共查询到20条相似文献,搜索用时 15 毫秒
1.
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
2.
What Controls the Magnetic Exchange Interaction in Mixed‐ and Homo‐Valent Mn7 Disc‐Like Clusters? A Theoretical Perspective 下载免费PDF全文
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
3.
Man‐Rong Li Maria Retuerto Zheng Deng Peter W. Stephens Mark Croft Qingzhen Huang Hui Wu Xiaoyu Deng Gabriel Kotliar Javier Snchez‐Benítez Joke Hadermann David Walker Martha Greenblatt 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2015,127(41):12237-12241
The first transition‐metal‐only double perovskite compound, Mn2+2Fe3+Re5+O6, with 17 unpaired d electrons displays ferrimagnetic ordering up to 520 K and a giant positive magnetoresistance of up to 220 % at 5 K and 8 T. These properties result from the ferrimagnetically coupled Fe and Re sublattice and are affected by a two‐to‐one magnetic‐structure transition of the Mn sublattice when a magnetic field is applied. Theoretical calculations indicate that the half‐metallic state can be mainly attributed to the spin polarization of the Fe and Re sites. 相似文献
4.
Dr. Cédric Tassel Yoshinori Kuno Yoshihiro Goto Dr. Takafumi Yamamoto Dr. Craig M. Brown Dr. James Hester Dr. Koji Fujita Dr. Masanobu Higashi Prof. Ryu Abe Prof. Katsuhisa Tanaka Dr. Yoji Kobayashi Prof. Hiroshi Kageyama 《Angewandte Chemie (International ed. in English)》2015,54(2):516-521
The synthesis, structure, and magnetic properties of a polar and magnetic oxynitride MnTaO2N are reported. High‐pressure synthesis at 6 GPa and 1400 °C allows for the stabilization of a high‐density structure containing middle‐to‐late transition metals. Synchrotron X‐ray and neutron diffraction studies revealed that MnTaO2N adopts the LiNbO3‐type structure, with a random distribution of O2? and N3? anions. MnTaO2N with an “orbital‐inactive” Mn2+ ion (d5; S=5/2) exhibits a nontrivial helical spin order at 25 K with a propagation vector of [0,0,δ] (δ≈0.3), which is different from the conventional G‐type order observed in other orbital‐inactive perovskite oxides and LiNbO3‐type oxides. This result suggests the presence of strong frustration because of the heavily tilted MnO4N2 octahedral network combined with the mixed O2?/N3? species that results in a distribution of (super)‐superexchange interactions. 相似文献
5.
Hysteretic Spin Crossover above Room Temperature and Magnetic Coupling in Trinuclear Transition‐Metal Complexes with Anionic 1,2,4‐Triazole Ligands 下载免费PDF全文
Dr. Verónica Gómez Dr. Jordi Benet‐Buchholz Dr. Eddy Martin Dr. J. R. Galán‐Mascarós 《Chemistry (Weinheim an der Bergstrasse, Germany)》2014,20(18):5369-5379
The reaction of 4‐(1,2,4‐triazol‐4‐yl)ethanesulfonate ( L ) with Zn2+, Cu2+, Ni2+, Co2+, and Fe2+ gave a series of analogous neutral trinuclear complexes with the formula [M3(μ‐ L )6(H2O)6] ( 1 – 5 ). These compounds were characterized by single‐crystal X‐ray diffraction, thermogravimetry, and elemental analysis. The magnetic properties of compounds 2 – 5 were studied. Complexes 2 – 4 show weak antiferromagnetic superexchange, with J values of ?0.33 ( 2 ), ?9.56 ( 3 ), and ?4.50 cm?1 ( 4 ) (exchange Hamiltonian H=?2 J (S1S2+S2S3)). Compound 5 shows two additional crystallographic phases ( 5 b and 5 c ) that can be obtained by dehydration and/or thermal treatment. These three phases exhibit distinct magnetic behavior. The Fe2+ centers in 5 are in high‐spin (HS) configuration at room temperature, with the central one exhibiting a non‐cooperative gradual spin transition below 250 K with T1/2=150 K. In 5 b , the central Fe2+ stays in its low‐spin (LS) state at room temperature, and cooperative spin transition occurs at higher temperatures and with the appearance of memory effect (T1/2↑=357 K and T1/2↓=343 K). In the case of 5 c , all iron centers remain in their HS configuration down to very low temperatures, with weak antiferromagnetic coupling (J=?1.16 cm?1). Compound 5 b exhibits spin transition with memory effect at the highest temperature reported, which matches the remarkable features of coordination polymers. 相似文献
6.
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
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.
Dramatic Influence of an Anionic Donor on the Oxygen‐Atom Transfer Reactivity of a MnV–Oxo Complex 下载免费PDF全文
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
9.
Vibe B. Jakobsen Elzbieta Trzop Laurence C. Gavin Emiel Dobbelaar Shalinee Chikara Xiaxin Ding Kane Esien Helge Müller‐Bunz Solveig Felton Vivien S. Zapf Eric Collet Michael A. Carpenter Grace G. Morgan 《Angewandte Chemie (International ed. in English)》2020,59(32):13305-13312
Domain wall motion is detected for the first time during the transition to a ferroelastic and spin state ordered phase of a spin crossover complex. Single‐crystal X‐ray diffraction and resonant ultrasound spectroscopy (RUS) revealed two distinct symmetry‐breaking phase transitions in the mononuclear Mn3+ compound [Mn(3,5‐diBr‐sal2(323))]BPh4, 1. The first at 250 K, involves the space group change Cc→Pc and is thermodynamically continuous, while the second, Pc→P1 at 85 K, is discontinuous and related to spin crossover and spin state ordering. Stress‐induced domain wall mobility was interpreted on the basis of a steep increase in acoustic loss immediately below the the Pc‐P1 transition 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.
Shuhui Lv Xiaojuan Liu Hongping Li Lin Han Zhongchang Wang Jian Meng 《Journal of computational chemistry》2012,33(16):1433-1439
The ground state of double perovskite oxide La2CoMnO6 (LCMO) and how it is influenced by external pressure and antisite disorder are investigated systematically by first‐principles calculations. We find, on the consideration of both the electron correlation and spin–orbital coupling effect, that the LCMO takes on insulating nature, yet is transformed to half metallicity once the external pressure is introduced. Such tuning is accompanied by a spin‐state transition of Co2+ from the high‐spin state (te) to low‐spin state (te) because of the enhancement of crystal‐field splitting under pressure. Using mean‐field approximation theory, Curie temperature of LCMO with Co2+ being in low‐spin state is predicted to be higher than that in high‐spin state, which is attributed to the enhanced ferromagnetic double exchange interaction arising from the shrinkage of Co? O and Mn? O bonds as well as to the increase in bond angle of Co? O? Mn under pressure. We also find that antisite disorder in LCMO enables such transition from insulating to half‐metallic state as well, which is associated with the spin‐state transition of antisite Co from high to low state. It is proposed that the substitution of La3+ for the rare‐earth (RE) ions with smaller ionic radii could open up an avenue to induce a spin‐state transition of Co, rendering thereby the RE2CoMnO6 a promising half‐metallic material. © 2012 Wiley Periodicals, Inc. 相似文献
12.
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
13.
The Role of Ligand‐Field States in the Ultrafast Photophysical Cycle of the Prototypical Iron(II) Spin‐Crossover Compound [Fe(ptz)6](BF4)2 下载免费PDF全文
Andrea Marino Dr. Pradip Chakraborty Dr. Marina Servol Dr. Maciej Lorenc Prof. Eric Collet Prof. Andreas Hauser 《Angewandte Chemie (International ed. in English)》2014,53(15):3863-3867
Light‐induced excited spin‐state trapping (LIESST) in iron(II) spin‐crossover compounds, that is, the light‐induced population of the high‐spin (S=2) state below the thermal transition temperature, was discovered thirty years ago. For irradiation into metal–ligand charge transfer (MLCT) bands of the low‐spin (S=0) species the acknowledged sequence takes the system from the initially excited 1MLCT to the high‐spin state via the 3MLCT state within ca. 150 fs, thereby bypassing low‐lying ligand‐field (LF) states. Nevertheless, these play a role, as borne out by the observation of LIESST and reverse‐LIESST on irradiation directly into the LF bands for systems with only high‐energy MLCT states. Herein we elucidate the ultrafast reverse‐LIESST pathway by identifying the lowest energy S=1 LF state as an intermediate state with a lifetime of 39 ps for the light‐induced high‐spin to low‐spin conversion on irradiation into the spin‐allowed LF transition of the high‐spin species in the NIR. 相似文献
14.
Dr. Cedric Tassel Yoshinori Goto Daichi Watabe Ya Tang Dr. Honcheng Lu Yoshinori Kuno Fumitaka Takeiri Dr. Takafumi Yamamoto Dr. Craig M. Brown Dr. James Hester Dr. Yoji Kobayashi Prof. Hiroshi Kageyama 《Angewandte Chemie (International ed. in English)》2016,55(33):9667-9670
The high‐pressure synthesis of a manganese oxyhydride LaSrMnO3.3H0.7 is reported. Neutron and X‐ray Rietveld analyses showed that this compound adopts the K2NiF4 structure with hydride ions positioned exclusively at the equatorial site. This result makes a striking contrast to topochemical reductions of LaSrMnO4 that result in only oxygen‐deficient phases down to LaSrMnO3.5. This suggests that high H2 pressure plays a key role in stabilizing the oxyhydride phase, offering an opportunity to synthesize other transition‐metal oxyhydrides. Magnetic susceptibility revealed a spin‐glass transition at 24 K that is due to competing ferromagnetic (Mn2+–Mn3+) and antiferromagnetic (Mn2+–Mn2, Mn3+–Mn3+) interactions. 相似文献
15.
Kepenekian M Vetere V Le Guennic B Maldivi P Robert V 《Chemistry (Weinheim an der Bergstrasse, Germany)》2011,17(43):12045-12050
The redox and spin versatilities of manganese–porphyrin complexes [MnIIP] are examined to construct a redox‐switchable device. The electronic structure of [MnIIIP]+ was analyzed by using wavefunction‐based calculations (complete active spaces plus single excitations on top of the active spaces, that is, CAS+singles). A non‐negligible σ‐type electron‐transfer configuration is present in the [MnIIIP]+ S=2 ground state. By contrast, the [MnIIP.]+ valence tautomer is a purely π‐type intramolecular charge transfer, thus reflecting an S=3 spin state as a result of the strong ferromagnetic interaction (J=30 meV) between the S=5/2 MnII ion and the S=1/2 porphyrin radical cation P.+. The change of the redox‐sensitive site in the valence tautomer leads to a ‘triangular scheme’ that involves a critical step in which a simultaneous electron transfer and spin change are expected to induce bistability. From the wavefunction inspection, a meso‐substituted porphyrin candidate was designed to support this scenario. The complete active‐space second‐order perturbation theory (CASPT2) adiabatic energy difference between the S=2 and the S=3 spin states was reduced down to 0.15 eV, thereby giving rise to a metastable S=3 state characterized by a 0.10 Å extension of the porphyrin cavity radius. These results not only confirm the rather versatile nature of these inorganic systems but also demonstrate that redox and spin changes are intermingled in this class of compounds and can be used for applied devices. 相似文献
16.
Taito Murakami Dr. Takafumi Yamamoto Dr. Cédric Tassel Dr. Hiroshi Takatsu Dr. Clemens Ritter Prof. Yoshitami Ajiro Prof. Hiroshi Kageyama 《Angewandte Chemie (International ed. in English)》2016,55(34):9877-9880
The NiAs‐type structure is one of the most common structures in solids, but metal order has been almost exclusively limited to chalcogenides. The synthesis of HfMnSb2 is reported with a novel metal‐ordered NiAs‐type structure. HfMnSb2 undergoes a conical spin order below 270 K, in marked contrast to conventional magnetic order observed in NiAs‐type pnictides. We argue that the layered arrangement of Hf and Mn makes it a quasi 2D magnet, where the Mn layers with localized magnetic moments (Mn2+; S=5/2) can interact only through RKKY interactions, instead of metal–metal bonding that is otherwise dominant for typical NiAs‐type pnictides. This result suggests that controlling order–disorder in NiAs‐type pnictides enables a study of 2D‐to‐3D crossover behavior in itinerant magnetic system. 相似文献
17.
Synthesis,Structures, and Magnetic Properties of Chiral One‐dimensional CrIII‐MnIII Heterobimetallic Complexes Based on [(Tp)Cr(CN)3]– 下载免费PDF全文
Two CrIII‐MnIII heterobimetallic compounds, [Mn((R,R)‐5‐MeOSalcy)Cr(Tp)(CN)3 · 2CH3CN]n ( 1‐RR ) and [Mn((S,S)‐5‐MeOSalcy)Cr(Tp)(CN)3·2CH3CN]n ( 1‐SS ) [Salcy = N,N′‐(1,2‐cyclohexanediylethylene)bis(salicylideneiminato) dianion], were synthesized by using the tricyanometalate building block, [(Tp)Cr(CN)3]– [Tp = tris(pyrazolyl) hydroborate] and chiral MnIII Schiff base precursors. Structural analyses and circular dichroism (CD) spectra revealed that 1‐RR and 1‐SS are a pair of enantiomers containing a neutral cyano‐bridged zigzag chain with (–Cr–C≡N–Mn–N≡C–)n as the repeating unit. Magnetic studies show that antiferromagnetic couplings between CrIII and MnIII ions occur by cyanide bridges. 1‐RR and 1‐SS present metamagnetic, spin‐canting, and antiferromagnetic order behaviors at low temperatures. 相似文献
18.
Y. Miyazaki T. Sakakibara H. Miyasaka N. Matsumoto M. Sorai 《Journal of Thermal Analysis and Calorimetry》2005,81(3):603-607
Summary Heat capacity measurements of the two-dimensional metal-assembled complex, (NEt4)[{MnIII(salen)}2FeIII(CN)6] [Et=ethyl, salen= N,N’-ethylenebis(salicylideneaminato) dianion], were performed in the temperature range between 0.2 and 300 K by adiabatic calorimetry. A ferrimagnetic phase transition was observed at Tc1=7.51 K. Furthermore, another small magnetic phase transition appeared at Tc2=0.78 K. Above Tc1, a heat capacity tail arising from the short-range ordering of the spins characteristic of two-dimensional magnets was found. The magnetic enthalpy and entropy were evaluated to be ΔH=291 J mol-1 and ΔS=27.4 J K-1 mol-1, respectively. The experimental magnetic entropy agrees roughly with ΔS=Rln(5·5·2) (=32.5 J K-1 mol-1; R being the gas constant), which is expected for the metal complex with two Mn(III) ions in high-spin state (spin quantum number S=2) and one Fe(III) ion in low-spin state (S=1/2). The heat capacity tail above Tc1 became small by grinding and pressing the crystal. This mechanochemical effect would be attributed to the increase of lattice defects and imperfections in the crystal lattice, leading not only to formation of the crystal with a different magnetic phase transition temperature but also to decrease of the magnetic heat capacity and thus the magnetic enthalpy and entropy. 相似文献
19.
Studies of a Large Odd‐Numbered Odd‐Electron Metal Ring: Inelastic Neutron Scattering and Muon Spin Relaxation Spectroscopy of Cr8Mn 下载免费PDF全文
Dr. Michael L. Baker Dr. Tom Lancaster Alessandro Chiesa Prof. Giuseppe Amoretti Dr. Peter J. Baker Claire Barker Prof. Stephen J. Blundell Prof. Stefano Carretta Prof. David Collison Prof. Hans U. Güdel Dr. Tatiana Guidi Prof. Eric J. L. McInnes Dr. Johannes S. Möller Dr. Hannu Mutka Dr. Jacques Ollivier Dr. Francis L. Pratt Prof. Paolo Santini Dr. Floriana Tuna Dr. Iñigo J. Vitorica‐Yrezabal Dr. Grigore A. Timco Prof. Richard E. P. Winpenny 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(5):1779-1788
The spin dynamics of Cr8Mn, a nine‐membered antiferromagnetic (AF) molecular nanomagnet, are investigated. Cr8Mn is a rare example of a large odd‐membered AF ring, and has an odd‐number of 3d‐electrons present. Odd‐membered AF rings are unusual and of interest due to the presence of competing exchange interactions that result in frustrated‐spin ground states. The chemical synthesis and structures of two Cr8Mn variants that differ only in their crystal packing are reported. Evidence of spin frustration is investigated by inelastic neutron scattering (INS) and muon spin relaxation spectroscopy (μSR). From INS studies we accurately determine an appropriate microscopic spin Hamiltonian and we show that μSR is sensitive to the ground‐spin‐state crossing from S=1/2 to S=3/2 in Cr8Mn. The estimated width of the muon asymmetry resonance is consistent with the presence of an avoided crossing. The investigation of the internal spin structure of the ground state, through the analysis of spin‐pair correlations and scalar‐spin chirality, shows a non‐collinear spin structure that fluctuates between non‐planar states of opposite chiralities. 相似文献
20.
Magnetic “Molecular Oligomers” Based on Decametallic Supertetrahedra: A Giant Mn49 Cuboctahedron and its Mn25Na4 Fragment 下载免费PDF全文
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