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Berlin Brandenburg

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  • Wieghardt, Karl  (12)
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  • 1
    Language: English
    In: Inorganic chemistry, 14 May 2007, Vol.46(10), pp.4187-96
    Description: The preparation and structural characterization of the neutral, square planar complexes [PtII(tbpy)(A)] (1), [PtII(tbpy)(B)] (2), and [PtII(PPh3)2(B)] (3) have been accomplished, where (tbpy) = 4,4'-di-tert-butylpyridine, (A)2- = 3,6-bis(trimethylsilyl)-1,2-benzenedithiolate(2-), and (B)2- = 1,2-bis(4-tert-butylphenyl)ethylene-1,2-dithiolate(2-) and (A*)1- and (B*)1- represent the corresponding monoanionic radicals. Electrochemical and chemical one-electron oxidation of 1 and 2 in CH2Cl2 solution affords the monomeric monocations [PtII(tbpy)(A*)]+ (1a) and [PtII(tbpy)(B*)]+ (2a), both of which possess an S = 1/2 ground state. The corresponding spin doublet monocationic dimers [PtII2(tbpy)2(A)(A*)]+ (1b) and [PtII2(tbpy)2(B)(B*)]+ (2b) were electrochemically generated in solution (50% oxidation) and identified by X-band EPR spectroscopy. Complete one-electron oxidation of 1 and 2 yielded the diamagnetic dimers [PtII2(tbpy)2(A*)2]2+ (1c) and [PtII2(tbpy)2(B*)2]2+ (2c) which are in equilibrium with the corresponding paramagnetic monomers 1a and 2a in solution. The crystal structure of [PtII2(tbpy)2(B*)2](PF6)2.3CH2Cl2 (2c) revealed a centrosymmetric, lateral dimer whose bridging part is a PtII2(mu2-S)2 rhomb; the metal ions possess a square based pyramidal geometry. Solid-state sulfur K-edge X-ray absorption spectra of 1, 2, 2a, 2c, and [PtII(B*)2]0 (4) have been recorded, which clearly show that a sulfur-centered radical (B*)1- is present in 2a, 2c, and 4. The absence of ligand-based radicals in 1 and 2 is also clearly established. One-electron oxidation of [Pt(PPh3)2(B)] (3) afforded only the spin doublet species [PtII(PPh3)2(B*)]+ (3a); no dimer formation was detected. Synthesis and crystal structure of square planar [PtII(B*)2]0.thf are also reported.
    Keywords: Organoplatinum Compounds -- Chemical Synthesis
    ISSN: 0020-1669
    E-ISSN: 1520510X
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  • 2
    Language: English
    In: Science, 30 June 2006, Vol.312(5782), pp.1937-1941
    Description: The hexavalent state, considered to be the highest oxidation level accessible for iron, has previously been found only in the tetrahedral ferrate dianion, $FeO_4^{2-}$ . We report the photochemical synthesis of another Fe(VI) compound, an octahedrally coordinated dication bearing a terminal nitrido ligand. $M\ddot{o}ssbauer$ and x-ray absorption spectra, supported by density functional theory, are consistent with the octahedral structure having an $Fe \equiv N$ triple bond of 1.57 angstroms and a singlet $d_{xy}^2$ ground electronic configuration. The compound is stable at 77 kelvin and yields a highspin Fe(lll) species upon warming.
    Keywords: Physical sciences -- Chemistry -- Chemical reactions ; Physical sciences -- Physics -- Microphysics ; Physical sciences -- Chemistry -- Stereochemistry ; Physical sciences -- Physics -- Microphysics ; Physical sciences -- Chemistry -- Chemical compounds ; Physical sciences -- Chemistry -- Chemical bonding ; Physical sciences -- Physics -- Microphysics ; Physical sciences -- Chemistry -- Chemical elements ; Biological sciences -- Biology -- Biological taxonomies ; Physical sciences -- Physics -- Microphysics
    ISSN: 00368075
    E-ISSN: 10959203
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  • 3
    Language: English
    In: Inorganic chemistry, 19 October 2009, Vol.48(20), pp.9754-66
    Description: The reaction of [Ru(III)(cyclam)Cl(2)]Cl with 2 equiv of sodium N,N-diethyldithiocarbamate in methanol afforded [Ru(II)(cyclam)(Et(2)dtc)](BPh(4)) (1(BPh(4))). The same reaction with only 1 equiv of toluene-3,4-dithiol and a base yielded [Ru(cyclam)(tdt)](PF(6)) (2(PF(6))) which was oxidized by 1 equiv of ferrocenium hexafluorophosphate generating [Ru(cyclam)(tdt)](PF(6))(2) (2(ox)(PF(6))(2)). The crystal structures of 1 and 2 have been determined by X-ray crystallography at 100 K. The electronic structures of diamagnetic 1(BPh(4)), paramagnetic 2(PF(6)) (S = (1)/(2)), and diamagnetic 2(ox)(PF(6))(2) have been studied by magnetochemistry, spectroelectrochemistry, electron paramagnetic resonance spectroscopy, and (1)H NMR spectroscopy. X-ray absorption spectroscopy on Ru K- and L-edges as well as S K-edges has been employed. Finally, the molecular and electronic structures of all three species have been calculated by using density functional theory (B3LYP). It is shown that 2(ox) comprises an electronic structure which is best described by three resonance structures {[Ru(II)(cyclam)(tdt(0))](2+) [Ru(III)(cyclam)(tdt(*))](2+) [Ru(IV)(cyclam)(tdt(2-))](2+)} with a closed-shell singlet ground state. This is in stark contrast to the isoelectronic iron species, namely, [Fe(III)(cyclam)(tdt(*))](2+) which is a singlet diradical with a low-spin ferric ion coupled intramolecularly antiferromagnetically to a ligand pi radical monoanion (tdt(*))(-).
    Keywords: Crystallography, X-Ray ; Electrons ; Heterocyclic Compounds -- Chemistry ; Ruthenium Compounds -- Chemistry ; Thiocarbamates -- Chemistry
    ISSN: 00201669
    E-ISSN: 1520-510X
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  • 4
    Language: English
    In: Inorganic chemistry, 03 August 2009, Vol.48(15), pp.7430-45
    Description: The reaction of cis-[Fe(III)(cyclam)Cl(2)]Cl with 1 equiv of sodium N-diethyldithiocarbamate, toluene-3,4-dithiolate, and maleonitriledithiolate in methanol in the presence of triethylamine afforded the cations [Fe(III)(cyclam)(Et(2)dtc)](2+) (1), [Fe(III)(cyclam)(tdt)](+) (2), and [Fe(III)(cyclam)(mnt)](+) (3), which were isolated as triflate, hexafluorophosphate, and tetrafluoroborate salt, respectively, using sodium triflate, potassium hexafluorophosphate, or sodium tetrafluoroborate as the source for the counteranion. Complexes 1, 2, and 3 possess an S = (1)/(2) ground state (low-spin ferric d(5)). These salts were characterized by X-ray crystallography, UV-vis, Mössbauer, and electron paramagnetic resonance spectroscopies. Cyclic voltammetry revealed that 2 and 3 are reversibly one-electron-reduced, generating neutral 2(red) and 3(red), respectively, and one-electron-oxidized, generating dicationic 2(ox) and 3(ox), respectively. Fe and S K-edge X-ray absorption spectroscopy (XAS) revealed that 2 (S = (1)/(2)) and 2(ox) (S = 0) possess a low-spin ferric ion. Complexes 2 and 3 are S,S'-coordinated to a closed-shell dithiolate(2-) ligand, whereas 2(ox) and 3(ox) consist of a low-spin ferric ion antiferromagnetically coupled to a dithiolate(1-) pi radical ligand. They are singlet diradicals [Fe(III)(cyclam)(dithiolate(*))](2+). The analysis of the sulfur K pre-edge transitions reveals significant multiplet effects in the spectra of 2 and 2(ox), which provide rare experimental evidence for a singlet diradical description for 2(ox). Mössbauer spectroscopy on frozen solutions of 2(red) clearly show the presence of a high-spin ferrous ion (S = 2). The experimentally established electronic structures of the three members of the electron transfer series [Fe(cyclam)(dithiolate)](2+,+,0) have been verified by broken symmetry density functional theoretical calculations, which have been calibrated against the experiment by calculating XAS and Mössbauer spectra.
    Keywords: Iron -- Chemistry ; Lactams, Macrocyclic -- Chemistry ; Organometallic Compounds -- Chemistry ; Sulfhydryl Compounds -- Chemistry
    ISSN: 00201669
    E-ISSN: 1520-510X
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  • 5
    Language: English
    In: Chemistry – A European Journal, 22 March 2010, Vol.16(12), pp.3628-3645
    Description: A detailed spectroscopic and quantum chemical analysis is presented to elucidate the electronic structures of the octahedral complexes [Fe(Etdtc)(mnt)] (–, =3, 2, 1, 0) and their one‐electron oxidized analogues [Fe(Etdtc)(mnt)] (–); (mnt) represents maleonitriledithiolate(2−) and (Etdtc) is the diethyldithiocarbamato(1−) ligand. By using X‐ray crystallography, Mössbauer spectroscopy, and Fe and S K‐edge X‐ray absorption spectroscopy (XAS) it is convincingly shown that, in contrast to our previous studies on [Fe(cyclam)(mnt)] (cyclam=1,4,8,11‐tetraazacyclotetradecane), the oxidation of – is metal‐centered yielding the genuine Fe complexes –. For the latter complexes, a spin ground state of =1 has been established by magnetic susceptibility measurements, which indicates a low‐spin d configuration. DFT calculations at the B3LYP level support this electronic structure and exclude the presence of a ligand π radical coordinated to an intermediate‐spin ferric ion. Mössbauer parameters and XAS spectra have been calculated to calibrate our computational results against the experiment. Finally, a simple ligand‐field approach is presented to correlate the structural features obtained from X‐ray crystallography (100 K) with the spectroscopic data. : The electronic structures of [Fe(Etdtc)(mnt)] (mnt=maleonitriledithiolate and Etdtc=diethyldithiocarbamato; =3, 2, 1, 0) and their one‐electron oxidized analogues have been elucidated and correlated with the structural and spectroscopic parameters of the complexes (see figure). Despite the presence of noninnocent dithiolene ligands, the oxidized complexes are best described as genuine Fe complexes.
    Keywords: Density Functional Calculations ; Dithiolenes ; High‐Valent Iron ; S Ligands ; X‐Ray Absorption Spectroscopy
    ISSN: 0947-6539
    E-ISSN: 1521-3765
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  • 6
    Language: English
    In: Journal of the American Chemical Society, 12 September 2007, Vol.129(36), pp.11053-60
    Description: The characterization of high-valent iron species is of interest due to their relevance to biological reaction mechanisms. Recently, we have synthesized and characterized an [Fe(V)-nitrido-cyclam-acetato]+ complex, which has been characterized by Mössbauer, magnetic susceptibility data, and XAS spectroscopies combined with DFT calculations (Aliaga-Alcade, N.; DeBeer George, S.; Bill, E.; Wieghardt, K.; Neese, F. Angew. Chem., Int. Ed. 2005, 44, 2908-2912). The results of this study indicated that the [Fe(V)-nitrido-cyclam-acetato]+ complex is an unusual d3 system with a nearly orbitally degenerate S=1/2 ground state. Although the calculations predicted fairly different Fe-N stretching frequencies for the S=1/2 and the competing S=3/2 ground states, a direct experimental determination of this important fingerprint quantity was missing. Here we apply synchrotron-based nuclear resonance vibrational scattering (NRVS) to characterize the Fe-N stretching frequency of an Fe(V)-nitrido complex and its Fe(III)-azide precursor. The NRVS data show a new isolated band at 864 cm(-1) in the Fe(V)-nitrido complex that is absent in the precursor. The NRVS spectra are fit and simulated using a DFT approach, and the new feature is unambiguously assigned to a Fe(V)-N stretch. The calculated Fe-N stretching frequency is too high by approximately 75 cm(-1). Anharmonic contributions to the Fe-N stretching frequency have been evaluated and have been found to be small (-5.5 cm(-1)). The NRVS data provided a unique opportunity to obtain this vibrational information, which had eluded characterization by more traditional vibrational spectroscopies.
    Keywords: Magnetic Resonance Spectroscopy ; Iron -- Chemistry ; Nitrogen Compounds -- Chemistry
    ISSN: 0002-7863
    E-ISSN: 15205126
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  • 7
    Language: English
    In: Inorganic chemistry, 07 December 2009, Vol.48(23), pp.10926-41
    Description: The reaction of ReCl(5) with 3 equiv of a benzene-1,2-dithiolate derivative in CH(3)CN produced, after the addition of [C(8)H(16)N]Br ([C(8)H(16)N](+) is 5-azonia-spiro[4,4]nonane), brownish-green crystals of [C(8)H(16)N][Re(tms)(3)] (1c) and [C(8)H(16)N][Re(Cl(2)-bdt)(3)] (2c), where (tms)(2-) represents 3,6-bis(trimethylsilyl)benzene-1,2-dithiolate and (Cl(2)-bdt)(2-) is 3,6-dichlorobenzene-1,2-dithiolate. Chemical reduction of [Re(bdt)(3)] (3b) with n-butyllithium in the presence of PPh(4)Br yielded [PPh(4)][Re(bdt)(3)] (3c), where (bdt)(2-) is benzene-1,2-dithiolate. The three monoanionic complexes possess a diamagnetic ground state (Re(V), d(2), S = 0). The crystal structures of 1c x 2 CH(3)CN and 2c x C(3)H(6)O have been determined by X-ray crystallography. The electrochemistry establishes that the complexes are members of electron transfer series involving a monocation [Re(V)(L(*))(2)(L)](+) (S = 0(?)), a neutral [Re(V)(L(*))(L)(2)](0) (S = 1/2), a monoanion [Re(V)(L)(3)](1-) (S = 0), a dianion [Re(IV)(L)(3)](2-) (S = 1/2), and a trianion [Re(III)(L)(3)](3-) (S = 1(?)). The unique X-band EPR spectrum of the neutral species clearly describes a diamagnetic Re(V) d(2) central ion with the unpaired electron located in a purely ligand-centered molecular orbital, whereas it is metal-centered in the dianionic form: a Re(IV) d(3) ion with three dithiolate(2-) ligands. S K-edge and Re L-edge X-ray absorption spectroscopy confirms these assignments and furthermore shows that the monoanion has a Re(V) central ion with three dianionic ligands. The geometrical and electronic structures of all members of the electron transfer series have been calculated by density functional theoretical methods, and the S K-pre-edge spectra have been simulated and assigned using a time-dependent DFT protocol.
    Keywords: Electrons ; Models, Chemical ; Organometallic Compounds -- Chemistry ; Rhenium -- Chemistry
    ISSN: 00201669
    E-ISSN: 1520-510X
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  • 8
    Language: English
    In: Angewandte Chemie International Edition, 11 August 2008, Vol.47(34), pp.6384-6387
    Description: : An investigation of the electronic interplay between ligand radical(s) and a high‐valent metal center in the three‐member electron‐transfer series shown in the picture reveals that, upon oxidation and removal of both ligand radicals, the chromium center becomes reduced from Cr to Cr with concomitant formation of an imidyl radical (NR).
    Keywords: Bioinorganic Chemistry ; Chromium ; Electron Transfer ; N Ligands ; Radicals
    ISSN: 1433-7851
    E-ISSN: 1521-3773
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  • 9
    Language: English
    In: Angewandte Chemie International Edition, 06 May 2005, Vol.44(19), pp.2908-2912
    Description: : A high‐valent iron–nitrido species containing a Fe center is accessible by the photolysis of [(cyclam‐ac)FeN]. The identity of the resulting [(cyclam‐ac)Fe(N)] species was verified by spectroscopic methods, magnetic susceptibility data, and DFT calculations (see picture). Unexpectedly, the analysis provides strong evidence for a low‐spin d (=1/2) ground‐state electron configuration at the Fe center.
    Keywords: Electronic Structure ; Exafs Spectroscopy ; Iron ; Mössbauer Spectroscopy ; Nitrido Ligands
    ISSN: 1433-7851
    E-ISSN: 1521-3773
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  • 10
    Language: English
    In: Angewandte Chemie, 11 August 2008, Vol.120(34), pp.6484-6487
    Description: : Die Untersuchung des elektronischen Wechselspiels zwischen Ligandenradikal(en) und einem hochvalenten Metallzentrum in der im Bild gezeigten Elektronentransferreihe ergibt, dass bei der Oxidation und Entfernung beider Ligandenradikale das Chromzentrum von Cr zu Cr reduziert und ein Imidylradikal (NR) gebildet wird.
    Keywords: Bioanorganische Chemie ; Chrom ; Elektronentransfer ; N‐Liganden ; Radikale
    ISSN: 0044-8249
    E-ISSN: 1521-3757
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