We report on temperature dependent magnetic susceptibility and Mössbauer effect studies of the influence of hydrostatic pressure (up to 1.2 GPa) on dynamic electronic structure phenomena in 3d transition metal coordination compounds. The systems under investigation are mononuclear spin crossover compounds of iron (II) and chromium (II), dinuclear complexes of iron (II) exhibiting coexistence of intramolecular antiferromagnetic coupling and thermal spin crossover, 1D, 2D and 3D polynuclear spin crossover complexes of iron (II), a valence tautomeric system of cobalt (II) showing a thermal transition from a high spin [Co II (semiquinone)] to a low spin [Co II (catecholate)] species on lowering the temperature and a photomagnetically active Prussian blue type system with temperature-and pressure induced electron transfer. It is demonstrated that pressure effect studies can be very helpful in elucidating the mechanisms and cooperative interactions of solid state compounds with electronic bistability.Dedicated to Professor Peter Jutzi on the occasion of his 65th birthday.

PACS. 78.30G -Infrared and Raman spectra in inorganic crystals. PACS. 63.20P -Localized modes. PACS. 66.30H -Self-diffusion and ionic conduction in nonmetals.Abstract. -Far-IR static-electric-field experiments on KI : Ag+ reveal that the field-induced frequency shifts for the <(pocket,, vibrational gap modes are nearly two orders of magnitude smaller than the corresponding shifts measured for the low-frequency resonant modes. When combined with previously measured stress shifts and a quasi-harmonic perturbed shell-model calculation, these results firmly establish that the silver ion has a significant quadrupolar deformability, which has been proposed to play an important role in the dynamics of the silver ion in other systems.

The dual supergravity description of the flow between (2,0) five-brane theory and the non-commutative five-brane (OM) theory is examined at critical five-brane field strength. The self-duality of the field strength is shown to arise as a consequence of the supergravity solution. Open membrane solutions are examined in the background of the five brane giving rise to an M analogue of the non-commutative open string (NCOS) solution.

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