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1.
Jaszewski AR Petrie S Pace RJ Stranger R 《Chemistry (Weinheim an der Bergstrasse, Germany)》2011,17(20):5699-5713
Density functional theory (DFT) and time‐dependent DFT (TDDFT) calculations are reported on three sets of isomeric models of the {Mn4/Ca} water‐oxidizing complex of photosystem II (PS II), which share the general formula [CaMn4O4(N2C3H4)(RCOO)6]q?(H2O)n (R=H, CH3; q=?1, 0, +1, +2; n=3, 4, 5, 6, 7). Comparison with the full range of available data on Mn K‐edge X‐ray absorption energy values determined for the photosystem allows us to validate the structures that correspond to the particular S states and to determine their Mn oxidation patterns. By using a new TDDFT procedure, it is shown that variations in the absolute K‐edge energy values for a particular S state, reported by different research groups, can be quantitatively explained by different geometries adopted by the Mn cluster, which demonstrates flexibility in the position of the fourth ‘dangling’ Mn atom in relation to a cubane structure created by the Ca atom and the three other Mn atoms. Computational results show that each step of the S cycle occurs by removal of one electron directly from the Mn cluster. This Mn‐centered oxidation still agrees with the small difference observed experimentally between the K‐edge energy values of the S2 and S3 states of the photosystem, thus resolving a controversy as to whether this represents ligand‐centered or metal‐centered oxidation. The overall oxidation state of Mn atoms in the tetramanganese cluster during functional turnover changes from 2.75 for S0, 3.00 for S1, and 3.25 for S2 up to 3.50 for the S3 state, which is systematically 0.50 lower than the previously proposed oxidation states of the cluster. The calculations give insight into why these earlier, purely empirical, assignments of the Mn oxidation levels in PS II could be in error. 相似文献
2.
Photocatalytic Water Oxidation by a Mixed‐Valent MnIII3MnIVO3 Manganese Oxo Core that Mimics the Natural Oxygen‐Evolving Center
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Dr. Rami Al‐Oweini Dr. Andrea Sartorel Dr. Bassem S. Bassil Dr. Mirco Natali Dr. Serena Berardi Prof. Franco Scandola Prof. Ulrich Kortz Prof. Marcella Bonchio 《Angewandte Chemie (International ed. in English)》2014,53(42):11182-11185
The functional core of oxygenic photosynthesis is in charge of catalytic water oxidation by a multi‐redox MnIII/MnIV manifold that evolves through five electronic states (Si , where i=0–4). The synthetic model system of this catalytic cycle and of its S0→S4 intermediates is the expected turning point for artificial photosynthesis. The tetramanganese‐substituted tungstosilicate [MnIII3MnIVO3(CH3COO)3(A‐α‐SiW9O34)]6? (Mn4POM) offers an unprecedented mimicry of the natural system in its reduced S0 state; it features a hybrid organic–inorganic coordination sphere and is anchored on a polyoxotungstate. Evidence for its photosynthetic properties when combined with [Ru(bpy)3]2+ and S2O82? is obtained by nanosecond laser flash photolysis; its S0→S1 transition within milliseconds and multiple‐hole‐accumulating properties were studied. Photocatalytic oxygen evolution is achieved in a buffered medium (pH 5) with a quantum efficiency of 1.7 %. 相似文献
3.
Heng Wang Shun Hamanaka Prof. Toshihiko Yokoyama Dr. Hirofumi Yoshikawa Prof. Kunio Awaga 《化学:亚洲杂志》2011,6(4):1074-1079
In situ X‐ray absorption fine structure (XAFS) analyses were performed on rechargeable molecular cluster batteries (MCBs), which were formed by a lithium anode and cathode‐active material, [Mn12O12(CH3CH2C(CH3)2COO)16(H2O)4] with tert‐pentyl carboxylate ligand (abbreviated as Mn12tPe), and with eight Mn3+ and four Mn4+ centers. This mixed valence cluster compound is used in an effort to develop a reusable in situ battery cell that is suitable for such long‐term performance tests. The Mn12tPe MCBs exhibit a large capacity of approximately 210 Ah kg−1 in the voltage range V=4.0–2.0 V. The X‐ray absorption near‐edge structure (XANES) spectra exhibit a systematic change during the charging/discharging with an isosbestic point at 6555 eV, which strongly suggests that only either the Mn3+ or Mn4+ ions in the Mn12 skeleton are involved in this battery reaction. The averaged manganese valence, determined from the absorption‐edge energy, decreased monotonically from 3.3 to 2.5 in the first half of the discharging (4.0>V>2.8 V), but changed little in the second half (2.8>V>2.0 V). The former valence change indicates a reduction of the initial [Mn12]0 state by approximately ten electrons, which corresponds well with the half value of the observed capacity. Therefore, the large capacity of the Mn12 MCBs can be understood as being due to a combination of the redox change of the manganese ions and presumably a capacitance effect. The extended X‐ray absorption fine structure (EXAFS) indicates a gradual increase of the Mn2+ sites in the first half of the discharging, which is consistent with the XANES spectra. It can be concluded that the Mn12tPe MCBs would include a solid‐state electrochemical reaction, mainly between the neutral state [Mn12]0 and the super‐reduced state [Mn12]8− that is obtained by a local reduction of the eight Mn3+ ions in Mn12 toward Mn2+ ions. 相似文献
4.
Dr. Sandra Schinzel Johannes Schraut Dr. Alexei V. Arbuznikov Prof. Dr. Per E. M. Siegbahn Prof. Dr. Martin Kaupp 《Chemistry (Weinheim an der Bergstrasse, Germany)》2010,16(34):10424-10438
Metal and ligand hyperfine couplings of a previously suggested, energetically feasible Mn4Ca model cluster ( SG2009?1 ) for the S2 state of the oxygen‐evolving complex (OEC) of photosystem II (PSII) have been studied by broken‐symmetry density functional methods and compared with other suggested structural and spectroscopic models. This was carried out explicitly for different spin‐coupling patterns of the S=1/2 ground state of the MnIII(MnIV)3 cluster. By applying spin‐projection techniques and a scaling of the manganese hyperfine couplings, computation of the hyperfine and nuclear quadrupole coupling parameters allows a direct evaluation of the proposed models in comparison with data obtained from the simulation of EPR, ENDOR, and ESEEM spectra. The computation of 55Mn hyperfine couplings (HFCs) for SG2009?1 gives excellent agreement with experiment. However, at the current level of spin projection, the 55Mn HFCs do not appear sufficiently accurate to distinguish between different structural models. Yet, of all the models studied, SG2009?1 is the only one with the MnIII site at the MnC center, which is coordinated by histidine (D1‐His332). The computed histidine 14N HFC anisotropy for SG2009?1 gives much better agreement with ESEEM data than the other models, in which MnC is an MnIV site, thus supporting the validity of the model. The 13C HFCs of various carboxylates have been compared with 13C ENDOR data for PSII preparations with 13C‐labelled alanine. 相似文献
5.
Sun Hwa Lee Li Xu Dr. Byeong Kwon Park Yuri V. Mironov Dr. Soo Hyun Kim Young Ju Song Cheal Kim Prof. Dr. Youngmee Kim Dr. Sung‐Jin Kim Prof. Dr. 《Chemistry (Weinheim an der Bergstrasse, Germany)》2010,16(15):4678-4685
Two new tetranuclear chalcocyanide cluster complexes, [{Mn(saloph)H2O}4Re4Q4(CN)12]?4 CH3OH? 8 H2O (saloph=N,N′‐o‐phenylenebis(salicylidenaminato), Q=Se ( 1 ‐Se), Te ( 2 ‐Te)), have been synthesized by the diffusion of a methanolic solution of [PPh4]4[Re4Q4(CN)12] into a methanolic solution of [Mn(saloph)]+. The structure of 2 ‐Te has been determined by X‐ray crystallography. These rhenium cluster‐supported [MnIII(saloph)] complexes have been found to efficiently catalyze a wide range of olefin epoxidations under mild experimental conditions in the presence of meta‐chloroperbenzoic acid (mCPBA). Olefin epoxidation by these catalysts is proposed to involve the multiple active oxidants MnV?O, MnIV?O, and MnIII? OOC(O)R. Evidence in support of this interpretation has been derived from reactivity and Hammett studies, H218O‐exchange experiments, and the use of peroxyphenylacetic acid as a mechanistic probe. Moreover, it has been observed that the participation of MnV?O, MnIV?O, and MnIII? OOC(O)R can be controlled by changing the substrate concentration. This mechanism provides the greatest congruity with related oxidation reactions that employ certain Mn complexes as catalysts. 相似文献
6.
What Controls the Magnetic Exchange Interaction in Mixed‐ and Homo‐Valent Mn7 Disc‐Like Clusters? A Theoretical Perspective
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Kuduva R. Vignesh Dr. Stuart K. Langley Prof. Keith S. Murray Prof. Gopalan Rajaraman 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(7):2881-2892
Density functional theory (DFT) studies have been undertaken to compute the magnetic exchange and to probe the origin of the magnetic interactions in two hetero‐ and two homo‐valent heptanuclear manganese disc‐like clusters, of formula [MnII4MnIV3(tea)(teaH2)3(peolH)4] ( 1 ), [MnII4MnIII3F3(tea)(teaH)(teaH2)2(piv)4(Hpiv)(chp)3] ( 2 ), [MnII7(pppd)6(tea)(OH)3] ( 3 ) and [MnII7 (paa)6(OMe)6] ( 4 ) (teaH3=triethanolamine, peolH4=pentaerythritol, Hpiv=pivalic acid, Hchp=6‐chloro‐2‐hydroxypyridine, pppd=1‐phenyl‐3‐(2‐pyridyl) propane‐1,3‐dione; paaH=N‐(2‐pyridinyl)acetoacetamide). DFT calculations yield J values, which reproduce the magnetic susceptibility data very well for all four complexes; these studies are also highlighting the likely ageing/stability problems in two of the complexes. It is found that the spin ground states, S, for complexes 1 – 4 are drastically different, varying from S=29/2 to S=1/2. These values are found to be controlled by the nature of the oxidation state of the metal ions and minor differences present in the structures. Extensive magneto–structural correlations are developed for the seven building unit dimers present in the complexes, with the correlations unlocking the reasons behind the differences in the magnetic properties observed. Independent of the oxidation state of the metal ions, the Mn‐O‐Mn/Mn‐F‐Mn angles are found to be the key parameters, which significantly influence the sign as well as the magnitude of the J values. The magneto–structural correlations developed here, have broad applicability and can be utilised to understand the magnetic properties of other Mn clusters. 相似文献
7.
Tao Liu Bing‐Wu Wang Yi‐Hong Chen Zhe‐Ming Wang Prof. Song Gao Prof. 《无机化学与普通化学杂志》2008,634(4):778-783
Two mixed‐valent disc‐like hepta‐nuclear compounds of [FeIIFeIII6(tea)6](ClO4)2 ( 1Fe , tea = N(CH2CH2O)33?) and [MnII3MnIII4(nmdea)6(N3)6]·CH3OH ( 2Mn , nmdea = CH3N(CH2CH2O)22?) have been synthesized by the reaction of Fe(ClO4)2·6H2O with triethanolamine (H3tea) for the former and reaction of Mn(ClO4)2·6H2O with diethanolamine (H2nmdea) and NaN3 for the later, respectively. 1Fe has the cationic cluster with a planar [FeIIFeIII6] core consisting of one central FeII and six rim FeIII atoms in hexagonal arrangement. The Fe ions are linked by the oxo‐bridges from the alcohol arms in the manner of edge‐sharing of their coordination octahedra. 2Mn is a neutral cluster with a [MnII3MnIII4] core possessing one central MnII atom surrounded by six rim Mn ions, two MnII and four MnIII. The structure is similar to 1Fe but involves six terminal azido ligands, each coordinate one rim Mn ion. 1Fe showed dominant antiferromagnetic interaction within the cluster and long‐range ordering at 2.7 K. The cluster probably has a ground state of low spin of S = 5/2 or 4/2. The long‐range ordering is weak ferromagnetic, showing small hysteresis with a remnant magnetization of 0.3 Nβ and a coercive field of 40 Oe. Moreover, the isofield of lines 1Fe are far from superposition, indicating the presence of significant zero–field splitting. Ferromagnetic interactions are dominant in 2Mn . An intermediate spin ground state 25/2 is observed at low field. In high field of 50 kOe, the energetically lowest state is given by the ms = 31/2 component of the S = 31/2 multiplet due to the Zeeman effect. Despite of the large ground state, no single‐molecule magnet behavior was found above 2 K. 相似文献
8.
By using the spin-polarized DV-X-LCAO method, electronic states of neutral and cationic Mn
N
clusters (N=25) are calculated to study atomic bonding of Mn clusters. For the neutral Mn2 cluster, the equilibrium interatomic distance is much larger than that of the bulk crystal. The 3d-derived states are nearly half-filled, and the 4s-derived states are almost fully occupied,i.e. the electronic configuration is close to that of the isolated atom. These indicate that the Mn2 cluster is bound by the van der Waals force. The same situation is true for the larger neutral clusters while the equilibrium interatomic distance becomes smaller and thes-d mixing becomes larger. For the cationic clusters, the behaviors tend to become metallic. The equilibrium interatomic distances are smaller and thes-d mixings are larger than those of the corresponding neutral clusters. However, the Mn
2
+
and Mn
4
+
clusters still remain the van der Waals characters. Contrary to these clusters, the Mn
5
+
cluster, whose interatomic distance is smaller than that of the bulk crystal, shows strong metallic bonding. These results seem to correspond to the magic number observed on the mass spectroscopy of cationic Mn clusters. 相似文献
9.
Casper de Lichtenberg Christopher J. Kim Petko Chernev Richard J. Debus Johannes Messinger 《Chemical science》2021,12(38):12763
The molecular oxygen we breathe is produced from water-derived oxygen species bound to the Mn4CaO5 cluster in photosystem II (PSII). Present research points to the central oxo-bridge O5 as the ‘slow exchanging substrate water (Ws)’, while, in the S2 state, the terminal water ligands W2 and W3 are both discussed as the ‘fast exchanging substrate water (Wf)’. A critical point for the assignment of Wf is whether or not its exchange with bulk water is limited by barriers in the channels leading to the Mn4CaO5 cluster. In this study, we measured the rates of H216O/H218O substrate water exchange in the S2 and S3 states of PSII core complexes from wild-type (WT) Synechocystis sp. PCC 6803, and from two mutants, D1-D61A and D1-E189Q, that are expected to alter water access via the Cl1/O4 channels and the O1 channel, respectively. We found that the exchange rates of Wf and Ws were unaffected by the E189Q mutation (O1 channel), but strongly perturbed by the D61A mutation (Cl1/O4 channel). It is concluded that all channels have restrictions limiting the isotopic equilibration of the inner water pool near the Mn4CaO5 cluster, and that D61 participates in one such barrier. In the D61A mutant this barrier is lowered so that Wf exchange occurs more rapidly. This finding removes the main argument against Ca-bound W3 as fast substrate water in the S2 state, namely the indifference of the rate of Wf exchange towards Ca/Sr substitution.Access to the oxygen-evolving complex in photosynthesis is restricted by specific barriers in the channels connecting the Mn4CaO5 catalyst with bulk water. Together with other recent data, this finding allows assigning the two substrate waters. 相似文献
10.
Dmitri V. Konarev Alexey V. Kuzmin Salavat S. Khasanov Rimma N. Lyubovskaya 《Acta Crystallographica. Section C, Structural Chemistry》2014,70(5):449-451
The title complex salt, (C16H36N)[MnBr(C32H16N8)] or (TBA)[MnIIBr(Pc)] (TBA is tetrabutylammonium and Pc is phthalocyaninate), has been obtained as single crystals by the diffusion technique and its crystal structure was determined using X‐ray diffraction. The high‐spin (S = ) [MnIIBr(Pc)]− macrocycle has a concave conformation, with an average equatorial Mn—N(Pc) bond length of 2.1187 (19) Å, an axial Mn—Br bond length of 2.5493 (7) Å and with the MnII cation displaced out of the 24‐atom Pc plane by 0.894 (2) Å. The geometry of the MnIIN4 fragment in [MnIIBr(Pc)]− is similar to that of the high‐spin (S = ) manganese(II) tetraphenylporphyrin (TPP) in [MnII(1‐MeIm)(TPP)] (1‐MeIm is 1‐methylimidazole). 相似文献
11.
Synthesis,Structure, and Magnetic Properties of a Mn4 Cluster derived from Benzimidazole‐Alcohol Ligands
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The synthesis, crystal structure, and magnetic properties of a [MnIII3MnII(μ3‐O)(mbp)3(OAc)3] · 4H2O ( 1 ) [H2mbp = 2‐(1H‐benzimidazol‐2‐yl)‐2‐ methylpropane‐1,3‐diol] cluster are reported herein. Mn ions in compound 1 have a tetrahedron topology. Solid‐state direct current and alternating current magnetic susceptibility measurements on compound 1 reveal a ground state with ST = 7/2 as well as the probable single‐molecule magnetic behavior. 相似文献
12.
Changhui Chen Yang Chen Ruoqing Yao Yanxi Li Chunxi Zhang 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2019,131(12):3979-3982
The natural Mn4Ca cluster in photosystem II serves as a blueprint to develop artificial water‐splitting catalysts for the generation of solar fuel in artificial photosynthesis. Although significant advances have recently been achieved, it remains a great challenge to prepare robust artificial Mn4Ca clusters that precisely mimic the structure and function of the biological catalyst. Herein, we report the isolation and structural characterization of two Mn4CaO4 complexes with polar solvent molecules, acetonitrile or N,N‐dimethylformamide, which closely mimics the two water molecules on the calcium ion, as well as the oxidation states of the four manganese ions and the main geometric structure of the natural Mn4Ca cluster. These new artificial Mn4Ca complexes provide important chemical clues to understand the structure and mechanism of the biological system. 相似文献
13.
Dramatic Influence of an Anionic Donor on the Oxygen‐Atom Transfer Reactivity of a MnV–Oxo Complex
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Heather M. Neu Dr. Matthew G. Quesne Tzuhsiung Yang Dr. Katharine A. Prokop‐Prigge Prof. Kyle M. Lancaster James Donohoe Prof. Serena DeBeer Dr. Sam P. de Visser Prof. David P. Goldberg 《Chemistry (Weinheim an der Bergstrasse, Germany)》2014,20(45):14584-14588
Addition of an anionic donor to an MnV(O) porphyrinoid complex causes a dramatic increase in 2‐electron oxygen‐atom‐transfer (OAT) chemistry. The 6‐coordinate [MnV(O)(TBP8Cz)(CN)]? was generated from addition of Bu4N+CN? to the 5‐coordinate MnV(O) precursor. The cyanide‐ligated complex was characterized for the first time by Mn K‐edge X‐ray absorption spectroscopy (XAS) and gives Mn?O=1.53 Å, Mn?CN=2.21 Å. In combination with computational studies these distances were shown to correlate with a singlet ground state. Reaction of the CN? complex with thioethers results in OAT to give the corresponding sulfoxide and a 2e?‐reduced MnIII(CN)? complex. Kinetic measurements reveal a dramatic rate enhancement for OAT of approximately 24 000‐fold versus the same reaction for the parent 5‐coordinate complex. An Eyring analysis gives ΔH≠=14 kcal mol?1, ΔS≠=?10 cal mol?1 K?1. Computational studies fully support the structures, spin states, and relative reactivity of the 5‐ and 6‐coordinate MnV(O) complexes. 相似文献
14.
Magnetic “Molecular Oligomers” Based on Decametallic Supertetrahedra: A Giant Mn49 Cuboctahedron and its Mn25Na4 Fragment
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Dr. Maria Manoli Sofia Alexandrou Dr. Linh Pham Dr. Giulia Lorusso Dr. Wolfgang Wernsdorfer Dr. Marco Evangelisti Prof. George Christou Dr. Anastasios J. Tasiopoulos 《Angewandte Chemie (International ed. in English)》2016,55(2):679-684
Two nanosized Mn49 and Mn25Na4 clusters based on analogues of the high‐spin (S=22) [MnIII6MnII4(μ4‐O)4]18+ supertetrahedral core are reported. Mn49 and Mn25Na4 complexes consist of eight and four decametallic supertetrahedral subunits, respectively, display high virtual symmetry (Oh), and are unique examples of clusters based on a large number of tightly linked high nuclearity magnetic units. The complexes also have large spin ground‐state values (Mn49: S=61/2; Mn25Na4: S=51/2) with the Mn49 cluster displaying single‐molecule magnet (SMM) behavior and being the second largest reported homometallic SMM. 相似文献
15.
Surface and Structural Investigation of a MnOx Birnessite‐Type Water Oxidation Catalyst Formed under Photocatalytic Conditions
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Benjamin J. Deibert Jingming Zhang Paul F. Smith Dr. Karena W. Chapman Dr. Sylvie Rangan Debasis Banerjee Kui Tan Hao Wang Nicholas Pasquale Prof. Feng Chen Prof. Ki‐Bum Lee Prof. G. Charles Dismukes Prof. Yves J. Chabal Prof. Jing Li 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(40):14218-14228
Catalytically active MnOx species have been reported to form in situ from various Mn‐complexes during electrocatalytic and solution‐based water oxidation when employing cerium(IV) ammonium ammonium nitrate (CAN) oxidant as a sacrificial reagent. The full structural characterization of these oxides may be complicated by the presence of support material and lack of a pure bulk phase. For the first time, we show that highly active MnOx catalysts form without supports in situ under photocatalytic conditions. Our most active 4MnOx catalyst (~0.84 mmol O2 mol Mn?1 s?1) forms from a Mn4O4 bearing a metal–organic framework. 4MnOx is characterized by pair distribution function analysis (PDF), Raman spectroscopy, and HR‐TEM as a disordered, layered Mn‐oxide with high surface area (216 m2g?1) and small regions of crystallinity and layer flexibility. In contrast, the SMnOx formed from Mn2+ salt gives an amorphous species of lower surface area (80 m2g?1) and lower activity (~0.15 mmol O2 mol Mn?1 s?1). We compare these catalysts to crystalline hexagonal birnessite, which activates under the same conditions. Full deconvolution of the XPS Mn2p3/2 core levels detects enriched Mn3+ and Mn2+ content on the surfaces, which indicates possible disproportionation/comproportionation surface equilibria. 相似文献
16.
Zhi‐Yan Guo Chen‐Xuan Li Miao Gao Xiao Han Ying‐Jie Zhang Wen‐Jun Zhang Wen‐Wei Li 《Angewandte Chemie (International ed. in English)》2021,60(1):274-280
Transition metal (TM)‐based bimetallic spinel oxides can efficiently activate peroxymonosulfate (PMS) presumably attributed to enhanced electron transfer between TMs, but the existing model cannot fully explain the efficient TM redox cycling. Here, we discover a critical role of TM?O covalency in governing the intrinsic catalytic activity of Co3?xMnxO4 spinel oxides. Experimental and theoretical analysis reveals that the Co sites significantly raises the Mn valence and enlarges Mn?O covalency in octahedral configuration, thereby lowering the charge transfer energy to favor MnOh–PMS interaction. With appropriate MnIV/MnIII ratio to balance PMS adsorption and MnIV reduction, the Co1.1Mn1.9O4 exhibits remarkable catalytic activities for PMS activation and pollutant degradation, outperforming all the reported TM spinel oxides. The improved understandings on the origins of spinel oxides activity for PMS activation may inspire the development of more active and robust metal oxide catalysts. 相似文献
17.
Andrew D. Bond Sren P. V. Foghmoes Terence E. Warner 《Acta Crystallographica. Section C, Structural Chemistry》2011,67(3):i21-i23
The title compound, Cu0.5Mn2.5(PO4)2, is a copper–manganese phosphate solid solution with the graftonite‐type structure, viz. (Mn,Fe,Ca,Mg)3(PO4)2. The structure has three distinct metal cation sites, two of which are occupied by MnII and one of which accommodates CuII. Incorporation of CuII into the structure distorts the coordination geometry of the metal cation site from five‐coordinate square‐pyramidal towards four‐coordinate flattened tetrahedral, and serves to contract the structure principally along the c axis. 相似文献
18.
Susanne Mossin Henning Osholm Srensen Hgni Weihe 《Acta Crystallographica. Section C, Structural Chemistry》2002,58(4):m204-m206
The crystal structure of the low‐spin (S = 1) MnIII complex [Mn(CN)2(C10H24N4)]ClO4, or trans‐[Mn(CN)2(cyclam)](ClO4) (cyclam is the tetradentate amine ligand 1,4,8,11‐tetraazacyclotetradecane), is reported. The structural parameters in the Mn(cyclam) moiety are found to be insensitive to both the spin and the oxidation state of the Mn ion. The difference between high‐ and low‐spin MnIII complexes is that a pronounced tetragonal elongation of the coordination octahedron occurs in high‐spin complexes and a slight tetragonal compression is seen in low‐spin complexes, as in the title complex. 相似文献
19.
Song YJ Lee SH Park HM Kim SH Goo HG Eom GH Lee JH Lah MS Kim Y Kim SJ Lee JE Lee HI Kim C 《Chemistry (Weinheim an der Bergstrasse, Germany)》2011,17(26):7336-7344
Two new mononuclear nonheme manganese(III) complexes of tetradentate ligands containing two deprotonated amide moieties, [Mn(bpc)Cl(H2O)] ( 1 ) and [Mn(Me2bpb)Cl(H2O)] ? CH3OH ( 2 ), were prepared and characterized. Complex 2 has also been characterized by X‐ray crystallography. Magnetic measurements revealed that the complexes are high spin (S=5/2) MnIII species with typical magnetic moments of 4.76 and 4.95 μB, respectively. These nonheme MnIII complexes efficiently catalyzed olefin epoxidation and alcohol oxidation upon treatment with MCPBA under mild experimental conditions. Olefin epoxidation by these catalysts is proposed to involve the multiple active oxidants MnV?O, MnIV?O, and MnIII? OO(O)CR. Evidence for this approach was derived from reactivity and Hammett studies, KIE (kH/kD) values, H218O‐exchange experiments, and the use of peroxyphenylacetic acid as a mechanistic probe. In addition, it has been proposed that the participation of MnV?O, MnIV?O, and MnIII? OOR could be controlled by changing the substrate concentration, and that partitioning between heterolysis and homolysis of the O? O bond of a Mn‐acylperoxo intermediate (Mn? OOC(O)R) might be significantly affected by the nature of solvent, and that the O? O bond of the Mn? OOC(O)R might proceed predominantly by heterolytic cleavage in protic solvent. Therefore, a discrete MnV?O intermediate appeared to be the dominant reactive species in protic solvents. Furthermore, we have observed close similarities between these nonheme MnIII complex systems and Mn(saloph) catalysts previously reported, suggesting that this simultaneous operation of the three active oxidants might prevail in all the manganese‐catalyzed olefin epoxidations, including Mn(salen), Mn(nonheme), and even Mn(porphyrin) complexes. This mechanism provides the greatest congruity with related oxidation reactions by using certain Mn complexes as catalysts. 相似文献
20.
Guang‐Bo Che Jian Wang Chun‐Bo Liu Xiu‐Ying Li Bo Liu 《Acta Crystallographica. Section C, Structural Chemistry》2008,64(11):m362-m364
The title coordination polymer, poly[bis(μ4‐biphenyl‐2,2′‐dicarboxylato)(dipyrido[3,2‐a:2′,3′‐c]phenazine)manganese(II)], [Mn2(C14H8O4)2(C18H10N4)]n, was obtained through the reaction of MnCl2·4H2O, biphenyl‐2,2′‐dicarboxylic acid (H2dpdc) and dipyrido[3,2‐a:2′,3′‐c]phenazine (L) under hydrothermal conditions. The asymmetric unit contains two crystallographically unique MnII ions, one unique L ligand and two unique dpdc ligands. One Mn ion is six‐coordinated by four O atoms from three different dpdc ligands and two N atoms from one L ligand, adopting a distorted octahedral coordination geometry. The distortions from ideal octahedral geometry are largely due to the presence of chelating ligands and the resulting acute N—Mn—N and O—Mn—O angles. The second Mn ion is coordinated in a distorted trigonal bipyramidal fashion by five O atoms from four distinct dpdc ligands. Four MnII ions are bridged by the carboxylate groups of the dpdc ligands to form an unusual tetranuclear MnII cluster. Clusters are further connected by the aromatic backbone of the dicarboxylate ligands, forming a one‐dimensional chain structure along the b axis. The title compound is the first example of a chain structure based on a tetranuclear MnII cluster. 相似文献