Publications (79) View all
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Article: A New Family of Trinuclear Nickel(II) Complexes as Single-Molecule Magnets.
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ABSTRACT: Three new trinuclear nickel (II) complexes with the general composition [Ni(3) L(3) (OH)(X)](ClO(4) ) have been prepared in which X=Cl(-) (1), OCN(-) (2), or N(3) (-) (3) and HL is the tridentate N,N,O donor Schiff base ligand 2-[(3-dimethylaminopropylimino)methyl]phenol. Single-crystal structural analyses revealed that all three complexes have a similar Ni(3) core motif with three different types of bridging, namely phenoxido (μ(2) and μ(3) ), hydroxido (μ(3) ), and μ(2) -Cl (1), μ(1,1) -NCO (2), or μ(1,1) -N(3) (3). The nickel(II) ions adopt a compressed octahedron geometry. Single-crystal magnetization measurements on complex 1 revealed that the pseudo-three-fold axis of Ni(3) corresponds to a magnetic easy axis, being consistent with the magnetic anisotropy expected from the coordination structure of each nickel ion. Temperature-dependent magnetic measurements indicated ferromagnetic coupling leading to an S=3 ground state with 2J/k=17, 17, and 28 K for 1, 2, and 3, respectively, with the nickel atoms in an approximate equilateral triangle. The high-frequency EPR spectra in combination with spin Hamiltonian simulations that include zero-field splitting parameters D(Ni) /k=-5, -4, and -4 K for 1, 2, and 3, respectively, reproduced the EPR spectra well after a anisotropic exchange term was introduced. Anisotropic exchange was identified as D(i,j) /k=-0.9, -0.8, and -0.8 K for 1, 2, and 3, respectively, whereas no evidence of single-ion rhombic anisotropy was observed spectroscopically. Slow relaxation of the magnetization at low temperatures is evident from the frequency-dependence of the out-of-phase ac susceptibilities. Pulsed-field magnetization recorded at 0.5 K shows clear steps in the hysteresis loop at 0.5-1 T, which has been assigned to quantum tunneling, and is characteristic of single-molecule magnets.Chemistry 01/2013; · 5.93 Impact Factor -
Article: Coordination Polymers Containing Manganese(II)-Azido Layers Connected by Dipyridyl-tetrazine and 4,4'-Azobis(pyridine) Linkers.
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ABSTRACT: Two new polynuclear manganese(II) complexes [Mn(dptz)(N(3))(2)](n) (1) and [Mn(azpy)(N(3))(2)](n) (2) (where dptz = dipyridyl-tetrazine and azpy = 4,4'-azobis(pyridine)) have been synthesized by self-assembly of the ligand azide, together with dptz and azpy as secondary spacers. The compounds are characterized by single-crystal X-ray diffraction analyses and variable-temperature magnetic measurements. The structural analyses reveal that in complex 1, which is the first reported Mn(II) complex with the ligand dptz, two μ(1,3) bridging azides connect neighboring manganese ions in a zigzag manner to generate a neutral two-dimensional (2D) sheet which is further connected by the dptz ligands to form a three-dimensional (3D) framework. By contrast, complex 2 contains dimeric [Mn(2)(μ(1,1)-N(3))(2)](2+) fragments linked to four identical motifs by means of four single μ(1,3)-N(3) bridges, that generates a neutral 2D Mn(II)-azide sheet which is further interconnected by azpy ligands to neighboring manganese ions forming an unprecedented 3D network. Variable-temperature (2-300 K) magnetic susceptibility measurements show the presence of predominantly antiferromagnetic coupling for both complexes that has been reproduced with a regular antiferromagnetic S = 5/2 chain (J) with interchain interactions (j) modeled with the molecular field approximation with J = -7.1 cm(-1) and j' = -0.8 cm(-1) for 1 and J = -4.2 cm(-1) and j' = 0.1 cm(-1) for 2.Inorganic Chemistry 01/2013; · 4.60 Impact Factor -
Article: Synthesis and structure of mono-, di- and tri-nuclear copper(II) benzoate complexes with a tridentate N2O donor Schiff base ligand
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ABSTRACT: Three copper(II) complexes [CuL(PhCOOH)(ClO 4)] (1), [Cu 2 L 2 (PhCOO)](ClO 4) (2) and [Cu 3 L 2 {(o-NO 2)-PhCOO} 2 ](ClO 4) (3), where HL = 2-[1-(2-dimethylamino-ethylimino)-ethyl]-phenol, a well known Schiff base ligand, have been prepared and characterized by elemental analysis, IR and UV–Vis spectroscopy and single crystal X-ray diffraction studies. Complex 1 crystallizes in triclinic space group P À 1, complex 2 in monoclinic C 2 and complex 3 in monoclinic P2 1 /c. The co-ordination polyhedron around each copper atom is best described as an elongated (4 + 1) square pyramid. Complex 1 is mononuclear with a terminal benzoate, complex 2 is dinuclear containing a l 1,3 benzoate whereas complex 3 is trinuclear having a rare l 1,1,3 benzoate binding three copper centers simultaneously.Inorganica Chimica Acta 01/2013; · 1.85 Impact Factor -
Article: Differences in Nuclearity, Molecular Shapes, and Coordination Modes of Azide in the Complexes of Cd(II) and Hg(II) with a "Metalloligand" [CuL] (H(2)L = N,N'-Bis(salicylidene)-1,3-propanediamine): Characterization in Solid and in Solutions, and Theoretical Calculations.
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ABSTRACT: Two new heterometallic copper(II)-mercury(II) complexes [(CuL)Hg(N(3))(2)](n) (1) and [(CuL)(2)Hg(N(3))(2)] (2) and one copper(II)-cadmium(II) complex [(CuL)(2)Cd(N(3))(2)] (3) have been synthesized using "metalloligand" [CuL] (where H(2)L = N,N'-bis(salicylidene)-1,3-propanediamine) and structurally characterized. Complex 1 is a one-dimensional (1D) helical coordination polymer constructed by the joining of the dinuclear [(CuL)Hg(N(3))(2)] units through a single μ(-l,l) azido bridge. In the dinuclear unit the Hg(II) is bonded with two phenoxido oxygen atoms of "metalloligand" [CuL] and two nitrogen atoms of azido ligands. Complex 2 is a linear trinuclear entity, in which two terminal "metalloligands" [CuL] are coordinated to central Hg(II) through double phenoxido bridges. The azido ligands link the central mercury atom with the terminal copper atoms via μ(-l,3) bridges. In contrast, the trinuclear complex 3 is bent. Here, in addition to two double phenoxido bridges, central Cd(II) is bonded to two mutually cis nitrogen atoms of two terminal azido ligands. The variation in the coordination modes of the azido ligand seems to be responsible for the different molecular shapes of 2 and 3. Interestingly, bond distances between the Hg atoms and the central nitrogen atom of the azido ligands are 2.790(4) and 2.816(5) Å in 1 and 2.823(4) Å in 2. These bond distances are significantly less than the sum of van der Waals radii of mercury (2.04 Å) and nitrogen (1.55 Å) and considerably longer than the sum of their covalent radii (2.03 Å). However the distances are similar to reported Hg-N bond distances of some Hg(II) complexes. Therefore, we have performed a theoretical density functional theory study to know whether there is any interaction between the central nitrogen atom of the azido ligand and the mercury atoms. We have used the Bader's "atoms-in-molecules", energetic and orbital analyses to conclude that such interaction does not exist. The probable reason for different molecular shapes observed in trinuclear complexes of 2 and 3 also has been studied and explained by theoretical calculations and using the CSD. Electronic spectra, EPR spectra and ESI mass spectra show that all three complexes lose their solid state identity in solution.Inorganic Chemistry 11/2012; · 4.60 Impact Factor -
Article: Insertion of a Hydroxido Bridge into a Diphenoxido Dinuclear Copper(II) Complex: Drastic Change of the Magnetic Property from Strong Antiferromagnetic to Ferromagnetic and Enhancement in the Catecholase Activity.
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ABSTRACT: A diphenoxido-bridged dinuclear copper(II) complex, [Cu(2)L(2)(ClO(4))(2)] (1), has been synthesized using a tridentate reduced Schiff base ligand, 2-[[2-(diethylamino)ethylamino]methyl]phenol (HL). The addition of triethylamine to the methanolic solution of this complex produced a novel triple bridged (double phenoxido and single hydroxido) dinuclear copper(II) complex, [Cu(2)L(2)(OH)]ClO(4) (2). Both complexes 1 and 2 were characterized by X-ray structural analyses, variable-temperature magnetic susceptibility measurements, and spectroscopic methods. In 1, the two phenoxido bridges are equatorial-equatorial and the species shows strong antiferromagnetic coupling with J = -615.6(6.1) cm(-1). The inclusion of the equatorial-equatorial hydroxido bridge in 2 changes the Cu···Cu distance from 3.018 Å (avg.) to 2.798 Å (avg.), the positions of the phenoxido bridges to axial-equatorial, and the magnetic coupling to ferromagnetic with J = 50.1(1.4) cm(-1). Using 3,5-di-tert-butylcatechol as the substrate, the catecholase activity of the complexes has been studied in a methanol solution; compound 2 shows higher catecholase activity (k(cat) = 233.4 h(-1)) than compound 1 (k(cat) = 93.6 h(-1)). Both complexes generate identical species in solution, and they are interconvertible simply by changing the pH of their solutions. The higher catecholase activity of 2 seems to be due to the presence of the OH group, which increases the pH of its solution.Inorganic Chemistry 09/2012; 51(19):10111-21. · 4.60 Impact Factor
