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首页> 外文期刊>Acta Crystallographica, Section B. Structural Science >Revision of ferroelastic structures of n-heptyl- and n-octylammonium dihydrogen phosphate crystals
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Revision of ferroelastic structures of n-heptyl- and n-octylammonium dihydrogen phosphate crystals

机译：修订正庚基和正辛基磷酸二氢铵晶体的铁弹性结构

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摘要

This study deals with the structure determination of C7H15NH3+.H2PO4- (C7ADP) and C8H17NH3+.H2PO4- (C8ADP). The samples used in this study were not subjected to a phase transition after they had been crystallized. Unlike a previous structure determination, weak reflections, now with indices h = 2n + 1, were included. This means that both structures are described in unit cells with the lattice parameters a twice as long as given previously. Both structures are quite similar; two double layers of dihydrogen phosphates, which are interconnected by hydrogen bonds (2.52-2.62 Angstrom), pass through each unit cell. Alkylammonium groups interact with these dihydrogen phosphates via longer hydrogen bonds (>2.75 Angstrom), while the rest of the aliphatic chains interact via van der Waals contacts. All H atoms were localized and no disorder of the H atoms was detected. Both structures described in the space group P12(1)l exhibit a reproducible ferroelastic switching. The hypothetical prototypic phase is orthorhombic with the space group number 60 P2/b2(1)2(1)/a. All atoms except two hydrogen species exist in pairs linked by the lost symmetry operations derived from the prototypic space group and are brought close to each other - up to 0.25 Angstrom - under the action of them. Each of these two different hydrogens is involved in an asymmetric hydrogen bond between an oxygen pair. Under the action of a lost symmetry operation each of these hydrogens is displaced from one oxygen towards the other. Therefore, it is assumed that during the ferroelastic switching the jumps of these two hydrogen species take place between the pertinent hydrogen-bond acceptor and donor oxygens. Hence, these oxygens reverse their role as hydrogen-bond donors and accepters during the ferroelastic switching.
机译：本研究涉及C7H15NH3 + .H2PO4-（C7ADP）和C8H17NH3 + .H2PO4-（C8ADP）的结构测定。在本研究中使用的样品在结晶后不经历相变。与以前的结构确定不同，现在包括了折射率为h = 2n + 1的弱反射。这意味着在晶胞参数a中，两种结构都以单位单元描述，长度是先前给出的两倍。两种结构都非常相似。通过氢键（2.52-2.62埃）相互连接的两个磷酸二氢双层穿过每个晶胞。烷基铵基团通过更长的氢键（> 2.75埃）与这些磷酸二氢盐相互作用，而其余的脂族链则通过范德华接触而相互作用。所有H原子均已定位，未检测到H原子无序。在空间群P12（1）/ nl中描述的两种结构都表现出可重复的铁弹性转换。假设的原型阶段是正交的，空间组号为60 P2 / b2（1）/ n2（1）/ a。除两个氢物种外，所有原子成对存在，这些原子成对通过原型空间群衍生的对称损失而连接，并在它们的作用下彼此接近-高达0.25埃。这两个不同的氢中的每一个都涉及氧对之间的不对称氢键。在失去对称性的作用下，这些氢中的每一个都从一种氧向另一种氧转移。因此，假设在铁弹性转换期间，这两个氢物种的跃迁发生在相关的氢键受体和供体氧之间。因此，这些氧在铁弹性转换过程中逆转了它们作为氢键供体和受体的作用。

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