168 research outputs found
Proton Spin-Lattice Relaxation in Organic Molecular Solids: Polymorphism and the Dependence on Sample Preparation
We report solidâstate nuclear magnetic resonance 1H spinâlattice relaxation, singleâcrystal Xâray diffraction, powder Xâray diffraction, field emission scanning electron microscopy, and differential scanning calorimetry in solid samples of 2âethylanthracene (EA) and 2âethylanthraquinone (EAQ) that have been physically purified in different ways from the same commercial starting compounds. The solidâstate 1H spinâlattice relaxation is always nonâexponential at high temperatures as expected when CH3 rotation is responsible for the relaxation. The 1H spinâlattice relaxation experiments are very sensitive to the âseveralâmoleculeâ (clusters) structure of these van der Waals molecular solids. In the three differently prepared samples of EAQ, the relaxation also becomes very nonâexponential at low temperatures. This is very unusual and the decay of the nuclear magnetization can be fitted with both a stretched exponential and a double exponential. This unusual result correlates with the powder Xâray diffractometry results and suggests that the anomalous relaxation is due to crystallites of two (or more) different polymorphs (concomitant polymorphism)
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