catena-Poly[silver(I)-μ₂-4,4′-bipyri­dine-κ²N:N′-μ₃-chlorido]: self-assembly of a two-dimensional bilayer silver(I) coordination polymer from AgCl and a bipodal spacer

The title compound, [AgCl(C₁₀H₈N₂)]_n, was synthesized by reaction of silver(I) chloride with 4,4′-bipyridine (bipy) under ammoniacal conditions. The crystal structure reveals that the Ag and Cl atoms lie on twofold axes, while the bipy ligands also sit across twofold axes. The Ag^I center is five-coordinated by three Cl atoms and two N atoms from two symmetry-related bipy ligands in a distorted square-pyramidal geometry. The complex contains one-dimensional Ag^I–bipy chains, which are further linked by rarely formed T-frame μ₃-Cl to form a two-dimensional bilayer structure.

S1. Comment

The design and synthesis of inorganic–organic composite coordination polymers exhibiting novel structures and properties have provided exciting new prospects (Blake, Brooks et al., 1999; Blake, Champness et al., 1999; Blake et al., 2000; Evans & Lin, 2002; Kitagawa et al., 2004; Yaghi et al., 2003; Applegarth et al., 2005). As one of the important series of metal–organic frameworks, hybrid organic–inorganic materials, especially metal halides, have been attracting increasing attention (Engelhardt et al., 1989; Zhang et al., 2007, 2005). In recent years, a few hybrid copper halides constructed by N-donor ligands have been reported (Graham et al., 2000). However, to the best of our knowledge, Ag-X skeletons have rarely participated in constructing this kind of hybrid material, maybe due to the strong depositing trend of silver and halogens (Zhang et al., 2008; Bowmaker et al., 2005; Zartilas et al., 2007). 4,4'-Bipyridine (bipy) and its analogues are neutral linear ligands widely used as excellent spacers in the construction of novel metal–organic compounds including diverse motifs (Wang et al., 2007; Withersby et al., 1997). Recently, we have undertaken a series of investigations into the assembly of Ag^I cations 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 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 ordered functional coordination polymers. In an attempt to exploit AgCl–N-donor hybrid materials under ammoniacal conditions, we successfully synthesized the title two-dimensional coordination polymer, (I), with (4,4) net topology.

Single-crystal X-ray diffraction study reveals that the asymmetric unit of (I) comprises one Ag^I cation, one-half of a bipy molecule as bridging ligand and one Cl atom as counteranion. The Ag and Cl atoms lie on twofold axes. As shown in Fig. 1, the five-coordinated Ag^I center adopts a slightly distorted square-pyramidal geometry, which is completed by three Cl atoms and two N atoms from two independent bipy ligands. The Ag—N bond length is 2.285 (3) Å, and the Ag—Cl bonds are 2.6802 (18) and 2.9797 (10) Å, respectively, which are within normal ranges (Turner et al., 2005; Massoud & Langer, 2009; Oxtoby et al., 2002; Fan et al., 2007). Coordination of one Cl atom to three or more Ag atoms is well-known, but in most examples described, the geometry consists of four Ag atoms and four Cl atoms occupying the apices of a cube, with P-donor ligands coordinated to the Ag centers (Bowen et al., 1994; Zartilas et al., 2009).

The three µ₃-Cl atoms and one Ag atom of (I) are coplanar, with maximum and minimum Cl—Ag—Cl angles of 160.94 (5) and 99.53 (3)°, respectively. This planar T-frame µ₃-bridging mode of a Cl atom is still quite rare in AgCl-based hybrid materials to date (Blanco et al., 2002). The AgN₂Cl₃ square pyramid is slightly distorted, as indicated by the calculated value of the τ factor (Addison et al., 1984), which is 0.11 in (I) (for ideal square-pyramidal geometry, τ = 0).

The bipy ligand has a twisted non-planar conformation, with a dihedral angle between the two pyridyl rings of 41.96 (3)°. The bipy ligand acts as a bidentate N,N'-donor to link the Ag^I cations into one-dimensional chains, within which the N—Ag—N angle is 154.11 (18)°. This deviates from the value of 180° for linear two-coordinated Ag^I cations, due to the existence of the µ₃-Cl atoms of nearby Ag^I cations. The shortest Ag···Ag distance is 3.6631 (12) Å, which is obviously longer than twice the van der Waals radius of silver(I) (Bondi, 1964), indicating no direct metal–metal interaction between them.

In addition, as shown in Fig. 2, the Ag–bipy chains are further linked to form an ordered (4,4) net with the crystallographic dimensions of a rectangular subunit of 5.877 × 11.495 Å, in which Ag^I is assigned to be a four-connected node. Adjacent pairs of layers are cross-linked through µ₃-Cl atoms to form two-dimensional bilayers with a thickness of 2.680 Å, which is established by the separation distance between the Ag and Cl atoms. Furthermore, aromatic face-to-face contact between the pyridyl rings of adjacent bilayers remains a dominant supramolecular interaction in (I), with a shortest centroid-to-centroid separation distance of 3.623 (3) Å (offset distance 1.708 Å), and this extends the two-dimensional bilayer structure into a three-dimensional supramolecular framework and stabilizes the resulting molecular packing.

In conclusion, a new two-dimensional Ag^I coordination polymer with a bipodal rigid spacer was successfully synthesized. It is constructed by single crosslinking (4,4) nets through Ag–Cl pillars and exhibits a rare T-frame Cl atom in a µ₃-bridging mode.

S2. Experimental

All reagents and solvents were obtained commercially and used without further purification. AgCl (143 mg, 1 mmol) and 4,4'-bipyridine (156 mg, 1 mmol) were stirred in CH₃OH–H₂O mixed solvent (10 ml, v/v 1:1) for 30 min. Aqueous NH₃ solution (25%) was added dropwise until a clear solution was obtained. The formation of the product is not affected by changes in the reaction mole ratio of organic ligands to metal ions. The resultant solution was allowed to evaporate slowly in the dark at room temperature for several weeks to give colorless block crystals of (I). The crystals were isolated with deionized water and dried in air (yield ca 76% based on Ag). Elemental analysis, analysis calculated for AgC₁₀H₈N₂Cl: C 40.10, H 2.69, N 9.35%; found: C 40.15, H. 2.73, N 9.28%.

S3. Refinement

Aromatic H atoms were generated geometrically, with C—H = 0.93 Å, and allowed to ride on their parent atoms in the riding-model approximation, with U_iso(H) = 1.2U_eq(C).

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 coordination environment around the Ag^I center in (I), showing the atom-numbering scheme. Displacement ellipsoids are drawn at the 50% probability level. H atoms have been omitted for clarity. [Symmetry codes: (i) 1 - x, y, 3/2 - z; (ii) - x + 1 , - y + 1, -z + 1; (iii) - x + 1 , - y + 1, -z + 2; (iv) -x, y, -z + 1/2.]
	Fig. 2. Schematic representations of the two-dimensional bilayer structure of (I), formed by the crosslinking of pairs of (4,4) nets, viewed along two different directions.

catena-Poly[(µ₃-chloro)-(µ₂-4,4'-bipyridine-κ²N,N')silver(I)]

Crystal data

[Ag(C10H8N2)Cl]	F(000) = 584
Mr = 299.50	Dx = 2.174 Mg m^−3
Monoclinic, C2/c	Mo Kα radiation, λ = 0.71073 Å
Hall symbol: -C 2yc	Cell parameters from 1680 reflections
a = 12.870 (4) Å	θ = 4.6–56.7°
b = 13.548 (4) Å	µ = 2.45 mm^−1
c = 5.8772 (18) Å	T = 298 K
β = 116.729 (5)°	Block, colourless
V = 915.3 (5) Å^3	0.06 × 0.05 × 0.04 mm
Z = 4

Data collection

Oxford Gemini S Ultra diffractometer	910 independent reflections
Radiation source: sealed tube	891 reflections with I > 2σ(I)
Graphite monochromator	Rint = 0.063
Detector resolution: 16.1903 pixels mm^-1	θmax = 26.0°, θmin = 2.3°
ω scans	h = −15→15
Absorption correction: multi-scan (CrysAlis RED; Oxford Diffraction, 2008)	k = −16→14
Tmin = 0.867, Tmax = 0.909	l = −7→4
2362 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)] = 0.037	Hydrogen site location: inferred from neighbouring sites
wR(F^2) = 0.090	H-atom parameters constrained
S = 1.22	w = 1/[σ^2(Fo^2) + (0.0354P)^2 + 2.3807P] where P = (Fo^2 + 2Fc^2)/3
910 reflections	(Δ/σ)max = 0.002
65 parameters	Δρmax = 0.97 e Å^−3
0 restraints	Δρmin = −0.84 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	0.5000	0.58071 (4)	0.7500	0.0300 (2)
Cl1	0.5000	0.38288 (11)	0.7500	0.0229 (3)
C1	0.2475 (4)	0.6539 (3)	0.6797 (8)	0.0233 (9)
H1	0.2893	0.6724	0.8494	0.028*
C2	0.1286 (4)	0.6640 (3)	0.5649 (8)	0.0222 (9)
H2	0.0915	0.6901	0.6553	0.027*
C3	0.0643 (3)	0.6350 (3)	0.3135 (8)	0.0181 (8)
C4	0.1253 (4)	0.6013 (3)	0.1850 (9)	0.0242 (9)
H4	0.0858	0.5837	0.0141	0.029*
C5	0.2444 (4)	0.5941 (3)	0.3127 (9)	0.0240 (9)
H5	0.2840	0.5711	0.2241	0.029*
N1	0.3062 (3)	0.6185 (3)	0.5571 (7)	0.0214 (7)

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
Ag1	0.0116 (3)	0.0363 (3)	0.0377 (3)	0.000	0.0072 (2)	0.000
Cl1	0.0148 (7)	0.0299 (7)	0.0239 (7)	0.000	0.0086 (6)	0.000
C1	0.022 (2)	0.027 (2)	0.0199 (19)	−0.0015 (17)	0.0089 (17)	0.0000 (16)
C2	0.021 (2)	0.026 (2)	0.023 (2)	0.0003 (16)	0.0130 (17)	0.0010 (16)
C3	0.015 (2)	0.0178 (19)	0.0218 (19)	0.0015 (15)	0.0087 (16)	0.0020 (15)
C4	0.021 (2)	0.031 (2)	0.023 (2)	−0.0015 (17)	0.0124 (18)	−0.0025 (17)
C5	0.017 (2)	0.030 (2)	0.028 (2)	0.0009 (17)	0.0127 (18)	0.0000 (18)
N1	0.0151 (17)	0.0236 (17)	0.0248 (18)	0.0024 (13)	0.0084 (15)	0.0033 (14)

Geometric parameters (Å, º)

Ag1—N1^i	2.285 (3)	C2—H2	0.9300
Ag1—N1	2.285 (3)	C3—C4	1.388 (6)
Ag1—Cl1	2.6802 (18)	C3—C3^ii	1.478 (8)
C1—N1	1.345 (5)	C4—C5	1.375 (7)
C1—C2	1.373 (6)	C4—H4	0.9300
C1—H1	0.9300	C5—N1	1.333 (6)
C2—C3	1.386 (6)	C5—H5	0.9300
N1^i—Ag1—N1	154.11 (18)	C4—C3—C3^ii	120.2 (4)
N1^i—Ag1—Cl1	102.95 (9)	C5—C4—C3	119.4 (4)
N1—Ag1—Cl1	102.95 (9)	C5—C4—H4	120.3
N1—C1—C2	122.8 (4)	C3—C4—H4	120.3
N1—C1—H1	118.6	N1—C5—C4	123.3 (4)
C2—C1—H1	118.6	N1—C5—H5	118.4
C1—C2—C3	119.7 (4)	C4—C5—H5	118.4
C1—C2—H2	120.2	C5—N1—C1	117.3 (4)
C3—C2—H2	120.2	C5—N1—Ag1	117.9 (3)
C2—C3—C4	117.4 (4)	C1—N1—Ag1	124.4 (3)
C2—C3—C3^ii	122.3 (4)
N1—C1—C2—C3	1.3 (6)	C4—C5—N1—Ag1	171.4 (3)
C1—C2—C3—C4	−3.2 (6)	C2—C1—N1—C5	1.1 (6)
C1—C2—C3—C3^ii	174.1 (3)	C2—C1—N1—Ag1	−171.4 (3)
C2—C3—C4—C5	2.7 (6)	N1^i—Ag1—N1—C5	114.2 (3)
C3^ii—C3—C4—C5	−174.6 (3)	Cl1—Ag1—N1—C5	−65.8 (3)
C3—C4—C5—N1	−0.3 (7)	N1^i—Ag1—N1—C1	−73.3 (3)
C4—C5—N1—C1	−1.6 (6)	Cl1—Ag1—N1—C1	106.7 (3)

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