Solvothermal syntheses and crystal structures of two new thiogermanates [M(dap)3]4Ge4S10Cl4 (M?=?Co, Ni) with metal complexes as counterions

Abstract  

Two new transition-metal thiogermanates [M(dap)₃]₄Ge₄S₁₀Cl₄ (M = Co, Ni; dap = 1,2-propanediamine) have been solvothermally synthesized and structurally characterized. The two thiogermanates are isostructural and consist of discrete Ge₄S₁₀⁴⁻ adamantane-like ions, free Cl⁻ ions, and [M(dap)₃]²⁺ cations as counterions. The Ge₄S₁₀⁴⁻ anion is built from corner-sharing connection of four GeS₄⁴⁻ tetrahedra. Although some chalcogenidogermanates have been obtained by use of in situ generated transition-metal complexes as structure-directing agents under mild solvothermal conditions, their anions are usually dimeric [Ge₂Q₆]⁴⁻ (Q = S, Se) species. The new thiogermanates are rare examples of adamantane-like (Ge₄S₁₀⁴⁻) thiogermanates combined with transition-metal complexes. Their optical properties have been investigated by UV–Vis spectra.     

Reactivity of Binary and Ternary Sulfur Halides towards Transition-Metal Compounds

Binary sulfur fluorides exhibit an interesting reactivity towards transition metal complexes. They open up routes for the generation of sulfur-containing building blocks. Often ligands with particular properties can be constructed. This includes their ability to transfer sulfur atoms or polysulfide units as well as fluorination reactions. This Minireview provides an insight into the reactivity of the binary and ternary sulfur halides S₂Cl₂, SCl₂, SF₄, SF₆ and SF₅Cl towards transition-metal compounds.     

A new synthesis and the electrochemical behaviour of nickel(II) dithiophosphate and dithiophosphinate complexes

Summary The [Ni(S₂PR₂)₂] complexes (R=i-PrO, PhO, or Et) can be conveniently prepared by reaction of [Ni{P(OPh)₃}₄] with [R₂P(S)S]₂ (R=i-PrO, PhO, or Et) in refluxing CHCl₃. The electrochemical behaviour of the complexes in CH₂Cl₂ and MeCN has been studied by cyclic voltammetry and coulometry. The oxidation of complexes at a glassy carbon reveals an e.c. mechanism. The [Ni(S₂PR₂)₂] complexes undergo a one-electron irreversible reduction.     

Spectral and Structural Studies of the Copper(II) Complexes of 3, 4‐Hexanedione Bis(3‐azacyclothiosemicarbazones)

Copper(II) complexes of 3, 4‐hexanedione bis(piperidyl‐ and bis(hexamethyleneiminylthiosemicarbazone), H₂Hxpip and H₂Hxhexim, respectively, have been prepared and studied spectroscopically. The bis(thiosemicarbazones) have been characterized by their melting points, as well as IR, electronic and ¹H NMR spectra. Upon formation of their copper(II) complexes, loss of the hydrazinic hydrogen atoms occurs, and the ligands coordinate as dianionic, tetradentate N₂S₂ ligands. The crystal structures of H₂Hxpip, its 4‐coordinate copper(II) complex, [Cu(Hxpip)], and the related [Cu(Hxhexim)] have been determined by single crystal x‐ray diffraction. The nature of the four‐coordinate copper(II) complexes have also been characterized by ESR, IR, and electronic spectroscopy, as well as magnetic moments and elemental analyses.     

Stability and bonding of carbon(0)-iron−N2 complexes relevant to nitrogenase co-factor: EDA-NOCV analyses

The factors/structural features which are responsible for the binding, activation and reduction of N₂ to NH₃ by FeMoco of nitrogenase have not been completely understood well. Several relevant model complexes by Holland et al. and Peters et al. have been synthesized, characterized and studied by theoretical calculations. For a matter of fact, those complexes are much different than real active N₂-binding Fe-sites of FeMoco, which possesses a central C(4-) ion having an eight valence electrons as an μ₆-bridge. Here, a series of [(S₃C(0))Fe(II/I/0)-N₂]^n- complexes in different charged/spin states containing a coordinated σ- and π-donor C(0)-atom which possesses eight outer shell electrons [carbone, (Ph₃P)₂C(0); Ph₃P→C(0)←PPh₃] and three S-donor sites (i.e. ^-S-Ar), have been studied by DFT, QTAIM, and EDA-NOCV calculations. The effect of the weak field ligand on Fe-centres and the subsequent N₂-binding has been studied by EDA-NOCV analysis. The role of the oxidation state of Fe and N₂-binding in different charged and spin states of the complex have been investigated by EDA-NOCV analyses. The intrinsic interaction energies of the Fe−N₂ bond are in the range from −42/−35 to −67 kcal/mol in their corresponding ground states. The S₃C(0) donor set is argued here to be closer to the actual coordination environment of one of the six Fe-centres of nitrogenase. In comparison, the captivating model complexes reported by Holland et al. and Peter et al. possess a stronger π-acceptor C-ring (S₂C_ring donor, π-C donor) and stronger donor set like CP₃ (σ-C donor) ligands, respectively.     

Tris-Nethyl, m-tolyl)dithiocarbamato complexes of arsenic(III), antimony(III) and bismuth(III)

Tris-N(ethyl, m-tolyl) dithiocarbamato complexes of arsenic(III), antimony(III) and bismuth(III) abbreviated as As(S₂CNRR′)₃ Sb(S₂CNRR′)₃ and Bi(S₂CNRR′)₃, respectively, where R  C₂H₅ and R′  m-C₆H₄CH₃, have been synthesized. These complexes have been characterized on the basis of elemental analyses, molecular weight determinations, conductance measurements and infrared spectral studies. Thermal studies of these complexes have been carried out in nitrogen and air to determine their modes of decomposition. Kinetic parameters, such as apparent activation energy and order of reaction, have been determined by the graphical method of Coats and Redfern [1].     

Phenyl-cyclohexyl enaminoketone ligands and their Cu(II) complexes

Abstract

The liquid crystalline properties of 1-(alkylamino)-3-[(4″-hexyl-trans-cyclohexyl-4′-phenyl]-prop-1-en-3-one-s, from methyl to octadecyl, and their copper (II) complexes have been examined by optical, DSC, X-ray and EPR methods. The compounds are enantiotropic nematogens except those having the shortest and the longest terminal chains. Short chains promote the S_A phase in both ligands and complexes, whereas long chains promote S_C and crystal H phases for the ligands or S_A and S_C phases for the complexes. A partly bilayer smectic A_d phase is observed from ligands terminated with short non-polar substituents. Direct isotropisation from the crystal H phase for some of the compounds, as well as other phase transitions have been studied. The molecular shape of the complexes and the organization of their mesomorphic phases are discussed, based on the refractive indices and X-ray data.     

Solvent isotope effects upon the kinetics of some simple electrode reactions

The effects of replacing H₂O with D₂O solvent upon the electrochemical kinetics of simple transition-metal redox couples containing aquo, ammine or ethylenediamine ligands have been investigated at mercury electrodes as a means of exploring the possible contribution of ligand-aqueous solvent interactions to the activation barrier to outer-sphere electron transfer. The general interpretation of solvent isotope effects upon electrode kinetics is discussed; it is concluded that double-layer corrected isotopic rate ratios (k^H/k^D)^E determined at a constant electrode potential vs. an aqueous reference electrode, as well as those determined at the respective standard potentials in H₂O and D₂O (k_S^H/k_S^D), have particular significance since the solvent liquid-junction potential can be arranged to be essentially zero. For aquo redox couples, values of (k_S^H/k_S^D) were observed that are substantially greater than unity and appear to be at least partly due to a greater solvent-reorganization barrier in D₂O arising from ligand-solvent hydrogen bonding. For ammine and ethylenediamine complexes values of (k^H/k^D)^E substantially greater than, and smaller than, unity were observed upon the separate deuteration of the ligands and the surrounding solvent respectively. Comparison of isotope rate ratios for corresponding electrochemical and homogeneous outer-sphere reactions involving cationic ammine and aquo complexes yields values of (k^H/k^D) for the former processes that are typically markedly larger than those predicted by the Marcus model from the homogeneous rate ratios. These discrepancies appear to arise from differences in the solvent environments in the transition states for electrochemical and homogeneous reactions.     

NMR Reveals That a Highly Reactive Nonheme FeIV=O Complex Retains Its Six-Coordinate Geometry and S=1 State in Solution

The [Fe^IV(O)(Me₃NTB)]²⁺ (Me₃NTB=tris[(1-methyl-benzimidazol-2-yl)methyl]amine) complex 1 has been shown by Mössbauer spectroscopy to have an S=1 ground state at 4 K, but is proposed to become an S=2 trigonal-bipyramidal species at higher temperatures based on a DFT model to rationalize its very high C−H bond-cleavage reactivity. In this work, ¹H NMR spectroscopy was used to determine that 1 does not have C₃-symmetry in solution and is not an S=2 species. Our results show that 1 is unique among nonheme Fe^IV=O complexes in retaining its S=1 spin state and high reactivity at 193 K, providing evidence that S=1 Fe^IV=O complexes can be as reactive as their S=2 counterparts. This result emphasizes the need to identify factors besides the ground spin state of the Fe^IV=O center to rationalize nonheme oxoiron(IV) reactivity.     

Homogeneous Catalysis with Dicationic PdII Complexes: Aldol reaction of methyl isocyanoacetate with benzaldehyde

A series of dicationic Pd^II-acetonitrile complexes containing bi- and tridentate nitrogen and bidentate phosphine ligands (some of which are chiral) has been prepared as their BF₄ salts. The molecular structures for two of these, [Pd(CH₃CN)₂(bipy)] (BF₄)₂ ( 4 ) and [Pd(CH₃CN)((pybox)(i-Pr))] (BF₄)₂((S,S)-pybox(i-Pr) = 2,6-bis[(S)-4′-isopropyloxazolin-2′-yl]pyridine, 5 ) have been determined by X-ray diffraction. All of these complexes are shown to be effective homogeneous catalysts for the aldol-type condensation of the isonitrile, methyl isocyanoacetate, with benzaldehyde. Two isonitrile complexes, [Pd(2,2′-bipyridyl)(CNCH₂COOCH₃)₂] (BF₄)₂ and [Pd((S,S)-pybox(i-Pr))(CNCH₂COOCH₃)] (BF₄)₂, have also been prepared.     

Ruthenium dihydride complexes as enyne metathesis catalysts

Ruthenium–catalyzed enyne metathesis is a reliable and efficient method for the formation of 1,3-dienes, a common structural motif in synthetic organic chemistry. The development of new transition-metal complexes competent to catalyze enyne metathesis reactions remains an important research area. This report describes the use of ruthenium (IV) dihydride complexes with the general structure RuH₂Cl₂(PR₃)₂ as new catalysts for enyne metathesis. These ruthenium (IV) dihydrides have been largely unexplored as catalysts in metathesis-based transformations. The reactivity of these complexes with 1,6 and 1,7-enynes was investigated. The observed reaction products are consistent with the metathesis activity occurring through a ruthenium vinylidene intermediate.     

Syntheses and characterization of copper(II) complexes with Schiff-base ligands derived from ethylenediamine,diphenylethylenediamine and nitro,bromo and methoxy salicylaldehyde

Copper(II) quelates with Schiff bases derived from ethylenediamine, 1R,2R-(+)- or 1S,2S-(−)-1,2-diphenylethylenediamine and 5-X-salicylaldehyde (X=OCH₃, H, Br, NO₂) have been synthesized and characterized by elemental analysis and IR and UV-visible spectroscopies. The ORD and CD spectra of the chiral ligands and their related complexes have also been measured. The absorption and CD spectra of the metal complexes in the visible region are consistent with near square planar coordination geometries. Trends in absorption spectra over the series of complexes can be correlated with electronic effects of the substituents at position 5 of the salicylaldehyde. The sign patterns of the CD spectra in both UV and visible regions suggest the prevalence of δ and λ conformations for the chelate ring in the complexes of Schiff bases derived, respectively, from R,R- and S,S-diamines. Specific features of the CD spectra of the metal complexes are discussed in terms of the exciton chirality method.     

Electron-Rich Half-Sandwich Complexes—Metal Bases par excellence

Electron-rich, half-sandwich complexes of the type C_nR_nML₂ or C_nR_nMLL′ are built up of an aromatic five- or six-membered ring, a d⁸-metal, and either a pair of two-electron donors or an equivalent chelating ligand. Such complexes behave like Lewis bases and react with a wide variety of electrophiles, El or ElX, to form products with a new metal-element bond. According to their reactivity they are comparable to the Vaska-type compounds. Certain of the products obtained after addition of the electrophile undergo interesting subsequent reactions in which, for example, metal complexes containing molecules that are unstable in the free state, such as CS, CSe, CH₂S, CH₂Se, CH₂Te, CH₃CHS, CH₃CHSe, CH₂?C?S, CH₂?C?Se, and CH₂?C?Te are formed. Moreover, cycloadditions as well as reactions with coordinatively unsaturated transition-metal compounds which result in formation of heterometal binuclear complexes demonstrate that the metal bases C_nR_nML₂ and C_nR_nMLL′ are valuable synthetic building blocks. Furthermore, very recent investigations have indicated links between metal basicity and the problem of C? H activation.     

First-Principles Study of Ultrathin Molybdenum Sul des Nanowires: Electronic and Catalytic Hydrogen Evolution Properties

Molybdenum sulfides nanomaterials, such as one-dimensional (1D) nanotubes, nanoribbons, and two-dimensional (2D) nanosheets, have attracted intensive research interests for their novel electronic, optical, and catalytic properties. On the basis of first-principles calculation, here, we report a new series of 1D ultrathin molybdenum sulfides nanowires, including Mo₂S₆、Mo₃S₆ and Mo₆S₁₀ nanowires. Our results demonstrate that these ultrathin nanowires are both thermal and lattices dynamically stable, confirmed with the calculated phonon spectrum and Born-Oppenheimer molecular dynamic simulation at the temperature up to 600 K. The calculated elastic constant is 21.33, 103.22, and 163.00 eV/? for Mo₂S₆, Mo₃S₆, and Mo₆S₁₀ nanowires, respectively. Mo₂S₆ and Mo₃S₆ nanowires are semiconductors with band gap of 1.55 and 0.46 eV, while Mo₆S₁₀ nanowires is metal, implying their potential applications in electronics and optoelectronics. In particular, ultrathin molybdenum sulfides nanowires can be used as catalysts for hydrogen evolution reaction. The calculated Gibbs free energy change for hydrogen evolution is about -0.05 eV for Mo₂S₆ nanowire, comparable with those of Pt and H-MoS₂. The prediction of these 1D molybdenum sulfides nanowires may enrich the 1D family molybdenum sulfides and make a supplement to understand the high performance of hydrogen evolution reaction in transition-metal dichalcogenides.     

Formal Co(0), Fe(0), and Mn(0) complexes with NHC and styrene ligation

The limited knowledge on low-coordinate zero-valent transition-metal species has intrigued great synthetic efforts in developing ligand sets for their stabilization. While the combined ligand set of N-heterocyclic carbene (NHC) with vinylsilanes was the only known ligand system amenable to the stabilization of three-coordinate formal zero-valent cobalt, iron, and manganese complexes, the exploration on other ligands has proved that the ligand set of NHCs with styrene is equally effective in stabilizing three-coordinate formal zero-valent metal complexes in the form of (NHC)M(η²-CH₂CHPh)₂ (NHC = IPr, IMes; M = Co, Fe, Mn). These styrene complexes can be prepared by the one-pot reactions of MCl₂ with styrene, NHC and KC₈, and have been characterized by various spectroscopic methods. Preliminary reactivity study indicated that the interaction of [(IMes)Fe(η²-CH₂CHPh)₂] with DippN₃ produces the iron(IV) bisimido complex [(IMes)Fe(NDipp)₂] and styrene, which hints at the utility of these zero-valent metal styene complexes as synthons of the mono-coordinate species (NHC)M(0).     

Four-coordinated palladium(II) and platinum(II) complexes containing the Lewis-acid {M(S2CNHR)(PR3′)} group combined with a variety of other ligands

A new series of four-coordinated Pd(II) and Pt(II) complexes in which the Lewis-acid (14-electron) {M(S₂CNHR)(PR₃′)} group is combined with a variety of other ligands (such as RHNCS₂^?, I^?, SCN^?, SnCl₂I^?) has been synthesised and studied. The structures of the new compounds are discussed in relation to their specroscopic, magnetic and thermal properties. In the case of [M(S₂CNHR)₂(PR₃′)] complexes both the spectroscopic data (IR, ¹H NMR, UV-Vis) and their thermal behaviour strongly suggest the coexistence of two kinds of gem-disulphide ligands, one acting as a bidentate ligand and the other one as a unidentate. Also it was confirmed that the chemical behaviour of the bis(N-alkyldithiocarbamato) complexes of Pd(II) and Pt(II) towards tertiary phosphines is similar to that of the isoelectronic xanthate complexes rathe than to the bis(N,N-dialkyldithiocarbamato) complexes.     

Amine-tetrachloromethane charge transfer complexes: a structural and computational study

Abstract

Amine-tetrachloromethane charge-transfer complexes have recently been shown to be useful intermediates in transition-metal free solar light-assisted organic synthetic chemistry. Of particular promise is the complex of 1,4-diazabicyclo[2.2.2]octane (DABCO) which may serve as a starting point for several potential reactions involving oxidation of organic compounds. Here we disclose the crystal structure of the [DABCO???CCl₄] complex, and computational studies of two possible complex structures in their ground state, as well as in their first singlet and first triplet excited states.     

Untersuchungen zur Alkylierung von Bis-Stilbendithiolato-Komplexen des Ni(II), Pd(II) und Pt(II)

Investigation on the Alkylation of Bis-Stilbendithiolato Complexes of Ni^II, Pd^II, and Pt^II Alkylation reactions of co-ordinated ligands of the type of ethylene-bisthiol R₂S₂C₂²-proceed different depending on the substituents R. The neutral complexes isolated by a alkylation of the nickel bis-chelates (R = phenyl) according to Schrauzer and Rabinowitz and formulated by these authors as mixed ligand chelates of dithiolate and diether, were identified by us as complexes of the monoethers of the ligand. These nickel (II) complexes of the mono-ethers can not be alkylated further by alkyliodides. Oxidative coupling of two ligands yields disulfides which have been identified by mass spectroscopy thus indicating the original position of attack of the alkylating reagent. The formation of bis-monether complexes is reflected by the different charges on the S atoms of the model complex [Ni(CH₃S₂C₂H₂)(S₂C₂H₂)]- obtained from EHT and CNDO calculations. Both possible stereo-isomers have been isolated of the bis-methylmonether complex of Pt(II). Trans-[M((CH₃)(S₂C₂Ph₂))₂] (M = Ni(II), Pd(II)) form CH₂Cl₂ adducts. By treating the Ni-bis complexes of the monoalkylthioethers with iodine polyiodides are prepared. Binuclear Pd(II) complexes of composition [Pd₂((R)(S₂C₂Ph₂))₂Cl₂] could be prepared by metal exchange.     

REACTION BETWEEN [PdCl4]2- AND 5,5-DIMETHYL-2-THIOXOIMIDAZOLIDIN-4-ONE

Abstract

The reaction between 5,5-dimethyl-2-thioxoimidazolidin-4-one (H2L) and [PdCl₄]^2- has been studied in aqueous solution by potentiometric and spectrophotometric measurements. In the presence of the palladium salt, H₂L is completely monodeprotonated (HL^?); from spectrophotometric measurements, only two complexes having 1:1 and 1:2 Pd/ligand mol ratios have been identified. Potentiometric titrations, carried out on solutions with 1:1, 1:2, 1:3 and 1:4 metal/ligand mol ratios, show that these complexes must be formulated as Pd(HL)₂ and [Pd₂(HL)₂(μ-H₂O)(μ-OH)]⁺. Ionization constants of the pure ligand and formation constants of the complexes give pH distribution curves of the various species and the spectra of the two complexes. From MeOH, S-coordinated Pd(H₂L)_nCl₂ (n = 2–4) complexes have been separated in the solid state; from water, two complexes of formula Pd(H₂L)(HL)Cl and Pd(HL)Cl have been obtained with HL^? N,S-coordinated to the metal.