Adjacent Metal Centers Research Articles

Lanthanide(III)chloride-tetrahydrofuran solvates: structural patterns within the series LnCl 3(THF) n, where n = 2,3,3.5 and 4: crystal and molecular structures of [PrCl( μ-Cl) 2(THF) 2] n, [Nd( μ-Cl) 3(H 2O)(THF)] n and GdCl 3(THF) 4

Praseodymium(III), neodymium(III) and gadolinium(III) chloride adducts with tetrahydrofuran (THF) have been prepared and structurally characterized by X-ray crystallography. Removal of water from the corresponding hexahydrate LnCl 3(H 2O) 6 using thionyl chloride in the presence of excess THF provides light-green cubic crystals of [PrCl 3(THF) 2] n ( 1), blue block crystals of [NdCl 3(H 2O)(THF)] n ( 2) and colourless needle crystals of GdCl 3(THF) 4 ( 3). In 1 each praseodymium atom is seven-coordinate and is linked to (two) adjacent metal centres by double (μ-Cl) 2 halogen bridging units, resulting in a polymeric chain structure. The metal geometry approximates to distorted pentagonal bipyramidal with PrCl bridge 2.852(6)–2.891(5), PrCl terminal 2.668(6), PrO THF 2.51(1) (axial), 2.53(2) Å (equatorial). In 2 the structure is a two-dimensional cross-linked polymer in which each neodymium atom is connected to (three) others via double (μ-Cl) 2 halogen bridge bonds. he coordination sphere of each metal centre comprises six chlorine atoms [NdCl bridge 2.816(3)–2.938(3) Å] and two oxygen atoms belonging to a THF molecule [NdO, 2.548(6) Å] and a water molecule [NdO, 2.490(7) Å], respectively. Hydrogen bonding interactions involving halogen atoms and coordinated water molecules from adjacent metal units (intermolecular) are observed, OH3·Cl 3.147–3.350 Å. In 3 the molecular structure is based on a seven-coordinate pentagonal bipyramidal metal geometry in which two chlorides occupy the axial positions with the other chloride and the four solvate (THF) molecules making up the equatorial plane. GdCl 2.60(2)–2.66(2), GdO 2.40(2)–2.52(3) Å. In addition, general comments concerning structural relationships within the series LnCl 3(THF) n , where n = 2, 3, 3.5 and 4, are discussed.

Molecular Magnets Constructed from Cyanometalate Building Blocks

Abstract The properties of magnetic solids constructed from cyanometalate building blocks are reviewed. Most of these solids adopt face-centered cubic lattices in which adjacent metal centers are linked by CN bridges; they are analogues of the long-known inorganic coordination polymer Prussian blue. Ferromagnets, ferrimagnets, and metamagnets can be obtained depending on the building blocks used. The effects of linkage disorder, site vacancies, and the inclusion of metal ions with orbitally degenerate ground states on the magnetic ordering temperature and hysteretic behavior are discussed. Substitution of lowvalent early transition metals such as vanadium(II) into the lattice leads to remarkably high magnetic ordering temperatures, in some cases above 200 K. The large exchange couplings in these vanadium-based molecular magnets are attributed to strong π-backbonding interactions with the cyanide π* orbitals.

Bismuth(III) chloride complexation with diphosphine and diarsine oxide ligands: formation and crystal structures of [BiCl3{Ph2P(O)CH2P(O)Ph2}]2 and [BiCl3{As(O)MePh2}{Ph2As(O)Ch2CH2As(O)Ph2}] n

The reactions of bismuth(III) chloride and Ph2PCH2PPh2(dppm) and Ph2AsCH2CH2AsPh2-(dpae) have been studied. The yellow products isolated initially were characterised by spectroscopic (1H and 31P NMR, IR) and microanalytical data as the 1:1 addition compounds BiCl3·dppm and BiCl3·dpae respectively. Recrystallisation of these products from boiling acetonitrile/charcoal effected oxidation of the ligands and resulted in the formation of two new molecular adducts whose structures have been determined by X-ray crystallography. Crystals of [BiCl3{Ph2P(O)CH2P(O)Ph2}]21 are triclinic, space group P with Z= 2. There are two independent centrosymmetric molecules in the unit cell with similar edge–edge shared bioctahedral structures. Each bismuth centre is six-co-ordinate with approximal octahedral geometry being bonded to two terminal chlorine atoms, two bridging chlorine atoms and two oxygen (ligand) atoms. In situ ligand oxidation dppm → Ph2P(O)CH2P(O)Ph2 occurs and the resulting bidentate (OO′) chelation gives rise to puckered six-membered [graphic omitted] ring formation. Crystals of [BiCl3{As(O)MePh2}{Ph2As(O)CH2CH2As(O)Ph2}]n2 are monoclinic, space group P21/a with Z= 4. The structure consists of one-dimensional polymeric chains. Here the in situ ligand oxidation is more complex and results in the formation of two arsine oxide ligands, viz. dpae → Ph2As(O)CH2CH2As(O)Ph2+ As(O)MePh2 both of which are involved in co-ordination to BiIII. Each bismuth atom is bonded in an approximately mer-octahedral arrangement to three terminal chlorine atoms and three oxygen (ligand) atoms. Of the latter, one is provided by a monodentate As(O)MePh2 molecule and the other two by separate Ph2As(O)CH2CH2As(O)Ph2 molecules which, by virtue of their bidentate bridging mode, are linked to adjacent metal centres.

Synthesis, structure and properties of lanthanide(III) picrate complexes with trans-1,4-dithiane-1,4-dioxide (TDTD)

A series of isomorphous lanthanide complexes, having general formula M(pic) 3(TDTD) 1.5 (M  CeEr, Yb and Y), was synthesized and characterized by microanalyses, infrared spectra and visible emission spectrum for the Eu complex. Crystal structures were determined for the Ce and Eu derivatives; for the other complexes only cell parameters were obtained and reported. The compounds crystallize with a monoclinic cell, space group P2 1/ c with Z=4. The metal ions are nine-coordinated with a tricapped trigonal prismatic coordination polyhedron, achieved via the bonding of three bidentate picrate units and three oxygens of the TDTD ligands. The TDTD moieties are shared by adjacent metal centers, forming three-dimensional polymers.

Alkyne-to-vinylidene tautomerism mediated by two adjacent metal centers. Structures of iridium complexes [Ir2I2(CO)2(.mu.-CCHR)(Ph2PCH2PPh2)2] (R = H, Ph)

Alkyne-to-vinylidene tautomerism mediated by two adjacent metal centers. Structures of iridium complexes [Ir2I2(CO)2(.mu.-CCHR)(Ph2PCH2PPh2)2] (R = H, Ph)

Hydrogen migration in Fe 3(CO) 9H 4

The Fenske-Hall method of semi-empirical molecular orbital calculations was used to analyze the capped transition metal cluster Fe 3(CO) 9CH 4. This type of cluster is of interest because it can be used as a model for the activation of hydrocarbons on metal surface catalysts. The process of hydrogen migration between the metal base and the cap was studied, with particular emphasis on the agostic MCH interaction, which occurs in some isomers of the compound. For the three isomers produced in the migration process, the primary distinction that leads to the variation in stabilities among these structures is the extent of metal-metal overlap between 3d orbitals of the iron atoms. It was found that, if there are hydrogen atoms bridging the metal centers at the base of the complex, the isomer is stabilized by the reduction of overlap between atomic orbitals on adjacent metal centers, thereby reducing the impact of filled metal-metal antibonding orbitals. Agostic interactions between cap hydrogens and the base also tend to stabilize the compound. This was found to be largely due to a reorganization of the bond between the carbon in the capping group and the agostic metals. In addition, Mulliken overlap populations indicate that the hydrogens involved in MCH agostic interactions also reduce metal-metal overlap.

Metal Binding by Amino Acids: Preparation and Crystal Structures of Lithium, Sodium, and Potassium Hydrogen Bis‐L‐pyroglutamate

AbstractLithium, sodium and potassium hydrogen bis‐L‐pyroglutamate [Li(L‐pGlu)(L‐pGluH)], [Na(L‐pGlu)(L‐pGluH)] and [K(L‐pGlu)(L‐pGluH)], respectively, have been prepared by reaction of aqueous solutions of the metal hydroxides with L‐pyroglutamic acid in the molar ratio 1:2, or in methanol. Crystalline samples of the salts could be obtained by slow evaporation of solutions of the salts in methanol. In the solid state, Li(L‐pGlu)(L‐pGluH) adopts a chain structure with the lithium atoms arranged in double strands. Adjacent metal centers are bridged by the carboxylate groups of the L‐pGlu− ligands. The L‐pGluH ligands are attached to the metal centers through the amide oxygen atoms. Na(L‐pGlu)(L‐pGluH) forms a three‐dimensional coordination polymer with two half‐occupied sodium positions, one L‐pGlu− and one L‐pGluH ligand in the asymmetric unit. The carboxyl and carboxylate groups of the L‐pGluH and the L‐pGlu− ligands are bridging the sodium centers, giving rise to eight‐membered rings, which consist of two sodium atoms, a carboxyl and a carboxylate group. The hydrogen atoms of the carboxyl group of the L‐pGluH ligands are involved in strong hydrogen bonds between a carboxyl and an adjacent carboxylate oxygen atom. K(L‐pGlu)(L‐pGluH) adopts a layer structure with strands of potassium atoms. The metal centers are connected through bridging carboxyl and carboxylate groups of the L‐pGluH and L‐pGlu− ligands, respectively. The structure features eight‐membered ring units comparable to those observed for Na(L‐pGlu)(L‐pGluH), again with the hydrogen atom of the carboxyl group engaged in a strong transannular hydrogen bond. The amide oxygen atoms of the L‐pGlu− and the L‐pGluH ligands are coordinated to the metal centers of adjacent coordination chains. The results of 1H‐ and 13CNMR investigations of aqueous solutions of the compounds indicate extensive electrolytic dissociation in dilute solutions.

Oxidation state and electron transfer properties of heteronuclear termetallocenes [{(C 5H 5)M} 2{η 5 : η 5′ - C 10H 8} 2M′] n+ ( n  1, M  Fe, M′  Co; n  2, M  Co, M′  Os, Ru): An electrochemical study

Electrochemical reduction of termetallocenes containing different kinds of metal atoms, [{(C 5H 5)M} 2{η 5:η 5′- C 10H 8} 2M′] n+ ( n  1, M  Fe, M′  Co; n  2, M  Co, M′  Os, Ru), in a 0.1 M solution of Bu 4N +PF 6 − in CH 3CN leads to anions and dianions, while electrochemical oxidation leads to trications and tetracations. Δ E° separations indicate interactions only between adjacent metal centres. The identical metallocene moieties in the molecule behave more like independent, non-interacting units.

Intramolecular energy transfer in Ru(II)-Ru(II) and Ru(II)-Cr(III) polynuclear complexes

Ligand-bridged polynuclear complexes made up of metal-containing subunits with long-lived excited states are suited for the study of intramolecular electronic energy transfer. Using Ru(II) and Cr(III) complex units as building blocks and cyanide as bridging ligand, a number of Ru(II)-Ru(II), Ru(II)-Cr(III) polynuclear complexes have been synthesized. Efficient intramolecular energy transfer between adjacent metal centers occurs in these systems, as shown by quenching and photosensitization of the appropriate emissions. When the behavior of the polynuclear complex is compared with that of the component subunits, a number of interesting effect, luminescence shift, enhanced population of the emitting state, photoprotection, excited-state intervalance transfer, chemiluminescent charge recombination. Possible developments of the results towards the design of photonic molecular devices are discussed.

Stabilization of mixed valence states in partly oxidized one-dimensional transition metal systems

The spatial hole-state properties of partly oxidized one-dimensional (1D) organometallic solids with weak metal-metal interactions (either due to large separations between the corresponding building blocks or due to bridging organic ligand functions) have been studied in the crystal orbital (CO) formalism based on the tight-binding technique. The numerical analysis is restricted to insulating band states. The employed computational model is a semiempirical self-consistent-field (SCF) Hartree-Fock (HF) CO variant derived within the INDO (intermediate neglect of differential overlap) approximation. We have adopted a simple averaging procedure for the “open shell” systems which is based on a density operator that has its origin in the grand canonical (GC) ensemble in order to avoid the numerical difficulties of restricted or unrestricted tight-binding calculations on the oxidized 1D chains. The present method, however, is not related to temperature-dependent equilibria in statistical mechanics but is only a formal, highly efficient approach for the formation of average-states in the mean-field approximation. As one-dimensional models we have adopted the infinite tetracyanatonickelate(II), Ni(CN) 4 2− 1, and the cyclopentadienylmanganese(I), MnCp2, systems. The electron removal processes in both 1D materials are more (1) or less (2) metal-centered ( $$3d_{z^2 } $$ states). The mean-field ground states of both oxidized modifications correspond to broken symmetry CDW (charge density wave) solutions that lead to mixed valence states with inequivalent numbers of electrons at adjacent transition metal centers. This symmetry breaking guarantees that important left-right correlations between the 3d atoms are taken into account even in the SCF HF approximation. The valence trapping in1 is strong, i.e. the mutual charge separation between the Ni centers amounts to 0.87e. The bridging organic π ligands in2 prevent such pronounced differences of the net charges at the Mn centers and cause a reduction of the charge separation to 0.09e–0.14e.

Selective formation of trans olefins by a catalytic hydrogenation of alkynes mediated at two adjacent metal centers

Selective formation of trans olefins by a catalytic hydrogenation of alkynes mediated at two adjacent metal centers

Interactions in metal clusters. Acceleration of substitution by prior substitution at adjacent metal centers

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTInteractions in metal clusters. Acceleration of substitution by prior substitution at adjacent metal centersKarin J. Karel and Jack R. NortonCite this: J. Am. Chem. Soc. 1974, 96, 21, 6812–6813Publication Date (Print):October 1, 1974Publication History Published online1 May 2002Published inissue 1 October 1974https://doi.org/10.1021/ja00828a072RIGHTS & PERMISSIONSArticle Views94Altmetric-Citations70LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (225 KB) Get e-Alerts Get e-Alerts