Chemistry Journal of Moldova

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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DOI: dx.doi.org/10.19261/cjm.2006.01(1).11

Graphical Abstract: The complexes of general formula Cu(H₂L) (II); [CuLn(L)(NO₃)(H₂O)_n] (where H₄L=N,NI-bis[2- hydroxy(3-

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