The coordination polymer poly[(μ₃-3-amino­carbonyl­pyrazine-2-carboxyl­ato-κ³N¹:O²:O^2′)silver(I)]

The title compound, [Ag(C₆H₄N₃O₃)]_n or [Ag(pyzca)]_n (where pyzca is 3-amino­carbonyl­pyrazine-2-carboxyl­ate), (I), was obtained by silver-catalysed partial hydrolysis of pyrazine-2,3-dicarbonitrile in aqueous solution. The compound has a distorted trigonal–planar coordination geometry around the Ag^I ion, with each ligand bridging three Ag^I ions to form a one-dimensional strand of mol­ecules parallel to the b axis. An extensive hydrogen-bond pattern connects these strands to form a three-dimensional network of mog topology.

S1. Comment

The design of metal coordination polymers has attracted considerable interest, particularly with respect to supramolecular chemistry. The choice of ligands coordinated to the metal centres is often the most important factor (Batten et al., 2009). We attempted to synthesize a new silver(I) compound with high dimensionality using the µ-N,N' bridging ligand pyrazine-2,3-dicarbonitrile, but unexpectedly obtained the title silver(I) compound, (I), with the ligand 3-aminocarbonylpyrazine-2-carboxylate (pyzca).

Pyzca is an intermediate compound formed during hydrolysis of the corresponding dicarboxamide to the dicarboxylic acid. Only two structures containing this ligand were found in the Cambridge Structural Database (CSD, updated August 2010; Allen, 2002): [Ni(pyzca)₂(H₂O)₂]H₂O was obtained upon hydrolysis of pyrazine-2,3-dicarboxamide catalysed by Ni(NO₃)₂ (Heyn & Dietzel, 2007), while [Co(tren)(pyzca)](ClO₄)Cl [where tren is tris-(2-aminoethyl)amine] (Mukhopadhyay et al., 2009) was obtained via direct reaction of the pyzca ligand with [Co(tren)Cl₂]Cl and NaClO₄ in water. In both these monomeric compounds, pyzca acts as a µ-N,O chelating ligand. Compound (I) is the first coordination polymer obtained from partial hydrolysis of pyrazine-2,3-dicarbonitrile in an aqueous medium. The reaction was relatively slow, catalysed by AgNO₃ (Heyn & Dietzel, 2007) as a Lewis acid, and hence only a few crystals were formed.

A search of the CSD revealed no structures containing the commercially available pyrazine-2,3-dicarbonitrile (the starting ligand), i.e. not even the structure of the ligand has yet been determined. For pyrazine-2,3-dicarboxamide, four Cu^II structures (Mondal & Ray, 1977; Klein et al., 1983) with the ligand in a µ-N,O chelating mode and one Ag^I structure (Massoud et al., 2009) with the ligand in a µ-N,N' bridging mode have been reported. In contrast, many compounds of pyrazine-2,3-dicarboxylic acid with alkali (Tombul et al., 2006, 2007; Tombul, Güven & Büyükgüngör, 2008; Tombul, Güven & Svoboda, 2008; Tombul & Guven, 2009) and transition metals (Zou et al., 1998, 1999; Konar et al., 2004; Xu et al., 2008) have been synthesized and structurally characterized.

The structure and atom-numbering scheme for (I) are shown in Fig. 1. The Ag^I ion is coordinated by three ligands, two via one carboxylate O atom and one via a ring N atom, forming a distorted trigonal–planar geometry at the Ag^I ion. The pyzca ligand acts as a µ₃-N,O,O' bridging ligand to three Ag^I ions, while the amide group (O81 and N82) and the second pyrazine ring N atom (N4) serve as hydrogen-bond donors or acceptors. These three Ag^I ions deviate from the plane of the pyrazine ring, with torsion angles O71—Ag1—N1—C1 = 41.7 (4), O72—Ag1—N1—C2 = -150.3 (4), O71—Ag1—N1—C6 = -151.2 (3) and O72—Ag1—N1—C6 = 16.8 (3)°. This coordination geometry leads to the formation of successive eight- and ten-membered rings building up an infinite one-dimensional strand of molecules parallel to the b axis, with the free amide groups projecting outwards. Similar strands were found in {[Ag(pyrazine-2,3-dicarboxylato)][NH₄]}_n (Smith et al., 1995) and {[Ag₂(pyrazine-2,3-dicarboxylato)(NH₃)]}_n (Jaber et al., 1994), where ten- and 14-membered rings were formed instead. Selected bond distances and angles for (I) and for related Ni^II (Heyn & Dietzel, 2007), Co^II (Mukhopadhyay et al., 2009) and Ag^I (Smith et al., 1995; Jaber et al., 1994) compounds are compared in Table 2. In contrast with the four above-mentioned compounds, (I) has a longer metal—N bond distance. The Ni^II (Heyn & Dietzel, 2007) and Co^II (Mukhopadhyay et al., 2009) compounds have much shorter bond distances, asociated with their smaller ionic radii, while the two Ag^I pyrazine-2,3-dicarboxylate compounds (Smith et al., 1995; Jaber et al., 1994) have comparable distances and angles to (I), consistent with their similar topology.

Extensive inter- and intramolecular hydrogen bonds of N—H···O, N—H···N and C—H···O types (Table 1) connect the one-dimensional strands of (I). The hydrogen bonds between opposite amide groups (N82—H82A···O81ⁱ; symmetry codes in Fig. 2) form inversion-symmetric eight-membered rings, with a graph-set symbol (Bernstein et al., 1995) of R²₂(8), extending the structure to form a two-dimensional sheet (Fig. 2a). The plane of the strands is (102), whereas the sheets lie parallel to (101). Almost perpendicular to this strong and well known supramolecular synthon we find a three-centre amide–pyrazine hydrogen-bond system forming eight- (N82—H82B···O81ⁱⁱ) and ten-membered rings (N82—H82B···N4ⁱⁱⁱ) with graph-set symbols of R²₂(8) and R²₂(10), respectively, which further extends the structure to form a three-dimensional network (Fig. 2b).

Often a clearer description and better understanding of such a structure can be obtained by network analysis, a concept introduced by Wells (1954, 1977) and further developed by O'Keeffe and others (O'Keeffe & Hyde, 1996). Recently, we have successfully used this technique on a number of hydrogen-bonded systems (Abu-Youssef et al., 2006; Johansson et al., 2007; Wallentin et al., 2009). Briefly, the method involves finding the topology symbol [a three letter code, often preceded by the point symbol (or Schläfli symbol) of the net, describing the number of different rings (O'Keeffe et al., 2010; Blatov et al., 2010)] of the three-dimensional-net, and this then gives a reduced, and often informative, description of the structure. The structures can thus, in many cases, be related to a small number of high-symmetry nets (Ockwig et al., 2005) found from geometric considerations or from inorganic-type structures and minerals.

The first step in such an analysis is to assign nodes, and in this case the Ag dimeric unit is an obvious choice as it clearly connects to four different ligands. For further analysis of the hydrogen-bond connectivities, simplicity is one of the main guidelines; a net with high symmetry that contributes to the understanding of the structure is better than a complicated multinodal net that might not even have been recorded previously. Thus, we consider the strong double N82—H82A···O81ⁱ hydrogen bonds and the likewise strong double N82—H82B···N4ⁱⁱⁱ hydrogen bonds as forming the links between the ligands and two Ag dimeric nodes, and two other ligands giving a network with two different four-connected vertices. In doing so, we clearly ignore not only the intramolecular N82—H82B···N4 hydrogen bonds but also the N82—H82B···O81ⁱⁱ interaction. The latter is clearly much weaker than the N82—H82A···O81ⁱ hydrogen bond of the same type, and, considering the larger covalent radius of N compared with O, also weaker than the N82—H82B···N4ⁱⁱⁱ interaction. However, more importantly, this interaction does not connect two ligands to each other; instead, it forms a double hydrogen-bond motif connecting four ligands. Thus, a network description incorporating this intermolecular bond as well would give a complicated three-nodal net and we would not gain anything in terms of describing or understanding the structure.

The complete assignment, shown in the second scheme, gives three- and four-connected nets. The Ag^I node is close to square planar (angles 109° and 71°), but the pyzca node has a very distorted geometry, as shown in Fig. 3(a), when compared with the ideal mog net topology shown in Fig. 3(b) (see discussion below).

Analysis of the resulting topology using the SYSTRE program (Delgado Friedrichs, 2007) shows that the net belongs to a class of binodal networks combining square-planar and tetrahedral nodes, and more specifically a (4².6².8²)₂(4.6⁴.8)-mog net (from the mineral moganite) (Delgado Friedrichs et al., 2003; Öhrström & Larsson, 2005; O'Keeffe et al., 2008). The most common of this type of topology is the pts net (Ockwig et al., 2005), and only a few examples are known of the mog net (Kostakis et al., 2009).

Some weaker Ag···O and Ag···Ag interactions with other strands above and below the parent strand support the three-dimensional structure [Ag1···O72^vi = 2.714 (3), Ag1···O71 = 2.956 (4), Ag1···O72ⁱⁱⁱ = 3.3010 (4) and Ag1···Ag1^iv = 3.4000 (6) Å; symmetry codes: (iii) -x, 1 - y, 1 - z; (iv) -x, -y, 1 - z; (vi) 1 - x, 1 - y, 1 - z], as well as the aforementioned weaker amide—amide interaction.

The Ag···Ag interaction is at the limit of the double van der Waals radius of silver (standard reference?), and was therefore neglected when assigning the network structure. No π–π stacking could be found between pyrazine rings.

Related literature

For related literature, see: Abu-Youssef, Langer & Öhrström (2006); Allen (2002); Batten et al. (2009); Bernstein et al. (1995); Blatov et al. (2010); Delgado (2007); Delgado Friedrichs, O'Keeffe & Yaghi (2003); Heyn & Dietzel (2007); Jaber et al. (1994); Johansson et al. (2007); Klein et al. (1983); Konar et al. (2004); Kostakis et al. (2009); Massoud et al. (2009); Mondal & Ray (1977); Mukhopadhyay et al. (2009); O'Keeffe & Hyde (1996); O'Keeffe et al. (2008, 2010); Ockwig et al. (2005); Smith et al. (1995); Tombul & Guven (2009); Tombul et al. (2006, 2007); Tombul, Güven & Büyükgüngör (2008); Tombul, Güven & Svoboda (2008); Wallentin et al. (2009); Wells (1954, 1977); Xu et al. (2008); Zou et al. (1998, 1999); Öhrström & Larsson (2005).

S2. Experimental

An ethanolic solution of pyrazine-2,3-dicarbonitrile (0.5 g, 4 mmol) was added to an aqueous solution of AgNO₃ (0.34 g, 2 mmol). The mixture was allowed to stand undisturbed for one month in a dark place. Colourless plates of (I) suitable for X-ray measurements were collected and dried in air, with a yield of ~10% relative to Ag.

S3. Refinement

Aromatic H atoms were constrained to ideal geometry, with C—H = 0.95 Å and N—H = 0.88 Å, and with U_iso(H) = 1.2U_eq(C,N). The NH₂ H atoms were located in a difference Fourier synthesis map and refined isotropically, with a restraint on a common N—H distance with an s.u. of 0.02 Å. The maximum feature of the residual electron density is 1.20 e Å^-3, close to the Ag^I atom.

Computing details

Data collection: SMART (Bruker, 2003); cell refinement: SAINT (Bruker, 2003); data reduction: SAINT (Bruker, 2003) and SADABS (Sheldrick, 2003); program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: DIAMOND (Brandenburg, 2010); software used to prepare material for publication: SHELXTL (Sheldrick, 2008) and SYSTRE (Delgado Friedrichs, 2007); topology codes from the RCSR (O'Keeffe et al., 2010).

Figures

	Fig. 1. The structure of (I), with the atom-numbering scheme. Displacement ellipsoids are drawn at the 50% probability level. [Symmetry codes: (i) -x, -y + 1, -z + 1; (ii) x, y - 1, z.]
	Fig. 2. (a) A perspective view of (I), perpendicular to (101), showing the eight- and ten-membered rings building up a one-dimensional strand parallel to the b axis. N—H···O hydrogen bonds (broken lines) connect the one-dimensional strands to form a two-dimensional sheet. (b) A perspective view of (I), showing the eight- and ten-membered rings formed via both N—H···O (long-dashed lines) and N—H···N (short-dashed lines) hydrogen bonds, which extend the structure into a three-dimensional network. The shortest Ag···O interactions are drawn as dotted lines, where the Ag···O distance is 2.714 (3) Å. Atoms H5 and H6 have been omitted for clarity. [Symmetry codes: (i) -x + 1, -y + 2, -z + 2; (ii) x + 1, y, z; (iii) -x + 2, -y + 1, -z + 2.]
	Fig. 3. (a) A perspective view of (I), showing the three-dimensional (mog net) structure supported by N—H···O and N—H···N hydrogen bonds (broken lines). (b) A perspective view, showing the ideal mog net.

poly[(µ₃-3-aminocarbonylpyrazine-2-carboxylato- κ³N¹:O²:O^2')silver(I)]

Crystal data

[Ag(C6H4N3O3)]	Z = 2
Mr = 273.99	F(000) = 264
Triclinic, P1	Dx = 2.644 Mg m^−3
Hall symbol: -P 1	Mo Kα radiation, λ = 0.71073 Å
a = 5.0540 (2) Å	Cell parameters from 2079 reflections
b = 6.2507 (2) Å	θ = 3.3–30.5°
c = 10.9778 (2) Å	µ = 2.90 mm^−1
α = 85.570 (1)°	T = 153 K
β = 88.638 (1)°	Plate, colourless
γ = 84.509 (2)°	0.04 × 0.04 × 0.02 mm
V = 344.13 (2) Å^3

Data collection

Siemens SMART CCD area-detector diffractometer	2079 independent reflections
Radiation source: fine-focus sealed tube	1540 reflections with I > 2σ(I)
Graphite monochromator	Rint = 0.062
ω scans	θmax = 30.5°, θmin = 3.3°
Absorption correction: multi-scan (SADABS; Sheldrick, 2003)	h = −7→7
Tmin = 0.228, Tmax = 0.944	k = −8→8
5479 measured reflections	l = −15→15

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)] = 0.047	Hydrogen site location: inferred from neighbouring sites
wR(F^2) = 0.091	H atoms treated by a mixture of independent and constrained refinement
S = 1.01	w = 1/[σ^2(Fo^2) + (0.0327P)^2 + 0.3143P] where P = (Fo^2 + 2Fc^2)/3
2079 reflections	(Δ/σ)max < 0.001
126 parameters	Δρmax = 1.01 e Å^−3
1 restraint	Δρmin = −1.02 e Å^−3

Special details

Experimental. Data were collected at 153 K using a Siemens SMART CCD diffractometer equipped with LT-2 A cooling device. A full sphere of reciprocal space was scanned by 0.3° steps in ω with a crystal-to-detector distance of 3.97 cm, 1 second per frame. Preliminary orientation matrix was obtained from the first 100 frames using SMART (Bruker, 2008). The collected frames were integrated using the preliminary orientation matrix which was updated every 100 frames. Final cell parameters were obtained by refinement on the position of 5479 reflections with I > 10σ(I) after integration of all the frames data using SAINT (Bruker, 2008).

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	0.19100 (8)	0.19788 (7)	0.53132 (4)	0.02272 (14)
N1	0.4983 (8)	0.3292 (6)	0.6624 (4)	0.0158 (8)
C2	0.4599 (8)	0.5182 (7)	0.7126 (4)	0.0111 (9)
C3	0.6072 (9)	0.5530 (7)	0.8148 (4)	0.0126 (9)
N4	0.8088 (8)	0.4137 (6)	0.8546 (4)	0.0157 (8)
C5	0.8575 (9)	0.2340 (7)	0.7971 (4)	0.0169 (10)
H5	1.0069	0.1362	0.8197	0.020*
C6	0.6961 (9)	0.1871 (8)	0.7058 (4)	0.0171 (10)
H6	0.7252	0.0508	0.6725	0.021*
C7	0.2693 (9)	0.6865 (7)	0.6451 (4)	0.0130 (9)
O71	0.0484 (7)	0.6300 (6)	0.6191 (3)	0.0240 (8)
O72	0.3641 (7)	0.8591 (5)	0.6103 (3)	0.0223 (8)
C8	0.5434 (9)	0.7446 (7)	0.8886 (4)	0.0146 (9)
O81	0.3250 (6)	0.8486 (5)	0.8827 (3)	0.0204 (8)
N82	0.7371 (9)	0.7870 (7)	0.9607 (4)	0.0234 (10)
H82A	0.690 (11)	0.886 (8)	1.008 (5)	0.030 (17)*
H82B	0.883 (11)	0.702 (10)	0.958 (6)	0.06 (2)*

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
Ag1	0.0207 (2)	0.0251 (2)	0.0212 (2)	0.00306 (15)	−0.00908 (14)	0.00183 (15)
N1	0.0142 (19)	0.013 (2)	0.019 (2)	0.0004 (16)	−0.0024 (16)	−0.0015 (16)
C2	0.009 (2)	0.012 (2)	0.012 (2)	−0.0029 (17)	−0.0003 (16)	0.0003 (17)
C3	0.011 (2)	0.010 (2)	0.016 (2)	−0.0025 (17)	−0.0014 (17)	0.0014 (18)
N4	0.016 (2)	0.013 (2)	0.017 (2)	0.0010 (16)	−0.0027 (16)	0.0007 (16)
C5	0.014 (2)	0.011 (2)	0.024 (3)	0.0023 (18)	−0.0053 (19)	0.0027 (19)
C6	0.017 (2)	0.013 (2)	0.022 (3)	0.0032 (18)	−0.0004 (19)	−0.0051 (19)
C7	0.017 (2)	0.011 (2)	0.011 (2)	−0.0003 (18)	−0.0051 (18)	−0.0041 (17)
O71	0.0144 (17)	0.026 (2)	0.031 (2)	−0.0050 (15)	−0.0108 (15)	0.0110 (16)
O72	0.0215 (18)	0.0147 (18)	0.030 (2)	−0.0038 (15)	−0.0048 (15)	0.0032 (15)
C8	0.018 (2)	0.014 (2)	0.011 (2)	−0.0015 (19)	−0.0016 (18)	0.0028 (18)
O81	0.0179 (17)	0.0201 (19)	0.0228 (19)	0.0074 (14)	−0.0063 (14)	−0.0074 (15)
N82	0.021 (2)	0.022 (3)	0.028 (3)	0.007 (2)	−0.0084 (19)	−0.015 (2)

Geometric parameters (Å, º)

Ag1—O71^i	2.218 (3)	C5—H5	0.9500
Ag1—O72^ii	2.324 (3)	C6—H6	0.9500
Ag1—N1	2.385 (4)	C7—O72	1.251 (6)
N1—C2	1.338 (6)	C7—O71	1.249 (6)
N1—C6	1.342 (6)	O71—Ag1^i	2.218 (3)
C2—C3	1.402 (6)	O72—Ag1^iii	2.324 (3)
C2—C7	1.518 (6)	C8—O81	1.227 (5)
C3—N4	1.335 (6)	C8—N82	1.332 (6)
C3—C8	1.503 (6)	N82—H82A	0.85 (5)
N4—C5	1.330 (6)	N82—H82B	0.87 (5)
C5—C6	1.374 (7)
O71^i—Ag1—O72^ii	143.64 (13)	C6—C5—H5	119.3
O71^i—Ag1—N1	129.91 (13)	N1—C6—C5	121.6 (4)
O72^ii—Ag1—N1	84.79 (13)	N1—C6—H6	119.2
C2—N1—C6	117.7 (4)	C5—C6—H6	119.2
C2—N1—Ag1	124.4 (3)	O72—C7—O71	127.2 (4)
C6—N1—Ag1	116.7 (3)	O72—C7—C2	115.3 (4)
N1—C2—C3	119.6 (4)	O71—C7—C2	116.9 (4)
N1—C2—C7	115.1 (4)	C7—O71—Ag1^i	121.4 (3)
C3—C2—C7	125.1 (4)	C7—O72—Ag1^iii	135.3 (3)
N4—C3—C2	121.8 (4)	O81—C8—N82	123.9 (5)
N4—C3—C8	115.7 (4)	O81—C8—C3	121.0 (4)
C2—C3—C8	122.5 (4)	N82—C8—C3	115.1 (4)
C5—N4—C3	117.3 (4)	C8—N82—H82A	113 (4)
N4—C5—C6	121.3 (4)	C8—N82—H82B	116 (5)
N4—C5—H5	119.3	H82A—N82—H82B	130 (6)
O71^i—Ag1—N1—C2	41.7 (4)	C2—N1—C6—C5	−1.1 (7)
O72^ii—Ag1—N1—C2	−150.3 (4)	Ag1—N1—C6—C5	−169.1 (4)
O71^i—Ag1—N1—C6	−151.2 (3)	N4—C5—C6—N1	6.6 (8)
O72^ii—Ag1—N1—C6	16.8 (3)	N1—C2—C7—O72	−121.7 (5)
C6—N1—C2—C3	−6.1 (6)	C3—C2—C7—O72	53.4 (6)
Ag1—N1—C2—C3	160.9 (3)	N1—C2—C7—O71	50.7 (6)
C6—N1—C2—C7	169.2 (4)	C3—C2—C7—O71	−134.2 (5)
Ag1—N1—C2—C7	−23.8 (5)	O72—C7—O71—Ag1^i	13.7 (7)
N1—C2—C3—N4	8.5 (7)	C2—C7—O71—Ag1^i	−157.6 (3)
C7—C2—C3—N4	−166.3 (4)	O71—C7—O72—Ag1^iii	19.6 (8)
N1—C2—C3—C8	−169.4 (4)	C2—C7—O72—Ag1^iii	−168.9 (3)
C7—C2—C3—C8	15.8 (7)	N4—C3—C8—O81	−159.6 (4)
C2—C3—N4—C5	−3.1 (7)	C2—C3—C8—O81	18.5 (7)
C8—C3—N4—C5	174.9 (4)	N4—C3—C8—N82	19.1 (6)
C3—N4—C5—C6	−4.2 (7)	C2—C3—C8—N82	−162.9 (4)

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

Hydrogen-bond geometry (Å, º)

D—H···A	D—H	H···A	D···A	D—H···A
N82—H82A···O81^iv	0.85 (5)	2.12 (5)	2.947 (5)	165 (6)
N82—H82B···O81^v	0.87 (5)	2.59 (6)	3.123 (6)	121 (6)
N82—H82B···N4	0.87 (5)	2.27 (7)	2.678 (6)	109 (5)
N82—H82B···N4^vi	0.87 (5)	2.63 (6)	3.198 (6)	125 (6)
C5—H5···O81^vii	0.95	2.37	3.307 (5)	170
C6—H6···O72^ii	0.95	2.42	3.032 (6)	122

Symmetry codes: (ii) x, y−1, z; (iv) −x+1, −y+2, −z+2; (v) x+1, y, z; (vi) −x+2, −y+1, −z+2; (vii) x+1, y−1, z.