Solid-state dynamics

Only three aspects of the dynamics of spin equilibria in the solid state will be reviewed. One is the classification of the rates of spin interconversion based on spectroscopic properties observed in the solid. The second is the direct measurement of spin state lifetimes in crystals and powders. The third, the comparison of these with the dynamics observed in solutions, will be described in the course of the discussion. 

The temperature dependence of the spin state populations in solids, as measured by magnetic susceptibility or any of the other properties which differ with the spin state, falls into two classes. In one class there 

The physical and spectroscopic properties of a spin-equilibrium complex can appear to be either the average or the superposition of the properties of the separate spin states. Which occurs is dependent on the time scale of the observation relative to the relaxation time of the equilibrium. Thus the electronic and vibrational spectra always appear as a superposition of the two isomers because each spin state possesses a distinctive potential energy surface with its characteristic electronic and vibrational properties. On the other hand, the NMR spectra appear as the average of the spectra of the two spin states, for all but the slowest interconversions, because the frequency of the interconversion is high compared with the frequency differences of the chemical shifts or the inverse of the spin relaxation times of the two isomers. 

The two techniques which have been used effectively to set limits on the rates of spin state interconversions are Mossbauer and EPR spectroscopies. As described in Section III,E, the lifetime of the excited nuclear state involved in the Mossbauer effect is 10 7 second. Thus the observation of the Mossbauer spectrum can immediately classify the spin state lifetime as greater than or less than 10 7 second. Both conditions have been observed, as was described in Section III,E. 

There is some evidence that the strength of intermolecular forces determines the degree of cooperativity and the rate of spin state interconversion in the lattice (154,155). This is a reasonable hypothesis, for it assumes a continuum of behavior, from very weak interactions, which reflect intramolecular properties, to strong intermolecular forces, which cause cooperative phase transitions and abrupt spin state changes. Neutral complexes with a molecular lattice and little or no hydrogen bonding between the molecules, such as some iron(III) 

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Cheruzel, L.E., Pometum, M.S., Cecil, M.R., Mashuta, M.S., Wittebort, R.J. and Buchanan, R.M. (2003) Structures and solid-state dynamics of onedimensional water chains stabilized by imidazole channels. Angewandte... 

This article examines the dynamics of spin-equilibrium processes, principally from studies in solutions. The properties of the complexes which are relevant to the dynamics studies are first reviewed. Then the techniques used to observe these rapid processes are described. Some aspects of solid-state dynamics are mentioned. Finally, some implications for the description of intersystem crossing processes in excited states and for spin equilibria in heme proteins are described. 

Excited states (vertical) Solvent effects ESR Solid state dynamics Infinite systems Geminal functional theory... 

Khuong, T.A.V., Nunez, J.E., Godinez, C.E. and Garcia-Garibay, M.A. (2006) Crystalline molecular machines a quest toward solid-state dynamics and function. Acc. Chem. Res., 39, 413-422. 

Remembering that NMR and X-ray diffraction (XRD) afford complementary information on solid-state dynamics (roughly speaking, NMR measures the depth whereas XRD sees the shape at the bottom of a potential well) and that it is not necessarily true that the flattest well is the shallowest (compare for instance I and II,... 

Recombination Dynamics in the Solid State Dynamics of Quenching Processes in the Solid State Summary of Quenching Processes in the Solid State Optical and Electrical Properties of (pflra-Phenylene)-Type Polymers with an Increasing... 

Huang, Y. Q., Jiang, S. L., Wu, L. B., and Hua, Y. Q. 2004. Characterization of LLDPE/nano-Si02 composites by solid-state dynamic mechanical spectroscopy. Polymer Testing 23 9-15. 

The work of Fitzsimmons and co-workers illustrates the value of Mossbauer spectroscopy in the study of dynamic molecular behavior. Specifically, they found that [(C6Hv)Fe(CO)3]BF4 shows solid-state dynamic behavior at room temperature and above and static behavior at 78 K. Finally, low-temperature Mossbauer spectral studies have revealed the onset of slow paramagnetic... 

For inhomogeneously broadened line shapes it necessarily follows that no information about time-dependent fluctuations of the chromophore s transition frequency (which I will call spectral dynamics) can be obtained from the line shape itself. This does not mean that such dynamic fluctuations do not occur it simply means that either their amplitude is much smaller than the inhomogeneous line width or that their time scale is much longer than the inverse of the inhomogeneous line width. In either case these dynamic fluctuations are of great interest because they result from time-dependent changes in the local environments of chromophores, and hence can provide information about solid-state dynamics. 

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