Bis{1,4-bis[(3-butylimidazolium-1-yl)methyl]benzene}silver(I) bis(hexafluoridophosphate)

The asymmetric unit of the title complex, [Ag2(C22H30N4)2](PF6)2, consists of one AgI ion, one 1,4-bis[(3-butylimidazolium-1-yl)methyl]benzene ligand and one discrete hexafluoridophosphate anion. The formula unit is generated by an inversion center. The unique AgI ion is coordinated by two C atoms of two heterocyclic carbene ligands in an essentially linear geometry. In the crystal structure, cations and anions are linked through weak C—H⋯F hydrogen bonds, forming a three-dimensional network.


Experimental
Silver oxide, Ag 2 O, (0.13 g, 0.56 mmol) was added to a solution of 1,4-bis(3-butylimidazolium-1-yl-metyl)benzene bis(hexafluoroposphate) (0.30 g, 0.467 mmol) in acetonitrile (40 ml). The mixture was refluxed at (343-363)K for 20 hr in glassware wrapped with aluminium foil to exclude the light. The resulting mixture was filtered through celite to remove excess Ag 2 O. After evaporation of the solvent, the white residue was washed with diethyl ether (2X5 ml) to afford the complex as a white powder. The yield was (0.25g, 45%), m.p = 550-552K. Crystal suitable for X-ray was obtained by slow evaporation of the salt solution in acetonitrile at 281K.

Refinement
All H atoms were positioned geometrically with C-H = 0.93-0.97 Å and were refined using a riding model, with U iso (H) = 1.2 or 1.5 U eq (C). The highest peak in the final difference map is found at a distance of 0.87 Å from C8 and the deepest trough is 1.37 Å from H22C. Fig. 1. The molecular structure of the title compound, showing 30% probability displacement ellipsoids and the atom-numbering scheme. N1A-N4A/C1A-C22A/P1A and F1A-F6A are generated by the symmetry code -x+1, -y+1, -z (H atoms are omitted for clarity).

Special details
Experimental. The crystal was placed in the cold stream of an Oxford Cryosystems Cobra open-flow nitrogen cryostat (Cosier & Glazer, 1986) operating at 100.0 (1) K.
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.