Dynamical processes in crystalline organometallic complexes

Braga, Dario

doi:10.1021/cr00012a007

Cited by 162 publications

(108 citation statements)

References 55 publications

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“…A pronounced maximum in the temperature dependence of the nuclear spin relaxation rate, as measured here for Al 50 , was already reported in several compounds, where molecular motions in a multiwell potential frame are responsible for this quadrupolar relaxation behavior [32][33][34][35][36]. Here, either the rotation of CH 3 groups or reorientational motions of the Cp* rings can be responsible for these motions.…”

Section: Discussionsupporting

confidence: 80%

“…For CH 3 rotors appearing in benzene derivatives values for E eff are typically in the range of 10-50 meV (100-500 K), see the recent compilation of Prager and Heidemann [35]. On the other hand, barriers for ring re-orientations are typically of the order of a few tens of kJ/mol ($1000 K) [36]. It appears therefore more plausible to attribute the observed dynamics to reorientations of the Cp* rings.…”

Section: Discussionmentioning

confidence: 99%

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27Al NMR Study of the Metal Cluster Compound Al50C120H180

et al. 2007

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We present an 27 Al NMR study of the metal cluster compound Al 50 Cp* 12 which is composed of (identical) Al 50 clusters, each surrounded by a Cp* ligand shell, and arranged in a crystalline 3D array (here Cp* = pentamethylcyclopentadienyl = C 5 (CH 3 ) 5 ). The compound is found to be non-conducting, the nuclear spin-lattice relaxation in the temperature range 100-300 K being predominantly due to reorientational motions of the Cp* rings. These lead to a pronounced maximum in the relaxation rate at T $ 170 K, corresponding to an activation energy of about 850 K. Data for the related compound Al 4 Cp* 4 , containing very much smaller Al 4 clusters are also presented. A comparison is drawn with the quadrupolar relaxation recently observed for the non-conducting fraction of Ga 84 molecules in the metal cluster compound Ga 84 [N(SiMe 3 ) 2 ] 20 -Li 6 Br 2 (thf) 20 AE2toluene.

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Section: Discussionsupporting

confidence: 80%

Section: Discussionmentioning

confidence: 99%

27Al NMR Study of the Metal Cluster Compound Al50C120H180

et al. 2007

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“…I want to turn now to the polymorphism of ferrocene, bis(cyclopentadienyl)iron, a topic that has been discussed from different standpoints in two recent reviews (Braga, 1992;Dunitz, 1993). The transition-metal metallocenes have very similar molecular shapes and might be expected to show very similar packing arrangements in their crystals.…”

Section: Polymorphism Of Ferrocenementioning

confidence: 99%

Phase changes and chemical reactions in molecular crystals

Dunitz¹

1995

Acta Crystallogr Sect B

144

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Changes in the attitude of crystallographers to phase changes and chemical reactions in molecular solids over the last 50 years are sketched. Various ways of classifying polymorphic modifications and structural changes in solids are discussed, and examples are given. The methods applied include multi-temperature crystal structure analysis, analysis of anisotropic displacement parameters, differential scanning calorimetry, solid-state NMR and visual observation. The importance of defects in influencing the kinetics of solid-solid phase changes is stressed.

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“…#FEROCE29) which reports C-H distances of 1.04, 2.18, and 3.28Å within the Cp ring. In addition to the work by Brock et al 22 , there has been much discussion on the proper interpretation of the ferrocene diffraction data 23 , and we hope that NMR might be able to provide some additional insight.…”

Section: Resultsmentioning

confidence: 84%

Isotropic proton-detected local-field nuclear magnetic resonance in solids

Havlin

Walls

Pines

2005

The Journal of Chemical Physics

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A new nuclear magnetic resonance (NMR) method is presented which produces linear, isotropic protondetected local-field spectra for I N S spin systems in powdered samples. The method, HETeronuclear Isotropic Evolution (HETIE), refocuses the anisotropic portion of the heteronuclear dipolar coupling frequencies by evolving the system under a series of specially designed Hamiltonians and evolution pathways.The theory behind HETIE is presented along with experimental studies conducted on a powdered sample of ferrocene, demonstrating the methodology outlined in this paper. Applications of HETIE for structural determination in solid-state NMR are discussed.

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Dynamical processes in crystalline organometallic complexes

Cited by 162 publications

References 55 publications

27Al NMR Study of the Metal Cluster Compound Al50C120H180

27Al NMR Study of the Metal Cluster Compound Al50C120H180

Phase changes and chemical reactions in molecular crystals

Isotropic proton-detected local-field nuclear magnetic resonance in solids

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