Bis(1,3-dimethyl-1H-imidazolium) hexa-fluoro-silicate: the second monoclinic polymorph

Area of Science:

• Crystallography
• Materials Science
• Supramolecular Chemistry

Background:

• Polymorphism is common in ionic compounds, affecting their physical properties.
• Understanding crystal packing is crucial for designing materials with specific characteristics.

Purpose of the Study:

• To characterize a newly discovered polymorph of 2C5H9N2(+)·SiF6(2-).
• To compare its crystal structure and packing with a previously reported polymorph.

Main Methods:

• Single-crystal X-ray diffraction was used to determine the crystal structure of the new polymorph.
• Analysis of crystallographic data to compare symmetry and intermolecular interactions.

Main Results:

• The new polymorph (I) crystallizes in space group P21/n, distinct from the known polymorph (Ia) in space group C2/c.
• Polymorph (I) shows parallel arrangement of imidazolium cations, while (Ia) exhibits a herringbone structure.
• Distinct C-H⋯F interactions in (I) lead to layers parallel to the ac plane, differing from the bc plane layers in (Ia).

Conclusions:

• The discovery of a new polymorph highlights the structural diversity of 2C5H9N2(+)·SiF6(2-).
• Differences in crystal packing and symmetry between polymorphs can be attributed to variations in intermolecular interactions, particularly C-H⋯F contacts.