Phase transitions in two-dimensional anisotropic chain systems: submonolayers of Sr adsorbed on Mo(112)

Ordered phases of Sr on Mo(112) and their phase transitions have been studied up to one physical monolayer as a function of both coverage and temperature using optical LEED. Starting at a coverage of 0.07, islands of a p(8×1) structure are formed at 100 K, which coexist with a disordered lattice gas. The formation of incommensurate structures with properties of floating solids starts already at coverages slightly above the completed p(8×1) commensurate structure (θ=0.125). The latter itself behaves like a floating solid and undergoes a depinning transition at T≈125 K, similar to the next commensurate structure, p(5×1), which is formed at θ=0.20. Floating solids are found in the whole coverage range between 0.12 and 0.23. At higher coverage coexistence between p(5×1) and c(2×2) structures is found, which melt by forming intermediate two-dimensional eutectics, i.e. coexistence regions with their melts, with an eutectic point at θ=0.37, T_eu=310 K. Close to a coverage of 0.5 a homogenous phase is formed, which disorders by a continuous phase transition, as explicitly tested by determination of the critical exponents β of the order parameter and ν of the correlation length. It is shown that the system belongs to the universality class of the Ising model. An incommensurate phase is again formed at higher coverage due to uniaxial compression of the layers. The behaviour at low coverages can be qualitatively understood assuming lateral interactions along the furrows mainly caused by dipole–dipole interactions and electrostatic screening of the adsorbate induced charge redistribution.     

Ferrocenyl‐Functionalised Molybdenum Imido Complexes: An Approach to Redox‐Tunable Olefin Polymerisation Catalysts

[(FcdippN)₂MoCl₂(DME)] ( 1 ) was used as starting material for the synthesis of the novel ferrocenyl‐functionalised complexes [(FcdippN)₂Mo(CH₂CMe₂Ph)₂] ( 2 ), [(FcdippN)₂Mo(OTf)₂(DME)] ( 3 ), and [(FcdippN)Mo(CHCMe₂Ph)(O^tBu)₂] ( 4 ) (Fcdipp = 4‐ferrocenyl‐2,6‐diisopropylphenyl). The crystal structure of 2 was determined. Electrochemical investigations by cyclic voltammetry suggest a communication of the ferrocenyl unit and the molybdenum centre in these compounds. The monoalkylation of [(DippN)₂MoCl₂(DME)] ( 5 ) to [(DippN)₂Mo(CH₂CMe₂Ph)Cl] ( 6 ) (Dipp = 2,6‐diisopropylphenyl) was achieved.     

Über das Lithiumchloromolybdat Li[Mo6Cl13]

On the Lithium Chloromolybdate Li[Mo₆Cl₁₃] Li[Mo₆Cl₁₃] was obtained as single phase product from a solid state reaction of MoCl₅, Mo powder, and LiCl at 800 °C. The structure as refined by single crystal X‐ray diffraction, contains one‐dimensional [Mo₆Cl Cl Cl ]^– chains, formed by Cl^a–a bridges. Lithium ions are located in tunnels along the chain‐direction, each of them being surrounded by a distorted tetrahedral arrangement of outer chlorine ligands (Cl^a) belonging to four different clusters.     

Luminescent and Photoredox-Active Molybdenum(0) Complexes Competitive with Isoelectronic Ruthenium(II) Polypyridines

Ruthenium(II) complexes with chelating polypyridine ligands are among the most frequently investigated compounds in photophysics and photochemistry, owing to their favorable luminescence and photoredox properties. Equally good photoluminescence performance and attractive photocatalytic behavior is now achievable with isoelectronic molybdenum(0) complexes. The zero-valent oxidation state of molybdenum is stabilized by carbonyl or isocyanide ligands, and metal-to-ligand charge transfer (MLCT) excited states analogous to those in ruthenium(II) complexes can be established. Microsecond MLCT excited-state lifetimes and photoluminescence quantum yields up to 0.2 have been achieved in solution at room temperature, and the emission wavelength has become tunable over a large range. The molybdenum(0) complexes are stronger photoreductants than ruthenium(II) polypyridines and can therefore perform more challenging chemical reductions. The triplet nature of their luminescent MLCT states allows sensitization of photon upconversion via triplet-triplet annihilation, to convert low-energy input radiation into higher-energy output fluorescence. This review summarizes the current state of the art concerning luminescent molybdenum(0) complexes and highlights their application potential. Molybdenum is roughly 140 times more abundant and far cheaper than ruthenium, hence this research is relevant in the greater context of finding more sustainable alternatives to using precious and rare transition metals in photophysics and photochemistry.     

[Mo12S12O12(OH)12(H2O)6]: A Cyclic Molecular Cluster Based on the [Mo2S2O2]2+ Building Block

The pH-dependent self-condensation of the [Mo ₂ S ₂ O ₂ ] ²⁺ complex fragment gives the wheellike Mo₁₂ cluster depicted on the right (ball-and-stick model; large balls: S, medium balls: O, small balls: Mo). Applying this synthetic strategy to other starting materials could provide access to other polyoxothiometalates with well-defined cavities.     

Zur Reaktion von tert-Butyl-phosphaalkin mit Molybdänkomplexen

Reaction of tert -Butyl-phosphaalkyne with Molybdenum Complexes The reaction of tBuC≡P with [(CH₃CN)₃Mo(CO)₃] leads to the complex [Mo(CO)₄〈Mo(CO)₂(η⁴-P₃CtBu){η⁴-P₂(CtBu)₂}〉] 1 as well as to the alkyne complexes [Mo(CO)₄〈{P₃(CtBu)₂}{Mo(CO)₂(CtBu)}{η³-P₂(CtBu)₂}〉] 2 and [Mo(CtBu){η⁴-P₂(CtBu)₂(CO)}{η⁵-P₃(CtBu)₂}] 3 . All compounds are characterized by X-ray structural analysis, by NMR- and IR spectroscopy and by mass spectrometry. In complex 1 a 1,3-diphosphacyclobutadiene and a 1,2,4-triphosphacyclobutadiene are connected by two molybdenum carbonyl centres. In 2 a 1,3-diphosphacyclobutadiene is π- and a novel 1,2,4-triphospholyl ligand is σ-bonded at two Mo centres. A characteristic feature of 3 besides a π co-ordinated 1,2,4-triphospholyl ligand is a 3,4-diphosphacyclopentadienone as ligand, formed via CO insertion during the cyclodimerisation of two phosphaalkynes.     

钼蓝光度法测定蔗糖的研究

试验中发现,在0.27 mol.L-1硫酸介质中,钼酸铵与蔗糖发生显色反应生成钼蓝,所生成的钼蓝最大吸收波长在700 nm,蔗糖溶液在0.15~19.07 mg.L-1服从比耳定律,表观摩尔吸光系数为1.35×104L.mol-1.cm-1。方法的选择性良好,用于甘蔗汁样品的测定,结果的RSD在0.53%~0.66%之间,相应于测定的蔗糖浓度范围为119~157 g.L-1,回收率在97.9%~102.4%。     

Synthese und Struktur von Mo2NCl7

Synthesis and Structure of Mo₂NCl₇ The reaction of VN with MoCl₅ at 175 °C in a sealed glass ampoule yields the molybdenum(V) nitride chloride Mo₂NCl₇ in form of air sensitive black crystals with the triclinic space group P1¯ and a = 905.7(8); b = 975.4((6); c = 1283.4(8) pm, α = 103.13(4)°; β = 109.83(5)° und γ = 98.58(5)°. The crystal structure is built up from dinuclear units [Mo₂N₂Cl₇]^3— and [Mo₂Cl₇]³⁺, which are connected by asymmetric nitrido bridges to form endless chains. Within both dinuclear units the Mo atoms are bridged by three Cl atoms resulting in a Mo‐Mo distance of 349.2(3) pm in the unit [Mo₂N₂Cl₇]^3—. In case of [Mo₂Cl₇]³⁺, however, a shorter Mo‐Mo distance of 289.4(3) pm is observed, which can be interpreted by a single bond. Correspondingly a reduced magnetic moment of 0.95 B.M. per Mo atom is observed.     

Synthese und Kristallstrukturen der Nitrido‐Chloro‐Molybdate [Mg(THF)4{NMoCl4(THF)}2] · 4 CH2Cl2 und [Li(12‐Krone‐4)(NMoCl4)]2 · 2 CH2Cl2

Syntheses and Crystal Structures of the Nitrido‐chloro‐molybdates [Mg(THF)₄{NMoCl₄(THF)}₂] · 4 CH₂Cl₂ and [Li(12‐Crown‐4)(NMoCl₄)]₂ · 2 CH₂Cl₂ Both the title compounds as well as [Li(12‐crown‐4)₂]⁺MoNCl₄^– were made from MoNCl₃ and the chlorides MgCl₂ and LiCl, respectively, in dichloromethane suspensions in the presence of tetrahydrofuran and 12‐crown‐4, respectively. They form orange‐red moisture‐sensitive crystals, which were characterized by their IR spectra and partly by crystal structure analyses. [Mg(THF)₄{NMoCl₄(THF)}₂] · 4 CH₂Cl₂ ( 1 ): space group C2/m, Z = 2, lattice dimensions at –50 °C: a = 1736.6(1), b = 1194.8(1), c = 1293.5(2) pm; β = 90.87(1)°; R₁ = 0.037. In 1 the magnesium ion is coordinated octahedrally by the oxygen atoms of the four THF molecules and in trans‐position by the nitrogen atoms of the two [N≡MoCl₄(THF)]^– ions. [Li(12‐crown‐4)(NMoCl₄)]₂ · 2 CH₂Cl₂ ( 2 ): space group P 1, Z = 1, lattice dimensions at –70 °C: a = 930.4(1), b = 957.9(1), c = 1264.6(1) pm; α = 68.91(1)°, β = 81.38(1)°, γ = 63.84(1)°; R₁ = 0.0643. 2 forms a centrosymmetric ion ensemble in the dimeric cation of which, i. e. [Li(12‐crown‐4)]₂²⁺, the lithium ions on the one hand are connected to the four oxygen atoms each of the crown ether molecules in a way not yet known; and in addition, each of the lithium ions enters into a intermolecular Li–O bond with neighboring crown ether molecules under formation of a Li₂O₂ four‐membered ring. The two N≡MoCl₄^– counterions are loosely coordinated to one oxygen atom each of the crown ether molecules with Mo–O distances of 320.2 pm.     

Synthesis,Structure, and Decomposition of (NH4)2[Mo6Cl14] · H2O

(NH₄)₂[Mo₆Cl₁₄] · H₂O ( 1 ) was prepared from reactions of MoCl₂ in ethanol with aqueous NH₄Cl solution. It crystallizes in the monoclinic space group I2/a (no. 15), Z = 4 with a = 912.3(1), b = 1491.2(2), c = 1724.8(2) pm, β = 92.25(1)°; R1 = 0.023 (based on F values) and wR2 = 0.059 (based on F² values), for all measured X‐ray reflections. The structure of the cluster anion can be given as [(Mo₆Cl)Cl]^2– (i = inner, a = outer ligands). Thermal stability studies show that 1 loses crystal water followed by the loss of NH₄Cl above 350 °C to yield MoCl₂. The water‐free compound (NH₄)₂[Mo₆Cl₁₄] ( 2 ) was synthesized by solid state reaction of MoCl₂ and NH₄Cl in a sealed quartz ampoule at 270 °C. No single‐crystals could be obtained. Decompositions of 1 and 2 under nitrogen and argon exhibited the loss of NH₄Cl at about 350 °C. Decomposition under NH₃ resulted in the formation of MoN and Mo₂N at 540 °C and 720 °C, respectively.