Ammine(2,2′-bipyridine-κ²N,N′)silver(I) nitrate: a dimer formed by π–π stacking and ligand-unsupported Ag...Ag inter­actions

Reaction of AgNO₃ and 2,2′-bipyridine (bipy) under ultrasonic treatment gave the title compound, [Ag(C₁₀H₈N₂)(NH₃)]NO₃. The crystal structure consists of dimers formed by two symmetry-related Ag^I–bipy monomers connected through intra-dimer π–π stacking and ligand-unsupported Ag...Ag inter­actions. A crystallographic C2 axis passes through the mid-point of and is perpendicular to the Ag...Agⁱ(−x + 1, y, −z + ) axis. In addition, each Ag^I cation is coordinated by one chelating bipy ligand and one ammine ligand, giving a trigonal coordination environment capped by the symmetry-equivalent Ag atom. Mol­ecules are assembled by Ag...Ag, π–π, hydrogen-bond (N—H...O and C—H...O) and weak Ag...π inter­actions into a three-dimensional framework. Comparing the products synthesized under different mechanical treatments, we found that reaction conditions have a significant influence on the resulting structures. The luminescence properties of the title compound are also discussed.

S1. Comment

Self-assembled coordination structures are one of the most attractive areas of materials research due to their intriguing structural topologies and functional properties such as molecular adsorption, magnetism, and luminescence (Biradha et al., 2006; Wu et al., 2009; Blake, Brooks et al., 1999; Blake, Champness et al., 1999; Evans & Lin, 2002; Kitagawa et al., 2004; Yaghi et al., 2003), and much attention is focused on their design and construction. However, the factors that govern the formation of such complexes are complicated and include not only the inherent properties of metal ions and ligand structure, but also anion-directed interactions as well as reaction conditions (Bu et al., 2003; Kong et al., 2008, 2009). In addition to covalent bonds, noncovalent interactions such as Ag···Ag, π–π, hydrogen bonds and cation···π interactions also play important roles in controlling molecular packing (Pedireddi et al., 1996; Kolotuchin et al., 1995; Li et al., 2006; Sun et al., 2003; Lough et al., 2000; Massoud & Langer, 2009; Goodgame et al., 2002). Because the central C—C bond of bipy (bipyridine) can rotate freely, bipy cannot just be regarded as a chelating ligand (Kaes et al., 2000; Marchetti et al., 2007), but also as a potential spacer between metal centers by acting as a bridging ligand with an anti configuration (Yu et al., 2007; Forniés et al., 1993). Therefore, bipy and its derivatives are widely used in the construction of novel Ag^I-containing complexes incorporating diverse supramolecular interactions (Hung-Low et al., 2009; Ye et al., 2005). Recently, we have pursued systematic investigations into the assembly of Ag^I cations with different angular and linear bipodal N-donor ligands, such as aminopyrimidine and aminopyrazine (e.g. Luo, Huang, Chen et al., 2008; Luo, Huang, Zhang et al., 2008; Luo et al., 2009; Sun, Luo, Huang et al., 2009; Sun, Luo, Xu et al., 2009; Sun, Luo, Zhang et al., 2009), with the principal aim of obtaining supramolecular complexes or multifunctional coordination polymers. In an attempt to exploit the influence of synthesis conditions on the structures of the AgNO₃–bipy system, we successfully obtained the title compound, (I), and the known coordination polymer, (II) {catena-[(µ₂-nitrato-O,O,O')-(2,2'-bipyridine-N,N')-silver(I)]; Bowmaker et al., 2005} in the same solvent system.

The asymmetric unit of (I) contains one Ag^I cation, one bipy ligand, one coordinated ammonia molecule and one nitrate anion. As shown in Fig. 1, the Ag^I cation is coordinated in a trigonal planar fashion by three N atoms from one bipy ligand and one ammonia molecule, with bond angles ranging from 72.36 (12) to 145.23 (14) °. The Ag – N_bipy bond lengths are identical within experimental error (Table 1) and comparable to reported values (Oxtoby et al., 2002; Fan et al., 2007; Nicola et al., 2007). The pyridyl rings of the bipy are nearly coplanar with a twist angle of 4.8 (5)°. With an Ag—N bond length of 2.135 (4) Å, the coordinated ammonia molecule plays a role as terminator, obstructing aggregation of (I). Because of the labile nature of the this Ag—N bond, the presence of the ammonia in the coordination sphere of the metal center offers a potential coordination site in the molecule. Two symmetry-related Ag^I--bipy monomers aggregate to a dimer with a head-to-head arrangement through intra-dimer π–π stacking and a ligand-unsupported Ag···Ag interaction (Tong et al., 1999), where the Ag···Agⁱ interaction has a distance of 3.0456 (16) Å. This is significantly shorter than twice the van der Waals radius of Ag^I (3.44 Å; Bondi, 1964) and the completed coordination sphere of the Ag centers can thus be described as capped trigonal planar. The other cases where such short contacts exist between non-bridged Ag^I cations are found in Ag(imidazole)₂ClO₄ (Eastland et al., 1980) and [Cu(ethylenediamine)₃][Ag₂(CN)₄] (Kappenstein et al.,1988). A crystallographic C2 axis passes perpendicularly through the midpoint of this Ag···Agⁱ axis. This weak bonding interaction between two d¹⁰ cations is possible via the participation of 5s and 5p orbitals which are close in energy to the 4d orbitals. Intra-dimer π–π stacking also contributes to the reinforcement of this Ag···Ag interaction (Venkatalakshmi et al., 1992). Moreover, the π–π stacking [Cg1···Cg2ⁱ = 3.628 (3) Å (intra-dimer) and Cg1···Cg2^vi = 3.711 (3) Å (inter-dimer); Cg1 and Cg2 are the centroids of the N1/C1–C5 and N2/C6–10 rings, respectively; symmetry codes: (i) – x + 1, y, – z + 1/2; (vi) – x + 1 , – y + 1 , – z; Fig. 2] and weak Ag···C interactions [Ag1···C6^vi = 3.386 (4) and Ag1···C7^vi = 3.393 (5) Å; symmetry code: (vi) – x + 1 , – y + 1 , – z] act as a `glue' to reinforce the dimers, forming a column along the c axis, in which the dimers are arranged in a head-to-tail orientation. In addition, the nitrate anion acts as an acceptor and is hydrogen bonded to three different symmetry equivalents of the ammonia molecules (Table 2). Non-classic C_pyridyl—H···O hydrogen bonds [average C···O distance: 3.280 (5) Å; Table 2] and classic N—H···O hydrogen bonds link adjacent columns to form the resulting three-dimensional supramolecular framework (Fig. 3).

The effects of the synthesis conditions on the structure of the AgNO₃–bipy system were investigated in the ultrasonic and stirred methods with the same solvent system (methanol-water; 15 ml, 1:2 v/v). Under the stirred condition, we could only obtain coordination polymer (II), first reported by the A. H. White group (Bowmaker et al., 2005). In the structure of (II), the nitrate not only acts as a coordinated anion but also as a bridging anion to link Ag^I–bipy cationic units into one-dimensional zigzag chains. The difference between the structures of (I) and (II) originates mainly from the different mechanical treatments which cause the ammonia molecule and nitrate anion to play different roles in the construction of (I) and (II).

It is known that the free bipy molecule displays a weak luminescence at circa 530 nm in the solid state at room temperature. As shown in Fig. 4, compound (I) exhibits an intense emission maximum at 469 nm upon excitation at 345 nm, which may be attributed to the intraligand emission from the bipy (Wang et al., 2004). Compared with that of the free bipy molecule, the blue shift and the luminescent enhancement of the emission at 469 nm may be due to the chelation of the bipy ligand to the Ag^I, which effectively increases the rigidity and coplanarity of the ligand and reduces the loss of energy by nonradiative decay of the intraligand emission excited state (Zhang et al., 2003; Qian & Wang 2002).

Related literature

For related literature, see: Biradha et al. (2006); Blake, Brooks, Champness, Cooke, Deveson, Fenske, Hubberstey, Li & Schröder (1999); Blake, Champness, Hubberstey, Li, Withersby & Schröder (1999); Bondi (1964); Bowmaker et al. (2005); Bu et al. (2003); Eastland et al. (1980); Evans & Lin (2002); Forniés et al. (1993); Goodgame et al. (2002); Hung-Low, Renz & Klausmeyer (2009); Kaes et al. (2000); Kappenstein et al. (1988); Kitagawa et al. (2004); Kolotuchin et al. (1995); Kong et al. (2008, 2009); Li et al. (2006); Lough et al. (2000); Luo et al. (2009); Luo, Huang, Chen, Lin & Zheng (2008); Luo, Huang, Zhang, Lin & Zheng (2008); Marchetti et al. (2007); Massoud & Langer (2009); Nicola et al. (2007); Pedireddi et al. (1996); Qian & Wang (2002); Sun et al. (2003); Sun, Luo, Huang, Zhang & Zheng (2009); Tong et al. (1999); Wang et al. (2004); Wu et al. (2009); Yaghi et al. (2003); Ye et al. (2005); Yu et al. (2007); Zhang et al. (2003).

S2. Experimental

All reagents and solvents were used as obtained commercially without further purification. A mixture of AgNO₃ (170 mg, 1 mmol) and 2,2'-bipyridine (156 mg, 1 mmol) was added to a methanol–water solvent mixture (15 ml, 1:2 v/v) under ultrasonic conditions, which helped to dissolve the white precipitation. An aqueous NH₃ solution (25%) was added dropwise to the mixture to give a clear solution. The resulting solution was left to evaporate slowly in the dark at room temperature for several weeks to give crystals of (I) in the form of yellow prisms. The crystals were washed using deionized water and dried in air (yield: circa 51%, based on Ag). Analysis calculated for C₂₀H₂₂Ag₂N₈O₆: C 35.01, H 3.23, N 16.33%; found: C 34.95, H. 3.14, N 16.27%.

S3. Refinement

The aromatic H atoms were generated geometrically (C—H 0.93Å) and were allowed to ride on their parent atoms in the riding model approximations, with U_iso(H) = 1.2U_eq(C). The positions of the ammonia H atoms were located from difference maps and refned with the N—H distances restrained to 0.89 (2) Å with U_iso(H) = 1.5U_eq(N).

Computing details

Data collection: CrysAlis CCD (Oxford Diffraction, 2008); cell refinement: CrysAlis RED (Oxford Diffraction, 2008); data reduction: CrysAlis RED (Oxford Diffraction, 2008); program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: DIAMOND (Brandenburg, 2008) and SHELXTL (Sheldrick, 2008); software used to prepare material for publication: SHELXL97 (Sheldrick, 2008), publCIF (Westrip, 2010).

Figures

	Fig. 1. The structure of (I), with the atom-numbering scheme, showing the coordination environment around the Ag^I centre. Displacement ellipsoids are drawn at the 50% probability level. H atoms are shown as spheres of arbitrary radius.
	Fig. 2. A ball–stick perspective view of the π–π stacking (green dashed lines) between the pyridyl rings of neighboring bipy ligands and the Ag···Ag interaction (golden dashed lines). H atoms and nitrate anions are omitted for clarity.
	Fig. 3. A ball–stick perspective view of the three-dimensional supramolecular framework incorporating hydrogen bonds (dashed lines). [The unit-cell box looks very strange; does this need to be redrawn?]
	Fig. 4. Photoinduced emission spectrum of (I) (solid line) and free bipy (dotted line) in the solid state.

Ammine(2,2'-bipyridine-κ²N,N')silver(I) nitrate

Crystal data

[Ag(C10H8N2)(NH3)]NO3	F(000) = 1360
Mr = 343.10	Dx = 1.897 Mg m^−3
Monoclinic, C2/c	Mo Kα radiation, λ = 0.71073 Å
Hall symbol: -C 2yc	Cell parameters from 3049 reflections
a = 17.685 (9) Å	θ = 5.4–56.9°
b = 10.690 (5) Å	µ = 1.68 mm^−1
c = 12.748 (7) Å	T = 298 K
β = 94.457 (12)°	Prism, yellow
V = 2403 (2) Å^3	0.10 × 0.08 × 0.08 mm
Z = 8

Data collection

Oxford Diffraction Gemini S Ultra diffractometer	2320 independent reflections
Radiation source: sealed tube	2161 reflections with I > 2σ(I)
Graphite monochromator	Rint = 0.030
Detector resolution: 16.1903 pixels mm^-1	θmax = 26.0°, θmin = 2.2°
ω scans	h = −17→21
Absorption correction: multi-scan (CrysAlis RED; Oxford Diffraction, 2008)	k = −13→5
Tmin = 0.850, Tmax = 0.877	l = −15→14
4406 measured reflections

Refinement

Refinement on F^2	Primary atom site location: structure-invariant direct methods
Least-squares matrix: full	Secondary atom site location: difference Fourier map
R[F^2 > 2σ(F^2)] = 0.044	Hydrogen site location: inferred from neighbouring sites
wR(F^2) = 0.112	H atoms treated by a mixture of independent and constrained refinement
S = 1.21	w = 1/[σ^2(Fo^2) + (0.0452P)^2 + 2.9467P] where P = (Fo^2 + 2Fc^2)/3
2320 reflections	(Δ/σ)max < 0.001
172 parameters	Δρmax = 0.85 e Å^−3
6 restraints	Δρmin = −0.59 e Å^−3

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. Refinement of F² against ALL reflections. The weighted R-factor wR and goodness of fit S are based on F², conventional R-factors R are based on F, with F set to zero for negative F². The threshold expression of F² > 2sigma(F²) is used only for calculating R-factors(gt) etc. and is not relevant to the choice of reflections for refinement. R-factors based on F² 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 (Ų)

	x	y	z	Uiso*/Ueq
Ag1	0.47287 (2)	0.67735 (3)	0.13367 (3)	0.04812 (18)
C1	0.6485 (3)	0.5882 (4)	0.1571 (3)	0.0401 (10)
H1	0.6573	0.6733	0.1674	0.048*
C2	0.7100 (3)	0.5087 (5)	0.1566 (4)	0.0492 (11)
H2	0.7591	0.5394	0.1680	0.059*
C3	0.6974 (3)	0.3850 (4)	0.1391 (4)	0.0456 (11)
H3	0.7379	0.3297	0.1379	0.055*
C4	0.6239 (2)	0.3421 (4)	0.1233 (4)	0.0362 (9)
H4	0.6144	0.2578	0.1099	0.043*
C5	0.5642 (2)	0.4260 (3)	0.1275 (3)	0.0307 (8)
C6	0.4836 (2)	0.3854 (3)	0.1149 (3)	0.0275 (8)
C7	0.4630 (2)	0.2606 (4)	0.1049 (3)	0.0362 (9)
H7	0.5001	0.1988	0.1054	0.043*
C8	0.3873 (3)	0.2284 (4)	0.0944 (4)	0.0427 (10)
H8	0.3729	0.1448	0.0884	0.051*
C9	0.3337 (3)	0.3205 (4)	0.0928 (4)	0.0411 (10)
H9	0.2823	0.3013	0.0856	0.049*
C10	0.3579 (2)	0.4425 (4)	0.1021 (3)	0.0368 (9)
H10	0.3214	0.5053	0.1009	0.044*
N1	0.5773 (2)	0.5483 (3)	0.1434 (3)	0.0329 (7)
N2	0.43030 (19)	0.4753 (3)	0.1126 (3)	0.0328 (7)
N3	0.4346 (2)	0.8667 (3)	0.1352 (3)	0.0403 (8)
H3A	0.472 (2)	0.920 (4)	0.135 (3)	0.060*
H3B	0.411 (2)	0.886 (5)	0.192 (2)	0.060*
H3C	0.401 (2)	0.887 (5)	0.082 (3)	0.060*
N4	0.86176 (19)	0.4851 (3)	0.3840 (3)	0.0371 (8)
O1	0.9264 (2)	0.5243 (3)	0.3790 (5)	0.099 (2)
O2	0.82189 (19)	0.5343 (3)	0.4472 (3)	0.0529 (8)
O3	0.83974 (19)	0.3966 (3)	0.3291 (3)	0.0533 (8)

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
Ag1	0.0854 (3)	0.0242 (2)	0.0354 (2)	0.01682 (14)	0.00884 (19)	0.00001 (12)
C1	0.054 (3)	0.031 (2)	0.036 (2)	−0.0101 (18)	0.0120 (19)	0.0048 (17)
C2	0.042 (3)	0.052 (3)	0.054 (3)	−0.010 (2)	0.009 (2)	0.013 (2)
C3	0.042 (2)	0.044 (2)	0.052 (3)	0.0081 (19)	0.006 (2)	0.011 (2)
C4	0.036 (2)	0.0322 (19)	0.041 (2)	0.0062 (16)	0.0069 (18)	0.0066 (17)
C5	0.042 (2)	0.0244 (17)	0.0260 (19)	0.0018 (15)	0.0056 (16)	0.0037 (14)
C6	0.038 (2)	0.0220 (17)	0.0225 (17)	0.0070 (14)	0.0037 (15)	0.0002 (14)
C7	0.042 (2)	0.0275 (19)	0.040 (2)	0.0072 (16)	0.0076 (18)	−0.0060 (17)
C8	0.049 (3)	0.033 (2)	0.047 (3)	−0.0042 (18)	0.007 (2)	−0.0055 (19)
C9	0.037 (2)	0.048 (3)	0.038 (2)	−0.0024 (18)	0.0035 (19)	−0.0060 (18)
C10	0.042 (2)	0.039 (2)	0.030 (2)	0.0127 (18)	0.0017 (17)	−0.0022 (17)
N1	0.047 (2)	0.0262 (15)	0.0269 (16)	−0.0006 (14)	0.0083 (14)	0.0004 (13)
N2	0.041 (2)	0.0281 (16)	0.0290 (17)	0.0107 (14)	−0.0002 (14)	−0.0034 (13)
N3	0.050 (2)	0.0258 (17)	0.046 (2)	0.0099 (15)	0.0082 (17)	−0.0006 (15)
N4	0.0317 (18)	0.0240 (15)	0.056 (2)	0.0007 (13)	0.0035 (16)	0.0020 (15)
O1	0.051 (2)	0.039 (2)	0.215 (6)	−0.0162 (17)	0.057 (3)	−0.038 (3)
O2	0.0487 (19)	0.0536 (19)	0.057 (2)	0.0024 (15)	0.0091 (16)	−0.0148 (17)
O3	0.058 (2)	0.0475 (18)	0.055 (2)	−0.0100 (16)	0.0092 (16)	−0.0213 (16)

Geometric parameters (Å, º)

Ag1—N3	2.135 (4)	C6—C7	1.387 (6)
Ag1—N2	2.296 (3)	C7—C8	1.378 (6)
Ag1—N1	2.302 (3)	C7—H7	0.9300
Ag1—Ag1^i	3.0456 (16)	C8—C9	1.366 (6)
C1—N1	1.328 (6)	C8—H8	0.9300
C1—C2	1.380 (7)	C9—C10	1.374 (6)
C1—H1	0.9300	C9—H9	0.9300
C2—C3	1.357 (7)	C10—N2	1.325 (6)
C2—H2	0.9300	C10—H10	0.9300
C3—C4	1.378 (6)	N3—H3A	0.872 (19)
C3—H3	0.9300	N3—H3B	0.891 (19)
C4—C5	1.389 (5)	N3—H3C	0.884 (19)
C4—H4	0.9300	N4—O3	1.223 (4)
C5—N1	1.340 (5)	N4—O1	1.223 (5)
C5—C6	1.487 (6)	N4—O2	1.229 (5)
C6—N2	1.345 (5)
N3—Ag1—N2	142.34 (14)	C6—C7—H7	120.1
N3—Ag1—N1	145.25 (14)	C9—C8—C7	119.2 (4)
N2—Ag1—N1	72.36 (12)	C9—C8—H8	120.4
N3—Ag1—Ag1^i	93.86 (11)	C7—C8—H8	120.4
N2—Ag1—Ag1^i	100.92 (8)	C8—C9—C10	118.2 (4)
N1—Ag1—Ag1^i	75.91 (8)	C8—C9—H9	120.9
N1—C1—C2	122.7 (4)	C10—C9—H9	120.9
N1—C1—H1	118.6	N2—C10—C9	123.5 (4)
C2—C1—H1	118.6	N2—C10—H10	118.2
C3—C2—C1	118.8 (4)	C9—C10—H10	118.2
C3—C2—H2	120.6	C1—N1—C5	119.0 (4)
C1—C2—H2	120.6	C1—N1—Ag1	124.3 (3)
C2—C3—C4	119.3 (4)	C5—N1—Ag1	116.6 (3)
C2—C3—H3	120.3	C10—N2—C6	118.9 (3)
C4—C3—H3	120.3	C10—N2—Ag1	124.5 (3)
C3—C4—C5	119.3 (4)	C6—N2—Ag1	116.5 (3)
C3—C4—H4	120.3	Ag1—N3—H3A	112 (4)
C5—C4—H4	120.3	Ag1—N3—H3B	113 (3)
N1—C5—C4	120.9 (4)	H3A—N3—H3B	105 (3)
N1—C5—C6	117.0 (3)	Ag1—N3—H3C	114 (4)
C4—C5—C6	122.1 (3)	H3A—N3—H3C	107 (3)
N2—C6—C7	120.4 (4)	H3B—N3—H3C	103 (3)
N2—C6—C5	117.3 (3)	O3—N4—O1	119.5 (4)
C7—C6—C5	122.3 (3)	O3—N4—O2	122.2 (4)
C8—C7—C6	119.8 (4)	O1—N4—O2	118.2 (4)
C8—C7—H7	120.1
N1—C5—C6—N2	4.8 (5)	N3—Ag1—Ag1^i—N3^i	−36.3 (2)

Symmetry code: (i) −x+1, y, −z+1/2.

Hydrogen-bond geometry (Å, º)

D—H···A	D—H	H···A	D···A	D—H···A
N3—H3A···O1^ii	0.87 (2)	2.14 (2)	2.998 (6)	170 (5)
N3—H3B···O3^iii	0.89 (2)	2.23 (2)	3.110 (5)	169 (4)
N3—H3C···O2^iv	0.88 (2)	2.30 (2)	3.177 (5)	172 (5)
C1—H1···O3^ii	0.93	2.39	3.307 (5)	169
C7—H7···O1^v	0.93	2.27	3.192 (5)	169
C10—H10···O2^i	0.93	2.58	3.340 (6)	139

Symmetry codes: (i) −x+1, y, −z+1/2; (ii) −x+3/2, y+1/2, −z+1/2; (iii) x−1/2, y+1/2, z; (iv) x−1/2, −y+3/2, z−1/2; (v) −x+3/2, y−1/2, −z+1/2.