锰团簇Mn5和Mn6结构与磁性的分析

用密度泛函方法对过渡金属Mn₅, Mn₆的各种可能构型, 在PW91/ZoraTZ2P水平上进行了理论研究. 计算结果表明: 构型是自旋变化、磁性的敏感因素, Mn₅最稳定构型为弱铁磁性的三角双锥体(磁矩为3, D_3h). Mn₆的最稳定构型为铁磁性的畸变八面体(磁矩为16, C_4v). 各种异构体虽然多重度不同, 但每个原子的自旋极化度均在3以上. 构型稳定与否取决于原子间的交换耦合作用, 而原子间的这种作用又与自旋极化度的方向、大小息息相关.     

A Cationic Metal Glue Strategy for Expanding Paramagnetic Hetero-Multinuclear Metal-Oxo Clusters within Polyoxometalate Ligands

Precise structural design of large hetero-multinuclear metal-oxo clusters is crucial for controlling their large spin ground states and multielectron redox properties for application as a single-molecule magnet (SMM), molecular magnetic refrigeration, and efficient redox catalyst. However, it is difficult to synthesize large hetero-multinuclear metal oxo clusters as designed because the final structures are unpredictable when employing conventional one-step condensation reaction of metal cations and ligands. Herein, we report a “cationic metal glue strategy” for increasing the size and nuclearity of hetero-multinuclear metal-oxo clusters by using lacunary-type anionic molecular metal oxides (polyoxometalates, POMs) as rigid multidentate ligands. The employed method enabled the synthesis of {(FeMn₄)Mn₂Ln₂(FeMn₄)} oxo clusters (Ln=Gd, Tb, Dy, and Lu), which are the largest among previously reported paramagnetic hetero-multinuclear metal-oxo clusters in POMs and showed unique SMM properties. These clusters were synthesized by conjugating {FeMn₄} oxo clusters with Mn and Ln cations as glues in a predictable way, indicating that the “cationic metal glue strategy” would be a powerful tool to construct desired large hetero-multinuclear metal clusters precisely and effectively.     

Ab initio study of magnetic interactions of manganese-oxide clusters

The manganese clusters have attracted much attention in relation with the oxygen evolving center (OEC) in photosystem II (PS II) system, which catalyzes the water oxidation reaction. Previously, we examined various spin-structures of Mn(II)₄O₄ model clusters, of which all of magnetic interactions are antiferromagnetic. In this study, we investigated electronic and magnetic structures of simple model clusters, Mn₄O₄(OAc)₆ and Mn₃CaO₄(OAc)₆ using spin unrestricted B3LYP (UB3LYP) method. The UB3LYP method is a standard tool for this study and has been in fact employed by many researchers. However, several peculiar features are observed for these model clusters: for instance the most stable spin state becomes the highest spin state for Mn(IV)₄O₄(OAc)₆ although this model cluster consists of superexchange type of units, Mn(IV)₂O₂ that usually favors antiferromagnetic spin alignments. Implications of the comparative results are discussed in relation to the electrophilic (or radical) mechanism for the O-O bond formation in the OEC.     

The structure of manganese dioxide and position of proton studied by neutron diffraction with isotopic substitution

The position of proton inside manganese dioxide, γ-MnO₂, was studied by the total neutron-scattering technique using H/D isotopic substitution. The first-order difference was obtained by subtracting the results for the two different isotopic compositions and obtaining the weighted sum of partial structure factors and radial distribution functions related to the structure around hydrogens. The deuterium-substituted γ-MnO₂ was prepared by de-intercalation of the proton via an oxidative treatment prior to re-intercalation with deuterium. The proton occupied two different positions with the H-O length of 1.0 and 1.9 Å, which corresponds to the ‘Ruetschi’ and ‘Coleman’ protons, respectively. The former protons situated in the Mn⁴⁺ vacant site and the latter in the tunnel centered in an oxygen octahedron. The isotopic substitution technique and the structure around protons are discussed in details.     

A combined diffraction and dielectric properties investigation of Ba3MnNb2O9 complex perovskites

A combined synthesis, diffraction and dielectric properties investigation of the dependence (and effect) of Mn²⁺/Nb⁵⁺ ordering in Ba₃MnNb₂O₉ (BMN) upon annealing atmosphere and processing conditions has been carried out. Annealing in different atmospheres was not found to significantly alter either nominal stoichiometry or structure type. The obtained structure type (disordered metrically cubic or ordered trigonal) as well as the measured electrical properties (in particular, the dielectric loss) were, however, found to be sensitive to the synthesis route. Samples obtained via solid-state reaction were found to be predominantly of 1:2 Mn²⁺/Nb⁵⁺ ordered, trigonal structure type whereas samples obtained via an aqueous solution route were found to be of a Mn²⁺/Nb⁵⁺ ‘disordered’, metrically cubic structure type. All solid-state synthesized samples showed reasonable dielectric properties. The microwave dielectric constant and dielectric quality factor, Q, at 8 GHz of an as-synthesized BMN sample were 38 and 100, respectively. By contrast, the dielectric loss of the metrically cubic, Mn²⁺/Nb⁵⁺ ‘disordered’ samples obtained via an aqueous solution synthesis process were significantly worse.     

A model for thermal spin relaxation in rotating ferromagnetic clusters

A model for thermal spin relaxation in isolated ferromagnetic clusters is proposed and investigated theoretically by means of nonequilibrium thermodynamics. It is shown that thermal agitation mediates relaxation of the spin towards the total angular momentum vector of the cluster so that the clusters are magnetically polarized in the direction of their rotational axis. A relaxation mechanism via thermal moment of inertia fluctuations is proposed. The results are discussed for a Fe₁₂₅-cluster.     

Size Effect on Local Magnetic Moments in Ferrimagnetic Molecular Complexes: An XMCD Investigation

Summary.  Molecular chemistry allows to synthesize new magnetic systems with controlled properties such as size, magnetization or anisotropy. The theoretical study of the magnetic properties of small molecules (from 2 to 10 metallic cations per molecule) predicts that the magnetization at saturation of each ion does not reach the expected value for uncoupled ions when the magnetic interaction is antiferromagnetic. The quantum origin of this effect is due to the linear combination of several spin states building the wave function of the ground state and clusters of finite size and of finite spin value exhibit this property. When single crystals are available, spin densities on each atom can be experimentally given by Polarized Neutron Diffraction (PND) experiments. In the case of bimetallic MnCu powdered samples, we will show that X-ray Magnetic Circular Dichroism (XMCD) spectroscopy can be used to follow the evolution of the spin distribution on the Mn^II and Cu^II sites when passing from a dinuclear MnCu unit to a one dimensional (MnCu) _n compound. Corresponding author. E-mail: Christophe.Cartier@lure.u-psud.fr Received September 4, 2002; accepted September 6, 2002     

Dark singlet oxygenation of organic substrates in single-phase and multiphase microemulsion systems

The disproportionation of hydrogen peroxide catalyzed by molybdate anions provides an effective non-photochemical source of singlet oxygen ¹O₂, (¹Δ_g). Microemulsions are the preferred media to carry out ‘dark’ singlet oxygenation of labile and hydrophobic substrates. Single-phase and multiphase microemulsion systems have been developed and improved for the last decade and their respective advantages and limitations are shortly reviewed and discussed.     

Magnetic “Molecular Oligomers” Based on Decametallic Supertetrahedra: A Giant Mn49 Cuboctahedron and its Mn25Na4 Fragment

Two nanosized Mn₄₉ and Mn₂₅Na₄ clusters based on analogues of the high‐spin (S=22) [Mn^III₆Mn^II₄(μ₄‐O)₄]¹⁸⁺ supertetrahedral core are reported. Mn₄₉ and Mn₂₅Na₄ complexes consist of eight and four decametallic supertetrahedral subunits, respectively, display high virtual symmetry (O_h), and are unique examples of clusters based on a large number of tightly linked high nuclearity magnetic units. The complexes also have large spin ground‐state values (Mn₄₉: S=61/2; Mn₂₅Na₄: S=51/2) with the Mn₄₉ cluster displaying single‐molecule magnet (SMM) behavior and being the second largest reported homometallic SMM.     

Influence of molecular electronic properties on the IR spectra of dimeric hydrogen bond systems: polarized spectra of 2-hydroxybenzothiazole and 2-mercaptobenzothiazole crystals

We have studied the polarized IR spectra of the hydrogen-bonded molecular crystals of 2-hydroxybenzothiazole (HBT) and 2-mercaptobenzothiazole (MBT). The crystal structure of 2-hydroxybenzothiazole was determined by X-ray diffraction. The polarized spectra of the crystals were measured, in the frequency ranges of the ν_N-H and ν_N-D bands, at room temperature, and at 77 K. In both systems an extremely strong H/D isotopic effect in the spectra was observed, involving reduction of the well-developed ν_N-H band fine structure to a single prominent ν_N-D line only. The two ν_N-H bands were also shown to exhibit almost identical properties, band shapes, temperature and dichroic properties included. The spectra were quantitatively reconstituted, along with the strong isotopic effect, when calculated using the ‘strong-coupling’ theory, assuming the centrosymmetric dimers of HBT or MBT to be the structural units responsible for the crystalline spectral properties. The similarity of the spectra of the two crystalline systems was considered to be a result of longer-distance couplings between the proton vibrations in the dimers, via the aromatic ring electrons. When investigating the ‘residual’ ν_N-H band shapes for crystals isotopically diluted by deuterium, we observed some ‘self-organization’ effects in the spectra, indicating the energetically favored presence of two identical hydrogen isotopes in each hydrogen bond dimer.     

Structures,Unimolecular Fragmentations,and Reactivities of the Self‐Assembled Multimetallic/Peptide Complexes [Mnn(GlyGly‐H)2n−1]+ and [Mnn+1(GlyGly‐H)2n]2+

Complexes of Mn²⁺ with deprotonated GlyGly are investigated by sustained off‐resonance irradiation collision‐induced dissociation (SORI‐CID), infrared multiple‐photon dissociation spectroscopy, ion–molecule reactions, and computational methods. Singly [Mn_n(GlyGly‐H)_2n?1]⁺ and doubly [Mn_n+1(GlyGly‐H)_2n]²⁺ charged clusters are formed from aqueous solutions of MnCl₂ and GlyGly by electrospray ionization. The most intense ion produced was the singly charged [M₂(GlyGly‐H)₃]⁺ cluster. Singly charged clusters show extensive fragmentations of small neutral molecules such as water and carbon dioxide as well as dissociation pathways related to the loss of NH₂CHCO and GlyGly. For the doubly charged clusters, however, loss of GlyGly is observed as the main dissociation pathway. Structure elucidation of [Mn₃(GlyGly‐H)₄]²⁺ clusters has also been done by IRMPD spectroscopy as well as DFT calculations. It is shown that the lowest energy structure of the [Mn₃(GlyGly‐H)₄]²⁺ cluster is deprotonated at all carboxylic acid groups and metal ions are coordinated with carbonyl oxygen atoms, and that all amine nitrogen atoms are hydrogen bonded to the amide hydrogen. A comparison of the calculated high‐spin (sextet) and low‐spin (quartet) state structures of [Mn₃(GlyGly‐H)₄]²⁺ is provided. IRMPD spectroscopic results are in agreement with the lowest energy high‐spin structure computed. Also, the gas‐phase reactivity of these complexes towards neutral CO and water was investigated. The parent complexes did not add any water or CO, presumably due to saturation at the metal cation. However, once some of the ligand was removed via CO₂ laser IRMPD, water was seen to add to the complex. These results are consistent with high‐spin Mn²⁺ complexes.     

A new terpyrrolic analogue of dipyrrolylquinoxalines: an efficient optical-based sensor for anions in organic media

The synthesis and X-ray structural characterization of a new terpyrrolic analog of dipyrrolylquinoxaline (DPQ) is described that contains two pyrrole anion recognition groups bridged by a central 1,2-linked pyrrole. Relative to the ‘parent’ DPQ system, this new terpyrrolic scaffold acts as an improved colorimetric and fluorescent sensor for halide and dihydrogen phosphate anions in organic media. This enhancement is particularly dramatic in the case of H₂PO₄⁻ (studied as its tetrabutylammonium salt); in CH₂Cl₂ it is bound with an affinity constant, K, of 17,500 M⁻¹ by the terpyrrole of this report vs. 80 M⁻¹ in the case of DPQ. The present findings thus support the emerging notion that a range of pyrrole-based anion recognition and sensing systems may be produced by replacing the central quinoxaline spacer in DPQs by other bridging subunits and that these new receptors may have properties that differ dramatically from their DPQ ‘parents’.     

New approach to CF3-containing polysubstituted anilines: reaction of β-trifluoroacetylvinyl ethers with enamines

The reaction of β-trifluoroacetylvinyl ethers with ‘push-pull’ enamines having a methyl group at the α-position was investigated. As a result, a set of CF₃-containing dialkyl anilines and their covalent hydrates were obtained. A possible reaction mechanism and the stability of the covalent hydrates obtained are discussed.     

Improved spin hamiltonian parameters for Mn2+ determined by EPR at zero magnetic field

EPR has been studied at zero magnetic field for high-spin Mn²⁺ in MgSO₄·7H₂O and NH₄Cl. Significant differences have been found between high-field EPR spin hamiltonmn parameters in the literature and those necessary to fit the complex zero-field spectra. Sources of the discrepancies are discussed in relation to the Mn²⁺ systems and more generally     

Effects of chloride ions on electrochemical reactions of manganese(III) complexes

Electrochemical reactions of manganese(III) complexes, Mn^III(L)X (L; salen, salpn, 5-NO₂–salen or 5-NO₂–salpn, X; Cl, Br or NO₂) and Mn^III(L’)₂X (L’; N-Bu-sal, N-Oct–sal, N-Oct–5-Br–sal or N-Oct–5-NO₂–sal, X; Cl or Br), were investigated by voltammetry at a glassy carbon electrode in the absence/presence of Cl⁻ in acetonitrile solution. By the addition of Cl⁻, oxidation processes of Mn^III(L)X and Mn^III(L’)₂X have been found to be improved from quasi-reversible to reversible, and their oxidation products, [Mn^IV(L)X]⁺ and [Mn^IV(L’)₂X]⁺, were stabilized by the combination with Cl⁻ resulting in [Mn^IV(L)Cl₂] and [Mn^IV(L’)₂Cl₂], respectively. On the other hand, the reduction processes of Mn^III(L)X and Mn^III(L’)₂Cl were not so significantly affected by Cl⁻ as those observed for their oxidation. Other types of manganese(III) complexes and iron(III) complex were also investigated. The present study may clarify the role of Cl⁻ being involved in OEC (oxygen-evolving center) in photosystem II.     

Triangle-shaped polycyclic aromatics based on tribenzocoronene: facile synthesis and physical properties

A series of triangle-shaped polycyclic aromatics have been developed according to a facile synthetic protocol with high yields. As revealed by X-ray single crystal data, their molecular conformation and packing arrangement are significantly influenced by the electronic properties and steric bulk of peripheral subunits. The ‘saddle’-shaped hexahalotribenzocoronenes (ClTBC and FTBC) possess C₂ symmetric structures and can self-assemble into well-defined columnar structures, dramatically different from hexabutyoxytribenzocoronene (TBC), which adopts a C₃ symmetric ‘double-concave’ structure and less efficient packing arrangement. In the compound trithiophenocoronene (TTC), the five-membered corner rings produce a more open bay-region periphery alleviating intramolecular steric congestion. As a result, the molecule adopts an almost planar conformation.     

Fullerene containing norbornenes: synthesis and ring-opening metathesis polymerization

New norbornenes with the covalently bonded fullerene C₆₀ have been prepared as monomers for ring-opening metathesis polymerization. Under the Grubbs catalyst these monomers smoothly enter homopolymerization as well as co-polymerization reactions with the parent ‘non-fullerene’ monomers. Homopolymers are insoluble in organic solvents whereas co-polymers obtained by 1:1 co-polymerization of the norbornenes with their ‘non-fullerene’ analogues are well soluble.     

Expansion of the spin-coupled wavefunction in Slater determinants

Summary The expansion of the spin-coupled wavefunction in Slater determinants constructed from nonorthogonal spin-orbitals is discussed. It proves possible to generate from cofactors of the appropriate overlap matrix all the density matrices, up to fourth order, required for the variational optimization of the wavefunction. The computational effort inherent in this super-cofactor strategy scales in a very acceptable manner with the number of electrons.     

Copper(I) oxide and benzoic acid ‘on water’: a highly practical and efficient catalytic system for copper(I)-catalyzed azide-alkyne cycloaddition

A simple combination of Cu₂O and PhCO₂H ‘on H₂O’ has been developed as a highly practical and efficient catalytic system for copper(I)-catalyzed azide-alkyne cycloaddition (CuAAC). It not only provides a further evidence for the strategy of carboxylic acids-promoted CuAAC, but also offers significant advantages to CuAAC because Cu₂O is one of the most stable and cheapest Cu(I) sources; PhCO₂H is one of the structurally simplest bidentate ligands; and water is the most ‘green’ solvent.     

Spin-free approach for evaluation of electronic matrix elements using character operators of ℒN

A spin-free method is presented for evaluating electronic matrix elements over a spin-independent many-electron Hamiltonian. The spin-adapted basis of configuration state functions is obtained using a nonorthogonal spin basis consisting of projected spin eigenfunctions. The general expressions for the matrix elements are given explicitly, and it is demonstrated how the matrix elements may be obtained simply from the knowledge of the irreducible characters of the permutation group ℒ_N. The presented formulas are very general and may be applied in connection with both spin-coupled valence bond studies and in conventional configuration interaction (CI) methods based on an orthonormal orbital basis. © 1996 John Wiley & Sons, Inc.