Peter Klüfers

Ludwig-Maximilians-University of Munich, München, Bavaria, Germany

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Publications (187)412.46 Total impact

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    ABSTRACT: One single photo-induced linkage NO isomer (PLI) is detected and characterized in the dinitrosyl pentacoordinated compound [RuBr(NO) 2 (PCyp 3 ) 2 ]BF 4 by a combination of photocrystallographic and IR analysis. In the ground state, the molecule adopts a trigonal–bipyramidal structure with the two NO ligands almost linear with angles Ru—N1—O1 = 168.92 (16), Ru—N2—O2 = 166.64 (16)°, and exactly equal distances of Ru—N = 1.7838 (17) and O—N = 1.158 (2) Å. After light irradiation of 405 nm at T = 10 K, the angle of Ru—N2—O2 changes to 114.2 (6)° by rotation of the O atom towards the Br ligand with increased distances of Ru—N2 = 1.992 (6) and N2—O2 = 1.184 (8) Å, forming a bent κ N bonded configuration. Using IR spectroscopy, the optimal wavelength and maximum population of 39 (1)% of the PLI is determined. In the ground state (GS), the two symmetric ν s (NO) and asymmetric ν as (NO) vibrations are measured at 1820 and 1778 cm −1 , respectively. Upon photo-irradiation, the detection of only one new vibrational ν(NO) stretching band at 1655 cm −1 , assigned to the antisymmetric coupled vibration mode and shifted to lower wavenumbers by −123 cm −1 , supports the photocrystallographic result. These experimental results are supported by additional DFT calculations, which reproduce the structural parameters and vibrational properties of both the ground state and the photo-induced linkage isomer well. Especially the experimentally characterized molecular structure of the PLI state corresponds to an energy minimum in the calculations; the stabilization of the bent κ N bonded configuration of the PLI state originates from specific intramolecular orbital overlap.
    No preview · Article · Dec 2015 · Acta Crystallographica Section B: Structural Science
  • Leonie Lindner · Peter Klüfers
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    ABSTRACT: The β-pyranose isomer of D-galactosylamine (1) formed complexes with three different cobalt(III) fragments. Crystals containing the dication [Co(tren)(β-D-Galp1N2H–1-κ2N1,O2)]2+ (3) showed coordination through the anomeric amino group (N1) and the deprotonated hydroxy group (O2) of the 4C1 β-pyranose form, which is also the major isomer of free galactosylamine. The cationic complexes [Co(fac-dien)(β-D-Galp1N2H–1-κ2N1,O2)]2+ (4) and [Co(phen)2(β-D-Galp1N2H–1-κ2N1,O2)]2+ (5) were analysed by NMR spectroscopy and showed the same coordination mode as 3. In terms of available ligand isomers it was shown that 1 exhibits an anomeric equilibrium in solution of both pyranose and both furanose forms as is typical for the parent glycose, galactose.
    No preview · Article · Jul 2015 · Zeitschrift für anorganische Chemie
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    ABSTRACT: Multiple light-induced reversible metastable NO linkage isomers (PLIs) have been detected in the dinitrosyl compound [RuCl(NO)2(PPh3)2]BF4 by a combination of photocrystallographic and IR analysis. The IR signature of three PLI states has been clearly identified, with estimated populations of 59% (PLI-1), 8% (PLI-2) and 5% (PLI-3) for a total population of the metastable state of 72%. The structural configuration of the major component (PLI-1) has been derived by X-ray photocrystallography. In the ground state, the structure is characterized by a bent and a linear nitrosyl, the bent one being oriented towards the linear equatorial nitrosyl with an Ru-N-O angle of 133.88 (9)°. X-ray Fourier difference maps indicate a selectivity of the photo-isomerization process in PLI-1: only the bent NO ligand changes its position, while the linear NO is unaffected. After irradiation at 405 nm, the orientation is changed by rotation towards the Cl ligand opposite the linear NO, with an Ru-N-O angle in this new position of 109 (1)°. The photocrystallographic analysis provides evidence that, in the photo-induced metastable state, the bent NO group is attached to the Ru atom through the N atom (Ru-N-O), rather than in an isonitrosyl Ru-O-N binding mode. In the IR spectra, the asymmetric NO vibrational band shifts by -33 cm(-1) to a lower value, whereas the symmetric band splits and shifts by 5 cm(-1) to a higher value and by -8 cm(-1) to a lower value. The down shift is a clear indication of the structural change, and the small upward shift in response to the new electronic configuration of the metastable structure. Variable-temperature IR kinetic measurements in the range 80-114 K show that the decay of the PLI-1 state follows an Arrhenius behaviour with an activation energy of 0.22 eV.
    Preview · Article · Jan 2015
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    Anna K E Gallien · Dominik Schaniel · Theo Woike · Peter Klüfers
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    ABSTRACT: Two different structure types were found for a series of mononuclear dinitrosyl complexes of the general formula [RuL2(NO)2X]BF4 (L = monodentate phosphane, X = Cl, Br, I). The {Ru(NO)2}(8)-type target compounds were prepared by the reduction of the respective {RuNO}(6) precursors and subsequent oxidative addition of (NO)BF4. About one half of the new compounds share their molecular structure with the hitherto only representative of this class of dinitrosyls, Pierpont and Eisenberg's [RuCl(NO)2(PPh3)2]PF6·C6H6 (Inorg. Chem., 1972, 11, 1088-1094). The Cs-symmetric cations exhibit both a linear and a bent Ru-N-O fragment, in line with a formal 6 + 2 split of the {Ru(NO)2}(8) electron sum in the sense of a [Ru(II)(NO(+))((1)NO(-))](2+) bonding. The coordination entity's configuration in this subgroup is described by IUPAC's polyhedral symbol SPY-5. Continuous shape measures (CShM) as defined by Alvarez et al. (Coord. Chem. Rev., 2005, 249, 1693-1708) reveal a uniform deviation from the L-M-L angles expected for SPY-5, in a narrower sense, towards a vacant octahedron (vOC-5). DFT calculations confirmed that Enemark and Feltham's analysis (Coord. Chem. Rev., 1974, 13, 339-406) of the electronic situation of the {Ru(NO)2}(8) group remains adequate. The same holds for the second subclass of new compounds the existence of which had been predicted in the same paper by Enemark and Feltham, namely C2v-symmetric, TBPY-5-type cations with two almost equally bonded nitrosyl ligands. In agreement with an 8 + 0 distribution of the relevant electrons, the formal [Ru(0)(NO(+))2](2+) entities are found for L/X couples that donate more electron density on the central metal. Two solid compounds (/, /) were found in both structures including the special case of the P(i)Pr3/Br couple /, which led to crystals that contained both structure types in the same solid. Conversely, four compounds showed a single form in the solid but both forms in dichloromethane solution in terms of the solutions' IR spectra. The irradiation of crystalline with blue laser light resulted in the photoisomerisation of, mainly, the bent (1)NO(-) ligand in terms of low-temperature IR spectroscopy.
    Preview · Article · Jul 2014 · Dalton Transactions
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    ABSTRACT: Crystals of the bis(tert-butyl)silylene (DTBS) derivatives of the tartaric acids were synthesized from D-, L-, rac-, and meso-tartaric acid and DTBS bis(trifluoromethanesulfonate): two polymorphs of Si2tBu4(L-Tart1,2;3,4H–4) (L-1a and L-1b), the mirror image of the denser modification (D-1b) as well as the racemate (2), and the meso analogue Si2tBu4(meso-Tart1,3;2,4H–4) (3). The structures were determined by single-crystal X-ray diffraction. The threo-configured D- and L- (and rac-) tartrates were coordinated by two tBu2Si units forming five-membered chelate rings, whereas the erythro-configured meso-tartrate formed six-membered chelate rings. The new compounds were analyzed by NMR techniques, including 29Si NMR spectroscopy, and single-crystal X-ray crystallography.
    Preview · Article · Jan 2014 · Zeitschrift für anorganische Chemie
  • Xaver Kästele · Christine Sturm · Peter Klüfers
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    ABSTRACT: (13)C NMR spectroscopy provides insight into the chemistry of carbohydrate-based ferric preparations. Specifically, it reveals whether oxygen atoms of the carbohydrate are directly bonded to the preparations' ferric centres or whether more distant interactions are present. After having validated the method by investigating the ferric solutions of low-molecular complexes as well as polynuclear ferric samples, it is demonstrated that common constituents of medically used ferric preparations such as sucrose and other glucose-based saccharides do not support ferric carbohydrate chelates. Instead, these carbohydrates reside outside the NMR-spectroscopically 'blinded' region about the ferric centres and experience the so-called Evans effect that can be used to measure the magnetic moment of the solutions. As a result, an easily accessible physicochemical parameter is provided to characterise commercial iron(III) preparations, namely the samples' magnetism in terms of the in-situ-measured spin-normalised effective Bohr magneton number μeff(2)/35. The procedure can, moreover, be combined with a facile NMR-spectroscopic iron assay.
    No preview · Article · Dec 2013 · European journal of pharmaceutics and biopharmaceutics: official journal of Arbeitsgemeinschaft fur Pharmazeutische Verfahrenstechnik e.V
  • Xaver Wurzenberger · Christine Neumann · Peter Klüfers
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    ABSTRACT: Allein schafft es das nicht! Da eine Jahn-Teller-Instabilität wie beim homologen Ferrat(II)-Ion fehlt, findet das Cobalt-Zentralatom im Bis(perfluorpinakolato)cobaltat(II) seine stabile Konformation näher bei der tetraedrischen Anordnung – sowohl laut DFT-Rechnungen als auch in einem isolierbaren Salz (siehe Bild).
    No preview · Article · May 2013 · Angewandte Chemie
  • Xaver Wurzenberger · Christine Neumann · Peter Klüfers
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    ABSTRACT: They can't do it alone: The Jahn-Teller instability found in the iron(II) species is missing in the homologous bis(perfluoropinacolato) cobalt(II) complex. Thus the stable conformation of the cobalt center is closer to tetrahedral than square planar, as shown by a DFT approach, and also in an isolatable salt.
    No preview · Article · May 2013 · Angewandte Chemie International Edition
  • Max Pfister · Sarah Illi · Peter Klüfers
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    ABSTRACT: Two isomers of the [Co(tren)(D-Glc1A1,2H(-2)-(KO1,2)-O-2)](+) (1) chelate are formed in equal parts in the reaction of [Co(tren)Cl-2]Cl and sodium gluconate. In contrast, the gluconate's 2-amino-2-deoxy derivative glucosaminate formed a single isomer of [Co(tren)(D-Glc1A2N1H(-1)-(KN)-N-2, O-2)](2+) (2). Crystals of the OC-6-34 isomer of 1, [1a]PF6 center dot H2O, showed the support of the metal-binding site by intramolecular hydrogen bonds. Due to the inertness of the cobalt(III) chelates, spectroscopy on redissolved crystals of [la]PF6 center dot H2O allowed the separation of the two C-13 NMR signal sets of the isomeric mixture. In a DFT approach, a small energy difference explained the formation of two isomers in the case of the gluconate. A larger difference was obtained for the glucosaminate, in line with the known rules for the stereospecific amino acid-Co(tren) chelation.
    No preview · Article · May 2013
  • Martin Steinborn · Mihael Suhanji · Peter Klüfers
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    ABSTRACT: Sugar phosphates provide metal-binding sites both at their sugar core and at their phosphate group(s). Mixed sugar-core-phosphate chelation has been considered as a typical bonding mode within the physiological pH range for the central metabolite d-fructose 1,6-bisphosphate. The ReVO(tmen) metal fragment was used to enrich this coordination type. The formation of the [ReO(tmen)(Fruf2,3H-21,6P2H2-κ3O2,3,P1)]- monoanion was determined by NMR spectroscopy and mass spectrometry. The model compound rac-glycerol 1-phosphate yielded similar results in terms of NMR spectroscopy. Crystal-structure analyses of [ReO(tmen)(rac-Glyc2,3H-21PH-κ3O2,3,P)]·2H2O and [ReO(phen)(rac-Glyc2,3H-21PH-κ3O2,3,P)]·MeOH confirmed the coordination pattern.
    No preview · Article · Feb 2013 · Dalton Transactions
  • Sandra Albrecht · Peter Klüfers
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    ABSTRACT: Fehling's solution is an aqueous alkaline solution (pH ca. 13) of D-, L-, or rac-tartrato-cuprates(II) and both excess tartrate and hydroxide. The isolation of crystalline solids succeeded for rac-tartrate-containing samples. Crystal structure analyses revealed the formulas K8[Cu10(rac-tartH-1)4(rac-tartH-2)4(H2O)4]·18H2O (1), Li4[Cu2(rac-tartH-2-κ2O1,O2:κ2O3,O4)2]·11.75H2O (2), and Na6[Cu(rac-tartH-2-κ2O2,O3)2]·14H2O (3). The cupric central atom is in a square-planar tetracoordination in the bis(diolato) chelate in 3, and in square-pyramidal 4+1 coordination in the mixed carboxylato-alkoxido chelates 1 and 2. In terms of stoichiometry, 3 is closest to typical Fehling recipes.
    No preview · Article · Feb 2013 · Zeitschrift für anorganische Chemie
  • Sarah Illi · Johanna Schulten · Peter Klüfers
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    ABSTRACT: Sialic acid represents a group of thirty derivates of neuraminic acid with various substituents at the amino residue and the alcoholic hydroxy groups. We analysed the behaviour of the tetracoordinated metal ions palladium(II) and silicon(IV) against the most important derivative N-acetylneuraminic acid (NANA). The molecular structures were assigned by a combined 1H, 13C and 29Si NMR-spectroscopic approach. Despite the presence of many different functional groups, the coordination chemistry of NANA with PdII follows established rules. Coordination via the N-acetyl-group – sterically impossible with PdII – was realised with SiIV.
    No preview · Article · Jan 2013 · Zeitschrift für anorganische Chemie
  • Thorsten Allscher · Peter Klüfers
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    ABSTRACT: Alditols ("sugar alcohols", "glycitols") form palladium(II) complexes in neutral aqueous solution if they can provide the threitol partial structure. This requirement excludes erythritol, ribitol, and allitol when applied to the common tetritols, pentitols, and hexitols. The remaining alditols are able to arrange their threo-tetraol-O(4) pattern to an almost planar rhomb, to which four Pd(II) N(2) (N(2) =bidentate nitrogen ligand) centres bind in a butterfly-shaped Pd(4) motif. Bridging is the exclusive bonding mode of the four alkoxido donors. In contrast to the butterfly complexes, all alditols are able to form a species at a pH intermediate between neutrality and the stronger alkaline conditions of non-bridging diolato-palladium(II) binding, namely, the μ-triolato bonding mode. A Pd(2) (μ-triolato) unit shows the middle O atom of a propanetriolato fragment as a bridging ligator, with the lateral O atoms binding in the terminal mode.
    No preview · Article · Aug 2012 · Chemistry - A European Journal
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    David Hess · Peter Klüfers
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    ABSTRACT: The title compound, C6H12O5, is the α-pyran­ose form of the reducing aldose 2-de­oxy-d-arabino-hexose. The six-membered pyran­ose ring adopts a 4 C 1 conformation, with the anomeric hy­droxy group in axial and the other substituents in equatorial positions. In the crystal, each of the four hy­droxy groups acts as an inter­molecular hydrogen-bond donor function, resulting in a three-dimensional hydrogen-bonded network.
    Preview · Article · Oct 2011 · Acta Crystallographica Section E Structure Reports Online
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    D. Hess · P. Klüfers
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    ABSTRACT: The title compound, C6H12O5, is the α-pyran­ose form of the reducing aldose 2-de­oxy-d-arabino-hexose. The six-membered pyran­ose ring adopts a 4C1 conformation, with the anomeric hy­droxy group in axial and the other substituents in equatorial positions. In the crystal, each of the four hy­droxy groups acts as an inter­molecular hydrogen-bond donor function, resulting in a three-dimensional hydrogen-bonded network.
    Preview · Article · Sep 2011 · Acta Crystallographica Section E Structure Reports Online
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    David Hess · Peter Klüfers
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    ABSTRACT: Phenylboronic acid esters are formed by the three common 2-deoxy aldoses: 2-deoxy-d-erythro-pentose ('2-deoxy-d-ribose'), 2-deoxy-d-lyxo-hexose ('2-deoxy-d-galactose'), and 2-deoxy-d-arabino-hexose ('2-deoxy-d-glucose'). The major species that was formed from equimolar quantities of boronic acid and the aldose, was the 3,4-monoester of the pentopyranose in a skew-boat conformation, and the 4,6-monoester in the case of the two hexopyranoses. A double molar quantity of boronic acid led, for both 2-deoxy-hexoses, to the diester of the open-chain aldehydo isomer as the major product: the 3,5:4,6-diester for the lyxo-configured deoxy-hexose, and the 3,4:5,6-diester of the arabino-configured isomer. Minor products of all reactions were identified by a combined NMR/DFT methodology.
    Preview · Article · Jul 2011 · Carbohydrate research
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    Johanna Schulten · Peter Klüfers
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    ABSTRACT: Excess di(tert-butyl)silylene (DTBS) bis(trifluoromethanesulfonate) formed bis-DTBS derivatives with the four aldopentoses (arabinose, lyxose, ribose and xylose). The structure of the bis-chelates was affected by the bulk of the DTBS groups and the requirement of flat silacycles in the case of five-membered chelate rings. These restrictions resulted in unusual cyclic bis-chelates for ribofuranose (κO(1,5),κO(2,3) bis-chelate) and lyxopyranose (κO(1,4),κO(2,3) bis-chelate of a twisted boat conformation). Most importantly, all aldopentoses formed bis-chelates of their open-chain aldehydo isomers. The bis-chelates of aldehydo-arabinose and -xylose were κO(2,3),κO(4,5)-bonded and thus exhibited five-membered chelate rings. The bis-chelates of aldehydo-lyxose and -ribose were κO(2,4),κO(3,5)-bonded and resembled six-membered chelate rings. For lyxose, the aldehydo bis-chelate was isolated as a solid. The molecular structures were assigned by a combined (1)H, (13)C, and (29)Si NMR spectroscopic approach, which was supported by X-ray analyses on crystals of the bis-DTBS chelates of κO(1,2),κO(3,5)-bonded rac-xylofuranose, κO(1,5),κO(2,3)-bonded d-ribofuranose, and κO(2,4),κO(3,5)-bonded aldehydo-d-lyxose.
    Preview · Article · Jul 2011 · Carbohydrate research
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    Xaver Wurzenberger · Holger Piotrowski · Peter Klüfers
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    ABSTRACT: We are indebted to Dr. R. Hochleitner, Mineralogische Staatssammlung München, for the eudialyte photograph, to Dr. E. Bedbur, Geologisches und Mineralogisches Museum der Universität Kiel, for the gillespite photograph, and W. Bauer for the SQUID measurements.
    Preview · Article · May 2011 · Angewandte Chemie International Edition
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    Xaver Wurzenberger · Holger Piotrowski · Peter Klüfers
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    ABSTRACT: Wir danken Dr. R. Hochleitner (Mineralogische Staatssammlung München) für die Eudialyt-Photographie, Dr. E. Bedbur (Geologisches und Mineralogisches Museum der Universität Kiel) für die Gillespit-Photographie und W. Bauer für SQUID-Messungen.
    Preview · Article · May 2011 · Angewandte Chemie
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    Thorsten Allscher · Yvonne Arendt · Peter Klüfers
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    ABSTRACT: Four methyl d-pentopyranosides (β-Ara, α-Lyx, β-Rib, β-Xyl), as well as Me-β-l-Ara, some of them residing in a well-defined conformation in the solution state (Ara, Xyl) and some showing pronounced chair inversion in solution (Lyx, Rib), form bidentate chelates of the general formula [Pd(chxn)(LH₋₂)-κO,O'] and [Pd(tmen)(LH₋₂)-κO,O'], chxn=(R,R)-cyclohexane-1,2-diamine, tmen=N,N,N',N'-ethane-1,2-diamine and L=glycoside, with Pd(II)N₂-type metal probes. The dynamic behaviour of the free glycosides is maintained in their chelates, the only case where the metal is bonded by a cis-vicinal diol function. Thus, one fluctuating chelate was detected with the lyxopyranoside in the κO(2,3) binding mode, and two fluctuating chelates were found for the ribopyranoside (κO(2,3) and κO(3,4)). No fluctuating chelate was found for the arabinopyranoside (the free arabinopyranoside being non-fluctuating as well), or for the xylopyranoside (no cis-vicinal diol function). In addition, syn-diaxial chelation (κO(2,4)) was observed for the ribopyranoside and the xylopyranoside. The spectroscopic results were supplemented by X-ray analyses.
    Preview · Article · Nov 2010 · Carbohydrate research