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1.
Létard JF Asthana S Shepherd HJ Guionneau P Goeta AE Suemura N Ishikawa R Kaizaki S 《Chemistry (Weinheim an der Bergstrasse, Germany)》2012,18(19):5924-5934
A comprehensive study of the magnetic and photomagnetic behaviors of cis-[Fe(picen)(NCS)(2) ] (picen = N,N'-bis(2-pyridylmethyl)1,2-ethanediamine) was carried out. The spin-equilibration was extremely slow in the vicinity of the thermal spin-transition. When the cooling speed was slower than 0.1?K min(-1), this complex was characterized by an abrupt thermal spin-transition at about 70?K. Measurement of the kinetics in the range 60-70?K was performed to approach the quasi-static hysteresis loop. At low temperatures, the metastable HS state was quenched by a rapid freezing process and the critical T(TIESST) temperature, which was associated with the thermally induced excited spin-state-trapping (TIESST) effect, was measured. At 10?K, this complex also exhibited the well-known light-induced excited spin-state-trapping (LIESST) effect and the T(LIESST) temperature was determined. The kinetics of the metastable HS states, which were generated from the freezing effect and from the light-induced excitation, was studied. Single-crystal X-ray diffraction as a function of speed-cooling and light conditions at 30?K revealed the mechanism of the spin-crossover in this complex as well as some direct relationships between its structural properties and its spin state. This spin-crossover (SCO) material represents a fascinating example in which the metastability of the HS state is in close vicinity to the thermal spin-transition region. Moreover, it is a beautiful example of a complex in which the metastable HS states can be generated, and then compared, either by the freezing effect or by the LIESST effect. 相似文献
2.
Spin‐State Ordering on One Sub‐lattice of a Mononuclear Iron(III) Spin Crossover Complex Exhibiting LIESST and TIESST 下载免费PDF全文
Dr. Kevin D. Murnaghan Dr. Chiara Carbonera Dr. Loic Toupet Dr. Michael Griffin Dr. Marinela M. Dîrtu Dr. Cédric Desplanches Prof. Dr. Yann Garcia Prof. Eric Collet Prof. Jean‐François Létard Dr. Grace G. Morgan 《Chemistry (Weinheim an der Bergstrasse, Germany)》2014,20(19):5613-5618
The two‐step spin crossover in mononuclear iron(III) complex [Fe(salpm)2]ClO4 ? 0.5 EtOH ( 1 ) is shown to be accompanied by a structural phase transition as concluded from 57Fe Mössbauer spectroscopy and single crystal X‐ray diffraction, with spin‐state ordering on just one of two sub‐lattices in the intermediate magnetic and structural phase. The complex also exhibits thermal‐ and light‐induced spin‐state trapping (TIESST and LIESST), and relaxation from the LIESST and TIESST excited states occurs via the broken symmetry intermediate phase. Two relaxation events are evident in both experiments, that is, two T(LIESST) and two T(TIESST) values are recorded. The change in symmetry which accompanies the TIESST effect was followed in real time using single crystal diffraction. After flash freezing at 15 K the crystal was warmed to 40 K at which temperature superstructure reflections were observed to appear and disappear within a 10 000 s time range. In the frame of the international year of crystallography, these results illustrate how X‐ray diffraction makes it possible to understand complex ordering phenomena. 相似文献
3.
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
4.
Theerapoom Boonprab Seok J. Lee Shane G. Telfer Keith S. Murray Wasinee Phonsri Guillaume Chastanet Eric Collet Elzbieta Trzop Guy N. L. Jameson Phimphaka Harding David J. Harding 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2019,131(34):11937-11941
Molecular magnetic switches are expected to form the functional components of future nanodevices. Herein we combine detailed (photo‐) crystallography and magnetic studies to reveal the unusual switching properties of an iron(III) complex, between low (LS) and high (HS) spin states. On cooling, it exhibits a partial thermal conversion associated with a reconstructive phase transition from a [HS‐HS] to a [LS‐HS] phase with a hysteresis of 25 K. Photoexcitation at low temperature allows access to a [LS‐LS] phase, never observed at thermal equilibrium. As well as reporting the first iron(III) spin crossover complex to exhibit reverse‐LIESST (light‐induced excited spin state trapping), we also reveal a hidden hysteresis of 30 K between the hidden [LS‐LS] and [HS‐LS] phases. Moreover, we demonstrate that FeIII spin‐crossover (SCO) complexes can be just as effective as FeII systems, and with the advantage of being air‐stable, they are ideally suited for use in molecular electronics. 相似文献
5.
J. Alberto Rodríguez‐Velamazán Dr. Chiara Carbonera Dr. Miguel Castro Dr. Elías Palacios Dr. Takafumi Kitazawa Prof. Dr. Jean‐François Létard Prof. Dr. Ramón Burriel Prof. Dr. 《Chemistry (Weinheim an der Bergstrasse, Germany)》2010,16(29):8785-8796
In the series of polymeric spin‐crossover compounds Fe(X‐py)2[Ag(CN)2)]2 (py=pyridine, X=H, 3‐Cl, 3‐methyl, 4‐methyl, 3,4‐dimethyl), magnetic and calorimetric measurements have revealed that the conversion from the high‐spin (HS) to the low‐spin (LS) state occurs by two‐step transitions for three out of five members of the family (X=H, 4‐methyl, and X=3,4‐dimethyl). The two other compounds (X=3‐Cl and 3‐methyl) show respectively an incomplete spin transition and no transition at all, the latter remaining in the HS state in the whole temperature range. The spin‐crossover behaviour of the compound undergoing two‐step transitions is well described by a thermodynamic model that considers both steps. Calculations with this model show low cooperativity in this type of systems. Reflectivity and photomagnetic experiments reveal that all of the compounds except that with X=3‐methyl undergo light‐induced excited spin state trapping (LIESST) at low temperatures. Isothermal HS‐to‐LS relaxation curves at different temperatures support the low‐cooperativity character by following an exponential decay law, although in the thermally activated regime and for aX=H and X=3,4‐dimethyl the behaviour is well described by a double exponential function in accordance with the two‐step thermal spin transition. The thermodynamic parameters determined from this isothermal analysis were used for simulation of thermal relaxation curves, which nicely reproduce the experimental data. 相似文献
6.
An Investigation of Photo‐ and Pressure‐Induced Effects in a Pair of Isostructural Two‐Dimensional Spin‐Crossover Framework Materials 下载免费PDF全文
Dr. Natasha F. Sciortino Dr. Suzanne M. Neville Dr. Cédric Desplanches Dr. Jean‐François Létard Dr. Victor Martinez Prof. José Antonio Real Dr. Boujemaa Moubaraki Prof. Keith S. Murray Prof. Cameron J. Kepert 《Chemistry (Weinheim an der Bergstrasse, Germany)》2014,20(24):7448-7457
Two new isostructural iron(II) spin‐crossover (SCO) framework (SCOF) materials of the type [Fe(dpms)2(NCX)2] (dpms=4,4′‐dipyridylmethyl sulfide; X=S ( SCOF‐6(S) ), X=Se ( SCOF‐6(Se) )) have been synthesized. The 2D framework materials consist of undulating and interpenetrated rhomboid (4,4) nets. SCOF‐6(S) displays an incomplete SCO transition with only approximately 30 % conversion of high‐spin (HS) to low‐spin iron(II) sites over the temperature range 300–4 K (T1/2=75 K). In contrast, the NCSe? analogue, SCOF‐6(Se) , displays a complete SCO transition (T1/2=135 K). Photomagnetic characterizations reveal quantitative light‐ induced excited spin‐state trapping (LIESST) of metastable HS iron(II) sites at 10 K. The temperature at which the photoinduced stored information is erased is 58 and 50 K for SCOF‐6(S) and SCOF‐6(Se) , respectively. Variable‐pressure magnetic measurements were performed on SCOF‐6(S) , revealing that with increasing pressure both the T1/2 value and the extent of spin conversion are increased; with pressures exceeding 5.2 kbar a complete thermal transition is achieved. This study confirms that kinetic trapping effects are responsible for hindering a complete thermally induced spin transition in SCOF‐6(S) at ambient pressure due to an interplay between close T1/2 and T(LIESST) values. 相似文献
7.
Luqiong Zhang Yongfeng Tong Massine Kelai Amandine Bellec Jrme Lagoute Cyril Chacon Yann Girard Sylvie Rousset Marie‐Laure Boillot Eric Rivire Talal Mallah Edwige Otero Marie‐Anne Arrio Philippe Sainctavit Vincent Repain 《Angewandte Chemie (International ed. in English)》2020,59(32):13341-13346
Light‐induced spin‐state switching is one of the most attractive properties of spin‐crossover materials. In bulk, low‐spin (LS) to high‐spin (HS) conversion via the light‐induced excited spin‐state trapping (LIESST) effect may be achieved with a visible light, while the HS‐to‐LS one (reverse‐LIESST) requires an excitation in the near‐infrared range. Now, it is shown that those phenomena are strongly modified at the interface with a metal. Indeed, an anomalous spin conversion is presented from HS state to LS state under blue light illumination for FeII spin‐crossover molecules that are in direct contact with metallic (111) single‐crystal surfaces (copper, silver, and gold). To interpret this anomalous spin‐state switching, a new mechanism is proposed for the spin conversion based on the light absorption by the substrate that can generate low energy valence photoelectrons promoting molecular vibrational excitations and subsequent spin‐state switching at the molecule–metal interface. 相似文献
8.
The thermal and light induced spin transition in [Fe(0.35)Ni(0.65)(mtz)(6)](ClO(4))(2) (mtz = 1-methyl-1H-tetrazole) was studied by (57)Fe M?ssbauer spectroscopy and magnetic susceptibility measurements. In addition to the spin transition of the iron(II) complexes the compound undergoes a structural phase transition. The high-temperature structure could be determined by X-ray crystallography of the isomorphous [Fe(0.25)Ni(0.75)(mtz)(6)](ClO(4))(2) complex at room temperature. The X-ray structural analysis shows this complex to be rhombohedric, space group R&thremacr;, with a = 10.865(2) ? and c = 23.65(1) ? with three molecules in the unit cell. The transition to the low-temperature structure occurs at approximately 60 K without changing the spin state of the molecules. By subsequent heating of the complex the high-temperature structure is reached again between ca. 170 and 200 K. The spin transition behavior is strongly influenced by the structural changes, and the observed spin transition curves are completely different for the high- and low-temperature phases. In the high-temperature structure a complete and gradual spin transition between 220 and 120 K (T(1/2)(gamma(HS) = 0.5) = 185 K) is detected; the high-spin (HS) state is represented by one HS doublet in the M?ssbauer spectra. In the low-temperature structure a two-step transition curve is detected in the heating mode. About 36% of the molecules show a LS (low-spin) --> HS transition between ca 50 and 75 K. Then the HS fraction stays constant up to 150 K. A further increase in the high-spin fraction is observed at temperatures above 150 K. In this structural phase the HS state is represented by two different HS doublets in the M?ssbauer spectra. The formation of metastable HS states by making use of the LIESST effect is only possible in the low-temperature structure. By excitation of the LS molecules with green light, two different HS states are populated which show very different relaxation behavior. One HS state shows a relaxation to the LS state even at 10 K; the other HS state shows a very slow HS --> LS relaxation at 60 K (within days), leading to the HS fraction corresponding to the thermal equilibrium value. 相似文献
9.
Costa JS Balde C Carbonera C Denux D Wattiaux A Desplanches C Ader JP Gütlich P Létard JF 《Inorganic chemistry》2007,46(10):4114-4119
A comprehensive study of the photomagnetic behavior of the [Fe(L222N5)(CN)2].H2O complex has been carried out. This complex is characterized by a low-spin (LS) iron(II)-metal center up to 400 K and exhibits at 10 K the well-known Light-Induced Excited Spin State Trapping (LIESST) effect. The critical LIESST temperature (T(LIESST)) has been measured to be 105 K. The kinetics of the transition from the metastable high-spin (HS) state to the low-spin state have been determined and used for reproducing the experimental T(LIESST) curve. This study represents a second example of a fully low-spin iron(II)-metal complex up to 400 K, which can be photoexcited at low temperature with an atypical long-lived metastable HS state. This underlines the preponderant role of the inner coordination sphere for stabilizing the lifetime of the photoinduced HS state. 相似文献
10.
Manabu Nakaya Wataru Kosaka Hitoshi Miyasaka Yuki Komatsumaru Shogo Kawaguchi Kunihisa Sugimoto Yingjie Zhang Masaaki Nakamura Leonard F. Lindoy Shinya Hayami 《Angewandte Chemie (International ed. in English)》2020,59(26):10658-10665
CO2‐responsive spin‐state conversion between high‐spin (HS) and low‐spin (LS) states at room temperature was achieved in a monomeric cobalt(II) complex. A neutral cobalt(II) complex, [CoII(COO‐terpy)2]?4 H2O ( 1?4 H2O ), stably formed cavities generated via π–π stacking motifs and hydrogen bond networks, resulting in the accommodation of four water molecules. Crystalline 1?4 H2O transformed to solvent‐free 1 without loss of porosity by heating to 420 K. Compound 1 exhibited a selective CO2 adsorption via a gate‐open type of the structural modification. Furthermore, the HS/LS transition temperature (T1/2) was able to be tuned by the CO2 pressure over a wide temperature range. Unlike 1 exhibits the HS state at 290 K, the CO2‐accomodated form 1?CO2 (P =110 kPa) was stabilized in the LS state at 290 K, probably caused by a chemical pressure effect by CO2 accommodation, which provides reversible spin‐state conversion by introducing/evacuating CO2 gas into/from 1 . 相似文献
11.
Hoa V. Phan Pradip Chakraborty Meimei Chen Yitzi M. Calm Dr. Kirill Kovnir Lawrence K. Keniley Jr. Jordan M. Hoyt Elisabeth S. Knowles Dr. Céline Besnard Prof. Mark W. Meisel Prof. Andreas Hauser Prof. Catalina Achim Prof. Michael Shatruk 《Chemistry (Weinheim an der Bergstrasse, Germany)》2012,18(49):15805-15815
Three iron(II) complexes, [Fe(TPMA)(BIM)](ClO4)2?0.5H2O ( 1 ), [Fe(TPMA)(XBIM)](ClO4)2 ( 2 ), and [Fe(TPMA)(XBBIM)](ClO4)2 ?0.75CH3OH ( 3 ), were prepared by reactions of FeII perchlorate and the corresponding ligands (TPMA=tris(2‐pyridylmethyl)amine, BIM=2,2′‐biimidazole, XBIM=1,1′‐(α,α′‐o‐xylyl)‐2,2′‐biimidazole, XBBIM=1,1′‐(α,α′‐o‐xylyl)‐2,2′‐bibenzimidazole). The compounds were investigated by a combination of X‐ray crystallography, magnetic and photomagnetic measurements, and Mössbauer and optical absorption spectroscopy. Complex 1 exhibits a gradual spin crossover (SCO) with T1/2=190 K, whereas 2 exhibits an abrupt SCO with approximately 7 K thermal hysteresis (T1/2=196 K on cooling and 203 K on heating). Complex 3 is in the high‐spin state in the 2–300 K range. The difference in the magnetic behavior was traced to differences between the inter‐ and intramolecular interactions in 1 and 2 . The crystal packing of 2 features a hierarchy of intermolecular interactions that result in increased cooperativity and abruptness of the spin transition. In 3 , steric repulsion between H atoms of one of the pyridyl substituents of TPMA and one of the benzene rings of XBBIM results in a strong distortion of the FeII coordination environment, which stabilizes the high‐spin state of the complex. Both 1 and 2 exhibit a photoinduced low‐spin to high‐spin transition (LIESST effect) at 5 K. The difference in the character of intermolecular interactions of 1 and 2 also manifests in the kinetics of the decay of the photoinduced high‐spin state. For 1 , the decay rate constant follows the single‐exponential law, whereas for 2 it is a stretched exponential, reflecting the hierarchical nature of intermolecular contacts. The structural parameters of the photoinduced high‐spin state at 50 K are similar to those determined for the high‐spin state at 295 K. This study shows that N‐alkylation of BIM has a negligible effect on the ligand field strength. Therefore, the combination of TPMA and BIM offers a promising ligand platform for the design of functionalized SCO complexes. 相似文献
12.
Structural Investigation of the High Spin→Low Spin Relaxation Dynamics of the Porous Coordination Network [Fe(pz)Pt(CN)4]⋅2.6 H2O 下载免费PDF全文
Teresa Delgado Dr. Antoine Tissot Dr. Céline Besnard Dr. Laure Guénée Dr. Philip Pattison Prof. Andreas Hauser 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(9):3664-3670
The Hoffman‐type coordination compound [Fe(pz)Pt(CN)4] ? 2.6 H2O (pz=pyrazine) shows a cooperative thermal spin transition at around 270 K. Synchrotron powder X‐Ray diffraction studies reveal that a quantitative photoinduced conversion from the low‐spin (LS) state into the high‐spin (HS) state, based on the light‐induced excited spin‐state trapping effect, can be achieved at 10 K in a microcrystalline powder. Time‐resolved measurements evidence that the HS→LS relaxation proceeds by a two‐step mechanism: a random HS→LS conversion at the beginning of the relaxation is followed by a nucleation and growth process, which proceeds until a quantitative HS→LS transformation has been reached. 相似文献
13.
Iron(II) Spin‐Crossover Complexes in Ultrathin Films: Electronic Structure and Spin‐State Switching by Visible and Vacuum‐UV Light 下载免费PDF全文
E. Ludwig H. Naggert Dr. M. Kalläne S. Rohlf E. Kröger Dr. A. Bannwarth A. Quer Dr. K. Rossnagel Prof. Dr. L. Kipp Prof. Dr. F. Tuczek 《Angewandte Chemie (International ed. in English)》2014,53(11):3019-3023
The electronic structure of the iron(II) spin crossover complex [Fe(H2bpz)2(phen)] deposited as an ultrathin film on Au(111) is determined by means of UV‐photoelectron spectroscopy (UPS) in the high‐spin and in the low‐spin state. This also allows monitoring the thermal as well as photoinduced spin transition in this system. Moreover, the complex is excited to the metastable high‐spin state by irradiation with vacuum‐UV light. Relaxation rates after photoexcitation are determined as a function of temperature. They exhibit a transition from thermally activated to tunneling behavior and are two orders of magnitude higher than in the bulk material. 相似文献
14.
Chou‐Fu Sheu Dr. Kowa Chen Szu‐Miao Chen Yuh‐Sheng Wen Gene‐Hsiang Lee Dr. Jin‐Ming Chen Dr. Jyh‐Fu Lee Dr. Bing‐Ming Cheng Dr. Hwo‐Shuenn Sheu Dr. Nobuhiro Yasuda Dr. Yoshiki Ozawa Prof. Koshiro Toriumi Prof. Yu Wang Prof. 《Chemistry (Weinheim an der Bergstrasse, Germany)》2009,15(10):2384-2393
Switchable molecules : The electronic configurations of the Fe center in trans‐[Fe(tzpy)2(NCS)2] in low‐spin, high‐spin, and LIESST states (LIESST=light‐induced excited spin‐state trapping) were confirmed by K‐ and L‐edge X‐ray absorption and magnetic measurements. The molecular structures at 40 K before and after irradiation are superimposed in the picture, which demonstrates a single‐crystal‐to‐single‐crystal transition by irradiation.
15.
The reaction of [FeL(MeOH)2] (L being a tetradentate [N2O2]2? coordinating Schiff base like ligand [([3,3′]‐[1,2‐phenylenebis(iminomethylidyne)]bis(2,4‐pentane‐dionato)(2‐)N,N′,O2,O2′], MeOH = methanol) with 4,4′‐bipyridine (bipy) results in the formation of a new iron(II ) spin crossover coordination polymer of the formula [FeL(bipy)] ( 1 ). T‐dependent susceptibility measurements revealed an abrupt HS ? LS spin transition with an approximately 18 K‐wide thermal hysteresis loop (T1/2↑ = 237 K and T1/2↓ = 219 K). The isolation of crystals suitable for X‐ray structure analysis allowed the determination of the motive of the molecule structure of the first 1‐D chain compound with hysteresis in the HS form at 250 K. Despite the low qualtity of the data, we were able to obtain some insight into the interplay of covalent and elastic interactions that are both responsible for the high cooperative interactions during the spin transition in this compound. 相似文献
16.
Yamada M Fukumoto E Ooidemizu M Bréfuel N Matsumoto N Iijima S Kojima M Re N Dahan F Tuchagues JP 《Inorganic chemistry》2005,44(20):6967-6974
A 2D layered spin crossover complex, [FeIIH3L(Me)]Cl.I3, has been synthesized from the reaction of FeIIICl3, a tripod ligand (H3LMe = tris[2-(((2-methylimidazoyl-4-yl)methylidene)amino)ethyl]amine), and NaI in methanol. The compound showed an abrupt spin transition between the HS (S = 2) and LS (S = 0) states at T(1/2) = 110 K without hysteresis. The crystal structures of the HS and LS states were determined at 180 and 90 K. A 2D layered structure is composed of NH...Cl- hydrogen bonds between the Cl- ion and three neighboring imidazole groups of [FeIIH3LMe]2+. The green light irradiation at 5 K induced the LIESST effect, and the thermal relaxation process from the HS to LS state showed a sigmoid curve at T > 55 K. 相似文献
17.
Baldé C Desplanches C Wattiaux A Guionneau P Gütlich P Létard JF 《Dalton transactions (Cambridge, England : 2003)》2008,(20):2702-2707
The thermal and light-induced spin transitions in [Fe(x)Zn(1-x)(phen)2(NCS)2] (phen = 1,10-phenantholine) have been investigated by magnetic susceptibility, photomagnetism and diffuse reflectivity measurements. These complexes display a thermal spin transition and undergo the light-induced excited spin state trapping (LIESST) effect at low temperatures. For each compound, the thermal spin transition temperature, T1/2, and the relaxation temperature of the photo-induced high-spin state, T(LIESST), have been systematically determined. It appears that T1/2 decreases with the metal dilution while T(LIESST) remains unchanged. This behaviour is discussed on the basis of the kinetic study governing the photo-induced back conversion. 相似文献
18.
Dr. Laurence J. Kershaw Cook Dr. Helena J. Shepherd Dr. Tim P. Comyn Dr. Chérif Baldé Dr. Oscar Cespedes Dr. Guillaume Chastanet Prof. Malcolm A. Halcrow 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(12):4805-4816
Crystalline [Fe(bppSMe)2][BF4]2 ( 1 ; bppSMe=4‐(methylsulfanyl)‐2,6‐di(pyrazol‐1‐yl)pyridine) undergoes an abrupt spin‐crossover (SCO) event at 265±5 K. The crystals also undergo a separate phase transition near 205 K, involving a contraction of the unit‐cell a axis to one‐third of its original value (high‐temperature phase 1; Pbcn, Z=12; low‐temperature phase 2; Pbcn, Z=4). The SCO‐active phase 1 contains two unique molecular environments, one of which appears to undergo SCO more gradually than the other. In contrast, powder samples of 1 retain phase 1 between 140–300 K, although their SCO behaviour is essentially identical to the single crystals. The compounds [Fe(bppBr)2][BF4]2 ( 2 ; bppBr=4‐bromo‐2,6‐di(pyrazol‐1‐yl)pyridine) and [Fe(bppI)2][BF4]2 ( 3 ; bppI=4‐iodo‐2,6‐di(pyrazol‐1‐yl)‐pyridine) exhibit more gradual SCO near room temperature, and adopt phase 2 in both spin states. Comparison of 1 – 3 reveals that the more cooperative spin transition in 1 , and its separate crystallographic phase transition, can both be attributed to an intermolecular steric interaction involving the methylsulfanyl substituents. All three compounds exhibit the light‐induced excited‐spin‐state trapping (LIESST) effect with T(LIESST=70–80 K), but show complicated LIESST relaxation kinetics involving both weakly cooperative (exponential) and strongly cooperative (sigmoidal) components. 相似文献
19.
Yi Shan Ye Xiu Qin Chen You De Cai Bin Fei Pierre Dechambenoit Mathieu Rouzires Corine Mathonire Rodolphe Clrac Xin Bao 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2019,131(52):19064-19067
A mononuclear FeII complex that shows a high‐spin (S=2) paramagnetic behavior at all temperatures (with standard temperature‐scan rates, ≈1 K min?1) has, in fact, a low‐spin (S=0) ground state below 100 K. This low‐spin state is not easily accessible due to the extremely slow dynamics of the spin‐crossover process—a full relaxation from the metastable high‐spin state to the low‐spin ground state takes more than 5 h below 80 K. Bidirectional photo‐switching of the FeII state is achieved reproducibly by two selective irradiations (at 530–590 and 830–850 nm). The slow dynamics of the spin‐crossover and the strong structural cooperativity result in a remarkably wide 95‐K hysteresis loop induced by both temperature and selected light stimuli. 相似文献
20.
Stabilization of the Low‐Spin State in a Mononuclear Iron(II) Complex and High‐Temperature Cooperative Spin Crossover Mediated by Hydrogen Bonding 下载免费PDF全文
Dr. Sipeng Zheng Niels R. M. Reintjens Dr. Maxime A. Siegler Dr. Olivier Roubeau Prof. Elisabeth Bouwman Andrii Rudavskyi Prof. Remco W. A. Havenith Dr. Sylvestre Bonnet 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(1):331-339
The tetrapyridyl ligand bbpya (bbpya=N,N‐bis(2,2′‐bipyrid‐6‐yl)amine) and its mononuclear coordination compound [Fe(bbpya)(NCS)2] ( 1 ) were prepared. According to magnetic susceptibility, differential scanning calorimetry fitted to Sorai’s domain model, and powder X‐ray diffraction measurements, 1 is low‐spin at room temperature, and it exhibits spin crossover (SCO) at an exceptionally high transition temperature of T1/2=418 K. Although the SCO of compound 1 spans a temperature range of more than 150 K, it is characterized by a wide (21 K) and dissymmetric hysteresis cycle, which suggests cooperativity. The crystal structure of the LS phase of compound 1 shows strong N?H???S intermolecular H‐bonding interactions that explain, at least in part, the cooperative SCO behavior observed for complex 1 . DFT and CASPT2 calculations under vacuum demonstrate that the bbpya ligand generates a stronger ligand field around the iron(II) core than its analogue bapbpy (N,N′‐di(pyrid‐2‐yl)‐2,2′‐bipyridine‐6,6′‐diamine); this stabilizes the LS state and destabilizes the HS state in 1 compared with [Fe(bapbpy)(NCS)2] ( 2 ). Periodic DFT calculations suggest that crystal‐packing effects are significant for compound 2 , in which they destabilize the HS state by about 1500 cm?1. The much lower transition temperature found for the SCO of 2 compared to 1 appears to be due to the combined effects of the different ligand field strengths and crystal packing. 相似文献