Potassium bis[bis(1-benzyl-3-methylimidazolium)silver(I)] tris(hexafluoridophosphate)

In the title compound, K[Ag(C11H12N2)2]2(PF6)3, the 12-coordinate potassium cation lies on a crystallographic twofold axis and one of the hexafluorophosphate anions is generated by symmetry. In the complex cation, the AgI ion is coordinated by two C atoms; the two imidazolium rings are orientated at a dihedral angle of 8.14 (14)°. In the 1-benzyl-3-methylimidazolium units, the dihedral angles between imidazolium and phenyl rings are 80.47 (15) and 76.53 (14)°. The F atoms of the general-position hexafluorophosphate anion are disordered over two sets of sites in a 0.767 (17):0.233 (17) ratio. In the crystal, the hexafluorophosphate anions link the cations into three-dimensional networks via intermolecular C—H⋯F hydrogen bonds and are further consolidated by π–π stacking [centroid–centroid distances = 3.5518 (15) Å] interactions.


Related literature
For the stability of the temperature controller used in the data collection, see: Cosier & Glazer (1986). For related structures, see: Haque et al. (2010a,b). For bond-length data, see: Allen et al. (1987).
Data collection: APEX2 (Bruker, 2009); cell refinement: SAINT (Bruker, 2009); data reduction: SAINT; program(s) used to solve structure: SHELXTL (Sheldrick, 2008); program(s) used to refine structure: SHELXTL; molecular graphics: SHELXTL; software used to prepare material for publication: SHELXTL and PLATON (Spek, 2009(Spek, ). al., 1996. Among these complexes, the family of silver NHC complexes have been receiving continuous attention (Zhou et al., 2008). The in-situ deprotonation method using Ag 2 O as a basic metal source developed by Lin and co-workers (Wang & Lin, 1998) has been widely employed to synthesise these Ag-NHC complexes. The silver complexes act as effective carbene transfer agents to other metals and are much more stable than the free carbene (Lin & Vasam, 2007). Biological activity of many Ag-NHC complexes as antimicrobial and antitumour agents has been confirmed (Ray et al., 2007;Özdemir et al., 2010;Medvetz et al., 2008).

Experimental
To a stirred solution of 1-benzyl-3-methylimidazolium hexafluorophosphate (0.5 g, 1.57 mmol) in acetonitrile (40 ml), Ag 2 O (0.37 g, 1.6 mmol) was added. The mixture was refluxed at 70 °C for 18 h in glassware wrapped in aluminum foil to exclude the light. The mixture was filtered through celite to remove excess Ag 2 O and the solvent was evaporated under vacuum. The white residue was washed with diethyl ether (2 × 3 ml) to afford the complex as a white powder, the yield was 0.66 g, 70.3%, m. p. = 421-423 K. Colourless blocks of (I) were obtained by slow diffusion of diethyl ether into a solution of the complex in acetonitrile at ambient temperature.
supplementary materials sup-2 Refinement All H atoms were positioned geometrically and refined using a riding model with C-H = 0.93-0.97 Å and U iso (H) = 1.2 or 1.5 U eq (C). A rotating-group model was applied for the methyl groups. Six fluorine atoms (F1A-F6A) of the hexafluorophosphate anion are disordered over two positions with refined site-occupancies of 0.767 (17) : 0.233 (17). The minor component of disorder was refined isotropically and subjected to rigid bond and similarity restraints. The highest residual electron density peak is located at 0.82 Å from Ag1 and the deepest hole is located at 0.69 Å from Ag1. Fig. 1. The molecular structure of (I) showing 50% probability displacement ellipsoids for non-H atoms. Both major and minor components of disorder are shown. Symmetry code: ($) -x, -y, -z. Coordination interactions between K cation and hexafluorophosphate anions have been omitted for clarity.
Geometry. All esds (except the esd in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell esds are taken into account individually in the estimation of esds in distances, angles and torsion angles; correlations between esds in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell esds is used for estimating esds 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 > 2sigma(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.