A two-dimensional undulating Ag^I coordination polymer constructed of Ag-C and Ag-O bonds: poly[[[[mu]₃-(5,6-[eta]):[kappa]O²:[kappa]O²-(±)-(1S,2S,3R,4R)-3-carb­oxy-7-oxa­bicyclo­[2.2.1]hept-5-ene-2-carboxyl­ato]silver(I)] mono­hydrate]

The title coordination polymer, {[Ag(C₈H₇O₅)]·H₂O}_n, is built from Ag⁺ cations and singly protonated dehydro­nor­can­tharidin (SP-DNC) anions, with a distorted trigonal-planar geometry at the metal centre. The coordination number of Ag^I is three (with one Ag-[pi] bond and two Ag-O bonds, one from each of three different SP-DNC ligands), if only formal Ag-ligand bonds are considered, but can be regarded as five if longer weak Ag...O inter­actions are also included. The two-dimensional corrugated-sheet coordination polymer forms a non-inter­penetrating framework with (4.8²) topology. Disordered water mol­ecules are sandwiched between the sheets.

S1. Comment

As an important derivative of cantharidin, 7-oxabicyclo[2.2.1]hept-5-ene-2,3-exo-dicarboxylic anhydride (dehydronorcantharidin, hereinafter DNC) is effective in inhibiting the growth of tumour cells (Xian et al., 2005; Shimi et al., 1982) and sensitizing tumours to chemotherapy (Li et al., 2008). The crystal structure of DNC has been reported three times so far (Baggio et al., 1972; Ramírez et al., 1998; Goh et al., 2008), but the structures of its metal complexes have not yet been reported. Many metal complexes are known to have antimicrobial or antineoplastic activities. We have synthesized some such complexes based on DNC, and this article describes the crystal structure of the title silver complex, (Ag–SP-DNC)_∞, (I), which is a coordination polymer built from Ag⁺ cations and singly protonated DNC anions (abbreviated as SP-DNC) with a novel two-dimensional (4,8²) noninterpenetrating framework.

As shown in Fig. 1, each SP-DNC anion binds one Ag⁺ cation via C═C at one end and two Ag⁺ cations via carboxyl atom O5 at the other end. Meanwhile, each Ag⁺ cation is coordinated to three SP-DNC anions to give rise to a two-dimensional network. Of these three SP-DNC anions, two provide two O atoms and the third contributes a C═C bond, with Ag—C distances of 2.377 (3) and 2.381 (3)Å. These are short and nearly equal, suggesting a strong interaction between the Ag⁺ cation and the π orbital of the double bond (Fig. 2a). Customarily, the Ag—π interaction is considered as a single coordination site (Cottram & Steel, 2006), so the coordination number is 3. Rather than a severely distorted triangular pyramid geometry, the coordination environment of Ag⁺ is more like a distorted trigonal-planar geometry, for the distance between Ag⁺ and the least-squares plane through the coordinated atoms C5, C6, O5(x + 1/2, -y + 1/2, z + 1/2) and O5(-x + 1/2, y + 1/2, -z + 3/2) is only 0.3993 (5) Å.

Apart from the three-membered ring constructed by Ag⁺ and C═C, there are two types of chelating rings around the Ag⁺ cations. Two SP-DNC-bridged Ag⁺ cations, together with the two bridging O5 atoms, form a four-membered ring with an Ag···Ag nonbonding distance of 3.7035 (8) Å. Four Ag⁺ cations and four SP-DNC anions link together to form 24-membered rings. If each SP-DNC anion around the Ag⁺ cation is simplified as a node, then the Ag⁺ cation can be simplified as a 3-connecting node, and the coordination polymer has a two-dimensional (4,8²) net that extends along the bc plane of the unit cell (Fig. 2b). This type of net consists of three connected nodes shared by one tetragonal square unit and two octagons, as predicted by Wells (1984) and first observed by Schröder and co-workers in 2000 (Long et al., 2000).

In the above analysis we described a three-coordinated Ag⁺ cation in which the Ag—µ-O (both O5) bond lengths are 2.299 (2) and 2.415 (2) Å. However, we could also include longer, weaker, interactions between Ag and O (Huang et al., 2004; Young & Hanton, 2008; Steed et al., 2003; Novitchi et al., 2010; Dean et al., 2004) and regard both O1 and O2 as also being coordinated to Ag⁺, with bond lengths of 2.753 (2) and 2.744 (2) Å, respectively. Thus, the coordination number of Ag⁺ would become 5, but still with three SP-DNC anions: one provides C═C, the second gives three O atoms (O1, O2 and O5) and the third gives one O atom (O5). This kind of coordination mode was predicated by Casida and co-workers in 1987 (Matsuzawa et al., 1987) and this is the first example, to the best of our knowledge. The two-dimensional net has a vertex symbol (3.20.6.7.9.20), but is still (4.8²) if the SP-DNC anion is simplified as a node, as mentioned above.

The coordination polymer produces an extended two-dimensional zigzag-type architecture in which water molecules are sandwiched between two undulating tapes (Fig. 3). The distance between two adjacent tapes is 12.746 (3) Å and the water molecules occupy the centre of the void space between these tapes. The two tapes are held together via hydrogen bonds between them and the water molecules (Table 2). The water H atoms were found to be disordered over two positions, which were determined from the difference Fourier map and modelled with site-occupancy factors from refinement of 0.837 (2) (for H8 and H9) and 0.163 (2) (for H8A and H9A). Splitting the occupancies of the H atoms reduced the final R and U_iso values.

Related literature

For related literature, see: Baggio et al. (1972); Cottram & Steel (2006); Dean et al. (2004); Goh et al. (2008); Huang et al. (2004); Li et al. (2008); Long et al. (2000); Matsuzawa et al. (1987); Novitchi et al. (2010); Ramírez et al. (1998); Shimi et al. (1982); Steed et al. (2003); Wells (1984); Xian et al. (2005); Young & Hanton (2008).

S2. Experimental

Crystals of (Ag–SP-DNC)_∞, (I), were obtained from the reaction of DNC and AgNO₃ (1:1 molar ratio) in water at room temperature. Elemental analysis for (I), calculated: C 31.09, H 2.94, O 31.06%; found: C 31.01, H 3.05, O 31.24%.

S3. Refinement

All H atoms were found in a difference map and refined isotropically. The water H atoms were disordered over two positions, which were determined from the difference Fourier map and modelled with site-occupancy factors from refinement of 0.837 (2) (for H8 and H9) and 0.163 (2) (for H8A and H9A).

Computing details

Data collection: SMART (Bruker, 2000); cell refinement: SMART (Bruker, 2000); data reduction: SAINT (Bruker, 2000); program(s) used to solve structure: SHELXTL (Sheldrick, 2008); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: SHELXTL (Sheldrick, 2008); software used to prepare material for publication: SHELXL97 (Sheldrick, 2008).

Figures

	Fig. 1. The crystal structure of (I), showing the atom-numbering scheme. Displacement ellipsoids are drawn at the 30% probability level. [Symmetry codes: (i) x - 1/2, -y + 1/2, z - 1/2; (ii) -x + 1/2, y - 1/2, -z + 3/2.]
	Fig. 2. (a) A portion of an infinite two-dimensional sheet framework in (I), viewed along the a axis. All H atoms, water molecules, C8 atoms and noncoordinated O atoms have been omitted for clarity. (b) A two-dimensional (4,8^2) topological diagram of (I).
	Fig. 3. A view of the overlapping undulating tapes, viewed along the [101] axis. The two tapes on the left have been simplified by abstracting SP-DNC anions into dummy atoms, and all of the water molecules are shown in space-filling mode.

poly[[[µ₃-(5,6-η):κO²:κO²-(±)- (1S,2S,3R,4R)-3-carboxy-7- oxabicyclo[2.2.1]hept-5-ene-2-carboxylato]silver(I)] monohydrate]

Crystal data

[Ag(C8H7O5)]·H2O	F(000) = 608.0
Mr = 309.02	Dx = 2.346 Mg m^−3
Monoclinic, P21/n	Mo Kα radiation, λ = 0.71073 Å
Hall symbol: -P 2yn	Cell parameters from 380 reflections
a = 9.885 (2) Å	θ = 2.5–28.3°
b = 7.0011 (15) Å	µ = 2.31 mm^−1
c = 12.746 (3) Å	T = 298 K
β = 97.280 (3)°	Block, colourless
V = 874.9 (3) Å^3	0.32 × 0.27 × 0.12 mm
Z = 4

Data collection

Bruker SMART CCD area-detector diffractometer	1995 independent reflections
Radiation source: fine-focus sealed tube	1868 reflections with I > 2σ(I)
Graphite monochromator	Rint = 0.039
ϕ and ω scans	θmax = 28.3°, θmin = 2.5°
Absorption correction: multi-scan (SADABS; Bruker, 2000)	h = −13→12
Tmin = 0.482, Tmax = 0.758	k = −7→9
4990 measured reflections	l = −11→16

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)] = 0.030	H atoms treated by a mixture of independent and constrained refinement
wR(F^2) = 0.080	w = 1/[σ^2(Fo^2) + (0.0475P)^2 + 0.2021P] where P = (Fo^2 + 2Fc^2)/3
S = 1.05	(Δ/σ)max = 0.001
1995 reflections	Δρmax = 0.87 e Å^−3
164 parameters	Δρmin = −0.95 e Å^−3
6 restraints	Extinction correction: SHELXL97 (Sheldrick, 2008), Fc^*=kFc[1+0.001xFc^2λ^3/sin(2θ)]^-1/4
Primary atom site location: structure-invariant direct methods	Extinction coefficient: 0.0130 (12)

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 > 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	Occ. (<1)
Ag1	0.42686 (2)	0.47589 (3)	0.859527 (16)	0.02830 (13)
O1	0.26789 (17)	0.2554 (3)	0.68466 (14)	0.0245 (4)
O2	0.2957 (2)	−0.1098 (3)	0.54062 (16)	0.0330 (5)
O3	0.3032 (3)	0.0244 (3)	0.38335 (18)	0.0323 (5)
H7	0.2515	−0.0729	0.3615	0.078 (16)*
O4	0.0788 (2)	0.4234 (3)	0.37832 (18)	0.0366 (5)
O5	0.06616 (19)	0.1838 (3)	0.48871 (15)	0.0284 (4)
C1	0.2524 (3)	0.4381 (4)	0.6326 (2)	0.0232 (5)
H1	0.1729	0.4954	0.6443	0.037 (11)*
C2	0.2635 (2)	0.3839 (3)	0.5156 (2)	0.0192 (5)
C3	0.3691 (3)	0.2182 (4)	0.5327 (2)	0.0208 (5)
C4	0.4006 (3)	0.2119 (4)	0.6552 (2)	0.0221 (5)
C5	0.4791 (3)	0.3919 (4)	0.6885 (2)	0.0240 (5)
C6	0.3867 (3)	0.5341 (4)	0.6741 (2)	0.0227 (5)
C7	0.1258 (3)	0.3281 (3)	0.45580 (19)	0.0210 (5)
C8	0.3176 (3)	0.0280 (4)	0.4884 (2)	0.0233 (6)
O6	0.3323 (2)	0.2410 (3)	0.19795 (17)	0.0380 (5)
H8	0.3522	0.2190	0.1316	0.006 (5)*	0.84 (4)
H9	0.3279	0.1862	0.2552	0.007 (5)*	0.84 (4)
H8A	0.3685	0.1253	0.1709	0.007 (5)*	0.16 (4)
H9A	0.2596	0.1960	0.1853	0.007 (5)*	0.16 (4)
H2	0.304 (3)	0.484 (4)	0.486 (3)	0.023 (9)*
H3	0.443 (3)	0.243 (5)	0.501 (2)	0.025 (7)*
H4	0.434 (3)	0.100 (4)	0.688 (2)	0.013 (6)*
H5	0.570 (3)	0.404 (4)	0.695 (2)	0.024 (7)*
H6	0.398 (3)	0.665 (5)	0.669 (2)	0.027 (8)*

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
Ag1	0.03320 (18)	0.03385 (18)	0.01679 (17)	0.00838 (8)	−0.00093 (10)	−0.00330 (7)
O1	0.0273 (9)	0.0275 (10)	0.0196 (9)	−0.0034 (7)	0.0069 (7)	0.0010 (8)
O2	0.0486 (12)	0.0223 (10)	0.0279 (11)	0.0008 (8)	0.0038 (9)	0.0035 (8)
O3	0.0528 (14)	0.0264 (10)	0.0186 (11)	−0.0049 (9)	0.0081 (10)	−0.0049 (8)
O4	0.0402 (12)	0.0331 (11)	0.0318 (12)	−0.0087 (9)	−0.0138 (9)	0.0117 (10)
O5	0.0310 (10)	0.0292 (10)	0.0237 (10)	−0.0098 (8)	−0.0009 (8)	0.0032 (8)
C1	0.0223 (12)	0.0253 (13)	0.0217 (13)	0.0057 (10)	0.0015 (10)	−0.0057 (11)
C2	0.0225 (11)	0.0170 (11)	0.0179 (11)	−0.0003 (9)	0.0018 (9)	0.0016 (9)
C3	0.0241 (12)	0.0214 (11)	0.0177 (12)	0.0006 (9)	0.0058 (10)	−0.0006 (10)
C4	0.0268 (13)	0.0207 (12)	0.0184 (12)	0.0051 (10)	0.0009 (10)	0.0005 (10)
C5	0.0231 (13)	0.0292 (14)	0.0196 (12)	0.0005 (10)	0.0028 (10)	−0.0026 (11)
C6	0.0294 (14)	0.0211 (12)	0.0170 (13)	−0.0017 (10)	0.0006 (11)	−0.0013 (9)
C7	0.0273 (12)	0.0179 (11)	0.0178 (12)	0.0011 (9)	0.0030 (10)	−0.0030 (9)
C8	0.0265 (14)	0.0225 (13)	0.0216 (15)	0.0041 (9)	0.0053 (11)	−0.0019 (10)
O6	0.0562 (14)	0.0284 (10)	0.0295 (11)	0.0069 (10)	0.0060 (10)	0.0059 (9)

Geometric parameters (Å, º)

Ag1—O5^i	2.2985 (19)	C1—C2	1.556 (4)
Ag1—C5	2.377 (3)	C1—H1	0.9107
Ag1—C6	2.381 (3)	C2—C7	1.525 (3)
Ag1—O5^ii	2.4149 (19)	C2—C3	1.557 (3)
Ag1—O2^ii	2.744 (2)	C2—H2	0.91 (3)
Ag1—O1^ii	2.7529 (18)	C3—C8	1.509 (3)
O1—C1	1.440 (3)	C3—C4	1.554 (3)
O1—C4	1.442 (3)	C3—H3	0.90 (3)
O1—Ag1^iii	2.7529 (18)	C4—C5	1.512 (4)
O2—C8	1.207 (3)	C4—H4	0.93 (3)
O2—Ag1^iii	2.744 (2)	C5—C6	1.348 (4)
O3—C8	1.329 (4)	C5—H5	0.90 (3)
O3—H7	0.8760	C6—H6	0.93 (3)
O4—C7	1.233 (3)	O6—H8	0.9060
O5—C7	1.268 (3)	O6—H9	0.8300
O5—Ag1^iv	2.2985 (19)	O6—H8A	0.9670
O5—Ag1^iii	2.4149 (19)	O6—H9A	0.7824
C1—C6	1.522 (4)
O5^i—Ag1—C5	110.88 (8)	C8—C3—C2	114.6 (2)
O5^i—Ag1—C6	143.47 (8)	C4—C3—C2	101.92 (19)
C5—Ag1—C6	32.91 (9)	C8—C3—H3	105 (2)
O5^i—Ag1—O5^ii	76.45 (7)	C4—C3—H3	112.9 (19)
C5—Ag1—O5^ii	153.66 (8)	C2—C3—H3	111 (2)
C6—Ag1—O5^ii	132.53 (8)	O1—C4—C5	101.68 (19)
O5^i—Ag1—O2^ii	90.23 (7)	O1—C4—C3	100.51 (19)
C5—Ag1—O2^ii	130.65 (8)	C5—C4—C3	106.8 (2)
C6—Ag1—O2^ii	117.07 (8)	O1—C4—H4	109.8 (16)
O5^ii—Ag1—O2^ii	72.76 (6)	C5—C4—H4	115.9 (17)
O5^i—Ag1—O1^ii	146.34 (6)	C3—C4—H4	119.6 (18)
C5—Ag1—O1^ii	102.47 (8)	C6—C5—C4	105.2 (2)
C6—Ag1—O1^ii	69.58 (8)	C6—C5—Ag1	73.70 (16)
O5^ii—Ag1—O1^ii	71.55 (6)	C4—C5—Ag1	107.46 (16)
O2^ii—Ag1—O1^ii	70.70 (6)	C6—C5—H5	127 (2)
C1—O1—C4	96.61 (17)	C4—C5—H5	125 (2)
C1—O1—Ag1^iii	120.41 (14)	Ag1—C5—H5	103 (2)
C4—O1—Ag1^iii	115.61 (14)	C5—C6—C1	105.5 (2)
C8—O2—Ag1^iii	106.90 (17)	C5—C6—Ag1	73.39 (16)
C8—O3—H7	108.6	C1—C6—Ag1	107.33 (17)
C7—O5—Ag1^iv	114.34 (16)	C5—C6—H6	130.8 (19)
C7—O5—Ag1^iii	141.10 (17)	C1—C6—H6	121.5 (19)
Ag1^iv—O5—Ag1^iii	103.55 (7)	Ag1—C6—H6	103.1 (19)
O1—C1—C6	101.2 (2)	O4—C7—O5	123.6 (2)
O1—C1—C2	102.05 (19)	O4—C7—C2	118.9 (2)
C6—C1—C2	106.0 (2)	O5—C7—C2	117.5 (2)
O1—C1—H1	111.1	O2—C8—O3	122.5 (3)
C6—C1—H1	118.8	O2—C8—C3	125.1 (3)
C2—C1—H1	115.5	O3—C8—C3	112.4 (2)
C7—C2—C1	112.0 (2)	H8—O6—H9	141.6
C7—C2—C3	114.8 (2)	H8—O6—H8A	52.4
C1—C2—C3	100.11 (19)	H9—O6—H8A	89.3
C7—C2—H2	114 (2)	H8—O6—H9A	92.4
C1—C2—H2	107 (2)	H9—O6—H9A	81.1
C3—C2—H2	108 (2)	H8A—O6—H9A	87.7
C8—C3—C4	111.5 (2)

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

Hydrogen-bond geometry (Å, º)

D—H···A	D—H	H···A	D···A	D—H···A
O3—H7···O6^v	0.88	1.67	2.540 (3)	170
C6—H6···O2^vi	0.93 (3)	2.40 (3)	3.087 (3)	130 (2)
C1—H1···O4^vii	0.91	2.53	3.400 (4)	159

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