Frank Neese

Max Planck Institute for Chemical Energy Conversion, Mülheim-on-Ruhr, North Rhine-Westphalia, Germany

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Publications (426)2373.16 Total impact

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    ABSTRACT: A disulfide-bridged diiron complex with [Fe-S-S-Fe] core, which represents an isomer of the common biological [2Fe-2S] ferredoxin-type clusters, was synthesized using strongly σ-donating macrocyclic tetracarbene capping ligands. Though the complex is quite labile in solution, single crystals were obtained, and the structure was elucidated by X-ray diffraction. The electron-rich iron-sulfur core is found to show rather unusual magnetic and electronic properties. Experimental data and density functional theory studies indicate extremely strong antiferromagnetic coupling (-J > 800 cm(-1)) between two low-spin iron(III) ions via the S2(2-) bridge, and the intense near-IR absorption characteristic for the [Fe-S-S-Fe] core was assigned to a S → Fe ligand-to-metal charge transfer transition.
    Inorganic Chemistry 10/2015; 54(20). DOI:10.1021/acs.inorgchem.5b01446 · 4.76 Impact Factor
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    ABSTRACT: Over the past several decades, tremendous efforts have been invested in finding molecules that display slow relaxation of magnetization and hence act as single-molecule magnets (SMMs). While initial research was strongly focused on polynuclear transition metal complexes, it has become increasingly evident that SMM behavior can also be displayed in relatively simple mononuclear transition metal complexes. One of the first examples of a mononuclear SMM that shows a slow relaxation of the magnetization in the absence of an external magnetic field is the cobalt(II) tetra-thiolate [Co(SPh)4](2-). Fascinatingly, substitution of the donor ligand atom by oxygen or selenium dramatically changes zero-field splitting (ZFS) and relaxation time. Clearly, these large variations call for an in-depth electronic structure investigation in order to develop a qualitative understanding of the observed phenomena. In this work, we present a systematic theoretical study of a whole series of complexes (PPh4)2[Co(XPh)4] (X = O, S, Se) using multireference ab initio methods. To this end, we employ the recently proposed ab initio ligand field theory, which allows us to translate the ab initio results into the framework of ligand field theory. Magneto-structural correlations are then developed that take into account the nature of metal-ligand covalent bonding, ligand spin-orbit coupling, and geometric distortions away from pure tetrahedral symmetry. The absolute value of zero-field splitting increases when the ligand field strength decreases across the series from O to Te. The zero-field splitting of the ground state of the hypothetical [Co(TePh)4](2-) complex is computed to be about twice as large as for the well-known (PPh4)2[Co(SPh)4] compound. It is shown that due to the π-anisotropy of the ligand donor atoms (S, Se) magneto-structural correlations in [Co(OPh)4](2-) complex differ from [Co(S/SePh)4](2-). In the case of almost isotropic OPh ligand, only variations in the first coordination sphere affect magnetic properties, but in the case of S/SePh ligand, variations in the first and second coordination sphere become equally important for magnetic properties.
    Inorganic Chemistry 10/2015; 54(20). DOI:10.1021/acs.inorgchem.5b01706 · 4.76 Impact Factor
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    ABSTRACT: Zero-field splitting (ZFS) parameters of nondeuterated metalloporphyrins [Fe(TPP)X] (X = F, Br, I; H2TPP = tetraphenylporphyrin) have been directly determined by inelastic neutron scattering (INS). The ZFS values are D = 4.49(9) cm-1 for tetragonal polycrystalline [Fe(TPP)F], and D = 8.8(2) cm-1, E = 0.1(2) cm-1 and D = 13.4(6) cm-1, E = 0.3(6) cm-1 for monoclinic polycrystalline [Fe(TPP)Br] and [Fe(TPP)I], respectively. Along with our recent report of the ZFS value of D = 6.33(8) cm-1 for tetragonal polycrystalline [Fe(TPP)Cl], these data provide a rare, complete determination of ZFS parameters in a metalloporphyrin halide series. The electronic structure of [Fe(TPP)X] (X = F, Cl, Br, I) has been studied by multireference ab initio methods: the complete active space self-consistent field (CASSCF) and the N-electron valence perturbation theory (NEVPT2) with the aim of exploring the origin of the large and positive zero-field splitting D of the 6A1 ground state. D was calculated from wave functions of the electronic multiplets spanned by the d5 configuration of Fe(III) along with spin-orbit coupling accounted for by quasi degenerate perturbation theory. Results reproduce trends of D from inelastic neutron scattering data increasing in the order from F, Cl, Br, to I. A mapping of energy eigenvalues and eigenfunctions of the S = 3/2 excited states on ligand field theory was used to characterize the σ- and π-antibonding effects decreasing from F to I. This is in agreement with similar results deduced from ab initio calculations on CrX63- complexes and also with the spectrochemical series showing a decrease of the ligand field in the same directions. A correlation is found between the increase of D and decrease of the π- and σ-antibonding energies eλX (λ = σ, π) in the series from X = F to I. Analysis of this correlation using second-order perturbation theory expressions in terms of angular overlap parameters rationalizes the experimentally deduced trend. D parameters from CASSCF and NEVPT2 results have been calibrated against those from the INS data, yielding a predictive power of these approaches. Methods to improve the quantitative agreement between ab initio calculated and experimental D and spectroscopic transitions for high-spin Fe(III) complexes are proposed.
    Inorganic Chemistry 10/2015; 54(20):151002080148004. DOI:10.1021/acs.inorgchem.5b01505 · 4.76 Impact Factor
  • Vera Krewald · Frank Neese · Dimitrios A. Pantazis ·
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    ABSTRACT: A frequent challenge when dealing with multinuclear transition metal clusters in biology is to determine the absolute oxidation states of the individual metal ions and to identify how they evolve during catalytic turnover. The oxygen-evolving complex of biological photosynthesis, an active site that harbors an oxo-bridged Mn4Ca cluster as the water-oxidizing species, offers a prime example of such a challenge that withstood satisfactory resolution for decades. A multitude of experimental studies have approached this question and have offered insights from different angles, but they were also accompanied by incomplete or inconclusive interpretations. Only very recently, through a combination of experiment and theory, has a definitive assignment of the individual Mn oxidation states been achieved for all observable catalytic states of the complex. Here we review the information obtained by structural and spectroscopic methods, describe the interpretation and synthesis achieved through quantum chemistry, and summarize our current understanding of the electronic structure of nature’s water splitting catalyst.
    Israel Journal of Chemistry (Online) 09/2015; DOI:10.1002/ijch.201500051 · 2.22 Impact Factor
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    ABSTRACT: The high-spin (S = 1) tetrahedral NiII complex [Ni{iPr2(Se)NP(Se)iPr2}2] was investigated by magnetometry, spectroscopic and quantum chemical methods. Angle-resolved magnetometry studies revealed the orientation of the magnetization principal axes. The very large zero-field splitting (zfs), D = 45.40(2) cm-1, E = 1.91(2) cm-1, of the complex was accurately determined by far-infrared magnetic spectroscopy, directly observing transitions between the spin sublevels of the triplet ground state. These are the largest zfs values ever determined - directly  for a high-spin NiII complex. Ab initio calculations further probed the electronic structure of the system, elucidating the factors controlling the sign and magnitude of D. The latter is dominated by spin-orbit coupling contributions of the Ni ions, whereas the corresponding effects of the Se atoms are remarkably smaller.
    Journal of the American Chemical Society 09/2015; 137(40). DOI:10.1021/jacs.5b06716 · 12.11 Impact Factor
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    ABSTRACT: First principle calculations of extended x-ray absorption fine structure (EXAFS) data have seen widespread use in bioinorganic chemistry, perhaps most notably for modeling the Mn4Ca site in the oxygen evolving complex (OEC) of photosystem II (PSII). The logic implied by the calculations rests on the assumption that it is possible to a priori predict an accurate EXAFS spectrum provided that the underlying geometric structure is correct. The present study investigates the extent to which this is possible using state of the art EXAFS theory. The FEFF program is used to evaluate the ability of a multiple scattering-based approach to directly calculate the EXAFS spectrum of crystallographically-defined model complexes. The results of these parameter free predictions are compared with the more traditional approach of fitting FEFF calculated spectra to experimental data. A series of seven crystallographically characterized Mn monomers and dimers is used as a test set. The largest deviations between the FEFF calculated EXAFS spectra and the experimental EXAFS spectra arise from the amplitudes. The amplitude errors result from a combination of errors in calculated S02 and Debye-Waller values, as well as uncertainties in background subtraction. Additional errors may be attributed to structural parameters, particularly in cases where reliable high-resolution crystal structures are not available. Based on these investigations, the strengths and weaknesses of using first principle EXAFS calculations as a predictive tool are discussed. We demonstrate that a range of DFT optimized structures of the OEC may all be considered consistent with experimental EXAFS data and that caution must be exercised when using EXAFS data to obtain topological arrangements of complex clusters.
    Journal of the American Chemical Society 09/2015; 137(40). DOI:10.1021/jacs.5b00783 · 12.11 Impact Factor
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    ABSTRACT: Hemilabile ligands, which have one donor that can reversibly bind to a metal, are widely used in transition-metal catalysts to create open coordination sites. This change in coordination at the metal can also cause spin-state changes. Here, we explore a cobalt(I) system that is poised on the brink of hemilability and of a spin-state change and can rapidly interconvert between different spin states with different structures ("spin isomers"). The new cobalt(I) monocarbonyl complex L(tBu)Co(CO) (2) is a singlet ((1)2) in the solid state, with an unprecedented diketiminate binding mode where one of the C═C double bonds of an aromatic ring completes a pseudo-square-planar coordination. Dissolving the compound gives a substantial population of the triplet ((3)2), which has exceptionally large uniaxial zero-field splitting due to strong spin-orbit coupling with a low-lying excited state. The interconversion of the two spin isomers is rapid, even at low temperature, and temperature-dependent NMR and electronic absorption spectroscopy studies show the energy differences quantitatively. Spectroscopically validated computations corroborate the presence of a low minimum-energy crossing point (MECP) between the two potential energy surfaces and elucidate the detailed pathway through which the β-diketiminate ligand "slips" between bidentate and arene-bound forms: rather than dissociation, the cobalt slides along the aromatic system in a pathway that balances strain energy and cobalt-ligand bonding. These results show that multiple spin states are easily accessible in this hemilabile system and map the thermodynamics and mechanism of the transition.
    Journal of the American Chemical Society 08/2015; 137(33). DOI:10.1021/jacs.5b06078 · 12.11 Impact Factor
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    ABSTRACT: The metabolism of many anaerobes relies on [NiFe]-hydrogenases, whose characterization when bound to substrates has proven non-trivial. Presented here is direct evidence for a hydride bridge in the active site of the 57 Fe-labelled fully reduced Ni-R form of Desulfovibrio vulgaris Miyazaki F [NiFe]-hydrogenase. A unique ' wagging' mode involving H- motion perpendicular to the Ni(μ1/4-H)57 Fe plane was studied using 57 Fe-specific nuclear resonance vibrational spectroscopy and density functional theory (DFT) calculations. On Ni(μ1/4-D) 57 Fe deuteride substitution, this wagging causes a characteristic perturbation of Fe-CO/CN bands. Spectra have been interpreted by comparison with Ni(μ1/4-H/D) 57 Fe enzyme mimics [(dppe)Ni(μ1/4-pdt)(μ1/4-H/D) 57 Fe(CO)3 ]+ and DFT calculations, which collectively indicate a low-spin Ni(II)(μ1/4-H)Fe(II) core for Ni-R, with H- binding Ni more tightly than Fe. The present methodology is also relevant to characterizing Fe-H moieties in other important natural and synthetic catalysts.
    Nature Communications 08/2015; 6. DOI:10.1038/ncomms8890 · 11.47 Impact Factor
  • Dmytro Bykov · Frank Neese ·
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    ABSTRACT: In this Forum Article, an extensive discussion of the mechanism of six-electron, seven-proton nitrite reduction by the cytochrome c nitrite reductase enzyme is presented. On the basis of previous studies, the entire mechanism is summarized and a unified picture of the most plausible sequence of elementary steps is presented. According to this scheme, the mechanism can be divided into five functional stages. The first phase of the reaction consists of substrate binding and N-O bond cleavage. Here His277 plays a crucial role as a proton donor. In this step, the N-O bond is cleaved heterolytically through double protonation of the substrate. The second phase of the mechanism consists of two proton-coupled electron-transfer events, leading to an HNO intermediate. The third phase involves the formation of hydroxylamine, where Arg114 provides the necessary proton for the reaction. The second N-O bond is cleaved in the fourth phase of the mechanism, again triggered by proton transfer from His277. The Tyr218 side chain governs the fifth and last phase of the mechanism. It consists of radical transfer and ammonia formation. Thus, this mechanism implies that all conserved active-site side chains work in a concerted way in order to achieve this complex chemical transformation from nitrite to ammonia. The Forum Article also provides a detailed discussion of the density functional theory based cluster model approach to bioinorganic reactivity. A variety of questions are considered: the resting state of enzyme and substrate binding modes, interaction with the metal site and with active-site side chains, electron- and proton-transfer events, substrate dissociation, etc.
    Inorganic Chemistry 08/2015; 54(19). DOI:10.1021/acs.inorgchem.5b01506 · 4.76 Impact Factor
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    ABSTRACT: Multifrequency pulsed EPR data are reported for a series of oxygen bridged (µ-oxo/ µ-hydroxo) bimetallic manganese complexes where the oxygen is labeled with the magnetically active isotope (17)O (I = 5/2). Two synthetic complexes and two biological metallocofactors are examined: a planar bis-µ-oxo bridged complex and a bent, bis-µ-oxo-µ-carboxylato bridge complex; the di-manganese catalase, which catalyzes the dismutation of H2O2 to H2O and O2; and the recently identified manganese/iron cofactor of the R2lox protein, a homologue of the small subunit of the ribonuclotide reductase enzyme (class 1c). High field (W-band) hyperfine EPR spectroscopies are demonstrated to be ideal methods to characterize the (17)O magnetic interactions, allowing a magnetic finger-print for the bridging oxygen ligand to be developed. It is shown that the μ-oxo bridge motif displays small positive isotropic hyperfine coupling constant of about +5 to +8 MHz and an anisotropic/dipolar coupling of -9 MHz. In addition, protonation of the bridge is correlated with an increase of the hyperfine coupling constant. Broken symmetry Density Functional Theory is evaluated as a predictive tool for estimating hyperfine coupling of bridging species. Experimental and theoretical results provide a framework for the characterization of oxygen bridge in Mn metallocofactor systems, including water oxidizing cofactor of Photosystem II, allowing substrate/solvent interface to be examined throughout its catalytic cycle.
    The Journal of Physical Chemistry B 07/2015; 119(43). DOI:10.1021/acs.jpcb.5b04614 · 3.30 Impact Factor
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    Dimitrios G Liakos · Frank Neese ·
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    ABSTRACT: The recently developed domain-based local pair natural orbital coupled cluster theory with single, double, and perturbative triple excitations (DLPNO-CCSD(T)) delivers results that are closely approaching those of the parent canonical coupled cluster method at a small fraction of the computational cost. A recent extended benchmark study established that, depending on the three main truncation thresholds, it is possible to approach the canonical CCSD(T) results within 1 kJ (default setting, TightPNO), 1 kcal/mol (default setting, NormalPNO), and 2−3 kcal (default setting, LoosePNO). Although thresholds for calculations with TightPNO are 2−4 times slower than those based on NormalPNO thresholds, they are still many orders of magnitude faster than canonical CCSD(T) calculations, even for small and medium sized molecules where there is little locality. The computational effort for the coupled cluster step scales nearly linearly with system size. Since, in many instances, the coupled cluster step in DLPNO-CCSD(T) is cheaper or at least not much more expensive than the preceding Hartree−Fock calculation, it is useful to compare the method against modern density functional theory (DFT), which requires an effort comparable to that of Hartree−Fock theory (at least if Hartree−Fock exchange is part of the functional definition). Double hybrid density functionals (DHDF's) even require a MP2-like step. The purpose of this article is to evaluate the cost vs accuracy ratio of DLPNO-CCSD(T) against modern DFT (including the PBE, B3LYP, M06-2X, B2PLYP, and B2GP-PLYP functionals and, where applicable, their van der Waals corrected counterparts). To eliminate any possible bias in favor of DLPNO-CCSD(T), we have chosen established benchmark sets that were specifically proposed for evaluating DFT functionals. It is demonstrated that DLPNO-CCSD(T) with any of the three default thresholds is more accurate than any of the DFT functionals. Furthermore, using the aug-cc-pVTZ basis set and the LoosePNO default settings, DLPNO-CCSD(T) is only about 1.2 times slower than B3LYP. With NormalPNO thresholds, DLPNO-CCSD(T) is about a factor of 2 slower than B3LYP and shows a mean absolute deviation of less than 1 kcal/mol to the reference values for the four different data sets used. Our conclusion is that coupled cluster energies can indeed be obtained at near DFT cost.
    Journal of Chemical Theory and Computation 07/2015; 11(9). DOI:10.1021/acs.jctc.5b00359 · 5.50 Impact Factor
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    Bhaskar Mondal · Frank Neese · Shengfa Ye ·
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    ABSTRACT: The development of efficient catalysts with base metals for CO2 hydrogenation has always been a major thrust of interest. A series of experimental and theoretical work has revealed that the catalytic cycle typically involves two key steps, namely, base-promoted heterolytic H2 splitting and hydride transfer to CO2, either of which can be the rate-determining step (RDS) of the entire reaction. To explore the determining factor for the nature of RDS, we present herein a comparative mechanistic investigation on CO2 hydrogenation mediated by [M(H)(η(2)-H2)(PP3(Ph))](n+) (M = Fe(II), Ru(II), and Co(III); PP3(Ph) = tris(2-(diphenylphosphino)phenyl)phosphine) type complexes. In order to construct reliable free energy profiles, we used highly correlated wave function based ab initio methods of the coupled cluster type alongside the standard density functional theory. Our calculations demonstrate that the hydricity of the metal-hydride intermediate generated by H2 splitting dictates the nature of the RDS for the Fe(II) and Co(III) systems, while the RDS for the Ru(II) catalyst appears to be ambiguous. CO2 hydrogenation catalyzed by the Fe(II) complex that possesses moderate hydricity traverses an H2-splitting RDS, whereas the RDS for the high-hydricity Co(III) species is found to be the hydride transfer. Thus, our findings suggest that hydricity can be used as a practical guide in future catalyst design. Enhancing the electron-accepting ability of low-hydricity catalysts is likely to improve their catalytic performance, while increasing the electron-donating ability of high-hydricity complexes may speed up CO2 conversion. Moreover, we also established the active roles of base NEt3 in directing the heterolytic H2 splitting and assisting product release through the formation of an acid-base complex.
    Inorganic Chemistry 07/2015; 54(15). DOI:10.1021/acs.inorgchem.5b00469 · 4.76 Impact Factor
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    ABSTRACT: In this work, a systematic infrastructure is described that formalizes concepts implicit in previous work and greatly simplifies computer implementation of reduced-scaling electronic structure methods. The key concept is sparse representation of tensors using chains of sparse maps between two index sets. Sparse map representation can be viewed as a generalization of compressed sparse row, a common representation of a sparse matrix, to tensor data. By combining few elementary operations on sparse maps (inversion, chaining, intersection, etc.), complex algorithms can be developed, illustrated here by a linear-scaling transformation of three-center Coulomb integrals based on our compact code library that implements sparse maps and operations on them. The sparsity of the three-center integrals arises from spatial locality of the basis functions and domain density fitting approximation. A novel feature of our approach is the use of differential overlap integrals computed in linear-scaling fashion for screening products of basis functions. Finally, a robust linear scaling domain based local pair natural orbital second-order Möller-Plesset (DLPNO-MP2) method is described based on the sparse map infrastructure that only depends on a minimal number of cutoff parameters that can be systematically tightened to approach 100% of the canonical MP2 correlation energy. With default truncation thresholds, DLPNO-MP2 recovers more than 99.9% of the canonical resolution of the identity MP2 (RI-MP2) energy while still showing a very early crossover with respect to the computational effort. Based on extensive benchmark calculations, relative energies are reproduced with an error of typically <0.2 kcal/mol. The efficiency of the local MP2 (LMP2) method can be drastically improved by carrying out the LMP2 iterations in a basis of pair natural orbitals. While the present work focuses on local electron correlation, it is of much broader applicability to computation with sparse tensors in quantum chemistry and beyond.
    The Journal of Chemical Physics 07/2015; 143(3):034108. DOI:10.1063/1.4926879 · 2.95 Impact Factor
  • Mahesh Sundararajan · Frank Neese ·
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    ABSTRACT: Nitrite ligand can coordinate with the transition metal through either N- or O-, which is known as linkage isomerism and is believed to occur in metalloproteins. In contrast to the commonly found N-binding motif of nitrite to iron in synthetic models, the less commonly observed O-binding of nitrite to myoglobin ( Copeland , D. M. ; Soares , A. S. ; West , A. H. ; Richter-Addo , G. B. J. Inorg. Biol. Chem. 2006, 100 , 1413 - 1425 ) and hemoglobin ( Yi , J. ; Safo , M. K. ; Richter-Addo , G. Biochemistry , 2008 , 47 , 8247 - 8249 ) reported by Richter-Addo and co-workers is intriguing. On the basis of site-directed mutagenesis studies, it was argued that the distal histidine modulates this unique binding. However, EPR measurements on nitrite binding to methemoglobin could not rule out the possibility of N-bound species to low spin ferric iron. Given to the very similar active sites, there exists a controversy within the two powerful experimental techniques in identifying the coordination motif of nitrite to myoglobin, which is central to understanding the denitrification mechanism. Herein, we report the computation of spin Hamiltonian EPR parameters of different linkage isomers of nitrite bound myoglobin using wave function based "ab initio" and density functional theories to shed light on the binding motif of nitrite to ferric iron. Our predicted spin Hamiltonian parameters agree closely with the experimental EPR data, which provides strong support for the crystallographically implied O-binding to the low-spin ferric heme. This unique O-binding of nitrite to iron is modulated by the distal histidine whose contributions to the active site electronic structure have been successfully quantified. Our quantum chemical insights on the electronic structure of this intermediate are crucial for understanding the structure-function relationship of other metal-nitrite species found in various metalloenzymes.
    Inorganic Chemistry 07/2015; 54(15). DOI:10.1021/acs.inorgchem.5b00557 · 4.76 Impact Factor
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    ABSTRACT: A series of density functional theory (DFT) calculations on the full [Mo(HIPT)N3N] catalyst are performed to obtain an energy profile of the Schrock cycle. This is a continuation of our earlier investigation of this cycle in which the bulky hexaisopropyterphenyl (HIPT) substituents of the ligand were replaced by hydrogen atoms (Angew. Chem., Int. Ed. 2005, 44, 5639). In an effort to provide a treatment that is as converged as possible from a quantum-chemical point of view, the present study now fully takes the HIPT moieties into account. Moreover, structures and energies are calculated with a near-saturated basis set, leading to models with 280 atoms and 4850 basis functions. Solvent and scalar relativistic effects have been treated using the conductor-like screening model and zeroth-order regular approximation, respectively. Free reaction enthalpies are evaluated using the PBE and B3LYP functionals. A comparison to the available experimental data reveals much better agreement with the experiment than preceding DFT treatments of the Schrock cycle. In particular, free reaction enthalpies of reduction steps and NH3/N2 exchange are now excellently reproduced.
    Inorganic Chemistry 06/2015; 54(19). DOI:10.1021/acs.inorgchem.5b00787 · 4.76 Impact Factor
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    ABSTRACT: Carboxylate-bridged Mn(ii)-Ca(ii) complexes are potentially relevant for mimicking the first stages of the Oxygen-Evolving Complex (OEC) assembly process. Here, we report on new homonuclear Ca(ii) and heteronuclear Mn(ii)-Ca(ii) complexes with carboxylate-functionalized tripodal tris(2-pyridylmethyl)amine ligands, the heptadentate H3tpaa, previously reported, and the new hexadentate H2tpada, containing respectively three and two carboxylate units. The mononuclear [Ca(Htpaa)(OH2)] () and dinuclear [Ca(tpada)(OH2)2]2 () calcium complexes, as well as the tetranuclear [{Mn(tpaa)}2{Ca(OH2)5(μ-OH2)}2][Mn(tpaa)]2 (·) and dinuclear [Mn(tpada)ClCa(OH2)2.67(MeOH)2.33]Cl () heterometallic species have been structurally characterized; the syntheses of and · being previously reported by us (Inorg. Chem., 2015, 54, 1283). The Mn(ii) and Ca(ii) are linked by two μ1,1-bridging carboxylates in , while only one μ1,3-carboxylate bridge connects each Ca(2+) ion to each Mn(ii) in . A variable number of water molecules (n = 1 to 7) are coordinated to Ca in all complexes, most of them being involved in hydrogen-bond networks, in analogy to what occurs in the photosystem II. All donor atoms of the tpaa(3-) and tpada(2-) ligands are coordinated to the Mn(2+) ions, despite the unusually long distance between the Mn(2+) ion and the tertiary amine imposed by the constraining nature of the ligands, as supported by theoretical calculations. Solid state EPR spectroscopy, in combination with DFT calculations, has also shown that the Ca(2+) ion has an effect on the electronic parameters (zero field splitting) of the linked Mn(ii) in the case of (μ1,1-carboxylate bridges). In (μ1,3-carboxylate bridge) the Ca(2+) ion induces only slight structural changes in the Mn coordination sphere.
    Dalton Transactions 06/2015; 44(28). DOI:10.1039/c5dt01776a · 4.20 Impact Factor
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    ABSTRACT: Herein, we describe a uncommon example of manganese-thiolate complex, which is capable of activating dioxygen and catalyzing its 2-electron reduction to generate H2O2. The structurally characterized dimercapto-bridged MnII dimer [MnII2(LS)(LSH)]ClO4 (MnII2SH) is formed by reaction of the LS ligand (2,2'-(2,2'-bipyridine-6,6'-iyl)bis(1,1-diphenylethanethiolate) with MnII. The unusual presence of a pendant thiol group bound to one MnII ion in MnII2SH is evidenced both in solid state and in solution. The MnII2SH complex reacts with dioxygen in CH3CN, leading to the formation of a rare mono μ-hydroxo dinuclear MnIII complex, [(MnIII2(LS)2(OH)]ClO4 (MnIII2OH), which has also been structurally characterized. When MnII2SH reacts with O2 in the presence of a proton source, 2,6-lutidinium tetrafluoroborate (up to 50 eq.), the formation of a new Mn species is observed, assigned to a bis μ-thiolato dinuclear MnIII complex with two terminal thiolate groups (MnIII2), with the concomitant production of H2O2 up to a ~40% vs. MnII2SH. The addition of a catalytic amount of MnII2SH to an air-saturated solution of MenFc (n = 8 or 10) and 2,6-lutidinium tetrafluoroborate results in the quantitative and efficient oxidation of MenFc by O2 to afford the respective ferricenium derivates (MenFc+ with n = 8 or 10). Hydrogen peroxide is mainly produced during the catalytic reduction of dioxygen with 80-84 % selectivity, making the MnII2SH complex a rare Mn-based active catalyst for 2-electron O2 reduction.
    Journal of the American Chemical Society 06/2015; 137(26). DOI:10.1021/jacs.5b04917 · 12.11 Impact Factor
  • Ondrej Demel · Jiri Pittner · Frank Neese ·
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    ABSTRACT: This paper reports the development of a local variant of Mukherjee’s state-specific multireference coupled cluster method based on the pair natural orbital approach (LPNO-MkCC). The current implementation is restricted to single and double excitations. The performance of the LPNO-MkCCSD method was tested on calculations of naphthyne isomers, tetramethyleneethane, and β-carotene molecules. The results show that 99.7–99.8% of correlation energy was recovered with respect to the MkCC method based on canonical orbitals. Moreover, the errors of relative energies between different isomers or along a potential energy curve (with respect to the canonical method) are below 0.4 kcal/mol, safely within the chemical accuracy. The computational efficiency of our implementation of LPNO-MkCCSD in the ORCA program allows calculation of the β-carotene molecule (96 atoms and 1984 basis functions) on a single CPU core.
    Journal of Chemical Theory and Computation 06/2015; 11(7):150611153720009. DOI:10.1021/acs.jctc.5b00334 · 5.50 Impact Factor
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    Bhaskar Mondal · Jinshuai Song · Frank Neese · Shengfa Ye ·
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    ABSTRACT: The global energy and environmental concerns related to the excess CO2 concentration in the atmosphere have intensified the research and development regarding CO2 utilization. Due to the high stability and inertness of CO2, CO2 functionalization under mild conditions has been proven to be extremely challenging. Nature has, however, evolved efficient pathways to achieve this difficult transformation. Herein, we compare the mechanisms of CO2 two-electron reduction followed by synthetic catalysts and those by carbon monoxide dehydrogenase and formate dehydrogenase in order to provide more mechanistic insights into future catalyst design. Copyright © 2014 Elsevier Ltd. All rights reserved.
    Current Opinion in Chemical Biology 04/2015; 25. DOI:10.1016/j.cbpa.2014.12.022 · 6.81 Impact Factor
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    ABSTRACT: In the context of a global artificial photosynthesis (GAP) project, we review our current work on nature's water splitting catalyst. In a recent report (Cox et al. 2014 Science 345, 804-808 (doi:10.1126/science.1254910)), we showed that the catalyst-a Mn4O5Ca cofactor-converts into an 'activated' form immediately prior to the O-O bond formation step. This activated state, which represents an all Mn(IV) complex, is similar to the structure observed by X-ray crystallography but requires the coordination of an additional water molecule. Such a structure locates two oxygens, both derived from water, in close proximity, which probably come together to form the product O2 molecule. We speculate that formation of the activated catalyst state requires inherent structural flexibility. These features represent new design criteria for the development of biomimetic and bioinspired model systems for water splitting catalysts using first-row transition metals with the aim of delivering globally deployable artificial photosynthesis technologies.
    Interface focus: a theme supplement of Journal of the Royal Society interface 04/2015; 5(3):20150009-20150009. DOI:10.1098/rsfs.2015.0009 · 2.63 Impact Factor

Publication Stats

18k Citations
2,373.16 Total Impact Points


  • 2012-2015
    • Max Planck Institute for Chemical Energy Conversion
      Mülheim-on-Ruhr, North Rhine-Westphalia, Germany
    • Università degli Studi di Salerno
      • Department of BioMedical and Pharmaceutical Sciences FARMABIOMED
      Fisciano, Campania, Italy
    • Universitat Rovira i Virgili
      • Department of Physical and Inorganic Chemistry
      Tarraco, Catalonia, Spain
  • 2014
    • Jacobs University
      • SES - School of Engineering & Science
      Bremen, Bremen, Germany
  • 2012-2013
    • Bulgarian Academy of Sciences
      • Institute of General and Inorganic Chemistry
      Ulpia Serdica, Sofia-Capital, Bulgaria
  • 2003-2013
    • Max Planck Institute for Chemistry
      Mayence, Rheinland-Pfalz, Germany
  • 2006-2012
    • University of Bonn
      • Institute of Physical and Theoretical Chemistry
      Bonn, North Rhine-Westphalia, Germany
    • Cornell University
      • Department of Chemistry and Chemical Biology
      Итак, New York, United States
  • 2009
    • University of Rochester
      • Department of Chemistry
      Rochester, New York, United States
  • 2008
    • University of Wisconsin–Madison
      Madison, Wisconsin, United States
    • University of Münster
      • Institute of Organic Chemistry
      Muenster, North Rhine-Westphalia, Germany
  • 2005
    • Max Planck Institute for Coal Research
      Mülheim-on-Ruhr, North Rhine-Westphalia, Germany
    • Christian-Albrechts-Universität zu Kiel
      • Institute of Inorganic Chemistry
      Kiel, Schleswig-Holstein, Germany
    • Universität Paderborn
      • Department of Physics
      Paderborn, North Rhine-Westphalia, Germany
    • The University of Arizona
      • Department of Chemistry and Biochemistry (College of Science)
      Tucson, Arizona, United States
  • 2002
    • Universitätsklinikum Erlangen
      Erlangen, Bavaria, Germany
  • 1998-2002
    • Stanford University
      • Department of Chemistry
      Stanford, CA, United States
  • 1997-2002
    • Universität Konstanz
      • Faculty of Sciences
      Constance, Baden-Württemberg, Germany