Beckmann Peter A, Ford Jamie, Malachowski William P, McGhie Andrew R, Moore Curtis E, Rheingold Arnold L, Sloan Gilbert J, Szewczyk Steven T
Department of Physics, Bryn Mawr College, Bryn Mawr, Pennsylvania, USA.
Nanoscale Characterization Facility Singh Center for Nanotechnology, University of Pennsylvania, Philadelphia, Pennsylvania, USA.
Chemphyschem. 2018 Sep 18;19(18):2423-2436. doi: 10.1002/cphc.201800237. Epub 2018 Jun 28.
We report solid-state nuclear magnetic resonance 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 H spin-lattice relaxation is always non-exponential at high temperatures as expected when CH rotation is responsible for the relaxation. The 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).
我们报告了对2-乙基蒽（EA）和2-乙基蒽醌（EAQ）固体样品进行的固态核磁共振氢自旋晶格弛豫、单晶X射线衍射、粉末X射线衍射、场发射扫描电子显微镜和差示扫描量热法研究。这些样品是从相同的市售起始化合物通过不同方式物理纯化得到的。正如预期的那样，当CH旋转导致弛豫时，在高温下固态氢自旋晶格弛豫总是非指数型的。氢自旋晶格弛豫实验对这些范德华分子固体的“多分子”（团簇）结构非常敏感。在三种不同制备的EAQ样品中，弛豫在低温下也变得非常非指数型。这非常不寻常，并且核磁化强度的衰减可以用拉伸指数和双指数来拟合。这一不寻常的结果与粉末X射线衍射结果相关，并表明异常弛豫是由于两种（或更多）不同多晶型（伴随多晶型）的微晶所致。
