Arkhipov Sergey G, Losev Evgeniy A, Boldyreva Elena V
Novosibirsk State University Pirogova str. 2, Novosibirsk 630090, Russian Federation.
Institute of Solid State Chemistry and Mechanochemistry SB RAS, Kutateladze str. 18, Novosibirsk 630128, Russian Federation.
Acta Crystallogr C Struct Chem. 2017 Jan 1;73(Pt 1):13-19. doi: 10.1107/S2053229616018271.
Molecular salts and cocrystals of amino acids have potential applications as molecular materials with nonlinear optical, ferroelectric, piezoelectric, and other various target physical properties. The wide choice of amino acids and coformers makes it possible to design various crystal structures. The amino acid-maleic acid system provides a perfect example of a rich variety of crystal structures with different stoichiometries, symmetries and packing motifs built from the molecular building blocks, which are either exactly the same, or differ merely by protonation or as optical isomers. The present paper reports the crystal structures of two new salts of the DL-norvaline-maleic acid system with 1:1 and 2:1 stoichiometries, namely DL-norvalinium hydrogen maleate, CHNO·CHO, (I), and DL-norvalinium hydrogen maleate-DL-norvaline, CHNO·CHO·CHNO, (II). These are the first examples of molecular salts of DL-norvaline with an organic anion. The crystal structure of (I) has the same C(12) structure-forming motif which is common for hydrogen maleates of amino acids. The structure of (II) has dimeric cations. Of special interest is that the single crystals of (I) which are originally formed on crystallization from aqueous solution transform into single crystals of (II) if stored in the mother liquor for several hours.
氨基酸的分子盐和共晶体作为具有非线性光学、铁电、压电及其他各种目标物理性质的分子材料具有潜在应用。氨基酸和共形成物的广泛选择使得设计各种晶体结构成为可能。氨基酸 - 马来酸体系提供了一个完美的例子，展示了由分子构建单元构建的具有不同化学计量比、对称性和堆积模式的丰富多样的晶体结构，这些分子构建单元要么完全相同，要么仅因质子化或作为旋光异构体而有所不同。本文报道了DL - 正缬氨酸 - 马来酸体系中两种具有1:1和2:1化学计量比的新盐的晶体结构，即DL - 正缬氨酸氢马来酸盐，CHNO·CHO，(I)，和DL - 正缬氨酸氢马来酸盐 - DL - 正缬氨酸，CHNO·CHO·CHNO，(II)。这些是DL - 正缬氨酸与有机阴离子形成分子盐的首个例子。(I)的晶体结构具有与氨基酸氢马来酸盐常见的相同的C(12)结构形成基序。(II)的结构具有二聚阳离子。特别有趣的是，最初从水溶液中结晶形成的(I)的单晶如果在母液中储存数小时会转变为(II)的单晶。
