Search results for "Magnetism"
showing 10 items of 1934 documents
Antiferromagnetic porous metal-organic framework containing mixed-valence [Mn(II)4Mn(III)2(μ4-O)2]10+ units with catecholase activity and selective g…
2012
A multifunctional porous metal organic framework based on mixed-valence hexa-nuclear [Mn(III)(2)Mn(II)(4)O(2)(pyz)(2)(C(6)H(5)CH(2)COO)(10)] (pyz = pyrazine) units has been synthesized. The complex has been characterized by elemental analysis, IR spectroscopy, single-crystal X-ray diffraction analysis, and variable-temperature magnetic measurements. The structural analysis reveals that the bidentate pyz molecules connect each [Mn(6)] unit to its four [Mn(6)] neighbors through the peripheral Mn(II) centers, giving rise to a three-dimensional (3D) distorted diamond-like porous framework. Variable-temperature (2-300 K) magnetic susceptibility measurements show the presence of dominant antiferr…
A Unique Discrete Tetranuclear Cu′–Cu(N-N)2Cu–Cu′ Copper(II) Complex, Built from a μ3-1,2,4-Triazolato-μ-carboxylato Ligand, as an Effective DNA Clea…
2012
The title compound, characterized by means of an X-ray structure analysis, represents an easy example of a noncatena "1 + 2 + 1" tetranuclear copper(II) μ(3)-triazolate compound. [Cu(4)(atc)(2)(dien)(4)(ClO(4))(2)](ClO(4))(2)·2H(2)O (1), where H(2)atc = 5-amino-l,2,4-triazole-3-carboxylic acid and dien = diethylenetriamine = 1,4,7-triazaheptane, contains two copper atoms linked by a double diazinic bridge, each of which is further connected to a third and fourth copper atom (Cu') through the triply bridging triazolato ring and the bidentate carboxylato group of the atc(2-) ligands. The copper-copper distances within the tetranuclear unit are Cu-Cu = 4.059 Å, Cu-Cu' = 5.686 and 6.370 Å, and …
Experimental and Theoretical Studies on Magnetic Exchange in Silole-Bridged Diradicals.
2006
International audience; Five bis(tert-butylnitroxide) diradicals connected by a silole [2,5-R2-3,4-diphenylsilole; R = Me3CN(®O.bul.)Z; Z = p-C6H4 (7a), p-C6H4C6H4-p (7b), 1,4-naphthalenediyl (7c), m-C6H4 (7d)] or a thiophene [2,5-R2-thiophene; R = p-Me3CN(®O.bul.)C6H4 (12)] ring as a coupler were studied. Compd. 12 crystallizes in the orthorhombic space group Pna21 with a 20.752(5), b 5.826(5), and c 34.309(5) .ANG.. X-ray crystal structure detn., electronic spectroscopy, variable-temp. EPR spectroscopy, SQUID measurements and DFT computations (UB3LYP/6-31+G*) were used to study the mol. conformations and electronic spin coupling in this series of mols. Whereas compds. 7b, 7c, and 7d are q…
One-dimensional metal-organic framework with unprecedented heptanuclear copper units.
2007
The reaction of copper(II) sulfate, copper(II) chloride, 3,5-diacetylamino-1,2,4-triazole, and 3-acetylamino-5-amino-1,2,4-triazole in water yields green, plate-shaped crystals of [[{Cu3(mu3-OH(1/2))L(H2O)2Cl}2{mu-Cu(H2O)2Cl2}].12H2O]n (1), where L is a new triazole-derived macrocyclic ligand. The structure of 1 consists of heptanuclear (H)OCuII(3)-CuII-CuII(3)O(H) entities linked in pairs through symmetric mu3-O...H...O-mu3 hydrogen bonds to form a double-stranded one-dimensional network. A significant overall antiferromagnetic behavior has been observed for 1.
Site-specific Labelling with a Metal Chelator for Protein-structure Refinement
2004
A single free Cys sidechain in the N-terminal domain of the E. coli arginine repressor was covalently derivatized with S-cysteaminyl-EDTA for site-specific attachment of paramagnetic metal ions. The effects of chelated metal ions were monitored with (15)N-HSQC spectra. Complexation of Co(2+), which has a fast relaxing electron spin, resulted in significant pseudocontact shifts, but also in peak doubling which was attributed to the possibility of forming two different stereoisomers of the EDTA-Co(2+) complex. In contrast, complexation of Cu(2+) or Mn(2+), which have slowly relaxing electron spins, did not produce chemical shift changes and yielded self-consistent sets of paramagnetic relaxat…
A chirality-induced alpha phase and a novel molecular magnetic metal in the BEDT-TTF/tris(croconate)ferrate(iii) hybrid molecular system
2006
The novel paramagnetic and chiral anion [Fe(C5O5)3]32 has been combined with the organic donor BEDT-TTF (= ET = bis(ethylenedithio)tetrathiafulvalene) to yield the first chirality- induced α phase and a paramagnetic metal. Gomez Garcia, Carlos, Carlos.Gomez@uv.es ; Coronado Miralles, Eugenio, Eugenio.Coronado@uv.es ; Gimenez Saiz, Carlos, Carlos.Gimenez@uv.es
A Binuclear MnIII Complex of a Scorpiand-Like Ligand Displaying a Single Unsupported MnIII–O–MnIII Bridge
2012
The crystal structure of a binuclear Mn(III) complex of a scorpiand-like ligand (L) displays an unsupported single oxo bridging ligand with a Mn(III)-O-Mn(III) angle of 174.7°. Magnetic susceptibility measurements indicate strong antiferromagnetic coupling between the two metal centers. DFT calculations have been carried out to understand the magnetic behavior and to analyze the nature of the observed Jahn-Teller distortion. Paramagnetic (1)H NMR has been applied to rationalize the formation and magnetic features of the complexes formed in solution.
New BDH-TTP/[MIII(C5O5)3]3– (M = Fe, Ga) Isostructural Molecular Metals
2012
Two new isostructural molecular metals-(BDH-TTP)(6)[M(III)(C(5)O(5))(3)]·CH(2)Cl(2) (BDH-TTP = 2,5-bis(1,3-dithiolan-2-ylidene)-1,3,4,6-tetrathiapentalene, where M = Fe (1) and Ga (2))-have been prepared and fully characterized. Compound 1 is a molecular conductor showing paramagnetic behavior, which is due to the presence of isolated [Fe(C(5)O(5))(3)](3-) complexes with high-spin S = (5)/(2) Fe(III) metal ions. The conductivity originates from the BDH-TTP organic donors arranged in a κ-type molecular packing. At 4 kbar, compound 1 behaves as a metal down to ∼100 K, showing high conductivity (∼10 S cm(-1)) at room temperature. When applying a pressure higher than 7 kbar, the metal-insulator…
Co(II) chemistry of 2,6-bis(2-pyridylcarbonyl)pyridine: an icosanuclear Co cluster exhibiting superparamagnetic relaxation.
2006
High-nuclearity transition-metal complexes (clusters) are of special interest in chemistry and physics because, both in terms of size and physical properties, they bridge the gap between the microscopic and macroscopic world, and between quantum and classical systems. In terms of size, the smallest classical nanoparticles fabricated today are the same size as the largest metal clusters that are synthesized by bottom-up methods. In terms of physical properties, certain transition-metal clusters exhibit single-molecule magnetism at low temperatures, that is, they retain their magnetization in zero field in a manner analogous to that of classical macroscopic magnets, but at the same time they …
Formation and mixed-valent behaviour of a substituted tetraferrocenylstannane.
2010
A tetrasubstituted tetraferrocenylstannane is formed from 1-bromoferrocene-1′-carboxylic acid methyl ester and copper bronze. The molecular structure is almost perfectly tetrahedral with Fe⋯Fe distances of around 6 A. In solution two sequential one-electron processes and one two-electron process are indicative of mixed-valent intermediates. Intermetallic interactions have been probed by preparative oxidation, paramagnetic NMR spectroscopy, Mosbauer spectroscopy, UV/Vis/NIR spectroscopy and DFT calculations.