1,720,999 research outputs found
Efficient syntheses of some versatile 3,5-bifunctional pyrazole building blocks
No full textA series of convenient synthetic procedures are reported for pyrazole derivatives with carbonyl or ester groups in the 3- and 5-positions and variable substitution pattern at C4 and at the functional side arms. All compounds have been characterized by (1)H and (13)C NMR spectroscopy, elemental analyses, and mass spectrometry. In addition, the structures of several pyrazole derivatives have been determined by single crystal X-ray diffraction, which provides insight into the effect of functional side arms on the hydrogen-bonded supramolecular motifs of NH-pyrazoles
One-Pot Synthesis of a New Magnetically Coupled Heterometallic Cu2Mn2 [2 x 2] Molecular Grid
No full textThe heterometallic [2 x 2] grid-type complex [Cu2Mn2(pop)(4)(OAc)(4)]center dot 7H(2)O (1) has been selectively synthesized in a targeted one-pot reaction. Single-crystal X-ray analysis shows the expected structure with identical metal ions located at diagonal vertices of the grid. Magnetochemical studies reveal that 1 has a ferrimagnetic spin ground state with some admixture of low-lying excited states.DFG [SFB 602
Effect of metal ionic radius and chelate ring alternation motif on stabilization of trivalent nickel and copper in binuclear complexes with double cis-oximato bridges
No full textOxime ligands are able to form stable binuclear species with copper(II) ions in aqueous solution. They also have a strong tendency to decrease the Mn+/(n-1)+ redox potentials of the central ions. Ligands possessing the hydroxyimino groups together with other powerful sigma-donor groups can be very efficient chelating agents able to facilitate the stabilisation of high oxidation states of 3d-metals. Here we report the synthesis, structural characterization and redox behaviour of mononuclear and binuclear complexes based on hydroxyiminoamide tetradentate open-chain ligands. In all mononuclear anionic complexes the central atom is situated in a square-planar surrounding of four nitrogen atoms. This pseudo-macrocyclic conformation is due to the presence of short intramolecular hydrogen bonds uniting the cis-oximate oxygen atoms. The square-planar surrounding of the strong sigma-donors facilitates efficient stabilization of the trivalent state of copper and nickel ions. In cyclic voltammetry studies the quasi-reversible processes M2+-->M3+ can be observed. In the binuclear complexes the coordinatively saturated octahedral ion M is bound to the two oxygen atoms of the bridging oximate groups and the four nitrogen atoms of the tetradentate ligand tren. Two metal ions (M and M') are linked by the double cis-oximate bridge and are incorporated in a six-membered bimetallic chelate ring. Metallamacrocycle formation leads to certain changes in the structural parameters of the binuclear complexes as compared to those observed in the mononuclear species. Also the study of the electrochemical activity of binuclear complexes has shown important differences in their redox behaviour as compared to their mononuclear precursors
Binuclear manganese(III) complexes of an unsymmetric pyrazolate-based compartmental ligand with hard donor set
No full textThe synthesis, crystal structure and magnetic properties of manganese(III) binuclear complexes [Mn(2)(III)(L-3H)(2)(CH(3)OH)(4)]center dot 2CH(3)OH (1) and [Mn(2)(III)(L-3H)(2)(Py)(4)]center dot 2Py (2) (L = 3-[(1E)-N-hydroxyethanimidoyl]- 4-methyl-1H-pyrazole-5-carboxylic acid) are reported. The ligand contains two distinct donor compartments formed by the pyrazolate-N and the oxime or the carboxylic groups. The complexes were characterized by X-ray single crystal diffraction, revealing that both 1 and 2 consist of dinuclear units in which the two metal ions are linked by double pyrazolate bridges with a planar {Mn(2)N(4)} core. Cryomagnetic measurements show antiferromagnetic interaction with g = 1.99, J = -3.6 cm (1), Theta = -2.02 K for 1 and g = 2.00, J = -3.7 cm (1), Theta = 1.43 K for 2. (C) 2010 Elsevier B. V. All rights reserved
Bis(acetato-κ2O,O′)bis(3,5-dimethyl-1H-pyrazole-κN2)copper(II)
No full textIn the title compound, [Cu(C2H3O2)2(C5H8N2)2], the CuII atom has a distorted tetragonal–bipyramidal geometry, with the equatorial plane formed by two N atoms belonging to two 3,5-dimethyl-1H-pyrazole ligands and two O atoms from two acetate anions. The second O atoms of the acetate groups provide elongated Cu—O axial contacts, so that the acetates appear to be coordinated in a pseudo-chelate fashion. The pyrazole ligands are situated in cis positions with respect to each other. In the crystal structure, molecules are linked through intermolecular N—H...O hydrogen bonds, forming a one-dimensional chain
Chloridotris(3,5-dimethyl-1H-pyrazole-κN2)(formato-κO)copper(II)–dichloridobis(3,5-dimethyl-1H-pyrazole-κN2)copper(II) (2/1)
No full textThe asymmetric unit of the title compound, [Cu(CHO2)Cl(C5H8N2)3]2·[CuCl2(C5H8N2)2] or 2[A]·[B], contains one A molecule and one half-molecule of B, located on a centre of inversion. The CuII environments in A and B are different. In A, the CuII atom is coordinated by three N atoms from three 3,5-dimethyl-1H-pyrazole (L) ligands, one O atom from a formate ligand and a chloride anion in an axial position [Cu—Cl = 2.4275 (7) Å] in a distorted tetragonal–pyramidal geometry. The CuII atom in B is coordinated by two N atoms from two L ligands and two chloride anions [Cu—Cl = 2.2524 (6) Å] in a distorted square-planar geometry. In the crystal, intermolecular N—H...O hydrogen bonds link molecules A into centrosymmetric dimers. Intermolecular N—H...Cl hydrogen bonds further link these dimers with the B molecules, forming chains propagating in [101]
Spin Crossover in Fe(II)-M(II) Cyanoheterobimetallic Frameworks (M = Ni, Pd, Pt) with 2-Substituted Pyrazines
No full textDiscovery of spin-crossover (SCO) behavior in the family of Fen-based Hofmann clathrates has led to a "new rush" in the field of bistable molecular materials. To date this class of,SCO complexes is represented by several dozens of individual compounds, and areas of their potential application steadily increase. Starting from Fe2+, square planar tetracyanometalates M-II(CN)(4)(2-) (Mn = Ni, Pd, Pt) and 2-substituted pyrazines Xpz (X = Cl, Me, I) as coligands we obtained a series of nine new Hofmann clathrate-like coordination frameworks. X-ray diffraction reveals that in these complexes Fen ion has a pseudo-octahedral coordination environment supported by four mu(4)-tetracyanometallates forming its equatorial coordination environment. Depending on the nature of X and M, axial positions are occupied by two 2X-pyrazines (X = Cl and M-II = Ni (1), Pd (2), Pt (3); X = Me and M-II = Ni (4), Pd (5)) or one 2X-pyrazine and one water molecule (X = I and M-II = Ni (7), Pd (8), Pt (9)), or, alternatively, two distinct Fe-II positions with either two pyrazines or two water molecules (X = Me and M-II = Pt (6)) are observed. Temperature'behavior of magnetic susceptibility indicates that all compounds bearing FeN6 units (1-6) display cooperative spin transition, while Fe-II ions in N5O or N4O2 surrounding are high spin (HS). Structural changes in the nearest Fen environment upon low-spin (LS) to HS transition, which include ca. 10% Fe-N distance increase, lead to the cell expansion. Mossbauer spectroscopy is used to characterize the spin state of all HS, LS, and intermediate phases of 1-9 (see abstract figure). Effects of a pyrazine substituent and M-II nature on the hyperfine parameters in both spin states are established
Synthesis and structure of [2 x 2] molecular grid copper(II) and nickel(II) complexes with a new polydentate oxime-containing Schiff base ligand
No full textA new polynucleating oxime-containing Schiff base ligand, 2-hydroxyimino-N'-[1-(2-pyridyl)ethylidene]propanohydrazone (Hpop), has been synthesized and fully characterized. pH potentiometric, electrospray ionization mass spectrometric, and spectrophotometric studies of complex formation in H(2)O/DMSO solution confirmed the preference for polynuclear complexes with 3d metal ions. Single-crystal X-ray diffraction analyses of [Ni(4)(pop)(4)(HCOO)(4)]center dot 7H(2)O (1), [Cu(4)(pop-H)(4)(HCOOH)(4)] center dot H(2)O (2), and [Cu(4)(pop-H)(4)(H(2)O)(4)] center dot 9H(2)O (3) indicated the presence of a [2 x 2] molecular grid structure in all three compounds but distinct configurations of the cores: a head-to-tail ligand arrangement with overall S(4) symmetry of the grid in the Cu(2+) complexes as opposed to a head-to-head ligand arrangement with (noncrystallographic) O(2) grid symmetry for the Ni(2+) complex. A cryomagnetic study of 3 revealed intramolecular ferromagnetic exchange between copper ions in the grid, while in 1, antiferromagnetic interactions between the metal ions were observed
Regular High-Nuclearity Species from Square Building Blocks: A Triangular 3 x [2 x 2] Ni-12 Complex Generated by the Self-assembly of Three [2 x 2] Ni-4 Molecular Grids
No full textA dodecanuclear 3 x [2 x 2] nickel(II) complex has been obtained via the self-association of three tetranuclear [2 x 2] molecular grids. X-ray diffraction shows a "propeller-like" structure of the [Ni-4](3) scaffold with a central mu(3)-hydroxide. The dodecanuclear species remains stable in solution and can be deposited without decomposition on highly ordered pyrolytic graphite surfaces
Iron (II) isothiocyanate complexes with substituted pyrazines: Experimental and theoretical views on their electronic structure
No full textSynthesis, structural, magnetic. Mossbauer and thermal studies of isothiocyanate iron (II) complexes with substituted pyrazines (iodo-, bromo- and amino-derivatives) are discussed here. Complexes with iodo- and bromo-derivatives were found to have the composition [Fe(Ipz)(2)(SCN)(2)(H2O)(2)]center dot 2Ipz (1) and [Fe(Brpz)(2)(SCN)(2)(H2O)(2)]center dot 2Brpz (2), whereas in the case of amino-functionalized pyrazine the formation of [Fe(NH(2)pz)(4)(SCN)(2)] (3) was observed. 3D organization of the molecular complexes is stabilized within different hydrogen, halogen and lone pair-it interactions. Spin state of iron (II) ions in 1-3 was determined as high spin by Mossbauer and magnetic measurements. DFT calculations for the obtained iron (II) complexes were carried out to analyze the electronic structure and to support experimentally measured Mossbauer parameters with theoretical predictions. (C) 2014 Elsevier Ltd. All rights reserved.DAA
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