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- PublicationAccès libreSynthesis, crystal structures and magnetic properties of trinuclear oxo-centered homo- and mixed-valence manganese pivalate complexes with imidazole (Im) and 1-methylimidazole (1-MeIm): [Mn3III0(02CCMe3)6 (Im)3](Me3CC02)•0.5Me3CC02H and [Mn2IIIMnII0(02CCMe3)6(1-MeIm)3](2006)
;Baca, Svetlana G. ; ;Ambrus, Christina ;Malinovskii, Stanislav T. ;Malaestean, Iurii ;Gerbeleu, NicolaeDecurtins, SilvioTwo new μ3-oxo-centered trinuclear manganese complexes, one of them a homo-valence [Mn3III0(02CCMe3)6 (Im)3](Me3CC02)•0.5Me3CC02H (1) pivalate complex and the other a mixed-valence [Mn2IIIMnII0(02CCMe3)6(1-MeIm)3] (2) pivalate complex (where Im = imidazole, 1-MeIm = 1-methylimidazole), have been synthesized and characterized by IR spectroscopy, thermogravimetric analysis, X-ray crystallography and magnetochemistry. Complexes 1 and 2 are μ3-oxo-trinuclear compounds with the three manganese atoms bridged by six pivalate groups. At each axial position there is an Im (1) or 1-MeIm (2) molecule. In both compounds, the manganese coordination geometry is slightly distorted octahedral, consisting of the oxygen of the central triangle, four oxygen atoms from bridging pivalate ligands, and a terminal Im or 1-MeIm nitrogen atom. The crystal packing of 1 involves hydrogen bonding between complex cations [Mn3O(Piv)6(Im)3]+ and outersphere pivalate ions, whereas in compound 2 interactions of the C–Hπ type, formed by both the aromatic and methyl C–H groups of 1-MeIm molecules, are present. Magnetic studies reveal that both compounds represent antiferromagnetically coupled, spin-frustrated triangular systems exhibiting weak to moderate exchange coupling constants.
- PublicationAccès libreSynthesis, structure and magnetic properties of two end-on double azido bridged nickel(II) dinuclear entities incorporating N,N,N-coordinating tridentate reduced Schiff base ligands(2006)
;Sarkar, Sumana ;Mondal, Amrita ;El Fallah, Mohamed Salah ;Ribas, Joan ;Chopra, Deepak ;Krishna Rajak, KajalComplexes of the general formula [Ni2L2 (μ1,1-N3)2(N3)2] have been synthesised in good yields by reacting Ni(NO3)2 • 6H2O with L in the presence of excess of sodium azide in methanol at room temperature. Here L is N,N-bis(2-pyridylmethyl)amine (L1) and N-(2-pyridylmethyl)-N′,N′-diethylethylenediamine (L2). The X-ray structures of both compounds reveal that the N,N,N coordinating reduced Schiff bases are ligated facially. The Ni–Nazido–Ni angle is 100° and the NiNi separation is 3.2 Å. The variable temperature magnetic susceptibility measurements of the two complexes show ferromagnetic behavior.
- PublicationAccès librePreparation of donor–acceptor substituted fluorostilbenes and crystal chemistry of fluorinated (E)-4-(4-halogeno-styryl)-benzonitriles(2009)
;Mariaca, Raúl ;Labat, Gaël ;Behrnd, Norwid-Rasmus ;Bonin, Michel ;Helbling, Fabien ;Eggli, Patrick ;Couderc, Gaëtan ;Neels, Antonia ;Hulliger, JürgThe syntheses and crystal structures of a series of fluoro-substituted halogeno (Cl, Br, I)-cyano-stilbenes containing donor and acceptor groups (D-π-A) are reported. These molecules show a tendency to form antiparallel chain-like structures and herringbone packing, crystallising predominantly in a centric space group. However, second harmonic generation measurements bear evidence for orientational disorder leading to partial polar order below the ordinary X-ray structure determination limit. Some co-crystals are isostructural with their components. The non-fluoro as well as the halogeno-fluoro substituted components of co-crystals seem to impose their crystal structure on the complementary fluoro- or cyano–fluoro substituted components. Co-crystallization enhanced the deviation from centrosymmetry.
- PublicationAccès libreSynthesis, structure and DNA interaction of cobalt(III) bis-complexes of 1,3-bis(2-pyridylimino)isoindoline and 1,4,7-triazacyclononane(2005)
;Tamil Selvi, Pitchumony ;Palaniandavar, MallayanThe complex [CoL2](ClO4) • MeOH (1), where HL is the tridentate 3N ligand 1,3-bis(2-pyridylimino)isoindoline, has been isolated and its X-ray crystal structure successfully determined. It possesses a distorted octahedral structure in which both the ligands are coordinated meridionally to cobalt(III) via one deprotonated isoindoline (L−) and two pyridine nitrogen atoms. Interestingly, the average dihedral angle between pyridine and isoindoline rings is 25.9°, indicating that the ligand is twisted upon coordination to cobalt(III). The interaction of the complex with calf-thymus DNA has been studied using various spectral methods and viscosity and electrochemical measurements. For comparison, the DNA interaction of [Co(tacn)2]Cl3 (2), where tacn is facially coordinating 1,4,7-triazacyclononane, has been also studied. The ligand-based electronic spectral band of 1 and the N(σ) → Co(III) charge transfer band of 2 exhibit moderate hypochromism with small or no blue shift on interaction with DNA. The intrinsic binding constants calculated reveal that the monopositive complex ion [CoL2]+ exhibits a DNA-binding affinity lower than the tripositive complex ion [Co(tacn)2]3+. The steric clashes with DNA exterior caused by the second L− ligand bound to cobalt(III), apart from the lower overall positive charge on the [CoL2]+ complex, dictates its DNA-binding mode to be surface binding rather than partial intercalative interaction expected of the extended aromatic chromophore of deprotonated isoindoline anion. An enhancement in relative viscosity of CT DNA on binding to 1 is consistent with its DNA surface binding. On the other hand, a slight decrease in viscosity of CT DNA was observed on binding to 2 revealing that the smaller cation leads to bending (kinking) and hence shortening of DNA chain length. The electrochemical studies indicate that the DNA-bound complexes are stabilised in the higher Co(III) rather than the lower Co(II) oxidation state, suggesting the importance of electrostatic forces of DNA interaction.
- PublicationAccès libreSynthesis, structure and magnetic properties of cobalt(II) and copper(II) coordination polymers assembled by phthalate and 4-methylimidazole(2004)
;Baca, Svetlana G. ;Malinovskii, Stanislav T. ;Franz, Patrick ;Ambrus, Christina ; ;Gerbeleu, NicolaeDecurtins, SilvioNew coordination polymers [M (Pht)(4-MeIm)2 (H2O)]n (M=Co (1), Cu (2); Pht2−=dianion of o-phthalic acid; 4-MeIm=4-methylimidazole) have been synthesized and characterized by IR spectroscopy, X-ray crystallography, thermogravimetric analysis and magnetic measurements. The crystal structures of 1 and 2 are isostructural and consist of [M (4-MeIm)2(H2O)] building units linked in infinite 1D helical chains by 1,6-bridging phthalate ions which also act as chelating ligands through two O atoms from one carboxylate group in the case of 1. In complex 1, each Co(II) atom adopts a distorted octahedral N2O4 geometry being coordinated by two N atoms from two 4-MeIm, three O atoms of two phthalate residues and one O atom of a water molecule, whereas the square-pyramidal N2O3 coordination of the Cu(II) atom in 2 includes two N atoms of N-containing ligands, two O atoms of two carboxylate groups from different Pht, and a water molecule. An additional strong O–HO hydrogen bond between a carboxylate group of the phthalate ligand and a coordinated water molecule join the 1D helical chains to form a 2D network in both compounds. The thermal dependences of the magnetic susceptibilities of the polymeric helical Co(II) chain compound 1 were simulated within the temperature range 20–300 K as a single ion case, whereas for the Cu(II) compound 2, the simulations between 25 and 300 K, were made for a linear chain using the Bonner–Fisher approximation. Modelling the experimental data of compound 1 with MAGPACK resulted in: g=2.6,