Zur komplexchemie von 4-zentren-π-systemen : XII. Glyoxaldiiminkomplexe: 1H-nmr-spektren und long range-kopplungen

Glyoxaldiimines (I) RN=CHCH=NR show in the NMR a downfield shift of glyoxalic protons (H_gly) when complexed to

(II: M = Mo, W), but increasing high field shifts when going to

(III) and

complexes (IV). In the tungsten complexes II H_glyW coupling satellites are resolved (J(WH) ≈4–6 Hz); in the phosphine compounds III, IV long range PH_gly coupling is clearly visible. Mechanisms of spinspin interaction are briefly discussed in connection with the EPR results on monoanionic radicals of II–IV.     

Quantum-chaotic scattering effects in semiconductor microstructures

We show that classical chaotic scattering has experimentally measurable consequences for the quantum conductance of semiconductor microstructures. These include the existence of conductance fluctuations-a sensitivity of the conductance to either Fermi energy or magnetic field-and weak-localization-a change in the average conductance upon applying a magnetic field. We develop a semiclassical theory and present numerical results for these two effects in which we model the microstructures by billiards attached to leads. We find that the difference between chaotic and regular classical scattering produces a qualitative difference in the fluctuation spectrum and weak-localization lineshape of chaotic and nonchaotic structures. While the semiclassical theory within the diagonal approximation accounts well for the weak-localization lineshape and for the spectrum of the fluctuations, we uncover a surprising failure of the semiclassical diagonal-approximation theory in describing the magnitude of these quantum transport effects.