Chemistry Journal of Moldova

DOI: dx.doi.org/10.19261/cjm.2007.02(1).06

Graphical Abstract: Thiolato-bridged complex [Cu^I₄Cu^II₄(peampt)₄Cl₈]·2H₂O (Hpeampt = 1-(2-pyridylethyl)amino) methylpropane-2-thiol) has been synthesized and characterized by the elemental analysis, IR and UV-vis spectroscopies and magnetic susceptibility measurement. The X-ray crystal structure analysis of this complex shows a localized mixed-valence octanuclear cage structure made up of four trigonal-bipyramidal Cu^IIN₂SCl₂, two trigonal CuIS2Cl, and two tetrahedral Cu^IS₂Cl₂ coordination sites. Temperature dependence of magnetic susceptibility (4.5— 300 K) shows that a fairly strong antiferromagnetic interaction is operating between the four Cu^II ions.


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DOI: dx.doi.org/10.19261/cjm.2007.02(1).07

Graphical Abstract: The solid-state structure of the tri-potassium calix[4]arene dihydroxyphosphonate salt is presented. In this structure, two potassium cations bridge between layers of dimeric calixarene diphosphonate units and two other potassium cations bridge along the face of the layers. The ubiquitous dimeric association of the calixarenes shows the highest interdigitation value so far observed. As expected, the cations are solvated and are complexed exo with respect to calixarene crown. The octahedral coordination sphere of the potassium cations is formed by two phosphonate groups of the calixarenes and four water molecules. Electrostatic forces represent the major element of interaction in the solid-state system.


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DOI: dx.doi.org/10.19261/cjm.2007.02(1).08

Graphical Abstract: The interaction of cis-Re₂(RCOO)₂Cl₄, trans-Re₂(RCOO)₂Cl₄, Re₂(RCOO)₃Cl₃ and Re₂(RCOO)₄Cl₂ (where R - alkyl group) with 1,3,5-triphenylverdazyle radical in 1,2-dichlorethane was investigated. It is discovered, that gradual substitution of halogenide ligands by carboxylates in dirhenium(III) clusters led to slowing down of reaction with a radical due to different influence of these ligands on parameters of rhenium - rhenium bond. Presented data showed perspectivity of Re₂⁶⁺-substances applications as therapeutic agents due to their low toxicity and antiradical properties that occured by δ-component of quadruple Re-Re bond electron transition.


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DOI: dx.doi.org/10.19261/cjm.2007.02(1).09

Graphical Abstract: Interactions of a series of indole-3-alkanoic acids (with n-alkanoic acid side-chains from C1 to C4) with iron(III) in acidic aqueous solutions have been shown to comprise two parallel processes including complexation and redox transformations giving iron(II) hexaaquo complexes. The structure and composition of the reaction products are discussed, as analysed using a combination of instrumental techniques including 57Fe Mössbauer, vibrational and HNMR spectroscopies.


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DOI: dx.doi.org/10.19261/cjm.2007.02(1).10

Graphical Abstract: Four new heteronuclear lanthanide complexes with general formula [Ge(OH)(μ-HDTPA)LnGe(OH) (μ-DTPA)] (Ln = Sm – Dy) were synthesized and subsequently characterized by different physico- chemical methods. The structures of new compounds have been proposed. In considered complexes the 4f-luminescence of three-charged ions of samarium, europium, terbium and dysprosium is realized at UV-excitation. It is noteworthy that it is the first observation of 4f-luminescence in water solutions of heteronuclear f-p-complexes. The comparison of luminescent characteristics of hetero- and homonuclear landthanide complexes is described and discussed as well.

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DOI: dx.doi.org/10.19261/cjm.2007.02(1).17

Graphical Abstract: In this paper we give a short overview of our efforts in the understanding of the magnetic properties of the fascinating nanoscopic cluster K₆[V^IV₁₅As₆O₄₂(H₂O)]·8H₂O (hereafter V15) exhibiting layers of magnetization. We analyze EPR and adiabatic magnetization of the V15 cluster with a triangular VIV3 array causing spin frustration. A model for V15 includes isotropic and antisymmetric (AS) exchange interactions in the general form compatible with the trigonal symmetry. Orientation of the AS vector (but not only its absolute value) is shown to play an important physical role in spin-frustrated systems. We were able to reach perfect fit to the experimental data on the stepwise dependence of magnetization vs. field at ultra-low temperatures. Furthermore, it was possible for the first time to estimate precisely two components of the AS vector coupling constant, namely, in-plane component and the perpendicular part. We show that only intramultiplet transitions in EPR are allowed when the vector of AS exchange is normal to the plane of vanadium triangle, meanwhile the in-plane part of AS exchange gives rise to a series of weak intermultiplet transitions. Experimental data on high-frequency EPR of V15 at low temperatures are discussed. The spin-vibronic effects in trimeric spin frustrated clusters are also studied and an important role of the interplay between the AS exchange and Jahn-Teller interaction is revealed. The results clarify the concept of spin-frustration in view of its magnetic and spectroscopic manifestations in metal clusters.


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DOI: dx.doi.org/10.19261/cjm.2006.01(1).03

Graphical Abstract: The magnetic susceptibility (χT) of an unusual dissymmetric binuclear manganese corboxylate complex has been measured from 2 to 300K. The magnetic data which have been fitted with help of the Heisenberg Dirac Van Vleck HDVV spin-exchange Hamiltonian H = − J S 1 S 2 , indicate that an antiferromagnetic interaction equal to J = -0.90(1) cm-1 is present. A correlation between J values and Mn-H2O-Mn angles has been tempted.


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DOI: dx.doi.org/10.19261/cjm.2006.01(1).04

Graphical Abstract: Reaction in methanol solution of the trinuclear ‘basic’ chromium(III) acetate with Pr(NO₃)₃⋅5H₂O and further extraction by chloroform-acetone mixture led to the formation of novel unusual [Cr₃O(CH₃COO)₆(H₂O)₃]NO₃⋅HNO₃⋅H₂O (1) cluster with one “free” molecule of nitric acid. Complex 1 crystallizes in the monoclinic space group P21/c with, at room temperature, a = 13.624(2), b = 15.032(2), c = 15.180(2) Å, β = 112.98(3) °, Z = 4, and V = 2862.09 Å3. The obtained crystalline compound has been synthesized and characterized by IR and UV/Vis methods.


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DOI: dx.doi.org/10.19261/cjm.2006.01(1).05

Graphical Abstract: Heterometallic complexes of chromium (III) with some 3d metals have been synthesized based on nitrilotriacetic acid (H₃nta), like M(bpy)₂Cr₂(OH)₂(nta)₂·nH₂O, where M = Mn²⁺, Co²⁺, Ni²⁺ and Zn²⁺; bpy = α,α′- bipyridine; n = 8 or 9. Their chemical composition has been determined from the results of the elemental analysis and thermogravimetric study. The coordination modes of the nta3 ̄ ligand and the type of chemical bonds have been proposed basing on IR spectra.


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DOI: dx.doi.org/10.19261/cjm.2006.01(1).09

Graphical Abstract: The novel bis(μ3-oxo) tetranuclear trichloracetate cluster, [Fe₄O₂(CCl₃COO)₈(THF)₂(DMF)(H₂O)]⋅THF (1), has been synthesised and subsequently characterised by X-ray structure analysis, magnetic measurements and infra red (IR). The structure of cluster is “butterfly” type. The Fe···Fe separation has the value of 2.883(1) - 3.441(7) Å. The coordination number of iron (III) is 6. Magnetic studies reveal the presence of an antiferromagnetic exchange in the parallelogram skeletons of the tetranuclear species. Using the spin Hamiltonian H = -2Jwb(Ŝ1Ŝ2 + Ŝ2Ŝ3 + Ŝ3Ŝ4 + Ŝ4Ŝ1) - 2JbbŜ2Ŝ4v+ gμβ(Ŝ1z + Ŝ2z +Ŝ3z + Ŝ4z)B, the fitting parameters Jbb = - 14.3 cm-1, Jwb = - 32.1 cm-1 , g = 2.07, ρparam. -5 impur. = 4.2 %, ΘCurie-Weiss const. = -0.5 K and R = 6.8·10 were obtained.

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