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.     

Insight into the influence of terminal ligands on magnetic exchange coupling in a series of dimeric copper(II) acetate adducts

A combination of experimental (SQUID magnetometry) and quantum-chemical (BS-DFT, CASSCF(n,m)/NEVPT2, DDCI3) methods is used to probe the influence of terminal ligands on magnetic exchange coupling in the series of [Cu₂(μ₂-OAc)₄L₂] complexes with O-donor terminal ligands extended by two novel complexes containing phosphine oxide ligands. The possibilities and limitations of these approaches are discussed. The influence of terminal ligands on magnetic superexchange interaction was quantified by two contributions—the first contribution is associated with structural changes within the {Cu(μ₂-OAc)₄Cu} core, while the second contribution is due to the difference in the electronic influence of different terminal ligands at a given core geometry. Both contributions were found to be approximately of the same order of magnitude. These results indicate that magnetic exchange coupling, known to be highly sensitive to the distortions in core geometry, is not solely determined by the core structure. Our findings are consistent with the fact that various one- and multiparameter magnetostructural correlations reported in the literature have only a qualitative predictive capability.     

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).     

Carboxylate clusters with the M<Subscript>4</Subscript>O<Subscript>4</Subscript> cubane-like core: pivalate cocrystal containing Co<Superscript>II</Superscript> and Ni<Superscript>II</Superscript>

Joint thermolysis of the dinuclear pivalate complexes M₂(μ-H₂O)(μ-Piv)₂(Piv)₂(HPiv)₄ (M = Co (1) and Ni (2), Piv^- is the pivalate anion), in decane at 174 °C at the reactant ratio 1: 1 followed by treatment of the dry thermolysis product with methanol afforded crystals of a new cocrystallization product of the molecules containing the heterometallic cubane-like core M₄(Co,Ni)O₄. According to the X-ray diffraction data and the results of magnetic measurements, inductively coupled plasma atomic emission spectrometry (ICP-AES), and investigations of the solid-state thermal decomposition products, the isolated cocrystallization product has the general formula [Co_1.6Ni_2.4(μ₃-OMe)₄(μ₂-Piv)₂(pg² -Piv)₂(MeOH)₄] ·4MeOH (3·4MeOH). Thermolysis of the crystals of the solvate 3·4MeOH is a destructive process accompanied by the intramolecular redox reaction. A mixture of metallic Ni and cobalt oxide (CoO) are the final solid decomposition products of 3 · 4MeOH in an argon atmosphere, whereas a mixture of the phases NiO, Co₃O₄, and NiCo₂O₄ is formed in air.     

Magnetic activity of nanostructured biopolymeric nanomagnets

The magnetic properties of arabinogalactan-stabilized iron-containing nanobiocomposites, which include magnetite nanoparticles, were studied. The magnetic characteristics of samples were measured on a SQUID magnetometer in the temperature range of 5–320 K and magnetic fields of up to 1.5·10⁴ G. The coercive force and the residual magnetization of ferroarabinogalactan nanocomposites are inversely dependent on the magnetite nanoparticle size.     

Structure and magentic properties of novel chelate complexes of copper(II) and nickel(II) with nitroxide radical ethyl-2-(1-oxyl-2,2,5,5-tetramethylimidazolidin-4-yliden)-3-oxopropanoate

Chelate complexes of copper(II) and nickel(II) with anions of nitroxide radical ethyl-2-(1-oxyl-2,2,5,5-tetramethylimidazolidin-4-yliden)-3-oxopropanoate (HL) are synthesized. The compounds have molecular structure and zero magnetic dimensionality. CuL₂ crystallizes as two polymorphs having mononuclear structure. Ni₂L₄ forms dimeric molecules by virtue of the bridging function of the aldehyde oxygen atoms. Magnetic properties of Ni₂L₄ are determined by antiferromagnetic exchange interactions between the Ni(II) ions (-48(1) K) propagated through the oxygen bridges     

Paramagnetic triangular rhenium sulfide cluster [Re3S4(Dppe)3(NCS)3]Br

A new cluster [Re₃S₄(Dppe)₃(NCS)₃]Br (Dppe = Ph₂PCH₂CH₂PPh₂) is synthesized. The molecular and crystal structures of the cluster are determined by X-ray diffraction analysis. The magnetochemical data indicate the high-spin ground state (S = 3/2) of the cluster at room temperature.     

Coordination compounds of some 3d metals with 3-methyl-1-phenyl-4-formylpyrazol-5-one

CuL₂ · 1.5H₂O and ML₂ · 2H₂O · 2EtOH (M = Co²⁺, Ni²⁺, Mn²⁺) coordination compounds were synthesized via the exchange reaction between the sodium salt of 3-methyl-1-phenyl-4-formylpyrazol-5-one (HL) and metal chlorides.The synthesized compounds were studied by thermogravimetry, magnetochemistry, and electron and IR spectroscopy. The complexes CuL₂ · 2Py and CoL₂ · 2Py · MeOH were obtained via recrystallization from a methanol-pyridine mixture, and their structures were studied by X-ray diffraction. Pyrazolone was found to be coordinated in the deprotonated enol form and to form six-membered chelate rings with a metal. The coordination polyhedron of a metal cation was found to be a square bipyramid (Cu²⁺) or an axially elongated octahedron (Co²⁺) with its vertices occupied by the oxygen atoms of 3-methyl-1-phenyl-4-formylpyrazol-5-one and the nitrogen atoms of pyridine.     

On the beam propagation through active media

An analytical iterative procedure has been established to determine the amplitude of a laser beam propagating through an active medium. The treatment is valid for both homogeneous and inhomogeneous broadening, and for arbitrary inhomogeneities of the parameters characterizing the active medium, namely, the refractive index, the small-signal gain and the saturation intensity. After a supplementary approximation, a thin-sheet gain approach is derived from the first iteration. The formalism enables us to provide analytical criteria for evaluating both the accuracy of each iteration and the propagation distances for which the thin-sheet solution can be used. This revised version was published online in November 2006 with corrections to the Cover Date.     

��Jumping�� crystals: structures and properties of CuII complexes with N-methylimidazolyl- and N-methyltriazolyl-substituted nitronyl nitroxides

To find the factors favorable for the appearance of chemomechanical activity of heterospin crystals, a series of new heterospin complexes were synthesized and characterized. It includes [Cu(tfac)₂L^Im ₂]·2CH₂Cl₂, [Cu(tfac)₂L^Im ₂]·2EtOH, [[Cu(pfu)₂]₂L^Im ₃]·1/2CH₂Cl₂, [Cu(pfh)₂L^Im ₂]·1/2CH₂Cl₂, [Cu(piv)₂L^Im ₂]·2MeOH, [Co(piv)₂L^Im ₂], [ $ Cu(hfac)_2 L^{CD_3 } _2 $ ], [Cu(hfac)₂L^Tr]₂·CH₂Cl₂, and [Cu(hfac)₂L^Tr ₂] (L^Im, $ L^{CD_3 } $ , and L^Tr are N-methylimidazolyl-, N-trideuteriomethylimidazolyl-, and N-methyltriazolyl-substituted nitronyl nitroxides, respectively; tfac, hfac, pfu, pfh, and piv are the charged coordinated diamagnetic ligands 1,1,5,5-tetrafluoropentane-2,4-dionate, 1,1,1,5,5,5-hexafluoropentane-2,4-dionate, 1,1,1,2,2,3,3,4,4,8,8,9,9,10,10,11,11,11-octadecafluoroundecane-5,7-dionate, 1,1,1,5,5,6,6,6-octafluorohexane-2,4-dionate, and 2,2-dimethylpropionate, respectively). The crystal and molecular structures of all compounds were determined. The results of the X-ray diffraction study of the complex [Ni(hfac)₂L^Im ₂] synthesized earlier are reported. In the solid state of the complexes [Cu(pfh)₂L^Im ₂] and [Co(piv)₂L^Im ₂], the paramagnetic ligands are cis-coordinated to the central atom in a monodentate fashion via the donor N atom of the imidazole ring. In the dinuclear complexes [[Cu(pfu)₂]₂L^Im ₃] and [Cu(hfac)₂L^Tr]₂, the paramagnetic ligands are also in cis positions but act as bridges through coordination of the donor N atoms of the azole ring and the O atom of the nitronyl nitroxide moiety to different Cu²⁺ ions. In the solid complexes $ Cu(hfac)_2 L^{CD_3 } _2 $ , [Cu(hfac)₂L^Tr ₂], [Cu(tfac)₂L^Im ₂]·2CH₂Cl₂, [Cu(tfac)₂L^Im ₂]·2EtOH, and [Cu(piv)₂L^Im ₂]·2MeOH, the nitronyl nitroxide radicals in the mononuclear heterospin molecules are in trans positions. The packing motif in the crystal structures of the complexes $ Cu(hfac)_2 L^{CD_3 } _2 $ , [Cu(tfac)₂L^Im ₂]·2CH₂Cl₂, and [Cu(tfac)₂L^Im ₂]·2EtOH is the same as that in the previously studied complexes [M(hfac)₂L^Im ₂] exhibiting chemomechanical activity. Among the complexes under consideration, only crystals of $ Cu(hfac)_2 L^{CD_3 } _2 $ can exhibit chemomechanical activity, that is to make jumps upon heating or irradiation. The results of the present study suggest that the packing of the solid-state structure plays a key role in the generation of mechanical activity of the crystals.