Spin-Peierls transition in NaV2O5 in high magnetic fields

We investigate the magnetic field dependence of the spin-Peierls transition in NaV$_2$O$_5$ in the field range 16T-30T. The transition temperature exhibits a very weak variation with the field, suggesting a novel mechanism for the formation of the spin-Peierls state. We argue that a charge ordering transition accompanied by singlet formation is consistent with our observations.Comment: 4 pages, 3 figures, final version to appear in Phys. Rev. B (RC

Novel synthesis of 4(5)-monosubstituted imidazoles via cycloaddition of tosylmethyl isocyanide to aldimines

4(5)-Monosubstituted imidazoles (9) have been prepared via base-induced cycloaddition of tosylmethyl isocyanide (TosMIC) to N-(dimethylsulfamoyl)aldimines (2) or N-tosylaldimines (3). In the first case, N-(dimethylsulfamoyl)imidazoles 8 are the initial reaction products, from which the dimethylsulfamoyl group is readily removed with aqueous HBr. In the second case, the tosyl group of 1-tosylimidazoles 10 is lost spontaneously to give 4(5)-monosubstituted imidazoles 9 in one operation. (C) 1997 Elsevier Science Ltd

Ultrafast Light-Driven Nanomotors Based on an Acridane Stator

A series Of Molecular motors featuring a symmetrical acridane stator is reported. Photochemical and thermal isomerization experiments confirm that this stator, in combination with a thiopyran rotor, results in molecular rotary motion in which the rate-determining thermal helix inversion proceeds effectively only at temperatures above 373 K. The introduction of a cyclopentanylidene rotor unit results in a decrease in steric hindrance with respect to the stator, and as a consequence, a 10(12)-fold increase in the rate of thermal helix inversion is observed. Nanosecond transient absorption spectroscopy allows for the thermal processes to be followed accurately at ambient temperature. The rotary motor is shown to be able to operate at 0.5 MHz rotational frequencies Under optimal conditions

Coordination chemistry and X-ray studies with novel sterically constrained diphosphonite ligands

The coordination of two novel, sterically constrained diphosphonite ligands (1 and 2) towards different Pd, Pt and Rh precursors was studied. Complexes of this hitherto unexplored class of diphosphonites, based on rigid xanthene backbones, were characterized by x-ray crystallog. as well as by NMR and IR spectroscopy. A short and concise overview is given on the scarce literature on phosphonite related chem. Structural differences in the complexes obtained due to steric influences of the ligands are discussed. Ligand 1, bearing 2-tert-butylphenolate groups, led to orthometalated complexes cis-[MCl{1-k3C,P,P}] (M = Pd, Pt) and to trans-[RhCl(CO)(1)]. These complexes were compared with those formed with ligand 2, bearing 2,2'-dioxo-3,3'-di-tert-butyl-5,5'-dimethoxy-1,1'-biphenyl groups, preventing orthometalation. Trans-[PdCl2(2)], cis-[PtCl2(2)] and trans-[RhCl(CO)(2)] were structurally characterized. Valuable data were collected on chem. shifts, Pt-P coupling consts., as well as CO stretch frequencies of Rh-CO complexes as important tools for structural characterization of such complexe