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1.
We report here the synthesis and the investigation of the magnetic properties of a series of binuclear lanthanide complexes belonging to the metallacrown family. The isostructural complexes have a core structure with the general formula [Ga4Ln2(shi3–)4(Hshi2–)2(H2shi)2(C5H5N)4(CH3OH)x(H2O)xxC5H5xCH3OH·xH2O (where H3shi = salicylhydroxamic acid and Ln = GdIII1; TbIII2; DyIII3; ErIII4; YIII5; YIII0.9DyIII0.16). Apart from the Er-containing complex, all complexes exhibit an antiferromagnetic exchange coupling leading to a diamagnetic ground state. Magnetic studies, below 2 K, on a single crystal of 3 using a micro-squid array reveal an opening of the magnetic hysteresis cycle at zero field. The dynamic susceptibility studies of 3 and of the diluted DyY 6 complexes reveal the presence of two relaxation processes for 3 that are due to the excited ferromagnetic state and to the uncoupled DyIII ions. The antiferromagnetic coupling in 3 was shown to be mainly due to an exchange mechanism, which accounts for about 2/3 of the energy gap between the antiferro- and the ferromagnetic states. The overlap integrals between the Natural Spin Orbitals (NSOs) of the mononuclear fragments, which are related to the magnitude of the antiferromagnetic exchange, are one order of magnitude larger for the Dy2 than for the Er2 complex.  相似文献   

2.
Artificial smart materials with switchable multifunctionality are of immense interest owing to their wide application in sensors, displays and memory devices. Lanthanide complexes are promising multifunctional materials integrating optical and magnetic characteristics. However, synergistic manipulation of different physical properties in lanthanide systems is still challenging. Herein we designed and synthesized a mononuclear complex [DyIII(SCN)3(depma)2(4-hpy)2] (1), which incorporates 9-diethylphosphonomethylanthracene (depma) as a photo-active component and 4-hydroxypyridine (4-hpy) as a polar component. This compound shows several unusual features: (a) reversible thermo-responsive phase transition associated with the order–disorder transition of 4-hpy and SCN, which leads to thermochromic behavior and dielectric anomaly; (b) reversible photo-induced dimerization of anthracene groups, which leads to synergistic switching of luminescence, magnetic and dielectric properties. To our knowledge, compound 1 is the first example of lanthanide complexes that show stimuli-triggered synergistic and reversible switching of luminescence, magnetic and dielectric properties.

[DyIII(SCN)3(depma)2(4-hpy)2] (1) shows reversible thermo-induced phase transition associated with thermochromism and dielectric anomaly and photo-induced dimerization with synergistic switching of luminescence, magnetic and dielectric properties.  相似文献   

3.
A series of heterometallic carboxylate 1D polymers of the general formula [LnIIICd2(piv)7(H2O)2]n·nMeCN (LnIII = Sm (1), Eu (2), Tb (3), Dy (4), Ho (5), Er (6), Yb (7); piv = anion of trimethylacetic acid) was synthesized and structurally characterized. The use of CdII instead of ZnII under similar synthetic conditions resulted in the formation of 1D polymers, in contrast to molecular trinuclear complexes with LnIIIZn2 cores. All complexes 1–7 are isostructural. The luminescent emission and excitation spectra for 2–4 have been studied, the luminescence decay kinetics for 2 and 3 was measured. Magnetic properties of the complexes 3–5 and 7 have been studied; 4 and 7 exhibited the properties of field-induced single-molecule magnets in an applied external magnetic field. Magnetic properties of 4 and 7 were modelled using results of SA-CASSCF/SO-RASSI calculations and SINGLE_ANISO procedure. Based on the analysis of the magnetization relaxation and the results of ab initio calculations, it was found that relaxation in 4 predominantly occurred by the sum of the Raman and QTM mechanisms, and by the sum of the direct and Raman mechanisms in the case of 7.  相似文献   

4.
The first families of alkaline-earth stannylides [Ae(SnPh3)2·(thf)x] (Ae = Ca, x = 3, 1; Sr, x = 3, 2; Ba, x = 4, 3) and [Ae{Sn(SiMe3)3}2·(thf)x] (Ae = Ca, x = 4, 4; Sr, x = 4, 5; Ba, x = 4, 6), where Ae is a large alkaline earth with direct Ae–Sn bonds, are presented. All complexes have been characterised by high-resolution solution NMR spectroscopy, including 119Sn NMR, and by X-ray diffraction crystallography. The molecular structures of [Ca(SnPh3)2·(thf)4] (1′), [Sr(SnPh3)2·(thf)4] (2′), [Ba(SnPh3)2·(thf)5] (3′), 4, 5 and [Ba{Sn(SiMe3)3}2·(thf)5] (6′), most of which crystallised as higher thf solvates than their parents 1–6, were established by XRD analysis; the experimentally determined Sn–Ae–Sn′ angles lie in the range 158.10(3)–179.33(4)°. In a given series, the 119Sn NMR chemical shifts are slightly deshielded upon descending group 2 from Ca to Ba, while the silyl-substituted stannyls are much more shielded than the phenyl ones (δ119Sn/ppm: 1′, −133.4; 2′, −123.6; 3′, −95.5; 4, −856.8; 5, −848.2; 6′, −792.7). The bonding and electronic properties of these complexes were also analysed by DFT calculations. The combined spectroscopic, crystallographic and computational analysis of these complexes provide some insight into the main features of these unique families of homoleptic complexes. A comprehensive DFT study (Wiberg bond index, QTAIM and energy decomposition analysis) points at a primarily ionic Ae–Sn bonding, with a small covalent contribution, in these series of complexes; the Sn–Ae–Sn′ angle is associated with a flat energy potential surface around its minimum, consistent with the broad range of values determined by experimental and computational methods.

The complete series of heterobimetallic alkaline-earth distannyls [Ae{SnR3}2·(thf)x] (Ae = Ca, Sr, Ba) have been prepared for R = Ph and SiMe3, and their bonding and electronic properties have been comprehensively investigated.  相似文献   

5.
While alkylperoxomanganese(iii) (MnIII–OOR) intermediates are proposed in the catalytic cycles of several manganese-dependent enzymes, their characterization has proven to be a challenge due to their inherent thermal instability. Fundamental understanding of the structural and electronic properties of these important intermediates is limited to a series of complexes with thiolate-containing N4S ligands. These well-characterized complexes are metastable yet unreactive in the direct oxidation of organic substrates. Because the stability and reactivity of MnIII–OOR complexes are likely to be highly dependent on their local coordination environment, we have generated two new MnIII–OOR complexes using a new amide-containing N5 ligand. Using the 2-(bis((6-methylpyridin-2-yl)methyl)amino)-N-(quinolin-8-yl)acetamide (H6Medpaq) ligand, we generated the [MnIII(OOtBu)(6Medpaq)]OTf and [MnIII(OOCm)(6Medpaq)]OTf complexes through reaction of their MnII or MnIII precursors with tBuOOH and CmOOH, respectively. Both of the new MnIII–OOR complexes are stable at room-temperature (t1/2 = 5 and 8 days, respectively, at 298 K in CH3CN) and capable of reacting directly with phosphine substrates. The stability of these MnIII–OOR adducts render them amenable for detailed characterization, including by X-ray crystallography for [MnIII(OOCm)(6Medpaq)]OTf. Thermal decomposition studies support a decay pathway of the MnIII–OOR complexes by O–O bond homolysis. In contrast, direct reaction of [MnIII(OOCm)(6Medpaq)]+ with PPh3 provided evidence of heterolytic cleavage of the O–O bond. These studies reveal that both the stability and chemical reactivity of MnIII–OOR complexes can be tuned by the local coordination sphere.

A pair of room-temperature-stable MnIII–alkylperoxo complexes were characterized and shown to oxidize PPh3. Thermal decomposition studies provide evidence of both homolysis and heterolysis of the MnIII–alkylperoxo O–O bond.  相似文献   

6.
A set of new triple molybdates, LixNa1-xCaGd0.5(MoO4)3:Ho3+0.05/Yb3+0.45, was successfully manufactured by the microwave-accompanied sol–gel-based process (MAS). Yellow molybdate phosphors LixNa1-xCaGd0.5(MoO4)3:Ho3+0.05/Yb3+0.45 with variation of the LixNa1-x (x = 0, 0.05, 0.1, 0.2, 0.3) ratio under constant doping amounts of Ho3+ = 0.05 and Yb3+ = 0.45 were obtained, and the effect of Li+ on their spectroscopic features was investigated. The crystal structures of LixNa1-xCaGd0.5(MoO4)3:Ho3+0.05/Yb3+0.45 (x = 0, 0.05, 0.1, 0.2, 0.3) at room temperature were determined in space group I41/a by Rietveld analysis. Pure NaCaGd0.5Ho0.05Yb0.45(MoO4)3 has a scheelite-type structure with cell parameters a = 5.2077 (2) and c = 11.3657 (5) Å, V = 308.24 (3) Å3, Z = 4. In Li-doped samples, big cation sites are occupied by a mixture of (Li,Na,Gd,Ho,Yb) ions, and this provides a linear cell volume decrease with increasing Li doping level. The evaluated upconversion (UC) behavior and Raman spectroscopic results of the phosphors are discussed in detail. Under excitation at 980 nm, the phosphors provide yellow color emission based on the 5S2/5F45I8 green emission and the 5F55I8 red emission. The incorporated Li+ ions gave rise to local symmetry distortion (LSD) around the cations in the substituted crystalline structure by the Ho3+ and Yb3+ ions, and they further affected the UC transition probabilities in triple molybdates LixNa1-xCaGd0.5(MoO4)3:Ho3+0.05/Yb3+0.45. The complex UC intensity dependence on the Li content is explained by the specificity of unit cell distortion in a disordered large ion system within the scheelite crystal structure. The Raman spectra of LixNa1-xCaGd0.5(MoO4)3 doped with Ho3+ and Yb3+ ions were totally superimposed with the luminescence signal of Ho3+ ions in the range of Mo–O stretching vibrations, and increasing the Li+ content resulted in a change in the Ho3+ multiplet intensity. The individual chromaticity points (ICP) for the LiNaCaGd(MoO4)3:Ho3+,Yb3+ phosphors correspond to the equal-energy point in the standard CIE (Commission Internationale de L’Eclairage) coordinates.  相似文献   

7.
A terminal FeIIIOH complex, [FeIII(L)(OH)]2− (1), has been synthesized and structurally characterized (H4L = 1,2-bis(2-hydroxy-2-methylpropanamido)benzene). The oxidation reaction of 1 with one equiv. of tris(4-bromophenyl)ammoniumyl hexachloroantimonate (TBAH) or ceric ammonium nitrate (CAN) in acetonitrile at −45 °C results in the formation of a FeIIIOH ligand radical complex, [FeIII(L˙)(OH)] (2), which is hereby characterized by UV-visible, 1H nuclear magnetic resonance, electron paramagnetic resonance, and X-ray absorption spectroscopy techniques. The reaction of 2 with a triphenylcarbon radical further gives triphenylmethanol and mimics the so-called oxygen rebound step of Cpd II of cytochrome P450. Furthermore, the reaction of 2 was explored with different 4-substituted-2,6-di-tert-butylphenols. Based on kinetic analysis, a hydrogen atom transfer (HAT) mechanism has been established. A pKa value of 19.3 and a BDFE value of 78.2 kcal/mol have been estimated for complex 2.

One-electron oxidation of an FeIII–OH complex (1) results in the formation of a FeIII–OH ligand radical complex (2). Its reaction with (C6H5)3C˙ results in the formation of (C6H5)3COH, which is a functional mimic of compound II of cytochrome P450.  相似文献   

8.
A new series of mononuclear Ho3+ complexes derived from the β-diketonate anions: 4,4,4-trifluoro-1-phenyl-1,3-butanedioneate (btfa) and 4,4,4-trifuoro-1-(naphthalen-2-yl)-1,3-butanedionate (ntfa) have been synthesized, [Ho(btfa)3(H2O)2] (1a), [Ho(ntfa)3(MeOH)2] (1b), (1), [Ho(btfa)3(phen)] (2), [Ho(btfa)3(bipy)] (3), [Ho(btfa)3(di-tbubipy)] (4), [Ho(ntfa)3(Me2bipy)] (5), and [Ho(ntfa)3(bipy)] (6), where phen is 1,10-phenantroline, bipy is 2,2′-bipyridyl, di-tbubipy is 4,4′-di-tert-butyl-2,2′-bipyridyl, and Me2bipy is 4,4′-dimethyl-2,2′-bipyridyl. These compounds have been characterized by elemental microanalysis and infrared spectroscopy as well as single-crystal X-ray difraction for 2–6. The central Ho3+ ions in these compounds display coordination number 8. The luminescence-emission properties of the pyridyl adducts 2–6 display a strong characteristic band in the visible region at 661 nm and a series of bands in the NIR region (excitation wavelengths (λex) of 367 nm for 2–4 and 380 nm for 5 and 6). The magnetic properties of the complexes revealed magnetically uncoupled Ho3+ compounds with no field-induced, single-molecule magnet (SMMs).  相似文献   

9.
Lanthanide metallocenophanes are an intriguing class of organometallic complexes that feature rare six-coordinate trigonal prismatic coordination environments of 4f elements with close intramolecular proximity to transition metal ions. Herein, we present a systematic study of the structural and magnetic properties of the ferrocenophanes, [LnFc3(THF)2Li2], of the late trivalent lanthanide ions (Ln = Gd (1), Ho (2), Er (3), Tm (4), Yb (5), Lu (6)). One major structural trend within this class of complexes is the increasing diferrocenyl (Fc2−) average twist angle with decreasing ionic radius (rion) of the central Ln ion, resulting in the largest average Fc2− twist angles for the Lu3+ compound 6. Such high sensitivity of the twist angle to changes in rion is unique to the here presented ferrocenophane complexes and likely due to the large trigonal plane separation enforced by the ligand (>3.2 Å). This geometry also allows the non-Kramers ion Ho3+ to exhibit slow magnetic relaxation in the absence of applied dc fields, rendering compound 2 a rare example of a Ho-based single-molecule magnet (SMM) with barriers to magnetization reversal (U) of 110–131 cm−1. In contrast, compounds featuring Ln ions with prolate electron density (3–5) don''t show slow magnetization dynamics under the same conditions. The observed trends in magnetic properties of 2–5 are supported by state-of-the-art ab initio calculations. Finally, the magneto-structural relationship of the trigonal prismatic Ho-[1]ferrocenophane motif was further investigated by axial ligand (THF in 2) exchange to yield [HoFc3(THF*)2Li2] (2-THF*) and [HoFc3(py)2Li2] (2-py) motifs. We find that larger average Fc2− twist angles (in 2-THF* and 2-py as compared to in 2) result in faster magnetic relaxation times at a given temperature.

Lanthanide ferrocenophanes are an intriguing class of organometallic complexes that feature rare six-coordinate trigonal prismatic coordination environments of 4f elements with close intramolecular proximity to iron ions.  相似文献   

10.
The isolable chelating bis(N-heterocyclic silylenyl)-substituted terphenyl ligand [SiII(Terp)SiII] as well as its bis(phosphine) analogue [PIII(Terp)PIII] have been synthesised and fully characterised. Their reaction with Ni(cod)2 (cod = cycloocta-1,5-diene) affords the corresponding 16 VE nickel(0) complexes with an intramolecular η2-arene coordination of Ni, [E(Terp)E]Ni(η2-arene) (E = PIII, SiII; arene = phenylene spacer). Due to a strong cooperativity of the Si and Ni sites in H2 activation and H atom transfer, [SiII(Terp)SiII]Ni(η2-arene) mediates very effectively and chemoselectively the homogeneously catalysed hydrogenation of olefins bearing functional groups at 1 bar H2 pressure and room temperature; in contrast, the bis(phosphine) analogous complex shows only poor activity. Catalytic and stoichiometric experiments revealed the important role of the η2-coordination of the Ni(0) site by the intramolecular phenylene with respect to the hydrogenation activity of [SiII(Terp)SiII]Ni(η2-arene). The mechanism has been established by kinetic measurements, including kinetic isotope effect (KIE) and Hammet-plot correlation. With this system, the currently highest performance of a homogeneous nickel-based hydrogenation catalyst of olefins (TON = 9800, TOF = 6800 h−1) could be realised.

The isolable chelating bis(N-heterocyclic silylenyl)-substituted terphenyl ligand [SiII(Terp)SiII] as well as its bis(phosphine) analogue [PIII(Terp)PIII] have been synthesised and fully characterised.  相似文献   

11.
Europium and terbium mixed-ligand complexes with cinnamic acid of composition Ln(Cin)3· nD · xH2O, where Ln = Eu3+or Tb3+, Cin is a cinnamate ion (C6H5CH=CHCOO), D = 1,10-phenantroline, 2,2"-dipyridyl, benzotriazole (n= 2, x= 0), triphenylphosphine oxide (n= 1, x= 2), or H2O (n= 0 or 1, x= 0), were synthesized. The compounds were characterized by elemental analysis, IR and luminescence spectroscopy. The Stark structure of the 5 D 07 F j(j= 0, 1, 2) electronic transitions in the low-temperature luminescence spectra of europium complexes was analyzed. IR study has revealed a bidentate coordination of the cinnamate ion in the compounds.  相似文献   

12.
The first use of methyl 2-pyridyl ketoxime (mepaoH) in homometallic lanthanide(III) [Ln(III)] chemistry is described. The 1:2 reactions of Ln(NO3)3·nH2O (Ln = Nd, Eu, Gd, Tb, Dy; n = 5, 6) and mepaoH in MeCN have provided access to complexes [Ln2(O2CMe)4(NO3)2(mepaoH)2] (Ln = Nd, 1; Ln = Eu, 2; Ln = Gd, 3; Ln = Tb, 4; Ln = Dy, 5); the acetato ligands derive from the LnIII—mediated hydrolysis of MeCN. The 1:1 and 1:2 reactions between Dy(O2CMe)3·4H2O and mepaoH in MeOH/MeCN led to the all-acetato complex [Dy2(O2CMe)6(mepaoH)2] (6). Treatment of 6 with one equivalent of HNO3 gave 5. The structures of 1, 5, and 6 were solved by single-crystal X-ray crystallography. Elemental analyses and IR spectroscopy provide strong evidence that 2–4 display similar structural characteristics with 1 and 5. The structures of 1–5 consist of dinuclear molecules in which the two LnIII centers are bridged by two bidentate bridging (η1:η1:μ2) and two chelating-bridging (η1:η2:μ2) acetate groups. The LnIII atoms are each chelated by a N,N’-bidentate mepaoH ligand and a near-symmetrical bidentate nitrato group. The molecular structure of 6 is similar to that of 5, the main difference being the presence of two chelating acetato groups in the former instead of the two chelating nitrato groups in the latter. The geometry of the 9-coordinate LnIII centers in 1, 5 and 6 can be best described as a muffin-type (MFF-9). The 3D lattices of the isomorphous 1 and 5 are built through H-bonding, π⋯π stacking and C-H⋯π interactions, while the 3D architecture of 6 is stabilized by H bonds. The IR spectra of the complexes are discussed in terms of the coordination modes of the organic and inorganic ligands involved. The Eu(III) complex 2 displays a red, metal-ion centered emission in the solid state; the TbIII atom in solid 4 emits light in the same region with the ligand. Magnetic susceptibility studies in the 2.0–300 K range reveal weak antiferromagnetic intramolecular GdIII…GdIII exchange interactions in 3; the J value is −0.09(1) cm−1 based on the spin Hamiltonian Ĥ = −J(ŜGd1·ŜGd2).  相似文献   

13.
Two novel complexes, (EnH2)1.5[HoIII(Ttha)] · 4.5H2O (I) (En = ethylenediamine and H6Ttha = triethylenetetramine-N,N,N′,N″,N?,N?-hexaacetic acid) and (EnH2)[HoIII(Egta)(H2O)]2 · 6H2O (II) (H4Egta = ethyleneglycol-bis(2-aminoethylether)-N,N,N′,N′-tetraacetic acid), were synthesized and their crystal structures were determined by single crystal X-ray diffraction techniques. Complex I has a nine-coordinate mononuclear structure with distorted tricapped trigonal prismatic conformation and crystallizes in the monoclinic crystal system with P2/n space group. The crystal data are as follows: a = 17.7541(18), b = 9.6810(10), c = 22.166(2) Å, β = 118.913(2)°, and V = 3335.0(6) Å3. Complex II has a mononuclear nine-coordinate structure with pseudo-monocapped square antiprismatic conformation and crystallizes in the monoclinic crystal system with P21/n space group. The crystal data are as follows: a = 12.978(8), b = 12.685(8), c = 14.905(9) Å, β = 105.333(7)°, and V = 2366(2) Å3. In I, there are two types of EnH 2 2+ anions. They connect to [HoIII(Ttha)]3? by hydrogen bonds leading to the formation of 3D pore structure along z axis. In II, EnH 2 2+ cation connects three adjacent [HoIII(Egta)(H2O)]? complex anions through hydrogen bonds, these hydrogen bonds lead to the formation of 2D network structure in [101] plane. The results showed that ligand structures play a crucial role in crystal and molecular structure of their complexes. In addition, the protonated (EnH 2 2+ ) cations conjugating to [HoIII(Ttha)]3? and [HoIII(Egta)(H2O)]? complex anions are reviewed, which act as an important beginning for study of Ho(III) complexes conjugating with other various amino and heterocyclic biomolecule.  相似文献   

14.
Homoleptic cerous complexes Ce[N(SiMe3)2]3, [Ce{OSi(OtBu)3}3]2 and [Ce{OSiiPr3}3]2 were employed as thermally robust, weakly nucleophilic precursors to assess their reactivity towards 1,4-quinones in non-aqueous solution. The strongly oxidizing quinones 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ) or tetrachloro-1,4-benzoquinone (Cl4BQ) readily form hydroquinolato-bridged ceric complexes of the composition [(CeIVL3)22-O2C6R4)]. Less oxidising quinones like 2,5-di-tert-butyl-1,4-benzoquinone (tBu2BQ) tend to engage in redox equilibria with the ceric hydroquinolato-bridged form being stable only in the solid state. Even less oxidising quinones such as tetramethyl-1,4-benzoquinone (Me4BQ) afford cerous semiquinolates of the type [(CeIIIL2(thf)2)(μ2-O2C6Me4)]2. All complexes were characterised by X-ray diffraction, 1H, 13C{1H} and 29Si NMR spectroscopy, DRIFT spectroscopy, UV-Vis spectroscopy and CV measurements. The species putatively formed during the electrochemical reduction of [CeIV{N(SiMe3)2}3]22-O2C6H4) could be mimicked by chemical reduction with CoIICp2 yielding [(CeIII{N(SiMe3)2}3)22-O2C6H4)][CoIIICp2]2.

Para-quinones reveal distinct reactivity towards homoleptic cerous silylamide and siloxide complexes depending on both their oxidizing power and the supporting ligand L.  相似文献   

15.
The oxidation of transition metals such as manganese and copper by dioxygen (O2) is of great interest to chemists and biochemists for fundamental and practical reasons. In this report, the O2 reactivities of 1:1 and 1:2 mixtures of [(TPP)MnII] (1; TPP: Tetraphenylporphyrin) and [(tmpa)CuI(MeCN)]+ (2; TMPA: Tris(2-pyridylmethyl)amine) in 2-methyltetrahydrofuran (MeTHF) are described. Variable-temperature (−110 °C to room temperature) absorption spectroscopic measurements support that, at low temperature, oxygenation of the (TPP)Mn/Cu mixtures leads to rapid formation of a cupric superoxo intermediate, [(tmpa)CuII(O2•–)]+ (3), independent of the presence of the manganese porphyrin complex (1). Complex 3 subsequently reacts with 1 to form a heterobinuclear μ-peroxo species, [(tmpa)CuII–(O22–)–MnIII(TPP)]+ (4; λmax = 443 nm), which thermally converts to a μ-oxo complex, [(tmpa)CuII–O–MnIII(TPP)]+ (5; λmax = 434 and 466 nm), confirmed by electrospray ionization mass spectrometry and nuclear magnetic resonance spectroscopy. In the 1:2 (TPP)Mn/Cu mixture, 4 is subsequently attacked by a second equivalent of 3, giving a bis-μ-peroxo species, i.e., [(tmpa)CuII−(O22−)−MnIV(TPP)−(O22−)−CuII(tmpa)]2+ (7; λmax = 420 nm and δpyrrolic = −44.90 ppm). The final decomposition product of the (TPP)Mn/Cu/O2 chemistry in MeTHF is [(TPP)MnIII(MeTHF)2]+ (6), whose X-ray structure is also presented and compared to literature analogs.  相似文献   

16.
A mixed-valent trinuclear complex with 1,3-bis(5-chlorosalicylideneamino)-2-propanol (H3clsalpr) was synthesized, and the crystal structure was determined by the single-crystal X-ray diffraction method at 90 K. The molecule is a trinuclear CoIII-CoII-CoIII complex with octahedral geometries, having a tetradentate chelate of the Schiff-base ligand, bridging acetate, monodentate acetate coordination to each terminal Co3+ ion and four bridging phenoxido-oxygen of two Schiff-base ligands, and two bridging acetate-oxygen atoms for the central Co2+ ion. The electronic spectral feature is consistent with the mixed valent CoIII-CoII-CoIII. Variable-temperature magnetic susceptibility data could be analyzed by consideration of the axial distortion of the central Co2+ ion with the parameters Δ = –254 cm−1, λ = –58 cm−1, κ = 0.93, tip = 0.00436 cm3 mol−1, θ = –0.469 K, gz = 6.90, and gx = 2.64, in accordance with a large anisotropy. The cyclic voltammogram showed an irreversible reduction wave at approximately −1.2 V·vs. Fc/Fc+, assignable to the reduction of the terminal Co3+ ions.  相似文献   

17.
Heme iron and nonheme dimanganese catalases protect biological systems against oxidative damage caused by hydrogen peroxide. Rubrerythrins are ferritine-like nonheme diiron proteins, which are structurally and mechanistically distinct from the heme-type catalase but similar to a dimanganese KatB enzyme. In order to gain more insight into the mechanism of this curious enzyme reaction, non-heme structural and functional models were carried out by the use of mononuclear [FeII(L1–4)(solvent)3](ClO4)2 (1–4) (L1 = 1,3-bis(2-pyridyl-imino)isoindoline, L2 = 1,3-bis(4′-methyl-2-pyridyl-imino)isoindoline, L3 = 1,3-bis(4′-Chloro-2-pyridyl-imino)isoindoline, L4 = 1,3-bis(5′-chloro-2-pyridyl-imino)isoindoline) complexes as catalysts, where the possible reactive intermediates, diiron-perroxo [FeIII2(μ-O)(μ-1,2-O2)(L1-L4)2(Solv)2]2+ (5–8) complexes are known and well-characterized. All the complexes displayed catalase-like activity, which provided clear evidence for the formation of diiron-peroxo species during the catalytic cycle. We also found that the fine-tuning of iron redox states is a critical issue, both the formation rate and the reactivity of the diiron-peroxo species showed linear correlation with the FeIII/FeII redox potentials. Their stability and reactivity towards H2O2 was also investigated and based on kinetic and mechanistic studies a plausible mechanism, including a rate-determining hydrogen atom transfer between the H2O2 and diiron-peroxo species, was proposed. The present results provide one of the first examples of a nonheme diiron-peroxo complex, which shows a catalase-like reaction.  相似文献   

18.
A series of four isostructural dodecanuclear complexes [MnIII9MnII2LnIII(O)8(OH)(piv)16(NO3)(CH3CN)]·xCH3CN·yC7H16 (piv = pivalate; x = ½, y = ¾, Ln = Tb (1); x = 2, y = ½, Ln = Dy (2), Ho (3), and Y (4)) has been prepared for which the structural motif described as ‘a lanthanide ion nested in a large manganese shell’ is observed. All compounds show out-of-phase signals in their ac susceptibilities, and their single-molecule magnet behaviour was confirmed by single-crystal micro-SQUID studies of 1-3 which show hysteresis loops of molecular origin at T < 1.0 K. The SMM behaviour observed in compounds 1-3 is more pronounced than that for 4, which contains the diamagnetic YIII ion. This is principally the result of ferromagnetic coupling between the paramagnetic anisotropic LnIII ions (TbIII, DyIII and HoIII) and the manganese shell, which enhances the total spin ground state of the complexes.  相似文献   

19.
225Ac-based radiopharmaceuticals have the potential to become invaluable in designated cancer therapy. However, the limited understanding of the solution chemistry and bonding properties of actinium has hindered the development of existing and emerging targeted radiotherapeutics, which also poses a significant challenge in the discovery of new agents. Herein, we report the geometric and electronic structural properties of hydrated AcIII cations in the [AcIII(H2O)n]3+ (n = 4–11) complexes in aqueous solution and gas-phase using density functional theory. We found that nine water molecules coordinated to the AcIII cation is the most stable complex due to an enhanced hydration Gibbs free energy. This complex adopts a closed-shell 18-electron configuration (1S21P61D10) of a superatom state, which indicates a non-negligible covalent character and involves H2O → AcIII σ donation interaction between s-/p-/d-type atomic orbitals of the Ac atom and 2p atomic orbitals of the O atoms. Furthermore, potentially existing 10-coordinated complexes need to overcome an energy barrier (>0.10 eV) caused by hydrogen bonding to convert to 9-coordination. These results imply the importance of superatom states in actinide chemistry generally, and specifically in AcIII solution chemistry, and highlight the conversion mechanism between different coordination numbers.

The stable 9-coordinated complex adopts a closed-shell 18-electron configuration of a 1S21P61D10 jellium state, while potential 10-coordinated complexes need to overcome an energy barrier (>0.10 eV) caused by hydrogen bonding to convert to 9-coordination.  相似文献   

20.
The use of radical bridging ligands to facilitate strong magnetic exchange between paramagnetic metal centers represents a key step toward the realization of single-molecule magnets with high operating temperatures. Moreover, bridging ligands that allow the incorporation of high-anisotropy metal ions are particularly advantageous. Toward these ends, we report the synthesis and detailed characterization of the dinuclear hydroquinone-bridged complexes [(Me6tren)2MII2(C6H4O22−)]2+ (Me6tren = tris(2-dimethylaminoethyl)amine; M = Fe, Co, Ni) and their one-electron-oxidized, semiquinone-bridged analogues [(Me6tren)2MII2(C6H4O2˙)]3+. Single-crystal X-ray diffraction shows that the Me6tren ligand restrains the metal centers in a trigonal bipyramidal geometry, and coordination of the bridging hydro- or semiquinone ligand results in a parallel alignment of the three-fold axes. We quantify the p-benzosemiquinone–transition metal magnetic exchange coupling for the first time and find that the nickel(ii) complex exhibits a substantial J < −600 cm−1, resulting in a well-isolated S = 3/2 ground state even as high as 300 K. The iron and cobalt complexes feature metal–semiquinone exchange constants of J = −144(1) and −252(2) cm−1, respectively, which are substantially larger in magnitude than those reported for related bis(bidentate) semiquinoid complexes. Finally, the semiquinone-bridged cobalt and nickel complexes exhibit field-induced slow magnetic relaxation, with relaxation barriers of Ueff = 22 and 46 cm−1, respectively. Remarkably, the Orbach relaxation observed for the Ni complex is in stark contrast to the fast processes that dominate relaxation in related mononuclear NiII complexes, thus demonstrating that strong magnetic coupling can engender slow magnetic relaxation.

A semiquinone radical bridging two trigonal bipyramidal metal centers facilitates strong magnetic exchange and single-molecule magnet behavior.  相似文献   

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