7-Benzyl-3-methyl-6-phenylimidazo[2,1-b][1,3]thiazol-7-ium chloride 0.75-hydrate

Theasymmetric unit of the title salt, C19H17N2S+·Cl−·0.75H2O, contains two symmetrically independent formula units of the carbenium salt along with three water molecules. The water molecules are only 50% occupated, and one of them is positioned in a hydrophobic pocket not forming any hydrogen bonds. The conformation of the independent cations is very similar, with dihedral angles of 61.0 (2) and 61.5 (3)° between the benzene rings. They form quasi-centrosymmetric couples via π–π stacking interactions between the benzene and imidazo[2,1-b]thiazole rings [centroid–centroid distances = 3.718 (3) and 3.663 (3) Å]. In the crystal, O—H⋯Cl hydrogen bonds lead to the formation of a helical anion–water chain along the c-axis direction. The cations connect to the anion–water chain through C—H⋯Cl interactions, generating a three-dimensional supramolecular network. O—H⋯S hydrogen bonds and C—H⋯O interactions also occur.


Related literature
For applications in catalysis of abnormal N-heterocyclic carbenes, see: Mattson et al. (2006); Liu et al. (2008); Padmanaban et al. (2011). For related structures, see: Huang et al. (2011); Akkurt et al. (2011Akkurt et al. ( , 2007; Song et al. (2008  Hydrogen-bond geometry (Å , ).  (Akkurt et al. (2011(Akkurt et al. ( , 2007, Huang et al. (2011), Song et al. (2008), herein we report the synthesis and structure of the title compound. The molecular structure of the title compound is depicted in Fig. 1. The crystallographic asymmetric unit of I, contains two 7-benzyl-3-methyl-6-phenyl-imidazo[2,1-b]thiazol-7-ium cation, two chlorine anion and three water molecule. As shown in Fig.2, the dihedral angle between benzene ring A and B is 60.85, while C and D is 61.66, indicating the two cations in the unit cell are not equivalent. The two symmetrically independent cations are stabilized by π-π stacking interactions, with a separation of 3.718 and 3.663 Å between the centroids of the benzene and thiazole rings. Another interesting part of the structure of title compound is the helical chain (Cl1-O3w-Cl2-O1w) formed entirely by the O-H···Cl hydrogen-bonding interactions ( Fig.3 & Fig.4)

Refinement
All H atoms attached to carbons were geometrically fixed and allowed to ride on the corresponding non-H atom with C-H = 0.96 Å, and U iso (H) = 1.5Ueq(C) of the attached C atom for methyl H atoms and 1.2Ueq(C) for other H atoms.
Positions of the methyl atoms were optimized rotationally. The water H atoms were located from a Fourier map and their distances were constrained to 0.86 Å and the U iso (H) = 1.5Ueq(O).

Figure 1
The molecular structure of (I), with atom labels and 30% probability displacement ellipsoids.

Figure 2
The pi···pi stacking between two symmetrically independent cations.

Figure 3
The hydrogen bonded helical anion-water chain and the hydrogen bonding between Cl-ion and the cations.

7-Benzyl-3-methyl-6-phenylimidazo[2,1-b][1,3]thiazol-7-ium chloride 0.75-hydrate
where P = (F o 2 + 2F c 2 )/3 (Δ/σ) max < 0.001 Δρ max = 0.30 e Å −3 Δρ min = −0.28 e Å −3 Extinction correction: SHELXL97 (Sheldrick, 2008), Fc * =kFc[1+0.001xFc 2 λ 3 /sin(2θ)] -1/4 Extinction coefficient: 0.0045 (7) Absolute structure: Flack (1983) Flack parameter: 0.04 (7) Special details Geometry. All e.s.d.'s (except the e.s.d. in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell e.s.d.'s are taken into account individually in the estimation of e.s.d.'s in distances, angles and torsion angles; correlations between e.s.d.'s in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell e.s.d.'s is used for estimating e.s.d.'s involving l.s. planes. Refinement. Refinement of F 2 against ALL reflections. The weighted R-factor wR and goodness of fit S are based on F 2 , conventional R-factors R are based on F, with F set to zero for negative F 2 . The threshold expression of F 2 > σ(F 2 ) is used only for calculating R-factors(gt) etc. and is not relevant to the choice of reflections for refinement. R-factors based on F 2 are statistically about twice as large as those based on F, and R-factors based on ALL data will be even larger.