Crystal structure of bis[(4/?*,51?*)2-amino-4,5-ira/is-dihydroxy- l,3-dimethoxy-4,5-dihydroimidazolium] hexafluorosilicate, [C5H12N304]2[SiF6]

C10H24F6N6O8SÌ, tetragonal, PA /̂n (no. 86), a = 15.646(1) Â, c = 8.2024(5) Â, V = 2007.9 Â, Ζ = 4, Rgl(F) = 0.052, wRrefiF) = 0.117, T= 233 K. Source of material The racemic title compound was unexpectedly obtained from a mixture of 2-azido-l,3-dimethoxyimidazolium hexafluorophosphate [1], dimethyl acetylenedicarboxylate and copper wire in methanol. Suitable crystals were harvested after allowing the mixture to stand for one month open to the laboratory atmosphere at ambient temperature with occasional refilling of methanol. The yield was less than 1 %. Experimental details Hydrogen atoms at N3,03 and 04 were refined isotropically with bond restraints (d=0.89 Â). Due to the small size of the crystal, a better reflections to parameters ratio could not be obtained. Discussion No matter how ill-conceived this experiment was (considering the reactivity of alkynes and the choice of catalyst [2]), the outcome was still spectacular. Clearly, the hexafluorosilicate anion is the result of hydrolysis of hexafluorophosphate and subsequent attack of hydrogen fluoride on the glass of the test tube, whereas the unintended formation of the novel cation remains a mistery. The only compounds which are closely related, but not of a cationic nature, have been claimed in an outdated patent [3]. Infrared microscopy of the crystal showed a strong absorption at 723 cm' which supports the presence of the hexafluorosilicate anion [4]. The imidazoline ring adopts an envelope conformation, where C3 deviates by 0.33 Â from the N1-C1-N2-C2 plane. The two hydroxy groups exhibit a trans configuration with an 03—C2C3-04 torsion angle of 98°. The methoxy groups also adopt an anti orientation with respect to the ring. The Si atom occupies a symmetry center. Each cation donates three hydrogen bonds to F atoms of the hexafluorosilicate anion and, in addition, one to another cation. Hydrogen bond characteristics (H—acceptor distance, donor—acceptor distance, donor-Η—acceptor angle) are as follows: Ol-H-Eì ' 1.83 Â, 2.714 Â, 175°; 03-H-Fl ü 1.76 Â, 2.651 Â, 172°; Ν3-Η···Ρ3 1.93 Â, 2.770 Â, 160°; N311-03* 2.07 Â, 2.886 Â, 153°. Symmetry code (i): l-x,l-y,-z; (ii): V2+y,l-jt,V2+z; (iii): Vtïy,Ι-λ,-Vi+z. Table 1. Data collection and handling. Crystal: Wavelength: μ· Diffractometer, scan mode: 2θαηχ· N(/l£/)measured» N(hkl}aòquc· Criterion for /obs, N(hkl)#: N(param}rrñacd'· Programs: colorless prism, size 0.03 χ 0.0S χ 0.31 mm Mo Ka radiation (0.71073 Â) 2.24 cm" Nonius Kappa CCD, φ/ω 46.2° 9279,1396 /obs > 2 af/obsj, 995 159 SHELXS-97 [5], SHELXL-97 [6] Table 2. Atomic coordinates and displacement parameters (in Â). * Correspondence author (e-mail: [email protected]) Atom Site X y ζ Uìso H(3A) 8g 0.948(3) 0.456(3) -0.135(5) 0.06(2) H(3B) 8g 0.928(3) 0.372(2) -0.044(5) 0.06(2) H(30) 8g 0.803(2) 0.474(3) 0.438(6) 0.08(2) H(40) 8g 0.675(3) 0.578(3) 0.073(6) 0.07(2) H(2) 8« 0.6984 0.4576 0.1760 0.044 H(3) 8g 0.8141 0.5918 0.2473 0.045 H(4A) 8g 0.8486 0.2268 0.2452 0.085 H(4B) 8« 0.8389 0.3058 0.3646 0.085 H(4C) 8« 0.9175 0.3010 0.2432 0.085 H(5A) 8g 0.9111 0.6983 -0.1753 0.092 Hiss) 8« 0.8167 0.6884 -0.1084 0.092 H(5C) 8g 0.8515 0.6246 -0.2428 0.092