Crystal structure of 1,3-diisopropyl-4,5-dimethylimidazolium oxalic acid monomethyl ester, C14H24N2O4

C14H24N2O4, monoclinic, P21/n (no. 14), a = 8.1862(8) A, b = 10.313(1) A, c = 18.534(2) A, b = 101.018(8)°, V = 1535.8 A, Z = 4, Rgt(F) = 0.0567, wRref(F ) = 0.1064, T = 173 K. Source of material The ti tle com pound was pre pared by ad di tion of ox alic acid monomethyl es ter (0.203g, 1.95 mmol) to a solution containing 0.351g (1.95 mmol) of 1,3-diisopropyl-4,5-dimethylimidazol-2ylidene (see [1]), in 30ml of dry diethylether at -25 °C. Af ter stirring over night at room tem per a ture, the precipitate was fil tered off, washed with dry diethylether and dried under reduced pressure. Yield: 0.432g (78%). The solid was recrystallized from acetone / diethylether as colour less crys tals. Discussion Sta ble heterocyclic carbenes have been in the cen ter of our in ter est as strong nucleophiles, they re act with Broenstedt ac ids and have con se quently been used as se lec tive deprotonation re agents [2]. The re sulted imidazolium com pounds play an im por tant role in the con struc tion of ionic liq uids, which can be po ten tially used as phar ma ceu ti cal sol vents [3]. Ap par ently their prop er ties are in flu enced by interionic in ter ac tions which have been de tected mainly in their 2H-de riv a tives as hy dro gen bonds. The na ture of the hy dro gen bonds de pends on the prop er ties of the counterions, and ap pears to be weaker with hard and less ba sic counterions. The close in ter ac tion of the C–H···X (X = S, O, N) hy dro gen bonds have at tracted con sid er able in ter est in var i ous or ganic com pounds to un der stand their crys tal struc tures. The pos si bil ity of 2H-imidazolium ions to form sta ble C–H···O bonds have been re ported re cently [4, 5], sug gest ing that hy dro gen bonds may act as an ad di tional sta bi liz ing fac tor in their crys tal struc tures. By con tin u ing our in ves ti ga tions on the struc tural chem is try of imidazolium salts [4, 6], we be came in ter ested in the struc ture of the monomethyl es ter ox a late ion linked to an or ganic cat ion by a hy dro gen bond. Sev eral note wor thy fea tures are ev i dent in the Xray struc ture of the ti tle com pound, C14H24N2O4, it has a cat ionan ion pair in the asym met ric unit that con tains an ion pair linked by C–H···O hy dro gen bond. Ap par ently, this in ter ac tion is typ i cally weak and a view on the interionic dis tances of the ti tle com pound re veals the pres ence of sep a rated ions in the unit cell [C(1)–H(1) = 0.91(2) ; H(1) · · ·O(21) = 2.26(4) A; C(1)–H(1)–O(21) = 175.0(1)°]. The flank ing car bonyl [C(22)–O(20) = 1.234(2) A] bond length is lon ger than [C(23)–O(24) = 1.202 (2) A] as a con se quence of the neg a tive charge. This in di cates that the for mal neg a tive charge is mainly delocalized at O(21)–C(22)–O(20), the bond dis tance of [C(22)–C(23) = 1.530 (3) A] in the an ion moi ety is clearly in dic a tive of a C–C sin gle bond [7]. In ad di tion, the ti tle com pound ex hib i ts an ap prox i mately l in ear C–H·· ·O in ter ac t ion [C(1)–H(1)–O(21) = 175.0(1)°]. The bond dis tances and an gles of imidazolium cat ion and monomethyl ox a late an ion are in agree ment with those re ported in the lit er a ture [8, 9]. Z. Kristallogr. NCS 228 (2013) xxx-xxx / DOI 10.1524/ncrs.2013.0034 1 © by Oldenbourg Wissenschaftsverlag, Munchen Crystal: colourless plates, size 0.10 0.20 0.25 mm Wavelength: Mo Ka radiation (0.71073 A) m: 0.90 cm Diffractometer, scan mode: STOE IPDS, j scans 2qmax: 52.74° N(hkl)measured, N(hkl)unique: 21398, 3131 Criterion for Iobs, N(hkl)gt: Iobs > 2 s(Iobs), 2482 N(param)refined: 278 Programs: SHELX[10], X-AREA[11], X-RED32[11] Table 1. Data collection and handling.