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Proton Spin‐Lattice Relaxation in Organic Molecular Solids: Polymorphism and the Dependence on Sample Preparation
Author(s) -
Beckmann Peter A.,
Ford Jamie,
Malachowski William P.,
McGhie Andrew R.,
Moore Curtis E.,
Rheingold Arnold L.,
Sloan Gilbert J.,
Szewczyk Steven T.
Publication year - 2018
Publication title -
chemphyschem
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.016
H-Index - 140
eISSN - 1439-7641
pISSN - 1439-4235
DOI - 10.1002/cphc.201800237
Subject(s) - crystallite , spin–lattice relaxation , relaxation (psychology) , molecular solid , chemistry , van der waals force , magnetization , spin–spin relaxation , spin diffusion , proton , nuclear magnetic resonance , molecule , crystallography , thermodynamics , magnetic field , organic chemistry , physics , diffusion , psychology , social psychology , quantum mechanics
We report solid‐state nuclear magnetic resonance 1 H spin‐lattice relaxation, single‐crystal X‐ray diffraction, powder X‐ray diffraction, field emission scanning electron microscopy, and differential scanning calorimetry in solid samples of 2‐ethylanthracene (EA) and 2‐ethylanthraquinone (EAQ) that have been physically purified in different ways from the same commercial starting compounds. The solid‐state 1 H spin‐lattice relaxation is always non‐exponential at high temperatures as expected when CH 3 rotation is responsible for the relaxation. The 1 H spin‐lattice relaxation experiments are very sensitive to the “several‐molecule” (clusters) structure of these van der Waals molecular solids. In the three differently prepared samples of EAQ, the relaxation also becomes very non‐exponential 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 X‐ray diffractometry results and suggests that the anomalous relaxation is due to crystallites of two (or more) different polymorphs (concomitant polymorphism).