Rheniumkomplexe mit heterocyclischen Thiolen – Synthesen und Strukturen

Rhenium Compounds Containing Heterocyclic Thiols – Syntheses and Structures Reactions of trans‐[ReOCl₃(PPh₃)₂] with 1,3‐thiazoline‐2‐thiol (thiazSH), pyridine‐2‐thiol (pyrSH) or pyrimidine‐2‐thiol (pyrmSH) result in the formation of rhenium(V) oxo complexes or rhenium(III) species depending on the conditions applied. mer‐[ReOCl₃(thiazSH)(OPPh₃)], trans‐[ReCl₃(PPh₃)(thiazSH)₂], [ReO(2‐propO)(PPh₃)Cl(pyrS‐S,N)], cis‐[ReCl₂(PPh₃)₂(pyrS‐S,N)] and [ReCl₂(PPh₃)₂(pyrmS‐S,N)] have been isolated from such reactions and structurally characterized. cis‐[ReCl₂(PPh₃)₂(pyrS‐S,N)] and [ReCl₂(PPh₃)₂(pyrmS‐S,N)] are obtained in better yields by ligand substitution on trans‐[ReCl₃(MeCN)(PPh₃)₂]. The reaction between (n‐Bu₄N)[ReOCl₄] and purine‐6‐thiol (purinSH) gives the oxo‐bridged [O{ReO(purinS‐S,N)₂}₂].     

SOCl2 and POCl3 as reducing agents for TcO 4 − formation and EPR detection of Tc(VI)-compounds

Pertechnetate, TcO ₄ ^– , is reduced by thionyl chloride and phosphoryl chloride, respectively, to yield semistable Tc(VI) intermediates which can easily be detected by EPR spectroscopy. Spectra are recorded in liquid and frozen solutions. EPR data as well as chemical behaviour suggest the compounds obtained to be oxochloro complexes of technetium(VI).     

Phosphaniminato-Komplexe von Cobalt und Zink mit Heterocubanstruktur. Die Kristallstrukturen von [CoI(NPMe3)]4 und [ZnI(NPMe3)]4

Phosphoraneiminato Complexes of Cobalt and Zinc with Heterocubane Structure. Crystal Structures of [CoI(NPMe₃)]₄ and [ZnI(NPMe₃)]₄ The title compounds have been prepared from CoI₂ and ZnI₂, respectively, and Me₃SiNPMe₃ by fusion reactions at 180°C in the presence of sodium fluoride. They crystallize from dichloromethane as dark green (Co) or colourless (Zn) single crystals including three molecules CH₂Cl₂ per formula unit, which were characterized by crystal structure determinations. [CoI(NPMe₃)]₄ · 3 CH₂Cl₂: Space group P3m1, Z = 2, structure solution with 2376 independent reflections, R = 0.033. Lattice dimensions at ?50°C: a = b = 1455.8, c = 1270.5 pm. [ZnI(NPMe₃)]₄ · 3 CH₂Cl₂: Space group P3m1, Z = 2, structure solution with 2197 independent reflections, R = 0.043. Lattice dimensions at ?60°C: a = b = 1454.9, c = 1270.5 pm. Both complexes are isostructural with one another. They form heterocubane structures in which the metal atoms are linked via μ₃-N-bridges of the phosphoraneiminato groups with M₄N₄ bridge-type bond angles close to 90°.     

The Reaction of Cs2[Tc(NO)F5] with BF3 in Acetonitrile: Formation and Structure of [{Tc(NO)(CH3CN)4}2(μ‐F)](BF4)3

The deep blue, paramagnetic Cs₂[Tc^II(NO)F₅] is formed during reactions of pertechnetate, acetohydroxamic acid, and CsF in aqueous HF. A reaction of Cs₂[Tc(NO)F₅] with BF₃ · MeOH in acetonitrile gives yellow blocks of the fluorido‐bridged dimer [{Tc^I(NO)(CH₃CN)₄}₂F](BF₄)₃. The compound is stable as solid and in acetonitrile solutions. The complex cation contains a bent μ‐F^– ligand and two linear nitrosyl groups.     

Asymmetry and structural information in preferential attachment graphs

Graph symmetries intervene in diverse applications, from enumeration, to graph structure compression, to the discovery of graph dynamics (e.g., node arrival order inference). Whereas Erd?s‐Rényi graphs are typically asymmetric, real networks are highly symmetric. So a natural question is whether preferential attachment graphs, where in each step a new node with m edges is added, exhibit any symmetry. In recent work it was proved that preferential attachment graphs are symmetric for m = 1, and there is some nonnegligible probability of symmetry for m = 2. It was conjectured that these graphs are asymmetric when m ≥ 3. We settle this conjecture in the affirmative, then use it to estimate the structural entropy of the model. To do this, we also give bounds on the number of ways that the given graph structure could have arisen by preferential attachment. These results have further implications for information theoretic problems of interest on preferential attachment graphs.     

Deformable two-dimensional photonic crystal slab for cavity optomechanics

We have designed photonic crystal suspended membranes with optimized optical and mechanical properties for cavity optomechanics. Such resonators sustain vibration modes in the megahertz range with quality factors of a few thousand. Thanks to a two-dimensional square lattice of holes, their reflectivity at normal incidence at 1064?nm reaches values as high as 95%. These two features, combined with the very low mass of the membrane, open the way to the use of such periodic structures as deformable end mirrors in Fabry-Perot cavities for the investigation of cavity optomechanical effects.     

Phase-matched frequency doubling at photonic band edges: efficiency scaling as the fifth power of the length

By exploiting the unique properties of periodic stratified media we demonstrate simultaneously phase matching and enhancement of the optical field under second order nonlinear interaction. This leads to a second harmonic efficiency growth faster than the fifth power of the structure length, far better than the usual quadratic behavior associated with second order nonlinear effects.     

EPR detection of [Cu(mnt)X2]2−—A possible halogenide stabilized intermediate in ligand exchange reactions

During the reaction of [Cu(mnt)₂]^2? with CuX₂ (X = Cl, Br) [Cu(mnt)X₂]^2? species are formed and characterized EPR spectroscopically supporting a dissociative mechanism for ligand exchange reactions between [Cu(mnt)₂]^2? and other Cu(II), Ni(II) and Pd(II) complexes which contain unsaturated dichalcogeno ligands.     

Darstellung,Strukturen und EPR-Spektren der Rhenium(II)-Nitrosylkomplexe [Re(NO)Cl2(PPh3)(OPPh3)(OReO3)], [Re(NO)Cl2(OPPh3)2(OReO3)] und [Re(NO)Cl2(OPPh3)3](ReO4)

Synthesis, Structures, and EPR-Spectra of the Rhenium(II) Nitrosyl Complexes [Re(NO)Cl₂(PPh₃)(OPPh₃)(OReO₃)], [Re(NO)Cl₂(OPPh₃)₂(OReO₃)], and [Re(NO)Cl₂(OPPh₃)₃](ReO₄) The paramagnetic rhenium(II) nitrosyl complexes [Re(NO)Cl₂(PPh₃)(OPPh₃)(OReO₃)], [Re(NO)Cl₂(OPPh₃)₂ · (OReO₃)], and [Re(NO)Cl₂(OPPh₃)₃](ReO₄) are formed during the reaction of [ReOCl₃(PPh₃)₂] with NO gas in CH₂Cl₂/EtOH. These and two other Re^II complexes with 5 d⁵ ”︁low-spin”︁”︁-configuration can be observed during the reaction EPR spectroscopically. Crystal structure analysis shows linear coordinated NO ligands (Re–N–O-angles between 171.9 and 177.3°). Three OPPh₃ ligands are meridionally coordinated in the final product of the reaction, [Re(NO)Cl₂(OPPh₃)₃][ReO₄] (monoclinic, P2₁/c, a = 13.47(1), b = 17.56(1), c = 24.69(2) Å, β = 95.12(4)°, Z = 4). [Re(NO)Cl₂(PPh₃)(OPPh₃)(OReO₃)] (triclinic P 1, a = 10.561(6), b = 11.770(4), c = 18.483(8) Å, α = 77.29(3), β = 73.53(3), γ = 64.70(4)°, Z = 2) and [Re(NO)Cl₂ (OPPh₃)₂(OReO₃)] (monoclinic P2₁/c, a = 10.652(1), b = 31.638(4), c = 11.886(1) Å, β = 115.59(1)°), Z = 4) can be isolated at shorter reaction times besides the complexes [Re(NO)Cl₃(Ph₃P)₂], [Re(NO)Cl₃(Ph₃P) · (Ph₃PO)], and [ReCl₄(Ph₃P)₂].