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ABSTRACT: A series of the trinuclear [{Fe(3MeO-L)2}2{[small micro]6-(Ln(?2-NO3)(H2O)}][round bullet, filled]nH2O, (Ln = Gd (2a), Tb (2b), Dy (2c), Ho (2d), Er (2e), Y (2f), H2-3MeO-L = 2-hydroxy-3-methoxy-phenylsalicylaldimine) complexes was prepared and thoroughly characterized. The crystal structure of 2b was determined and it revealed that the heterotrinuclear complex consists of two anionic [Fe(3MeO-L)2]- subunits coordinated to the [Tb(H2O)(?2-NO3)]2+ bridging moiety through the phenolato and methoxy oxygen atoms. The angular distortion within the coordination polyhedron of the [Fe(3MeO-L)2]- subunits grows significantly upon coordination to the Ln atom of the bridging moiety, which consequently induces the increase in the parameter of the axial magnetic anisotropy. This conclusion is obvious from the comparison and analysis of the structural (XRD) and magnetic data of the yttrium involving trimer 2f and the precursor complex (Pr3NH)[Fe(3MeO-L)2] (1, Pr3NH = the tripropylammonium cation), where DFe(1) = +0.80 cm-1 and DFe(2f) = +1.64 cm-1. Furthermore, a weak antiferromagnetic interaction between the Fe(III) centres was found in 2f (JFeFe = -0.26 cm-1). The magnetic parameters of 2f were used in the fitting of the magnetic properties of 2a as constraints. The ferromagnetic nature of the Fe-Gd interaction in 2a was confirmed, with JGdFe = +1.40 cm-1, DGd = -0.26 cm-1. Moreover, in the case of the Tb (2b) and Dy (2c) compounds the slow relaxation of magnetization at low temperature (below 1.9 K) was observed upon dehydration of the parent compounds.
Dalton Transactions. 01/2012;
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ABSTRACT: Two new tetranuclear complexes, [Zn(2)Cr(2)(NCS)(4)(Dea)(2)(HDea)(2)].4DMSO (1; DMSO = dimethyl sulfoxide) and [Zn(2)Cr(2)(NCS)(4)(Dea)(2)(HDea)(2)].2CH(3)CN (2), were prepared from zinc oxide, Reinecke's salt, NH(4)[Cr(NCS)(4)(NH(3))(2)].H(2)O, ammonium thiocyanate, and a nonaqueous solution of diethanolamine (H(2)Dea) in a reaction carried out under open air. Both compounds have similar centrosymmetric crystal structures based on a tetranuclear {Zn(2)Cr(2)(mu(3)-O)(2)(mu-O)(4)} core. Variable-temperature magnetic susceptibility measurements of 1 and 2 show weak antiferromagnetic coupling between chromium centers. The magnetic data and high-field, high-frequency electron paramagnetic resonance spectra were analyzed in terms of the spin Hamiltonian H = JS(1).S(2) - j(S(1).S(2) + mu(B)B{g(1)}S(1) + D(Cr){S(z1)(2) - S(1)(S(1) + 1)/3} + E(Cr)(S(x1)(2) - S(y1)(2)) + mu(B)B{g(2)}S(2) + D(Cr){S(z2)(2) - S(2)(S(2) + 1)/3} + E(Cr)(S(x2)(2) - S(y2)(2)) + D(12){S(z1)S(z2) - S(1).S(2)/3} + E(12)(S(x1)S(x2) - S(y1)S(y2)) with J = 13.7 cm(-1), j = 1.1 cm(-1), D(Cr) = 0.3864 cm(-1), E(Cr) = -0.1104 cm(-1), D(12) = -0.1873 cm(-1), and E(12) = -0.0155 cm(-1) for 1 and J = 9.4 cm(-1), j = 0.8 cm(-1), D(Cr) = 0.3564 cm(-1), E(Cr) = -0.0647 cm(-1), D(12) = -0.1850 cm(-1), and E(12) = -0.0112 cm(-1) for 2. Density functional theory (DFT) calculations were employed to calculate the zero-field splitting on Cr(3+) ions. Calculations of the exchange integrals J were attempted by using the "broken-symmetry" DFT method.
Inorganic Chemistry 06/2010; 49(12):5460-71. · 4.60 Impact Factor
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ABSTRACT: The magnetostructural D correlation interrelates the zero-field-splitting parameter D withdrawn from the magnetic data with the structural tetragonality parameter D(str). This correlation allows the quantitative prediction that D < 0 occurs for the tetragonally compressed nickel(II) complexes.
Inorganic Chemistry 04/2010; 49(9):3971-3. · 4.60 Impact Factor
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ABSTRACT: The complex [Fe(II){(CN)Fe(III)L(5)}(6)]Cl(2) consists of a mixed-valence heptanuclear cyanide-bridged unit formed of a Schiff-base pentadentate ligand L(5) and it shows a spin crossover of the peripheral Fe(III) centres.
Dalton Transactions 03/2010; 39(9):2198-200. · 3.84 Impact Factor
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ABSTRACT: A new heterometallic Mn/Cr molecular wheel complex has been synthesized using zerovalent manganese, Reineckes salt, ammonium thiocyanate and triethanolamine (H(3)tea) as starting materials. The compound [Mn(3)Cr(4)(NCS)(6)(Htea)(6)] (1) has been characterized in terms of its electrochemical, IR and EPR spectroscopic as well as its magnetic properties. The magnetic susceptibility and magnetization data were treated simultaneously during the optimization routine and resulted in J(Mn-Cr) = +0.43 cm(-1), J(Cr-Cr) = -4.75 cm(-1), J(Mn-Mn) = +1.78 cm(-1), g(eff) = 1.878 with the ground state S = 15/2.
Dalton Transactions 03/2010; 39(9):2344-9. · 3.84 Impact Factor
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ABSTRACT: A novel heterometallic tetranuclear complex [Cr(3)Cd(NCS)(4)(H(2)tea)(Htea)(3)].3CH(3)OH () has been prepared using cadmium oxide, Reinecke's salt, ammonium thiocyanate and a methanol solution of triethanolamine (H(3)tea) in air. Crystallographic investigations reveal that the molecular structure of the complex is based on an uncommon asymmetric {Cr(3)Cd(mu(3)-O)(2)(mu-O)(4)} core with firstly observed terminal coordination of the NCS-groups in such molecular structure type. A network of O-HO hydrogen bonds as well as SS interactions link the molecules into a two-dimensional supramolecular network. Variable-temperature (1.8-300 K) magnetic susceptibility measurements show a change of the mu(B) value at low temperature, indicative of antiferromagnetic interactions (J = -7.45 cm(-1)) between chromium(iii) centers.
Dalton Transactions 02/2010; 39(7):1734-9. · 3.84 Impact Factor
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ABSTRACT: A one-pot synthetic procedure yields the octanuclear Fe(III) complexes Fe(8)(micro(4-)O)(4)(micro-pz(*))(12)X(40, where X = Cl and pz(*) = pyrazolate anion (pz = C(3)H(3)N(2)-) (1), 4-Cl-pz (2), and 4-Me-pz (3) or X = Br and pz(*) = pz (4). The crystal structures of complexes 1-4, determined by X-ray diffraction, show an Fe(4)O(4)-cubane core encapsulated in a shell composed of four interwoven Fe(micro-pz(*))(3)X units. Complexes 1-4 have been characterized by 1H NMR, infrared, and Raman spectroscopies. Mössbauer spectroscopic analysis distinguishes the cubane and outer Fe(III) centers by their different isomer shift and quadrupole splitting values. Electrochemical analyses by cyclic voltammetry show four consecutive, closely spaced, reversible reduction processes for each of the four complexes. Magnetic susceptibility studies, corroborated by density functional theory calculations, reveal weak antiferromagnetic coupling among the four cubane Fe centers and strong antiferromagnetic coupling between cubane and outer Fe atoms of 1. The structural similarity between the antiferromagnetic Fe(8)(micro(4-)O)(4) core of 1-4 and the antiferromagnetic units contained in the minerals ferrihydrite and maghemite is demonstrated by X-ray and Mössbauer data.
Inorganic Chemistry 02/2008; 47(2):645-55. · 4.60 Impact Factor
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ABSTRACT: A comparison is made between the structural, spectroscopic, electrochemical, and magnetic properties of pyrazolate versus carboxylate complexes [Fe3(mu3(mu3O)(mu-LL)6Cl3]2- containing the Fe3(mu3-O)-motif. While the Fe3(mu3-O)-cores are structurally indistinguishable in the two types of complexes, their magnetic properties deviate from the expected values as a result of a through-pyrazole contribution to the overall antiferromagnetic exchange with J1/hc = -80.1 cm(-1) and J2/hc = -72.4 cm(-1), or J1/hc = 70.6 cm(-1) and J2/hc = -80.8 cm(-1), (Hex = -J1(S1S2 + S2S3) - J2S1S3). The magnetic properties of the pyrazolate complexes are further tuned by an antisymmetric exchange interaction term.
Inorganic Chemistry 01/2008; 46(26):10981-9. · 4.60 Impact Factor
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ABSTRACT: A comparison is made between the structural, spectroscopic, electrochemical, and magnetic properties of pyrazolate versus carboxylate complexes [Fe3(μ3(μ3O)(μ-LL)6Cl3]2− containing the Fe3(μ3-O)-motif. While the Fe3(μ3-O)-cores are structurally indistinguishable in the two types of complexes, their magnetic properties deviate from the expected values as a result of a through-pyrazole contribution to the overall antiferromagnetic exchange with J1/hc = −80.1 cm−1 and J2/hc = −72.4 cm−1, or J1/hc = 70.6 cm−1 and J2/hc = −80.8 cm−1, (Hex = −J1(S1S2 + S2S3) − J2S1S3). The magnetic properties of the pyrazolate complexes are further tuned by an antisymmetric exchange interaction term.
11/2007;
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Journal of the American Chemical Society 09/2007; 129(34):10306-7. · 9.91 Impact Factor
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ABSTRACT: The complexes of general formula [ML]2[Mn(NCS)4](ClO4)2 (where M = Cu(II), Ni(II); L = N-dl-5,7,7,12,14,14-hexamethyl-1,4,8,11-tetraazacyclotetradeca-4,11-diene) were obtained and the crystal structures of both heteronuclear compounds were determined at 173 K. Complex [CuL]2[Mn(NCS)4](ClO4)2 (1) crystallizes in a monoclinic space group, C2/c, with a = 41.297(9) A, b = 7.571(2) A, c = 16.417(4) A, beta = 96.97(15) degrees, Z = 8, whereas complex [NiL]2[Mn(NCS)4](ClO4)2.H2O (2) crystallizes in a monoclinic space group, P2/c, with a = 21.018(5) A, b = 7.627(2) A, c = 16.295(4) A, beta = 104.47(1) degrees, Z = 4. The magnetic behaviour of (1) and (2) has been investigated over the temperature range 1.8-300 K. Complex (1) displays ferromagnetic coupling inside the trinuclear core of CuMnCu and compound (2) behaves like a mononuclear Mn(II) system. The magnetic properties of the second compound (2) with a similar trinuclear structure shows that Ni(II) ions have a diamagnetic character and a rather weak zero-field splitting at the central Mn(II) ion occurs. Finally, the magnitudes of the Cu(II)-M(II) interactions with M = Ni and Mn have been compared and qualitatively justified.
Dalton Transactions 08/2007; · 3.84 Impact Factor
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ABSTRACT: The Schiff condensation of 2-pyridinecarboxaldehyde N-oxide with 2-aminophenol gave a tridentate ligand, abbreviated as Hpoxap. This ligand bears the functionality of a terminating group in a trinuclear complex [Mn(poxap)Mn(ac)4Mn(poxap)], where ac- is the acetate bridge. The magnetic data were treated simultaneously during the fitting procedure with the spin Hamiltonian containing isotropic exchange, the zero-field splitting parameters, and the molecular-field correction and resulted in JMn-Mn/hc = -4.73 cm-1, gMn(t) = 1.96, DMn(t)/hc = -0.45 cm-1, and zj/hc = +0.45 cm-1 with ground state S = 5/2, where t = terminal atom. At low temperature, the features of a ferromagnetic correlation become evident.
Inorganic Chemistry 04/2007; 46(5):1544-6. · 4.60 Impact Factor
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ABSTRACT: A mononuclear cobalt(II) complex CoL5, containing the pentadentate O2N3 salen-type Schiff-base ligand H2L5=N,N[prime or minute]-bis(3-tert-butyl-2-hydroxy-5-methylbenzylidenyl)-1,7-diamino-4-methyl-4-azaheptane, exhibits magnetic ordering at 4 K as proven by ac magnetic susceptibility (both in- and out-of-phase), magnetization, field-cooled magnetization and zero-field cooled magnetization measurements.
Dalton Transactions 05/2005; · 3.84 Impact Factor
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ABSTRACT: A novel heteronuclear exchange-coupled complex [Cr(III)[(CN)Fe(III)((5)L)](3)(CN)(3)] containing a pentadentate blocking ligand (5)L was synthesized. The X-ray structure shows that a meridional isomer applies with inequivalent Fe(III) centers. The complex exhibits a thermally induced spin crossover along with the exchange coupling. Mössbauer spectra indicate a spin transition between S = (1)/(2) and S = (5)/(2) states although a considerable amount of Fe(III) centers stays high-spin at T = 6 K. The magnetization, the magnetic susceptibility, and the Mössbauer data were fitted in one run with a spin crossover model taking into account exchange interactions among all metal centers.
Inorganic Chemistry 08/2004; 43(14):4103-5. · 4.60 Impact Factor
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ABSTRACT: Triethylenetetramine (L(4)) was used as a tetradentate blocking ligand that, after complexation with Ni(II), leaves two sites ready for ligation with tricyanomethanide. The formed binuclear complex [L(4)Ni(NCC(CN)CN)(2)NiL(4)](ClO(4))(2) exhibits a ferromagnetic coupling with J/hc = +0.15 cm(-1) and g(Ni) = 2.126; below 16 K, a ferromagnetic ordering is evidenced by ac magnetic susceptibility (both in-phase and out-of-phase), magnetization, field-cooled magnetization, and zero-field-cooled magnetization measurements.
Inorganic Chemistry 11/2003; 42(22):6965-7. · 4.60 Impact Factor
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ABSTRACT: Magnetic susceptibility and EPR studies show that trinuclear Cu(II)-pyrazolato complexes with a Cu(3)(mu3-X)2 core (X = Cl, Br) are ferromagnetically coupled: J(Cu-Cu) = +28.6 cm(-1) (X = Cl), +3.1 cm(-1) (X = Br). The orderly transition from an antiferromagnetic to a ferromagnetic exchange among the Cu centers of Cu(3)(mu3-X) complexes, X = O, OH, Cl, Br, follows the change of the Cu-X-Cu angle from 120 degrees to approximately 80 degrees. The crystal structures of [Bu4N]2"[Cu3(mu3-Br)2(mu-pz*)3Br3] (pz* = pz (1a) or 4-O2N-pz (1b), pz = pyrazolato anion, C(3)H(3)N(2)(1-)) are presented.
Inorganic Chemistry 10/2003; 42(19):5801-3. · 4.60 Impact Factor
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04/2002;
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ABSTRACT: Visible spectrophotometry was used to study the kinetics of metal substitution in the system Cu(amben)/Ni(DMF)(6)(ClO(4))(2)/R(4)NX in DMF at 298 K and I = 0.2 M (Bu(4)NPF(6)) (H(2)amben = N,N'-ethylenebis(2-aminobenzaldimine); X = Br(-)(), SCN(-), Cl(-); DMF = N,N-dimethylformamide). The rate of nickel for copper substitution is markedly affected by the nature of the anion X, the order of reactivity being ClO(4)- < Br(-) < SCN(-) < Cl(-). For X = Cl(-) and under excess conditions [(Cu(amben)] < [Ni(DMF)(6)(ClO(4))(2)], [BzEt(3)NCl]), the overall process is triphasic and multiwavelength analysis in the range 350-900 nm yields the experimental rate constants k(obsd)(1), k(obsd)(2), and k(obsd)(3). Rate constant k(obsd)(1) is nickel and chloride dependent, whereas k(obsd)(2) and k(obsd)(3) are not. For the rate of disappearance of Cu(amben), v = -d[Cu(amben)]/dt, it is found that v ~ [Cl](tot)(2) at [Ni(DMF)(6)(ClO(4))(2)](0) = constant and v ~ [Ni](tot)(3) at [nickel]:[chloride] = 1:2 ([Cl](tot) and [Ni](tot) refer to the total concentration of chloride and nickel, respectively). These dependencies suggest a second-order rate law, v = k(1)[Cu(amben)]["NiCl(2)"], for the first step, with k(1) = 64 +/- 8 M(-)(1) s(-)(1) at 298 K. In view of the ligand properties of Cu(amben) it is concluded that the species "NiCl(2)" is tetrahedral Ni(DMF)(2)Cl(2) which reacts with Cu(amben) as ligand to form a binuclear adduct in the first step. It is suggested that the observed rate effects of the anions X are linked with their ability to favor the formation of nickel species with reduced coordination number, such as four-coordinate Ni(DMF)(2)X(2). The mechanism of the overall process of nickel for copper substitution in Cu(amben) is discussed. The results of the analysis of the visible spectra of Cu(amben) and Ni(amben) and of MO calculations on the charge distribution in these complexes are reported.
Inorganic Chemistry 09/1998; 37(16):3999-4005. · 4.60 Impact Factor
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ABSTRACT: Syntheses and properties of low-valent clusters [X{Co(&mgr;-CO)(PMe(3))(2)}(3)], X = none (1), H (2), and H(3) (3), are reported. All solids are isostructural as explicitly shown by single-crystal structure data. The molecular structures of C(21)H(54)Co(3)O(3)P(6) (1) and C(21)H(57)Co(3)O(3)P(6) (3) contain central Co(3) units which form perfect equilateral triangles with Co-Co distances of 2.4055(5) and 2.432(1) Å, respectively. Both compounds crystallize in trigonal space group R&thremacr;c, with Z = 6: 1, a = 10.678(1) Å, c = 52.298(11) Å; 3, a = 10.679(2) Å, c = 52.729(12) Å. Compounds 1 and 2 form a continuous range of solid solutions. Powder samples exhibit molecular paramagnetism of different extent: At 298 K the effective magnetic moments for 1-3 are &mgr;(eff)/&mgr;(B) = 1.9, 3.1, and 2.7, respectively. The magnetic behavior could be rationalized in terms of the Curie-Weiss law for a one electron system (1) and two electron system (2). The two electron approximation has been discussed as well for 3 above 6.2 K. A description of the scope of exchange coupling is presented for 1.
Inorganic Chemistry 10/1997; 36(20):4303-4306. · 4.60 Impact Factor
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Journal of Coordination Chemistry. 12/1996; 40(4):293-309.
