Direct Metal-metal Interaction Research Articles

N-Alkyl substituted triazenide-bridged homoleptic iron(II) dimers with an exceptionally short Fe-Fe bond.

Dinuclear transition metal complexes with direct metal-metal interactions have the potential to generate unique reactivities and properties. Using asymmetric triazine ligands HN3tBuR (R = Et, iPr, nBu) featuring different alkyl substituents at 1,3-N centers, we report here the first rational synthesis of 'tetragonal lantern' type Fe(II) triazenides [Fe2(N3tBuR)4] [R = Et (1), iPr (2), nBu (3)] having an exceptionally short Fe-Fe distance (2.167-2.174 Å). Unlike the previously reported lantern structures with related amidinate or guanidinate ligands, highly air-sensitive 1-3 show a lower spin ground state, as indicated by Mössbauer, 1H NMR and DFT studies.

A post-modification strategy to precisely construct dual-atom sites for oxygen reduction electrocatalysis

Dual-atom catalysts (DACs) afford promising potential for oxygen reduction electrocatalysis due to their high atomic efficiency and high intrinsic activity. However, precise construction of dual-atom sites remains a challenge. In this work, a post-modification strategy is proposed to precisely fabricate DACs for oxygen reduction electrocatalysis. Concretely, a secondary metal precursor is introduced to the primary single-atom sites to introduce direct metal–metal interaction, which ensures the formation of desired atom pair structure during the subsequent pyrolysis process and allows for successful construction of DACs. The as-prepared FeCo-NC DAC exhibits superior oxygen reduction electrocatalytic activity with a half-wave potential of 0.91 V vs. reversible hydrogen electrode. Zn–air batteries equipped with the FeCo-NC DAC demonstrate higher peak power density than those with the Pt/C benchmark. More importantly, this post-modification strategy is demonstrated universal to achieve a variety of dual-atom sites. This work presents an effective synthesis methodology for precise construction of catalytic materials and propels their applications in energy-related devices.

Strong Electronic and Magnetic Coupling in M4 (M = Ni, Cu) Clusters via Direct Orbital Interactions between Low-Coordinate Metal Centers.

We present an extensive study of tetranuclear transition-metal cluster compounds M4(NPtBu3)4 and [M4(NPtBu3)4][B(C6F5)4] (M = Ni, Cu; tBu = tert-butyl), which feature low-coordinate metal centers and direct metal-metal orbital overlap. X-ray diffraction, electrochemical, magnetic, spectroscopic, and computational analysis elucidate the nature of the bonding interactions in these clusters and the impact of these interactions on the electronic and magnetic properties. Direct orbital overlap results in strongly coupled, large-spin ground states in the [Ni4(NPtBu3)4]+/0 clusters and fully delocalized, spin-correlated electrons. Correlated electronic structure calculations confirm the presence of ferromagnetic ground states that arise from direct exchange between magnetic orbitals, and, in the case of the neutral cluster, itinerant electron magnetism similar to that in metallic ferromagnets. The cationic nickel cluster also possesses large magnetic anisotropy exemplified by a large, positive axial zero-field splitting parameter of D = +7.95 or +9.2 cm-1, as determined by magnetometry or electron paramagnetic resonance spectroscopy, respectively. The [Ni4(NPtBu3)4]+ cluster is also the first molecule with easy-plane magnetic anisotropy to exhibit zero-field slow magnetic relaxation, and under a small applied field, it exhibits relaxation exclusively through an Orbach mechanism with a spin relaxation barrier of 16 cm-1. The S = 1/2 complex [Cu4(NPtBu3)4]+ exhibits slow magnetic relaxation via a Raman process on the millisecond time scale, supporting the presence of slow relaxation via an Orbach process in the nickel analogue. Overall, this work highlights the unique electronic and magnetic properties that can be realized in metal clusters featuring direct metal-metal orbital interactions between low-coordinate metal centers.

Trends in the Bond Multiplicity of Cr2, Cr3, and Cr2M (M = Zn, Ni, Fe, Mn) Complexes Extracted from Multiconfigurational Wave Functions.

Extended metal atom chains constitute an interesting class of molecules from both theoretical and applied points of view. In the chromium-based series Cr2M(dpa)4X2 (with M = Zn, Ni, Fe, Mn, Cr), the direct metal-metal interactions span a wide range of possibilities and so do their associated properties. The multiplicity and symmetry components of the metal-metal bond are herein analyzed via the effective bond order (EBO) concept using complete active space self-consistent field wave functions and compared with similar bimetallic Cr2L4X2 systems. The bond multiplicity follows a trend dominated by the Cr-Cr distance which, in turn, depends on the nature of the axial ligand (X). Cr2M compounds present asymmetric structures with virtually no interaction between the Cr2 unit and M, whereas fully symmetric structures with delocalized bonding among the three metals are also possible in Cr3 complexes. In such cases, a strategy that involves localization of the molecular orbitals into each Cr-Cr pair is applied to quantify the contribution of each pair to the overall metal-metal bond multiplicity.

Meeting the Challenge of Magnetic Coupling in a Triply-Bridged Chromium Dimer: Complementary Broken-Symmetry Density Functional Theory and Multireference Density Matrix Renormalization Group Perspectives.

Face-sharing octahedral dinuclear Cr(III) compounds with d3–d3 electronic configurations represent nontrivial examples of electronic complexity, posing particular challenges for theoretical and computational studies. A tris-hydroxy-bridged Cr(III)–Cr(III) system has proven to be a richly rewarding target for studies of magnetism and electron paramagnetic resonance spectroscopy. It was also reported to be a peculiarly difficult system to treat with density functional theory (DFT). In this work the magnetic coupling problem for this dimer is approached with broken-symmetry (BS)-DFT and multireference calculations that utilize the density matrix renormalization group (DMRG) to handle full-valence active spaces. BS-DFT is shown to recover the correct ordering and energy spacing of Heisenberg spin states if used in conjunction with appropriate spin projection procedures, albeit with pronounced functional sensitivity. The contrasting conclusions of previous studies are traced to incorrect inclusion of electronically excited configurations. Analysis of the direct and differential overlap of corresponding orbital pairs from the BS-DFT solution indicates that metal–metal through-space interaction is the dominant contributor to antiferromagnetic coupling. At the DFT level a procedure that utilizes pseudopotential substitution is demonstrated that allows evaluation of the direct exchange vs superexchange contributions. A complementary description is obtained with DMRG-SCF calculations that enable state-averaged CASSCF calculations with both metal and bridge orbitals in the active space. A localized orbital subspace analysis supports the DFT conclusions that in contrast to doubly bridged isoelectronic analogues, antiferromagnetic coupling in the chromium dimer arises primarily from direct metal–metal interaction but is significantly enhanced by ligand-mediated superexchange.

Persistent three- and four-atom orbital molecules in the spinel AlV2O4

Electronic instabilities in transition metal compounds can lead to ground states containing orbital molecules when direct metal-metal orbital interactions occur. The largest reported orbital molecules are V717+ heptamers that emerge below a 700 K charge ordering transition in the spinel AlV2O4. However, x-ray total scattering analysis shows that the apparent heptamers are actually pairs of spin-singlet V39+ trimers and V48+ tetramers, and that these orbital molecules persist to at least 1100 K although they become `hidden' by disorder in the average cubic structure above the charge ordering transition.

μ2-m-Xylylenebis(salicylaldiminato)-bis(η4-1,5-cyclooctadiene)dirhodium(I) dichloromethane solvate

In the title solvate, [Rh2(C22H18N2O2)(C8H12)2]·CH2Cl2, each organometallic mol­ecule is composed of two RhI cations, the tetra­dentate dianion α,α′-bis­(salicylaldiminato)-m-xylene and two 1,5-cyclo­octa­diene (COD) ligands. Each RhI atom is coordinated by one O atom [Rh—O = 2.044 (2) and 2.026 (2) Å], one N atom [Rh—N = 2.083 (2) and 2.090 (2) Å], and one COD ligand via two η2-bonds, each directed toward the mid-point of a C=C bond (Cg): Rh—Cg = 2.007 (2), 2.013 (2), 2.000 (2) and 2.021 (2) Å. Each RhI atom has a quasi-square-planar coordination geometry, with average r.m.s. deviations of 0.159 (1) and 0.204 (1) Å from the mean planes defined by Rh and the termini of its four coordinating bonds. The two COD ligands have quasi-C 2 symmetry, twisted from ideal C 2v symmetry by 30.0 (3) and −33.1 (3)°, and are quasi-enanti­omers of one another. The intra­molecular Rh⋯Rh distance of 5.9432 (3) Å suggests that there is no direct metal–metal inter­action.

Catena-Poly[[aqua(3-methylbenzoato-κ2O,O′)lead(II)]-μ-3-methylbenzoato-κ4O:O,O′:O′

The reaction of lead(II) acetate and 3-methyl­benzoic acid (MBA) in aqueous solution yielded the title polymer, [Pb(C8H7O2)2(H2O)]n. The asymmetric unit contains two PbII atoms, four MBA ligands and two water mol­ecules. Each PbII cation is hepta­coordinated and chelated by four carboxyl­ate O atoms from two MBA ligands. The Pb atoms are bridged through the carboxyl­ate O atoms from another two MBA ligands, leading to a central Pb2O2 core. The Pb—O bond lengths are in the range 2.325 (3)–2.757 (4) Å. The intra- and inter­dimer Pb⋯Pb distances are 4.2942 (3) and 4.2283 (3) Å, respectively, indicating little direct metal–metal inter­action. The coordinating water mol­ecules and carboxyl­ate O atoms are involved in extensive O—H⋯O hydrogen-bonding inter­actions. The complex has an extended ladder-like chain structure and the chains are assembled by hydrogen bonds and π–π inter­actions [centroid–centroid distance = 3.6246 (3) Å] into a three-dimensional supra­molecular structure.

Direct Metal−Metal Interaction Contributions to Quadratic Hyperpolarizability: A Study on Dirhenium Complexes

We present a comparative study of the metal-metal interaction effect on the static quadratic hyperpolarizabilities of two typical dinuclear rhenium clusters. The electronic structures, excitation spectra, dipolar moments, static polarizabilities, and quadratic hyperpolarizabilities of the two complexes with direct metal-metal interactions have been computed and analyzed with the use of high-level DFT/TDDFT methods. The geometries and the first intense excitations agree with the relevant reported measurements. The orbital decomposition scheme ( J. Phys. Chem. A 2006, 110, 1014-1021) has been applied to analyze the relationship between the electronic structures and nonlinear optical (NLO) properties of these two complexes. We propose an unprecedented NLO response mechanism featuring the contribution of the direct metal-metal interaction transition process in these dinuclear rhenium complexes. This contribution positively enhances the quadratic hyperpolarizability and relates to the intensity of the metal-metal interactions of the complexes. The results are helpful to the development of NLO chromophores in polynuclear metal clusters through the molecular design technique.

Magnetotransport properties of Ba$_{2}$MnRuO$_{6}$ and LaBaMnRuO$_6$

The structural, magnetic, and transport properties of double perovskites Ba <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> MnRuO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">6</sub> (BMRO) and LaBaMnRuO <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">6 </sub> (LBMRO) have been investigated. Rietveld analysis of powder x-ray diffraction data show that BMRO adopts 9R rhombohedral structure with space group R3macrm while the partial doping of Ba by La leads the structure to orthorhombic with Pbnm space group. Structural as well as magnetic studies revealed that Ru ions are tetravalent in both compounds. The superexchange interactions between Mn <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3+</sup> (t <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2g</sub> <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> e <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">g</sub> <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1</sup> )-O-Ru <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4+</sup> (t <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2g</sub> <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sup> ) lead to a ferromagnetic ordering in LBMRO. The direct metal-metal interactions are to be invoked to understand the weak magnetic nature of BMRO. Transport studies reveal that both samples have insulating behavior with variable range hopping type of conduction. Magnetoresistance (MR) measurements show a positive magnetoresistance (~ 5 % for 1 T) in BMRO, which is not significantly varying within the temperature range measured while LBMRO exhibit a negative magneto resistance (~ 25% for 1 T at 80 K), which increases while decreasing the temperature

Meet The Guest Editor

Dr. Jozsef L. Margitfalvi received his M.S. degree in Chemical Engineering in Moscow at Mendlejeff Chemical Technological University in 1965 with a strong emphasis in petroleum chemistry and refinery technology. After 4 years of industrial practice in Hungary, he continued his study as a postgraduate student in Moscow. He investigated homogeneous catalytic epoxidation of cyclohexene and received his Ph.D. degree in 1972. Next, Dr. Margitfalvi joined the Institute of Isotopes in Budapest as a research fellow, where he studied the thermal decomposition patterns of different organometallic compounds. Based on these investigations, different supported metal catalyst were prepared. During 1978-1979, he worked at the Worchester Polytechnic Institute in Massachusetts under professor Alvin Weiss. In 1979, Dr. Margitfalvi joined the Central Research Institute for Chemistry and became a senior research associate and group leader. He conducted research in the area of preparation and modification of supported metal catalysts used in hydrocarbon reactions and developed the method of “Controlled Surface Reactions” for the preparation of supported bimetallic catalysts with direct metal-metal interaction. Since 1985, his main interest has been “catalysis in organic reactions” with the focus on catalyst design and modification for selective hydrogenations, reductive amination and carbonyl activation. In 1985, Dr. Margitfalvi received the title of invited “Associate Professor” at the Department of Organic Chemistry at University of Szeged. In the period of 1989-1991, he joined the Swiss Institute ETH in Zurich as a guest scientist. Under Prof. Alfons Baiker he investigated asymmetric hydrogenation of ethyl pyruvate. After returning to Hungary, Dr. Margitfalvi reorganized his research group under the name “Surface Reactions and Catalysis.” In 1995, this group was reorganized further into the “Department of Organic Catalysis,” and he was appointed as the head of this new department. In 1996, Dr. Margitfalvi received the highest academic degree in Hungary, the title “Doctor of the Hungarian Academy of Sciences”. In 1999, he edited a special issue for Applied Catalysis on the topic, “Catalysis by anchored and encapsulated species.” After reorganization of the Central Research Institute for Chemistry into the Chemical Research Center in 1999, he expressed his interest to start research in the area of combinatorial catalysis. By 2002, his group had developed a new catalyst library optimization method, the Holographic Research Strategy. By incorporating an information mining tool, this method became a fast and reliable informatics platform for catalyst library optimization and visualization of multi-dimensional experimental space. In addition to the investigation of chemo- and asymmetric hydrogenation reaction, Dr. Margitfalvi launched a new project aimed at the examination of different oxidation and oxygen transfer reactions, such as CO oxidation, PROX reaction, and oxidative sulfur removal from diesel fuel. His other new research project is the investigation of catalytic reactions for hydrogen production, such as reforming of various alcohols. He has established industrial contacts with different European and US companies in the area of fine chemistry and combinatorial catalysis and is representing Hungary in the European Federation of Catalysis Societies (EFCATS). His hobbies are electronic music (both listening and creating), traveling, sports (soccer, tennis, table tennis, etc.) and reading. SELECTED PUBLICATIONS [1] Vegvari, L.; Tompos, A.; G bolos, S.; Margitfalvi, J.L. Holographic research strategy for catalyst library design. Description of a new powerful optimization method. Catal. Today, 2003, 81, 517-527. [2] Tompos, A.; Margitfalvi, J.L.; Tfirst, E.; Vegvari, L. Information mining using artificial neural networks and “holographic research strategy”. Appl. Catal. A-Gen., 2003, 254, 161-168. [3] Tompos, A.; Margitfalvi, J.L.; Tfirst, E.; Vegvari, L.; Jaloull, M.A.; Khalfalla, H.A.; Elgarni, M.M. Development of catalyst libraries for total oxidation of methane. A case study for combined application of holographic research strategy and artificial neural networks in catalyst library design. Appl. Catal. AGen., 2005, 285, 65-75........

Covering sleeves can shield the high-voltage coils from lead chatter in an integrated bipolar ICD lead

Integrated bipolar implantable cardioverter-defibrillator (ICD) leads use the distal high-voltage coil as both the ventricular sensing anode and the distal shocking electrode. Mechanical interactions between the distal ICD coil and other intracardiac leads have been reported to result in electrical oversensing and inappropriate ICD therapies. We sought to determine whether covering sleeves over the high-voltage coils of an integrated bipolar ICD lead could prevent sensed artefact from mechanical lead interactions. Endotak Reliance 0157 and Endotak Reliance-G 0185 leads, the latter with expanded polytetrafluoroethylene (ePTFE) sleeves covering the high-voltage coils, were connected to ICD generators and the leads were submerged in saline. Device programmers were used to communicate with the ICD generators, providing real-time electrogram recording throughout testing. A series of mechanical interactions were performed with the ICD leads, including sliding and striking each distal coil against metal and non-metal components of other ICD and pacemaker leads. All direct metal-metal interactions resulted in sensed electrical artefact, including interactions between the bare ICD coil and another bare ICD coil or metal pacemaker ring. Identical mechanical interactions where metal-metal contact was prevented due to an interposed ePTFE covering sleeve were electrically silent with no sensed artefact. A covering sleeve over the distal high-voltage coil of an integrated bipolar ICD lead can mechanically shield the lead from metal-metal interactions, which might otherwise result in sensed artefact and inappropriate ICD therapies or withholding of pacing output. This finding has implications for lead selection when a new ICD lead is to be implanted adjacent to abandoned intracardiac leads or lead fragments.

A facile and general approach to the Rh–M (M = Co, Rh) single bond supported by ortho-carborane-1,2-dichalcogenolato ligands

A series of hetero- and homo-dinuclear complexes with direct metal-metal interaction are synthesized through reaction of Cp*Rh[E(2)C(2)(B(10)H(10))] (E = S (1a), Se (1b)) and CpRh[S(2)C(2)(B(10)H(10))] (2a) with low valent half-sandwich CpCo(CO)(2) or CpRh(C(2)H(4))(2) under moderate conditions. The resulting products, namely (Cp*Rh)(CpCo)[E(2)C(2)(B(10)H(10))] (E = S(3a); Se(3b)), (Cp*Rh)(CpRh)[E(2)C(2)(B(10)H(10))] (E = S(4a); Se(4b)) and (CpRh)(CpRh)[S(2)C(2)(B(10)H(10))] (5a), are fully characterized by IR and NMR spectroscopy and elemental analysis. The molecular structures of 3a, 3b, 4a, 4b and 5a are established by X-ray crystallography analyses, and the Rh-Co (2.4778(11) (3a) and 2.5092(16) (3b) A) and Rh-Rh bonds (2.5721(8) (4a), 2.6112(10) (4b), 2.5627(10) (5a) A) fall in the range of single bonds.

Electronic structure of [(CpCr)[(CO)3M]]mu-Cot (M = Cr, Fe): a theoretical study.

The electronic structure of two cyclooctatetraene-bridged dinuclear first-row transition metal complexes of the type [(CpM)[(CO)3M']]mu-Cot (M = Cr; M' = Fe (1), Cr (2)) was investigated by complete active space self-consistent field (CASSCF) calculations. In this context the differences in the binding capabilities of the complex fragments CpM and (CO)3M are discussed on the basis of extended Huckel molecular orbital (MO) calculations. The geometries used for the CASSCF calculations for complex 1 were obtained from the crystal structure. For 2 a model structure was established by geometry optimization using density functional methods. The CASSCF results agree well with the experimental findings and provide insight into the binding situation of the two compounds. Complex 1 can be regarded as being composed of a chromocene-like subunit CpCr(eta5-C5H5) and the fragment (CO)3Fe(eta3-C3H3). A direct metal-metal bond is found, involving one initially singly occupied orbital of each fragment, leading to a doublet ground state for 1 with the remaining unpaired electron localized at the chromium center. For 2 no such direct metal-metal bond can be recognized. A very weak direct metal-metal interaction is induced by electron donation from the Cot2- ligand into a formally unoccupied metal-metal binding orbital combination. In the quartet ground state all three unpaired electrons are localized at the chromium center of the formally doubly positive charged CpCr unit, on which complex fragment [(CO)3Cr(eta5-Cot)]2- acts like a cyclopentadienyl ligand. The coordination sphere of the chromium center of the CpCr unit resembles that of a metallocene metal center and its metal 3d occupation scheme corresponds to that of vanadocene.

Theoretical Overview of Pd(I) and Pt(I) Dimers with Bridging Phosphido Ligand(s).

A review of all of the known structural stereotypes of dimeric Pt(I) or Pd(I) systems with at least one bridging phosphido group is presented. The nature of the direct metal-metal interaction is affected by the number, nature, and disposition of the various coligands. It appears that in some cases a bent M-M bond is by itself a center of nucleophilicity. On the other hand, it is experimentally known that the bridging phosphido ligand is a competing nucleophile, giving rise to an agostic interaction in Pd(2), but not in Pt(2), derivatives. MO theory is used to outline the major electronic features and correlation between different prototypes. Besides a qualitative approach based on the EHMO method, DFT and MP2 methods were used to reproduce the experimental structures and to explore the possibility of unknown tautomers.

Coordination modes of the cyanoacetate ion; silver(I) and bis(η-cyclopentadineyl)tatinium(IV) cyanoacetates. X-ray crystal structures of [Ag(NCCH 2CO 2)] and [TiCp 2(NCCH 2CO 2) 2

Polymeric silver(I) cyanoacetate contains the classical bis(carboxylato- O, O′) bridged metal dimer arrays in which each pair of adjacent metal atoms is doubly bridged by co-planar carboxylate groups in the syn-syn conformation. These dimeric units are extended into a polymeric chain by terminal linkage of all cyano-nitrogen atoms to silver atoms of adjacent dimer units. In this manner, an individual cyanoacetate anion is O, O′, N-bonded to three different silver centres. EHMO calculations suggest weak direct metal-metal interactions can result from the mixing of metal s and p orbitals into the d 10 shells. Reactions of silver(I) or sodium cyanoacetates with [(η-C 5H 5) 2TiCl 2] afford the bis(cyanoacetato) complex [(η-C 5H 5) 2Ti(O 2CCH 2CN) 2] which has a solid state structure involving O-unidentate carboxylate groups, the cyano-nitrogen atoms not being bonded to a metal. This compound can also be prepared from [(η-C 5H 5) 2Ti(CH 3) 2] and cyanoacetic acid.

Protonation of the CoRh bond in CoRh( μ- CO)( CO) 2( μ- dppm) 2

The electronic structure of CoRh(μ-CO)(CO) 2(μ-H 2PCH 2PH 2) 2 and CoRh(μ-H)(μ-CO)(CO) 2(μ-H 2PCH 2PH 2) 2 has been investigated by means of density functional calculations (DFT). The tetrahedral environment around the cobalt atom is the origin of the lack of direct metal-metal interaction in the former complex. In the protonated form a three-center, two-electron interaction emerges, inducing a slight lessening of the CoRh separation. The fluxionality process has also been investigated. The energy barrier for the exchange of the semibridging carbonyl with the terminal CoCO carbonyl has been computed to be 19 kcal mol −1. A second pathway involving the terminal RhCO group appears 18 kcal mol −1 above.

Dinuclear rhodium-rhodium and rhodium-palladium complexes with different bridging ligands. Crystal structure of [Rh 2(μ-SPPh 2)(μ-Cl)(COD) 2

Homo- and hetero-dinuclear complexes of general formulae [Rh 2(μ-SPPh 2)(μ-Cl)(diolefin) 2] (diolefin = 1,5-cyclooctadiene (CO (1), tetrafluorobenzobarrelene (TFB) (2)) and [RhPd( μ-SPPh 2)( μ-Cl)(diolefin) η 3-C 3H 5)] (diolefin = COD (4), 2,5-norbornadiene (NBD) (5)), containing one chloride anion and one thiophosphinito group as bridging ligands, have been synthesised by redistribution reactions starting from the corresponding homo-bridged compounds [Rh 2(μ-SPPh 2) 2(diolefin) 2, [Rh 2(μ-Cl) 2(diolefin) 2] or [Pd 2( μ-Cl) 2( η 3-C 3H 5) 2]. The structural X-ray analysis carried out for one member of this series, [Rh 2(μ-SPPh 2)(μ-Cl)(COD) 2], has shown the bridging P, S-coordination of the thiophosphinito ligand. The intermetallic separation, 3.291(2) Å, excludes any significant direct metal-metal interaction.

Density functional description of the bonding in the μ3-chalcogenido hexanuclear octahedral clusters [Co6(μ3-X)8(PEt3)6] (X = S, Se, Te)

Abstract Density functional theory (DFT) in the local density approximation has been applied to describe the bonding in the μ 3 -chalcogenido hexanuclear cobalt clusters of formula [Co 6 ( μ 3 -X) 8 (PR 3 ) 6 ] (X = S, Se, Te). The geometries of the clusters have been optimised and the bonding interactions in the sulfide derivative have been analysed using a fragment decomposition scheme. Direct metal-metal interactions are negligible. The electrochemical behaviour reported for the sulfide cluster has been rationalised.

The preparation and structural characterization of a double-helical binuclear dicobalt(II) complex of 2,2′: 6′,2″: 6″,2‴: 6‴, 2⁗-quinquepyridine; the x-ray crystal structure of acetato( O,O′)bis (2,2′: 6′,2″: 6″,2‴: 6‴, 2⁗-quinquepyridine)dicobalt(II) hexafluorophosphate tris-acetonitrile solvate

The reaction of cobalt(II) acetate with 2,2′: 6′,2″: 6″,2⋖: 6⋖,2⁗-quinquepyridine ( L) in acetonitrile results in the spontaneous assembly of a binuclear double helical complex. The electrochemical behaviour of this compound is complex. The driving force for the assembly of the complex is probably associated with the close stacking contacts between approximately co-planar pyridine rings; there are no direct metal-metal interactions.