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1.
《Polyhedron》2007,26(9-11):2325-2329
The precursors [Fe(III)(5XL)Cl] (5XLH2 = N,N′-bis(1-hydroxy-2-benzyliden)-1,6-diamino-3-X-hexane, X = N,S) are high-spin (S = 5/2) complexes. This precursors are combined with the bridging unit [(NC)5Fe(II)-CN-Co(III)(CN)5]6− to yield star-shaped dodecanuclear clusters, [(5XLFe(III)-NC)5Fe(II)-CN-Co(III)(CN-Fe(III)5XL)5]Cl4. The star-shaped compounds are high-spin systems at room temperature. On cooling to 20 K some of the iron(III) centers in the N-star switch to the low-spin state as proven by Mössbauer spectroscopy, i.e. multiple electronic transitions, while the S-star remains in the high-spin state.  相似文献   

2.
The precursor [FeIII(L)Cl] (LH2 = N,N′-bis(2′-hydroxy-benzyliden)-1,6-diamino-3-azahexane) has been prepared and Mössbauer spectroscopy assigned a high-spin (S = 5/2) state at room temperature. The precursor is combined with the bridging units [SbV(X)6]? (X = CN?, NCS?) to yield star-shaped heptanuclear clusters [(LFeIII–X)6SbV]Cl5. The star-shaped compounds are in general high-spin systems at room temperature. On cooling to 20 K some of the iron(III) centers switch to the low-spin state as indicated by Mössbauer spectroscopy, i.e. multiple electronic transitions. While the cyano-bridged complex performs a multiple spin transition the thiocyanate-compound shows no significant population at both temperatures.  相似文献   

3.
F. Renz  St. Jung  M. Klein  M. Menzel  A.F. Thünemann 《Polyhedron》2009,28(9-10):1818-1821
The precursor [FeIII(L)Cl] (LH2 = N,N′-bis(2′-hydroxy-benzyliden)-1,6-diamino-3-N-hexane is a high-spin (S = 5/2) complex. This precursor is combined with the bridging units [SnIV(X)4] (X = CN?, NCS?) to yield star-shaped pentanuclear clusters, [(LFeIII–X)4Sn]Cl4. For X = CN? the 57Fe-Mössbauer data show a multiple spin transition between iron(III) in the high-spin and low-spin state, while the 119mSn-Mössbauer data indicate a valence tautomerism between Sn(IV) and Sn(II). Changing the bridging unit from X = CN? to X = NCS? turns the switchability off.  相似文献   

4.
Spectral and molecular model computations on homo-dinuclear complexes [M2L2(H2O)2Cl2] [L = 1-(salicylaldeneamino)-3-hydroxypropane, M = Cr3+, Mn3+, Fe3+, Co3+, Ni3+ or Cu3+] are consistent with a distorted hexa-coordinate geometry. X-band EPR spectral data indicated a rhombic distortion around Cu(II) ion. Magnetic moment and 57Fe Mössbauer data confirmed a high-spin state electronic configuration (t2g3eg2, S = 5/2) and asymmetric ligand environment around Fe(III) with nuclear transitions Fe(±3/2  1/2) exhibiting Kramer's double degeneracy. The neighboring Fe(III) nuclei in the homo-dinuclear species are antiferromagnetically coupled.  相似文献   

5.
Novel films consist of multi-walled carbon nanotubes (MWCNT) were fabricated by means of catalytic chemical vapor deposition (CVD) technique with decomposition of either acetonitrile (ACN) or benzene (BZ) using ferrocene (FeCp2) as catalyst. The electrochemical and thermodynamic behavior of the ferrocyanide/ferricyanide, [Fe(CN)6]3−/4− redox couple on synthesized MWCNT-based films was investigated by means of cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) techniques at T = (278.15, 283.15, 293.15, and 303.15) K. The redox couple [Fe(CN)6]3−/4− behaves quasi-reversibly on fabricated MWCNT-based films and its reversibility is enhanced upon increasing temperature. Namely, the findings establish that with the rise in temperature the barrier for interfacial electron transfer decreases, leading, consequently, to an enhancement of the kinetics of the charge transfer process. According to thermodynamics the equilibrium of the redox process is shifted towards the formation of [Fe(CN)6]3− at elevated temperatures.  相似文献   

6.
The complexes with long alkyl chains {[Fe(C16-trz)3](ClO4)2}n (1), [Fe(C15-BPT)2(NCS)2] (2), [Fe(C16-salen)Cl] (3), [Fe(C16-salmmen)Cl] (4), K[Fe(C16-salen)(CN)2] (5), K[Fe(C16-salmmen)(CN)2] (6), Na[Fe(C16-salmmen)(CN)2] (7), [Mn(C16-salen)Cl] (8), [Ni(C16-salen)] (9), [Cu(C16-salen)] (10) were synthesized (C16-trz = 4-hexadecyl-1,2,4-triazole, C15-BPT = N-(3,5-di-2-pyridinyl-4H-1,2,4-triazol-4-yl)-hexadecanecarboxamide, C16-salen = N,N-bis[4-(hexadecyloxy)salicylidene]ethylenediamine, C16-salmmen = N,N′-bis[4-(hexadecyloxy)salicylidene]-1,2-diaminopropane). Langmuir–Blodgett (LB) films of compounds 110 were prepared (Scheme 1). The transfers of the molecules from onto the gas–water surface to glass substrate were confirmed by UV–Vis spectra. The second harmonic generation (SHG) were estimated for the LB films formed by the metal complexes. The SHG was observed for the complexes with the long alkyl chains in LB film. The order of the intensity for the SHG related with the number of unpaired d electrons or the d electron configurations.  相似文献   

7.
The precursor [FeIII(L)Cl (L = N,N′-bis(2′-hydroxy-3′-methyl-benzyliden)-1,7-diamino-4-azaheptane) is combined with [Mo(CN)8]4? yields a star shaped nona-nuclear cluster, [MoIV{(CN)FeIII(L)}8]Cl4. This Fe8Mo molecule is a high-spin system at room temperature. On cooling to 20 K some of the iron(III) centres in the molybdenum(IV)-star switch to the low-spin state as proven by Mössbauer spectroscopy. This molecule was deposited on TiO2 nanowires by electrostatic interactions between the cluster cations and the surface functionalized titanium oxide nanowire. The synthesis and surface binding of the multistable molecular switch was demonstrated using IR and UV–Vis spectroscopy (high-resolution) transmission electron microscopy ((HR)TEM) and Mössbauer spectroscopy. High- and low-temperature Mössbauer spectra indicate that the spin state transition of the free cluster molecules is preserved after surface binding. The above results emphasize the possibility of fabricating molecule-based low-dimensional structures by using traditional bottom-up approaches based on the electrostatic interaction between the cluster cations and polymer functionalized nanowires. These results can be generalized for the application to both charged and non-charged molecules.  相似文献   

8.
A new molecule-based magnetic material [Mn2(Saloph)2(μ-OH)][Ni(bdt)2](CH3CN)2 was prepared by the metathesis of [Mn(Saloph)(H2O)(ClO4)] (S = 2) and TBA[Ni(bdt)2] (S = 1/2). In the crystal, [Ni(bdt)2]? anions form square lattices which are separated from each other by the layers of antiferromagnetically coupled binuclear cations [Mn2(Saloph)2(μ-OH)]+. The magnetic susceptibility of the material coincides with the sum of the S = 2 van Vleck dimer model and S = 1/2 Heisenberg ferromagnetic square lattice model with 2J = ?92.4 and +4.5 K, respectively. The origin of the ferromagnetic interaction can be explained by the T-shaped intermolecular overlap mode of SOMOs which spreads to the ends of [Ni(bdt)2]? molecules.  相似文献   

9.
The newly prepared homo-bimetallic complexes [M2(imda)2(H2O)4], [M2(imda)2(Bipy)2] (M = Co, Ni or Cu) and [Fe2(imda)2(H2O)3Cl] (H2imda = iminodiacetic acid and Bipy = 2,2′-bipyridine) have been studied employing IR, FAB-mass, 1H and 13C NMR, EPR and ligand field spectra, which indicated a high-spin state of metal ion with hexa-coordinate environment. 57Fe Mössbauer data of the homo-bimetallic complex [Fe2(imda)2(H2O)3Cl] confirm a high-spin configuration with Fe (±3/2  1/2) nuclear transitions and the presence of Kramer's double degeneracy. At RT, the spin–spin interactions of the neighbouring nuclei (Fe3+–Fe3+ = S5/2–S5/2) are anti-ferromagnetically coupled. However, at LNT, the complex acquires a mixed-valent [FeIII–FeII] composition corroborated from the X-band EPR data. CV studies indicated the presence of quasi-reversible redox CuII/I, CuII/III, FeIII/II, FeIII/I and FeII/I couples.  相似文献   

10.
《Polyhedron》2007,26(9-11):2291-2298
The reaction of [NEt4]3[Cr(CN)6] with titanium(III) p-toluenesulfonate at a pH of 2 affords a gray solid whose metal content and spectroscopic and magnetic properties are fully consistent with it being a Prussian blue material of stoichiometry “TiIII[CrIII(CN)6] · H2O”. The carbon, nitrogen, and hydrogen content, however, are not consistent with this stoichiometry, and further investigation showed that the gray material has a powder X-ray diffraction profile, infrared spectrum, and magnetic properties very similar to those of the “all-chromium” Prussian blue CrII[CrIII(CN)6]0.67 · 6H2O. All data, including the C, H, and N weight percentages, are consistent with the conclusion that the material isolated is a nanocomposite of CrII[CrIII(CN)6]0.67 · xH2O and TiO2 in the ratio of 1–1.6. These results suggest that TiIII reduces some of the [CrIII(CN)6]3− ions to generate TiIV and CrII; the former hydrolyzes to amorphous TiO2 · 2H2O, the latter loses its bound CN ligands and reacts with unreacted [CrIII(CN)6]3− ions to generate the crystalline all-chromium PB species. The electrochemical potentials suggest that the [CrIII(CN)6]3− ion should not be reduced by TiIII; evidently, this unfavorable reaction is driven by the insolubility of the reaction products. The results constitute a cautionary tale in two respects: first, that the characterization of Prussian blue materials must be conducted with care and, second, that the insolubility of Prussian blue analogues can sometimes drive reactions that in solution are thermodynamically unfavorable.  相似文献   

11.
《Polyhedron》2005,24(16-17):2165-2172
Five new hydrogen-bonded solvated iron(II) complexes of pyrazolyl- and imidazolyl-based N,N-chelating ligands have been synthesised. Water to ligand-NH hydrogen-bonded bridges occur in the pseudo-dimeric complexes {cis-[Fe(pypzH)2(NCX)2]2(μ-OH2)(H2O)2} · H2O · MeOH (where X = S or Se), and in the chain complex {cis-[Fe(pypzH)2(NCS)2](μ-OH2)}n. A “half” spin-crossover (Tc = 125 K) was observed in the dimeric X = Se complex by means of magnetic measurements and no thermal hysteresis occurred between 4 and 300 K. The crystal structure at 123 K showed Fe–N distances consistent with the magnetism. Each Fe in the dimeric unit was structurally equivalent in the HS–LS state. Removal of the solvate molecules led to HS–HS behaviour over the temperature range 4–300 K. The pseudo-dimer with X = S also showed HS–HS behaviour as did the monomeric analogue cis-[Fe(pypzH)2(NCS)2]H2O and a structurally different methanol-bridged dimer {cis-[Fe(pyimH)2(NCS)2]2(μ-MeOH)2} · 2MeOH (pypzH = 2-(1H-pyrazol-3-yl)-pyridine; pyimH = 2-(1H-imidazol-2-yl)-pyridine).  相似文献   

12.
《Polyhedron》2007,26(9-11):2189-2199
In order to study the templating effect of the cation and the resulting impact on the magnetic properties, reactions of M(II) salts with [cation][Au(CN)2] were conducted, yielding a series of coordination polymers of the form [cation]{M[Au(CN)2]3} (cation = nBu4N+, PPN+ (bis(triphenylphosphoranylidene)ammonium); M = Ni(II) and Co(II)). The structures of nBu4N{M[Au(CN)2]3} and PPN{M[Au(CN)2]3} (M = Ni and Co) contain two distinct 3-D anionic frameworks of {M[Au(CN)2]3}, hence the framework was sensitive to the cation, but not to the identity of the metal center. In nBu4N{M[Au(CN)2]3}, the metal centers are connected by [Au(CN)2] units to form six 2-D (4, 4) rectangular grids that are fused through the M centers to yield a complex three-dimensional framework which accommodates the nBu4N+ cations. In PPN{M[Au(CN)2]3}, the framework adopts a simpler non-interpenetrated Prussian-blue-type pseudo-cubic array, with the PPN+ cations occupying each cavity; no reduction in dimensionality occurs despite the large cation size. In the presence of water, {Co(H2O)2[Au(CN)2]2} · nBu4N[Au(CN)2] was obtained, a 2-D layered polymer that contains neutral sheets of {Co(H2O)2[Au(CN)2]2} which are separated by nBu4N[Au(CN)2] layers; aurophilic interactions of 3.4250(13) Å and hydrogen-bonding connect the layers. The magnetic properties of all compounds were investigated by SQUID magnetometry. The Ni(II) polymers have similar magnetic behaviour, which are dominated by zero-field splitting with very weak antiferromagnetic interactions at low temperature (D  2–3 cm−1, zJ < 1 cm−1). The magnetic behaviour of all of the Co(II) polymers were found to be very similar, and dominated by single-ion effects (i.e. a large first-order orbital contribution). No significant magnetic coupling is observed in any of these coordination polymers, suggesting that the [Au(CN)2] bridging unit behaves as a poor mediator of magnetic exchange in these high-dimensionality systems.  相似文献   

13.
《Polyhedron》2007,26(9-11):1984-1988
Two π-radicals, 3-pyridinyl-phenylanthracene(iminonitroxide) (3) and 3-pyridinyl-phenylanthracene-(nitronylnitroxide) (4) were designed as candidates of the ligand for the metal complexes to clarify the exchange interactions between the paramagnetic centers of the metal ions and the photo-excited high-spin states of the purely organic π-radical. Compounds 3 and 4 were synthesized and their magnetic properties were examined, showing weak antiferromagnetic interactions, θ = −1.5 K for 3 and −0.7 K for 4. The photo-excited states of 3 and 4 were investigated by time-resolved ESR and clarified that both π-radicals have the quartet (S = 3/2) high-spin states as their lowest photo-excited states. Two metal complexes [Fe(III)(L)(4)] · (BPh4) (Low spin) (LH2 = N,N′-bis(1-hydroxy-2-benzyliden)-1,7-diamino-4-azaheptane) and [Cu(II)(hfac)2(4)2] using 4 were prepared. Their magnetic behaviors are well analyzed with the Bleaney–Bowers model with J/kB =  0.86 K and three S = 1/2 spin cluster model with J/kB = −1.0 K, respectively, showing weak antiferromagnetic interactions between the paramagnetic centers of the metal ions and the π-radical in the ground state.  相似文献   

14.
《Polyhedron》2005,24(16-17):2437-2442
The synthesis and magnetic characterization of pyrazolato-bridged dinuclear complexes [{M(NCS)(4-Phpy)}2(μ-bpypz)2] (Hbpypz = 3,5-bis(2-pyridyl)-pyrazole; 4-Phpy = 4-phenylpyridine; M = Co2+ (1) and Fe2+ (2)) are described together with the X-ray crystal analysis of the cobalt complex. The structure of 1 shows that the desired coordination has been achieved with the cobalt atoms being coordinated to two bpypz to form the dimer. The X-ray diffraction patterns show 1 and 2 to be isomorphous at room temperature. 2 displays a single spin-crossover transition between the [HS–HS] and [LS–LS] states with Tc = 150 K.  相似文献   

15.
New Schiff base (H2L) ligand is prepared via condensation of o-phthaldehyde and 2-aminobenzoic acid in 1:2 ratio. Metal complexes are prepared and characterized using elemental analyses, IR, solid reflectance, magnetic moment, molar conductance, 1H NMR, ESR and thermal analysis (TGA). From the elemental analyses data, the complexes were proposed to have the general formulae [MCl(L)(H2O)]·2H2O (where M = Cr(III) and Fe(III)); [M(L)]·yH2O (where M = Mn(II), Ni(II), Cu(II) and Zn(II), y = 1–2) and [M(L)(H2O)nyH2O (where M = Co(II) (n = y = 2), Co(II) (n = y = 1), Ni(II) (n = 2, y = 1). The molar conductance data reveal that all the metal chelates were non-electrolytes. IR spectra show that H2L is coordinated to the metal ions in a bi-negative tetradentate manner with NOON donor sites of the azomethine-N and carboxylate-O. The 1H NMR spectral data indicate that the two carboxylate protons are also displaced during complexation. From the magnetic and solid reflectance spectra, it was found that the geometrical structure of these complexes are octahedral (Cr(III), Fe(III), Co(II) and Ni(II)), square planar (Cu(II)), trigonal bipyramidal (Co(II)) and tetrahedral (Mn(II), Ni(II) and Zn(II)). The thermal behaviour of these chelates showed that the hydrated complexes losses water molecules of hydration in the first step followed immediately by decomposition of the ligand molecule in the subsequent steps. The biological activity data show that the metal complexes to be more potent/antibacterial than the parent Shciff base ligand against one or more bacterial species.  相似文献   

16.
The electrochemical measurements were carried out by using thermophilic cytochrome P450 CYP119A2 (P450st) modified with poly(ethylene oxide) (PEO) in PEO200 as an electrochemical solvent. The PEO modified P450st gave clear reduction–oxidation peaks by cyclic voltammetry in oxygen-free PEO200 up to 120 °C. The midpoint potential measured for the P450st was −120 mV vs. [Fe(CN)6]4−/[Fe(CN)6]3− at 120 °C. The peak separation, ΔE, was 16 mV at 100 mV/s. The estimated electron transfer rate of PEO-P450st at 120 °C was 35.1 s−1. The faster electron transfer reaction was achieved at higher temperatures. The electrochemical reduction of dioxygen was observed at 115 °C with the PEO-modified P450st system.  相似文献   

17.
A novel Fe(III) spin-crossover complex, [Fe(qsal)2][Ni(dmise)2] · 2CH3CN 1 [qsalH = N-(8-quinolyl)-salicylaldimine, dmise = 4,5-dithiolato-1,3-dithiole-2-selone] was prepared. The magnetic susceptibility measurements revealed 1 exhibited a cooperative spin transition with a thermal hysteresis loop of 15 K. The high and the low temperature structures of 1 indicated three-dimensional intermolecular π?π interactions play a key role in the cooperative spin transition, accompanying a reversible molecular slipping of π-dimer of Ni(dmise)2 along the molecular long axis. The transfer integral calculation for 1 suggested the π-dimer of Ni(dmise)2 is in the spin singlet state.  相似文献   

18.
The light-induced spin and structure changes upon excitation of the singlet metal-to-ligand charge transfer (1MLCT) state of Fe(II)-polypyridine complexes are investigated in detail in the case of aqueous iron(II)-tris-bipyridine ([FeII(bpy)3]2+) by a combination of ultrafast optical and X-ray spectroscopies. Polychromatic femtosecond fluorescence up-conversion, transient absorption studies in the 290–600 nm region and femtosecond X-ray absorption spectroscopy allow us to retrieve the entire photocycle upon excitation of the 1MLCT state from the singlet low-spin ground state (1GS) as the following sequence: 1,3MLCT  5T  1GS, which does not involve intermediate singlet and triplet ligand-field states. The population time of the HS state is found to be ~150 fs, leaving it in a vibrationally hot state that relaxes in 2–3 ps, before decaying to the ground state in 650 ps. We also determine the structure of the high-spin quintet excited state by picosecond X-ray absorption spectroscopy at the K-edge of Fe. We argue that given the many common electronic (ordering of electronic states) and structural (Fe–N bond elongation in the high-spin state, Fe–N mode frequencies, etc.) similarities between all Fe(II)-polypyridine complexes, the results on the electronic relaxation processes reported in the case of [FeII(bpy)3]2+ are of general validity to the entire family of Fe(II)-polypyridine complexes.  相似文献   

19.
《Polyhedron》2007,26(9-11):1764-1772
Variable temperature magnetic susceptibility, Mössbauer spectroscopic and X-ray crystallographic studies are described on two structurally similar families of dinuclear iron(II) spin crossover (SCO) complexes of formula [Fe(NCX)(py)]2(μ-L)2, where L is either a 3,5-bis(2-pyridyl)-pyrazolate bridging ligand, bpypz, examples of which have been earlier reported by Kaizaki and coworkers, or a corresponding 3,5-bis(2-pyridyl)-1,2,4-triazolate, bpytz. Compounds synthesised were [Fe(NCS)(py)]2(μ-bpypz)2 (1), [Fe(NCSe)(py)]2(μ-bpypz)2 (2), [Fe(NCS)(py)]2(μ-bpytz)2 (3), [Fe(NCSe)(py)]2(μ-bpytz)2 (4), [Fe(NCBH3)(py)]2(μ-bpytz)2 (5). The crystal and molecular structures of 1 and 3 are very similar in their HS–HS forms (HS = high spin d6). In contrast to reported SCO behaviour for precipitated samples of 1, also repeated here, crystals of 1 show only HS–HS behaviour with no spin crossover transition. Complex 3 likewise displays HS–HS magnetism, with very weak antiferromagnetic coupling. Compound 5 displays a well resolved two-step, full spin transition from HS–HS to LS–LS states while compound 2 shows a one step transition. The Mössbauer data for 2 and 5 show unusual features at low temperatures.  相似文献   

20.
The reaction of [Cp1IrCl2]2 (Cp* = η5  C5Me5) with the tridentate 3-thiapentane-1,5-dithiolate ligand, S(CH2CH2S)2 (tpdt), led to the formation of [Cp1Ir(η3  tpdt)] (1) in 81% isolated yield. Subsequent reactions of 1 with [Cp1IrCl2]2 in 2:1 and 1:1 molar equiv ratios resulted in the formation of [Cp1Ir(μ  η2:η3  tpdt)Cp1IrCl][PF6] (2) and [Cp1Irμ  η2:η3  tpdt)Cp1IrCl][Cp1IrCl3] (3) in 86 and 79% yields, respectively, based on 1, whereas the reactions of 1 with [(COD)IrCl]2 (COD = 1,5-cyclooctadiene) in 2:1 and 1:1 molar equiv ratios resulted in the formation of the homo-bimetallic derivatives Cp1Ir(μ  η1:η3  tpdt)(COD)IrCl (4) (92% yield) and [Cp1Ir(μ  η2:η3  tpdt)(COD)Ir] [(COD)IrCl2] (5) (82% yield). Reactions between 1 and [(COD)RhCl]2, yielded the hetero-bimetallic derivatives Cp1Ir(μ  η1:η3  tpdt)(COD)RhCl (6) and [Cp1Ir(μ  η2:η3  tpdt)(COD)Rh][(COD)RhCl2] (7), in 92 and 93% yields, respectively. The reaction of 1 with methyl iodide gave mono-methylated derivative [Cp1Ir(η3-C4H8S3Me)]I (8) (93% yield). All these compounds have been comprehensively characterized.  相似文献   

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