共查询到20条相似文献,搜索用时 45 毫秒
1.
Two tetracyanometalate building blocks, [Fe(5,5′-dmbipy)(CN)4]? (2) and [Fe(4,4′-dmbipy)(CN)4]? (3) (5,5′-dmbipy = 5,5′-dimethyl-2,2′-bipyridine; 4,4′-dmbipy = 4,4′-dimethyl-2,2′-bipyridine), and two cyano-bridged heterobimetallic complexes, [Cu2(bpca)2(H2O)2Fe2(5,5′-dmbipy)2(CN)8] · 2[Cu(bpca)Fe(5,5′-dmbipy)(CN)4] · 4H2O (4) and [Cu(bpca)Fe(4,4′-dmbipy)(CN)4]n (5) (bpca = bis(2-pyridylcarbonyl)amidate), have been synthesized and structurally characterized. Complex 4 contains two dinuclear and one tetranuclear heterobimetallic clusters in an asymmetric unit whereas the structure of complex 5 features a one-dimensional heterobimetallic zigzag chain. The Cu(II) ion is penta-coordinated in the form of a distorted square-based pyramid. Magnetic studies show ferromagnetic coupling between Cu(II) and Fe(III) ions with g = 2.28, J1 = 2.64 cm?1, J2 = 5.40 cm?1 and TIP = ?2.36 × 10?3 for complex 4, and g = 2.17, J = 4.82 cm?1 and zJ′ = 0.029 cm?1 for complex 5. 相似文献
2.
《Inorganica chimica acta》2006,359(5):1351-1356
Energy-transfer rate-constants from photo-excited [Ru(N–N)3]2+ (N–N = 2,2′-bipyridine (bpy), 4,4′-dimethyl-2,2′-bipyridine (4dmb), 5,5′-dimethyl-2,2′-bipyridine (5dmb)) to [Cr(O–O)3]3− (O–O2− = ox2− ((COO−)2), mal2− (CH2(COO−)2)) and [Cr(CN)6]3− in encounter complexes were evaluated in aqueous solutions containing alkali metal ion. The rate constant depends on the molecular size of the ruthenium(II) complex: 1.8 × 108 s−1 for [Ru(bpy)3]2+ (molecular radius, r = 5.8 Å), 1.4 × 108 s−1 for [Ru(5dmb)3]2+ (r = 6.1 Å) and 0.96 × 108 s−1 for [Ru(4dmb)3]2+ (r = 6.7 Å) in the system of [Ru(N–N)3]2+–[Cr(ox)3]3− in aqueous solution. However, the rate constant is much more sensitive to the chromate(III) complex than to ruthenium(II) complex; 1.8 × 108 s−1 and 0.43 × 108 s−1 for [Cr(ox)3]3− (r = 4.0 Å) and [Cr(mal)3]3− (r = 4.2 Å) in the [Ru(bpy)3]2+–[Cr(O–O)3]3− systems, respectively. We conclude that the congeniality between the donor’s and acceptor’s ligands in encounter complex plays an important role in energy transfer in aqueous solution. 相似文献
3.
Jonathon E. Beves David J. Bray Jack K. Clegg Edwin C. Constable Catherine E. Housecroft Katrina A. Jolliffe Cameron J. Kepert Leonard F. Lindoy Markus Neuburger David J. Price Silvia Schaffner Frank Schaper 《Inorganica chimica acta》2008,361(9-10):2582-2590
The solid state structures of [Ni(1)2][NO3]2 · 2MeOH · 2H2O, [Fe(1)2][ClO4]2 · 2MeOH · 0.5H2O, [Ru(1)2][PF6]2 and [Ru(1)2][PF6][NO3] (1 = 4′-(4-pyridyl)-2,2′:6′,2″-terpyridine) are presented and the structural variation observed for the {M(1)2}2+ unit is discussed. Protonation of the pendant pyridine group in [Ru(1)2]2+ leads to the formation of a hydrogen-bonded, one-dimensional polymer [{Ru(1)(H1)}n]3n+ exemplifed by the solid-state structure of [{Ru(1)(H1)}{Fe(NCS)6} · 1.25H2O]n. 相似文献
4.
Iis Siti Jahro Djulia Onggo Susanto Imam Rahayu M. Carmen Muñoz Ana B. Gaspar Maksym Seredyuk Philipp Gütlich José Antonio Real 《Inorganica chimica acta》2008,361(14-15):4047-4054
Three new compounds formulated (ClO4)2[Fe(pq)3] (1), (BF4)2[Fe(pq)3] · EtOH (2) and {(ClO4)[MnCr(C2O4)3][Fe(pq)2(H2O)2]} (3), where pq is 2,2′-pyridylquinoline, have been synthesised and characterised. Despite the different crystal packing exhibited by 1 and 2, the cationic species [Fe(pq)3]2+ are structurally quite similar. At 293 K, the Fe–N bond lengths are characteristic of the iron(II) in the high-spin state. In contrast to 1, 2 undergoes a continuous spin transition. Indeed, at 95 K its structure experiences a noticeable change in the Fe–N bonds and angles, i.e. the Fe–N bonds shorten by 0.194 Å on the average. The magnetic behaviour confirms that 1 is fully high-spin in the 4–300 K temperature range while 2 shows a spin transition centred at T1/2 = 150 K. The corresponding enthalpy, entropy and interaction parameter are ΔH = 7.49 kJ mol?1, ΔS = 50 J K?1 mol?1and Γ = 1.35 kJ mol?1. Compound 3 has been obtained as a microcrystalline powder. The magnetic properties of 3 point at the occurrence of ferromagnetic coupling below 100 K and the onset of a ferromagnetic ordering below 10 K (Weiss constant equal to 6.8 K). The Mössbauer spectra of 3 show the occurrence of a magnetic order at T ? 4.2 K. 相似文献
5.
Roland J.W. Meesters Robert R. Wolfe Nicolaas E.P. Deutz 《Journal of chromatography. B, Analytical technologies in the biomedical and life sciences》2009,877(1-2):43-49
Whole-body protein synthesis and breakdown are measured by a combined tracer infusion protocol with the stable isotope amino acids l-[ring-2H5]-phenylalanine, l-[ring-2H2]-tyrosine and l-[ring-2H4]-tyrosine that enable the measurement of the phenylalanine to tyrosine conversion rate. We describe a liquid chromatography–tandem mass spectrometry (LC–MS/MS) method for the measurement of very low tracer–tracee ratios (TTR) of the amino acids l-phenylalanine and l-tyrosine in human plasma. TTR calibration curves of the tracers l-[ring-2H5]-phenylalanine, l-[ring-2H2]-tyrosine and l-[ring-2H4]-tyrosine were linear (r2 > 0.99) in the range between 0.01% and 5.0% TTR and lowest measurable TTR for the tracers was 0.01% at a physiological concentration of 60 μM. The method was applied successfully to plasma samples from a clinical study reaching a steady state enrichment plateau (mean ± SD) of 3.33 ± 0.19% for l-[ring-2H5]-phenylalanine, 2.40 ± 0.43% for l-[ring-2H2]-tyrosine and 0.29 ± 0.07% for l-[ring-2H4]-tyrosine, respectively. The LC–MS/MS method can be applied for measurement of very low plasma enrichments of phenylalanine and tyrosine for the determination of whole-body protein synthesis and breakdown rates in humans. 相似文献
6.
Ricardo González Natalia Barboza Raúl Chiozzone Carlos Kremer Donatella Armentano Giovanni De Munno Juan Faus 《Inorganica chimica acta》2008,361(9-10):2715-2720
The linkage isomers [Re(NCS)6]2? and [Re(NCS)5(SCN)]2? are obtained by the reaction of [ReBr6]2? with NCS? in dimethylformamide. Some differences in the chemical behavior allowed their separation and structural characterization in the form of (NBu4)2[Re(NCS)6] (1) and [Zn(NO3)(Me2phen)2]2[Re(NCS)5(SCN)] (2), respectively (Bu = n-C4H9 and Me2phen = 2,9-dimethyl-1,10-phenanthroline). 相似文献
7.
Kunio Awaga Yoshikatsu Umezono Wataru Fujita Hirofumi Yoshikawa HengBo Cui Hayao Kobayashi Sarah S. Staniland Neil Robertson 《Inorganica chimica acta》2008,361(14-15):3761-3770
We have examined the crystal structures and the electrical and magnetic properties of the molecular compounds of a thiazyl radical, 1,3,2-benzodithiazolyl (abbreviated as BDTA). BDTA was found to be a useful building block for molecular conductors and magnets because it can operate as a counter cation, a donor or a ligand, depending on its charge. (i) A charge-transfer complex, [BDTA][TCNQ], crystallizes into a uniform segregated stacking structure with a short contact between the donor and acceptor columns. In spite of the partial charge transfer between the two components, this complex exhibits semiconductive behaviour, probably due to a large electron correlation on BDTA. (ii) The crystal structure of [BDTA][Ni(mnt)2] (mnt = maleonitriledithiolate) consists of alternating stacking columns of S = 0 [BDTA]+ and S = 1/2 [Ni(mnt)2]?, in which a ferromagnetic coupling operates between the [Ni(mnt)2]? anions through the [BDTA] + cation. (iii) [BDTA]2[Cu(mnt)2] consists of an alternating stack of a head-to-head [BDTA]+ dimer and a planar [Cu(mnt)2]2? dianion. Short intermolecular S?S contacts between the stacks give rise to an ideal 1D Heisenberg antiferromagnetic chain of [Cu(mnt)2]2? with a coupling constant of J/kB = 16–17 K. (iv) The crystal structure of [BDTA]2[Co(mnt)2] is similar to that of [BDTA]2[Cu(mnt)2] at 253 K, but this salt undergoes a phase transition at 190 K, below which a partial electron transfer occurs from [Co(mnt)2]2? to one of the [BDTA]+ cations along with formation of a coordination bond. (v) [BDTA][Ni(dmit)2]2 (dmit = 1,3-dithiol-2-thione-4,5-dithiolate) exhibits room-temperature conductivity of 0.1 S cm?1 and semiconductive behaviour over the range 80–200 K, which can be interpreted in terms of multi-conducting bands. 相似文献
8.
《Inorganica chimica acta》2006,359(11):3549-3556
A series of cationic trispyrazolylmethane complexes of the general form [TmRM(CH3CN)3]2+ (Tm = tris(pyrazolyl)methane, 1, R = 3,5-Me2, M = Fe(II); 2, R = 3-Ph, M = Fe(II); 3, R = 3,5-Me2, M = Co(II); 4, R = 3-Ph, M = Co(II)) with ‘piano-stool’ structures was prepared by the reaction of the N3tripodal ligands (TmR)with [(CH3CN)6M](BF4)2 in a 1:1 stoichiometric ratio. Magnetic susceptibility measurements indicate that all four complexes with BF4− counter anions are paramagnetic, high-spin systems in the solid state with μeff at high temperatures of 5.2 (1, S = 2), 5.4 (2, S = 2), 4.9 (3, S = 3/2) and 4.6 (4, S = 3/2) BM, respectively. Comparisons of bond lengths from the metal centre to the TmR nitrogen donors, and from the metal centre to the acetonitrile nitrogen donors indicate that the neutral tripodal ligands appear to be more weakly coordinated to the metal centre than are the acetonitrile ligands. Reactions of these tripodal complexes with bidentate phosphine ligands, such as 1,2-diphosphinoethane or 1,2-bis(diallylphosphino)ethane leads to displacement of the tripodal ligand, or to the formation of more thermally stable bis-ligand complexes M(TmR)2 (R = 3,5-dimethyl). 相似文献
9.
Brigitte Guérin Véronique Dumulon-Perreault Marie-Claude Tremblay Samia Ait-Mohand Patrick Fournier Céléna Dubuc Simon Authier François Bénard 《Bioorganic & medicinal chemistry letters》2010,20(3):950-953
We substituted a truncated neuropeptide Y (NPY) analog, [Pro30, Tyr32, Leu34]NPY(28-36)NH2 also called BVD15, at various positions with DOTA (1,4,7,10-tetraazacyclododecane-1,4,7-10-tetraacetic acid) and evaluated the effect of the coupling position with the binding affinity for NPY Y1 receptors (NPY1R). Our data suggest that [Lys(DOTA)4]BVD15 (Ki = 63 ± 25 nM vs. Ki = 39 ± 34 nM for BVD15) is a potent NPY analog suitable for radiolabeling with metallo positron emitters for PET imaging of breast cancer. 相似文献
10.
Qing-Xiang Liu Xiao-Jun Zhao Xiu-Mei Wu Li-Na Yin Jian-Hua Guo Xiu-Guang Wang Jin-Cheng Feng 《Inorganica chimica acta》2008,361(9-10):2616-2622
The precursors bis[N-(alkyl)benzimidazoliumylmethyl]durene halide (1a: alkyl = C2H5, halide = Br?; 1b: alkyl = n-C4H9, halide = Cl?; durene = 1,2,4,5-tetramethylbenzene) and their two new NHC silver(I) complexes [Durene(CH2BimyEtAgBr)2] (2a) and [Durene(CH2BimynBuAgCl)2] (2b) (Bimy = benzimidazol-2-ylidene) have been prepared and characterized. In the crystal structures of 2a and 2b the aromatic π–π stacking interactions are observed. 相似文献
11.
Akito Kazama Akinobu Wada Hiroshi Sakiyama Md. Jamil Hossain Yuzo Nishida 《Inorganica chimica acta》2008,361(9-10):2918-2922
Two dinuclear metal complexes, [Co2(bhmp)(MeCO2)2]ClO4 · 2H2O (1) and [Ni2(bhmp)(MeCO2)2]ClO4 · 2H2O (2), were synthesized with a dinucleating ligand, 2,6-bis[bis(2-hydroxyethyl)aminomethyl]-4-methylphenol [H(bhmp)]. Both complexes were easily soluble in water as well as in DMF. Electronic spectra for both complexes were measured in both solvents and analyzed using the angular overlap model (AOM). From the electronic spectra and molar conductance, both complexes were determined to exist as [M2(bhmp)(MeCO2)2]+ (M = CoII or NiII) in DMF, dissociating perchlorate ions. On the other hand, in water, it was concluded that the acetate ions were partially dissociated and each complex existed as a mixture of some dissociated species, such as [M2(bhmp)(MeCO2)(H2O)2]2+ and [M2(bhmp)(H2O)4]3+ (M = CoII or NiII). Such dissociation was also confirmed by precipitation of the dissociated species when NaBPh4 was added into an aqueous solution of the nickel complex. 相似文献
12.
《Cell calcium》2015,58(5-6):366-375
In healthy pancreatic islets, glucose-stimulated changes in intracellular calcium ([Ca2+]i) provide a reasonable reflection of the patterns and relative amounts of insulin secretion. We report that [Ca2+]i in islets under stress, however, dissociates with insulin release in different ways for different stressors. Islets were exposed for 48 h to a variety of stressors: cytokines (low-grade inflammation), 28 mM glucose (28G, glucotoxicity), free fatty acids (FFAs, lipotoxicity), thapsigargin (ER stress), or rotenone (mitochondrial stress). We then measured [Ca2+]i and insulin release in parallel studies. Islets exposed to all stressors except rotenone displayed significantly elevated [Ca2+]i in low glucose, however, increased insulin secretion was only observed for 28G due to increased nifedipine-sensitive calcium-channel flux. Following 3–11 mM glucose stimulation, all stressors substantially reduced the peak glucose-stimulated [Ca2+]i response (first phase). Thapsigargin and cytokines also substantially impacted aspects of calcium influx and ER calcium handling. Stressors did not significantly impact insulin secretion in 11 mM glucose for any stressor, although FFAs showed a borderline reduction, which contributed to a significant decrease in the stimulation index (11:3 mM glucose) observed for FFAs and also for 28G. We also clamped [Ca2+]i using 30 mM KCl + 250 μM diazoxide to test the amplifying pathway. Only rotenone-treated islets showed a robust increase in 3–11 mM glucose-stimulated insulin secretion under clamped conditions, suggesting that low-level mitochondrial stress might activate the metabolic amplifying pathway. We conclude that different stressors dissociate [Ca2+]i from insulin secretion differently: ER stressors (thapsigargin, cytokines) primarily affect [Ca2+]i but not conventional insulin secretion and ‘metabolic’ stressors (FFAs, 28G, rotenone) impacted insulin secretion. 相似文献
13.
《Inorganica chimica acta》2006,359(4):1275-1281
Two new complexes of composition [Cu(2-NO2bz)2(3-pyme)2(H2O)2] (1) and/or [Cu{3,5-(NO2)2bz}2(3-pyme)2] (2) (3-pyme = 3-pyridylmethanol, ronicol or 3-pyridylcarbinol, 2-NO2bz = 2-nitrobenzoate and 3,5-(NO2)2bz = 3,5-dinitrobenzoate) have been prepared and studied by elemental analysis, electronic, infrared and EPR spectroscopy, magnetic susceptibility measurements and the structure of both complexes has been solved. Complex (1) shows an unusual molecular type of structure consisting of the [Cu(2-NO2bz)2(3-pyme)2(H2O)2] molecules held together by hydrogen bonds and van der Waals interactions. Complex (2) exhibits a polymeric chain-like structure [Cu{3,5-(NO2)2bz}2(3-pyme)2]n with copper atoms doubly bridged by two 3-pyridylmethanol molecules and the polymeric molecules are held together by van der Waals interactions. Complex (1) exhibits a magnetic moment μeff = 1.84 B.M. at 300 K that remains nearly constant within the temperature region (5–300 K). Further cooling results in lowering the magnetic moment to μeff = 1.82 B.M. at 1.8 K. The magnetic susceptibility temperature dependence obeys Curie–Weiss law with Curie constant of 0.423 cm3 K mol−1 and with Weiss constant of −0.06 K. The magnetic moment of (2) exhibits a small increase with a decrease in the temperature (μeff = 1.80 B.M. at 300 K and μeff = 1.85 B.M. at 1.8 K) with Curie constant of 0.409 cm3 K mol−1 and with Weiss constant of +1.1 K, which can indicate a very weak ferromagnetic interaction between the copper atoms within the chain. Applying the molecular field model resulted in obtaining zJ′ values −0.08 cm−1 for complex (1), and −0.07 cm−1 for complex (2), respectively, that could characterize intermolecular and interchain interactions transmitted through π–π stacking. 相似文献
14.
《Inorganica chimica acta》2006,359(5):1427-1434
A new method for the synthesis of metal dithiolenes with alkyl-substituted chelate rings has been investigated. The utility of the protected ene-1,2-dithiolate 3,4-bis-triisopropylsilanyl-sulfanyl-hex-3-ene as a precursor in reactions with metal halide and oxyhalide complexes was examined. Reaction conditions involve a 2:1 or 3:1 mol ratio of reactants in acetonitrile/THF or toluene at 50–80 °C for 24–36 h. Complex formation was observed as a result of Si–S bond cleavage by bound or free halide and oxo ligands. Members of four major structural families of dithiolene complexes were prepared in ca. 25–70% yields, including planar [Ni(S2C2Et2)2], square pyramidal [MI(S2C2Et2)2] (M = Co, Fe), [Fe(py)(S2C2Et2)2]1−, and [ReO(S2C2Et2)2]1−, centrosymmetric [M2(S2C2Et2)4]2− (M = Co, Mn), [M(S2C2Et2)3]1− (M = V, Nb), and trigonal prismatic [M(S2C2Et2)3] (M = Mo, W). Seven X-ray structure proofs are provided. It is concluded that the method is feasible and potentially extendable to other ring substituents, whose primary effects are on solubility and modulation of redox potentials. 相似文献
15.
Mònica Espinal Josefina Pons Jordi García-Antón Xavier Solans Mercè Font-Bardia Josep Ros 《Inorganica chimica acta》2008,361(9-10):2648-2658
Treatment of the tetradentate (NN′N′N) N-alkylaminopyrazole ligands 3,6-dimethyl-1,8-(3,5-dimethyl-1-pyrazolyl)-3,6-diazaoctane (ddad) and 1,4-bis[2-(3,5-dimethyl-1-pyrazolyl)ethyl]piperazine (bedp) with [PdCl2(CH3CN)2] in a 1:1 M/L ratio in acetonitrile produces [Pd2Cl4(L)] and [PdCl2(L)] (L = ddad and bedp). Treatment of the corresponding complex [PdCl2(L)] (L = ddad, bedp) in the presence of AgBF4 in CH2Cl2/methanol (2:1) or NaBF4 in acetonitrile gives [Pd(L)](BF4)2. The Pd(II) complexes have been characterised by elemental analyses, conductivity measurements, IR and 1H and 13C{1H} NMR spectroscopies when possible. The X-ray structure of the complex [Pd(ddad)]Cl2 · 3H2O has been determined. The Pd(II) is coordinated to the ddad ligand by two nitrogen atoms of pyrazolyl groups and two nitrogen atoms of the amine groups, in a slightly distorted square-planar geometry. 相似文献
16.
《Inorganica chimica acta》2006,359(5):1541-1548
The electronic structure of a series of 11 penta-coordinated dichloride mononuclear Mn(II) complexes [Mn(L)Cl2] (L = Cl-terpy, Br-terpy, OH-terpy, phenyl-terpy, tolyl-terpy, mesityl-terpy, EtO-terpy, Me2N-terpy, tBu3-terpy, py-phen, and dpya) has been investigated by a multifrequency EPR study (9–285 GHz). The X-ray structures of [Mn(Br-terpy)Cl2], [Mn(EtO-terpy)Cl2], [Mn(Me2N-terpy)Cl2] and [Mn(tolyl-terpy)Cl2] are described. The spin Hamiltonian parameters have been determined for all complexes and show that the steric and electronic effects of the N-tridentate ligand L do not induce appreciable variations on the zero field splitting parameters. The magnitude of D, close to 0.3 cm−1, is governed by the chloride anion. High-field EPR spectroscopy allows the determination of electronic parameters of mononuclear Mn(II) complexes characterized by relatively large magnitudes of D and the unambiguous interpretation of the X-band spectra of these kinds of complexes. 相似文献
17.
Philipp Hoffmann Michaela F. Hartmann Thomas Remer Klaus-Peter Zimmer Stefan A. Wudy 《Steroids》2010,75(13-14):1067-1074
Oestrogens, such as oestrone (E1), 17β-oestradiol (E2), oestriol (E3) and their biologically active metabolites 2-methoxyoestrone (2-MeOE1), 2-hydroxyoestradiol (2-OHE2) 16-ketooestradiol (16-OE2), 16-epioestriol (16-epiE3), as well as testosterone (T) play an important role in physiological and pathological developmental processes during human development. We therefore aimed at developing an isotope dilution/bench top gas chromatography–mass spectrometry (ID/GC–MS) method, based on benchtop GC–MS, for the simultaneous determination (‘profiling’) of the above analytes in children. The method consisted of equilibration of urine (5 ml) with a cocktail containing stable isotope-labelled analogues of the analytes as internal standards ([2,4-2H2]E1, [2,4,16,16-2H4]E2, [2,4,17-2H3]E3, [16,16,17-2H3]T, [1,4,16,16-2H4]2-MeOE1, [1,4,16,16,17-2H5]2-OHE2, [2,4,15,15,17-2H5]16-OE2 and [2,4-2H2]16-epiE3). Then, solid-phase extraction (C18 cartridges), enzymatic hydrolysis (sulphatase from Helix pomatia (type H-1)), re-extraction, purification by anion exchange chromatography and derivatisation to trimethylsilyl ethers followed. The samples were analysed by GC–MS (Agilent GC 6890N/5975MSD; fused silica capillary column 25 m × 0.2 mm i.d., film 0.10 μm). Calibration plots were linear and showed excellent reproducibility with coefficients of determination (r2) between 0.999 and 1.000. Intra- and inter-assay coefficients of variation (CV) were <2.21% for all quantified metabolites. Sensitivity was highest for 2-OHE2 (0.25 pg per absolute injection: signal-to-noise ratio (S/N) = 3) and lowest for 16-epiE3 (2 pg per absolute injection: S/N = 2.6), translating into corresponding urine sample analyte concentrations of 0.025 ng ml?1 and 0.2 ng ml?1, respectively. Accuracy – determined in a two-level spike experiment – showed relative errors ranging between 0.15% for 16-OE2 and 11.63% for 2-OHE2. Chromatography showed clear peak shapes for the components analysed. In summary, we describe a practical, sensitive and specific ID/GC–MS assay capable of profiling the above-mentioned steroids in human urine from childhood onwards. 相似文献
18.
Patrick L. Feng Christopher C. Beedle Changhyun Koo Jon Lawrence Stephen Hill David N. Hendrickson 《Inorganica chimica acta》2008,361(12-13):3465-3480
We review an extensive body of single-crystal high-frequency electron paramagnetic resonance (HFEPR) data in order to determine the transverse spin Hamiltonian parameters that control the tunneling of the direction of magnetization in a variety of integer and half-integer-spin single-molecule magnets (SMMs). The SMMs studied are members of the following families: S = 9/2 [Mn4O3Cl]6+; S = 5 [Mn3NiO4]6+; S = 6 [Mn3ZnO4]6+; and S = 4 [Ni4(OR)4]4+. HFEPR spectra for the half-integer S = 9/2 Mn4 complexes that have C3 symmetry do not provide measurable evidence for transverse spin Hamiltonian terms. This finding is consistent with the relatively large coercive field seen in the magnetization hysteresis loops for these complexes. On the other hand, a low symmetry S = 9/2 complex exhibits a much faster rate of ground-state magnetization tunneling, in agreement with HFEPR spectra for a powder sample that gives a rhombic zero-field splitting (ZFS) parameter of E = 0.140 cm?1. The S = 5 Mn3Ni systems exhibit magnetization tunneling that is much faster than seen for the high-symmetry S = 9/2 Mn4 complexes. This can be attributed to their integer-spin ground states. Like the C3 symmetry Mn4 SMMs, the HFEPR spectra for high-symmetry Mn3Ni complexes do not provide measurable evidence for transverse ZFS terms. However, the spectra exhibit broad peaks, suggesting distributions in the local molecular environments brought about by disordered solvate molecules. This disorder likely explains the fast tunneling in the high-symmetry S = 5 Mn3Ni systems, though one cannot rule out fourth- (and higher-) order interactions that cannot be detected by HFEPR due to the broad resonances. The one S = 6 Mn3Zn complex shows an even faster rate of tunneling compared to the isostructural S = 5 Mn3Ni complex. Finally, the S = 4 [Ni(hmp)(dmb)Cl]4 complex provides unique insights into the origin of fourth- (and higher-) order interactions found for many SMMs on the basis of analysis using a giant spin Hamiltonian (GSH) approximation. We conclude that the fourth-order anisotropy found for the S = 4 ground state of [Ni(hmp)(dmb)Cl]4 originates from the second-order ZFS interactions associated with the individual NiII ions, but only as a result of higher-order processes that occur via S-mixing between the ground state and higher-lying (S < 4) spin-multiplets. The S-mixing is relatively strong in this system because of comparable exchange and anisotropy energy scales. The relatively fast tunneling is a direct consequence of this S-mixing, as opposed to any intrinsic fourth-order (spin–orbit) anisotropy associated with NiII. 相似文献
19.
Stefania Tanase Marco Evangelisti L. Jos de Jongh Jan M.M. Smits René de Gelder 《Inorganica chimica acta》2008,361(12-13):3548-3554
The new d–f cyanido-bridged 1D assembly [Nd(pzam)3(H2O)Mo(CN)8] · H2O was prepared by self-assembly of pyrazine-2-carboxamide (pzam), Nd(NO3) · nH2O and (Bu3NH)3[Mo(CN)8] · 4H2O in acetonitrile. X-ray crystallographic studies indicate that the complex comprises chains of alternating, cyanido-bridged [Nd(pzam)3(H2O)]3+ and Mo(CN)8]3? fragments. The magneto-structural properties have been studied by field-dependent magnetization and specific heat measurements at low temperatures (?0.3 K). Below ≈10 K the Nd(III) moment is well approximated by an effective spin S = 1/2, with anisotropic g-tensor. The exchange coupling between the Nd(III) and the Mo(V) spins S = 1/2 along the structural chains is found to be ferromagnetic, with J/kB = 1.8 ± 0.2 K and approximately XY (planar) anisotropy. No evidence for 3D interchain magnetic ordering is found. A comparison with magneto-structural data of other cyanido-bridged complexes involving the Nd(III) ion is presented. 相似文献
20.
Barbara Modec 《Inorganica chimica acta》2008,361(9-10):2863-2870
A series of acetato complexes of molybdenum(V), based on the singly metal–metal bonded {Mo2O4}2+ structural fragment, has been prepared. A dinuclear (PyH)3[Mo2O4Cl4(OOCCH3)] · CH3CN (1) (PyH+ = pyridinium cation, C5H5NH+) was obtained upon the reaction of (PyH)5[MoOCl4(H2O)]3Cl2 with the equimolar solution of pyridine and acetic acid in acetonitrile at ambient conditions. The acetato ligand in 1 is coordinated to a pair of molybdenum atoms in a syn–syn bidentate bridging manner. (PyH)n[MoOBr4]n afforded in an analogous synthetic procedure a tetranuclear cluster, [Mo4O8(OOCCH3)3(OH)Py4] · 1/2CH 3CN · 1/2H2O (3), with a novel core which may be envisioned as the acetate- and hydroxide-assisted assembly of {Mo2O4}2+ building blocks. Its structure is presented in terms of known tetranuclear clusters which are also composed of two {Mo2O4}2+ units. The acetato ligands in 3 adopted apart from bidentate bridging binding modes also a monodentate one. Partial substitution of chlorido ligands in (PyH)3[Mo2O4Cl4(OOCCH3)] · CH3CN (1) with pyridine resulted in a neutral [Mo2O4Cl(OOCCH3)Py3] · PriOH · Py (2) which retained the original acetate coordination. The title compounds were fully characterized by X-ray diffraction studies and infrared vibrational spectroscopy. 相似文献