Surface structure and stability of MoSx model clusters

Density functional theory (DFT) computations have been carried out to study the structure and stability of MoSx clusters with the change of sulfur coverage at both Mo and S edges. DFT shows that adding sulfur to the Mo edge is always exothermic. However, deleting corner sulfur from the S edge is exothermic for 67 and 50% sulfur coverages, while deleting edge sulfur from the S edge is endothermic for 33 and 0% sulfur coverages. On the basis of the computed free energies along a wide range of H2S/H2 ratios, it is found that there are two stable structures with 33 and 50% sulfur coverages on the Mo edge by having 100% sulfur coverage on the S edge and one stable structure with 67% sulfur coverage on the S edge by having 0% sulfur coverage on the Mo edge. Under fully sulfiding atmosphere or at a very high H2S/H2 ratio, triangle MoSx structures with 100% sulfur coverage on the Mo edge are computed to be more stable than those with 100% sulfur coverage on the S edge, in agreement with the observation of scanning tunneling microscopy. In addition, the effects of cluster sizes on the surface structures are discussed.     

Probing lead(II) bonding environments in 4-substituted pyridine adducts of (2,6-Me2C6H3S)2Pb: an X-ray structural and solid-state 207Pb NMR study

The effect of subtle changes in the sigma-electron donor ability of 4-substituted pyridine ligands on the lead(II) coordination environment of (2,6-Me(2)C(6)H(3)S)(2)Pb (1) adducts has been examined. The reaction of 1 with a series of 4-substituted pyridines in toluene or dichloromethane results in the formation of 1:1 complexes [(2,6-Me(2)C(6)H(3)S)(2)Pb(pyCOH)](2) (3), [(2,6-Me(2)C(6)H(3)S)(2)Pb(pyOMe)](2) (4), and (2,6-Me(2)C(6)H(3)S)(2)Pb(pyNMe(2)) (5) (pyCOH = 4-pyridinecarboxaldehyde; pyOMe = 4-methoxypyridine; pyNMe2 = 4-dimethylaminopyridine), all of which have been structurally characterized by X-ray crystallography. The structures of 3 and 4 are dimeric and have psi-trigonal bipyramidal S(3)N bonding environments, with the 4-substituted pyridine nitrogen and bridging sulfur atoms in axial positions and two thiolate sulfur atoms in equatorial sites. Conversely, compound 5 is monomeric and exhibits a psi-trigonal pyramidal S(2)N bonding environment at lead(II). The observed structures may be rationalized in terms of a simple valence bond model and the sigma-electron donor ability of the 4-pyridine ligands as derived from the analysis of proton affinity values. Solid-state (207)Pb NMR experiments are applied in combination with density functional theory (DFT) calculations to provide further insight into the nature of bonding in 4, 5, and (2,6-Me(2)C(6)H(3)S)(2)Pb(py)(2) (2). The lead chemical shielding (CS) tensor parameters of 2, 4, and 5 reveal some of the largest chemical shielding anisotropies (CSA) observed in lead coordination complexes to date. DFT calculations using the Amsterdam Density Functional (ADF) program, which take into account relativistic effects using the zeroth-order regular approximation (ZORA), yield lead CS tensor components and orientations. Paramagnetic contributions to the lead CS tensor from individual pairs of occupied and virtual molecular orbitals (MOs) are examined to gain insight into the origin of the large CSA. The CS tensor is primarily influenced by mixing of the occupied MOs localized on the sulfur and lead atoms with virtual MOs largely comprised of lead 6p orbitals.     

From Eight‐Membered 10π Electron Sulfur–Nitrogen Cycles to Bicycles and Cages: A Theoretical Approach

A simple way of rationalizing the structures of cyclic, bicyclic, and tricyclic sulfur–nitrogen species and their congeners is presented. Starting from a planar tetrasulfur tetranitride with 12π electrons, we formally derived on paper a number of heterocyclic eight‐membered 10π electron species by reacting the 3p orbitals of two opposite sulfur centers with one radical each, or by replacing these centers by other atoms with five (P) or four (Si, C) valence electrons. This led to planar aromatic 10π electron systems, nonplanar bicyclic structures with a transannular S?S bond, and tricyclic structures by bridging the planar rings with an acceptor or donor unit. The final structures depend on the number of π electrons in the bridges. Intermediate biradicals are stabilized by Jahn–Teller distortion, giving transannular S?S bonds between the NSN units. This procedure may be summarized by two rules, which provide a rationale for the structures of a large number of sulfur–nitrogen‐based molecules. The long bonds between the NSN units show a p character of >95 %. The qualitative results have been compared with known molecular structures and the results of B3LYP/cc‐pVTZ calculations as well as CASSCF and CASVB calculations. B3LYP/cc‐pVTZ calculations have also provided the UV/Vis spectra and the NICS values of the planar 10π systems.     

Density functional theory study of triangular molybdenum sulfide nanocluster and CO adsorption on it

A systematic density functional theory study has been carried out on the structure and stability of triangular molybdenum sulfide (MoS(x)()) models. On the basis of the structural and energetic comparison, the triangle Mo(28)S(84) (VII) cluster has been identified as a reasonable structure for triangular MoS(x)() model. Under reductive atmosphere, the most stable structure has bridging sulfur on edge sites and two H(2)S at each corner site. It is found that CO adsorption at the corner site represents the most stable conformation. Along with other stretching modes, the computed frequency at 2102 cm(-1) for CO at the corner agrees perfectly with the experimental observation.     

Stability,Structure and Reconstruction of 1H-Edges in MoS2

Density functional studies of the edges of single-layer 1H-MoS₂ are presented. This phase presents a rich variability of edges that can influence the morphology and properties of MoS₂ nano-objects, play an important role in industrial chemical processes, and find future applications in energy storage, electronics and spintronics. The so-called Mo-100 %S edges vertical S-dimers were confirmed to be stable, however the authors also identified a family of metastable edges combining Mo atoms linked by two-electron donor symmetrical disulfide ligands and four-electron donor unsymmetrical disulfide ligands. These may be entropically favored, potentially stabilizing them at high temperatures as a “liquid edge” phase. For Mo-50 %S edges, S-bridge structures with 3× periodicity along the edge are the most stable, compatible with a Peierls’ distortion arising from the d-bands of the edge Mo atoms. An additional explanation for this periodicity is proposed through the formation of 3-center bonds.     

Electronic Properties of Triangle Molybdenum Disulfide (MoS2) Clusters with Different Sizes and Edges

The electronic structures and transition properties of three types of triangle MoS₂ clusters, A (Mo edge passivated with two S atoms), B (Mo edge passivated with one S atom), and C (S edge) have been explored using quantum chemistry methods. The highest occupied molecular orbital (HOMO)–lowest unoccupied molecular orbital (LUMO) gap of B and C is larger than that of A, due to the absence of the dangling of edge S atoms. The frontier orbitals (FMOs) of A can be divided into two categories, edge states from S_3p at the edge and hybrid states of Mo_4d and S_3p covering the whole cluster. Due to edge/corner states appearing in the FMOs of triangle MoS₂ clusters, their absorption spectra show unique characteristics along with the edge structure and size.     

Two Different Structural Motifs Observed for Dimeric Dialkylaluminum and Dialkylgallium Alkynides [R2E‐C≡C‐C6H5]2

The dialkylaluminum and dialkylgallium alkynides [R₂E‐C≡C‐R′]₂ (R = Me, CMe₃; E = Al, Ga; R′ = Ph) containing C≡C triple bonds attached to their central aluminum or gallium atoms are easily obtained by the reactions of dialkylelement chlorides with lithium alkynides or by treatment of the corresponding alkyne R‐C≡C‐H with dialkylaluminum or dialkylgallium hydrides. The first reaction is favored by the precipitation of LiCl, the second one by the formation of elemental hydrogen. All products form dimers in which the carbanionic carbon atoms of the alkynido groups adopt bridging positions, but, interestingly, different types of molecular structures were observed depending on the steric demand of the substituents terminally attached to the aluminum or gallium atoms. The small methyl substituents gave structures in which the aluminum or gallium atoms seemed to be side‐on coordinated by the C≡C triple bonds of almost linear E‐C≡C groups. In contrast, the more bulky tert‐butyl groups forced an arrangement in which the C≡C triple bonds were perpendicular to the E‐E axis of the molecules. Different bonding modes result, which were analyzed by quantum‐chemical calculations.     

DFT study into the reaction mechanism of CO methanation over pure MoS2

Mo‐based catalysts are commonly used in the direct methanation of CO; however, no integrated mechanism has been proposed due to limits in characterizing the nano‐sized active structures of MoS₂. Thus, we report our investigation into the mechanism of CO methanation over pure MoS₂ through density functional theory simulations, considering that only MoS₂ edge sites exhibit catalytic activity. Simulations revealed the presence of (010) and (110) surfaces on the MoS₂ edges. Both surfaces are reconstructed by the redistribution of surface sulfur atoms upon exposure to H₂/H₂S, and after sulfur coverage redistribution, S vacancies are generated for CO hydrogenation. The reaction mechanisms on both surfaces are discussed, with the S‐edge being better suited to CO methanation than Mo‐edge on the (010) surface. The rate‐controlling step differs between surfaces, and corresponds to the initial activation reaction, which was achieved more easily on the (110) surface.     

Single-component magnetic conductors based on Mo3S7 trinuclear clusters with outer dithiolate ligands

A trinuclear cluster complex containing the Mo(3)S(7) central unit coordinated to dithiolate ligands, in particular the organic dmit (1,3-dithia-2-thione-4,5-dithiolate) anion, has been used to prepare a single-component molecular conductor formed by the threefold symmetry magnetic building block Mo(3)S(7)(dmit)(3) (1). The [Mo(3)S(7)(dmit)(3)](2)(-) ([1](2)(-)) diamagnetic anion forms dimers by interaction between the electrophilic cluster axial sulfur atoms and the sulfur atoms of the outer dithiolate ligand. Additional contacts between adjacent dmit ligands result in chain formation. The two-electron oxidation of [1](2)(-) yields to a three-dimensional molecular solid formed by neutral Mo(3)S(7)(dmit)(3) (1) units with partially filled molecular orbitals, which exhibits sizable intermolecular electronic interactions together with a significant electron delocalization. It also contains large open channels. The interactions responsible for the conducting properties have been identified using a first-principle DFT approach and the calculated electronic structure has allowed us to model the magnetic behavior of the material with two competing antiferromagnetic interactions to produce a spin-frustrated extended network. The potential of this Mo(3)S(7) cluster complex to be modified together with the capability of filling the open channels with doping species paves the way to an entirely new set of molecular conductors and/or magnets.     

固氮酶催化活性中心及其化学模拟

固氮酶是固氮微生物在常温常压下固氮成氨的催化剂,其催化机理和化学模拟一直是国际上长期致力研究的对象.钼铁蛋白高分辨1.0单晶X射线衍射分析表明,固氮酶催化活性中心铁钼辅基的结构为Mo Fe7S9C(R-homocit),其中,Mo原子和3个u2-硫配体、1个组氨酸和1个高柠檬酸配位,形成八面体构型.高柠檬酸以α-烷氧基氧和α-羧基氧与钼螯合形成双齿配位,氨基酸残基上的组氨酸咪唑氮和半胱氨酸巯基与钼和铁单齿配位.在固氮酶铁钼辅基的生物合成过程中,高柠檬酸和咪唑侧基是在最后的合成步骤插入铁硫碳簇前驱体中,其中高柠檬酸和咪唑侧基有可能对质子传递以及稳定Mo Fe7S9C簇起到重要作用.本文从固氮酶铁钼辅基结构出发,结合最近本课题组从化学模拟出发,将固氮酶催化活性中心铁钼辅基结构修订为加氢新结构Mo Fe7S9C(R-Hhomocit)的研究,着重介绍了近年来国内外固氮酶活性中心、生物合成和催化作用机理的研究进展,并展望了固氮酶的研究前景.     

Ab initio study of structural stability of Mo-S clusters and size specific stoichiometries of magic clusters

Using first-principles calculations with ultrasoft pseudopotential formalism and the generalized gradient approximation for the exchange-correlation functional, we study the stability of MonSm (n =1-6 and m ranging from n to 3n) clusters and obtain the optimal stoichiometry for each n corresponding to the magic cluster. It is found that in this size range, the lowest-energy structures favor a core of metal atoms, which is covered by sulfur. In particular, we observe that for Mo6S14 isolated clusters, a 3D structure is significantly lower in energy as compared to platelet structures found recently on Au (111) surface. The composition ratio between S and Mo in the magic clusters is less than 2 for n=3 and greater than 2 for n<3. The structural stability of the magic clusters arises from the optimization of the Mo-Mo and Mo- S bonding as well as the symmetry of the cluster. Addition of a terminal sulfur in a magic cluster generally lowers its binding energy. The presence of partially occupied d-orbitals in Mo atoms contributes to Mo-Mo bonding and for higher S concentration it leads to sulfur-sulfur bond formation. The variation in energy due to a change in the sulfur composition suggests that sulfurization of the magic clusters is generally more favorable than desulfurization.     

Rearrangement of symmetrical dicubane clusters into topological analogues of the P cluster of nitrogenase: nature's choice?

Reaction schemes have been developed that lead to clusters having the topology of the PN cluster of nitrogenase. The single cubane clusters [(Tp)MFe3S4Cl3]z (M = Mo, z = 1-; M = V, z = 2-) react with PEt3 to give [(Tp)MFe3S4(PEt3)3]1+, which are reduced to the neutral edge-bridged double cubanes [(Tp)2M2Fe6S8(PEt3)4] with highly reduced (2[MFe3S4]1+) cores. Reaction of these clusters in acetonitrile with (Et4N)(HS) results in the formation of [(Tp)2Mo2Fe6S9(SH)2]3- and [(Tp)2V2Fe6S9(SH)2]4-. X-ray structures of the Et4N+ salts reveal the bridging pattern M2Fe6(mu2-S)2(mu3-S)6(mu6-S) in which two cuboidal MFe3(mu3-S)3 units share the common bridge atom mu6-S and are externally bridged by two mu2-S atoms. The M sites possess trigonal octahedral, and the Fe sites, distorted tetrahedral coordination. Hydrosulfide ligands and sulfide atoms simulate terminal cysteinate ligation and mu2 bridges, respectively, in the protein-bound cluster Fe8S7(mu2-SCys)2(SCys)4. The synthetic clusters have the same bridging pattern as the PN cluster and approach congruency with it. These clusters are the first molecular topological analogues of a PN cluster. Like the latter, they are substantially reduced (majority of Fe(II)).     

Synthesis and thermal characterization of sulfur containing methionine bridged cobalt(III) and copper(II) complex

The sulfur containing amino acid bridging polynuclear transition metal complex has been synthesized and characterized by different measurements such as UV?CVis, FT?CIR, C?CH?CN?CS, TG?CDTA, ICP-AES, differential scanning calorimeter (DSC), and XRD. DSC has showed negative specific heat of this polynuclear system and has used to evaluate some thermodynamic constants like activation energy (E _a), frequency factor (A), enthalpy, and entropy of that system. The specific heat capacity is measured at heating rate of 10?°C?min^?1 in room atmosphere of this polynuclear complex. The characterization of this complex has showed five Co(III) and four Cu(II) atoms and this complex contained ten sulfur containing methionine amino acid units.     

Regioselective and reversible carbon-nitrogen bond formation: synthesis, structure and reactivity of ureato-bridged complexes [Mo2(NAr)2(mu-X){mu-ArNC(O)NAr}(S2CNR2)2](Ar = Ph, p-tol; X = S, NAr; R = Me, Et, Pr)

Reaction of ArNCO with syn-[MoO(mu-O)(S2CNR2)]2 or syn-[MoO(mu-NAr)(S2CNR2)]2 at 110 degrees C leads to the facile formation of bridging ureato complexes [Mo2(NAr)2(mu-NAr){mu-ArNC(O)NAr}(S2CNR2)2](Ar = Ph, p-tol; R = Me, Et, Pr), formed upon substitution of all oxo ligands and addition of a further equivalent of isocyanate across one of the bridging imido ligands. Related sulfido-bridged complexes [Mo2(NAr)2(mu-S){mu-ArNC(O)NAr}(S2CNR2)2] have been prepared from syn-[Mo2O2(mu-O)(mu-S)(S2CNR2)2]. When reactions with syn-[MoO(mu-NAr)(S2CNEt2)]2 were followed by NMR, intermediates were observed, being formulated as [Mo2O(NAr)(mu-NAr){mu-ArNC(O)NAr}(S2CNEt2)2], which at higher temperatures convert to the fully substituted products. A crystallographic study of [Mo2(N-p-tol)2(mu-S){mu-p-tolNC(O)N-p-tol}(S2CNPr2)2] reveals that the bridging ureato ligand is bound asymmetrically to the dimolybdenum centre-molybdenum-nitrogen bonds trans to the terminal imido ligands being significantly elongated with respect to those cis-a result of the trans-influence of the terminal imido ligands. This trans-influence also leads to a trans-effect, whereby the exchange of aryl isocyanates can occur in a regioselective manner. This is followed by NMR studies and confirmed by a crystallographic study of [Mo2(N-p-tol)2(mu-N-p-tol){mu-p-tolNC(O)NPh}(S2CNEt2)2]--the PhNCO occupying the site trans to the terminal imido ligands. Ureato complexes also react with PhNCS, initially forming [Mo2(NAr)2(mu-S){mu-ArNC(O)NAr}(S2CNR2)2], resulting from exchange of the bridging imido ligand for sulfur, together with small amounts of [Mo2(NAr)2(mu-S)(mu-S2)(S2CNEt2)2], containing bridging sulfide and disulfide ligands. The ureato complexes [Mo2(NAr)2(mu-S){mu-ArNC(O)NAr}(S2CNR2)2] react further with PhNCS to give [Mo2(NAr)2(mu-S)2(S2CNR2)2]n (n = 1, 2), which exist in a dimer-tetramer equilibrium. In order to confirm these results crystallographic studies have been carried out on [Mo2(N-p-tol)2(mu-S)(mu-S2)(S2CNEt2)2] and [Mo2(N-p-tol)2(mu-S)2(S2CNPr2)2]2.     

The structure and possible catalytic sites of Mo(3)S(9) as a model of amorphous molybdenum trisulfide: a computational study

The structure and reactivity of Mo(3)S(9) clusters, taken as a model for amorphous molybdenum trisulfide, have been investigated at the B3LYP density functional level of theory. Two computed ground-state cluster structures are close in energy and have similar structural parameters and vibrational modes. These values agree well with the available experimental data. These cluster structures are considered to be formed simultaneously during the preparation process of catalysts. Their catalytic activity has been analyzed on the basis of frontier molecular orbital properties (FMO). It is mainly due to 4d-type orbitals of the unsaturated molybdenum centers without terminal sulfur coordination. The small HOMO-LUMO gaps suggest that Mo(3)S(9) clusters can act as Lewis acids or Lewis bases.     

Hydrogen-induced Sulfur Vacancies on the MoS2 Basal Plane Studied by Ambient Pressure XPS and DFT Calculations

Sulfur vacancy on an MoS₂ basal plane plays a crucial role in device performance and catalytic activity; thus, an understanding of the electronic states of sulfur vacancies is still an important issue. We investigate the electronic states on an MoS₂ basal plane by ambient-pressure X-ray photoelectron spectroscopy (AP-XPS) and density functional theory calculations while heating the system in hydrogen. The AP-XPS results show a decrease in the intensity ratio of S 2p to Mo 3d, indicating that sulfur vacancies are formed. Furthermore, low-energy components are observed in Mo 3d and S 2p spectra. To understand the changes in the electronic states induced by sulfur vacancy formation at the atomic scale, we calculate the core-level binding energies for the model vacancy surfaces. The calculated shifts for Mo 3d and S 2p with the formation of sulfur vacancy are consistent with the experimentally observed binding energy shifts. Mulliken charge analysis indicates that this is caused by an increase in the electronic density associated with the Mo and S atoms around the sulfur vacancy as compared to the pristine surface. The present investigation provides a guideline for sulfur vacancy engineering.     

Unprecedented stereoselective synthesis of catalytically active chiral Mo3CuS4 clusters

Cluster excision of polymeric {Mo3S7Cl4}n phases with chiral phosphane (+)-1,2-bis[(2R,5R)-2,5-(dimethylphospholan-1-yl)]ethane ((R,R)-Me-BPE) or with its enantiomer ((S,S)-Me-BPE) yields the stereoselective formation of the trinuclear cluster complexes [Mo3S4{(R,R)-Me-BPE}3Cl3]+ ([(P)-1]+) and [Mo3S4{(S,S)-Me-BPE}3Cl3]+ ([(M)-1]+), respectively. These complexes possess an incomplete cuboidal structure with the metal atoms defining an equilateral triangle and one capping and three bridging sulfur atoms. The P and M symbols refer to the rotation of the chlorine atoms around the C3 axis, with the capping sulphur atom pointing towards the viewer. Incorporation of copper into these trinuclear complexes affords heterodimetallic cubane-type compounds of formula [Mo3CuS4{(R,R)-Me-BPE}3Cl4]+ ([(P)-2]+) or [Mo3CuS4{(S,S)-Me-BPE}3Cl4]+ ([(M)-2]+), respectively, for which the chirality of the trinuclear precursor is preserved in the final product. Cationic complexes [(P)-1]+, [(M)-1]+, [(P)-2]+, and [(M)-2]+ combine the chirality of the metal cluster framework with that of the optically active diphosphane ligands. The known racemic [Mo3CuS4(dmpe)3Cl4]+ cluster (dmpe = 1,2-bis(dimethylphosphanyl)ethane) as well as the new enantiomerically pure Mo3CuS4 [(P)-2]+ and [(M)-2]+ complexes are efficient catalysts for the intramolecular cyclopropanation of 1-diazo-5-hexen-2-one (3) and for the intermolecular cyclopropanation of alkenes, such as styrene and 2-phenylpropene, with ethyl diazoacetate. In all cases, the cyclopropanation products were obtained in high yields. The diastereoselectivity in the intermolecular cyclopropanation of the alkenes and the enantioselectivity in the inter- or intramolecular processes are only moderate.     

CRYSTAL AND MOLECULAR STRUCTURE OF A NEW ISOMER OF THE COMPLEX W2S4[S2P（OEt）2]2

<正> C8H20O4P2S8W2, Mr = 866. 37, monoclinic, space group P21/ n, α= 10. 122(2),b=12. 813(3),c=18. 267(3) A ;β=90. 25(1)°;7 = 2639(2) A3;Z=4; Dc=2. 43gcm-3;λ(Mo Kα) = 0. 71069A ,μ= 110. 80cm-1,F(000) = 1624,final R = 0. 039 for 2906 observed reflections with I≥3σ(I). The tungsten atom in W2S4[S2P (OEt)2]2 is coordinated by five sulfur atoms,forming a square pyramid. Two WS5 units are linked together by sharing a S-S edge.     

ANALYSIS OF FRAGMENT INTERACTION AND ASSIGNMENT OF ELECTRONIC SPECTRUM FOR COMPLEX ION[S2MoS2FeCl2]^2—

<正> The electronic structures of complex ion [S2MoS2FeCl2]2- (1) and its fragments MoS42- (2) and FcCl2(3) have been calculated base on the LCAO-HFS method with restricted open shell or closed shell. The interaction between the fragments 3 and 2 and the formation of complex ion 1 have been discussed. It was found that the Fe(Ⅱ) donated electrons to the Mo(Ⅵ)and accepted electrons from the sulphur ligand and that the stability of complex ion 1 is contributed from both direct and indirect interactions through the bridging sulphur atoms. In addtion, the electron transition energies of complex ion 1 were calculated and its electronic absorptions were assigned. It was shown that the calculated wavelengths of the absorption bands are in agreement with the observed ones.     

氧族桥原子对类立方烷簇[Mo_4X_4Cp_4′]成键特征的影响(X=O,S,Se,Te;Cp′=Cp or Pr~iCp)

本文用EHMO法对(Mo_4X_4Cp′4](X=0,S,Se,Tc)四个类立方烷型簇合物的电子结构进行了计算,结果表明,桥基X从O到Te,前线区域分子轨道中桥基成分明显增加,能级普遍升高;Mo-Mo间作用有所增强;能隙ΔE(LUMO-HOMO)增大;Mulliken键级P的次序为P_(Mo-Se)>P_(Mo-S)>P_(Mo-Tc)>P_(Mo-o)>P_(Mo-Mo),说明第二过渡系元素Mo更倾向于与较重的se桥结合形成类立方烷型簇合物。