μ3-Chlorido-tris(bis{1-[2-(dimethylamino)ethyl]-3-methylimidazol-2-ylidene}silver(I)) dichloride

In the crystal structure of the title compound, [Ag3Cl(C8H15N3)6]Cl2, the AgI ion, which is located on a twofold rotation axis, exists in a T-shape coordination environment. Two carbene C atoms of the N-heterocyclic carbene (NHC) ligands are bonded tightly forming a slightly bent [Ag(NHC)2]+ cation [C—Ag—C angle = 162.80 (18)°]. Three of these complex cations are further aggregated by one bridging chloride anion, which is lying on a threefold rotoinversion axis and is only loosely binding to the Ag+ ions. The N atom of the amine group is not engaged in any coordinative bond.

In the crystal structure of the title compound, [Ag 3 Cl-(C 8 H 15 N 3 ) 6 ]Cl 2 , the Ag I ion, which is located on a twofold rotation axis, exists in a T-shape coordination environment. Two carbene C atoms of the N-heterocyclic carbene (NHC) ligands are bonded tightly forming a slightly bent [Ag(NHC) 2 ] + cation  ]. Three of these complex cations are further aggregated by one bridging chloride anion, which is lying on a threefold rotoinversion axis and is only loosely binding to the Ag + ions. The N atom of the amine group is not engaged in any coordinative bond.

Experimental
Just recently, we published the multifarious coordination patterns of such silver complexes (Topf, Hirtenlehner, Zabel et al., 2011): E.g., in the ionic compound [(C 8 H 15 N 3 ) 2 Ag][AgCl 2 ], which is formed from the respective imidazolium chloride and Ag 2 O in dichloromethane, the ions are aggregated to infinite chains with short silver-silver contacts. Treatment of this complex with HBF 4 yields the cluster (C 8 H 15 N 3 ) 4 Ag 10 Cl 10 with the carbene carbon atom binding in a unusual µ 2 -fashion to two silver atoms. In an attempt to prepare this cluster, crystals of the title compound were formed representing the third silver chloride complex in the series of this ligand. The formation of this complex is easily rationalized by the precipitation of AgCl from [(C 8 H 15 The silver atom is in a slightly bent linear coordination with an Ag1-C1 bond length of 2.099 (3) Å and an angle C1-Ag1-C1 i of 162.8 (2)°. Perpendicular to the C1-Ag1-C1 i vector, a chloride anion is loosely binding with an Ag1-Cl1 bond length of 2.981 (1) Å. The chloride Cl1 is linking three [(C 8 H 15 N 3 ) 2 Ag] + units in a µ 3 -fashion forming a D 3 symmteric trimeric aggregate. The net 2+ charge is balanced by two non-interacting chloride ions. Within other cationic species of the type [(NHC) 2 Ag] + , the imidazole ring planes are usually found in a coplanar arrangement due to a higher πbackbonding contribution compared to a perpendicular orientation. Presumably because of steric reasons, the [(C 8 H 15 N 3 ) 2 Ag] + moiety features an arrangement with both imidazole ring planes approaching a perpendicular orientation [N1-C1-C1 i -N1 i 89.8°]. The distance between two silver atoms within the trimer is 5.164 Å, which is well beyond the range of argentophilic interactions. It should be noted, that this aggregation pattern is very rare and to the best of our knowledge reported only for {[(NHC) 2 Ag] 3 (µ 3 -I)}I 2 (NHC = 1-methyl-3-picolyl-imidazol-2-ylidene) (Wang et al., 2006) and {[(NHC) 2 Au] 3 (µ 3 -Br)}Br 2 (NHC= 1-methyl-3-benzyl-imidazol-2-ylidene) .

Experimental
Crystals of the title compound were formed in an attempt to synthesize the silver cluster (C 8 H 15 N 3 ) 4 Ag 10 Cl 10 according to a literature procedure (Topf, Hirtenlehner, Zabel et al., 2011).

Refinement
The hydrogen atoms were placed in calculated positions with C-H = 0.95-0.99 Å and refined using a riding model with U iso (H) = 1.5 U eq (C) for methyl groups and U iso (H) = 1.2 U eq (C) for methylen and aromatic hydrogen atoms. The highest residual electron density peak is located 1.28 Å from H9A and the deepest hole is located 0.53 Å from C9.
Displacement ellipsoids for non-H atoms are drawn at the 50% probability level.  [Ag 3 Cl] 2+ cation in the crystals of the title compound. The H atoms and the methyl and 2-dimethyl-amino-ethyl groups are omitted for the sake of clarity (symmetry codes: (ii) -y + 1, x-y, z; (iv) y + 1/3, x -1/3, -z + 1/6). 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.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å 2 )
x y z U iso */U eq