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Cis Arrangement (cis + arrangement)
Selected AbstractsOxovanadium(IV) Complexes with Pyrazinecarboxylic Acids:The Coordinating Properties of Ligands with the (Naromatic, COO,) Donor SetEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 13 2006Eugenio Garribba Abstract Complex formation between the VIVO ion and four pyrazine derivatives, 2-pyrazinecarboxylic acid (pzc), 5-methyl-2-pyrazinecarboxylic acid (5-Mepzc), 2,3-pyrazinedicarboxylic acid (3-COOHpzc) and 5-hydroxy-2-pyrazinecarboxylic acid (5-OHpzc), was studied in aqueous solution and in the solid state through the combined application of potentiometric and spectroscopic (EPR and FT-IR) techniques. The results indicate that in acidic and neutral aqueous solution all theligands form mono(chelated), bis(chelated) and dinuclear species of composition VOL, VOL2 and (VO)2L2H,2. Hexacoordinated VOL2 complexes are characterised by a cis/trans isomerism, where cis and trans are the species with a water molecule bound in the cis or trans position with respect to the V=O group. The trans arrangement is favoured over the cis arrangement. Three solid derivatives, [VO(5-Mepzc)2] (1), cis -[VO(pzc)2(H2O)] (2) and cis -[VO(3-COOHpzc)2(H2O)] (3), were isolated and characterised. Based on the experimental results and on the data in the literature, the stability of cis and trans isomers in aqueous solution and in the solid state has been discussed, showing that with ligands of comparable basicity and size of the chelate ring the hydrophilicity favours the cis species and determines the relative amount of the two isomers. The analysis of the magnetic properties of the hydroxo-bridged VIVO dimers suggests that for the (VO)2L2H,2 species the anti -coplanar arrangement is realised. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006) [source] Synthesis, Characterization and Reactivity of New (,-Aminocarbyne)diruthenium Complexes Containing Alkynylimino LigandsEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 7 2004Luigi Busetto Abstract Addition of acetylides R,C,CLi [R, = Tol, Ph, Me3Si, nBu, C(Me)=CH2] to the diruthenium complexes [Ru2{,-CN(Me)(R)}(,-CO)(CO)(NCCMe3)(Cp)2]+ (R = Xy, 2a; Bz, 2b; Me, 2c) results in the formation of [Ru2{,-CN(Me)(R)}(,-CO)(CO){N(H)=C(CMe3)(C,CR,)}(Cp)2]+ (R = Xy, R, = Tol, 3a; R = Bz, R, = Tol, 3b; R = Me, R, = Tol, 3c; R = Xy, R, = Ph, 4a; R = Bz, R, = Ph, 4b; R = Me, R, = Ph, 4c; R = Bz R, = H, 5; R = Xy, R, = nBu, 6; R = Xy, R, = [C(Me)=CH2], 7), which contain an alkynylimino ligand, formed from addition of the acetylide to the Me3CCN ligand. Structural and spectroscopic studies show that all these complexes contain the two Cp ligands in a relative cis arrangement, whereas two isomers arise from the different orientation of the substituents on the bridging aminocarbyne ,-CN(Me)(R) when R , Me. Addition of secondary amines to 3,7 results in a stereo- and regioselective cis amination of the C,C triple bond to give the new complexes [Ru2{,-CN(Me)(R)}(,-CO)(CO){N(H)=C(CMe3)C(H)=C(NMe2)(Tol)}(Cp)2]+ (R = Xy, 8a; Bz, 8b; Me, 8c), [Ru2{,-CN(Me)(Xy)}(,-CO)(CO){N(H)=C(CMe3)C(H)=C(NC5H10)(Tol)}(Cp)2]+(9) and [Ru2{,-CN(Me)(Xy)}(,CO)(CO){N(H)=C(CMe3)C(H)=C(NMe2)C(Me)=CH2)}(Cp)2]+ (10) containing the hitherto unknown new imino-2-en-3-amine ligand. The solid-state structures of these products have been analyzed by X-ray analysis and, in solution, by NOE spectroscopic studies. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004) [source] First (Peroxo)vanadium(V) Complex with Heteroligand Formed in Reaction System , Synthesis, Structure and Reactivity of K[VO(O2)(omeida)]·H2O {omeida = N -[2-(2-oxomorpholine-4-yl)ethyl]iminodiacetato(2,)}EUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 11 2003Michal Sivák Abstract The crystalline peroxo complex of vanadium(V), K[VO(O2)(omeida)]·H2O, where omeida is a ,-lactone derivative, N -[2-(2-oxomorpholine-4-yl)ethyl]iminodiacetate(2,), has been obtained by reaction of vanadate with H2O2 and N -(2-hydroxyethyl)ethylenediaminetriacetic acid (HEDTA) in acidic aqueous solution at pH = 3 and 278 K. X-ray analysis revealed a distorted pentagonal-bipyramidal coordination around the vanadium atom, with a typical cis arrangement of oxo and peroxo ligands in apical and equatorial positions, respectively. Two amino nitrogen atoms of the tetradentate omeida(2,)-N1,N2,O1,O2 ligand occupy the neighbouring equatorial positions of the pentagonal plane, and two oxygen atoms of carboxymethyl groups bound to the same N1 nitrogen atom are in equatorial and apical positions. The six-membered lactone ring in omeida was formed in the reaction solution from carboxy and hydroxy groups not involved in coordination with the vanadium atom. The 51V NMR spectra of K[VO(O2)(omeida)]·H2O, and of peroxovanadate/HEDTA/H2O and vanadate/HEDTA/H2O solutions, as well as the 1H NMR spectrum of HEDTA, proved that lactone ring closure proceeds only in peroxovanadate but not vanadate solutions. Spectroscopic investigation of the oxygen transfer reaction from the peroxo ligand in [VO(O2)(omeida)], to the thiolato sulfur atom in [Co(en)2{S(CH2)2NH2}]2+ or [Co(en)2(cyst)]+, and of the oxidation of N -acetyl- L -cysteine by K[VO(O2)(omeida)]·H2O, revealed much more complicated reaction mechanisms than those of other (amino-polycarboxylato)monoperoxo complexes of vanadium(V). (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003) [source] Rational Design of Charge-Neutral, Near-Infrared-Emitting Osmium(II) Complexes and OLED FabricationADVANCED FUNCTIONAL MATERIALS, Issue 16 2009Tsang-Chi Lee Abstract A new series of charge neutral Os(II) isoquinolyl triazolate complexes (1,4) with both trans and cis arrangement of phosphine donors are synthesized, and their structural, electrochemical and photophysical properties are established. In sharp contrast to the cis -arranged complexes 2,4, the trans derivative 1, which shows a planar arrangement of chromophoric N -substituted chelates, offers the most effective extended , -delocalization and hence the lowest excited state energy gap. These complexes exhibit phosphorescence with peak wavelengths ranging from 692,805,nm in degassed CH2Cl2 at room temperature. Near-infrared (NIR)-emitting electroluminescent devices employing 6,wt % of 1 (or 4) doped in Alq3 host material are successfully fabricated. The devices incorporating 1 as NIR phosphor exhibit fairly intense emission with a peak wavelength at 814,nm. Forward radiant emittance reaches as high as 65.02,µW,cm,2, and a peak EQE of ,1.5% with devices employing Alq3, TPBi and/or TAZ as electron-transporting/exciton-blocking layers. Upon switching to phosphor 4, the electroluminescence blue shifts to 718,nm, while the maximum EQE and radiance increase to 2.7% and 93.26 (,W,cm,2) respectively. Their performances are optimized upon using TAZ as the electron transporting and exciton-blocking material. The OLEDs characterized represent the only NIR-emitting devices fabricated using charge-neutral and volatile Os(II) phosphors via thermal vacuum deposition. [source] Iron(II) Complexes with Bio-Inspired N,N,O Ligands as Oxidation Catalysts: Olefin Epoxidation and cis -DihydroxylationCHEMISTRY - A EUROPEAN JOURNAL, Issue 4 2008Pieter Abstract The Rieske dioxygenases are a group of non-heme iron enzymes, which catalyze the stereospecific cis -dihydroxylation of its substrates. Herein, we report the iron(II) coordination chemistry of the ligands 3,3-bis(1-methylimidazol-2-yl)propionate (L1) and its neutral propyl ester analogue propyl 3,3-bis(1-methylimidazol-2-yl)propionate (PrL1). The molecular structures of two iron(II) complexes with PrL1 were determined and two different coordination modes of the ligand were observed. In [FeII(PrL1)2](BPh4)2 (3) the ligand is facially coordinated to the metal with an N,N,O donor set, whereas in [FeII(PrL1)2(MeOH)2](OTf)2 (4) a bidentate N,N binding mode is found. In 4, the solvent molecules are in a cis arrangement with respect to each other. Complex 4 is a close structural mimic of the crystallographically characterized non-heme iron(II) enzyme apocarotenoid-15,15,-oxygenase (APO). The mechanistic features of APO are thought to be similar to those of the Rieske oxygenases, the original inspiration for this work. The non-heme iron complexes [FeII(PrL1)2](OTf)2 (2) and [FeII(PrL1)2](BPh4)2 (3) were tested in olefin oxidation reactions with H2O2 as the terminal oxidant. Whereas 2 was an active catalyst and both epoxide and cis -dihydroxylation products were observed, 3 showed negligible activity under the same conditions, illustrating the importance of the anion in the reaction. [source] Quantum mechanical study of the conformational behavior of proline and 4R-hydroxyproline dipeptide analogues in vacuum and in aqueous solutionJOURNAL OF COMPUTATIONAL CHEMISTRY, Issue 3 2002Caterina Benzi The conformational behavior of the title compounds has been investigated by Hartree,Fock, MP2, and DFT computations on the most significant structures related to variations of the backbone dihedral angles, cis/trans isomerism around the peptide bond, and diastereoisomeric puckering of the pyrrolidine ring. In vacuum the reversed , turn (,l), characterized by an intramolecular hydrogen bridge, corresponds to the absolute energy minimum for both puckerings (up and down) of the pyrrolidine ring. An additional energy minimum is found in the helix region, but only for an up puckering of the pyrrolidine ring. When solvent effects are included by means of the polarizable continuum model the conformer observed experimentally in condensed phases becomes the absolute minimum. The down puckering is always favored over its up counterpart, albeit by different amounts (0.4,0.5 kcal/mol for helical structures and about 2 kcal/mol for ,l structures). In helical structures cis arrangements of the peptide bond are only slightly less stable than their trans counterparts. This is no longer true for ,l structures, because the formation of an intramolecular hydrogen bond is possible only for trans peptide bonds. In most cases, proline and hydroxyproline show the same general trends; however, the electronegative 4(R) substituent of hydroxyproline leads to a strong preference for up puckerings irrespective of the backbone conformation. © 2002 Wiley Periodicals, Inc. J Comput Chem 23: 341,350, 2002 [source] | ||||||||||