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1.
Gabriel Bellavance Louis Barriault 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2014,126(26):6819-6822
The remarkable biological activities of polyprenylated polycyclic acylphloroglucinols (PPAPs) combined with their highly decorated bicyclo[3.3.1]nonane‐2,4,9‐trione frameworks have inspired synthetic organic chemists over the last decade. The concise total syntheses of four natural products PPAPs; hyperforin and papuaforins A–C, and the formal synthesis of nemorosone are reported. Key to the realization of this strategy is the short and scalable synthesis of densely substituted PPAP scaffolds through a gold(I)‐catalyzed 6‐endo‐dig carbocyclization of cyclic enol ethers for late‐stage functionalization. 相似文献
2.
Total Syntheses of Hyperforin and Papuaforins A–C,and Formal Synthesis of Nemorosone through a Gold(I)‐Catalyzed Carbocyclization 下载免费PDF全文
Gabriel Bellavance Prof. Louis Barriault 《Angewandte Chemie (International ed. in English)》2014,53(26):6701-6704
The remarkable biological activities of polyprenylated polycyclic acylphloroglucinols (PPAPs) combined with their highly decorated bicyclo[3.3.1]nonane‐2,4,9‐trione frameworks have inspired synthetic organic chemists over the last decade. The concise total syntheses of four natural products PPAPs; hyperforin and papuaforins A–C, and the formal synthesis of nemorosone are reported. Key to the realization of this strategy is the short and scalable synthesis of densely substituted PPAP scaffolds through a gold(I)‐catalyzed 6‐endo‐dig carbocyclization of cyclic enol ethers for late‐stage functionalization. 相似文献
3.
Federico Da Settimo Anna Maria Marini Gianluca Pardi Giampaolo Primofiore Silvia Salerno Francesca Simorini 《Journal of heterocyclic chemistry》2001,38(3):607-612
A new synthetic route to build the [1,2,4]triazino[3,4‐ f]purine nucleus is described. The novel [1,2,4]‐triazino[3,4‐ f]purine‐4,6,8(l H,7 H,9 H)‐trione derivatives were obtained by condensation of 8‐hydrazinotheophylline with appropriate glyoxylic acids via the intermediate hydrazones. 相似文献
4.
A Mechanistic Study on the Oxidative Degradation of Dibenzazepine Derivatives by Manganese(III) Complexes in Acidic Sulfate Media 下载免费PDF全文
The oxidative degradation of tricyclic antidepressants (TCA) was studied in the presence of a large excess of the oxidizing agent manganese(III) and its reduced form manganese(II) sulfate in acidic media. The products were detected and identified using UV–vis, ESI‐MS, IR, and EPR methods. The mechanism of the reaction was studied for the following two classes of TCA: 10,11‐dihydro‐5H‐dibenz[b, f]azepines and dibenz[b, f]azepines. The oxidative degradation between dibenz[b, f]azepines and the manganese(III) ions resulted in the formation of substituted acridine with the same substituent as in the origin dibenz[b, f]azepine derivative. The pseudo–first‐order rate constants (kobs) were determined for the degradation process. The dependences of the observed rate constants on the [MnIII] with a zero intercept were linear. The reaction between 10,11‐dihydro‐5H‐dibenz[b, f]azepines, and the manganese(III) sulfate ion resulted in oxidative dehydrogenation, which proceeded via the formation of the following two intermediates: a free organic radical and a dimer. Further oxidation of the second intermediate led to a positively charged radical dimer as the single final product. Linear dependences of the pseudo–first‐order rate constants (kobs) on the [MnIII] with a zero intercept were established for the degradation of 10,11‐dihydro‐5H‐dibenz[b, f]azepines. The observed rate constants were dependent on the [H+] and independent of the [TCA] within the excess concentration range of the manganese(III) complexes used in the isolation method. The radical product of the degradation of 10,11‐dihydro‐5H‐dibenz[b, f]azepines was not stable in the aqueous solution and was subsequently transformed to a nonradical dimer in the next slower step. The observed rate constants were independent of the [MnIII], independent of the [H+] and increased slightly with increasing TCA concentrations when TCA was used in excess. The mechanistic consequences of all of these results are discussed. 相似文献
5.
Praveen K. Thallapally Gautam R. Desiraju 《Acta Crystallographica. Section C, Structural Chemistry》2000,56(5):572-573
The title compound, 1,3,5‐tris(2‐cyanoethyl)‐1,3,5‐triazine‐2,4,6(1H,3H,5H)‐trione, C12H12N6O3, forms a layered structure stabilized by C—H?O and C—H?N hydrogen bonds. 相似文献
6.
Sandeep Nadella Dr. Paulraj M. Selvakumar Dr. Eringathodi Suresh Dr. Palani S. Subramanian Prof. Dr. Markus Albrecht Dr. Michael Giese Dr. Roland Fröhlich 《Chemistry (Weinheim an der Bergstrasse, Germany)》2012,18(52):16784-16792
Phenanthroline‐based hexadentate ligands L1 and L2 bearing two achiral semicarbazone or two chiral imine moieties as well as the respective mononuclear complexes incorporating various lanthanide ions, such as LaIII, EuIII, TbIII, LuIII, and YIII metal ions, were synthesized, and the crystal structures of [ML1Cl3] (M=LaIII, EuIII, TbIII, LuIII, or YIII) complexes were determined. Solvent or water molecules act as coligands for the rare‐earth metals in addition to halide anions. The big LnIII ion exhibits a coordination number (CN) of 10, whereas the corresponding EuIII, TbIII, LuIII, and YIII centers with smaller ionic radii show CN=9. Complexes of L2, namely [ML2Cl3] (M=EuIII, TbIII, LuIII, or YIII) ions could also be prepared. Only the complex of EuIII showed red luminescence, whereas all the others were nonluminescent. The emission properties of the Eu derivative can be applied as a photophysical signal for sensing various anions. The addition of phosphate anions leads to a unique change in the luminescence behavior. As a case study, the quenching behavior of adenosine‐5′‐triphosphate (ATP) was investigated at physiological pH value in an aqueous solvent. A specificity of the sensor for ATP relative to adenosine‐5′‐diphosphate (ADP) and adenosine‐5′‐monophosphate (AMP) was found. 31P NMR spectroscopic studies revealed the formation of a [EuL2(ATP)] coordination species. 相似文献
7.
The Crystal and the Electronic Structure of La2Li1/2Au1/2O4 The single crystal X‐ray investigation of the compound La2Li1/2AuIII1/2O4 yields a T′‐type structure (Nd2CuO4) with an ordered distribution of LiI and AuIII on the sites with square‐planar coordination (space group Ammm; a = 5.768 Å, b = 5.762 Å, c = 12.466 Å; c/a(b) = 2.165; a(Au–O) = 2.013(3) Å). Though CuIII possesses the same low‐spin d8‐configuration as AuIII, La2Li1/2Cu1/2O4 adopts the ordered T‐structure with strongly elongated CuO6 octahedra. The electronic and structural causes of the different behaviour are discussed. 相似文献
8.
Yan Wang Ying‐Zhong Shen 《Acta Crystallographica. Section C, Structural Chemistry》2008,64(8):m283-m285
The title novel heterometallic 3d–4f coordination polymer, {[CuEr2(C5HN2O4)2(C2O4)(H2O)6]·3H2O}n, has a three‐dimensional metal–organic framework composed of two types of metal atoms (one CuII and two ErIII) and two types of bridging anionic ligands [3,5‐dicarboxylatopyrazolate(3−) (ptc3−) and oxalate]. The CuII atom is four‐coordinated in a square geometry. The ErIII atoms are both eight‐coordinated, but the geometries at the two atoms appear different, viz. triangular dodecahedral and bicapped trigonal prismatic. One of the oxalate anions is located on a twofold axis and the other lies about an inversion centre. Both oxalate anions act as bis‐bidentate ligands bridging the latter type of Er atoms in parallel zigzag chains. The pdc3− anions act as quinquedentate ligands not only chelating the CuII and the triangular dodecahedral ErIII centres in a bis‐bidentate bridging mode, but also connecting to ErIII centres of both types in a monodentate bridging mode. Thus, a three‐dimensional metal–organic framework is generated, and hydrogen bonds link the metal–organic framework with the uncoordinated water molecules. This study describes the first example of a three‐dimensional 3d–4f coordination polymer based on pyrazole‐3,5‐dicarboxylate and oxalate, and therefore demonstrates further the usefulness of pyrazoledicarboxylate as a versatile multidentate ligand for constructing heterometallic 3d–4f coordination polymers with interesting architectures. 相似文献
9.
White Light Emissive DyIII Single‐Molecule Magnets Sensitized by Diamagnetic [CoIII(CN)6]3− Linkers 下载免费PDF全文
Dr. Szymon Chorazy Dr. Michał Rams Dr. Koji Nakabayashi Prof. Dr. Barbara Sieklucka Prof. Dr. Shin‐ichi Ohkoshi 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(22):7371-7375
The self‐assembly of DyIII–3‐hydroxypyridine (3‐OHpy) complexes with hexacyanidocobaltate(III) anions in water produces cyanido‐bridged {[DyIII(3‐OHpy)2(H2O)4] [CoIII(CN)6]}?H2O ( 1 ) chains. They reveal a single‐molecule magnet (SMM) behavior with a large zero direct current (dc) field energy barrier, ΔE=266(12) cm?1 (≈385 K), originating from the single‐ion property of eight‐coordinated DyIII of an elongated dodecahedral geometry, which are embedded with diamagnetic [CoIII(CN)6]3? ions into zig‐zag coordination chains. The SMM character is enhanced by the external dc magnetic field, which results in the ΔE of 320(23) cm?1 (≈460 K) at Hdc=1 kOe, and the opening of a butterfly hysteresis loop below 6 K. Complex 1 exhibits white DyIII‐based emission realized by energy transfer from CoIII and 3‐OHpy to DyIII. Low temperature emission spectra were correlated with SMM property giving the estimation of the zero field ΔE. 1 is a unique example of bifunctional magneto‐luminescent material combining white emission and slow magnetic relaxation with a large energy barrier, both controlled by rich structural and electronic interplay between DyIII, 3‐OHpy, and [CoIII(CN)6]3?. 相似文献
10.
Ligand π‐Radical Interaction with f‐Shell Unpaired Electrons in Phthalocyaninato–Lanthanoid Single‐Molecule Magnets: A Solution NMR Spectroscopic and DFT Study 下载免费PDF全文
Marko Damjanović Takaumi Morita Prof. Keiichi Katoh Prof. Masahiro Yamashita Prof. Markus Enders 《Chemistry (Weinheim an der Bergstrasse, Germany)》2015,21(41):14421-14432
The phthalocyaninato double‐decker complexes [M(obPc)2]0 (M= YIII, TbIII, DyIII; obPc=2,3,9,10,16,17,23,24‐octabutoxyphthalocyaninato), along with their reduced ([M(obPc)2]?[P(Ph)4]+; M=TbIII, DyIII) and oxidized ([M(obPc)2]+[SbCl6]? (M=YIII, TbIII) counterparts were studied with 1H, 13C and 2D NMR. From the NMR data of the neutral (i.e., with one unpaired electron in the ligands) and anionic TbIII complexes, along with the use of dispersion corrected DFT methods, it was possible to separate the metal‐centered and ligand‐centered contributions to the hyperfine NMR shift. These contributions to the 1H and 13C hyperfine NMR shifts were further analyzed in terms of pseudocontact and Fermi contact shifts. Furthermore, from a combination of NMR data and DFT calculations, we have determined the spin multiplicity of the neutral complexes [M(obPc)2]0 (M=TbIII and DyIII) at room temperature. From the NMR data of the cationic TbIII complex, for which actually no experimental structure determination is available, we have analyzed the structural changes induced by oxidation from its neutral/anionic species and shown that the interligand distance decreases upon oxidation. The fast electron exchange process between the neutral and anionic TbIII double‐decker complexes was also studied. 相似文献
11.
Jun‐Fang Guo Dr. Xiu‐Teng Wang Dr. Bing‐Wu Wang Dr. Guan‐Cheng Xu Dr. Song Gao Prof. Lap Szeto Wing‐Tak Wong Prof. Wai‐Yeung Wong Prof. Tai‐Chu Lau Prof. 《Chemistry (Weinheim an der Bergstrasse, Germany)》2010,16(11):3524-3535
Four cyano‐bridged 1D bimetallic polymers have been prepared by using the paramagnetic building block trans‐[Ru(acac)2(CN)2]? (Hacac=acetylacetone): {[{Ni(tren)}{Ru(acac)2(CN)2}][ClO4]?CH3OH}n ( 1 ) (tren=tris(2‐aminoethyl)amine), {[{Ni(cyclen)}{Ru(acac)2(CN)2}][ClO4]? CH3OH}n ( 2 ) (cyclen=1,4,7,10‐tetraazacyclododecane), {[{Fe(salen)}{Ru(acac)2(CN)2}]}n ( 3 ) (salen2?=N,N′‐bis(salicylidene)‐o‐ethyldiamine dianion) and [{Mn(5,5′‐Me2salen)}2{Ru(acac)2(CN)2}][Ru(acac)2(CN)2]? 2 CH3OH ( 4 ) (5,5′‐Me2salen=N,N′‐bis(5,5′‐dimethylsalicylidene)‐o‐ethylenediimine). Compounds 1 and 2 are 1D, zigzagged NiRu chains that exhibit ferromagnetic coupling between NiII and RuIII ions through cyano bridges with J=+1.92 cm?1, z J′=?1.37 cm?1, g=2.20 for 1 and J=+0.85 cm?1, z J′=?0.16 cm?1, g=2.24 for 2 . Compound 3 has a 1D linear chain structure that exhibits intrachain ferromagnetic coupling (J=+0.62 cm?1, z J′=?0.09 cm?1, g=2.08), but antiferromagnetic coupling occurs between FeRu chains, leading to metamagnetic behavior with TN=2.6 K. In compound 4 , two MnIII ions are coordinated to trans‐[Ru(acac)2(CN)2]? to form trinuclear Mn2Ru units, which are linked together by π–π stacking and weak Mn???O* interactions to form a 1D chain. Compound 4 shows slow magnetic relaxation below 3.0 K with ?=0.25, characteristic of superparamagnetic behavior. The MnIII???RuIII coupling constant (through cyano bridges) and the MnIII???MnIII coupling constant (between the trimers) are +0.87 and +0.24 cm?1, respectively. Compound 4 is a novel single‐chain magnet built from Mn2Ru trimers through noncovalent interactions. Density functional theory (DFT) combined with the broken symmetry state method was used to calculate the molecular magnetic orbitals and the magnetic exchange interactions between RuIII and M (M=NiII, FeIII, and MnIII) ions. To explain the somewhat unexpected ferromagnetic coupling between low‐spin RuIII and high‐spin FeIII and MnIII ions in compounds 3 and 4 , respectively, it is proposed that apart from the relative symmetries, the relative energies of the magnetic orbitals may also be important in determining the overall magnetic coupling in these bimetallic assemblies. 相似文献
12.
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
13.
The influence of magnetic interactions to the magnetization dynamics was well experimentally studied in a 3d‐4f single‐molecule magnet (SMM) [TbIII2FeIII3(μ5‐O)L2(NO3)4Cl] ( 1 , H4L = N,N,N’,N’‐tetrakis(2‐hydroxyethyl)ethylene diamine) and its diamagnetic‐ ion‐diluted samples. Significant ferromagnetic coupling between TbIII and FeIII ions and SMM behavior of 1 were observable, which proved clearly that the magnetic interaction between 3d‐4f spin carriers has also an excessive impact on fine‐tuning the magnetization dynamic behaviors of 3d‐4f complexes. 相似文献
14.
Dr. Jan Dreiser Kasper S. Pedersen Dr. Alexander Schnegg Dr. Karsten Holldack Joscha Nehrkorn Marc Sigrist Dr. Hannu Mutka Dr. Høgni Weihe Dr. Vladimir S. Mironov Prof. Jesper Bendix Prof. Oliver Waldmann 《Chemistry (Weinheim an der Bergstrasse, Germany)》2013,19(11):3693-3701
We have investigated the single‐molecule magnets [MnIII2(5‐Brsalen)2(MeOH)2MIII(CN)6]NEt4 (M=Os ( 1 ) and Ru ( 2 ); 5‐Brsalen=N,N′‐ethylenebis(5‐bromosalicylidene)iminate) by frequency‐domain Fourier‐transform terahertz electron paramagnetic resonance (THz‐EPR), inelastic neutron scattering, and superconducting quantum interference device (SQUID) magnetometry. The combination of all three techniques allows for the unambiguous experimental determination of the three‐axis anisotropic magnetic exchange coupling between MnIII and RuIII or OsIII ions, respectively. Analysis by means of a spin‐Hamiltonian parameterization yields excellent agreement with all experimental data. Furthermore, analytical calculations show that the observed exchange anisotropy is due to the bent geometry encountered in both 1 and 2 , whereas a linear geometry would lead to an Ising‐type exchange coupling. 相似文献
15.
Giulia Lavarda Daiki Shimizu Toms Torres Atsuhiro Osuka 《Angewandte Chemie (International ed. in English)》2020,59(8):3127-3130
Peripherally metalated porphyrinoids are promising functional π‐systems displaying characteristic optical, electronic, and catalytic properties. In this work, 5‐(2‐pyridyl)‐ and 5,10,15‐tri(2‐pyridyl)‐BIII‐subporphyrins were prepared and used to produce cyclometalated subporphyrins by reactions with [Cp*IrCl2]2, which proceeded through an efficient C?H activation to give the corresponding mono‐ and tri‐IrIII complexes, respectively. While the mono‐IrIII complex was obtained as a diastereomeric mixture, a C3‐symmetric tri‐IrIII complex with the three Cp*‐units all at the concave side was predominantly obtained in a high yield of 90 %, which displays weak NIR phosphorescence even at room temperature in degassed CH2Cl2, differently from the mono‐IrIII complexes. 相似文献
16.
Yin‐Shan Meng Yu‐Sen Qiao Prof. Dr. Yi‐Quan Zhang Dr. Shang‐Da Jiang Zhao‐Sha Meng Prof. Dr. Bing‐Wu Wang Prof. Dr. Zhe‐Ming Wang Prof. Dr. Song Gao 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(14):4704-4708
In recent years, plentiful lanthanide‐based (TbIII, DyIII, and ErIII) single‐molecule magnets (SMMs) were studied, while examples of other lanthanides, for example, TmIII are still unknown. Herein, for the first time, we show that by rationally manipulating the coordination sphere, two thulium compounds, 1 [(Tp)Tm(COT)] and 2 [(Tp*)Tm(COT)] (Tp=hydrotris(1‐pyrazolyl)borate; COT=cyclooctatetraenide; Tp*=hydrotris(3,5‐dimethyl‐1‐pyrazolyl)borate), can adopt the structure of non‐Kramers SMMs and exhibit their behaviors. Dynamic magnetic studies indicated that both compounds showed slow magnetic relaxation under dc field and a relatively high effective energy barrier (111 K for 1 , 46 K for 2 ). Magnetic diluted 1 a [(Tp)Tm0.05Y0.95(COT)] and 2 a [(Tp*)Tm0.05Y0.95(COT)] even exhibited magnetic relaxation under zero dc field. Relativistic ab initio calculations combined with single‐crystal angular‐resolved magnetometry measurements revealed the strong easy axis anisotropy and nearly degenerated ground doublet states. The comparison of 1 and 2 highlights the importance of local symmetry for obtaining Tm SMMs. 相似文献
17.
Comprehensive Evaluation of the Physicochemical Properties of LnIII Complexes of Aminoethyl‐DO3A as pH‐Responsive T1‐MRI Contrast Agents 下载免费PDF全文
Dr. Zsolt Baranyai Dr. Gabriele A. Rolla Dr. Roberto Negri Attila Forgács Prof. Giovanni B. Giovenzana Dr. Lorenzo Tei 《Chemistry (Weinheim an der Bergstrasse, Germany)》2014,20(10):2933-2944
N‐Substituted aminoethyl groups were attached to 1,4,7,10‐tetraazacyclododecane‐1,4,7‐triacetic acid (DO3A) with the aim to design pH‐responsive LnIII complexes based on the pH‐dependent on/off ligation of the amine nitrogen to the metal ion. The following ligands were synthesized: AE ‐ DO3A (aminoethyl‐DO3A), MAE ‐ DO3A (N‐methylaminoethyl‐DO3A), DMAE ‐ DO3A (N,N‐dimethylaminoethyl‐DO3A) and MEM ‐ AE ‐ DO3A (N‐methoxyethyl‐N‐methylaminoethyl‐DO3A). The physicochemical properties of the LnIII complexes were investigated for the evaluation of their potential applicability as magnetic resonance imaging (MRI) contrast agents. In particular, a 1H and 17O NMR relaxometric study was carried out for these GdIII complexes at two different pH values: at basic pH (pendant amino group coordinated to the metal centre) and at acidic pH (protonated amine, not interacting with the metal ion). EuIII complexes allow one to estimate the number of inner‐sphere water molecules through luminescence lifetime measurements and obtain some structural information through variable‐temperature (VT) high‐resolution 1H NMR studies. Equilibria between differently hydrated species were found for most of the complexes at both acidic and basic pH. The thermodynamic stability of CaII, ZnII, CuII and LnIII complexes and kinetics of formation and dissociation reactions of LnIII complexes of AE ‐ DO3A and DMAE ‐ DO3A were investigated showing stabilities comparable to currently approved GdIII‐based CAs. In detail, higher total basicity (Σlog KiH) and higher stability constants of LnIII complexes were found for AE ‐ DO3A with respect to DMAE ‐ DO3A (i.e., log KGd‐ AE‐DO3A =22.40 and log KGd‐ DMAE‐DO3A =20.56). The transmetallation reactions of GdIII complexes are very slow (Gd‐ AE ‐ DO3A : t1/2=2.7×104 h; Gd‐ DMAE ‐ DO3A : 1.1×105 h at pH 7.4 and 298 K) and occur through proton‐assisted dissociation. 相似文献
18.
Fabían Orozco Braulio Insuasty John N. Low Justo Cobo Christopher Glidewell 《Acta Crystallographica. Section C, Structural Chemistry》2008,64(3):o162-o165
The title compound, C36H16O6, (I), was obtained as a new and unexpected oxidation product of 1,2′‐biindene‐1′,3,3′(2H)‐trione. The molecules of (I) exhibit approximate, but noncrystallographic, twofold rotation symmetry and the central ring of the fused pentacyclic portion is distinctly puckered, with a conformation intermediate between half‐chair and screw‐boat. Six independent C—H...O hydrogen bonds link the molecules into a three‐dimensional framework structure of considerable complexity. Comparisons are drawn between the crystal structure of (I) and those of several simpler analogues, which show wide variation in their patterns of supramolecular aggregation. 相似文献
19.
Prof. Dr. Hitoshi Miyasaka Tomokura Madanbashi Ayumi Saitoh Dr. Natsuko Motokawa Ryuta Ishikawa Prof. Dr. Masahiro Yamashita Dr. Stefan Bahr Prof. Dr. Wolfgang Wernsdorfer Dr. Rodolphe Clérac 《Chemistry (Weinheim an der Bergstrasse, Germany)》2012,18(13):3942-3954
A series of isostructural cyano‐bridged MnIII(h.s.)–MIII(l.s.) alternating chains, [MnIII(5‐TMAMsalen)MIII(CN)6] ? 4H2O (5‐TMAMsalen2?=N,N′‐ethylenebis(5‐trimethylammoniomethylsalicylideneiminate), MnIII(h.s.)=high‐spin MnIII, MIII(l.s.)=low‐spin CoIII, Mn? Co ; FeIII, Mn? Fe ; MnIII, Mn? Mn ; CrIII, Mn? Cr ) was synthesized by assembling [MnIII(5‐TMAMsalen)]3+ and [MIII(CN)6]3?. The chains present in the four compounds, which crystallize in the monoclinic space group C2/c, are composed of an [‐MnIII‐NC‐MIII‐CN‐] repeating motif, for which the ‐NC‐MIII‐CN‐ motif is provided by the [MIII(CN)6]3? moiety adopting a trans bridging mode between [MnIII(5‐TMAMsalen)]3+ cations. The MnIII and MIII ions occupy special crystallographic positions: a C2 axis and an inversion center, respectively, forming a highly symmetrical chain with only one kind of cyano bridge. The Jahn–Teller axis of the MnIII(h.s.) ion is perpendicular to the N2O2 plane formed by the 5‐TMAMsalen tetradentate ligand. These Jahn–Teller axes are all perfectly aligned along the unique chain direction without a bending angle, although the chains are corrugated with an Mn‐Naxis‐C angle of about 144°. In the crystal structures, the chains are well separated with the nearest inter‐chain M???M distance being relatively large at 9 Å due to steric hindrance of the bulky trimethylammoniomethyl groups of the 5‐TMAMsalen ligand. The magnetic properties of these compounds have been thoroughly studied. Mn? Fe and Mn? Mn display intra‐chain ferromagnetic interactions, whereas Mn? Cr is characterized by an antiferromagnetic exchange that induces a ferrimagnetic spin arrangement along the chain. Detailed analyses of both static and dynamic magnetic properties have demonstrated without ambiguity the single‐chain magnet (SCM) behavior of these three systems, whereas Mn? Co is merely paramagnetic with SMn=2 and D/kB=?5.3 K (D being a zero‐field splitting parameter). At low temperatures, the Mn? M compounds with M=Fe, Mn, and Cr display remarkably large M versus H hysteresis loops for applied magnetic fields along the easy magnetic direction that corresponds to the chain direction. The temperature dependence of the associated relaxation time for this series of compounds systematically exhibits a crossover between two Arrhenius laws corresponding to infinite‐chain and finite‐chain regimes for the SCM behavior. These isostructural hetero‐spin SCMs offer a unique series of alternating [‐Mn‐NC‐M‐CN‐] chains, enabling physicists to test theoretical SCM models between the Ising and Heisenberg limits. 相似文献
20.
The ability of the tetraaza‐dithiophenolate ligand H2L2 (H2L2 = N,N′‐Bis‐[2‐thio‐3‐aminomethyl‐5‐tert‐butyl‐benzyl]propane‐1,3‐diamine) to form dinuclear chromium(III) complexes has been examined. Reaction of CrIICl2 with H2L2 in methanol in the presence of base followed by air‐oxidation afforded cis,cis‐[(L2)CrIII2(μ‐OH)(Cl)2]+ ( 1a ) and trans,trans‐[(L2)CrIII2(μ‐OH)(Cl)2]+ ( 1b ). Both compounds contain a confacial bioctahedral N2ClCrIII(μ‐SR)2(μ‐OH)CrIIIClN2 core. The isomers differ in the mutual orientation of the coligands and the conformation of the supporting ligand. In 1a both Cl? ligands are cis to the bridging OH function. In 1b they are in trans‐positions. Reaction of the hydroxo‐bridged complexes with HCl yielded the chloro‐bridged cations cis,cis‐[(L2)CrIII2(μ‐Cl)(Cl)2]+ ( 2a ) and trans,trans‐[(L2)CrIII2(μ‐Cl)(Cl)2]Cl ( 2b ), respectively. These bridge substitutions proceed with retention of the structures of the parent complexes 1a and 1b . 相似文献