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Effect of high pressure on the crystal structures of polymorphs of glycine

机译：高压对甘氨酸多晶型物晶体结构的影响

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The effect of high pressure on the crystal structures of alpha-, beta-, and gamma-glycine has been investigated. A new polymorph, delta-glycine, is obtained from beta glycine. delta-Glycine is monoclinic, P2(1)/a, a = 11.156(4), b = 5.8644(11), c = 5.3417(17) angstrom, beta = 125.83(4)degrees at 1.9 GPa. The transition, which occurs between 0 and 0.8 GPa, proceeds from a single crystal of beta-glycine to a single crystal of delta-glycine, resulting in an equal number of NH center dot center dot center dot O hydrogen bonds but an increase in the number and strength of CH center dot center dot center dot O hydrogen bonds, which act to close-up "holes" that are formed within the layers of beta-glycine in the centers of R-type hydrogen-bonded motifs. Trigonal gamma-glycine begins to undergo a transition to another high-pressure phase, e-glycine, at 1.9 GPa, but the transformation is destructive; it is essentially complete at 4.3 GPa. The structure is monoclinic Pn, a = 4.8887(10), b = 5.7541(11), c = 5.4419(11) angstrom, beta = 116.682(10)degrees at 4.3 GPa. The structure consists of layers similar to those observed in alpha-glycine with interlayer separations of 2.38 and 3.38 angstrom and CH center dot center dot center dot O interactions formed between the layers. Monoclinic alpha-glycine is known to be stable to 23 GPa, and we have obtained a single-crystal structure of this polymorph at 6.2 GPa. Super-short NH center dot center dot center dot O hydrogen bonds are not formed up to 6.2 GPa, and they only shorten significantly if they are formed parallel to CH center dot center dot center dot O hydrogen bonds, which strengthen, or vectors across holes which close-up, under pressure.
机译：已经研究了高压对α-，β-和γ-甘氨酸的晶体结构的影响。从β甘氨酸中获得了一种新的多晶型物δ-甘氨酸。 δ-甘氨酸为单斜晶系，P2（1）/ a，a = 11.156（4），b = 5.8644（11），c = 5.3417（17）埃，β= 1.9 GPa下的125.83（4）度。发生在0至0.8 GPa之间的跃迁从β-甘氨酸的单晶发展到δ-甘氨酸的单晶，导致NH中心点中心点中心点O氢键数目相等，但氢键中心点数目增加CH中心点中心点中心点O氢键的数量和强度，它们作用于在R型氢键基序中心的β-甘氨酸层内形成的特写“孔”。三角γ-甘氨酸在1.9 GPa处开始过渡到另一个高压相e-甘氨酸，但这种转化是破坏性的。它基本完成于4.3 GPa。结构为单斜晶Pn，在4.3 GPa时a = 4.8887（10），b = 5.7541（11），c = 5.4419（11）埃，beta = 116.682（10）度。该结构由与在α-甘氨酸中观察到的层相似的层组成，层间间距为2.38和3.38埃，并且在这些层之间形成CH中心点中心点中心点O相互作用。已知单斜晶α-甘氨酸稳定在23 GPa，并且我们已经在6.2 GPa获得了该多晶型物的单晶结构。高达6.2 GPa时不会形成超短NH中心点中心点中心点O氢键，并且只有与CH中心点中心点中心点O氢键平行形成才能显着缩短，氢键会增强或跨孔形成矢量哪个特写，在压力下。

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