Poly[bis­(μ₂-2-amino­pyrazine-κ²N¹:N⁴)(μ₂-nitrato-κ²O:O)(nitrato-κ²O,O′)disilver(I)]: an achiral two-dimensional coordination polymer forming chiral crystals

The solution reaction of AgNO₃ and 2-amino­pyrazine (apyz) in a 1:1 ratio gives rise to the title compound, [Ag₂(NO₃)₂(C₄H₅N₃)₂]_n, (I), which possesses a chiral crystal structure. In (I), both of the crystallographically independent Ag^I cations are coordinated in tetra­hedral geometries by two N atoms from two apyz ligands and two O atoms from nitrate anions; however, the Ag^I centers show two different coordination environments in which one is coordinated by two O atoms from two different symmetry-related nitrate anions and the second is coordinated by two O atoms from a single nitrate anion. The crystal structure consists of one-dimensional Ag^I–apyz chains, which are further extended by μ₂-κ²O:O nitrate anions into a two-dimensional (4,4) sheet. N—H...O and C_apyz—H...O hydrogen bonds connect neighboring sheets to form a three-dimensional supra­molecular framework.

S1. Comment

Interest in crystal engineering and supramolecular chemistry is rapidly increasing becuase of the diverse and aesthetic structural topologies of the products of such studies and their potential use in optical, electrical, catalytic and gas storage applications and even in drug delivery as functional solid materials (Blake, Brooks et al., 1999; Blake, Champness et al., 1999; Blake et al., 1997; Evans & Lin, 2002; Kitagawa et al., 2004; Yaghi et al., 2003; Applegarth et al., 2005). Particularly, there is considerable interest in chiral solid-state materials, owing to their potential application in asymmetric catalysis and chiral separation (Kesanli & Lin, 2003; Pidcock, 2005). Although these chiral materials can be synthesized from single chiral organic spacers with metal ions (Dai et al., 2005; Wang et al., 2008; Zaworotko, 2001), compounds presenting chiral crystal structures self-assembled from the Ag^I cation and achiral 2-aminopyrazine (apyz) ligand have not been documented yet. Recently, we have undertaken a series of investigations into the self-assembly of the Ag^I cation with different angular and linear bipodal N-donor ligands, such as aminopyrimidine and aminopyrazine (Luo, Huang, Chen et al., 2008; Luo, Huang, Zhang et al., 2008; Luo, Sun, Xu et al., 2009; Luo, Sun, Zhang, Huang & Zheng, 2009; Luo, Sun, Zhang, Xu 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 compounds or multifunctional coordination polymers. In an attempt to exploit the influence of anions on the Ag^I–apyz system, we surprisingly obtained the achiral coordination polymer (I), stacking to give a chiral crystal structure.

The asymmetric unit of (I) contains two different Ag^I cations, two apyz ligands and two nitrate anions. The coordination geometry of the Ag^I cation is tetrahedral, and each Ag^I cation is coordinated by two N atoms from two different apyz ligands and two O atoms from nitrate anions (Fig. 1). The geometric parameters, especially the bond angles around atoms Ag1 and Ag2, are obviously different. The bond angles around Ag1 and Ag2 open up from the ideal tetrahedral angle to 145.84 (14) and 150.84 (14)°, respectively,, while the remaining angles around atoms Ag1 and Ag2 are in the ranges 85.20 (12)–125.32 (12)° and 49.89 (9)–113.25 (12)°, respectively. The Ag—N and Ag—O bond lengths (Table 1) are comparable to those in related compounds (Fan et al., 2007; Oxtoby et al., 2002; Turner et al., 2005; Massoud & Langer, 2009; Massoud et al., 2009; Withersby et al., 1997; Zartilas et al., 2007). There are also weak Ag···C interactions with Ag···C distances in the range 3.314 (4)–3.322 (4) Å, which fall in the secondary bonding range (the sum of the van der Waals radii of Ag and C is 3.42 Å; Mascal et al., 2000). Some polymeric silver(I) compounds of aromatic ligands have been reported to present similar Ag···C interactions, with Ag···C bond distances of ca 2.80–3.38 Å (Blake et al., 2000; Khlobystov et al., 2001). Therefore, these interactions in (I) are very important, in the present case, for the packing of (I) in the solid state. Between neighboring chains, the shortest Ag···Ag separation is 3.6087 (6) Å, which is longer than twice the van der Waals radius of Ag^I (1.72 Å; Bondi, 1964), indicating no direct metal–metal interaction.

The apyz ligand acts in a µ₂-N,N'-bidentate fashion to link Ag^I cations to form a one-dimensional chain in which atoms Ag1 and Ag2 alternate. The nitrate anions show two different coordination modes, namely µ₂-κ²O:O and κ²O:O', which are found in many other silver(I) compounds (Cui & He, 2003; Faure et al., 1985; Chen et al., 2004). The µ₂-κ²O:O-nitrate anions play an important role in constructing the two-dimensional undulating sheet (Fig. 2) in which µ₂-κ²O:O-nitrate anions bridge the neighboring chains. Fig. 3 shows a schematic depiction of the sheet, which has a (4,4) topology (Batten & Robson, 1998), with Ag^I cations as the four-connected nodes and with meshes of dimensions 3.61 × 7.13 Å. In addition, amino groups from apyz ligands act as hydrogen-bond donors with N···O distances in the range 2.912 (5)–3.099 (5)Å (Table 2) to form intra-sheet N—H···O hydrogen bonds. apyz–nitrate C—H···O hydrogen bonds with C···O distances in the range 3.066 (5)–3.521 (5)Å not only support the N—H···O hydrogen bonds within the sheets but also link the sheets to form a three-dimensional network (Fig. 4).

Related literature

For related literature, see: Applegarth et al. (2005); Batten & Robson (1998); Blake et al. (1997, 2000); Blake, Brooks, Champness, Cooke, Deveson, Fenske, Hubberstey, Li & Schröder (1999); Blake, Champness, Hubberstey, Li, Withersby & Schröder (1999); Bondi (1964); Chen et al. (2004); Cui & He (2003); Dai et al. (2005); Evans & Lin (2002); Fan et al. (2007); Faure et al. (1985); Kesanli & Lin (2003); Khlobystov et al. (2001); Kitagawa et al. (2004); Luo et al. (2008a, 2008b, 2009a, 2009b, 2009c); Mascal et al. (2000); Massoud & Langer (2009); Massoud, Hefnawy, Langer, Khatab, Öhrstrom & Abu-Youssef (2009); Oxtoby et al. (2002); Pidcock (2005); Sun et al. (2009a, 2009b, 2009c); Turner et al. (2005); Wang et al. (2008); Withersby et al. (1997); Yaghi et al. (2003); Zartilas et al. (2007); Zaworotko (2001).

S2. Experimental

All reagents and solvents were used as obtained commercially without further purification. To an aqueous solution (14 ml) of AgNO₃ (170 mg, 1.0 mmol), aminopyrazine (95 mg, 1.0 mmol) in ethanol (12 ml) was added dropwise under continuous stirring. The resulting gray precipitate was filtered off, and the clear filtrate was left undisturbed for two weeks. Yellow block crystals suitable for X-ray measurements were formed, collected by filtration and dried in air with a yield of 62% with respect to the ligand. Analysis calculated for C₈H₁₀Ag₂N₈O₆: C 18.13, H 1.90, N 21.14%; found: C 18.18, H. 1.81, N 21.21%. IR (KBr, cm^-1): 3332 (s, br), 3142 (s, br), 1643 (vs), 1582 (vs), 1530 (s), 1475 (sh), 1207 (m), 1038 (w), 1001 (m), 828 (m), 619 (w), 431 (w).

S3. Refinement

All H atoms were fixed geometrically and treated as riding [C—H = 0.95 Å and N—H = 0.88 Å, with U_iso(H) = 1.2U_eq(C,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); software used to prepare material for publication: SHELXL97 (Sheldrick, 2008) and publCIF (Westrip, 2009).

Figures

	Fig. 1. The structure of (I), showing the atom-numbering scheme and the coordination environment around the Ag^I centre. Displacement ellipsoids are drawn at the 50% probability level. H atoms are shown as small spheres of arbitrary radii. [Symmetry codes: (i) x + 1, y, z; (ii) x - 1, y, z + 1; (iii) x + 1, y, z - 1.]
	Fig. 2. A ball–stick perspective view, along the b axis, of the two-dimensional sheet in (I). H atoms have been omitted for clarity.
	Fig. 3. A schematic view, along the b axis, of the (4,4)-net in (I).
	Fig. 4. A perspective view, along a axis, of the three-dimensional supramolecular framework incorporating N—H···O and C—H···O hydrogen bonds (dashed lines).

Poly[bis(µ₂-2-aminopyrazine-κ²N¹:N⁴)(µ₂-nitrato-κ²O:O)(nitrato-κ²O,O')disilver(I)]

Crystal data

[Ag2(NO3)2(C4H5N3)2]	F(000) = 512
Mr = 529.98	Dx = 2.504 Mg m^−3
Monoclinic, P21	Mo Kα radiation, λ = 0.71073 Å
Hall symbol: P 2yb	Cell parameters from 3225 reflections
a = 3.6087 (1) Å	θ = 2.6–30.7°
b = 15.4328 (5) Å	µ = 2.84 mm^−1
c = 12.7326 (3) Å	T = 123 K
β = 97.566 (2)°	Block, yellow
V = 702.93 (3) Å^3	0.18 × 0.15 × 0.12 mm
Z = 2

Data collection

Oxford Diffraction Gemini S Ultra diffractometer	2573 independent reflections
Radiation source: sealed tube	2436 reflections with I > 2σ(I)
Graphite monochromator	Rint = 0.034
Detector resolution: 16.1903 pixels mm^-1	θmax = 28.0°, θmin = 2.6°
ω scans	h = −4→4
Absorption correction: multi-scan (CrysAlis RED; Oxford Diffraction, 2008)	k = −19→20
Tmin = 0.629, Tmax = 0.727	l = −16→9
3805 measured reflections

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)] = 0.023	H-atom parameters constrained
wR(F^2) = 0.050	w = 1/[σ^2(Fo^2) + (0.029P)^2] where P = (Fo^2 + 2Fc^2)/3
S = 0.99	(Δ/σ)max = 0.001
2573 reflections	Δρmax = 0.61 e Å^−3
217 parameters	Δρmin = −0.72 e Å^−3
1 restraint	Absolute structure: Flack (1983), 812 Friedel pairs
Primary atom site location: structure-invariant direct methods	Absolute structure parameter: 0.01 (3)

Special details

Geometry. All s.u.s (except the s.u. in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell s.u.s are taken into account individually in the estimation of s.u. in distances, angles and torsion angles; correlations between s.u.s in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell s.u.s is used for estimating s.u.s 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.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Ų)

	x	y	z	Uiso*/Ueq
Ag1	0.42010 (9)	0.37067 (2)	0.49062 (2)	0.02087 (9)
Ag2	0.01504 (12)	0.501571 (17)	1.00046 (3)	0.01569 (8)
C1	0.2950 (10)	0.4925 (3)	0.6729 (3)	0.0153 (8)
H1A	0.2594	0.5314	0.6146	0.018*
C2	0.2157 (11)	0.5209 (3)	0.7694 (3)	0.0159 (9)
H2A	0.1304	0.5785	0.7770	0.019*
C3	0.3948 (10)	0.3882 (3)	0.8413 (3)	0.0128 (9)
H3A	0.4349	0.3502	0.9003	0.015*
C4	0.4818 (9)	0.3594 (3)	0.7417 (3)	0.0133 (9)
C5	0.6313 (10)	0.4911 (3)	0.3184 (3)	0.0151 (8)
H5A	0.6321	0.5309	0.3753	0.018*
C6	0.7421 (10)	0.5198 (3)	0.2250 (3)	0.0150 (9)
H6A	0.8115	0.5786	0.2179	0.018*
C7	0.6375 (9)	0.3836 (3)	0.1542 (3)	0.0149 (9)
H7A	0.6355	0.3445	0.0965	0.018*
C8	0.5167 (10)	0.3538 (3)	0.2498 (3)	0.0118 (9)
N1	0.4209 (9)	0.4123 (2)	0.6570 (3)	0.0137 (7)
N2	0.2587 (8)	0.4669 (2)	0.8544 (2)	0.0115 (7)
N3	0.6217 (9)	0.2797 (2)	0.7322 (3)	0.0160 (7)
H3B	0.6744	0.2616	0.6704	0.019*
H3C	0.6607	0.2455	0.7879	0.019*
N4	−0.0182 (10)	0.6935 (3)	1.0047 (3)	0.0161 (8)
N5	−0.0232 (9)	0.1835 (2)	0.4993 (3)	0.0161 (7)
N6	0.7521 (9)	0.4637 (2)	0.1430 (3)	0.0128 (7)
N7	0.3984 (9)	0.2723 (2)	0.2570 (3)	0.0176 (7)
H7B	0.3227	0.2539	0.3160	0.021*
H7C	0.3962	0.2369	0.2027	0.021*
N8	0.5220 (9)	0.4091 (2)	0.3325 (3)	0.0128 (7)
O1	−0.1876 (8)	0.6512 (2)	0.9287 (2)	0.0212 (7)
O2	0.1627 (8)	0.6533 (2)	1.0806 (2)	0.0202 (7)
O3	−0.0296 (11)	0.7741 (2)	1.0040 (3)	0.0200 (7)
O4	−0.0391 (8)	0.2616 (2)	0.5307 (3)	0.0253 (7)
O5	0.1130 (9)	0.1669 (2)	0.4183 (3)	0.0259 (7)
O6	−0.1440 (12)	0.1262 (2)	0.5528 (4)	0.0288 (10)

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
Ag1	0.03101 (16)	0.0228 (2)	0.01016 (13)	0.00459 (17)	0.00788 (10)	0.00217 (18)
Ag2	0.02284 (14)	0.01539 (17)	0.01002 (13)	0.0004 (2)	0.00649 (9)	0.00007 (19)
C1	0.0193 (18)	0.014 (2)	0.0127 (18)	−0.0002 (18)	0.0019 (13)	0.0025 (18)
C2	0.0182 (18)	0.011 (2)	0.019 (2)	0.0020 (15)	0.0030 (14)	−0.0002 (16)
C3	0.0138 (16)	0.011 (3)	0.0134 (17)	−0.0023 (15)	0.0016 (13)	0.0029 (16)
C4	0.0087 (15)	0.018 (3)	0.0134 (17)	−0.0035 (17)	0.0030 (12)	0.0008 (19)
C5	0.0163 (17)	0.013 (2)	0.0166 (18)	0.0007 (17)	0.0029 (13)	−0.0022 (18)
C6	0.0143 (17)	0.013 (2)	0.0173 (19)	0.0013 (15)	0.0021 (14)	−0.0005 (16)
C7	0.0149 (16)	0.019 (3)	0.0111 (16)	0.0012 (18)	0.0028 (12)	−0.0003 (19)
C8	0.0109 (15)	0.013 (3)	0.0117 (17)	0.0022 (14)	0.0025 (12)	−0.0002 (16)
N1	0.0170 (16)	0.0140 (18)	0.0110 (16)	−0.0002 (13)	0.0047 (13)	−0.0001 (14)
N2	0.0132 (15)	0.0139 (17)	0.0077 (15)	−0.0012 (13)	0.0027 (12)	−0.0022 (13)
N3	0.0219 (17)	0.0136 (18)	0.0128 (16)	0.0017 (14)	0.0034 (13)	0.0003 (15)
N4	0.0208 (19)	0.0121 (18)	0.0168 (19)	−0.0009 (16)	0.0074 (14)	−0.0014 (18)
N5	0.0151 (17)	0.0166 (19)	0.0165 (18)	−0.0002 (13)	0.0016 (13)	0.0010 (15)
N6	0.0140 (15)	0.0159 (18)	0.0086 (16)	0.0009 (13)	0.0023 (12)	0.0003 (14)
N7	0.0253 (17)	0.0153 (19)	0.0129 (17)	−0.0020 (14)	0.0052 (13)	−0.0001 (15)
N8	0.0134 (15)	0.0149 (17)	0.0100 (16)	0.0010 (13)	0.0013 (12)	−0.0011 (14)
O1	0.0275 (17)	0.0197 (18)	0.0148 (15)	−0.0019 (14)	−0.0029 (12)	−0.0020 (15)
O2	0.0280 (17)	0.0203 (18)	0.0117 (14)	0.0008 (13)	0.0006 (12)	0.0016 (14)
O3	0.0297 (19)	0.0073 (15)	0.0244 (17)	0.0017 (15)	0.0084 (13)	0.0018 (16)
O4	0.0245 (14)	0.0192 (18)	0.0330 (17)	0.0000 (13)	0.0074 (12)	−0.0075 (16)
O5	0.0316 (18)	0.0248 (19)	0.0241 (18)	−0.0042 (14)	0.0138 (14)	−0.0045 (15)
O6	0.028 (2)	0.029 (2)	0.031 (2)	−0.0020 (13)	0.0081 (17)	0.0152 (15)

Geometric parameters (Å, º)

Ag1—N1	2.214 (3)	C5—H5A	0.9500
Ag1—N8	2.176 (3)	C6—N6	1.360 (5)
Ag1—O4	2.463 (3)	C6—H6A	0.9500
Ag1—O4^i	2.577 (3)	C7—N6	1.317 (6)
Ag2—N2	2.224 (3)	C7—C8	1.422 (5)
Ag2—N6^ii	2.234 (3)	C7—H7A	0.9500
Ag2—O1	2.555 (3)	C8—N7	1.336 (6)
Ag2—O2	2.581 (3)	C8—N8	1.353 (5)
C1—N1	1.343 (6)	N3—H3B	0.8800
C1—C2	1.370 (6)	N3—H3C	0.8800
C1—H1A	0.9500	N4—O3	1.245 (5)
C2—N2	1.358 (5)	N4—O1	1.256 (5)
C2—H2A	0.9500	N4—O2	1.257 (5)
C3—N2	1.329 (5)	N5—O5	1.227 (4)
C3—C4	1.417 (5)	N5—O6	1.231 (5)
C3—H3A	0.9500	N5—O4	1.273 (5)
C4—N3	1.341 (6)	N6—Ag2^iii	2.234 (3)
C4—N1	1.347 (5)	N7—H7B	0.8800
C5—N8	1.345 (6)	N7—H7C	0.8800
C5—C6	1.376 (6)	O4—Ag1^iv	2.577 (3)
N1—Ag1—N8	145.84 (14)	N7—C8—N8	120.8 (4)
N1—Ag1—O4	85.20 (12)	N7—C8—C7	120.0 (4)
N1—Ag1—O4^i	95.44 (11)	N8—C8—C7	119.2 (4)
N8—Ag1—O4	125.32 (12)	C1—N1—C4	117.4 (4)
N8—Ag1—O4^i	98.35 (12)	C1—N1—Ag1	117.0 (3)
N2—Ag2—N6^ii	150.84 (14)	C4—N1—Ag1	124.7 (3)
N2—Ag2—O1	92.56 (12)	C3—N2—C2	117.7 (3)
N2—Ag2—O2	117.70 (12)	C3—N2—Ag2	121.2 (3)
N6^ii—Ag2—O1	113.25 (12)	C2—N2—Ag2	120.1 (3)
N6^ii—Ag2—O2	90.22 (12)	C4—N3—H3B	120.0
O1—Ag2—O2	49.89 (9)	C4—N3—H3C	120.0
O4—Ag1—O4^i	91.43 (12)	H3B—N3—H3C	120.0
N1—C1—C2	123.0 (4)	O3—N4—O1	120.1 (4)
N1—C1—H1A	118.5	O3—N4—O2	120.8 (4)
C2—C1—H1A	118.5	O1—N4—O2	119.1 (4)
N2—C2—C1	120.2 (4)	O5—N5—O6	121.7 (4)
N2—C2—H2A	119.9	O5—N5—O4	120.0 (4)
C1—C2—H2A	119.9	O6—N5—O4	118.2 (4)
N2—C3—C4	121.9 (4)	C7—N6—C6	118.3 (3)
N2—C3—H3A	119.1	N5—O4—Ag1^iv	128.4 (2)
C4—C3—H3A	119.1	C7—N6—Ag2^iii	120.4 (3)
N3—C4—N1	120.5 (4)	C6—N6—Ag2^iii	121.0 (3)
N3—C4—C3	119.9 (4)	C8—N7—H7B	120.0
N1—C4—C3	119.6 (4)	C8—N7—H7C	120.0
N8—C5—C6	122.8 (4)	H7B—N7—H7C	120.0
N8—C5—H5A	118.6	C5—N8—C8	117.7 (4)
C6—C5—H5A	118.6	C5—N8—Ag1	117.9 (3)
N6—C6—C5	119.9 (4)	C8—N8—Ag1	124.2 (3)
N6—C6—H6A	120.0	N4—O1—Ag2	96.1 (2)
C5—C6—H6A	120.0	N4—O2—Ag2	94.9 (2)
N6—C7—C8	122.1 (4)	N5—O4—Ag1	121.5 (2)
N6—C7—H7A	118.9	Ag1—O4—Ag1^iv	91.43 (12)
C8—C7—H7A	118.9

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

Hydrogen-bond geometry (Å, º)

D—H···A	D—H	H···A	D···A	D—H···A
N7—H7B···O5	0.88	2.08	2.912 (5)	157
N3—H3B···O4^i	0.88	2.17	2.998 (5)	156
N3—H3C···O2^v	0.88	2.23	3.099 (5)	172
N7—H7C···O1^vi	0.88	2.19	3.031 (5)	161
C1—H1A···O5^vii	0.95	2.49	3.211 (5)	133
C1—H1A···O6^vii	0.95	2.57	3.521 (6)	175
C5—H5A···O6^viii	0.95	2.44	3.108 (6)	127
C5—H5A···O6^vii	0.95	2.55	3.299 (6)	136
C3—H3A···O3^ix	0.95	2.34	3.066 (5)	133
C6—H6A···O2^iii	0.95	2.56	3.266 (5)	131
C7—H7A···O3^x	0.95	2.31	3.109 (5)	142

Symmetry codes: (i) x+1, y, z; (iii) x+1, y, z−1; (v) −x+1, y−1/2, −z+2; (vi) −x, y−1/2, −z+1; (vii) −x, y+1/2, −z+1; (viii) −x+1, y+1/2, −z+1; (ix) −x, y−1/2, −z+2; (x) −x+1, y−1/2, −z+1.