II)/Au(III) complex. - Sorsche, Dieter; Schaub, Markus; Heinemann, Frank Wilhelm; Habermehl, Johannes; Kuhri, Susanne; Guldi, Dirk Michael; Guthmuller, Julien; Rau, Sven (Dalton Transactions, 2016)
The synthesis and characterization of a mixed metal ruthenium(ii)/gold(iii) complex bridged by tetrapyridophenazine (tpphz) are described. It is isostructural and isoelectronic to the well-known photocatalysts with palladium(ii) or platinum(ii). Concentration dependent (1)H-NMR spectroscopy and XRD studies show that the electrostatic repulsion between the gold(iii) moieties exceeds the attractive π-stacking interaction. Theoretical calculations based on the new structural data confirm an increased positive charge on the bridging ligand as well as significantly altered orbital symmetry as compared to the previously investigated palladium(ii) complex. This is the first example of a tpphz ruthenium(ii) complex where π-stacking is completely inhibited. The detailed investigation of the solid-state structure showed for the first time in bimetallic tpphz bridged complexes no significant torsion within the bridging ligand itself. Although catalytic performance for proton reduction by gold(iii) is naturally not observed, its photochemical decomposition in colloidal gold particles could be shown by TEM and DLS.

Study of the effect of the introduction of Tris(bipyridine)ruthenium(II) chloride into silicon dioxide particles by spectrofluorometry methods - Irgibayeva, Irina; Mantel, Arthur; Barashkov, Nikolay; Lu, Olga; Yensebayeva, Akbota; Aldongarov, Anuar; Mendigaliyeva, Svetlana; Barashkova, Irina (Spectrochimica Acta Part A-Molecular and Biomolecular Spectroscopy, 2021)
The Stoeber reaction was used to grow silica microparticles in the presence of the fluorescent dye Tris(bipyridine)ruthenium (II) chloride. The diameter of the obtained particles varies from about 150 to 280 nm depending on the dye concentration. Using spectrofluorometry methods, concentration quenching of fluorescence of dye solutions was studied before and after growing the microparticles. It was found out that the concentration quenching of fluorescence decreases significantly after its incorporation into the silicon dioxide microparticles upon excitation in the short-wavelength region of the spectrum.
CRIS-Team Scopus Importer:2020-10-23
Keywords: Concentration quenching; Excitation spectra; Fluorescence spectra; Silica microparticles; Stoeber reaction; Tris(bipyridine)ruthenium (II) chloride