Crystal structures of the hexa-fluorido-phosphate salts of the isomeric 2-, 3- and 4-cyano-1-methyl-pyridinium cations and determination of solid-state inter-action energies.

Joel T Mague,Kevin E Riley,David Olivier,Lynn V Koplitz,Francesca Vaccaro,Erin Larrabee

doi:10.1107/s2056989018011003

Abstract

The synthesis and crystal structures of the isomeric mol-ecular salts 2-, 3- and 4-cyano-1-methyl-pyridinium hexa-fluorido-phosphate, C7H7N2+·PF6-, are reported. In 2-cyano-1-methyl-pyridinium hexa-fluorido-phosphate, C-H⋯F hydrogen bonds form chains extending along the c-axis direction, which are associated through C-H⋯F hydrogen bonds and P-F⋯π(ring) inter-actions into stepped layers. For 3-cyano-1-methyl-pyridinium hexa-fluorido-phosphate, corrugated sheets parallel to [001] are generated by C-H⋯F hydrogen bonds and P-F⋯π(ring) inter-actions. The sheets are weakly associated by a weak inter-action of the cyano group with the six-membered ring of the cation. In 4-cyano-1-methyl-pyridinium hexa-fluorido-phosphate, C-H⋯F hydrogen bonds form a more open three-dimensional network in which stacks of cations and of anions are aligned with the b-axis direction. Dispersion-corrected density functional theory (DFT-D) calculations were carried out in order to elucidate some of the energetic aspects of the solid-state structures. The results indicate that the distribution of charge within a mol-ecular ionic cation can play a large role in determining the strength of a cation-anion inter-action within a crystal structure. Crystals of 2-cyano-1-methyl-pyridinium hexa-fluorido-phosphate are twinned by a 180° rotation about the c* axis. The anion in 3-cyano-1-methyl-pyridinium hexa-fluorido-phosphate is rotationally disordered by 38.2 (1)° in an 0.848 (3):0.152 (3) ratio.

Highlights

Chemical contextMethylpyridinium cations (CMP) was generated by the significantly different melting behaviors of 3-CMP chloride and iodide (Koplitz et al, 2003)
In 2-cyano-1-methylpyridinium hexafluoridophosphate, C—HÁ Á ÁF hydrogen bonds form chains extending along the c-axis direction, which are associated through C—HÁ Á ÁF hydrogen bonds and P—FÁ Á Á(ring) interactions into stepped layers
For 3-cyano-1-methylpyridinium hexafluoridophosphate, corrugated sheets parallel to [001] are generated by C—HÁ Á ÁF hydrogen bonds and P—FÁ Á Á(ring) interactions

Summary

Chemical context

Methylpyridinium cations (CMP) was generated by the significantly different melting behaviors of 3-CMP chloride and iodide (Koplitz et al, 2003). This was attributed to a greater amount of C—HÁ Á ÁN and C—HÁ Á ÁX (X = ClÀ, IÀ). Relatively few crystal structures of CMP salts had been published so in order to investigate the packing and non-covalent interactions for these cations in the solid state, structures of salts of the 2-, 3- and 4-CMP+ cations with a variety of anions including BrÀ (Kammer et al, 2012b; Mague et al, 2005; Nguyen et al, 2015b), I3À (Nguyen et al, 2016), IÀ (Kammer et al, 2012a, 2013), ClO4À (Nguyen et al, 2014; Nguyen et al, 2015a; McCormick et al, 2014), NO3À. Symmetry codes: (i) Àx þ 12; y þ 12; Àz þ 32; (ii) x þ 12; Ày þ 32; z þ 12; (iii) x þ 12; Ày þ 32; z À 12; (iv) Àx þ 32; y þ 12; Àz þ 32

Supramolecular features

DFT studies

Database survey

Synthesis and crystallization

Refinement details

Funding information