ORIGINAL PAPER Mechanochemical Complexation of Diethyl N,N ´ -[1,3-(2- methyl)phenyl]dioxalamate and Resorcinol: Conformational Twist and X-Ray Helical Supramolecular Architecture Juan Saulo Gonza ´lez-Gonza ´lez 1 • Oscar Zu ´n ˜ iga-Lemus 1 • Francisco J. Martı ´nez-Martı ´nez 2 • Jorge Gonzalez 2 • Efre ´n V. Garcı ´a-Ba ´ez 3 • Itzia I. Padilla-Martı ´nez 3 Received: 26 September 2014 / Accepted: 6 May 2015 / Published online: 13 May 2015 Ó Springer Science+Business Media New York 2015 Abstract The cocrystal formed by diethyl N,N ´ -[1,3-(2- methyl)phenyl]dioxalamate (1) and resorcinol (2), namely 1Á2 cryst (C 21 H 24 N 2 O 8 ) was prepared by mechanochemical complexation. IR spectroscopy and powder X-ray diffraction studies allowed to determine the complexation and the con- formational switching of the ethyl oxalamate side arms. In the crystal structure of 1Á2 cryst , complexation occurs through O–HÁÁÁO=C hydrogen-bonding interactions with the par- ticipation of phenolic O–H as donor and amide carbonyl group as acceptor. The steric hindrance of the CH 3 group in the C-2 position of the aromatic ring leads to a meso–helical supramolecular architecture forming a C 2 2 (16) chain motif. Crystal data: monoclinic, C2/c space group, a = 34.9054(13) A ˚ , b = 8.0434(5) A ˚ , c = 5.1577(8) A ˚ , b = 97.521(3)°. Graphical Abstract The cocrystal formed by diethyl N,N ´ - [1,3-(2-methyl)phenyl]dioxalamate and resorcinol, pre- pared by mechanochemical complexation. Keywords Cocrystal Á Helix Á Hydrogen bond Á Phenyldioxalamate Á Resorcinol Introduction The study of self-assembled supramolecular helicoidal systems, inspired in biological structures such as peptides, DNA double helix and tobacco mosaic virus, is an active area of current research [1]. Hydrogen bonding is the most important noncovalent interaction used in the design of supramolecular helices, allowing the development of supramolecular systems such as helical polymers [2], DNA assemblies [3] and helicenes [4, 5]. Mechanochemistry is a green chemistry method, which is used to promote chemical reactions in the solid state by mechanical energy. It has been applied in organic, inor- ganic and organometallic synthesis, polymer and materials chemistry, metallurgy and pharmaceutics. In crystal engi- neering, mechanochemistry is used to break and form noncovalent interactions, which leads to the formation of cocrystals, cages, interlocked structures and frameworks [6–11]. & Juan Saulo Gonza ´lez-Gonza ´lez juan_saulo@unca.edu.mx 1 Instituto de Farmacobiologı ´a, Universidad de la Can ˜ada, Carretera Teotitla ´n-San Antonio Nanahuatipan km 1.7 s/n, 68540 Teotitla ´n de Flores Mago ´n, Oaxaca, Mexico 2 Facultad de Ciencias Quı ´micas, Universidad de Colima, km 9 Carretera Colima-Coquimatla ´n, 28400 Coquimatla ´n, Colima, Mexico 3 Departamento de Ciencias Ba ´sicas, Unidad Profesional Interdisciplinaria de Biotecnologı ´a del Instituto Polite ´cnico Nacional, Av. Acueducto s/n Barrio la Laguna Ticoma ´n, 07340 Mexico, DF, Mexico 123 J Chem Crystallogr (2015) 45:244–250 DOI 10.1007/s10870-015-0589-8