Fano effect in a T-shaped double quantum dot structure in the presence of Rashba spin-orbit coupling

The influence of Rashba spin-orbit coupling on the Fano lineshape of the conductance spectrum in a T-shaped double quantum dot structure is theoretically studied. By second-quantizing the electron Hamiltonian in this structure, it is found that the Rashba interaction brings about a spin-flip interdot hopping term. With the enhancement of the Rashba interaction, this term separates the two resonant peaks in the conductance spectrum from each other. More importantly, it causes the broadening of the narrow Fano peak, and the narrowing of the broader peak. Finally, the asymmetric Fano lineshape changes into a symmetric profile in the global conductance spectrum.     

Structural variation, dynamics, and catalytic application of palladium(II) complexes of di-N-heterocyclic carbene-amine ligands

A series of palladium(II) complexes incorporating di-NHC-amine ligands has been prepared and their structural, dynamic and catalytic behaviour investigated. The complexes [trans-(kappa(2)-(tBu)CN(Bn)C(tBu))PdCl(2)] (12) and [trans-(kappa(2)-(Mes)CN(H)C(Mes))PdCl(2)] (13) do not exhibit interaction between the amine nitrogen and palladium atom respectively. NMR spectroscopy between -40 and 25 degrees C shows that the di-NHC-amine ligand is flexible expressing C(s) symmetry and for 13 rotation of the mesityl groups is prevented. In the related C(1) complex [(kappa(3)-(tBu)CN(H)C(tBu))PdCl][Cl] (14) coordination of NHC moieties and amine nitrogen atom is observed between -40 and 25 degrees C. Reaction between 12-14 and two equivalents of AgBF(4) in acetonitrile gives the analogous complexes [trans-(kappa(2)-(tBu)CN(Bn)C(tBu))Pd(MeCN)(2)][BF(4)](2) (15), [trans-(kappa(2)-(Mes)CN(H)C(Mes))Pd(MeCN)(2)][BF(4)](2) (16) and [(kappa(3)-(tBu)CN(H)C(tBu))Pd(MeCN)][BF(4)](2) (17) indicating that ligand structure determines amine coordination. The single crystal X-ray structures of 12, 17 and two ligand imidazolium salt precursors (tBu)C(H)N(Bn)C(H)(tBu)][Cl](2) (2) and [(tBu)C(H)N(H)C(H)(tBu)][BPh(4)](2) (4) have been determined. Complexes 12-14 and 15-17 have been shown to be active precatalysts for Heck and hydroamination reactions respectively.     

Evolving Opportunities in Structure Solution from Powder Diffraction Data—Crystal Structure Determination of a Molecular System with Twelve Variable Torsion Angles

The genetic algorithm approach , in which a population of trial structures is allowed to evolve subject to well-defined procedures for mating, mutation, and natural selection, was employed to solve the complex molecular crystal structure of Ph₂P(O)(CH₂)₇P(O)Ph₂ directly from powder diffraction data. The structure solution reveals an interesting (perhaps unexpected) molecular conformation (see picture), which emphasizes the importance of allowing complete conformational flexibility of the molecule in the structure solution calculation.     

Sensitized Lanthanide‐Ion Luminescence with Aryl‐Substituted N‐(2‐Nitrophenyl)acetamide‐Derived Chromophores

The syntheses of the two tetraazamacrocyclic ligands L1 and L2 bearing a [(methoxy‐2‐nitrophenyl)amino]carbonyl chromophore, i.e., an N‐(methoxy‐2‐nitrophenyl)acetamide moiety, together with their corresponding lanthanide‐ion complexes are described. A combined spectroscopic (UV/VIS, ¹H‐NMR), structural (X‐ray), and theoretical (DFT) investigation revealed that the absorption properties of the chromophores were dictated by the extent of electronic delocalisation, which in turn was determined by the position of the MeO substituent at the aromatic ring. X‐Ray crystallographic studies showed that when attached to the macrocycle, both isomeric forms of the N‐(methoxy‐2‐nitrophenyl)acetamide unit can participate in coordination, via the C?O, to an encapsulated potassium cation. Luminescence measurements confirmed that such a binding mode also exists in solution for the corresponding lanthanide complexes (q ca. ≤1), with the para‐MeO derivative allowing longer wavelength sensitization (λ_ex 330 nm).     

A Rhenium Tricarbonyl 4′‐Oxo‐terpy Trimer as a Luminescent Molecular Vessel with a Removable Silver Stopper

Shining metal cups : A luminescent tube of triangular cross‐section and stoppered by a silver ion (see picture: Re yellow, N blue, O red) is formed in two steps from commercial materials. The silver ion can be removed to give a tube, and both species are potential hosts for small ions and molecules; a change in luminescence is triggered by the encapsulation of silver.

     

Synthesis of 2,4-disubstituted piperidines via radical cyclization: unexpected enhancement in diastereoselectivity with tris(trimethylsilyl)silane

A novel approach to 2,4-disubstituted piperidines is reported, involving the radical cyclization of 7-substituted-6-aza-8-bromooct-2-enoates. Cyclization with tributyltin hydride affords the trans piperidines with trans/cis diastereomeric ratios ranging typically from 3:1 to 6:1. Cyclization with tris(trimethylsilyl)silane affords the same products with diastereomeric ratios of up to 99:1 in certain cases. The enhancement in diastereoselectivity results from the selective rearrangement of the minor stereoisomer through a cascade process involving radical cyclization to the piperidine radical, 1,5-radical translocation, and attack of the translocated radical onto the sulfonamide with extrusion of SO2 in a Smiles-type rearrangement. Slower trapping of the piperidine radical by tris(trimethylsilyl)silane compared to tributyltin hydride accounts for the occurrence of the rearrangement cascade in the former case.     

Co-ordination behaviour of a novel bisthiourea tripodal ligand: structural, spectroscopic and electrochemical properties of a series of transition metal complexes

The synthesis of a thiourea substituted derivative of tris(pyridyl-2-methyl)amine (TPA) is reported. Two of the three pyridine rings are substituted in the 6-position with benzoylthiourea groups. These thiourea groups undergo intramolecular hydrogen bonding to form six-membered rings which leaves one N-H group available to form hydrogen bonds with other molecules. This reports details how the complexation of this new ligand with transition metal ions yields complexes with differing geometries. Seven co-ordinate Mn(II) and Cd(II), six co-ordinate Ni(II) and five co-ordinate Co(II), Cu(II) and Zn(II) complexes have been isolated.