Poly[(μ-2,3-diethyl-7,8-dimethylquinoxaline-κ2 N:N)(2,3-diethyl-7,8-dimethylquinoxaline-κN)-μ-nitrato-κ2 O:O′-nitrato-κ2 O,O′-disilver(I)]

The structure of the title compound, [Ag2(NO3)2(C14H18N2)2] n , contains subtle differences in ligand, metal, and counter-anion coordination. One quinoxaline ligand uses one of its quinoxaline N atoms to bond to one silver cation. That silver cation is bound to a second quinoxaline which, in turn, is bound to a second silver atom, thereby using both of its quinoxaline N atoms. A nitrate group bonds with one of its O atoms to the first silver and uses the same oxygen to bond to a silver atom (related by symmetry to the second), thereby forming an extended network. The second nitrate group on the other silver bonds via two nitrate O atoms; one silver cation therefore has a coordination number of three whereas the second has a coordination number of four.

The structure of the title compound, [C 14 H 18 N 2 ) 2 Ag 2 ](NO 3 ) 2 , contains subtle differences in ligand, metal, and counter-anion coordination.One quinoxaline ligand uses one of its quinoxaline N atoms to bond to one silver cation.That silver cation is bound to a second quinoxaline which, in turn, is bound to a second silver atom; thereby using both of its quinoxaline N atoms.A nitrate group bonds with one of its O atoms to the first silver and uses the same oxygen to bond to a silver atom (related by symmetry to the second), thereby forming an extended network.The second nitrate group on the other silver bonds via two nitrate O atoms; one silver cation therefore has a coordination number of three whereas the second has a coordination number of four.One of the quinoxaline ligands has a disordered ethyl group.

Structure description
There are many known structures of polymeric silver(I) quinoxaline complexes.Yeh et al. (2009) have made catena complexes of silver and 2,3-diphenylquinoxaline with tetrafluoroborate in water, tetrafluoroborate in acetonitrile, perchlorate in acetonitrile, trifluoromethanesulfonate, and hexafluoroantimonate salts.When they used nitrate salts, be they in water, dimethylformamide, or acetonitrile, the nitrate counter-anions acted as bridging ligands; in addition, in all of the structures, regardless of solvent or counteranion, the quinoxaline ligands are always bidentate and bridge silver cations.Patra et al. (2007) also studied several catena complexes of 1:1 molar amounts of silver with 2,3diphenylquinoxaline-silver perchlorate from methanol, silver tetrafluoroborate from ethanol, and again with silver nitrate to name a few.In all of these structures, the quinoxaline is bidentate and bridging and nitrate ions (if present) bridge silver cations.Finally, cationic silver-diphenylquinoxaline polymeric networks can even be isolated with large phosphato-molybdenum oxide anion clusters (Tian et al., 2016).As with the other complexes, the quinoxalines are bidentate and bridge silver cations.This is the first structure of a silver catena complex with 2,3diethyl-7,8-dimethylquinoxaline; however, unlike previous structures, the bonding behavior of the quinoxaline ligand is varied.There are subtle differences in ligand, metal, and counter-anion coordination in the crystal.The structure can be described loosely as a dimer -two sets of a metal, a ligand, and an anion; however, each part of those two sets has interesting differences.As can be seen in Fig. 1, the first silver atom (Ag1) is bound to a bidentate nitrate anion [with Ag-O distances of 2.498 (2) A ˚and 2.512 (2) A ˚] and a quinoxaline nitrogen (N1) at 2.2600 (17) A ˚. What is not seen in the ORTEP is that the silver is also bound to a bridging oxygen from the second nitrate (O4) at 2.3195 (19) A ˚, making the silver four-coordinate.The first quinoxaline (on the left in Fig. 1) is bidentate and bridging; making a bond with the second silver (Ag2) at 2.2492 (17) A ˚.The dimethylquinoxaline portion of the ligand is essentially flat, whereas the ethyl groups dangle above and below the plane formed by the dimer.The second silver (Ag2) is three-coordinate and bridges the two quinoxalines [Ag2-N3 has a bond distance of 2.2552 (17) A ˚], while also being bound to a bridging nitrate anion oxygen at a distance of 2.5956 (19) A ˚.The N2-Ag2-N3 bond angle is essentially linear at 173.50 (6) � which is commonly seen in bis-and catena complexes of silver(I).Finally, the dimer is capped by a second 2,3-diethyl-7,8-dimethylquinoxaline ligand.This ligand is monodentate and is not bridging.Also, unlike the other ligand, this quinoxaline exhibits a positional disorder of its outer ethyl group.The disordered ethyl group was refined to be 59.6 (1)/40.4(1)%.

Synthesis and crystallization
Silver nitrate was used as received from Fisher Scientific.The ligand, 2,3-diethyl-7,8-dimethylquinoxaline, was synthesized from the condensation of 4,5-dimethyl-1,2-phenylenediamine with 3,4-hexanedione.Purity of the ligand was confirmed prior to use by 1 H NMR. A 30 ml solution of 43 mg (0.20 mmol) of 2,3-diethyl-7,8-dimethylquinoxaline in warmed methanol was combined with a 10 ml methanol solution of 34 g (0.20 mmol) of silver nitrate and stirred for 1 minute.The solution was taken off heat and pipetted into test tubes which were covered with parafilm and place in amber vials in a drawer to keep them from direct light.Diffraction-quality, colorless crystals formed via slow evaporation of the solvent within 48-72 h.Crystals were harvested from the evaporating solutions and used immediately due to the decay of the silver(I) complex in light.

Refinement
Crystal data, data collection and structure refinement details are summarized in Table 1.One of the ethyl groups in a 2,3diethyl-7,8-dimethylquinoxaline are disordered.The thermal displacement parameters of the disordered carbons in the group were restrained as the amount of disorder was refined.The percent disorder of the ethyl group was determined to be 59.6 (1)/40.4(1)%.Thermal displacement parameters for the nitrate atoms were also restrained during refinement.

Special details
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.Hydrogen atoms on sp 2 and sp 3 carbons were placed at calculated positions with a C-H distance of 0.93 Å and 0.96 Å and were included in the refinement in riding motion approximation with U iso = 1.2U eq or 1.5U eq of the carrier atom, respectively.
Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å 2 )

Figure 1 A
Figure 1A view of the title compound(Farrugia, 2012).Displacement ellipsoids are drawn at the 50% probability level.