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1.
The coordination chemistry of the doubly base‐stabilised diborane(4), [HB(hpp)]2 (hpp=1,3,4,6,7,8‐hexahydro‐2H‐pyrimido‐[1,2‐a]pyrimidinate), was extended by the synthesis of new late transition‐metal complexes containing CuI and RhI fragments. A detailed experimental study was conducted and quantum‐chemical calculations on the metal–ligand bonding interactions for [HB(hpp)]2 complexes of Group 6, 9, 11 and 12 metals revealed the dominant B? H? M interactions in the case of early transition‐metal fragments, whereas the B? B? M bonding prevails in the case of the late d‐block compounds. These findings support the experimental results as reflected by the IR and NMR spectroscopic parameters of the investigated compounds. DFT calculations on [MeB(hpp)]2 and model reactions between [B2H4 ? 2NMe3] and [Rh(μ‐Cl)(C2H4)2] showed that the bicyclic guanidinate allows in principle for an oxidative addition of the B? B bond. However, the formation of σ‐complexes is thermodynamically favoured. The results point to the selective B? H or B? B bond‐activation of diborane compounds by complexation, depending on the chosen transition‐metal fragment.  相似文献   

2.
Model potential parameters and basis sets, presented previously for the transition metal atoms Sc through Hg, are tested in calculations of the transition metal compounds (CuF, CuCl, Cu2, TiCl4, ZrCl4, CoF63?, CoF62?, AgH, AuH, CrF6, ScO, ZrO, Cr2, Mo2). Calculated values of the bond distances, vibrational frequencies, and some transition energies (for Cu2 and CoF62?) are compared with those given by all-electron calculations with basis sets of high quality. Singlet-triplet splittings in Cu2 and correlation energies in CrF6n? (n = 0, 1, and 2) are also examined. The satisfactory results obtained by these calculations strongly support the contention that the model potential method is a reliable and economical alternative to the ab initio Hartree-Fock-Roothaan method.  相似文献   

3.
Chemical bonding is at the heart of chemistry. Recent work on high bond orders between homonuclear transition metal atoms has led to ultrashort metal?metal (TM?TM) distances defined as dM?M<1.900 Å. The present work is a computational design and characterization of novel main group species containing ultrashort metal?metal distances (1.728–1.866 Å) between two beryllium atoms in different molecular environments, including a rhombic Be2X2 (X=C, N) core, a vertical Be?Be axis in a 3D molecular star, and a horizontal Be?Be axis supported by N‐heterocyclic carbene (NHC) ligands. The ultrashort Be?Be distances are achieved by affixing bridging atoms to attract the beryllium atoms electrostatically or covalently. Among these species are five global minima and one chemically viable diberyllium complex, which provide potential targets for experimental realization.  相似文献   

4.
For a fundamental study on the development of novel extraction divalent metal, the extraction behaviour of copper(II), cobalt(II) and nickel(II) is studied with salicylidèneaniline (SAN). The phenol group in the Schiff base moiety leads to a large increase in the percentage of transition metal ions. SAN has both good reactivity towards metal ions and solubility in organic solvents. The solvent extraction of copper(II), cobalt(II) and nickel(II) with salicylidèneaniline from sulphate media is studied with the following parameters: pH, concentration of the extractant and the nature of diluent. The stoichiometry coefficients of the extracted species are determined by the slope analysis method. The extraction reaction proceeds by cation exchange mechanism and the extracted species are: CuL2HL, CoL2HL and NiL2. The extaction constants are evaluated for the different diluents. Under suitable conditions of pH, the solvent extraction of cobalt(II) and nickel(II) in different diluents leads to third phase formation. This tendency is confirmed from numerical extraction constants for both metal cations (log?K ex?=??15.10?±?0.03 for nickel(II) in CHCl3) and (log?K ex?=??12.56?±?0.04 for cobalt(II) in CHCl3). The extraction efficiency is found to follow the order Cu(II)?>?Co(II)?>?Ni(II).  相似文献   

5.
Composition‐adjustable spinel‐type metal oxides, MnxCo3?xO4?δ (x=0.8–1.4), were synthesized in ethanol solutions by a rapid inorganic self‐templating mechanism using KCl nanocrystals as the structure‐directing agent. The MnxCo3?xO4?δ materials showed ultrahigh oxygen evolution activity and strong durability in alkaline solutions, and are capable of delivering a current density of 10 mA cm?2 at 1.58 V versus the reversible hydrogen electrode in 0.1 M KOH solution, which is superior in comparison to IrO2 catalysts under identical experimental conditions, and comparable to the most active noble‐metal and transition‐metal oxygen evolution electrocatalysts reported so far. The high performance for catalytic oxygen evolution originates from both compositional and structural features of the synthesized materials. The moderate content of Mn doping into the spinel framework led to their improved electronic conductivity and strong oxidizing ability, and the well‐developed porosity, accompanied with the high affinity between OH? reactants and catalyst surface, contributed to the smooth mass transport, thus endowing them with superior oxygen evolution activity.  相似文献   

6.
7.
Nucleophilicity parameters (N, sN) of a group of representative diazaphospholenium hydrides were derived by kinetic investigations of their hydride transfer to a series of reference electrophiles with known electrophilicity (E) values, using the Mayr equation log k2=sN(N+E). The N scale covers over ten N units, ranging from the most reactive hydride donor (N=25.5) to the least of the scale (N=13.5). This discloses the highest N value ever quantified in terms of Mayr's nucleophilicity scales reported for neutral transition‐metal‐free hydride donors and implies an exceptional reactivity of this reagent. Even the least reactive hydride donor of this series is still a better hydride donor than those of many other nucleophiles such as the C?H, B?H, Si?H and transition‐metal M?H hydride donors. Structure–reactivity analysis reveals that the outstanding hydricity of 2‐H‐1,3,2‐diazaphospholene benefits from the unsaturated skeleton.  相似文献   

8.
Protonation of the metal‐bound oxy‐bidentate ligand in the model complexes of [(HS)3(NH3)M(OCH2COO)]q (M = Mo, Fe, V, Co; q = ?2, ?1) in the gas phase and in solutions of water and acetonitrile has been explored by the density functional approach. Calculations show that protonation of the carboxyl oxygen can open the α‐hydroxycarboxylate chelate ring ligated to a transition‐metal center under specific oxidation and spin states. The feasibility of the chelate ring opening by protonation depends on the electronic nature of the metal site in tune with conversion of a six‐coordinate with a five‐coordinate metal atom. Such selective dissociation of the metal‐bound chelate ligand manipulates the availability of an empty site at the metal center and significantly affects reactivity of the metal‐mediated chemical processes. Protonation changes the stability of species with different spin multiplicities and impels spin transition at the metal center in dissociation of the oxy‐bidentate ligand. Solvent environments of water and acetonitrile play an important role in stabilizing the negatively charged species. © 2006 Wiley Periodicals, Inc. Int J Quantum Chem, 2006  相似文献   

9.
Thermal activation of molecular oxygen is observed for the late‐transition‐metal cationic complexes [M(H)(OH)]+ with M=Fe, Co, and Ni. Most of the reactions proceed via insertion in a metal? hydride bond followed by the dissociation of the resulting metal hydroperoxide intermediate(s) upon losses of O, OH, and H2O. As indicated by labeling studies, the processes for the Ni complex are very specific such that the O‐atoms of the neutrals expelled originate almost exclusively from the substrate O2. In comparison to the [M(H)(OH)]+ cations, the ion? molecule reactions of the metal hydride systems [MH]+ (M=Fe, Co, Ni, Pd, and Pt) with dioxygen are rather inefficient, if they occur at all. However, for the solvated complexes [M(H)(H2O)]+ (M=Fe, Co, Ni), the reaction with O2 involving O? O bond activation show higher reactivity depending on the transition metal: 60% for the Ni, 16% for the Co, and only 4% for the Fe complex relative to the [Ni(H)(OH)]+/O2 couple.  相似文献   

10.
A new parameterization for the first transition metal has been proposed in the framework of CNDO /2 method. We carried out CNDO /2 calculation of hexamine complexes [M(NH3)6]2+ and hexa-aquo complexes [M(OH2)6]2+ in the high spin state where M = Mn, Fe, Co, Ni, and Cu, using new parameters. It is shown that the calculated order of binding energy is Mn? L < Fe? L < Co? L < Ni? L ≈ Cu? L (where L means the ligand), and is in good agreement with experiment. We discussed how the orbital nodes affect the nature of bonding between metal and ligand.  相似文献   

11.
We report the synthesis and spectroscopic identification of the trisbenzene complexes of strontium and barium M(Bz)3 (M=Sr, Ba) in low‐temperature Ne matrix. Both complexes are characterized by a D3 symmetric structure involving three equivalent η6‐bound benzene ligands and a closed‐shell singlet electronic ground state. The analysis of the electronic structure shows that the complexes exhibit metal–ligand bonds that are typical for transition metal compounds. The chemical bonds can be explained in terms of weak donation from the π MOs of benzene ligands into the vacant (n?1)d AOs of M and strong backdonation from the occupied (n?1)d AO of M into vacant π* MOs of benzene ligands. The metals in these 20‐electron complexes have 18 effective valence electrons, and, thus, fulfill the 18‐electron rule if only the metal–ligand bonding electrons are counted. The results suggest that the heavier alkaline earth atoms exhibit the full bonding scenario of transition metals.  相似文献   

12.
The IR. spectra of α-thenoyl-trifluoroacetone (HTTA) and seventeen of its chelates with metal(II) and -(III) ions of the first transition series have been determined. Three series of complexes are represented: the anhydrous metal(II) species, [M(TTA)2]n (M ? Ca, Mn, Co, Ni, Cu, Zn); metal(II) dihydrates, [M(TTA)2(H2O)2] (M ? Mn, Fe, Co, Ni, Zn); and the metal(III) chelates, [M(TTA)3] (M ? Sc, V, Cr, Mn, Fe, Ga). For each metal(II) complex, the spectra of the anhydrous and hydrated compounds are practically identical, suggesting that the anhydrous complexes have the polynuclear octahedral structure established for the corresponding acetylacetonates. Magnetic moment determinations reveal that complexes of the 3d4?3d7 ions all have spin-free configuration. Several vibrational bands with frequencies < 700 cm?1 are found to exhibit a frequency variation with d-orbital population which is consistent with the order of crystal field stabilization energies and hence with their assignment as coupled metal-oxygen stretching modes. Unique features of the spectra of [Cu(TTA)2] and [Mn(TTA)3] are ascribed to structural differences arising from Jahn-Teller distortion. Tentative assignments for the majority of the ligand vibrations are given.  相似文献   

13.
We report the synthesis and spectroscopic identification of the trisbenzene complexes of strontium and barium M(Bz)3 (M=Sr, Ba) in low‐temperature Ne matrix. Both complexes are characterized by a D3 symmetric structure involving three equivalent η6‐bound benzene ligands and a closed‐shell singlet electronic ground state. The analysis of the electronic structure shows that the complexes exhibit metal–ligand bonds that are typical for transition metal compounds. The chemical bonds can be explained in terms of weak donation from the π MOs of benzene ligands into the vacant (n?1)d AOs of M and strong backdonation from the occupied (n?1)d AO of M into vacant π* MOs of benzene ligands. The metals in these 20‐electron complexes have 18 effective valence electrons, and, thus, fulfill the 18‐electron rule if only the metal–ligand bonding electrons are counted. The results suggest that the heavier alkaline earth atoms exhibit the full bonding scenario of transition metals.  相似文献   

14.
Four binuclear transition metal complexes: [Cu2L(μ-OCH3)]?·?CH3OH, [Cu2H2L(μ-Cl)Cl2]?·?(CH3OH), [Cu2H2L(μ-Br)Br2]?·?(CH3OH), [(VO)2H2L(μ-Cl)]Cl2?·?(CH3OH) were synthesized by reaction of the Robson-type binucleating ligand H3L (2,6-diformyl-4-tert-butylphenol-bis-(1′-phthalazinylhydrazone)) with Cu(II) acetate, CuCl2, CuBr2 and VOCl2, correspondingly. IR and ESR spectra, elemental analysis, conductivity measurements, magnetochemical study and DFT calculations were used to characterize the ligand and isolated complexes. The ligand is a NNONN donor and its degree of deprotonation varies with the metal salt used for reaction (triply deprotonated form L?3 is observed in reaction with copper(II) acetate, while monodeprotonated form H2L? is found in complexes obtained from metal halides). All complexes contain an endogenous phenoxide bridge and an exogenous methoxide, chloride or bromide bridge. Magnetic data reveal existence of antiferromagnetic interactions between the metal ions (experimental 2J values are ?700, ?73, ?50 and ?190?cm?1, correspondingly). Broken symmetry approach at the UB3LYP/6-31G(d) level was used to theoretically calculate spin-spin coupling between metal centers. Obtained values ?570, ?62, ?53 and ?214?cm?1 are rather close to experimental ones and reproduce their counterrelation. Spin density distribution in the singlet and triplet states of the complexes is discussed.  相似文献   

15.
The first example of a transition‐metal‐catalyzed, meta‐selective C? H bromination procedure is reported. In the presence of catalytic [{Ru(p‐cymene)Cl2}2], tetrabutylammonium tribromide can be used to functionalize the meta C? H bond of 2‐phenylpyridine derivatives, thus affording difficult to access products which are highly predisposed to further derivatization. We demonstrate this utility with one‐pot bromination/arylation and bromination/alkenylation procedures to deliver meta‐arylated and meta‐alkenylated products, respectively, in a single step.  相似文献   

16.
A new transition‐metal‐containing Zintl phase, Eu10Cd6Bi12, was synthesized by combining the elements in excess molten Cd. Single‐crystal X‐ray diffraction studies indicated that this compound crystallizes in the orthorhombic space group Cmmm (No. 65) with a=7.840(2), b=24.060(7), and c=4.7809(14) Å. The crystal structure of Eu10Cd6Bi12 can be viewed as a stacking of a series of [Cd6Bi12] double layers, which are arranged alternately along the b axial direction. The layers are composed of corner‐ and edge‐shared CdBi4 tetrahedra, a common feature in the crystal chemistry of many transition‐metal Zintl phases. Electronic‐band‐structure calculations confirm the closed‐shell configuration of all constituent elements and corroborate the electron count inferred by the Zintl formalism, that is, [Eu2+]10[Cd2+]6[Bi3?]8[Bi2?]4. Magnetic‐susceptibility measurements confirm the divalency of europium and show the existence of a long‐range antiferromagnetic order of the Eu spins below 12.3 K.  相似文献   

17.
Silicon‐mediated fluoride abstraction is demonstrated as a means of generating the first fluorido‐cyanido transition metal complexes. This new synthetic approach is exemplified by the synthesis and characterization of the heteroleptic complexes, trans‐[MIVF4(CN)2]2? (M=Re, Os), obtained from their homoleptic [MIVF6]2? parents. As shown by combined high‐field electron paramagnetic resonance spectroscopy and magnetization measurements, the partial substitution of fluoride by cyanide ligands leads to a marked increase in the magnetic anisotropy of trans‐[ReF4(CN)2]2? as compared to [ReF6]2?, reflecting the severe departure from an ideal octahedral (Oh point group) ligand field. This methodology paves the way toward the realization of new heteroleptic transition metal complexes that may be used as highly anisotropic building‐blocks for the design of high‐performance molecule‐based magnetic materials.  相似文献   

18.
Rare‐earth metals have been mostly entrapped into fullerene cages to form endohedral clusterfullerenes, whereas non‐Group‐3 transition metals that can form clusterfullerenes are limited to titanium (Ti) and vanadium (V), and both are exclusively entrapped within an Ih‐C80 cage. Non‐Group‐3 transition‐metal‐containing endohedral fullerenes based on a C80 cage with D5h symmetry, VxSc3?xN@D5h‐C80 (x=1, 2), have now been synthesized, which exhibit two variable cluster compositions. The molecular structure of VSc2N@D5h‐C80 was unambiguously determined by X‐ray crystallography. According to a comparative study with the reported Ti‐ and V‐containing clusterfullerenes based on a Ih‐C80 cage and the analogous D5h‐C80‐based metal nitride clusterfullerenes containing rare‐earth metals only, the decisive role of the non‐Group‐3 transition metal on the formation of the corresponding D5h‐C80‐based clusterfullerenes is unraveled.  相似文献   

19.
By considering a transition‐metal ion in the field of some symmetrically placed ions, we illustrate the consequences of a continuous change of the structure of the ligands on the energies of the 3d electrons of the transition‐metal atom. Both a rigorous mathematical derivation and an analysis based on group theory are presented. For six ions surrounding the transition‐metal atom, a continuous DhD3dOhD3dD6d transition is observed, whereas for four ions, a continuous DhD2dTdD2dD4d transition results. Although the two systems possess many similarities, interesting differences are found as well. Finally, we demonstrate that when including orbital interactions between the ligands and the transition‐metal atom, quantitative differences occur. © 2006 Wiley Periodicals, Inc. Int J Quantum Chem, 2007  相似文献   

20.
Resorcinarene‐derived tetramethylene cavitands bearing a diphenylphosphino group grafted to their wider rim undergo facile, directed C?O bond breaking upon reaction with transition‐metal ions in the presence of nucleophiles. One possible reaction mechanism involves formation of a P,O‐chelate complex, which weakens the adjacent O?CH2 bond, leading to the formation of an oxacarbenium intermediate.  相似文献   

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