The crystal structure of 1-(4-carboxybutyl)-3- methyl-1 H -imidazol-3-ium hexa ﬂ uoridophosphate, C 9 H 15 F 6 N 2 O 2 P

C 9 H 15 F 6 N 2 O 2 P, triclinic, P 1 ̄ (no. 2), a = 8.678(8) Å, b = 9.085(9) Å, c = 10.279(8) Å, α = 84.23(2) ∘ , β = 79.02(2) ∘ , γ = 62.103(14) ∘ , V = 62.10(1) Å 3 , Z = 2, R gt ( F ) = 0.0730, wR ref ( F 2 ) = 0.1663, T = 296 K.


Source of material
The compound was obtained using commercial 1-(4carboxybutyl)-3-methyl-1H-imidazol-3-ium bromide through anion exchanging with potassium hexafluorophosphate.An amount of 0.01 mol 1-(4-carboxybutyl)-3-methyl-1H-imidazol-3-ium bromide, 0.01 mol potassium hexafluorophosphate and 10 mL distilled water were added to a 25 mL roundbottom flask.After being stirred by a magnetic stirrer for about 24 h, the mixture was transferred to a separatory funnel and extracted with 10 mL CH 2 Cl 2 , the organic phase was placed at room temperature and evaporated slow, finally the colorless crystals suitable for single crystal X-ray diffraction were obtained after about one week. 1

Experimental details
All H atoms were located at their calculated positions, with O-H = 0.82 (carboxyl) Å and C-H = 0.92 (methylene), 0.93 (imidazole ring) or 0.96 (methyl) Å, and refined isotropically through a riding model, with U iso (H) = 1.5 U eq (O, C) for carboxyl and methyl H atoms and 1.2 U eq (C) for methylene H atoms.The hexafluorophosphate group is disordered over two positions with site occupancy ratio of 0.49:0.51[3].Ionic liquids (ILs) are the important functional materials, they can be applied in the industry and research fields of catalysis [4], extraction [5], liquid crystals and electrochemistry [6].So focusing on the attentions from the researchers in decades, and many novel ILs with functional organics were designed and synthesized such as amino acid [7] and carboxylic acid [8].In this work, the bromide anion of 1-(4-carboxybutyl)-3-methyl-1H-imidazol-3-ium bromide was exchanged by hexafluorophosphate group, then yielded hexafluorophosphate salt ionic liquid containing imidazolecarboxylic acid.Single crystal X-ray diffraction clearly reveals that the Br − anions are completely substituted by hexafluorophosphate groups without residual Br − anions.In addition, there are no other guest molecules of solvents in the asymmetric unit of the structure.The carboxyl group connects imidazole ring by the twist-arrangement of four methylene groups.The bond distances between O atom and C atom are 1.254(6) and 1.289(5) Å for C5-O2 and C5-O1, respectively.They are close to each other, embodying the delocalized state for the C=O and C-O bonds of carboxyl, agreeing with others in the coordination polymer [9].
No classical hydrogen bonds exist in the structure of this compound.The hexafluorophosphate group and imidazolecarboxylic acid interact through C-H⋯F hydrogen bond with D or R 2 2 (8) style.On the other hand, two molecules of imidazolecarboxylic acid associate by O-H⋯O hydrogen bond R 2 2 (8) style from two carboxyls to form a dimer.Through those hydrogen bonds, the molecules are connected one by one to create a stable 3-dimensional network with ABAB fashion along b axis.The centroids distance between the centroid of one imidazole ring and the adjacent one is 8.878(8) Å, revealing that no π⋯π interactions are present in the crystals.

Table  :
Data collection and handling.

Table  :
Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å  ).