Bis([mu]-2-amino­pyridine)­bis­[(tri­fluoro­acetato)silver(I)]

The title compound, [Ag₂(C₂F₃O₂)₂(C₅H₆N₂)₂], is a dinuclear Ag^I complex with inversion symmetry. Each Ag atom is three-coordinated by two N atoms from two different 2-amino­pyridine ligands and by one O atom from a tri­fluoro­acetate anion, giving an approximately trigonal coordination environment. In the crystal packing, mol­ecules are connected by N-H...O and N-H...F hydrogen bonds, forming layers parallel to the (001) plane.

S1. Comment

Ag^I complexes with carboxylate anions as counterions or ligands are a group of metal compounds that, because of their wide usage in many fields, have been structurally characterized over the past 30 years (Smith et al., 1996; Kristiansson, 2001; Nomiya et al., 2000; Wei et al., 1998; Zheng et al., 2001). Studying the variety of products in the self-assembly processes between labile metal ions and flexible multidentate ligands is an interesting topic in supramolecular chemistry. The balance between the formation of different structures is often subtle. Factors that affect the coordination topology include not only the highly influential factors of metal and ligand coordination preferences but also anion-based influences. The latter factor is particularly notable in Ag^I coordination complexes (Erxleben, 2001; Khlobystov et al., 2001). Owing to the versatile coordination sphere of Ag^I, coordination numbers from two to six are possible, and because of the relatively weak nature of many Ag^I–ligand interactions, including some anion–Ag interactions, such compounds are particularly susceptible to the influence of weaker supramolecular forces. However, the different nucleophilicities and sizes of the anions must be a significant factor in recognizing the different molecular structures. More work needs to be done to understand better the controlling effect of anions, which is now becoming an interesting topic in supramolecular chemistry (Cai et al., 2002; Xu et al., 2001).

Recently, we have reported two Ag^I complexes with 2-aminopyridine and different counter-anions, viz. bis(2-aminopyridine-κN¹)(benzoato-κO)silver(I), (II) (Zhu, Usman et al., 2003) and bis(µ-4-chlorobenzoato-κ²O:O)bis[(2-aminopyridine-κN)disilver(I)], (III) (Zhu et al., 2004). These are both three-coordinate Ag^I complexes, although (II) is mononuclear and (III) is O-bridged dinuclear. In order to study the effects of the couter-anions in the construction of Ag^I coordination polymers with 2-aminopyridine, the structure of the novel title compound, (I), is reported here.

Complex (I) is a dinuclear Ag^I complex, which exhibits inversion symmetry (Fig. 1). Each Ag^I ion in the complex is three-coordinated by two N atoms from two different 2-aminopyridine ligands and by one O atom from a trifluoroacetate anion, giving an approximately trigonal coordination environment (Table 1). Atom Ag1 deviates from the N1/O2/N2ⁱ [symmetry code: (i) −x, 1 − y, 2 − z] trigonal plane by 0.188 (3) Å. The Ag1—N1 bond length [2.269 (3) Å] is a little longer than the corresponding bond length [2.230 (3) Å] in (II) and is much longer than that [2.137 (4) Å] in (III). These differences are probably caused by the coordination of atom N2 to the other Ag ion in (I), which decreases the electron density around atom N1 and weakens the bond strength between atoms Ag1 and N1. The structure of the present complex, with an eight-membered ring, is very different from that of (II) and (III). In (I), both the amine N atoms and the pyridine N atoms contribute to the coordination of the Ag atoms; however, in (II) and (III), only the pyridine N atoms take part in the coordination, while the amine N atoms participate in the formation of intermolecular N—H···O hydrogen bonds and do not coordinate to the Ag atoms.

The structural differences between (I) and compounds (II) and (III) might be caused by the different counter-ions used in the preparation of the complexes. In (I), the counter-ion is the trifluoroacetate anion, while in (II) and (III), the counter-ions are, respectively, the benzoate and 4-chlorobenzoate anions. The Ag—O(carboxylate) bond in (I) is weakened by the electro-attracting effect of the trifluoromethyl group. In fact, the Ag1—O2 bond length in (I) is slightly longer than the corresponding bond length [2.344 (4) Å] observed in (II) but is much shorter than the Ag···O weak interaction [2.813 (4) Å] observed in another Ag^I trifluoroacetate complex, viz. bis(4-aminopyridine)silver(I) trifluoroacetate, (IV), which is a mononuclear complex with a linear N(py)—Ag—N(py) bond (Zhu, Zeng et al., 2003). In (I), atom O2 is coordinated to atom Ag1 through a strong chemical bond, while in (IV), the O atom is connected to the Ag atom via a weak interaction.

In (I), another eight-membered ring (Ag1/N1/C5/N2/H2C/O1/C7/O2) is formed through an intramolecular N—H···O hydrogen bond. Furthermore, the dinuclear complexes are linked via N—H···O/F hydrogen bonds (Table 2) to form layers parallel to the (001) plane (Fig. 2). There are also π–π interactions between the pyridine rings at (x, y, z) and (-x, 1 − y, 1 − z), with a centroid separation of 3.78 (s.u.?) Å and a plane-to-plane distance of 3.34 (s.u.?) Å.

S2. Experimental

All reagents and solvents were used as obtained without further purification. Silver trifluoroacetate (0.1 mmol, 22.1 mg) and 2-aminopyridine (0.1 mmol, 9.4 mg) were dissolved in an ammonia solution (10 ml, 30%). The mixture was stirred for about 20 min at room temperature to give a clear colorless solution. The resulting solution was kept in air and, after slow evaporation of the solvent for 10 d, crystals of (I) formed, which were isolated, washed three times with water and dried in a vacuum desiccator using anhydrous CaCl₂ (yield 72%). Elemental analysis calculated: C 26.7, H 1.9, N 8.9%; found: C 26.5, H 2.0, N 8.9%.

S3. Refinement

The diffraction measured fraction θ_full was low (0.94) as a result of an unexpected error of the X-ray diffraction instrument during data collection. All H atoms were placed in idealized positions and constrained to ride on their parent atoms, with N—H distances of 0.90 Å and C—H distances of 0.96 Å, and with U_iso(H) values fixed at 0.08 Ų.

Computing details

Data collection: SMART (Bruker, 1998); cell refinement: SMART; data reduction: SAINT (Bruker, 1998); program(s) used to solve structure: SHELXS97 (Sheldrick, 1997); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997); molecular graphics: SHELXTL (Sheldrick, 1997); software used to prepare material for publication: SHELXTL.

Figures

	Fig. 1. The structure of (I), showing the atom-numbering scheme. Displacement ellipsoids are drawn at the 30% probability level. Broken lines show intramolecular hydrogen bonds. Atoms labelled with the suffix A are at the symmetry position (-x, 1 − y, 2 − z).
	Fig. 2. The crystal packing of (I), viewed along the c axis. Broken lines show intermolecular hydrogen bonds.

Bis(µ-2-aminopyridine)bis[(trifluoroacetato)silver(I)]

Crystal data

[Ag2(C2F3O2)2(C5H6N2)2]	Z = 2
Mr = 315.01	F(000) = 304
Triclinic, P1	Dx = 2.286 Mg m^−3
Hall symbol: -P 1	Mo Kα radiation, λ = 0.71073 Å
a = 6.791 (2) Å	Cell parameters from 872 reflections
b = 7.731 (2) Å	θ = 2.2–23.7°
c = 8.732 (2) Å	µ = 2.23 mm^−1
α = 92.01 (3)°	T = 293 K
β = 92.17 (3)°	Block, colorless
γ = 91.09 (3)°	0.31 × 0.22 × 0.20 mm
V = 457.7 (2) Å^3

Data collection

CCD area detector diffractometer	1789 independent reflections
Radiation source: fine-focus sealed tube	1712 reflections with I > 2σ(I)
Graphite monochromator	Rint = 0.016
ω scans	θmax = 26.5°, θmin = 2.3°
Absorption correction: multi-scan (SADABS; Sheldrick, 1996)	h = −8→8
Tmin = 0.545, Tmax = 0.664	k = −9→9
2109 measured reflections	l = −10→5

Refinement

Refinement on F^2	Secondary atom site location: difference Fourier map
Least-squares matrix: full	Hydrogen site location: inferred from neighbouring sites
R[F^2 > 2σ(F^2)] = 0.031	H-atom parameters constrained
wR(F^2) = 0.084	w = 1/[σ^2(Fo^2) + (0.0577P)^2 + 0.418P] where P = (Fo^2 + 2Fc^2)/3
S = 1.04	(Δ/σ)max < 0.001
1789 reflections	Δρmax = 0.81 e Å^−3
137 parameters	Δρmin = −0.87 e Å^−3
0 restraints	Extinction correction: SHELXL97, Fc^*=kFc[1+0.001xFc^2λ^3/sin(2θ)]^-1/4
Primary atom site location: structure-invariant direct methods	Extinction coefficient: 0.159 (7)

Special details

Geometry. All e.s.d.'s (except the e.s.d. in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell e.s.d.'s are taken into account individually in the estimation of e.s.d.'s in distances, angles and torsion angles; correlations between e.s.d.'s in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell e.s.d.'s is used for estimating e.s.d.'s 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 > σ(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	0.22514 (4)	0.46197 (3)	0.98705 (3)	0.03766 (18)
F1	0.5069 (5)	1.0916 (4)	1.2199 (7)	0.1096 (17)
F2	0.5786 (7)	0.8982 (6)	1.3736 (4)	0.1031 (15)
F3	0.7260 (5)	0.9128 (5)	1.1700 (5)	0.0821 (11)
O1	0.2279 (4)	0.8668 (4)	1.1347 (4)	0.0444 (7)
O2	0.4504 (4)	0.6560 (3)	1.1249 (3)	0.0415 (6)
N1	0.1615 (4)	0.6045 (4)	0.7684 (3)	0.0325 (6)
N2	−0.0733 (4)	0.7615 (4)	0.8968 (3)	0.0312 (6)
H2A	−0.1638	0.8422	0.8771	0.080*
H2C	0.0174	0.8099	0.9638	0.080*
C1	0.2574 (6)	0.5642 (5)	0.6406 (5)	0.0407 (8)
H1A	0.3629	0.4837	0.6475	0.080*
C2	0.2131 (6)	0.6338 (5)	0.5011 (5)	0.0436 (9)
H2B	0.2857	0.6022	0.4125	0.080*
C3	0.0613 (6)	0.7495 (5)	0.4918 (5)	0.0431 (9)
H3A	0.0236	0.7979	0.3955	0.080*
C4	−0.0360 (6)	0.7949 (5)	0.6219 (4)	0.0379 (8)
H4A	−0.1403	0.8769	0.6189	0.080*
C5	0.0200 (5)	0.7198 (4)	0.7591 (4)	0.0293 (7)
C6	0.5519 (6)	0.9291 (5)	1.2281 (4)	0.0384 (8)
C7	0.3927 (5)	0.8054 (4)	1.1527 (4)	0.0301 (7)

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
Ag1	0.0352 (2)	0.0344 (2)	0.0440 (2)	0.00374 (12)	0.00462 (12)	0.00587 (13)
F1	0.071 (2)	0.0339 (15)	0.219 (5)	−0.0004 (14)	−0.037 (3)	−0.019 (2)
F2	0.119 (3)	0.142 (4)	0.0436 (16)	−0.063 (3)	−0.0158 (17)	−0.0068 (19)
F3	0.0448 (16)	0.098 (2)	0.100 (2)	−0.0248 (15)	0.0229 (16)	−0.044 (2)
O1	0.0352 (14)	0.0422 (15)	0.0549 (16)	0.0095 (12)	−0.0075 (12)	−0.0068 (13)
O2	0.0369 (14)	0.0325 (13)	0.0543 (16)	0.0049 (10)	−0.0033 (12)	−0.0055 (12)
N1	0.0319 (15)	0.0305 (14)	0.0353 (15)	0.0038 (11)	0.0025 (11)	0.0036 (12)
N2	0.0325 (15)	0.0282 (13)	0.0331 (14)	0.0037 (11)	0.0015 (11)	0.0001 (11)
C1	0.039 (2)	0.0382 (19)	0.046 (2)	0.0060 (15)	0.0109 (16)	0.0033 (16)
C2	0.048 (2)	0.045 (2)	0.039 (2)	−0.0042 (17)	0.0157 (17)	0.0027 (17)
C3	0.051 (2)	0.040 (2)	0.0384 (19)	−0.0032 (17)	0.0008 (16)	0.0097 (16)
C4	0.041 (2)	0.0299 (17)	0.0427 (19)	0.0032 (14)	−0.0023 (15)	0.0062 (15)
C5	0.0295 (16)	0.0220 (14)	0.0365 (17)	−0.0029 (12)	0.0019 (13)	0.0021 (13)
C6	0.0340 (18)	0.0368 (18)	0.044 (2)	0.0023 (14)	0.0025 (15)	−0.0064 (16)
C7	0.0311 (17)	0.0310 (16)	0.0284 (15)	0.0030 (13)	0.0022 (12)	0.0014 (13)

Geometric parameters (Å, º)

Ag1—N1	2.269 (3)	N2—Ag1^i	2.283 (3)
Ag1—N2^i	2.283 (3)	N2—H2A	0.9001
Ag1—O2	2.384 (3)	N2—H2C	0.9000
Ag1—Ag1^i	3.140 (2)	C1—C2	1.374 (6)
F1—C6	1.303 (5)	C1—H1A	0.9600
F2—C6	1.308 (5)	C2—C3	1.380 (6)
F3—C6	1.311 (5)	C2—H2B	0.9600
O1—C7	1.230 (4)	C3—C4	1.374 (6)
O2—C7	1.246 (4)	C3—H3A	0.9600
N1—C5	1.326 (4)	C4—C5	1.392 (5)
N1—C1	1.343 (5)	C4—H4A	0.9600
N2—C5	1.411 (4)	C6—C7	1.542 (5)
N1—Ag1—N2^i	134.02 (11)	C1—C2—H2B	120.7
N1—Ag1—O2	102.19 (11)	C3—C2—H2B	121.1
N2^i—Ag1—O2	121.71 (10)	C4—C3—C2	119.3 (4)
N1—Ag1—Ag1^i	78.51 (8)	C4—C3—H3A	120.2
N2^i—Ag1—Ag1^i	70.47 (8)	C2—C3—H3A	120.4
O2—Ag1—Ag1^i	116.70 (7)	C3—C4—C5	118.7 (3)
C7—O2—Ag1	116.9 (2)	C3—C4—H4A	121.0
C5—N1—C1	117.9 (3)	C5—C4—H4A	120.3
C5—N1—Ag1	121.5 (2)	N1—C5—C4	122.5 (3)
C1—N1—Ag1	120.4 (2)	N1—C5—N2	116.0 (3)
C5—N2—Ag1^i	116.5 (2)	C4—C5—N2	121.5 (3)
C5—N2—H2A	108.0	F1—C6—F2	106.8 (4)
Ag1^i—N2—H2A	108.2	F1—C6—F3	106.7 (4)
C5—N2—H2C	108.2	F2—C6—F3	105.1 (4)
Ag1^i—N2—H2C	108.2	F1—C6—C7	113.1 (3)
H2A—N2—H2C	107.4	F2—C6—C7	110.7 (3)
N1—C1—C2	123.3 (4)	F3—C6—C7	113.9 (3)
N1—C1—H1A	118.2	O1—C7—O2	130.1 (3)
C2—C1—H1A	118.5	O1—C7—C6	115.6 (3)
C1—C2—C3	118.2 (4)	O2—C7—C6	114.2 (3)
N1—Ag1—O2—C7	57.9 (3)	C1—N1—C5—N2	−178.4 (3)
N2^i—Ag1—O2—C7	−107.8 (3)	Ag1—N1—C5—N2	6.5 (4)
N2^i—Ag1—N1—C5	76.0 (3)	C3—C4—C5—N1	−1.0 (5)
O2—Ag1—N1—C5	−87.1 (3)	C3—C4—C5—N2	179.7 (3)
N2^i—Ag1—N1—C1	−99.0 (3)	Ag1^i—N2—C5—N1	−59.4 (3)
O2—Ag1—N1—C1	98.0 (3)	Ag1^i—N2—C5—C4	120.0 (3)
Ag1^i—Ag1—N1—C1	−146.9 (3)	Ag1—O2—C7—O1	8.7 (5)
C5—N1—C1—C2	−1.4 (6)	Ag1—O2—C7—C6	−174.4 (2)
Ag1—N1—C1—C2	173.7 (3)	F1—C6—C7—O1	−19.4 (5)
N1—C1—C2—C3	−0.6 (6)	F2—C6—C7—O1	100.4 (4)
C1—C2—C3—C4	1.9 (6)	F3—C6—C7—O1	−141.5 (4)
C2—C3—C4—C5	−1.1 (6)	F1—C6—C7—O2	163.2 (4)
C1—N1—C5—C4	2.2 (5)	F2—C6—C7—O2	−77.0 (5)
Ag1—N1—C5—C4	−172.8 (3)	F3—C6—C7—O2	41.1 (5)

Symmetry code: (i) −x, −y+1, −z+2.

Hydrogen-bond geometry (Å, º)

D—H···A	D—H	H···A	D···A	D—H···A
N2—H2A···O1^ii	0.90	2.30	3.095 (4)	146
N2—H2A···F1^ii	0.90	2.52	3.314 (5)	148
N2—H2C···O1	0.90	2.06	2.943 (4)	167

Symmetry code: (ii) −x, −y+2, −z+2.