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Metal Atoms (metal + atom)
Kinds of Metal Atoms Terms modified by Metal Atoms Selected AbstractsLewis Acid Mediated Diastereoselective Reduction of N-Protected ,-Amino Ketones: Influence of the Nature of the Metal Atom and of the Nitrogen Protecting Group.CHEMINFORM, Issue 37 2004Giuseppe Bartoli Abstract For Abstract see ChemInform Abstract in Full Text. [source] Synthesis and Characterization of the D5h Isomer of the Endohedral Dimetallofullerene Ce2@C80: Two-Dimensional Circulation of Encapsulated Metal Atoms Inside a Fullerene CageCHEMISTRY - A EUROPEAN JOURNAL, Issue 37 2009Michio Yamada Dr. Abstract Herein we show the synthesis and characterization of the second known Ce2@C80 isomer. A 13C,NMR spectroscopic study revealed that the structure of the second isomer has D5h symmetry. Paramagnetic NMR spectral analysis and theoretical calculation display that the encapsulated Ce atoms circulate two-dimensionally along a band of ten contiguous hexagons inside a D5h -C80 cage, which is in sharp contrast to the three-dimensional circulation of two Ce atoms in an Ih -C80 cage. The electronic properties were revealed by means of electrochemical measurements. The D5h isomer of Ce2@C80 has a much smaller HOMO,LUMO gap than cluster fullerenes (M3N@C80, M=Sc, Tm, and Lu) with the same D5h -C80 cages. The chemical reactivity was investigated by using disilirane as a chemical probe. The high thermal reactivity toward 1,1,2,2-tetramesityl-1,2-disilirane is consistent with the trends of the redox potentials and the lower LUMO level of the D5h isomer of Ce2@C80 compared with that of C60. [source] The Role of C,H···H,B Interactions in Establishing Rotamer Configurations in Metallabis(dicarbollide) SystemsEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 16 2010Emilio José Juárez-Pérez Abstract The aim of this work is to explore the self-interaction capability of the anion [3,3,-Co(1,2-C2B9H11)2], through Ccluster,H···H,B (Cc,H···H,B) dihydrogen bonds. A set of theoretical and empirical data aiming to establish the main rules that account for the binding mode between the negatively charged borane framework made by [3,3,-Co(1,2-C2B9H11)2], and the [NMe4]+ ions have been compiled. The interaction between cation and anion is mainly electrostatic but the covalent contribution is also proven and quantified. The existing intermolecular H···H short contacts have been studied and are compared with available data from the Cambridge Structural Database. The results show that the electronic configuration of the transition metal atom in the sandwich complex is not enough to define the preferred rotamer due to the influence of the anion environment and the H···H interactions present in the solid state. We present a methodology with widely used theoretical tools to study cation···cobaltabisdicarbollide interactions in the solid state. [source] Unusual Magnetism of an Unsymmetrical Trinickel ChainEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 33 2008F. Albert Cotton Abstract An extended metal atom chain (EMAC) compound with an unsymmetrical trinickel core and the formula [Ni3(dpa)4(CH3CN)](PF6)2·2CH2Cl2 (1·2CH2Cl2, dpa is the anion of 2,2,-dipyridylamine) has the central Ni atom in an essentially square-planar configuration. Besides having four equatorial nitrogen atoms, the two terminal metal centers have axial interactions that are notably different with one having a strongly bound acetonitrile molecule with a Ni(3),N(3) distance of 2.108(5) Å while the other unit has a very weak interaction with an axial PF6 anion [Ni(1)···F(1) separation of 2.690 Å]. In these outer units, the Ni(3) atom is pulled out of the idealized plane of the four equatorial nitrogen atoms by 0.239 Å, while in the one with an axial PF6 anion the metal atom is pulled from the plane of the equatorial nitrogen atoms by only 0.097 Å. In 1 there are two unpaired electrons and an S = 1 state prevails from ca. 25 to 300 K. This magnetic behavior differs considerably from that of symmetrical trinickel EMACs with two strongly pyramidal terminal nickel atoms. A discussion of the effect of various axial ligands on the geometry of the terminal nickel atoms is provided. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008) [source] Pseudo-Octahedral Schiff Base Nickel(II) Complexes: Does Single Oxidation Always Lead to the Nickel(III) Valence Tautomer?EUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 27 2008Olaf Rotthaus Abstract With the aim of establishing correlations between the ligand structure and the oxidation site in nickel complexes from Schiff base ligands, five ligands and their nickel complexes have been synthesized. The prototypical asymmetric Schiff base ligand HL1 contains both phenol and pyridine pendant arms with a pivotal imine nitrogen atom. Ligands HL2,5 differ from HL1 by either their phenolate para substituent, the hybridization of the pivotal nitrogen atom, and/or the N-donor properties of the pyridine moiety. The five complexes [Ni(L1,5)2] are obtained by treating the corresponding ligands with 0.5 equiv. of Ni(OAc)2·4H2O in the presence of NEt3. X-ray crystal-structure diffraction studies as well as DFT calculations reveal that [Ni(L1,5)2] involves a high-spin nickel(II) ion within a pseudo-octahedral geometry. The two ligands are arranged in a meridional fashion when the pivotal nitrogen atom is an imine {as in [Ni(L1,2)2] and [Ni(L4,5)2]}, while the fac isomer is preferred in [Ni(L3)2] (amino pivotal nitrogen atom). [Ni(L1)2] is characterized by an oxidation potential at ,0.17 V vs. Fc+/Fc. The one-electron-oxidized species [Ni(L1)2]+ exhibits an EPR signal at g = 2.21 attributed to a phenoxyl radical that is antiferromagnetically coupled to a high-spin NiII ion. [Ni(L2)2] differs from [Ni(L1)2] by the phenolate para substituent (a tert -butyl instead of the methoxyl group) and exhibits an oxidation potential that is ca. 0.16 V higher. Compared to [Ni(L1)2]+ the cation [Ni(L2)2]+ exhibits a SOMO that is more localized on the metal atom. The EPR and electrochemical signatures of [Ni(L3)2]+ are similar to those of [Ni(L1)2]+, thus showing that an imino to amino substitution compensates for a methoxy to tert -butyl one. Replacement of the pyridine by a quinoline group in [Ni(L4,5)2] makes the complexes slightly harder to oxidize. The EPR signatures of the cations [Ni(L4,5)2]+ are roughly similar to those of the pyridine analogs [Ni(L1,2)2]+. The oxidation site is thus not significantly affected by changes in the N-donor properties of the terminal imino nitrogen atom.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008) [source] How Do the Different Defect Structures and Element Substitutions Affect the Nonlinear Optical Properties of Lacunary Keggin Polyoxometalates?EUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 20 2006A DFT Study Abstract Systematic DFT calculations have been carried out on the lacunary ,-Keggin polyoxometalate derivatives [PW11O39]7,, [XW9O34]n, (X = AlIII, SiIV, GeIV, PV, AsV, and SbV), [XW9M2O39]n,, and [XW9M3O40]n, (X = PV and SiIV, M = MoVI, VV, NbV, and TaV) to investigate the geometric structure and element substitution effects on the molecular nonlinear optical response. Analysis of the computed static second-order polarizability (,0) predicts that the molecular nonlinear optical activity of lacunary Keggin polyoxometalate derivatives can be modified by replacing the central heteroatom and the addenda metal atom. Substitution of the central Al atom or the addenda V atom causes significant enhancement in the molecular nonlinearity. Moreover, the ,0 values are substantially dependent on the defect structures. This class of inorganic complexes possesses remarkably large molecular optical nonlinearity, especially for the partial substitution complex [SiW9Nb2O39]10, (IIIc), which has a computed ,0 value of 2071.0 a.u. Thus, lacunary Keggin polyoxometalates could become excellent candidates in the field of second-order NLO. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006) [source] Chelate [2-(Iminoethyl)pyridine N -oxide]metal Complexes , Synthesis and Structural Comparison with Their Chemically Related 2-(Iminoethyl)pyridine-Derived SystemsEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 2 2006Katrin Nienkemper Abstract The N,O-chelate ligands 2-(iminoethyl)pyridine N -oxide (2a) and 2-(iminoethyl)-6-isopropylpyridine N -oxide (2b) were prepared by conventional synthetic routes, the latter involving a variant of the Reissert,Henze reaction. Treatment of 2a with FeCl2 resulted in a deoxygenation reaction of the ligand and formation of the salt [bis{2-(iminoethyl)pyridine}FeCl]+[FeCl4], (18a). In contrast, the reaction of 2a with PdCl2 or CoCl2 cleanly furnished the six-membered chelate [,N,O -2(iminoethyl)pyridine N -oxide]MCl2 complexes (19a, M = Pd) or (20a, M = Co), respectively, which were both characterised by X-ray diffraction. Treatment of 2b with [NiBr2(dme)], followed by crystallisation from THF, gave the complex [(,N,O - 2b)NiBr2(THF)] (21b), which features a distorted trigonal-bipyramidal coordination geometry of the central metal atom. The reaction of 2a with [NiBr2(dme)] gave the structurally related complex [(,N,O - 2a)NiBr2(,O - 2a)] (21a). The N,O-chelate Pd complex 19a was shown to be an active catalyst for the Suzuki coupling reaction. The ligand systems 2a,b and their related 2-(iminoethyl)pyridines 3a,b and a variety of metal complexes of ligands 3 were also prepared and characterised for comparison by X-ray diffraction. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006) [source] NMR T1 -Relaxation Measurements on Paramagnetic Organolanthanides:An Alternative Tool for Structure Determination in SolutionEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 12 2005Laurent Brachais Abstract 1H NMR investigations were conducted on four paramagnetic organolanthanides, all bearing the tetraisopropylcyclopentadienyl ligand Cp4i (HC5iPr4) in order to verify whether or not interactions observed in the solid state are maintained in solution. In some cases variable-temperature experiments were necessary to enhance the resolution and determine the best conditions for the study. The 1D NMR spectrum could be interpreted in every case. Complementary 2D COSY experiments allowed the full attribution of the signals. T1 (1H) relaxation values were determined for all the paramagnetic complexes at the most suitable temperature, and compared with those of the diamagnetic KCp4i. The same tendency was observed, with particular features concerning the isopropyl groups. Among the four methyl groups, one exhibits a much higher T1 value and one a much lower value; the two others are intermediate. This was interpreted as the result of a privileged conformation of the Cp4i ligand: the two ,-isopropyl groups take up a spatial orientation with one methyl group in the exo position, opposite to the metal atom, whereas the methyl groups of the two ,-isopropyl groups are equidistant from the metal atom. Whatever the nature of the metal (Nd, Sm), the oxidation state (SmII, SmIII) or the temperature (298, 363 K), this conformation is retained. The structure in solution seems to be different from that previously determined in the solid state. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005) [source] How the choice of a computational model could rule the chemical interpretation: The Ni(II) catalyzed ethylene dimerization as a case studyJOURNAL OF COMPUTATIONAL CHEMISTRY, Issue 5 2010Vincent Tognetti Abstract In this article, we present a critical study of the theoretical protocol used for the determination of the nickel(II) catalyzed ethylene dimerization mechanism, considered as a representative example of the various problems related to the modeling a catalytic cycle. The choice of an appropriate computational procedure is indeed crucial for the validity of the conclusions that will be drawn from the computational process. The influence of the exchange-correlation functional on energetic profiles and geometries, the role of the basis set describing the metal atom, as well as the importance of the chosen molecular model, have been thus examined in details. From the obtained results, some general conclusions and guidelines are presented, which could constitute useful warnings in modeling homogenous catalysis. Besides, the database constituted by our high-level calculations can be used within benchmarking procedures to assess the performances of new computational methods based on density functional theory. © 2009 Wiley Periodicals, Inc. J Comput Chem 2010 [source] Transition metal,boron complexes BnM: From bowls (n = 8,14) to tires (n = 14)JOURNAL OF COMPUTATIONAL CHEMISTRY, Issue 15 2006Si-Dian Li Abstract Transition metal,boron complexes BnM have been predicted at density functional theory level to be molecular bowls (n = 8,14) hosting a transition metal atom (M) inside or molecular tires (n = 14) centered with a transition metal atom. Small Bn clusters prove to be effective inorganic ligands to all the VB,VIIIB transition metal elements in the periodic table. Density functional evidences obtained in this work strongly suggest that bowl-shaped fullerene analogues of Bn units exist in small BnM complexes and the bowl-to-tire structural transition occur to the first-row transition metal complexes BnM (M = Mn, Fe, Co) at n = 14, a size obviously smaller than n = 20 where the 2D-3D structural transition occurs to bare Bn. The half-sandwich-type B12Cr (C3v), full sandwich-type (B12)2Cr (D3d), bowl-shaped B14Fe (C2), and tire-shaped B14Fe (D7d) and B14Fe, (C7v) are the most interesting prototypes to be targeted in future experiments. These BnM complexes may serve as building blocks to form extended boron-rich BnMm tubes or cages (m , 2) or as structural units to be placed inside carbon nanotubes with suitable diameters. © 2006 Wiley Periodicals, Inc. J Comput Chem, 2006 [source] Synchrotron techniques for metalloproteins and human disease in post genome eraJOURNAL OF SYNCHROTRON RADIATION, Issue 1 2004S. Samar Hasnain Metalloproteins make up some 30% of proteins in known genomes. Metalloproteins are a special class of proteins that utilise the unique properties of metal atoms in conjunction with the macromolecular assembly to perform life-sustaining processes. A number of metalloproteins are known to be involved in many disease states including ageing processes. The incorporation of the metal ion is a very tightly regulated process that, in vivo, very often requires specific chaperons to deliver and help incorporate the metal atom in the macromolecule. The lack of or inappropriate incorporation of metals along with genetic factors can lead to the mis-function of these proteins leading to disease. The mis-functions due to genetic alterations that lead to diseases like ALS (amyotrophic lateral sclerosis or motor neuron disease) and Creutzfeld Jacob disease (CJD) are now well recognised. Synchrotron radiation sources provide a unique set of structural tools, which in combination can prove extremely powerful in providing a comprehensive picture of these complex biological systems. In particular for metalloproteins, the combined use of X-ray crystallography, X-ray solution scattering and X-ray spectroscopy (XAFS) is extremely useful. We are currently engaged in a structural study where our aim is to characterize structurally and functionally metalloproteins and then transfer this knowledge to afford the problem of the mis-function of metalloproteins that lead to these terminal illnesses, either due to a gain of function/property or a loss of function/property. In this context, the benefits of adopting the `philosophy' being developed for the structural genomics effort are highlighted. [source] An ESCA study of the effectiveness of antiwear and extreme-pressure additives based on substituted phosphorodithioate derivatives, and a comparison with ZDDPLUBRICATION SCIENCE, Issue 2 2001M. C. Jain Ashless substituted dithiophosphoric acid derivatives (ADPs) are a new generation of multifunctional additives with promising antiwear (AW) and extreme-pressure (EP) characteristics. Three such additives synthesised in the authors' laboratory have been evaluated for their AW and EP properties by standard four-ball friction and wear tests. The friction-reducing properties of these additives were compared with those of a commercial zinc dialkyldithiophosphate (ZDDP). It was found that the phosphorodithioate compounds studied here possessed excellent AW/EP properties. Their AW characteristics were found to be comparable to those of ZDDP at low loads. However, at higher loads they show inferior AW characteristics in comparison to ZDDP. Nevertheless, ADP derived from cashew nut shell oil had a higher load-carrying capacity than ZDDP. The mechanism of the AW and EP behaviour exhibited by the different additives was investigated using X-ray photoelectron spectroscopy (XPS), Auger electron spectroscopy (AES), and scanning electron microscopy (SEM) of the worn surfaces formed during friction. XPS and AES analyses of the worn surfaces reveal that the tribochemical film formed on the ADP-tested surfaces consisted mainly of metal phosphates and only a small amount of metal sulphides, even though the ADPs contained twice the number of sulphur atoms than phosphorus atoms. The ZDDP-tested surface showed a mixture of metal sulphides and metal phosphates. Alkylamino substitution appeared to have no significant effect on the AW/EP properties of the additive. XPS and AES analyses also revealed that the tribochemical film formed on an ADP-tested surface was thicker than that present on the ZDDP-tested surface at low loads, whereas at higher loads the reverse was true. The higher weld load obtained for the blend containing cashew nut shell oil-derived ADP is attributed to the thicker adsorbed reaction film formed on the surface due to the long alkyl groups present in the original additive structure. Short-chain alkyl groups, however, form only a thin adsorbed layer, which may get rubbed off during the friction at high load. The low sulphide formation on ADP-tested surfaces was attributed to the absence of any metal atom in the additive, which would help in the formation of metal sulphides during tribofragmentation and further tribochemical reactions. [source] Multinuclear NMR study of some organoplatinum complexes containing multifunctional azines as chelating ligands,MAGNETIC RESONANCE IN CHEMISTRY, Issue 9 2004Dietrich Gudat Abstract 1H-detected indirect NMR techniques were used to determine 15N and 195Pt NMR parameters for a series of organoplatinum(IV) complexes and one platinum(II) complex containing nitrogen-based azobispyridine, bispyridyltetrazine, and bipyrimidine ligands. The inverse technique permitted the detection of small 4J(Pt,H) and 5J(Pt,H) long-range couplings and the acquisition of 15N NMR data in natural isotopic abundance via nJ(N,H) intra- and inter-ligand couplings, but failed in cases where coherence transfer is quenched by rapid relaxation of the metal atom. In one case, analysis of satellite patterns in a set of 1H,15N, 1H,195Pt and 1H,13C correlation spectra allowed a positive sign to be determined for 1J(Pt,15N). Qualitative arguments are presented to explain the observed 15N coordination shifts in complexes with different azine ligands in terms of azine,M dative bond formation and LnM,azine back-donation. Copyright © 2004 John Wiley & Sons, Ltd. [source] Synchrotron X-ray analysis of the electron density in CoF2 and ZnF2ACTA CRYSTALLOGRAPHICA SECTION B, Issue 2 2001Nicholas J. O'Toole Accurate structure factors for small crystals of the rutile-type structures CoF2, cobalt difluoride, and ZnF2, zinc difluoride, have been measured with focused , = 0.8400,(2),Å synchrotron X-radiation at room temperature. Phenomenological structural trends across the full series of rutile-type transition metal difluorides are analysed, showing the importance of the metal atom in the degree of distortion of the metal,F6 octahedra in these structures. Multipole models reveal strong asphericities in the electron density surrounding the transition metals, which are consistent with expectations from crystal field theory and the structural trends in these compounds. Transition metal 3d -orbital populations were computed from the multipole refinement parameters, showing significant repopulation of orbitals compared with the free atom, particularly for CoF2. [source] The ansa -zirconocene [bis(,5 -cyclopentadienyl)phenylphosphine]dichloridozirconium(IV)ACTA CRYSTALLOGRAPHICA SECTION C, Issue 3 2010Susanne Büschel In the title compound, [Zr(C16H13P)Cl2], the geometry at the metal atom is distorted tetrahedral; the Cl,Zr,Cl angle is 101.490,(16)° and the cyclopentadienyl (Cp) centroids subtend an angle of 122.63,(3)° at the Zr atom. The P atom lies 0.474,(3) and 0.496,(3),Å out of the planes of the Cp rings. The C,P,C angle of 91.42,(7)° reflects the pincer effect of the two Cp rings. Three C,H...Cl, one C,H...P, one C,H..., and one Cl...P interaction link the molecules to form thick layers parallel to the bc plane. [source] Probing the supramolecular interaction synthons of 1-benzofuran-2,3-dicarboxylic acid in its monoanionic formACTA CRYSTALLOGRAPHICA SECTION C, Issue 1 2009Rajesh Koner 1-Benzofuran-2,3-dicarboxylic acid (C10H6O5) is a dicarboxylic acid ligand which can readily engage in organometallic complexes with various metal ions. This ligand is characterized by an intramolecular hydrogen bond between the two carboxyl residues, and, as a monoanionic species, readily forms supramolecular adducts with different organic and inorganic cations. These are a 1:1 adduct with the dimethylammonium cation, namely dimethylammonium 3-carboxy-1-benzofuran-2-carboxylate, C2H8N+·C10H5O5,, (I), a 2:1 complex with Cu2+ ions in which four neutral imidazole molecules also coordinate the metal atom, namely bis(3-carboxy-1-benzofuran-2-carboxylato-,O3)tetrakis(1H -imidazole-,N3)copper(II), [Cu(C10H5O5)2(C3H4N2)4], (II), and a 4:1 adduct with [La(H2O)7]3+ ions, namely heptaaquabis(3-carboxy-1-benzofuran-2-carboxylato-,O3)lanthanum 3-carboxy-1-benzofuran-2-carboxylate 1-benzofuran-2,3-dicarboxylic acid solvate tetrahydrate, [La(C10H5O5)2(H2O)7](C10H5O5)·C10H6O5·4H2O, (III). In the crystal structure, complex (II) resides on inversion centres, while complex (III) resides on axes of twofold rotation. The crystal packing in all three structures reveals ,,, stacking interactions between the planar aromatic benzofuran residues, as well as hydrogen bonding between the components. The significance of this study lies in the first crystallographic characterization of the title framework, which consistently exhibits the presence of an intramolecular hydrogen bond and a consequent monoanionic-only nature. It shows further that the anion can coordinate readily to metal cations as a ligand, as well as acting as a monovalent counter-ion. Finally, the aromaticity of the flat benzofuran residue provides an additional supramolecular synthon that directs and facilitates the crystal packing of compounds (I),(III). [source] Strontium tetrafluoridoborate and barium tetrafluoridoborateACTA CRYSTALLOGRAPHICA SECTION C, Issue 9 2007Tina Buni In Sr(BF4)2, which is isomorphous with the previously published Ca(BF4)2, the metal atom possesses a coordination number of 8 with a square-antiprismatic environment. Each tetrafluoridoborate anion is bonded to four metal centers. In the barium derivative, the metal center, with symmetry 2/m, is surrounded by 14 F atoms. The B atom and two of the three independent F atoms occupy special positions with symmetry m. Each anion is connected to five Ba atoms. This structure differs significantly from an earlier published structure of Ba(BF4)2 [published as Ba2(BF4)4; Lin, Cheng, Chen & Huang (1998). Jiegon Huaxue, 17, 245]. The radial distribution functions for the present Ba(BF4)2 and earlier Ba2(BF4)4 structures differ significantly. [source] trans -[1,3-Bis(2,4,6-trimethylphenyl)imidazolidin-2-ylidene]dichlorido(triphenylphosphine-,P)palladium(II)ACTA CRYSTALLOGRAPHICA SECTION C, Issue 6 2007Hayati Türkmen The title complex, [PdCl2(C21H26N2)(C18H15P)], shows slightly distorted square-planar coordination around the PdII metal centre. The Pd,C bond distance between the N-heterocyclic ligand and the metal atom is 2.028,(5),Å. The dihedral angle between the two trimethylphenyl ring planes is 36.9,(2)°. [source] {Bis(3,5-Di- tert -butyl-2-oxidobenzyl)[2-(N,N -dimethylamino)ethyl]amine-,4N,N,,O,O,}zinc(II) and {bis(3- tert -butyl-5-methyl-2-oxidobenzyl)[2-(N,N -dimethylamino)ethyl]amine-,4N,N,,O,O,}(tetrahdyrofuran)zinc(II)ACTA CRYSTALLOGRAPHICA SECTION C, Issue 7 2006Ruth H. Howard The title zinc(II) complexes, [Zn(C34H54N2O2)], (II), and [Zn(C28H42N2O2)(C4H8O)], (III), were obtained as monomeric 1:1 complexes, in contrast with the calcium complexes supported by the same ligand class. Complex (II) crystallizes with two independent molecules in the asymmetric unit, which have similar geometric parameters. The donor atoms in (II) form a distorted trigonal,pyramidal arrangement around the zinc centre. Complex (III) contains a coordinated tetrahydrofuran molecule, resulting in a five-coordinate trigonal,bipyramidal arrangement around the Zn atom. The electron density provided by the coordination of this tetrahydrofuran molecule elongates the Zn,O and Zn,N bonds by approximately 0.07 and 0.10,Å, respectively, in comparison with (II). Neither (II) nor (III) is active as an ,-caprolactone polymerization catalyst. The data presented here demonstrate that Zn may bind both an ONNO ligand and an additional oxygen-based ligand. The lack of activity is thus not due to steric hinderance at the metal atom. [source] Ligand Association/Dissociation Paths and Ill-Defined Coordination NumbersCHEMISTRY - A EUROPEAN JOURNAL, Issue 22 2010Antonio Ruiz-Martínez Abstract The continuous shape measures approach provides a means for handling the common situation in which a metal atom presents an ill-defined coordination number. Those cases are characterized by the presence of secondary interactions to Lewis bases at distances significantly longer than those expected for a chemical bond. Systematic ways of analyzing ligand association/dissociation pathways that describe such structures and their application to a variety of specific cases are presented. The concepts and methodology presented here apply to molecules and extended solids as well and provide, when needed, a more flexible and precise stereochemical description of the metal coordination sphere than that of an integer coordination number and the associated polyhedral shape. El mètode de les mesures contínues de forma ens permet tractar la situació trobada freqüentment, en què un àtom metàl,lic presenta un nombre de coordinació no ben definit, caracteritzat per la presència d,interaccions secundàries amb bases de Lewis a distàncies significativament més llargues que les que correspondrien a un enllaç químic. Aquí es presenten formes sistemàtiques d,analitzar els camins d,associació/dissociació de lligands que descriuen aquestes estructures, així com llur aplicació a diverses famílies de compostos. Els conceptes i la metodologia presentats en aquest article s'apliquen tant a molècules com a sòlids infinits i ens proporcionen una descripció estereoquímica més flexible i alhora precisa de les esferes de coordinació que no pas un nombre de coordinació enter i la forma polièdrica associada. [source] Sandwich Compounds of Transition Metals with Cyclopolyenes and Isolobal Boron AnaloguesCHEMISTRY - A EUROPEAN JOURNAL, Issue 7 2010Tatyana Abstract A series of sandwich compounds of transition metals (M=Ni, Fe, Cr) with cyclic hydrocarbon (M(CH)n) and borane (M(BH2)n), ligands (including mixed hydrocarbon/borane sandwiches) has been studied using density functional theory (B3LYP/6-311+G(df,p)). Multicenter bonding between the central metal atom and basal cycloborane rings provides stabilization to planar cycloborane species. Large negative NICS values allude to aromatic character in the cycloboranes similar to the analogous cyclic hydrocarbons. The ability of cycloborane sandwiches to stabilize attached carbocations, radicals and carbanions is also assessed. [source] Homoleptic Organoderivatives of High-Valent Nickel(III)CHEMISTRY - A EUROPEAN JOURNAL, Issue 41 2009Pablo Abstract Homoleptic perhalophenyl derivatives of divalent nickel complexes with the general formula [NBu4]2[NiII(C6X5)4] [X=F (1), Cl (2)] have been prepared by low-temperature treatment of the halo-complex precursor [NBu4]2[NiBr4] with the corresponding organolithium reagent LiC6X5. Compounds 1 and 2 are electrochemically related by reversible one-electron exchange processes with the corresponding organometallate(III) compounds [NBu4][NiIII(C6X5)4] [X=F (3), Cl (4)]. The potentials of the [NiIII(C6X5)4],/[NiII(C6X5)4]2, couples are +0.07 and ,0.11,V for X=F or Cl, respectively. Compounds 3 and 4 have also been prepared and isolated in good yield by chemical oxidation of 1 or 2 with bromine or the amminium salt [N(C6H4Br-4)3][SbCl6]. The [NiIII(C6X5)4], species have SP -4 structures in the salts 3 and 4, as established by single-crystal X-ray diffraction methods. The [NiII(C6F5)4]2, ion in the parent compound 1 has also been found to exhibit a rather similar SP -4 structure. According to their SP -4 geometry, the NiIII compounds (d7) behave as S=1/2 systems both at microscopic (EPR) and macroscopic levels (ac and dc magnetization measurements). The spin Hamiltonian parameters obtained from the analysis of the magnetic behavior of 3 and 4 within the framework of ligand field theory show that the unpaired electron is centered mainly on the metal atom, with >97,% estimated d contribution. Thermal decomposition of 3 and 4 proceeds with formation of the corresponding C6X5C6X5 coupling compounds. [source] Synthesis, X-ray Single-Crystal Structure Determination, and Magnetic Properties of [Rb(benzo[18]crown-6)]+ Salts Containing Well-Ordered Fulleride Trianions C603,,CHEMISTRY - A EUROPEAN JOURNAL, Issue 13 2009Bele Boeddinghaus Dipl.-Chem. Abstract Finally, a structure with well-resolved C603,ions and S=1/2 spin system: The two novel title compounds have clearly S=1/2 and not S=3/2 electronic states, as expected for the occupation of the triply degenerate LUMO of C60. These structures with well-ordered fullerene trianions show that the expected Jahn,Teller distortion is not observable in X-ray diffraction experiments. Crystals of the composition [Rb(benzo[18]crown-6)]3[,3 -C60](C7H8)(C3H7NO)4.5 (1) and [Rb(benzo[18]crown-6)]3[C60](C3H7NO)5.33(C4H8O)1.66 (2) were synthesized by reduction of C60 with elemental rubidium in a mixture of dimethylformamide/tetrahydrofuran in the presence of benzo[18]crown-6. X-ray single-crystal structure determinations reveal well-ordered C60 trianions in both compounds. In contrast to previously reported structures of compounds containing C603, ions the present structure refinements allow the description of the buckyballs with good resolution (R1/wR2 for I>2,(I) (all data) are 0.030/0.069 (0.051/0.071) and 0.042/0.101 (0.076/0.108) for 1 and 2, respectively). In 1 the C603, unit coordinates in an ,3 -fashion to one Rb atom, whose coordination sphere is completed by one benzo[18]crown-6 and one dimethylformamide molecule. In 2 no coordination of the alkali metal atom to the C60 trianion is observed. Magnetic measurements for 1 reveal a magnetic moment of 1.74,,B, as expected for an isolated S=1/2 spin system. The high-quality data of the present studies allowed a comparison of structural details of C603, ions with other C60n, units (n=0, 2, 3) and a discussion of the structural Jahn,Teller distortions. [source] Muon Implantation of Metallocenes: FerroceneCHEMISTRY - A EUROPEAN JOURNAL, Issue 8 2007Upali Abstract Muon Spin Relaxation and Avoided Level Crossing (ALC) measurements of ferrocene are reported. The main features observed are five high field resonances in the ALC spectrum at about 3.26, 2.44, 2.04, 1.19 and 1.17,T, for the low-temperature phase at 18,K. The high-temperature phase at 295,K shows that only the last feature shifted down to about 0.49,T and a muon spin relaxation peak at about 0.106,T which approaches zero field when reaching the phase transition temperature of 164,K. A model involving three muoniated radicals, two with muonium addition to the cyclopentadienyl ring and the other to the metal atom, is postulated to rationalise these observations. A theoretical treatment involving spin-orbit coupling is found to be required to understand the Fe,Mu adduct, where an interesting interplay between the ferrocene ring dynamics and the spin-orbit coupling of the unpaired electron is shown to be important. The limiting temperature above which the full effect of spin-orbit interaction is observable in the ,SR spectra of ferrocene was estimated to be 584,K. Correlation time for the ring rotation dynamics of the Fe,Mu radical at this temperature is 3.2,ps. Estimated electron g values and the changes in zero-field splittings for this temperature range are also reported. [source] Computational Investigation of Hydrogen Adsorption by Alkali-Metal-Doped Organic Molecules: Role of AromaticityCHEMPHYSCHEM, Issue 2 2009Kancharlapally Srinivasu Abstract Hydrogen storage: Simple organic molecular systems (CnHn, n=4, 5, 6, 8) are proposed for hydrogen storage purposes based on the concept of aromaticity. The adsorption of hydrogen is attributed to pronounced charge transfer from the sodium atom (green, see picture) to the organic systems and the electrostatic interaction between the ion and hydrogen molecules. Theoretical studies on hydrogen adsorption in small organic molecular systems, such as cyclobutadiene (C4H4), the cyclopentadienyl radical (C5H5), benzene (C6H6), and cyclooctatetraene (C8H8) and their metal-doped modifications, are carried out. Our results reveal that the simple van der Waals surfaces of pure organic molecules are not good enough for hydrogen adsorption due to the weak interaction between hydrogen molecules and the organic molecular surface. However, doping of alkali-metal atoms in the above organic molecular systems increases their hydrogen adsorption ability significantly, mainly due to electron transfer from the metal atom to the carbon surface. This charged surface created around the metal atom is found to enhance the hydrogen adsorption capacity of the complex considerably, both in terms of interaction energy and the number of adsorbed hydrogen molecules, with a hydrogen adsorption capacity ranging from 10 to 12 wt,%. The role of aromaticity in such molecular systems is important in stabilizing these ionized organo-alkali-metal complexes. [source] A CuIINiII Complex with Ethylenediamine: Crystal Structure and Ferromagnetic Behaviour of an Aqua-Bridged Heterometallic Chain Containing Ambidentate Ni(OAc)42, BlocksEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 22 2010Oksana V. Nesterova Abstract A one-pot reaction of copper powder and nickel and ammonium acetates in a CH3OH solution of ethylenediamine (en) yields a unique 1D aqua-bridged polymer [Cu(en)2(,2 -H2O)2Ni(OAc)4]n·4nH2O (1) with an ambidentate Ni(OAc)42, fragment that has not been previously characterized. The basic structural motif of 1 contains a previously unreported heterometallic M(,2 -H2O)M, aqua-bridge chain with alternating metal atoms. A complex system of N/O,H···O hydrogen bonds strengthens the polymeric chains and links them into a supramolecular three-dimensional network. Variable-temperature magnetic susceptibility measurements of 1 revealed a weak ferromagnetic coupling (J = 1.1 cm,1) between the paramagnetic copper(II) and nickel(II) ions, which is transmitted through the oxygen bridges. [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] Synthesis and Characterization of Novel Titanium, Germanium, and Tin Silazane Complexes Bearing a Cyclohexasilazanetriido LigandEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 8 2007Christian Lehnert Abstract Novel heterometallic silazane complexes were synthesized by the reaction of 1-lithio-2,2,4,4,6,6-hexamethylcyclotrisilazane Li(HMCTS)H2 with the tetrachloride salts of titanium and germanium as well as by the reaction of 1,1,3,3,5,5-hexamethylcyclotrisilazane H3(HMCTS) with tin tetrachloride and excess triethylamine. The products [H3(DMCHS)TiCl] (1), [H3(DMCHS)GeCl] (2), and [H3(DMCHS)SnCl] (3) {H3(DMCHS) = 2,2,4,4,6,6,8,8,10,10,12,12-dodecamethylcyclohexasilazane-1,5,9-triido} were characterized by 1H-, 13C-, 14N-, and 29Si NMR spectroscopy, elemental analyses and single-crystal X-ray structure analyses. The complexes have a surprising and interesting structure, that of a new dodecamethylcyclohexasilazane system with the Ti, Ge, or Sn atom in the center. These metal atoms are coordinated by one chlorine atom and three nitrogen atoms. The metal centers are part of three six-membered hetero-silazane rings. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007) [source] Syntheses and Fluxional Processes of Diphenyl(2-thienyl)phosphane Derivatives of Triosmium ClustersEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 10 2006Nitsa K. Kiriakidou Kazemifar Abstract Thermal treatment of [Os3(CO)12] with diphenyl(2-thienyl)phosphane, Ph2P(C4H3S), results in the formation of [Os3(CO)12,x{Ph2P(C4H3S)}x] (x = 1,3, 1,3), but no C,H bond activation was observed. Reaction of [H2Os3(CO)10] with diphenyl(2-thienyl)phosphane at ambient temperature affords [HOs3(,-H)(CO)10{Ph2P(C4H3S)}] (4), but when the samereaction is repeated at elevated temperatures, the cyclometallated species [(,-H)Os3(CO)9{,3 -Ph2P(C4H2S)}] (5) and[(,-H)Os3(CO)8{,3 -Ph2P(C4H2S)}{Ph2P(C4H3S)}] (6) are formed. In addition, two more products, tentatively assigned as [(,-H)Os3(CO)6{,3 -Ph2P(C4H2S)}{,-Ph2P(C4H3S)}{Ph2P(C4H3S)}] (7) and [(,-H)Os3(CO)7{,-Ph2P(C4H2S)}{,-Ph2P(C4H3S)}{Ph2P(C4H3S)}] (8) are obtained. The dynamic behaviours of 2, 5 and 6 have been studied by variable-temperature (VT) 1H and 31P{1H} NMR spectroscopy. The VT 31P{1H} NMR spectra of [Os3(CO)10{Ph2P(C4H3S)}2] (2) demonstrate that a mixture of two isomers, which are in rapid exchange at room temperature, is present and that the less common cis - trans isomer, whose structure has been determined by X-ray crystallography, is favoured for this cluster. The VT 1H NMR spectra of 5 indicate the presence of two isomers which are proposed to arise from an oscillation of the ,,,2 -vinyl group of the thienyl moiety between two metal atoms. A similar fluxional process is proposed to occur in 6 and the assignment of the room-temperature structure(s) of this cluster was confirmed by 1H- 187Os 2D HMQC spectroscopy. In addition to 2, the solid-state structures of 3, 5 and 6 have been determined by X-ray crystallography. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006) [source] Dinuclear Complexes of MII Thiocyanate (M = Ni and Cu) Containing a Tridentate Schiff-Base Ligand: Synthesis, Structural Diversity and Magnetic PropertiesEUROPEAN JOURNAL OF INORGANIC CHEMISTRY, Issue 12 2005Suparna Banerjee Abstract A dinuclear NiII complex, [Ni2(L)2(H2O)(NCS)2]·3H2O (1) in which the metal atoms are bridged by one water molecule and two ,2 -phenolate ions, and a thiocyanato-bridged dimeric CuII complex, [Cu(L)NCS]2 (2) [L = tridentate Schiff-base ligand, N -(3-aminopropyl)salicylaldimine, derived from 1:1 condensation of salicylaldehyde and 1,3-diaminopropane], have been synthesized and characterized by IR and UV/Vis spectroscopy, cyclic voltammetry and single-crystal X-ray diffraction studies. The structure of 1 consists of dinuclear units with crystallographic C2 symmetry in which each NiII atom is in a distorted octahedral environment. The Ni,O distance and the Ni,O,Ni angle, through the bridged water molecule, are 2.240(11) Å and 82.5(5)°, respectively. The structure of 2 consists of dinuclear units bridged asymmetrically by di-,1,3 -NCS ions; each CuII ion is in a square-pyramidal environment with , = 0.25. Variable-temperature magnetic susceptibility studies indicate the presence of dominant ferromagnetic exchange coupling in complex 1 with J = 3.1 cm,1, whereas complex 2 exhibits weak antiferromagnetic coupling between the CuII centers with J = ,1.7 cm,1. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005) [source] | |||||||||||||||||||||||||||||||