Poly[μ₂-(N-hydroxy­pyridine-2-carboxamidine)-μ₂-nitrato-silver(I)]

In the title complex, [Ag(NO₃)(C₆H₇N₃O)]_n or [Ag(NO₃)(pyaoxH₂)] (pyaoxH₂ is N-hydroxy­pyridine-2-carboxamidine), the Ag⁺ ion is bridged by the pyaoxH₂ ligands and nitrate anions, giving rise to a two-dimensional mol­ecular structure. Each pyaoxH₂ ligand coordinates to two Ag⁺ ions using its pyridyl and carboxamidine N atoms, and the OH and the NH₂ groups are uncoordinated. Each nitrate anion uses two O atoms to coordinate to two Ag⁺ ions. The Ag...Ag separation via the pyaoxH₂ bridge is 2.869 (1) Å, markedly shorter than that of 6.452 (1) Å via the nitrate bridge. The two-dimensional structure is fishscale-like, and can be described as pyaoxH₂-bridged Ag₂ nodes that are further linked by nitrate anions. Hydrogen bonding between the amidine groups and the nitrate O atoms connects adjacent layers into a three-dimensional network.

S1. Comment

N-Hydroxypyridine-2-carboxamidine (pyaoxH₂) is structurally similar to pyridine-2-carbaldehyde oxime (paoH), which has been widely studied as a bridging ligand to construct polynuclear species. Such compounds have been found to show interesting magnetic properties and have therefore attracted much interest in recent years (Chaudhuri, 2003; Milios et al., 2006). However, pyaoxH₂ has received much less attention, and only a few mononuclear complexes have been structurally characterized, more than ten years ago (Näsäkkälä et al., 1989; Pearse, Raithby, Hay & Lewis, 1989; Pearse, Raithby & Lewis, 1989; Werner et al., 1996; Orama & Saarinen, 1996). The coordination chemistry of pyaoxH₂ awaits further elucidation. It is worth mentioning that special interest has been devoted to the oxime–Ag^I compound for hydrogen- bonded supramolecular architectures (Aakeröy et al., 1998). In this paper, we report the novel two-dimensional complex Ag(pyaoxH₂)NO₃, (I), which exhibits a three-dimensional hydrogen-bonded architecture.

Fig. 1 shows the environment of Ag1, coordinated by two N atoms from two pyaoxH₂ ligands and two O atoms from two nitrate anions. The Ag—N/O bond distances are in the range 2.274 (1)–2.531 (5) Å (Table 1), with the Ag—N bonds longer than the Ag—O bonds. The coordination configuration is distored tetrahedral. The deviation of atom Ag1 from the coordination plane defined by atoms N2, O1 and N4ⁱ [symmetry code: (i) -x + 1, y, -z + 1/2] is 0.284 (1) Å, showing significant distortion toward trigonal–bipyrimidal geometry, possibly as a result of the weak Ag···Ag contact [2.869 (1) Å]. The pyaoxH₂ ligand coordinates two Ag ions using the pyridyl and the oxime N atoms; therefore, the pyridine and the amidoxime group are not coplanar in order to avoid steric hindrance. Interestingly, the oxime O atoms are not involved in coordination. The N—O bond distance is 1.414 (2) Å, similar to that in mononuclear Zn^II or Cu^II complexes (Näsäkkälä et al., 1989; Pearse, Raithby, Hay & Lewis, 1989; Pearse, Raithby & Lewis, 1989; Werner et al., 1996; Orama & Saarinen, 1996). The dimeric Ag^I units bridged by one pyaoxH₂ ligand are related by a twofold axis and are further linked by nitrate anions, giving rise to a two-dimensional layer structure. Two O atoms of each nitrate anion are involved in coordination. The layer is fishscale-like, and each scale consists of six Ag atoms or three Ag₂ units. Within each layer, atom H4A attached to the oxime atom O4 shows interaction with the nonbridging atom O3 of the nitrate anion (Table 2).

Alternate fishscale layers have the opposite sense. The Ag^I ions are nearly coplanar within a layer, with the pyaoxH₂ ligands situated at two sides of the Ag layer. Two amide H atoms (H3A and H3B) of each pyaoxH₂ ligand are, respectively, connected to atoms O3^iv and O1^v [symmetry codes: (iv) -x + 3/2, -y + 3/2, -z + 1; (v) x, -y + 1, z + 1/2 of two nitrate anions in the adjacent layer. A weak interlayer C—H···O contact further links the neighbouring layers, giving rise to a three-dimensional supramolecular network.

Related literature

For related literature, see: Aakeröy et al. (1998); Bernasek (1957); Chaudhuri (2003); Milios et al. (2006); Orama & Saarinen (1996); Pearse, Raithby & Lewis (1989); Pearse, Raithby, Hay & Lewis (1989); Werner et al. (1996).

S2. Experimental

The ligand was prepared according to the literature method (Bernasek, 1957). Compound (I) was prepared in the dark by slow evaporation of an acetonitrile solution (10 ml) containing AgNO₃ (17.0 mg, 0.1 mmol) and pyaoxH₂ (13.7 mg, 0.1 mmol). After 3 d, colourless crystals were obtained (yield 60%).

S3. Refinement

H atoms were positioned geometrically and allowed for as riding atoms (C—H = 0.93 Å, N—H = 0.86 Å and O—H = 0.82 Å, with U_iso(H) = 1.2U_eq(C,N) or 1.5U_eq(O)]. Atoms O2 and O3 of the nitrate anion are disordered; the occupancies of the two sets of atom sites were initially refined and then fixed at the refined values 0.62 and 0.38. Constraints were applied to keep the NO₃ atoms in each orientation coplanar.

Computing details

Data collection: SMART (Bruker, 2000); cell refinement: SAINT (Bruker, 2000); data reduction: SAINT (Bruker, 2000); program(s) used to solve structure: SHELXS97 (Sheldrick, 1997); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997); molecular graphics: XP in SHELXTL (Sheldrick, 1998); software used to prepare material for publication: SHELXTL (Sheldrick, 1998).

Figures

	Fig. 1. A view of complex (I), showing 30% probability displacement ellipsoids and the atom-numbering scheme. H atoms attached to C atoms have been omitted for clarity [symmetry code: (i) -x + 1, y, -z + 1/2; (ii) -x + 3/2, y - 1/2, -z + 1/2; (iii) -x + 3/2, y + 1/2, -z + 1/2].
	Fig. 2. The layer structure in (I).

Poly[µ₂-(N-hydroxypyridine-2-carboxamidine)-µ₂-nitrato-silver(I)]

Crystal data

[Ag(NO3)(C6H7N3O)]	F(000) = 1200
Mr = 307.03	Dx = 2.114 Mg m^−3
Monoclinic, C2/c	Mo Kα radiation, λ = 0.71073 Å
Hall symbol: -C 2yc	Cell parameters from 6244 reflections
a = 15.0911 (14) Å	θ = 2.7–27.0°
b = 8.8890 (8) Å	µ = 2.09 mm^−1
c = 16.0727 (15) Å	T = 293 K
β = 116.536 (2)°	Platelet, colorless
V = 1928.9 (3) Å^3	0.25 × 0.20 × 0.12 mm
Z = 8

Data collection

Bruker SMART APEX CCD area-detector diffractometer	2110 independent reflections
Radiation source: fine-focus sealed tube	1777 reflections with I > 2σ(I)
Graphite monochromator	Rint = 0.022
Detector resolution: 0.68 pixels mm^-1	θmax = 27.0°, θmin = 2.7°
ϕ and ω scans	h = −19→19
Absorption correction: multi-scan (SADABS; Bruker, 2000)	k = −9→11
Tmin = 0.623, Tmax = 0.788	l = −20→17
6244 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)] = 0.032	Hydrogen site location: inferred from neighbouring sites
wR(F^2) = 0.065	H-atom parameters constrained
S = 1.03	w = 1/[σ^2(Fo^2) + (0.001P)^2 + 6.2P] where P = (Fo^2 + 2Fc^2)/3
2110 reflections	(Δ/σ)max = 0.003
155 parameters	Δρmax = 1.08 e Å^−3
10 restraints	Δρmin = −0.47 e Å^−3

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. The oxygen atoms O(2) and O(3) of nitrate anions experience serious positional disorder, and a split model has been used. The site occupancies of two sets of split atoms have been first refined, and afterwards fixed. Constraints have been applied to keep the NO3 atoms of each orientation planar.

The restraints involves the disorder of the nitrate anion since O2 and O3 were split. The ten restraints in the N—O bond distances (1.23 Å) and O···O separations (2.13 Å) of the nitrate anion were used.

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

	x	y	z	Uiso*/Ueq	Occ. (<1)
Ag1	0.594132 (12)	0.41694 (2)	0.248063 (12)	0.05581 (5)
O1	0.63654 (13)	0.6739 (2)	0.21900 (14)	0.0801 (6)
O2	0.73516 (19)	0.8439 (4)	0.2125 (2)	0.0913 (11)	0.62
O3	0.7492 (2)	0.7578 (4)	0.34127 (17)	0.0756 (10)	0.62
O2'	0.7508 (3)	0.7598 (7)	0.2039 (3)	0.0797 (17)	0.38
O3'	0.7414 (7)	0.8243 (7)	0.3282 (4)	0.160 (4)	0.38
O4	0.63909 (13)	0.64135 (17)	0.42184 (12)	0.0689 (5)
H4A	0.6711	0.6760	0.3964	0.103*
N1	0.70917 (12)	0.7554 (2)	0.25556 (12)	0.0558 (5)
N2	0.60729 (13)	0.49417 (19)	0.38838 (12)	0.0515 (5)
N3	0.63574 (16)	0.4589 (2)	0.54136 (14)	0.0700 (7)
H3A	0.6581	0.5487	0.5573	0.084*
H3B	0.6327	0.3986	0.5818	0.084*
N4	0.48737 (12)	0.2307 (2)	0.35481 (12)	0.0500 (5)
C1	0.60598 (14)	0.4134 (2)	0.45445 (14)	0.0468 (5)
C2	0.57274 (13)	0.2543 (2)	0.43098 (13)	0.0452 (5)
C3	0.62987 (16)	0.1385 (3)	0.48508 (16)	0.0570 (7)
H3	0.6885	0.1588	0.5379	0.068*
C4	0.59952 (18)	−0.0076 (3)	0.46035 (18)	0.0652 (8)
H4B	0.6375	−0.0875	0.4958	0.078*
C5	0.51281 (18)	−0.0330 (3)	0.38300 (18)	0.0658 (8)
H5	0.4906	−0.1307	0.3646	0.079*
C6	0.45888 (17)	0.0874 (3)	0.33281 (18)	0.0618 (7)
H6	0.3993	0.0688	0.2807	0.074*

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
Ag1	0.05009 (7)	0.05369 (10)	0.05920 (9)	−0.00540 (8)	0.02043 (6)	−0.00449 (8)
O1	0.0689 (9)	0.0584 (10)	0.0964 (12)	−0.0178 (8)	0.0221 (9)	0.0136 (9)
O2	0.0511 (13)	0.103 (2)	0.105 (2)	−0.0069 (15)	0.0208 (13)	0.0583 (16)
O3	0.0965 (17)	0.0725 (18)	0.0516 (14)	−0.0257 (16)	0.0274 (13)	−0.0160 (13)
O2'	0.052 (2)	0.121 (4)	0.059 (2)	−0.002 (3)	0.0198 (18)	0.037 (3)
O3'	0.169 (7)	0.111 (5)	0.147 (6)	−0.008 (5)	0.023 (5)	−0.087 (4)
O4	0.0955 (10)	0.0391 (8)	0.0785 (10)	−0.0145 (8)	0.0446 (8)	−0.0114 (7)
N1	0.0474 (8)	0.0505 (10)	0.0642 (10)	−0.0037 (8)	0.0200 (7)	0.0071 (9)
N2	0.0631 (9)	0.0314 (8)	0.0600 (9)	−0.0047 (8)	0.0275 (7)	−0.0061 (7)
N3	0.1002 (13)	0.0562 (11)	0.0522 (10)	−0.0187 (11)	0.0326 (9)	−0.0117 (8)
N4	0.0488 (8)	0.0426 (9)	0.0541 (9)	−0.0053 (8)	0.0190 (7)	0.0006 (7)
C1	0.0455 (8)	0.0408 (10)	0.0512 (10)	0.0011 (9)	0.0191 (7)	−0.0010 (9)
C2	0.0486 (8)	0.0429 (10)	0.0471 (9)	−0.0013 (9)	0.0239 (7)	−0.0010 (8)
C3	0.0568 (11)	0.0498 (12)	0.0549 (12)	0.0012 (10)	0.0165 (10)	0.0018 (10)
C4	0.0731 (13)	0.0460 (12)	0.0711 (14)	0.0061 (11)	0.0273 (11)	0.0083 (11)
C5	0.0755 (13)	0.0413 (12)	0.0804 (15)	−0.0109 (11)	0.0347 (11)	−0.0044 (11)
C6	0.0571 (11)	0.0486 (12)	0.0708 (14)	−0.0131 (11)	0.0207 (10)	−0.0054 (11)

Geometric parameters (Å, º)

Ag1—N4^i	2.2741 (17)	N2—C1	1.289 (3)
Ag1—N2	2.280 (2)	N3—C1	1.325 (3)
Ag1—O2^ii	2.450 (3)	N3—H3A	0.8600
Ag1—O1	2.4726 (18)	N3—H3B	0.8600
Ag1—O2'^ii	2.531 (5)	N4—C2	1.339 (2)
Ag1—Ag1^i	2.8695 (5)	N4—C6	1.340 (3)
O1—N1	1.223 (2)	C1—C2	1.492 (3)
O2—N1	1.223 (4)	C2—C3	1.374 (3)
O2—Ag1^iii	2.450 (3)	C3—C4	1.375 (3)
O3—N1	1.233 (3)	C3—H3	0.9300
O2'—N1	1.246 (5)	C4—C5	1.362 (3)
O2'—Ag1^iii	2.531 (5)	C4—H4B	0.9300
O3'—N1	1.211 (5)	C5—C6	1.368 (3)
O4—N2	1.414 (2)	C5—H5	0.9300
O4—H4A	0.8200	C6—H6	0.9300
N4^i—Ag1—N2	135.92 (7)	C1—N3—H3A	120.0
N4^i—Ag1—O2^ii	99.20 (8)	C1—N3—H3B	120.0
N2—Ag1—O2^ii	101.94 (9)	H3A—N3—H3B	120.0
N4^i—Ag1—O1	129.56 (7)	C2—N4—C6	117.05 (18)
N2—Ag1—O1	89.61 (7)	C2—N4—Ag1^i	122.50 (14)
O2^ii—Ag1—O1	87.87 (9)	C6—N4—Ag1^i	119.64 (13)
N4^i—Ag1—O2'^ii	86.89 (12)	N2—C1—N3	125.2 (2)
N2—Ag1—O2'^ii	101.80 (10)	N2—C1—C2	116.53 (19)
O1—Ag1—O2'^ii	106.59 (14)	N3—C1—C2	118.2 (2)
O2^ii—Ag1—Ag1^i	158.63 (9)	N4—C2—C3	122.42 (19)
O2'^ii—Ag1—Ag1^i	141.50 (13)	N4—C2—C1	117.23 (17)
N1—O1—Ag1	135.09 (14)	C3—C2—C1	120.33 (17)
N1—O2—Ag1^iii	126.18 (18)	C2—C3—C4	119.37 (19)
N1—O2'—Ag1^iii	119.2 (3)	C2—C3—H3	120.3
N2—O4—H4A	109.5	C4—C3—H3	120.3
O3'—N1—O1	130.6 (5)	C5—C4—C3	118.7 (2)
O1—N1—O2	123.7 (2)	C5—C4—H4B	120.6
O1—N1—O3	115.7 (2)	C3—C4—H4B	120.6
O2—N1—O3	120.1 (2)	C4—C5—C6	119.0 (2)
O3'—N1—O2'	121.4 (6)	C4—C5—H5	120.5
O1—N1—O2'	108.0 (3)	C6—C5—H5	120.5
C1—N2—O4	109.22 (18)	N4—C6—C5	123.5 (2)
C1—N2—Ag1	128.36 (14)	N4—C6—H6	118.3
O4—N2—Ag1	121.30 (14)	C5—C6—H6	118.3

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

Hydrogen-bond geometry (Å, º)

D—H···A	D—H	H···A	D···A	D—H···A
O4—H4A···O3	0.82	1.91	2.726 (4)	178
O4—H4A···O3′	0.82	2.26	3.061 (10)	166
N3—H3A···O3^iv	0.86	2.35	3.161 (3)	157
N3—H3B···O1^v	0.86	2.27	3.085 (3)	158
C3—H3···O2^v	0.93	2.57	3.274 (4)	133
C3—H3···O2′^v	0.93	2.51	3.284 (5)	141

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