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Transition Metal Complexes (transition + metal_complex)
Kinds of Transition Metal Complexes Selected AbstractsSynthesis and Transition Metal Complexes of Novel N,N,O Scorpionate Ligands Suitable for Solid Phase ImmobilisationEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 24 2006Eike Hübner Abstract Introduction of an allyl or a hydroxymethyl group to bis(3,5-dimethylpyrazol-1-yl)acetic acid (1) at the bridging carbon atom leads to the new tripodal N,N,O ligands 2,2-bis(3,5-dimethylpyrazol-1-yl)pent-4-enoic acid (Hbdmpzpen) (2) and 2,2-bis(3,5-dimethylpyrazol-1-yl)-3-hydroxypropionic acid (Hbdmpzhp) (3). These ligands exhibit similar chemical behaviour to that of 1, but they have the additional possibility to be immobilised to a solid phase. Esterification of the hydroxymethyl linker of 3 yields 2,2-bis(3,5-dimethylpyrazol-1-yl)-3-acetatopropionic acid (Hbdmpzap) (4). The molecular structures of 2, 3 and 4 all exhibit intramolecular hydrogen bridges. Introduction of a hydroxymethyl group to methyl bis(3,5-dimethylpyrazol-1-yl)acetate (5) yields methyl2,2-bis(3,5-dimethylpyrazol-1-yl)-3-hydroxypropionate(Mebdmpzhp) (6), which can be immobilised on Merrifield polymer to yield modified resin P - 6. To investigate the reactivity of these new ligands, manganese and rhenium complexes of 2, 3 and 4 have been studied. The molecular structures of the two manganese complexes [Mn(bdmpzpen)(CO)3] (7) and [Mn(bdmpzap)(CO)3] (8) have been confirmed by single-crystal X-ray structure determination. Saponification of polymer resin P - 6 and subsequent reaction with [ReBr(CO)5] yields rhenium tricarbonyl complexes anchored on Merrifield polymer (P -Re). Solid phase immobilisation of the [Mn(bdmpzpen)(CO)3] (7) and [Re(bdmpzpen)(CO)3] (9) complexes on 3-mercaptopropyl functionalised silica is initialised by AIBN. The tripodal coordination of manganese and rhenium in these functionalised Merrifield resins (P -Re) and silica (S -Mn, S -Re) is proven by a single A1 and two E signals in the IR spectra that are typical for unsymmetrical "piano stool" type carbonyl complexes. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006) [source] Catalytic Cross-Coupling Reaction of Esters with Organoboron Compounds and Decarbonylative Reduction of Esters with HCOONH4: A New Route to Acyl Transition Metal Complexes Through the Cleavage of Acyl,-Oxygen Bonds in Esters.CHEMINFORM, Issue 51 2004Hiroto Tatamidani Abstract For Abstract see ChemInform Abstract in Full Text. [source] [{Zn(enMe)2}2 (enMe)2{Zn2As8V12O40 (H2O)}]× 4H2O: A Hybrid Molecular Material Based on Covalently Linked Inorganic Zn,As,V Clusters and Transition Metal Complexes via enMe Ligands.CHEMINFORM, Issue 30 2004Shou-Tian Zheng Abstract For Abstract see ChemInform Abstract in Full Text. [source] Transition Metal Complexes with Heterocyclic Analogues of Fluorene.CHEMINFORM, Issue 5 2004Part 1. No abstract is available for this article. [source] Binuclear and Polynuclear Transition Metal Complexes with Macrocyclic Ligands.CHEMINFORM, Issue 40 2002Part 2. No abstract is available for this article. [source] ChemInform Abstract: A Novel Hydrogen Transfer Hydroalumination of Alkenes with Triisobutylaluminum Catalyzed by Pd and Other Late Transition Metal Complexes.CHEMINFORM, Issue 19 2001Sebastien Gagneur Abstract ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a "Full Text" option. The original article is trackable via the "References" option. [source] Transition Metal Complexes Coordinated by an NAD(P)H Model Compound and their Enhanced Hydride-Donating Abilities in the Presence of a BaseCHEMISTRY - A EUROPEAN JOURNAL, Issue 14 2005Atsuo Kobayashi Dr. Abstract The ruthenium(II) and rhenium(I) complexes containing an NAD(P)H model compound, 1-benzyl-1,4-dihydronicotinamide (BNAH), as ligand, [Ru(tpy)(bpy)(BNAH)]2+ (1,a) and [Re(bpy)(CO)3(BNAH)]+ (1,b), were quantitatively produced by the reaction of the corresponding metal hydrido complexes with BNA+ (1-benzylnicotinamidium cation). In the presence of base with pKa=8.9, 1,a and 1,b have much greater reducing power than "free" BNAH. The oxidation potentials of 1,a in the absence and the presence of triethylamine were 0.55 V and ,0.04 V, respectively, versus Ag/AgNO3, whereas that of "free" BNAH was 0.30 V. Spectroscopic results clearly showed that the base extracts a proton from the carbamoyl group on 1,a and 1,b to give the deprotonated BNAH coordinating to the transition-metal complexes [Ru(tpy)(bpy)(BNAH,H+)]+ (3,a) and [Re(bpy)(CO)3(BNAH,H+)] (3,b); this deprotonation underlies the enhancement in reducing ability. The deprotonated forms 3,a and 3,b can efficiently reduce other NAD(P) models to give the corresponding 1,4-dihydro form, resulting in the deprotonated BNA+ being coordinated to the metal complexes [Ru(tpy)(bpy)(BNA+,H+)]2+ (2,a) and [Re(bpy)(CO)3(BNA+,H+)]+ (2,b); "free" BNAH and the protonated adducts 1,a and 1,b cannot act in this way. X-ray crystallography was performed on the PF6, salt of 2,a, and showed that the deprotonated nitrogen atom on the carbamoyl group coordinates to the ruthenium(II) metal center with a bond length of 2.086(3) Å. Infrared spectral data suggested that the deprotonated carbamoyl group on the reduced forms 3,a and 3,b is converted to the imido group, and that the oxygen atom coordinates to the metal center. [source] Transition metal complexes of a cyclic pseudo hexapeptide: synthesis, complex formation and catalytic activities,,JOURNAL OF PEPTIDE SCIENCE, Issue 9 2008Huong Ngyen Abstract To contribute to a better understanding of metalloenzymes, we studied ion selectivity, complex formation tendencies and catalytic activities of linear and cyclic pseudopeptides. In this contribution, a linear and cyclic pseudo hexapeptide is described. The complex with transition metal ions and the sequence were designed using the programme COSMOS. Different routes of solid-phase synthesis were performed and compared using anchoring by C -terminus or a His side chain, using preformed pseudodipeptide building units or formation of N -functionalized peptide bond during stepwise assembly. The different strategies were compared regarding cyclization tendency, yield and purity. Side-chain anchoring to solid support favours the cyclization but leads to the formation of difficult to separate dioxopiperazine. Both routes require preformed building units. Complex-formation tendencies and selectivity for certain bivalent transition metal ions were experimentally estimated and compared to ones predicted theoretically. CD measurements indicate conformational changes by complex formation with different metal ions. Catalytic activities on oxidation of catechol and hydrolysis of bis-phosphate esters by some metal complexes of linear and cyclic peptide show only low catalytic activities compared to other model peptides and related metalloenzymes. The preference of the cyclic peptide for complexation of Ni2+ corresponds well to the predictions of COSMOS-NMR force field calculations. Copyright © 2008 European Peptide Society and John Wiley & Sons, Ltd. [source] Transition metal complexes with thiosemicarbazide-based ligands.ACTA CRYSTALLOGRAPHICA SECTION C, Issue 10 2002XLIV. The title complex, [Cu(NO3)(C10H14N4O2S)(H2O)](NO3), is the first metal complex with a Schiff base derived from isothiosemicarbazide and pyridoxal (pyridoxal is 3-hydroxy-5-hydroxymethyl-2-methylpyridine-4-carboxaldehyde). The CuII environment is a square pyramid, the equatorial plane of which is formed by the tridentate ONN -coordinated isothiosemicarbazone and one water molecule, while the nitrate ligand is in the apical position. The existence of numerous strong intermolecular hydrogen bonds, and weak C,H,O and C,H,, interactions, leads to a three-dimensional supramolecular structure. [source] Transition metal complexes with thiosemicarbazide-based ligands.ACTA CRYSTALLOGRAPHICA SECTION C, Issue 6 2002XLIII. In the title compound, [ZnCl(C2H7N3S)2]Cl, the ZnII ion is five-coordinated in a distorted trigonal,bipyramidal arrangement, with the hydrazine N atoms located in the apical positions. The structure is stabilized by N,H,Cl hydrogen bonds, which involve both the Cl atoms and all the hydrogen donors, except for one of the two thioamide N atoms. A comparison of the geometry of thiosemicarbazide and S -methylisothiosemicarbazide complexes with ZnII, CuII and NiII shows the pronounced influence of the hydrogen-bond network on the coordination geometry of ZnII compounds. [source] The First Heterohexametallic Transition-Metal ComplexEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 24 2007Rico Packheiser Abstract The synthesis and characterisation of a first heteromultimetallic transition metal complex with six different metal atoms (Fe, Ru, Re, Au, Cu and Ti), connected through carbon-rich bridging units, are reported. Complex {1-[(,2 -dppf)(,5 -C5H5)RuC,C]-3-[(bipy*)(CO)3ReC,C]-5-[PPh2AuC,C-bipy({[Ti](,-,,,-C,CSiMe3)2}Cu)]C6H3}PF6 is accessible in a consecutive reaction sequence by applying building blocks from a ligand and coordination complex library. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007) [source] New Approach Toward Fast Response Light-Emitting Electrochemical Cells Based on Neutral Iridium Complexes via Cation TransportADVANCED FUNCTIONAL MATERIALS, Issue 5 2009Tae-Hyuk Kwon Abstract Here, a new method is presented to increase the turn-on time and stability of light-emitting electrochemical cells (LECs). To this end, a neutral iridium complex (5) containing a pendant Na+ ion that is generally known to have a faster mobility in the solid film than bulky anions is introduced, instead of the classic ionic transition metal complex (iTMC) with counter anion (7). Synthesis, photophysical and electrochemical studies of these complexes are reported. In the device configuration of ITO/5 or 7+PEO (polyethylene oxide) (100,110,nm)/Au, as the voltage increases, complex 5 emits red light at ,3.6,V while complex 7 appears at ,5.6,V, although their electrochemical and photophysical gap are similar. Furthermore, at constant voltage, ,3,V, the turn-on time of complex 5 was less than 0.5,min, which is a 60-fold faster turn-on time compared to the iTMC (7) with PF6,. These results are presumably due to the faster delivery of the Na+ ions to the electrode compared to PF6, ions. Also, the device lifetime of complex 5 exhibits a six-fold increase in stability and a three-fold shorter time to reach maximum brightness at constant bias compared to the device made with complex 7. [source] Selected excitation for CAS-SDCI calculationsJOURNAL OF COMPUTATIONAL CHEMISTRY, Issue 3 2007Benoît Bories Abstract A new selected-configuration interaction method is proposed, based on the use of local orbitals. A corresponding code has been written, which is devoted to CI calculations of rather large systems (about 50,100 carbon-like atoms). Taking advantage of the locality, and then of the fact that interactions vanish when the distance is large, the dimension of the CI space is largely reduced. The determinants that would be created by long range excitations are expected to have a small weight in the wave function and are therefore eliminated. This selected excitation CI space is particularly suited for large molecules. It is tested on large polyene chains and on a transition metal complex. For large enough systems, the CPU time saving is important and, what is more noticeable, calculations that were impossible to perform without selection are feasible in this approach. © 2006 Wiley Periodicals, Inc. J Comput Chem 28: 632,643, 2007 [source] 11C,C bond formation by palladium-mediated cross-coupling of alkenylzirconocenes with [11C]methyl iodideJOURNAL OF LABELLED COMPOUNDS AND RADIOPHARMACEUTICALS, Issue 2 2006Frank R. Wuest Abstract A novel 11C,C bond formation based on the palladium-mediated cross-coupling reaction of alkenylzirconocenes with [11C]methyl iodide is described. The conversion of internal alkynes into the corresponding alkenylzirconocenes followed by transmetalation with Pd(PPh3)4 and subsequent cross-coupling with [11C]methyl iodide gave several 11C-labelled ,,,,-dimethyl-substituted alkenes. The palladium complex Pd(PPh3)4 proved to be superior to Pt(PPh3)4 or Ni(PPh3)4 as transition metal complex. The scope and limitations of the novel palladium-mediated cross-coupling reaction of alkenylzirconocenes with [11C]methyl iodide were tested with various internal alkynes. After heating at 60°C for 6 min radiochemical yields of up to 75% (based upon [11C]methyl iodide) could be achieved. Copyright © 2006 John Wiley & Sons, Ltd. [source] Recovery of transition metal complex by reverse flow adsorptionAICHE JOURNAL, Issue 1 2008Jeroen Dunnewijk Abstract Reverse flow adsorption (RFA) is a technique with a definite potential to prevent the leaching of a homogenous catalyst. In this work, we model an RFA-process for a continuous ideally stirred tank reactor with an adsorption bed upstream and another one downstream from the reactor. The model parameters concerning adsorption equilibrium and kinetics are taken from previous experimental studies on CoCl2 adsorption on polymer-bound trifenylfosfine. We use this model to study the concentration profiles of CoCl2 in the adsorption beds during consecutive adsorption,desorption cycles. The model calculations show that the concentration profile eventually reaches a fixed position after a number of adsorption,desorption cycles, even though internal mass transfer was a limiting factor. Hence, the transition metal is kept within the system boundaries, which is an essential requirement for the application of RFA. © 2007 American Institute of Chemical Engineers AIChE J, 2008 [source] Palladium bis(2,2,6,6-tetramethyl-3,5-heptanedionate) catalyzed alkoxycarbonylation and aminocarbonylation reactionsAPPLIED ORGANOMETALLIC CHEMISTRY, Issue 6 2009Pawan J. Tambade Abstract Palladium bis(2,2,6,6-tetramethyl-3,5-heptanedionate), a structurally well defined O -containing transition metal complex, is reported to be an efficient catalyst for alkoxycarbonylation and aminocarbonylation reactions under milder operating conditions. The system tolerated the carbonylative coupling of various aryl halides with phenol/alcohol and amines, providing good to excellent yields of desired products under optimized reaction conditions. Copyright © 2009 John Wiley & Sons, Ltd. [source] Synthesis, structure and reactivity of cationic base-stabilized gallyleneiron complexes,APPLIED ORGANOMETALLIC CHEMISTRY, Issue 6-7 2003Keiji Ueno Abstract Addition of 2,2,-bipyridine (bpy) to an acetonitrile solution of dichlorogallyliron complex FpGaCl2 (1: Fp = (,-C5H5)Fe(CO)2) afforded almost quantitatively a salt consisting of a cationic base-stabilized gallylene complex [FpGaCl·bpy]+ ([3a]+) and an anionic complex [FpGaCl3], ([4],). Reaction of Fp,GaCl2 (Fp, = Fp (1), Fp* (2); Fp* = (,-C5Me5)Fe(CO)2) with NaBPh4 in the presence of a bidentate donor (Do2) gave [Fp,GaCl·Do2]BPh4 where Do2 was bpy or 1,10-phenanthroline (phen). These cationic complexes may be useful precursors for the synthesis of gallyleneiron complexes with various substituents on the gallium atom. Indeed, reaction of [Fp*GaCl·phen]BPh4 ([5b]BPh4) with NaSpTol or Me3SiSpTol afforded the gallyleneiron complex [Fp*GaSpTol·phen]BPh4 ([6]BPh4), the first example of a gallium,transition metal complex having a thiolate group on the gallium atom. The molecular structures of [5b]BPh4 and [6]BPh4 were determined by single crystal X-ray diffraction. Copyright © 2003 John Wiley & Sons, Ltd. [source] Investigation of the stereodynamics of tris-(, -diimine),transition metal complexes by enantioselective dynamic MEKCELECTROPHORESIS, Issue 2 2009Sabrina Bremer Abstract Enantiomerization of octahedral tris(, -diimine),transition metal complexes was investigated by enantioselective dynamic MEKC. Varying both the transition metal ion (Fe2+, Fe3+, and Ni2+) and the bidentate diimine ligand (1,10-phenanthroline and 2,2,-bipyridyl), the enantiomer separations were performed either in a 100,mM sodium tetraborate buffer (pH 9.3) or in a 100,mM sodium tetraborate/sodium dihydrogenphosphate buffer (pH 8.0) both containing sodium cholate as chiral surfactant. The unified equation of dynamic chromatography was employed to determine apparent reaction rate constants from the electropherograms showing distinct plateau formation. Apparent activation parameters ,H, and ,S, were calculated from temperature-dependent measurements between 10.0 and 35.0°C in 2.5,K steps. It was found that the nature of the central metal ion and the ligand strongly influence the enantiomerization barrier. Surprisingly, complexes containing the 2,2,-bipyridyl ligand show highly negative activation entropies between ,103 and ,116,J (K,mol),1 while the activation entropy of tris(1,10-phenanthroline) complexes is positive indicating a different mechanism of interconversion. Furthermore, it was found that the Ni2+ complexes are stereostable under the conditions investigated here making them a lucent target as enantioselective catalysts. [source] Capillary electrophoresis as a probe of enantiospecific interactions between photoactive transition metal complexes and DNAELECTROPHORESIS, Issue 15 2003James P. Schaeper Abstract Recently, we have demonstrated the capacity to separate chiral transition metal (TM) complexes of the type [M(diimine)3]n+ using CE buffers containing chiral tartrate salts. In separate work, several chromium(III)- tris -diimine complexes in particular have been shown to bind enantioselectively with calf-thymus (CT) DNA, and a qualitative assessment of the relative strength and enantiospecificity of this interaction is of significant interest in the characterization of these complexes as potential DNA photocleavage agents. Here, we describe two convenient approaches to investigate such binding behavior using chiral CE. For complexes with lower DNA affinities exhibiting primarily surface binding, DNA itself is used as the chiral resolving agent in the electrophoretic buffer. In this approach, resolution of the TM complexes into their , and , isomers is achieved with the isomer eluting later exhibiting superior binding affinity toward DNA. For more strongly bound TM complexes containing ligands known to intercalate with DNA, the [Cr(diimine)3]3+ complexes are preincubated with oligonucleotide and subsequently enantiomerically resolved in a dibenzoyl- L -tartrate buffer system that facilitates analysis of the unbound TM species only. Differences in isomer binding affinity are distinguished by the relative peak areas of the ,- and ,-isomers, and relative binding strengths of different complexes can be inferred from comparison of the total amount of unbound complex at equivalent DNA/TM ratios. [source] Synthesis and Characterisation of Semi-Bridging Molybdenum Borylene ComplexesEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 27 2007Holger Braunschweig Abstract Investigation of the reactivity of the molybdenum borylene complex [(OC)5Mo=B=N(SiMe3)2] towards the late transition metal complexes [M(PCy3)2] (M = Pd, Pt) indicated the formation of [(OC)4Mo(, - CO){, - BN(SiMe3)2}Pd(PCy3)] and [(Cy3P)(OC)3Mo(, - CO){, - BN(SiMe3)2}Pt(PCy3)], respectively, as the first Mo-based semi-bridging borylene complexes. The new complexes were fully characterised spectroscopically and analysed by X-ray diffraction. The conclusions drawn from the experimental data for the ligand-metal interactions for this particular coordination mode of a borylene group were supported by DFT computations.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007) [source] Mixed f-d Metallomesogens with an Extended Rigid CoreEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 8 2005Koen Binnemans Abstract The liquid-crystalline behaviour of copper(II) and nickel(II) complexes of a mesogenic Schiff-base ligand derived from N,N' -disalicylidene-1,2-phenylenediamine (salophenH2) and of the corresponding trinuclear mixed copper(II)/lanthanum(III) and nickel(II)/lanthanum(III) complexes was investigated. High-temperature X-ray diffraction studies revealed that both the parent transition metal complexes and the mixed f-d complexes exhibit a hexagonal columnar phase (Colh) over an extended temperature range. Complex formation with lanthanum(III) nitrate resulted in an increase of the transition temperatures. The geometrical parameters (lattice parameters and column cross-section) of all the metal complexes are very similar, which indicates that the local organisation in the mesophase is the same despite their structural differences. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005) [source] Electronic Interactions in Ferrocene- and Ruthenocene-Functionalized Tetraazamacrcocyclic Ligand Complexes of FeII/III, CoII, NiII, CuII and ZnIIEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 2 2005Peter Comba Abstract The syntheses of ferrocene- and ruthenocene-functionalized tetraazamacrocyclic ligands and their corresponding transition metal complexes are described. Reaction of N,N, -bis(2-aminoethyl)-1,3-propanediamine (2,3,2-tet) with 1,1,-diformylferrocene and 1,1,-diformylruthenocene produces the ligands fcmac and rcmac in 81,85% yield. Examination of their CuII, NiII, CoII, ZnII and FeII/III complexes by IR, UV/Vis, EPR and Mössbauer spectroscopy as well as by electrochemical studies suggests electronic communication between the two metal centers of each complex. The molecular structure of [CuII(fcmac)(FBF3)]BF4, determined by X-ray structure analysis, is reported and shows that the distance between the two metals is 4.54 Å. Stability constants, determined by potentiometric titration, indicate that the copper(II) complexes are of similar stability as those with unfunctionalized tetraazamacrocyclic ligands (e.g. cyclam = 1,4,8,11-tetraazacyclotetradecane); stability constants of cobalt(II) complexes are about 2 log units smaller, those of nickel(II) and zinc(II) complexes are reduced by more than 10 log units. This selectivity is discussed on the basis of the structural studies. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005) [source] Atomic-orbital-symmetry based ,-, ,-, and ,-decomposition analysis of bond ordersINTERNATIONAL JOURNAL OF QUANTUM CHEMISTRY, Issue 11 2009Olga V. Sizova Abstract The atomic-orbital-symmetry based (AOSB) scheme for the decomposition of Mayer and Wiberg bond orders into ,-, ,-, and ,-components is used to investigate different types of covalent bonds. Four series of compounds are studied: simple molecules with homonuclear bonds, inorganic molecules with polar heteronuclear bonds, [Ru(CN)5(XY)]q transition metal complexes with ,-acceptor ligands, and dimetal complexes with multiple metal,metal bonds. © 2009 Wiley Periodicals, Inc. Int J Quantum Chem, 2009 [source] DFT calculations of light-induced excited states and comparison with time-resolved crystallographic resultsINTERNATIONAL JOURNAL OF QUANTUM CHEMISTRY, Issue 5 2005Philip Coppens Abstract DFT calculations of the ground and first excited states of several transition metal complexes have been performed to complement time-resolved diffraction experiments. The results from different functionals and relativistic treatments are tested against both diffraction and spectroscopic values. Calculations of the d8,d8 complex [Pt2(pyrophosphite)4]4, quantitatively reproduce metal,metal shortening on excitation to the triplet state and support bond formation between the two metal centers, as do calculations on [Rh2(1,3-diisocyanopropane)4]2+. Results on homoleptic and heteroleptic copper(I) 2,9-dimethyl,1,10-phenanthroline (dmp) complexes, which are investigated because of their potential for solar energy capture, confirm considerable molecular deformations on excitation. The distortion calculated for the isolated complex [Cu(dmp)(dmpe)]+ (dmpe=1,2-bis(dimethylphosphino)ethane) is significantly larger than observed in the crystal, indicating the constraining effect of the crystalline environment. The change in the net charge of the Cu atom upon photo-induced metal-to-ligand charge transfer is less than 0.2 e, showing the limitations of the formal Cu(I),Cu(II) designation. Electron density difference maps show a pronounced change in electronic structure of the Cu atom on excitation. © 2004 Wiley Periodicals, Inc. Int J Quantum Chem, 2005 [source] Molecular magnetism via resonating valence bonds for conjugated radicals and selected transition metal complexesINTERNATIONAL JOURNAL OF QUANTUM CHEMISTRY, Issue 4-5 2001D. J. Klein Abstract Currently there is considerable interest in the nature of exchange interactions leading to unpaired electrons in molecular and cluster magnets. Here, the focus is largely at a qualitative level, via a novel "mean-field" resonance-theoretic view, to deal with exchange couplings, so as to allow unpaired electrons in either (or both of) the ,- and ,-parts of a (largely organic) bipartite (or alternate) molecular network. The (quantitative) number and (qualitative) location of unpaired spins are dealt with by this simple approach, which also offers some (qualitative) information on the occurrence of low-lying higher-spin states. To illustrate the approach it is applied to a variety of systems where the spin sources are conjugated ,-network molecules and polymers, carbenes, variously defected graphites, and a few species involving transition metals, especially Cu. The discussion deals not only with traditional conjugated organics compounds but also with selected inorganic species. © 2001 John Wiley & Sons, Inc. Int J Quantum Chem, 2001 [source] Configuration interaction calculation of electronic g tensors in transition metal complexes,INTERNATIONAL JOURNAL OF QUANTUM CHEMISTRY, Issue 3-4 2001Frank Neese Abstract An algorithm for the calculation of electronic g tensors from configuration interaction (CI) wave functions and its implementation for any ground-state spin S is described. The algorithm can be used together with either single- or multireference CI wave functions but assumes a spatially nondegenerate ground state. A one-electron approximation to the spin,orbit coupling (SOC) operator is used. Presently the implementation uses the INDO/S model of Zerner and coworkers. Results are presented for a representative collection of Cu(II) complexes with N-, O-, and S-containing ligands. The calculations reproduce the trends in the experimental data well and show no systematic errors. For the test set the g values are reproduced with a standard deviation of 0.021. The method has therefore a good cost,performance ratio and is expected to be helpful in chemical and biochemical applications. Further improvements are feasible and necessary and are briefly discussed. © 2001 John Wiley & Sons, Inc. Int J Quant Chem 83: 104,114, 2001 [source] Spin states in polynuclear clusters: The [Fe2O2] core of the methane monooxygenase active siteJOURNAL OF COMPUTATIONAL CHEMISTRY, Issue 12 2006Carmen Herrmann Abstract The ability to provide a correct description of different spin states of mono- and polynuclear transition metal complexes is essential for a detailed investigation of reactions that are catalyzed by such complexes. We study the energetics of different total and local spin states of a dinuclear oxygen-bridged iron(IV) model for the intermediate Q of the hydroxylase component of methane monooxygenase by means of spin-unrestricted Kohn,Sham density functional theory. Because it is known that the spin state total energies depend systematically on the density functional, and that this dependence is intimately connected to the exact exchange admixture of present-day hybdrid functionals, we compare total energies, local and total spin values, and Heisenberg coupling constants calculated with the established functionals BP86 and B3LYP as well as with a modified B3LYP version with an exact exchange admixture ranging from 0 to 24%. It is found that exact exchange enhances local spin polarization. As the exact exchange admixture increases, the high-spin state is energetically favored, although the Broken-Symmetry state always is the ground state. Instead of the strict linear variation of the energy splittings observed for mononuclear complexes, a slightly nonlinear dependence is found. The Heisenberg coupling constants JFe1Fe2,evaluated according to three different proposals from the literature,are found to vary from ,129 to ,494cm,1 accordingly. The experimental finding that intermediate Q has an antiferromagnetic ground state is thus confirmed. © 2006 Wiley Periodicals, Inc. J Comput Chem 27: 1223,1239, 2006 [source] domain averaged Fermi holes;JOURNAL OF COMPUTATIONAL CHEMISTRY, Issue 15 2003chemical bond; The recently proposed approach based on the analysis of domain-averaged Fermi holes was applied to the study of the nature of metalmetal bonding in transition metal complexes and clusters. The main emphasis was put on the scrutiny of the systems assumed to contain direct multiple metalmetal bonds. The studied systems involve: (1) systems of the type M2X6 (M = Mo, W, X = CH3) anticipated to contain metalmetal triple bonds; (2) the molecule of W2Cl8(4,) as the representative of the systems with quadruple metalmetal bonding; (3) diatomic molecules Mo2 and V2 considered as the potential candidates for higher than quadruple metalmetal bonding. Although the resulting picture of bonding has been usually shown to agree with the original expectations based on early simple MO models, some examples were also found in which the conclusions of the reported analysis display dramatic sensitivity to the quality of the wave function used for the generation of the Fermi holes. In addition to this we also report some examples where the original theoretical predictions of multiplicity of metalmetal bonds have to be corrected. © 2003 Wiley Periodicals, Inc. J Comput Chem 24: 1829,1838, 2003 [source] Low- and high-spin iron (II) complexes studied by effective crystal field method combined with molecular mechanicsJOURNAL OF COMPUTATIONAL CHEMISTRY, Issue 14 2003M. B. Darkhovskii Abstract A computational method targeted to Werner-type complexes is developed on the basis of quantum mechanical effective Hamiltonian crystal field (EHCF) methodology (previously proposed for describing electronic structure of transition metal complexes) combined with the Gillespie,Kepert version of molecular mechanics (MM). It is a special version of the hybrid quantum/MM approach. The MM part is responsible for representing the whole molecule, including ligand atoms and metal ion coordination sphere, but leaving out the effects of the d -shell. The quantum mechanical EHCF part is limited to the metal ion d -shell. The method reproduces with reasonable accuracy geometry and spin states of the Fe(II) complexes with monodentate and polydentate aromatic ligands with nitrogen donor atoms. In this setting a single set of MM parameters set is shown to be sufficient for handling all spin states of the complexes under consideration. © 2003 Wiley Periodicals, Inc. J Comput Chem 14: 1703,1719, 2003 [source] Development of new pseudopotential methods: Improved model core potentials for the first-row transition metalsJOURNAL OF COMPUTATIONAL CHEMISTRY, Issue 9 2003Christopher C. Lovallo Abstract We have recently developed new nonrelativistic and scalar-relativistic pseudopotentials for the first-row transition metal and several main-group elements. These improved Model Core Potentials were tested on a variety of transition metal complexes to determine their accuracy in reproducing electronic structures, bond lengths, and harmonic vibrational frequencies with respect to both all-electron reference data as well as experimental data. The new potentials are also compared with the previous model core potentials available for the first-row transition metals. The new potentials do a superior job at reproducing atomic data, reproduce molecular data as well as the previous version, and in conjunction with new main-group pseudopotentials that have L-shell structure of the valence basis set, they are slightly faster. © 2003 Wiley Periodicals, Inc. J Comput Chem 9: 1009,1015, 2003 [source] | ||||||||||||||||||||||||||||