Choline dihydrogen phosphate

In the cystal structure of the title compound, (2-hydroxyethyl)trimethylammonium dihydrogen phosphate, C5H14NO+·H2PO4 −, two anions create dimeric structures via two O—H⋯O hydrogen bonds. The hydrogen-bonded dimers are connected by another O—H⋯O hydrogen bond with the hydroxyl groups of the cations, constructing a columner structure along the a axis. A number of C—H⋯O interactions are also present.

In the cystal structure of the title compound, (2-hydroxyethyl)trimethylammonium dihydrogen phosphate, C 5 H 14 -NO + ÁH 2 PO 4 À , two anions create dimeric structures via two O-HÁ Á ÁO hydrogen bonds. The hydrogen-bonded dimers are connected by another O-HÁ Á ÁO hydrogen bond with the hydroxyl groups of the cations, constructing a columner structure along the a axis. A number of C-HÁ Á ÁO interactions are also present.

Crystal data
Data collection: PROCESS-AUTO (Rigaku, 1998); cell refinement: PROCESS-AUTO; data reduction: CrystalStructure (Rigaku/ MSC, 2004); program(s) used to solve structure: SIR2004 (Burla et al., 2005); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: ORTEPIII (Burnett & Johnson (1996); software used to prepare material for publication: SHELXL97.  Some ionic liquids (ILs) possess negligible vapor pressure as well as fascinating features such as high thermal, chemical and electrochemical stability. ILs have gained increasing attention as green, multi-use reaction media as well as solvents for a electrochemistry and chemistry (Welton, 1999;Seddon, 1997;Wasserscheid & Welton, 2002). ILs are also currently being investigated for a variety of bio-applications including media for biocatalytic reactions (van Rantwijk et al., 2003;Zhao et al., 2008), biosensors (Ohno, 2005) and protein stabilization (Fujita et al., 2005;Byrne et al., 2007). We have been studying hydrated IL as solvents for proteins. We have already reported that some proteins are soluble, stable, and remain active in some hydrated ILs. For example, the title compounds, acts as an excellent preserver of proteins such as cytochrome c.

Structure Reports Online
The title compound (I) consists of cations and anions. The molecular structures of (I) are shown in Fig. 1. Two hydrogen bonds of O4-H···O2 connect anions and construct dimer along the b axis (Fig. 2). The dimers are connected with each other by the two hydrogen bonds of O5-H···O1 and O3-H···O5, through the hydroxyl group (Table 1). These hydrogen bonds create a columnar structure of anions and cations along the a axis. The columnar structures interact with each other by C-H···O hydrogen bond and van der Waals forces (Table 1).

Experimental
Choline bromide solution was treated on an ion exchange resin (Amberlite IRN77), then mixed with phosphoric acid solution. The solvent evaporated and the product was dried in vacuo. White powder was dissolved in methanol, then reprecipited by dropping in acetone. This reprecipitation was repeated four times. Final purification was achieved by drowning-out crystallization from methanol solution. Aceton was used as antisolvent. This drowning-out crystallization was repeated twice at room temperature for X-ray measurements. The compound was identified using 1 H NMR, DSC and Electrospray mass spectrometry.

Refinement
The H atoms of the OH groups were found in difference maps and refined freely. The other C-bound H atoms were subsequently refined as riding atoms, with C-H = 0.98 and 0.99Å and U iso (H) = 1.2 or 1.5U eq (C).  (2-hydroxyethyl)trimethylammonium dihydrogen phosphate as those based on F, and R-factors based on ALL data will be even larger.