title: Diazole-based powdered cocrystal featuring a helical hydrogen-bonded network: structure determination from PXRD, solid-state NMR and computer modeling.
abstract: We present the structure of a new equimolar 1:1 cocrystal formed by 3,5-dimethyl-1H-pyrazole (dmpz) and 4,5-dimethyl-1H-imidazole (dmim), determined by means of powder X-ray diffraction data combined with solid-state NMR that provided insight into topological details of hydrogen bonding connectivities and weak interactions such as CH···π contacts. The use of various 1D/2D (13)C, (15)N and (1)H high-resolution solid-state NMR techniques provided structural insight on local length scales revealing internuclear proximities and relative orientations between the dmim and dmpz molecular building blocks of the studied cocrystal. Molecular modeling and DFT calculations were also employed to generate meaningful structures. DFT refinement was able to decrease the figure of merit R(F(2)) from ~11% (PXRD only) to 5.4%. An attempt was made to rationalize the role of NH···N and CH···π contacts in stabilizing the reported cocrystal. For this purpose four imidazole derivatives with distinct placement of methyl substituents were reacted with dmpz to understand the effect of methylation in blocking or enabling certain intermolecular contacts. Only one imidazole derivative (dmim) was able to incorporate into the dmpz trimeric motif thus resulting in a cocrystal, which contains both hydrophobic (methyl groups) and hydrophilic components that self-assemble to form an atypical 1D network of helicoidal hydrogen bonded pattern, featuring structural similarities with alpha-helix arrangements in proteins. The 1:1 dmpz···dmim compound I is the first example of a cocrystal formed by two different azoles.
authors.affiliation: Department of Chemistry, CICECO, University of Aveiro, 3810-193 Aveiro, Portugal.
authors.forename: Mariana
authors.initials: M
authors.lastname: Sardo
authors.affiliation: Department of Chemistry, CICECO, University of Aveiro, 3810-193 Aveiro, Portugal.
authors.forename: Sérgio M
authors.initials: SM
authors.lastname: Santos
authors.affiliation: Department of Chemistry, CICECO, University of Aveiro, 3810-193 Aveiro, Portugal; Faculty of Chemistry, Taras Shevchenko National University of Kyiv, Volodymyrska s. 64/13, 01601 Kyiv, Ukraine.
authors.forename: Artem A
authors.initials: AA
authors.lastname: Babaryk
authors.affiliation: Departamento de Química Orgánica y Bio-Orgánica, Facultad de Ciencias, UNED, Senda del Rey 9, E-28040 Madrid, Spain.
authors.forename: Concepción
authors.initials: C
authors.lastname: López
authors.affiliation: Instituto de Química Médica (CSIC), Juan de la Cierva 3, E-28006 Madrid, Spain.
authors.forename: Ibon
authors.initials: I
authors.lastname: Alkorta
authors.affiliation: Instituto de Química Médica (CSIC), Juan de la Cierva 3, E-28006 Madrid, Spain.
authors.forename: José
authors.initials: J
authors.lastname: Elguero
authors.affiliation: Departamento de Química Orgánica y Bio-Orgánica, Facultad de Ciencias, UNED, Senda del Rey 9, E-28040 Madrid, Spain. Electronic address: rclaramunt@ccia.uned.es.
authors.forename: Rosa M
authors.initials: RM
authors.lastname: Claramunt
authors.affiliation: Department of Chemistry, CICECO, University of Aveiro, 3810-193 Aveiro, Portugal. Electronic address: lmafra@ua.pt.
authors.forename: Luís
authors.initials: L
authors.lastname: Mafra
keywords: CH···π interactions; Cocrystal; Crystal engineering; Diazole; Hydrogen bond network; NMR Crystallography; Solid-state NMR