New [4.4]cyclophanes: molecular parallelograms, triangles, rhombuses, pentagons, and supramolecular constructions

The fair or good yield synthesis of new [(4.4)(n)]cyclophanes (n = 1-5), starting from 1,4-bis(2-hydroxymethyl-5,5-dimethyl-1,3-dioxan-2-yl)benzene and several diacid-dichlorides, based on monomer and oligomer formation reactions (from 1 + 1 to 5 + 5), is reported. The structure and the complex architectures of the lattices for these cyclophanes are revealed by the X-ray molecular structure for five compounds, NMR investigations, and mass spectrometry measurements. Intramolecular and intermolecular CH-pi, p-pi, and pi-pi interactions are observed, both in solid state and solution.     

Monomeric, dimeric and hexameric resorcin[4]arene assemblies with alcohols in apolar solvents

Resorcin[4]arenes in an apolar solvent containing alcohols exist in three forms of self-assembled aggregates which have been characterised by the technique of diffusion NMR spectroscopy.     

Second-sphere interaction of anions with a weakly binding metal complex host: probing the effect of counteranions

The reaction of [Re(OTf)(CO)5] with N-methylimidazole (MeIm) afforded [Re(CO)3(MeIm)3]OTf (1). The reactions of 1 with KPF6, NaBPh4 and NaBAr'4 (Ar' = 3,5-bis(trifluoromethyl)phenyl) afforded [Re(CO)3(MeIm)3]PF6 (2) [Re(CO)3(MeIm)3]BPh4 (3) and [Re(CO)3(MeIm)3]BAr'4 (4) respectively. An analogous reaction using N-phenylimidazole (PhIm) yielded [Re(CO)3(PhIm)3]BAr'4 (7). These new compounds were characterized by IR and NMR, and the structures of 1 and 2 were determined by X-ray diffraction. Compounds [Re(CO)3(MeIm)3]2[PtCl6] (5), [Re(CO)3(MeIm)3][HSO4] (6), [Re(CO)3(PhIm)3][Br] (8) and [Re(CO)3(PhIm)3][NO3] (9) were crystallized from equimolar mixtures of either 4 or 7 and the tetrabutylammonium salt of the corresponding anion, and their structures were determined by X-ray diffraction. The solution behavior of 1-4, 7 toward several anions was studied spectroscopically, including the quantitative determination of binding constants by 1H NMR. The cationic tris(imidazole)complexes are stable against imidazole-by-anion substitution, and the main hydrogen bonding interactions involve the imidazole NC(H)N groups. The binding constants for compounds 1-4 with several external anions follow the order 1<2<3<4, indicating that the strength of the cationic complex-counteranion interaction follows the order OTf(-) > PF6(-) > BPh4(-) > BAr'4(-).     

Magnetization-dependent shift in ferromagnet/superconductor/ferromagnet trilayers with a strong ferromagnet

We have measured the superconducting transition temperature Tc of Ni/Nb/Ni trilayers when the magnetizations of the two outer Ni layers are parallel (P) and antiparallel (AP). The largest difference in occurs when the Nb thickness is just above the critical thickness at which superconductivity disappears completely. We have observed a difference in Tc between the P and AP states as large as 41 mK--a significant increase over earlier results in samples with higher Tc and with a CuNi alloy in place of the Ni. Our result also demonstrates that strong elemental ferromagnets are promising candidates for future investigations of ferromagnet/superconductor heterostructures.     

An unexpected reaction of trimethylsilyl fluorosulfonyldifluoroacetate (TFDA) with imidazoles. Formation of N-difluoromethylthioureas

A new reaction of the efficient difluorocarbene-generating reagent trimethylsilyl fluorosulfonyldifluoroacetate (TFDA) is reported in which molecules containing an N-alkylimidazole or benzimidazole structure undergo an unexpected one-pot conversion to N-difluoromethylthioureas. [reaction: see text].     

Electrochemical annulation of five-membered rings through dearomatization of furans and thiophenes

A new methodology for the annulation of five-membered carbocyclic rings onto enones through the dearomatizing electrochemical cyclization of furans and thiophenes has been developed.     

Magnetic behavior and clustering effects in Mn-doped boron nitride sheets

Ab initio calculations are performed in the framework of density functional theory on Mn-doped boron nitride sheets, which are candidates for two-dimensional diluted magnetic semiconductors (DMSs). Each type of substitution reveals a qualitatively different magnetic behavior encompassing ferromagnetic, anti-ferromagnetic and spin glass ordering. The ability of formation of these defects is also discussed. We analyze the dependence of the exchange couplings on the distance between impurities and the typical range and distribution are extracted. Multiple-impurity configurations are considered and the results are mapped on an Ising-type Hamiltonian with higher order exchange interactions, revealing deviations from the standard two-spin models. The percolation of interacting magnetic moments is discussed and the critical concentration is determined for the underlying transition from a ferromagnetic to a super-paramagnetic state. We conclude our study by providing the optimal conditions for doping in order to obtain a ferromagnetic DMS.     

Through‐space 19F–15N couplings for the assignment of stereochemistry in flubenzimine

Through‐space ¹⁹F–¹⁵N couplings revealed the configuration of flubenzimine, with the CF₃ group on N4 pointing towards the lone pair of N5. The ¹⁹F–¹⁵N coupling constants were measured at natural abundance using a spin‐state selective indirect‐detection pulse sequence. As ¹⁵N‐labelled proteins are routinely synthesized for NMR studies, through‐space ¹⁹F–¹⁵N couplings have the potential to probe the stereochemistry of these proteins by ¹⁹F labelling of some amino acids or can reveal the site of docking of fluorine‐containing drugs. Copyright © 2016 John Wiley & Sons, Ltd.