VII Transition Metals Research Articles

Electronic properties of germanene on pristine and defective MoS2 : A first-principles study

The synthesis of germanene on semiconducting substrates such as ${\mathrm{MoS}}_{2}$ has revealed that it exhibits a V-shaped density of states around the Fermi level, indicating the presence of Dirac electrons. Further experiments demonstrated that charge inhomogeneities of germanene on ${\mathrm{MoS}}_{2}$ appear as $n$- and $p$-type doped regions, the origin of which is not well understood. In this paper, by means of density functional theory calculations, we study germanene deposited on ${\mathrm{MoS}}_{2}$ considering various defect types and a variety of stacking configurations. We find that some native defects typical to ${\mathrm{MoS}}_{2}$ samples lead to the charge transfer between germanene and ${\mathrm{MoS}}_{2}$. Unlike vacancies and antisite defects, substitution of molybdenum by group IV-V and VII transition metal atoms does not lead to any midgap states, and appears as a plausible explanation for the experimentally observed charge puddles. Our results shed light on the mechanism of breaking the charge neutrality in Dirac materials without altering their electronic properties, which could be important for the realization of lateral $p\text{\ensuremath{-}}n$ junctions based on two-dimensional materials.

Layer parity dependent Raman-active modes and crystal symmetry in ReS2

${\mathrm{ReS}}_{2}$, a group VII transition metal dichalcogenide (TMD), bears immense prospect in optoelectronic, thermoelectric, catalytic, and energy storage applications. Its distorted structure and significant in-plane anisotropy introduce extra degree of freedom but, on the other hand, make it challenging to determine the absolute characteristics of the material. Here, through experimental and theoretical analysis, we present additional phonon modes in the Raman spectrum of layered ${\mathrm{ReS}}_{2}$ which, in literature, are regarded as ambiguous modes arising due to either double resonance or defects. However, we demonstrate that these additional phonon modes arise from the crystal symmetry. This report proves the most followed notion of a layer-independent monolayer (ML)-based unit cell of ${\mathrm{ReS}}_{2}$ to be misleading. We further demonstrate that the observed additional phonon modes are driven by unique layer-dependent variations in the crystal symmetry. Moreover, layer-parity-dependent splitting of ${E}_{g}^{1}$ mode and inversion symmetry breaking are discussed in detail. Such layer-dependent features have remained largely ignored in the literature. The results presented here may open new avenues for the application of this material and resolve several contradictions in its properties including the significance of stacking order, layer-dependent crystal symmetry, and shifting of Raman modes.

Linearly Polarized Excitons in Single- and Few-Layer ReS2 Crystals

Rhenium disulfide (ReS2), a layered group VII transition metal dichalcogenide, has been studied by optical spectroscopy. We demonstrate that the reduced crystal symmetry, as compared to the molybdenum and tungsten dichalcogenides, leads to anisotropic optical properties that persist from the bulk down to the monolayer limit. We find that the direct optical gap blueshifts from 1.47 eV in the bulk to 1.61 eV in the monolayer limit. In the ultrathin limit, we observe polarization-dependent absorption and polarized emission from the band-edge optical transitions. We thus establish ultrathin ReS2 as a birefringent material with strongly polarized direct optical transitions that vary in energy and orientation with sample thickness.

Synthesis, structure and DFT study of cymantrenyl Fischer carbene complexes of group VI and VII transition metals

Bi- and trimetallic carbene complexes of group VI and VII transition metals (Cr, Mo, W, Mn and Re), with CpMn(CO)3 as the initial synthon, have been synthesised according to the classical Fischer methodology. Crystal structures of the novel carbene complexes with general formula [Mx(CO)y-1{C(OEt)(MnCp(CO)3)}], where x = 1 then y = 3 or 6; x = 2 then y = 10, of the complexes are reported. A density functional theory (DFT) study was undertaken to determine natural bonding orbitals (NBOs) and conformational as well as isomeric aspects of the polymetallic complexes. Application of the second-order perturbation theory (SOPT) of the natural bond orbital (NBO) method revealed stabilizing interactions between the methylene C–H bonds and the carbonyl ligands of the carbene metal moiety. These stabilization interactions show a linear decrease for the group VI metal carbene complexes down the group.

Synthesis, Characterization, and Structural Studies of Multimetallic Ferrocenyl Carbene Complexes of Group VII Transition Metals

Fischer carbene complexes of the group VII transition metals (Mn and Re) containing at least two or three different transition metal substituents, all in electronic contact with the carbene carbon atom, were synthesized. The structural features and their relevance to bonding in the carbene multimetal compounds were investigated, as they represent indicators of possible reactivity sites in polymetallic carbene assemblies. For complexes of the type [ML(x){C(OR)R'}] (ML(x) = MnCp(CO)(2) or Re(2)(CO)(9)), ferrocenyl (Fc) was chosen as the R' substituent, while the OR substituent was systematically varied between an ethoxy or a titanoxy group, to yield the complexes 1a (ML(x) = MnCp(CO)(2), R = Et, R' = Fc), 2a (ML(x) = MnCp(CO)(2), R = TiCp(2)Cl, R' = Fc), 3a (ML(x) = Re(2)(CO)(9), R = Et, R' = Fc), and 4a (ML(x) = Re(2)(CO)(9), R = TiCp(2)Cl, R' = Fc). Direct lithiation of the ferrocene with n-BuLi/TMEDA at elevated temperatures, followed by the Fischer method of carbene preparation, resulted in formation of the novel biscarbene complexes with bridging ferrocen-1,1'-diyl (Fc') substituents [{π-Fe(C(5)H(4))(2)-C,C'}{C(OEt)ML(x)}(2)] (1b, ML(x) = MnCp(CO)(2); 3b, ML(x) = Re(2)(CO)(9)) or the unusual bimetallacyclic bridged biscarbene complexes [{π-TiCp(2)O(2)-O,O'}{π-Fe(C(5)H(4))(2)-C,C'}{CML(x)}(2)] (2b, ML(x) = MnCp(CO)(2); 4b, ML(x) = Re(2)(CO)(9)). The target compounds that were isolated displayed a variety of different geometric isomers and conformations. The greater reactivity of the binary dirhenium acylates in solution, compared to that of the cyclopentadienyl manganese acylate, resulted in a complex reaction mixture. Although the stabilization of hydroxycarbene or hydrido-acyl intermediates of dirhenium carbonyls could not be achieved, their existence in solution was confirmed by the isolation of [(π-H)(2)-(Re(CO)(4){C(O)Fc})(2)] (8), the unique dichloro-bridged biscarbene complex fac-[(π-Cl)(2)-(Re(CO)(3){C(OEt)Fc})(2)] (6), the known hydrido complex [Re(3)(CO)(14)H] (5), the acyl complex [Re(CO)(5){C(O)Fc}] (7), and the aldehyde-functionalized eq-[Re(2)(CO)(9){C(OTiCp(2)Cl)(Fc'CHO)}] (9).

The catalytic synthesis of thiacrowns from thiiranes by Group VI and VII transition metal carbonyl complexes

The synthesis of thiacrowns by the catalytic ring opening cyclooligomerization of thiirane has been investigated by using some Group VI and Group VII metal carbonyl complexes. The Group VI catalyst precursors were transition metal complexes of the form M(NCCH 3)(PR 3) x (CO) 5− x ( x=0, M=Cr, Mo and W; x=1, M=Cr, R=Ph; M=W, R=Ph, or OC 6H 4– p-Me). For Group VII, the manganese carbonyl cations: [Mn(NCCH 3)(L)(CO) 4] +, L=CO, PPh 3, PMe 2Ph, PEt 3, PBu 3 and P(OMe) 3 were studied. The yields of the thiacrowns were significantly improved by the addition of dialkyl acetylenedicarboxylates to the reactions catalyzed by the Group VI complexes, but these had no beneficial effect for thiacrown formation for the manganese catalysts. The principal thiacrown products are 1,4,7,10-tetrathiacyclododecane (12S4), 1,4,7,10,13-pentathiacyclopentadecane (15S5) and 1,4,7,10,13,16-hexathiacyclohexadecane (18S6). Some of the manganese catalysts also yield the cyclic polydisulfides (SCH 2CH 2S) n ( 1– 4) (where n=2–5), but the principal side product with the manganese catalysts is thiirane homopolymer. The phosphine-substituted catalysts give better yields of thiacrowns than the parent carbonyls in all cases.

Essays über Metallorganische Chemie V. Stand und Aussichten der Rhenium-Chemie in der Katalyse

The most recent review article on catalytic epoxidation reactions gives a rather discouraging statement of the heavier group VII transition metal compounds as oxidation catalysts [2]: “ The catalytic activity of technetium seems to be comparable to that of rhenium …, and both seem to be low.” The present account briefly describes the status of rhenium chemistry in catalysis, showing that there are many more perspectives than were first believed. It is shown that high-valent organorhenium oxides function as very effective catalysts in both olefin metathesis (heterogeneous catalysis) and in olefin oxidation (homogeneous catalysis). In this content it becomes evident that rhenium chemistry in general has been much less investigated and understood than that of the neighbouring elements tungsten and osmium. Furthermore, work concerning technetium compounds is necessary in order to gain better insight in catalytic and other properties of the corresponding rhenium compounds. Beyond the known, relationship between technetium and rhenium with regard to their inorganic and coordination compounds, the first similarities in the chemistry of their organic compounds are being uncovered, at the same time marked differences cannot be neglected.

Nitrosobenzene as a two-electron ligand in ?-cyclopentadienyl and carbonyl complexes with group VI and VII transition metals

1. Previously unknown derivatives of cymantrene and its rhenium analog [(η5-C5H5)M(CO)2(PhNO)] (M = Mn, Re) with nitrosobenzene as two-electron ligand, and also nitrosobenzene derivatives of group VI B metal carbonyl, were obtained and characterized. 2. All the compounds with PhNO ligands contain phenylnitrene and aniline ions in the mass spectra, the intensity of the latter being maximal. 3. In [W(CO)5(PhNO)], nitrosobenzene is extraordinarily easily reduced to the aniline ligand.

Thermodynamics of transition metal carbonyls II. Mn(CO) 5X, Tc(CO) 5X, Re(CO) 5X (X  Cl, Br, I)

The thermodynamic properties of the Group VII transition metal carbonyl halides M(CO) 5X (X  Cl, Br, I) are evaluated. Thermodynamic functions for the gaseous molecules are computed using literature data or estimated spectroscopic and structural data. Metal-halogen bond energies for the gaseous manganese molecules reported in the literature are reviewed and bond energies for the corresponding technetium and rhenium molecules are estimated. The results are used to compute the enthalpies and Gibbs free energies of formation of the molecules.

Basicity of transition metal carbonyl complexes : IX. An infrared study of lewis acid reactions with cyclopentadienyl and arene derivatives of groups VI and VII transition metal carbonyls and nitrosyls

The different courses of the interactions of cyclopentadienyl and arene derivatives of Group VI and VII transition metal carbonyl and transition complexes with Lewis acids, in solutions, have been studied by IR spectroscopy. The information of adducts involving the metal atom was observed for CpRe(CO) 2L (L = CO, PR 3) with SnCl 4, SnBr 4, TiCl 4; AreneM(CO) 3 (M = Cr, Mo, W) with SnCl 4, TiCl 4; and Ph 3PC 5H 4M(CO) 3 (M = Cr, Mo, W) with TiCl 4 and AlCl 3. Complexes CpM(CO) 2NO and CpM(CO(NO)PPh 3, depending on thier donor and acceptor nature, form adducts involving the oxygen atoms of CO or NO groups or the metal atom. CpCr(NO) 2Cl reacts with Lewis acids via the chlorine atom. The relative basicity of the different sites in the complexes investigated is discussed.

Carbonyl halides of the Group VII transition metals. VI. Further comments on derivatives of rhenium halocarbonyls and Bis(diphenylarsino)methane

A revision is made of the proposed structures of a series of rhenium halocarbonyls with dam on the basis of recent crystallographic evidence and a reassessment of N.M.R. data.

Carbonyl halides of the Group VII transition metals. V. Derivatives of manganese halocarbonyls with Bis(diphenylarsino)methane

The reactions between Mn(CO)5X(X = Cl, Br) and bis(diphenylarsino) methane, dam, have been studied. The most surprising feature of the system is the lack of complexes of the type [Mn(CO)3(dam)X]. Binuclear complexes [Mn2(CO)6(dam)X2] dominate the system and these show unusual disproportionation to Mn0 and Mn11. The reactions with the corresponding ditertiary phosphine, dpm, are much simpler and no binuclear complexes were observed. Infrared and N.M.R. studies have helped to elucidate the structures of the compounds prepared.

Basicity of transition metal carbonyl complexes: VIII. An infrared study of the reaction of aluminium chloride with some cyclopentadienyl and arenecarbonyl transition metal complexes

The interaction of cyclopentadienyl and arene derivatives of carbonyl complexes of Group V, VI and VII transition metals with AlCl 3 in benzene and CH 2Cl 2 solutions has been studied by IR spectroscopy. The formation of adducts involving the metal atom or the carbonyl oxygen atom was observed. The reaction path depends on the structure of the complex and on the nature of the solvent. In benzene the adduct formation at the CO ligand is more favourable than in CH 2Cl 2 solution. Introduction of a phosphine ligand in the place of the CO group or introduction of donor substituents into the π-ring increases the basicity of the central metal atom and makes adduct formation at the metal more probable. The basicity of the metal atom in complexes with the same ligands increases with increases of atomic number in the group. CpRe(CO) 2Br 2 forms adducts with AlCl 3 at the bromine atoms ( 1 1 and sol1 2 ). For Fe(CO) 4PPh 3 and Fe(CO) 3(PPh 3) 2 complex formation takes place at the iron atom.

Recent studies in photoinitiated polymerization

AbstractTwo types of photoinitiating systems are considered in this paper: (i) Group VII transition metal carbonyls in the presence of fluoro‐olefins and (ii) vanadium chelates and their derivatives.(i) The photoinitiating activities of Mn2(CO)10 and Re2(CO)10 in association with CF2 :CFCl, CF2 :CHF, CF2 :CH2, or CHF:CH2 have been studied. Methyl methacrylate was the monomer and the incident wavelengths were 436 nm and 365 nm for the manganese and Re2 (CO)10 at relatively low [T]. The kinetics of photoinitiation have been investigated. With rhenium derivatives, respectively. Of the above fluoro‐olefins, only CF2 :CFCl forms a photoinitiating system with Mn2(CO)10 while all are active with Re2(CO)10.In all the active systems the rate of polymerization ω increases with increasing fluoro‐olefin (T) concentration but finally reaches a plateau value; plateau conditions are achieved with Mn2(CO)10/CF2:CFCl (the system studied in most detail) the “sharpness” of the ω ‐ [CF2:CFCl] relation increases as the incident intensity decreases and the rate of consumption of manganese carbonyl is equal to the rate of initiation over the whole range of [CF2 :CFCl]. Quantum yields of photoinitiation have been determined for the various systems; they range from unity for Re2 (CO)10/CF2:CHF to 0.35 for Re2 (CO)10/CF2:CH2.Polymers prepared with the aid of these photoinitiators carry terminal groups in which the metal is covalently attached to the polymer chain through a unit derived from the fluoro‐olefin; for example with Mn2(CO)10/CF2:CFCl the terminal groups are (CO)5MnCF2CFCl. The initiating radicals are therefore formed by addition of an activated metal carbonyl species to the fluoro‐olefin and not by halogen abstraction as in systems such as Mn2(CO)10/CCl4, Mn2(CO)10/CBr4.On the basis of these and other results a mechanism is proposed in which photolysis of manganese carbonyl in methyl methacrylate solution leads reversibly to dissimilar fragments, only one of which forms an initiating radical with the fluoro‐olefin.The activity of fluoro‐olefins in these reactions (compared to the inertness of common vinyl monomers) is attributed to their ability to form relatively strong transition metal‐carbon bonds.(ii) Chloro‐oxobis‐(2,4‐pentanedionato) vanadium (V), VO(acac)2Cl, irradiated with light of Λ = 365 nm, initiates free‐radical polymerization of methyl methacrylate with a quantum yield of 0.02. The primary act is scission from the molecule of a chlorine atom, which is the initiating species. In the presence of an electron‐donor D (e.g., dimethylsulfoxide) ionic complexes a− are formed and photoiniate with much higher quantum yields (29‐fold in the case of dimethylsulfoxide). We believe that in these systems the primary act is electron‐transfer leading to D+ and VO(acac)2; subsequent reactions of D± then generate initiating radical species.Photolysis of the chelate VO(Q), OMe, in which Q iepresents the 8‐quinolyloxo ligand, generate initiating radicals which comprise both CH, O and CH, OH. These results provide to route to photosensitive polymers with side‐chains carrying vanadium chelates which may be used to synthesize graft copolymers and polymer networks. Preliminary experiments have indicated the feasibility of these processes.

Carbonyl halides of the Group VII transition metals. IV. Carbonyl halide complexes of rhenium(III)

The new halocarbonyl complexes of rhenium(III), [Re(CO)2X4]- (X = Cl, Br), have been synthesized by the halogen oxidation of [Re(CO)3X]4. On the basis of various physical measurements a cis octahedral structure is proposed for these anions.

Carbonyl halides of the Group VII transition metals. I. Halocarbonyls and halocarbonyl anions of rhenium(I)

The rhenium(1) halocarbonyls Re(CO)5X (X = Cl, Br, I) may be readily prepared by refluxing a solution of the free hexahalorhenate(1V) acid in hydrohalic acid with formic acid. Visible absorption spectral studies indicate that formation of the halocarbonyls takes place following an initial reduction to rhenium(111), but no halocarbonyls of this intermediate oxidation state were isolated. The concentration of rhenium, as well as the relative amounts of hydrohalic and formic acids in the reaction mixture, are important factors for efficient production of the halocarbonyls. If the halocarbonyls are refluxed in formic acid containing a decreased proportion of hydrohalic acid, decarbonylation occurs giving the halocarbonyl anions [Re(CO)4X]2- which can be isolated as their caesium salts or as the parent halocarbonyls [Re(CO)4X]2. Continued refluxing of the formic acid solution causes still further decarbonylation giving the halocarbonyl anions [Re(CO)3X3]2- (X = Cl, Br) which may also be isolated as their caesium salts. Alternatively, evaporation to dryness of these solutions without addition of cations gives the new rhenium(1) halocarbonyl aquo complexes Re(CO)3(H2O)2X (X = Cl, Br). In the case of the iodo system, decarbonylation did not proceed to the tricarbonyl stage.

Lewis Basicity of Metals. II. The Interaction of Group VI and VII Transition Metal Cyclopentadienyl Derivatives with BF3, BCl3, and B2H6

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTLewis Basicity of Metals. II. The Interaction of Group VI and VII Transition Metal Cyclopentadienyl Derivatives with BF3, BCl3, and B2H6M. P. Johnson and D. F. ShriverCite this: J. Am. Chem. Soc. 1966, 88, 2, 301–304Publication Date (Print):January 1, 1966Publication History Published online1 May 2002Published inissue 1 January 1966https://doi.org/10.1021/ja00954a022RIGHTS & PERMISSIONSArticle Views306Altmetric-Citations65LEARN 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 (490 KB) Get e-Alerts Get e-Alerts