“…This behavior may be related to an antiferromagnetic ordering due to uncompensated spin alignment. The maximum on this curve is found at T = 260 ± 6 K, which means that using a Bonner and Fisher fit would result in J < 0; the susceptibility passes through a rounded maximum at a temperature T max defined by kT max /| J | = 0.641, giving a value J = −282 ± 6 cm -1 . , 3 Thermal dependence of the magnetization at different magnetic field intensities H . Note the change of the magnetization from low to high field.…”
A new crystalline polymorphic phase of tetrakis(mu2-benzoato-O,O')-bis(dimethyl sulfoxide)dicopper(II) was obtained by direct synthesis, in space group P2(1)/n. The copper coordination is in a slightly distorted square pyramidal geometry with an intramolecular Cu...Cu distance of 2.6494(8) angstroms. The Cu-O distances of the two copper in a dimer are different, giving different chemical environments for each Cu ion. The crystal structure is built up of well-separated stacking columns oriented along the b-axis, with units uniformly spaced, producing a one-dimensional (1-D) zigzag chain through Cu(II)-S...S-Cu(II) interdimer interactions [S...S separation: 3.975(2) angstroms]. Magnetization measurements in the range 2-300 K indicate two magnetic orderings, at low temperature (T < 10 K) a weak ferromagnetic ordering is observed, and above this temperature an antiferromagnetic behavior takes place. ESR spectra at 300 and 77 K of a polycrystalline sample show the characteristic signal of zero-field with D = 0.354 cm(-1), consistent with a ferromagnetic Cu...Cu exchange interaction at low temperature.
“…This behavior may be related to an antiferromagnetic ordering due to uncompensated spin alignment. The maximum on this curve is found at T = 260 ± 6 K, which means that using a Bonner and Fisher fit would result in J < 0; the susceptibility passes through a rounded maximum at a temperature T max defined by kT max /| J | = 0.641, giving a value J = −282 ± 6 cm -1 . , 3 Thermal dependence of the magnetization at different magnetic field intensities H . Note the change of the magnetization from low to high field.…”
A new crystalline polymorphic phase of tetrakis(mu2-benzoato-O,O')-bis(dimethyl sulfoxide)dicopper(II) was obtained by direct synthesis, in space group P2(1)/n. The copper coordination is in a slightly distorted square pyramidal geometry with an intramolecular Cu...Cu distance of 2.6494(8) angstroms. The Cu-O distances of the two copper in a dimer are different, giving different chemical environments for each Cu ion. The crystal structure is built up of well-separated stacking columns oriented along the b-axis, with units uniformly spaced, producing a one-dimensional (1-D) zigzag chain through Cu(II)-S...S-Cu(II) interdimer interactions [S...S separation: 3.975(2) angstroms]. Magnetization measurements in the range 2-300 K indicate two magnetic orderings, at low temperature (T < 10 K) a weak ferromagnetic ordering is observed, and above this temperature an antiferromagnetic behavior takes place. ESR spectra at 300 and 77 K of a polycrystalline sample show the characteristic signal of zero-field with D = 0.354 cm(-1), consistent with a ferromagnetic Cu...Cu exchange interaction at low temperature.
The crystal structure and magnetic analysis of a cyclic tetranuclear copper() complex with formula [Cu 4 (phen) 4 (glyOH) 4 ](NO 3 ) 4 ؒ2H 2 O, where phen = 1,10-phenanthroline and glyOH = glycolate are described. Copper atoms are connected through bridging carboxylate groups from chelated glycolate units, forming a butterfly-type framework. Magnetic measurements as a function of temperature (2-300 K) and at 10, 100 and 1000 G were performed. The behaviour of the χ --T -T curves is characteristic of ferrimagnetic-type coupling. Several theoretical magnetic models were tested to study the experimental data. A tetranuclear model of S = 1/2 coupled spins in a C 2v symmetry, is the one that better describes the magnetic response of the solid product over the whole range of experimental conditions explored. This model allows us to suggest the existence of a very weak antiferromagnetic coupling for two different pairs of Cu() centers, and a weak ferromagnetic coupling between those pairs. Besides this, negligible magnetic coupling at the mean field level is proposed. It is important to point out that although the system is homonuclear, with coordination spheres which are chemically equivalent for all the metallic centers, and which shows (at room temperature) equivalent internuclear distances between first neighbouring copper atoms, different types of intramolecular magnetic coupling are inferred. To our knowledge, the complex here studied appears to be the first case of a cyclic tetranuclear Cu() system showing global ferrimagnetic coupling.
DALTON
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