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排序方式: 共有240条查询结果,搜索用时 15 毫秒
71.
Zhao JP Hu BW Zhang XF Yang Q El Fallah MS Ribas J Bu XH 《Inorganic chemistry》2010,49(24):11325-11332
Five new isomorphic three-dimensional (3D) heterometallic 3d-3d azide complexes, [CuNi(1-x)Co(x)(N(3))(2)(isonic)(2)](∞) (x = 0 for 1, x = 0.3 for 2, x = 0.5 for 3, x = 0.6 for 4, and x = 1 for 5), were obtained by assembling Cu(II), M(II) (Ni(II) and Co(II)), azide, and pyridyl carboxylate in hydrothermal condition. The 3D structure can be described as end on (EO) azide and syn,syn carboxylates mixed bridged alternate Cu-M chains linked by the pyridyl groups. Dominant ferromagnetic interactions were observed between the Cu(II) and M(II) ions in the chains. At low temperature diverse magnetic phenomena were presented in those complexes. As the Ni(II) ions were replaced by Co(II) ions with large anisotropy, the magnetism of the complexes change gradually from metamagnet to single-chain magnet (SCM)-like behaviors. 相似文献
72.
Luis P. Chimento Mónica Forte Gilberto M. Kremer Marlos O. Ribas 《General Relativity and Gravitation》2010,42(6):1523-1535
In this work a tachyonization of the ΛCDM model for a spatially flat Friedmann–Robertson–Walker space–time is proposed. A
tachyon field and a cosmological constant are considered as the sources of the gravitational field. Starting from a stability
analysis and from the exact solutions for a standard tachyon field driven by a given potential, the search for a large set
of cosmological models which contain the ΛCDM model is investigated. By the use of internal transformations two new kinds
of tachyon fields are derived from the standard tachyon field, namely, a complementary and a phantom tachyon fields. Numerical
solutions for the three kinds of tachyon fields are determined and it is shown that the standard and complementary tachyon
fields reproduces the ΛCDM model as a limiting case. The standard tachyon field can also describe a transition from an accelerated
to a decelerated regime, behaving as an inflationary field at early times and as a matter field at late times. The complementary
tachyon field always behaves as a matter field. The phantom tachyon field is characterized by a rapid expansion where its
energy density increases with time. 相似文献
73.
Konar S Corbella M Zangrando E Ribas J Chaudhuri NR 《Chemical communications (Cambridge, England)》2003,(12):1424-1425
An unprecedented interlocked 3D Fe(II) system, [Fe(squarate)(bpy)(2H2O)] x 3H2O, 1 (bpy = 4,4'-bipyridine), the first unequivocally ferromagnetically coupled squarato complex to be reported, has been synthesised and magnetically characterized. 相似文献
74.
Konar S Zangrando E Drew MG Ribas J Chaudhuri NR 《Dalton transactions (Cambridge, England : 2003)》2004,(2):260-266
The hydrothermal reactions of Ni(NO(3))(2).6H(2)O, disodium fumarate (fum) and 1,2-bis(4-pyridyl)ethane (bpe)/1,3-bis(4-pyridyl)propane (bpp) in aqueous-methanol medium yield one 3-D and one 2-D metal-organic hybrid material, [Ni(fum)(bpe)] (1) and [Ni(fum)(bpp)(H(2)O)] (2), respectively. Complex possesses a novel unprecedented structure, the first example of an "unusual mode" of a five-fold distorted interpenetrated network with metal-ligand linkages where the four six-membered windows in each adamantane-type cage are different. The structural characterization of complex 2 evidences a buckled sheet where nickel ions are in a distorted octahedral geometry, with two carboxylic groups, one acting as a bis-chelate, the other as a bis-monodentate ligand. The metal ion completes the coordination sphere through one water molecule and two bpp nitrogens in cis position. Variable-temperature magnetic measurements of complexes 1 and 2 reveal the existence of very weak antiferromagnetic intramolecular interactions and/or the presence of single-ion zero field splitting (D) of isolated Ni(II) ions in both the compounds. Experimentally, both the J parameters are close, comparable and very small. Considering zero-field splitting of Ni(II), the calculated D values are in agreement with values reported in the literature for Ni(II) ions. Complex 3, [[Co(phen)]](2)(fum)(2)](phen = 1,10-phenanthroline) is obtained by diffusing methanolic solution of 1,10-phenanthroline on an aqueous layer of disodium fumarate and Co(NO(3))(2).6H(2)O. It consists of dimeric Co(II)(phen) units, doubly bridged by carboxylate groups in a distorted syn-syn fashion. These fumarate anions act as bis-chelates to form corrugated sheets. The 2D layer has a (4,4) topology, with the nodes represented by the centres of the dimers. The magnetic data were fitted ignoring the very weak coupling through the fumarate pathway and using a dimer model. 相似文献
75.
Majumder A Choudhury CR Mitra S Rosair GM El Fallah MS Ribas J 《Chemical communications (Cambridge, England)》2005,(16):2158-2160
Atmospheric CO2 fixation by an aqueous solution containing Cu(ClO4)2.6H2O and 4-aminopyridine (4-apy) yields a novel example of a two-dimensional mu3-CO3 bridged copper(II) complex {[Cu(4-apy)2]3(mu3-CO3)2(ClO4)2.(1/2)CH3OH}n that has been characterized by IR, UV and X-ray crystallography; preliminary magnetic measurements show that complex exhibits long-range ordered ferromagnetic coupling. 相似文献
76.
Figuerola A Diaz C Ribas J Tangoulis V Sangregorio C Gatteschi D Maestro M Mahía J 《Inorganic chemistry》2003,42(17):5274-5281
The reaction of Ln(NO(3))(3).aq with K(3)[Fe(CN)(6)] or K(3)[Co(CN)(6)] and 2,2'-bipyridine in water led to five one-dimensional complexes: trans-[M(CN)(4)(mu-CN)(2)Ln(H(2)O)(4) (bpy)](n)().XnH(2)O.1.5nbpy (M = Fe(3+) or Co(3+); Ln = Sm(3+), Gd(3+), or Yb(3+); X = 4 or 5). The structures for [Fe(3)(+)-Sm(3+)] (1), [Fe(3)(+)-Gd(3+)] (2), [Fe(3)(+)-Yb(3+)] (3), [Co(3)(+)-Gd(3+)] (4), and [Co(3)(+)-Yb(3+)] (5) have been solved; they crystallize in the triclinic space P1 and are isomorphous. The [Fe(3+)-Sm(3+)] complex is a ferrimagnet, its magnetic studies suggesting the onset of weak ferromagnetic 3-D ordering at 3.5 K. The [Fe(3+)-Gd(3+)] interaction is weakly antiferromagnetic. The isotropic nature of Gd(3+) allowed us to evaluate the exchange interaction (J = 0.77 cm(-)(1)). 相似文献
77.
To explore the relationships between the structures of ligands and their complexes, we have synthesized and characterized a series of metal complexes with two structurally related ligands, 9-acridinecarboxylic acid (HL(1)) and 4-quinolinecarboxylate acid (HL(2)), [Cu(2)(mu(2)-OMe)(2)(L(1))(2)(H(2)O)(0.69)](n) 1, [Cu(2)(L(1))(4)(CH(3)OH)(2)] 2, [Cu(3)(L(1))(6)(CH(3)OH)(6)].3H(2)O 3, [Mn(3)(L(1))(6)(CH(3)OH)(6)].3H(2)O 4, [Co(3)(L(1))(6)(CH(3)OH)(6)].3H(2)O 5, [Cu(L(2))(2)](n) 6, [Mn(L(2))(2)(H(2)O)](n) 7, and [Co(L(2))(2)(H(2)O)](n) 8. 1 is a three-dimensional (3D) polymer with an interpenetrating NbO type network showing one-dimensional (1D) channels, whereas 2 and 3 take bi- and trinuclear structures, respectively, because of the differences in basicity of the reaction systems in preparing the three complexes. 4 and 5 have trinuclear structures similar to that of 3. In 1-5, ligand L(1) performs different coordination modes with N,O-bridging in 1 and O,O'-bridging in 2-5, and the metal ions also show different coordination geometries: square planar in 1, square pyramidal in 2, and octahedral in 3-5. 6 has a two-dimensional structure containing (4,4) grids in which L(2) adopts the N,O-bridging mode and the Cu(II) center takes square planar geometry. 7 and 8 are isostructural complexes showing 1D chain structures, with L(2) adopting the O,O-bridging mode. In addition, the intermolecular O-H...N hydrogen bonds and pi-pi stacking interactions further extend the complexes (except 1 and 6), forming 3D structures. The magnetic properties of 2-7 have been investigated and discussed in detail. 相似文献
78.
Figuerola A Ribas J Casanova D Maestro M Alvarez S Diaz C 《Inorganic chemistry》2005,44(20):6949-6958
The reaction of Ln(NO3)3(aq) with K3[Fe(CN)6] or K3[Co(CN)6] and 2,2'-bipyridine in water/ethanol led to 13 one-dimensional complexes: trans-[M(CN)4(mu-CN)2Ln(H2O)4(bpy)]n.4nH2O.1.5nbpy (Ln = Eu3+, Tb3+, Dy3+, Ho3+, Er3+, Tm3+, Lu3+; M = Fe3+, Co3+). The structures for [EuFe]n (1), [TbFe]n (2), [DyFe]n (3), [HoFe]n (4), [ErFe]n (5), [TmFe]n (6), [LuFe]n (7), [EuCo]n (8), [TbCo]n (9), [DyCo]n (10), [HoCo]n (11), [ErCo]n (12), and [TmCo]n (13) have been solved: they crystallize in the triclinic space group P and are isomorphous. They exhibit a supramolecular architecture created by the interplay of coordinative, hydrogen bonding, and pi-pi interactions. A stereochemical study of the eight-vertex polyhedra of the lanthanide ions, based on continuous shape measures, is presented. The Ln3+-Fe3+ interaction is antiferromagnetic in [DyFe]n and [TbFe]n. For [EuFe]n, [HoFe]n, [ErFe]n, and [TmFe]n, there is no sign of any significant interaction. The magnetic behavior of [DyFe]n suggests the onset of weak long-range ferromagnetic ordering at 2.5 K. 相似文献
79.
F. Brandolini M. De Poli P. Pavan R.V. Ribas D. Bazzacco C.R. Rossi-Alvarez 《The European Physical Journal A - Hadrons and Nuclei》1999,6(2):149-155
The g-factors of some members of the ground state band and of the 2+ state in the %-vibrational band have been measured in 160,162,164Dy using the Coulomb Excitation Transient Field technique, induced by 58Ni projectiles at 230, 210 and 217 MeV, respectively. The g-factors in the ground state band are consistent with a constant value, while that of the 2+% states is about 20% larger in average than those in the ground state band. Results are discussed in the frame of the systematics in this nuclear region. 相似文献
80.
F. Brandolini S. M. Lenzi D. R. Napoli R. V. Ribas H. Somacal C. A. Ur D. Bazzacco J. A. Cameron G. de Angelis M. De Poli A. Gadea C. Fahlander S. Lunardi M. A. Nagarajan C. Rossi Alvarez C. Svensson 《Acta Physica Hungarica A》1998,7(1):113-114
Lifetimes have been determined in the ground state band in48Cr and found in agreement with Shell Model calculations. 相似文献