title: New 1:1 and 2:1 salts in the `DL-norvaline-maleic acid' system as an example of assembling various crystal structures from similar supramolecular building blocks.
abstract: 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, C5H12NO2+·C4H3O4-, (I), and DL-norvalinium hydrogen maleate-DL-norvaline, C5H12NO2+·C4H3O4-·C5H11NO2, (II). These are the first examples of molecular salts of DL-norvaline with an organic anion. The crystal structure of (I) has the same C22(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.
authors.affiliation: Novosibirsk State University Pirogova str. 2, Novosibirsk 630090, Russian Federation.
authors.forename: Sergey G
authors.initials: SG
authors.lastname: Arkhipov
authors.affiliation: Novosibirsk State University Pirogova str. 2, Novosibirsk 630090, Russian Federation.
authors.forename: Evgeniy A
authors.initials: EA
authors.lastname: Losev
authors.affiliation: Institute of Solid State Chemistry and Mechanochemistry SB RAS, Kutateladze str. 18, Novosibirsk 630128, Russian Federation.
authors.forename: Elena V
authors.initials: EV
authors.lastname: Boldyreva
keywords: amino acid salt; crystal engineering; crystal structure; dl-norvaline; hydrogen bond; maleic acid