Synthesis, crystal structure and magnetic properties of a polymeric copper(II) schiff-base complex having binuclear units covalently linked by isonicotinate ligands

The polynuclear copper(II) complex [{Cu2L(O2CC5H4N)}·C2H5OH]x (1), where H3L is a 1:2 Schiff base derived from 1,3-diaminopropan-2-ol and salicylaldehyde, has been prepared and structurally characterized. The structure consists of a one-dimensional zigzag chain in which the binuclear [Cu2L]+ units are covalently linked by isonicotinate ligands to give a syndiotactic arrangement of the copper ions protruding outside the chain. In the basic unit, the copper(II) centres are bridged by an alkoxo and a carboxylato ligand, giving a Cu···Cu distance of 3.492(3) Å and a Cu-O-Cu angle of 130.9(2)° . While one copper centre has a square-planar geometry, the other copper is squarepyramidal with the pyridine nitrogen being the axial ligand. The visible electronic spectrum of 1 shows a broad d-d band at 615 nm. The complex shows a rhombic X-band EPR spectral pattern in the polycrystalline phase at 77 K. Magnetic susceptibility measurements in the temperature range 22 to 295 K demonstrate the antiferromagnetic behaviour of 1. A theoretical fit to the magnetic data is based on a model assuming 1 as an equimolar mixture of copper atoms belonging to an antiferromagnetically coupled one-dimensional Heisenberg chain with the other copper atoms outside the chain behaving like paramagnetic centres

Single crystal magnetic susceptibility of the quasi-one-dimensional antiferromagnet KFeS<SUB>2</SUB>

The single crystal magnetic susceptibility of the quasi-one-dimensional antiferromagnet KFeS<SUB>2</SUB> is reported. The high temperature isotropic susceptibility is typical of a spin-&#189; Heisenberg chain. The intra- and interchain exchange constants are -44.7 K and 53.94 K, respectively. At 250 K, KFeS<SUB>2</SUB> exhibits a well defined transition to a three-dimensionally ordered antiferromagnetic state. The calculated perpendicular susceptibility at 0 K considering the zero point reduction in magnetisation for a S = &#189; one-dimensional chain from spin wave theory is close to the projected value obtained from the experimental data

Regular versus alternating (FeS4)(n) chains: Magnetism in KFeS2 and CsFeS2

We report crystal magnetic susceptibility results of two S = 1/2 one-dimensional Heisenberg antiferromagnets, KFeS2 and CsFeS2. Both compounds consist of (FeS4)(n) chains with an average Fe-Fe distance of 2.7 Angstrom. In KFeS2, all intrachain Fe-Fe distances are identical. Its magnetic susceptibility is typical of a regular antiferromagnetic chain with spin-spin exchange parameter J = -440.7 K. In CsFeS2, however, the Fe-Fe distances alternate between 2.61 and 2.82 Angstrom. This is reflected in its magnetic susceptibility, which could be fitted with J = -640 K, and the degree of alternation, alpha = 0.3. These compounds form a unique pair, and allow for a convenient experimental comparison of the magnetic properties of regular versus alternating Heisenberg chains

Spin crossover in the ship-in-a-bottle compound: cobalt(II) tris(bipyridyl) encapsulated in zeolite-Y

The ship-in-a-bottle compound, cobalt(II) tris(bipyridyl) complex cation encapsulated in the zeolite-Y supereage, exhibits a thermally driven interconversion between a low- spin and a high-spin state-a phenomenon not observed for this ion either in solution or in the solid state. From a study of the magnetism and optical spectroscopy of the encapsulated and uneneapsulated species, supported by molecular modelling and ligand field calculations, such a spin behaviour is shown to be intramolecular in origin. The topology of the supercage forces the ion to adopt an octahedral geometry less distorted than that in its free state

Spin crossover in the ship-in-a-bottle compound: cobalt(II) tris(bipyridyl) encapsulated in zeolite-Y

The ship-in-a-bottle compound, cobalt(II) tris(bipyridyl) complex cation encapsulated in the zeolite-Y supercage, exhibits a thermally driven interconversion between a low-spin and a high-spin state - a phenomenon not observed for this ion either in solution or in the solid state. From a study of the magnetism and optical spectroscopy of the encapsulated and unencapsulated species, supported by molecular modelling and ligand field calculations, such a spin behaviour is shown to be intramolecular in origin. The topology of the supercage forces the ion to adopt an octahedral geometry less distorted than that in its free state

Single crystal magnetic susceptibility of the quasi-one-dimensional antiferromagnet KFeS2KFeS_2

The single crystal magnetic susceptibility of the quasi-one-dimensional antiferromagnet $KFeS_2$ is reported. The high temperature isotropic susceptibility is typical of a spin-l/2 Heisenberg chain. The intra- and inter- chain exchange constants are -44.7 K and 53.94 K, respectively. At 250 K, $KFeS_2$ exhibits a well defined transition to a three-dimensionally ordered antiferromagnetic state. The calculated perpendicular susceptibility at 0 K considering the zero point reduction in magnetisation for a S = l/2 one-dimensional chain from spin wave theory is close to the projected value obtained from the experimental data

Synthesis, Crystal Structure, and Magnetic Properties of a Ferromagnetically Coupled Angular Trinuclear Copper(11) Complex [Cu3(02CMe)4(bpy)s(HzO)](PF)62

The synthesis, X-ray crystal structure, and magnetic properties of an angular trinuclear copper(II) complex [Cu3(O2CMC)4(bpy)3(H2O)](PF6)2 (1), obtained from a reaction of Cu2(O2CMe)4(H2O)2 With 2,2'-bipyridine (bpy) and NH4PF6 in ethanol, are reported. Complex 1 crystallizes in triclinic space group P1BAR with a = 11.529(1) angstrom, b = 12.121(2) angstrom, c = 17.153(2) angstrom, alpha = 82.01(1)-degrees, beta = 79.42(1)-degrees, gamma = 89.62(1)-degrees, and Z = 2. A total of 6928 data with I > 2.5sigma(I) were refined to R = 0.0441 and R(w) = 0.0557. The structure consists of a trinuclear core bridged by four acetate ligands showing different bonding modes. The coordination geometry at each copper is distorted square-pyramidal with a CuN2O2...O chromophore. The Cu...Cu distances are 3.198(1) angstrom, 4.568(1) angstrom, and 6.277(1) angstrom. There are two monoatomic acetate bridges showing Cu-O-Cu angles of 93.1(1) and 97.5(1)-degrees. Magnetic studies in the temperature range 39-297 K show the presence of a strong ferromagnetically coupled dicopper(II) unit (2J = +158 cm-1) and an essentially isolated copper(II) center (2J' = -0.4 cm-1) in 1. The EPR spectra display an axial spectrum giving g(parallel-to) = 2.28 (A(parallel-to) = 160 X 10(-4) cm-1) and g(perpendicular-to) = 2.06 (A(perpendicular-to) = 12 X 10(-4) cm-1) for the normal copper and two intense isotropic signals with g values 2.70 and 1.74 for the strongly coupled copper pair. The structural features of 1 compare well with the first generation models for ascorbate oxidase

Synthesis, crystal structure and magnetic properties of a polymeric copper(II) Schiff-base complex having binuclear units covalently linked by isonicotinate ligands

The polynuclear copper(II) complex [{Cu2L(O2CC5H4N)}. C2H5OH](x) (1), where H3L is a 1&ratio;2 Schiff base derived from 1,3-diaminopropan-2-ol and salicylaldehyde, has been prepared and structurally characterized. The structure consists of a one-dimensional zigzag chain in which the binuclear [Cu2L](+) units are covalently linked by isonicotinate ligands to give a syndiotactic arrangement of the copper ions protruding outside the chain. In the basic unit, the copper(II) centres are bridged by an alkoxo and a carboxylato ligand, giving a Cu ... Cu distance of 3.492(3) Angstrom and a Cu-O-Cu angle of 130.9(2)degrees. While one copper centre has a square-planar geometry, the other copper is square-pyramidal with the pyridine nitrogen being the axial ligand. The visible electronic spectrum of 1 shows a broad d-d band at 615 nm. The complex shows a rhombic X-band EPR spectral pattern in the polycrystalline phase at 77 K. Magnetic susceptibility measurements in the temperature range 22 to 295 K demonstrate the antiferromagnetic behaviour of 1. A theoretical fit to the magnetic data is based on a model assuming 1 as an equimolar mixture of copper atoms belonging to an antiferromagnetically coupled one-dimensional Heisenberg chain with the other copper atoms outside the chain behaving like paramagnetic centres

Synthesis and x-ray Structural Studies on a New Class of Pentanuclear Copper(II) Complexes Containing a [Cu5(.mu.3-OH)2(.mu.-O2CMe)6]2+ Core and Terminal Imidazole Ligands

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