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Berlin Brandenburg

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  • George, Serena Debeer  (7)
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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: 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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  • 4
    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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  • 5
    Language: English
    In: Inorganic chemistry, 04 August 2008, Vol.47(15), pp.6804-24
    Description: The ligand L (2-) (H 2L = N, N'-dimethyl- N, N'-bis(3,5-di- t-butyl-2-hydroxybenzyl)-1,2-diaminoethane) has been employed for the synthesis of two mononuclear Fe (III) complexes, namely, [LFe(eta (2)-NO 3)] and [LFeCl]. L (2-) is comprised of four strongly electron-donating groups (two tert-amines and two phenolates) that increase the electron density at the coordinated ferric ions. This property should facilitate oxidation of the complexes, that is, stabilization of the oxidized species. The molecular structures in the solid state have been established by X-ray diffraction studies. [LFeCl] is five-coordinate in a square-pyramidal coordination environment with the ligand adopting a trans-conformation, while [LFe(eta (2)-NO 3)] is six-coordinate in a distorted octahedral environment with the ligand in a beta-cis conformation. The electronic structures have been studied using magnetization, EPR, Mossbauer (with and without applied field), UV-vis-NIR, and X-ray absorption spectroscopies, which demonstrate highly anisotropic covalency from the strong sigma- and pi-donating phenolates. This analysis is supported by DFT calculations on [LFeCl]. The variations of the well-understood spectroscopic data in the solid state to the spectroscopic data in solution have been used to obtain insight in the molecular structure of the two complexes in solution. While the molecular structures of the solid states are retained in solutions of nonpolar aprotic solvents, there is, however, one common molecular structure in all protic polar solvents. The analysis of the LMCT transitions and the rhombicity E/ D clearly establish that both compounds exhibit a beta-cis conformation in these protic polar solvents. These two open coordination sites, cis to each other, allow access for two potential ligands in close proximity. Electrochemical analysis establishes two reversible oxidation waves for [LFeCl] at +0.55 V and +0.93 V vs Fc (+)/Fc and one reversible oxidation wave at +0.59 V with an irreversible oxidation at +1.07 V vs Fc (+)/Fc for [LFe(eta (2)-NO 3)]. The one- and the two-electron oxidations of [LFeCl] by chronoamperometry have been followed spectroscopically. The increase of a strong band centered at 420 nm indicates the formulation of [LFeCl] (+) as a Fe (III) monophenoxyl radical complex and of [LFeCl] (2+) as a Fe (III) bisphenoxyl radical complex. These studies imply that the ligand L (2-) is capable of providing a flexible coordination geometry with two binding sites for substrates and the allocation of two oxidation equivalents on the ligand.
    Keywords: Electrons ; Benzyl Compounds -- Chemistry ; Ethylamines -- Chemistry ; Iron -- Chemistry ; Organometallic Compounds -- Chemical Synthesis
    ISSN: 00201669
    E-ISSN: 1520-510X
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  • 6
    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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  • 7
    Language: English
    In: Science (New York, N.Y.), 30 June 2006, Vol.312(5782), pp.1937-41
    Description: The hexavalent state, considered to be the highest oxidation level accessible for iron, has previously been found only in the tetrahedral ferrate dianion, FeO4(2-). We report the photochemical synthesis of another Fe(VI) compound, an octahedrally coordinated dication bearing a terminal nitrido ligand. Mössbauer and x-ray absorption spectra, supported by density functional theory, are consistent with the octahedral structure having an FeN triple bond of 1.57 angstroms and a singlet d2(xy) ground electronic configuration. The compound is stable at 77 kelvin and yields a high-spin Fe(III) species upon warming.
    Keywords: Iron -- Chemistry ; Organometallic Compounds -- Chemistry
    E-ISSN: 1095-9203
    Source: MEDLINE/PubMed (U.S. National Library of Medicine)
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