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Zn Complexes (zn + complex)

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Chemistry	100%

Selected Abstracts

Toward an Allosteric Metallated Container

EUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 2 2009
Helga Szelke
Abstract Polytopic ligands L1 and L2 in which three 2,2,-bipyridine units are linked to a central tris(pyrid-2-yl)amine (L1) or tris(pyrid-2-yl)methanol (L2) moiety by alkyl spacers were prepared by multistep organic syntheses. The parent tris(pyrid-2-yl)-type ligands were shown to be modest-to-good chelators for Zn2+ and Cu2+ ions in solution, and bi- and tridentate N-coordination was confirmed by crystal structures of CuII and RuII complexes, respectively. FeII and RuII smoothly form stable, cage-like 1:1 complexes with L1 and L2, in which the metal ion is coordinated to the tris(bpy) site of the ligands. The vacant tris(pyrid-2-yl) site of these complexes is, however, a poor donor site for Zn2+ and Cu2+ ions. In addition, FeII modulates the coordination behaviour of the tris(pyrid-2-yl) site toward Zn2+: Whereas tris(5-methylpyrid-2-yl)amine forms a 2:1 complex with Zn2+ in CH2Cl2, [Fe(L1)]2+ forms a 1:1 Zn complex. Spectrophotometric titrations suggest that [Fe(L2)]2+ forms a polynuclear Zn2+ complex in CH2Cl2, possibly involving bridging coordination of the alcohol OH group, which contrasts the smooth formation of a 2:1 complex of the parent tris(pyrid-2-yl)-type ligand with Zn. FeII might therefore be considered as an allosteric effector, which modulates the metal binding properties of the second tris(pyrid-2-yl) site of L1 and L2. Contrary to expectation, Zn2+ and Cu2+ appear to associate weakly with donor atoms directed toward the exterior of the cage-like complexes [Fe(Ln)]2+ and [Ru(L1)]2+, rather than locating in the interior of the container by tripodal coordination to the tris(pyrid-2-yl) site.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009) [source]

Photophysical and Energy-Transfer Properties of (Salen)zinc Complexes and Supramolecular Assemblies

EUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 12 2003
Kathryn E. Splan
Abstract The absorption, emission, and energy-transfer properties of monomeric and supramolecular (salen)Zn complexes (square and rectangular assemblies) are reported. The monomeric complexes fluoresce in solution, displaying photophysical behavior similar to typical (porphyrin)zinc complexes. Rhenium coordination chemistry is used to assemble molecular rectangles and squares that largely retain the photophysical properties of the parent compounds. Host-guest assemblies obtained by binding a fifth (salen)Zn complex to a tetrakis(salen) square are capable of efficient salen-to-salen electronic energy transfer. Energy transfer flow through these systems can be manipulated by modification of the salen building-block structure. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003) [source]

A heterotrimetallic Cu,Co,Zn complex with the 2,2,-iminodiethanol ligand

ACTA CRYSTALLOGRAPHICA SECTION C, Issue 6 2006
Dmytro S. Nesterov
The crystal structure of the title compound, triacetato-1,O;3,4O,O,-(2,2,-iminodiethanol)-1,3O,N,O,-bis(,-2,2,-iminodiethanolato)-1,2O:2,6O,N,O,:3,2O,-cobalt(III)copper(II)zinc(II), [CoCuZn(C4H9NO2)2(C2H3O2)3(C4H11NO2)], shows a molecule with a triangular three-metal core. The metal sites were refined with full occupancies, but the possibility that the Zn and Cu positions are actually mixed Cu/Zn sites cannot be excluded. The intermetallic Cu,Co and Co,Zn distances are 2.924,(3) and 2.906,(3),Å, respectively. The neutral molecules are held together by N,H,O hydrogen bonds involving amine groups from the 2,2,-iminodiethanol ligands and acetate groups to build two-dimensional layers. [source]

Receptor versus Counterion: Capability of N,N, -Bis(2-aminobenzyl)-diazacrowns for Giving Endo- and/or Exocyclic Coordination of ZnII

EUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 13 2007
Lea Vaiana
Abstract The structure of ZnII complexes with receptors L1 and L2[L1 = N,N, -bis(2-aminobenzyl)-1,10-diaza-15-crown-5 and L2 = N,N, -bis(2-aminobenzyl)-4,13-diaza-18-crown-6] was studied both in the solid state and in acetonitrile solution. Both receptors form mononuclear ZnII complexes in this solvent, while no evidence for the formation of dinuclear complexes was obtained. This is in contrast with previous investigations that demonstrated the formation of dinuclear complexes of L2 with first-row transition metals such as NiII, CoII and CuII. Compounds of formula [Zn(L1)](ClO4)2 (1), [Zn(L1)](NO3)2·2CH3CN (2), [Zn(L2)](ClO4)2 (3) and [Zn(L2)(NO3)2] (4) were isolated and structurally characterised by X-ray diffraction analyses. L1 forms seven-coordinate ZnII complexes in the presence of both nitrate and perchlorate anions, as a consequence of the good fit between the macrocyclic cavity and the ionic radius of the metal ion. The ZnII ion is deeply buried into the receptor cavity and the anions are forced to remain out of the metal coordination sphere. The cation [Zn(L1)]2+ present in 1 and 2 is one of the very few examples of seven-coordinate Zn complexes. Receptor L2 provides a very rare example of a macrocyclic receptor allowing endocyclic and exocyclic coordination on the same guest cation, depending on the nature of the anion present. Thus, in 3 the ZnII ion is endocyclically coordinated, placed inside the crown hole coordinated to four donor atoms of the ligand in a distorted tetrahedral environment, whereas in 4, the presence of a strongly coordinating anion such as nitrate results in an exocyclic coordination of ZnII, which is directly bound only to the two primarily amine groups of L2 and two nitrate ligands. Spectrophotometric titrations of [Zn(L2)]2+ with tetrabutylammonium nitrate in acetonitrile solution demonstrate the stepwise formation of 1:1 and 1:2 adducts with this anion in acetonitrile solution. The [Zn(L1)]2+, [Zn(L2)]2+ and [Zn(L2)(NO3)2] systems were characterised by means of DFT calculations (B3LYP model). The calculated geometries show an excellent agreement with the experimental structures obtained from X-ray diffraction analyses. Calculated binding energies of the macrocyclic ligands to ZnII are also consistent with the experimental data.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007) [source]

Complexes of the Bicyclic Multifunctional Sulfur-Nitrogen Ligand F3CCN5S3 with Co2+, Zn2+, Cu2+, and Cd,

EUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 17 2005
Carsten Knapp
Abstract The ability of the sulfur-nitrogen-carbon bicycle F3CCN5S3 to act as a donor towards transition metal cations has been investigated. F3CCN5S3 forms complexes with [M(SO2)2](AsF6)2 [M = Co, Cu, Zn, Cd] in the ratio 2:1 of the composition [M(F3CCN5S3)2(OSO)2(FAsF5)2] [M = Co (1), Zn (3)], [Cu(F3CCN5S3)2(,-F)(,-F2AsF4)]2 (4), and [Cd(F3CCN5S3)(,-F3CCN5S3)(,2 -F2AsF4)2]2 (5) in liquid sulfur dioxide. In the octahedral Co and Zn complexes F3CCN5S3 coordinates as a monodentate ligand through the bridging nitrogen atom N5, which carries the highest negative charge according to theoretical calculations. With Cu2+ a dinuclear structure with a central planar, four-membered Cu2F2 ring is formed, which has the shortest Cu···Cu distance of all structurally characterized Cu2F2 units. Similar to the Co and Zn complexes, F3CCN5S3 acts as a terminal monodentate ligand in the Cu compound. The reaction with the larger and softer Cd2+ cation results in a dinuclear complex that contains terminal and bridging F3CCN5S3 ligands. The bridging ligands coordinate through N5 and a nitrogen atom neighboring the carbon atom. In addition, a third weak bonding interaction between one fluorine atom of the trifluoromethyl substituent and the Cd2+ center is observed. The formation of the different structures and the versatile coordination modes of the F3CCN5S3 ligand are discussed. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005) [source]

Photophysical and Energy-Transfer Properties of (Salen)zinc Complexes and Supramolecular Assemblies

Allosteric Tuning of the Intra-Cavity Binding Properties of a Calix[6]arene through External Binding to a ZnII Center Coordinated to Amino Side Chains

CHEMISTRY - A EUROPEAN JOURNAL, Issue 7 2007
Ulrich Darbost Dr.
Abstract Molecular recognition by calix[6]arene-based receptors bearing three primary alkylamino side chain arms (1) is described. Complexation of ZnII ion provides the dinuclear ,-hydroxo complex , XRD characterization of which, together with solution studies, provided evidence of its hosting of neutral polar organic guests G. Treatment of this complex with a carboxylic acid or a sulfonamide (XH) results in the formation of mononuclear species , one of which (X = Cl) has been characterized by XRD. A dicationic complex is obtained upon treatment of with a mixture of an alkylamine and a strong acid. Each of these ZnII complexes features a tetrahedral metal ion bound to the three amino arms of ligand 1 and to an exogenous ligand (either HO,, X,, or RNH2) sitting outside of the cavity. As a result, the metal ion structures the calixarene core, constraining it in a cone conformation suitable for guest hosting. The receptor properties of these compounds have been explored in detail and are compared with those of the trisammonium receptor , based on the same calixarene core, as well as those of the trisimidazole-based dicationic Zn funnel complexes. This study reveals very different host properties, in spite of the common hydrophobic, ,-basic, and hydrogen-bonding acceptor properties of the calixarene cores. A harder external ligand produces a less polarized receptor that is consequently particularly sensitive to the hydrogen-bonding ability of its guest. The less electron-rich the apical ligand, and a fortiori the trisammonium host, the more sensitive the receptor to the dipole moment of the guest. All this stands in contrast with the funnel Zn complexes, in which the coordination link plays a dominant role. It is also shown that the asymmetry of an exo -coordinated enantiopure amino ligand is sensed by the guest. This supramolecular system nicely illustrates how the receptor properties of a hydrophobic cavity can be allosterically tuned by the environment. [source]