Magnetic properties of bridged azido complexes

It was shown on the basis of the generalized angular overlap model that specific features of the electronic structure of the N₃ ^– anion in polynuclear complexes with the M(_1,1-N_{3 2}M magnetic fragment should result in strong ferromagnetism. The _1,3-N₃ coordination mode favors antiferromagnetic properties. The theoretical results agree with experimental magnetostructural correlations.     

Nitrates and bis(dithiooxalato)nickelates(II) of biacetyldihydrazone complexes

Summary Biacetyldihydrazone (BdH) complexes [M(BdH)₃](NO₃)₂ (M=Co^II, Ni^II, Cu^II or Zn^II); [Fe(BdH)₃](NO₃)₃; [M(BdH)₃][Ni(dto)₂] (M=Co^II, Ni^II or Zn^II; dto=dithiooxalate); [Cu(BdH)₂][Ni(dto)₂] and [Fe(BdH)₃]₂[Ni(dto)₂]₃ have been prepared and characterized by chemical analysis, conductance measurements, electronic and i.r. spectral studies and cyclic voltammetry.A mononuclear octahedral configuration is proposed for all cationic complexes, excepting [Cu(BdH)₂][Ni(dto)₂, which is probably a dithiooxalate bridged dimer.     

Magnetic properties of spacer-armed dinuclear copper(II) complexes

The results of static magnetic susceptibility studies of spacer-armed dinuclear copper(II) complexes with dicarboxylic acid acylhydrazones are described. Weak exchange coupling between paramagnetic centers has been detected with an exchange parameter value of −2J ∼ 1–7 cm⁻¹. Short intermolecular contacts give rise to additional weak antiferromagnetic exchange coupling between copper cations comparable in terms of energy with superexchange inside the dinuclear complex (−zJ′ ∼ 0.6–5.0 cm⁻¹).     

Magnetic properties of binuclear high-spin trimethylacetate nickel(II) complexes

The static magnetic susceptibility of mononuclear trimethylacetate nickel complex Ni(NH₂Ph)₄(OOCCMe₃)₂ (3) and binuclear complexes Ni₂(μ-OH₂)(μ-OOCCMe₃)₂(OOCCMe₃)₂(dipy)₂ (4) and Ni₂(μ-OOCCMe₃)₄py₂ (5) was measured in the temperature range of 2–300 K. The magnetic behavior of3 is typical of mononuclear complexes with the Ni¹¹ atom in the octahedral environment. Numerical calculations of the temperature dependence of magnetic susceptibility with inclusion of isotropic exchange interactions (J) and single-ion initial splitting parameters showed that the magnetic behavior of complexes4 and 5 can be interpreted in terms of ferromagnetic (for4) and antiferromagnetic (for5) interactions. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 3, pp. 437–442, March, 2000.     

Magnetic properties of oxidation products of phthalocyanine complexes with metal chlorides with electron acceptor properties

The effect of charge transfer complex formation on the oxidisability of various phthalocyanines complexes with Lewis acids has been investigated. Multistep electron transfer between phthalocyanine as electron donor and the molecules of electron acceptor was found to be possible, leading to the formation of mono- and polycation radicals with characteristic magnetic properties. The structure of the transition products has been established and an oxidation mechanism is suggested.     

Magnetic properties of lanthanide organometallic sandwich complexes produced in a molecular beam

The magnetic properties of gas-phase terbium–cyclooctatetraene multi-decker sandwich complexes, Tb_n(C₈H₈)_n+1 were measured using a Stern-Gerlach type magnetic deflection approach. Beams of Tb_n(C₈H₈)_n+1 complexes displayed one-sided deflection toward high field – indicating that fast spin relaxation occurs within the complexes as they pass through the magnetic field. The magnetic moment for Tb_n(C₈H₈)_n+1 (n = 1−5) was evaluated using the Langevin model. Evolution of magnetic moment with the complex size is discussed with electronic structures for oxidation states of Tb^3+/2+ ions, implying the possibility of antiferromagnetic interaction of two adjacent Tb²⁺ ions.     

Magnetic properties of copper(II) complexes with some hydrazones of substituted salicylaldehydes

A series of novel mono-and binuclear copper(II) complexes with substituted salicylaldehyde acylhydrazones H₂L of the formula CuL · xH2O (x = 0 and 1) and [Cu(HL)](ClO₄)(CH₃OH) were synthesized. The isolated dimeric complexes of copper acetate were found to exist as isomers with different bridging atoms. In dimers showing a superexchange between the paramagnetic centers through bridging phenoxide O atoms, the antiferromagnetic exchange couplings were much stronger than those in complexes with bridging O atoms of the a-oxyazine fragment.     

Magnetic properties of transition metal complexes with 2,2′-bipyridin-5-yl t-butyl nitroxide

Complexes [Mn^II(5bpno)₃(ClO₄)₂], [Mn^II(5bpno)(CH₃OH)₂Cl₂], [Cu^II(5bpno)₂(ClO₄)₂], and [Cu^II(5bpno)Cl₂] were prepared, where 5bpno stands for 2,2′-bipyridin-5-yl t-butyl nitroxide. X-ray crystallographic analysis clarified that the Cu ion in [Cu(5bpno)₂(ClO₄)₂] was tetra-coordinate with four nitrogen atoms forming two chelate rings. Magnetic measurements revealed the presence of ferromagnetic couplings in the Mn complexes, whereas the Cu complexes showed antiferromagnetic couplings. Magnetic exchange couplings between the metal and radical spins through the intervening pyridine ring can be explained in terms of the spin-polarization mechanism.     

Magnetic properties of new complexes of 3d metal chlorides with 3-amino-4-ethoxycarbonylpyrazole

New complexes of Co(II), Ni(II), and Cu(II) chlorides with 3-amino-4-ethoxycarbonylpyrazole (L) of the composition ML₂Cl₂ are synthesized. The compounds are studied by powder X-ray diffraction, electronic and IR spectroscopy, static magnetic susceptibility (temperature range 2–300 K). It is found that in the ML₂Cl₂ complexes (M = Co(II), Ni(II), Cu(II)) ferromagnetic exchange interactions between the unpaired electrons of metal ions occur. In [CoL₂Cl₂] and [NiL₂Cl₂] compounds a transition to the magnetically ordered state (T _c ? 10–12 K) is observed.     

Magnetic property studies of manganese-phosphate complexes

Phosphoric acid forms two distinct coordination compounds with manganese salts in aqueous media, a two-dimensional layered structure, [Mn(HPO4).(H2O)3], 1, under ambient conditions, and a three-dimensional synthetic mineral, [Mn5(mu-OH2)2(HPO4)2(PO4)2(H2O)2], 2, under hydrothermal procedures, at 120 degrees C. In compound 1, the oxygen atom of the doubly deprotonated phosphoric acid interconnects the metal centers to form a layered structure. The neutral hydrophilic layers of 1 are separated by 5.5 A and may potentially intercalate hydrophilic organic guest molecules. The metal centers in 2 are octahedral and bridged by PO4(3-), HPO4(2-), and OH2 groups to form a complex three-dimensional network. XPS analysis on 1 and 2 confirms that manganese exists in the +2 oxidation state. Compound 2 is a poor ion exchanger, but some improvement is observed on partial dehydration. The magnetic properties of both 1 and 2 were studied in detail to examine the amplitude of the magnetic interactions through phosphate ligand bridges. While 1 reveals dominant antiferromagnetic interactions between the spin carriers, a complete investigation of the magnetic properties of 2 revealed its true nature to be a glassy magnet.     

Magnetic and spectroscopic properties of copper(II) complexes with 1-salicoyl-4-phenylthiosemicarbazide

Summary Cu^II complexes of 1-salicoyl-4-phenylthiosemicarbazide (SPT) have been synthesized and characterized by means of elemental analysis, magnetic measurements, and i.r. and e.p.r. spectroscopic methods; ¹H- and ¹³C-n.m.r. and mass spectral data on the thiosemicarbazide are also reported. A paramagnetic complex _eff= 1.298 B.M., is formed with copper(II) sulphate; the low magnetic moment and the e.p.r. spectral data suggest a binuclear species. A diamagnetic complex due to a strong Cu-Cu interaction has been isolated with copper(II) chloride.     

Magnetic coupling in dinuclear Gd complexes

A spin density functional (SDFT) study of carboxylate-bridged and diazenido-bridged dinuclear gadolinium compounds is presented. Calculated magnetic coupling constants for the carboxylate-bridged structures are in good agreement with experimental data, confirming the ability of the broken symmetry approach used in this work to predict magnetic behavior in such compounds. The systematic trend wherein symmetrically bridged complexes are antiferromagnetically coupled and asymmetrically bridged are ferromagnetically coupled is reproduced by the SDFT calculations. The mechanism underlying magnetic coupling in closed- and open-shell dinuclear complexes is described using a perturbative molecular orbital model that focuses the influence of the 4f(7)-5d exchange interaction on molecular orbitals with significant 5d-orbital character for the complex [[[(Me(3)Si)(2)N](2)(thf)Gd](2)(N(2))]. Open-shell electronic configurations facilitate strong ferromagnetic coupling, whereas in closed-shell systems antiferromagnetic coupling is usually preferred.     

Synthesis and characterization of biacetyldihydrazone complexes of cobalt(II), copper(II), nickel(II) and iron(III)

Summary Biacetyldihydrazone (BdH) complexes [M(BdH)₃](ClO₄)₂ (M=Co^IIor Cu^II) and [M(BdH)₃](NO₃)_2,3 (M = Ni^IIor Fe^III) have been prepared and characterized by chemical analysis, conductance measurements, electronic, i.r. and e.p.r. spectral studies and magnetic subsceptibilities measurements. A mononuclear octahedral configuration is proposed for all complexes studied.     

Magnetic properties of a new N-TEMPO-tert-butyl substituted salicylaldimines and their biradical palladium(II) complexes

A new TEMPO bearing tert-butylated salicylaldimines 1 and 2, as well as early reported 3, and their bis(N-TEMPO-tert-butylated salicylaldiminato)palladium(II) biradical complexes 4–6 have been synthesized and characterized by elemental analyses, IR, UV/vis, ESR and an SQUID magnetometer. The solid state g-factors (2.0116–2.0168) for 4–6 suggest the existence of the significant metal-orbital contribution to the SOMO of nitroxyl radicals. The χ_mT vs. T plots for 1 and 2 indicate that the χ_mT decreases as T is lowered from 300 to 20 K, suggesting the existence of weak antiferromagnetic interactions in these radicals. Variable-temperature dependence (10–300 K) magnetic susceptibility data for biradical complexes 4–6 revealed the existence of ferromagnetic and antiferromagnetic behavior around at 10–220 K range for 4. The 1/χ_m data for 1–6 follow the Curie–Weiss law with negative θ throughout the above temperature range.     

Magnetic properties of poly(propylene imine)-copper dendromesogenic complexes: An EPR study.

Copper(II) complexes formed by coordination of the Cu(II) ion with liquid-crystalline poly(propylene imine) dendrimer ligand (L) of the first (complex 1) and second (complex 2) generations with various Cu(II) contents (x = Cu/L) have been studied by electron paramagnetic resonance (EPR) spectroscopy. The existence of a redox-active blue complex 1 (x = 1.9) and the copper(II) nitrate electron transfer associated with the valence tautomerism are revealed for the first time in copper-based dendrimers. It has been shown that the electronic structure of the blue complex 1 (x = 1.9) is adequately described as a mixed-valence dimer containing d9- and diamagnetic d10-configurated copper ions, and an antiferromagnetically coupled NO3* radical arising on the nitrate-bridged counter ligand. The activation energy value found for the electron transfer is about 0.35 meV, which indicates a low-energy charge dynamic. The ability of the blue and green complexes 1 (x = 1.9) dissolved in isotropic solvents to orient themselves in the magnetic field was revealed by EPR spectroscopy. The degree of orientation of the molecular z axis (S(z)) of these complexes in the magnetic field differs, depending on the type of copper(II)-complexing site in the dendrimer ligand, and can reach 0.76, which is close to S(z) = 1 (completely aligned system). A combination of magnetic and orientational parameters indicates an NO4 environment of the Cu(II) ion in green complex 1 (x = 1.9), and confirms the chain structure with intermolecular Cu(II)-NO3-Cu(II) bridges between Cu(II) centres in columns.     

Thermal properties of complexes

Complexes of saponified polyacrylonitrile with the bivalent metals Ca, Co, Cu, Mg, Ni and Zn, were obtained. Thermal analysis of the complexes was carried out. The highest thermal stability was found for the complexes with Co and Ni.