Polymeric (O-ethyl di­thio­carbonato)silver(I)

The title compound, [Ag(C₃H₅OS₂)]_n, is polymeric in the solid state and adopts a layered structure in which each Ag atom is five-coordinated in a distorted trigonal-bipyramidal geometry defined by four S atoms belonging to four different xanthate groups and by a neigbouring Ag atom [Ag...Ag = 3.0540 (8) Å]. Each S atom is three-coordinated to one C and two Ag atoms. The structure can be envisaged as being formed by Ag₂(S₂COEt)₂ units in which every S atom is bonded to another Ag atom from a different unit and the Ag atoms are also bonded to two different S atoms of two other units. The result is a two-dimensional network of condensed metallacycles of six or eight atoms.

S1. Comment

Silver thiolates have been known for a long time, and their low solubility suggests they are polymeric in nature. This property has been confirmed, in the case of the silver(I) complexes of dithiocarbamates, by the determination of the crystal structures of [Ag(S₂CNR₂)] (R = Et and n-Pr). The α forms of [Ag(S₂CNEt₂)] (Yamaguchi et al., 1976) and [Ag(S₂CNPr₂)] (Hesse & Nilson, 1969) contain discrete hexameric molecules in which the Ag atoms form a somewhat distorted octahedron with six comparatively short and six longer edges. The short edges correspond to metal–metal distances comparable to those in the metallic phase of silver. All Ag atoms are connected to five atoms, viz. two Ag and three S atoms, while the S atoms are bonded to one or two Ag atoms. In these hexameric units, the terminal Ag atom in one molecule is bridged by a S atom to that in the adjacent hexamer (Ag—S = 2.99 Å), thus forming a chain structure. The β modification of [Ag(S₂CNEt₂)] (Anacker-Eickhoff, 1982) is a true high polymer, in which the Ag atom and the ligands are linked in chains. All the Ag atoms are coordinated to four S atoms, with distances ranging from 2.51 to 2.74 Å. In addition, there are two short metal–metal distances per six Ag atoms. By contrast, the difficulty in obtaining suitable crystals has not allowed, to date, the determination of the crystal structures of the silver(I) xanthates, [Ag(S₂COR)] (Kowala & Swan, 1966). In spite of their low solubility, the silver xantates can react easily. When different ligands are added to suspensions of polymeric silver xanthates, monomeric soluble adducts, whose structures are well known, can be obtained. An example of one of these adducts is [Ag(S₂COEt)(PPh₃)₂], of which two polymorphic modifications have been described (Tiekink, 1988; Ara et al., 2003).

We obtained crystals of Ag(S₂COEt), (I), from the reaction of [Zn(S₂COEt)₂] and O₃ClOAgPPh₃, in which the [Ag(PPh₃)₄](ClO₄) complex (Cotton & Goodgame, 1960; Engelhardt et al., 1985) is the main product, and we studied the structure of (I) in order to determine the nature of the Ag-atom geometry and the mode of coordination of the xanthate ligand. The structure of (I) consists of a two-dimensional polymeric array of molecules. All Ag atoms in each layer have the same environment, viz. a distorted trigonal bipyramid in which the three S atoms are located in the equatorial positions, and the axial positons are occupied by an S and an Ag atom. The S—Ag—S angles in the trigonal plane range from 109.40 (3) to 124.38 (5)°, the S_eq—Ag—Ag angles range from 75.73 (4) to 98.08 (4)°, the S_eq—Ag—S_ax angles range from 84.41 (4) to 105.36 (5)° and the Ag—Ag—S_ax angle is 168.43 (4)°. The Ag—S_eq distances are very similar and range from 2.5073 (15) to 2.5578 (14) Å. By contrast the Ag—S_ax distance is significantly longer [2.8379 (14) Å]. The Ag···Ag distance of 3.0540 (8) Å is long enough to postulate only a weak interaction between the two metal atoms (Wang & Mak, 2001). In addition to this weak interaction, both Ag atoms are bonded by a bridging xanthate ligand in which the S1—S2 distance of 3.0201 (19) Å is somewhat longer than the bite distance shown by chelating xanthate ligands (Chan et al., 1982). All the S atoms in the structure are three-coordinated (to two Ag atoms and one C atom), thus forming a distorted non-planar trigonal environment, with the S atoms lying above or below the coordination plane (0.8520 and 0.7701 Å for S1 and S2, respectively). The xanthate ligand can be considered as a tetradentate group, since each S atom is bonded to two different Ag atoms. The bonding mode within the xanthate ligand can be represented by the valence-bond formalism shown below (Diagram 1) (Coucouvanis, 1970). In general, resonance forms (a) and (b) best describe the structures of the xanthate complexes, but in (I), the short C1—O and long S—C1 distances (Table 1) suggest that the contribution of resonance structure (c) is not negligible. The structure is best envisaged as being formed by units of two Ag atoms bridged by two xanthate ligands. If the Ag···Ag interaction is disregarded, these units form cycles of eight atoms (two Ag, four S and two C atoms). Each S atom is also bonded to another Ag atom from a different unit, thus forming a cycle of six atoms (two Ag, three S and one C atom). Thus, the whole array consists of non-planar fused metallacycles of six and eight atoms, in which all atoms belong to both types of cycle.

S2. Experimental

[Zn(S₂COEt)₂] (0.1 g, 0.325 mmol) and O₃ClOAgPPh₃ (0.471 g, 1.302 mmol) were mixed in dichloromethane (20 ml). After 15 min, the resulting yellow solid was removed by filtration. The solution was evaporated to ca 5 ml, and a layer of n-hexane was added carefully and allowed to diffuse through the solution. After one week, a mixture of yellow (I) and colorless crystals of [Ag(PPh₃)₄][ClO₄] was obtained, and the crystals were separated by hand. Complex [Ag(PPh₃)₄][ClO₄] was identified on the basis of its IR spectrum (Cotton & Goodgame, 1960) and elemental analyses (calculated for C₇₂H₆₀AgClO₄P₄: C 68.82, H 4.77%; found: C 68.54, H 4.62%).

S3. Refinement

The final electron-density difference map showed four peaks above 1 e Å⁻³ (max. 2.08, min. −1.25), all of them located less than 1 Å away from the Ag atom. These residual densities are probably a consequence of an insufficient absorption-correction procedure.

Computing details

Data collection: SMART (Bruker, 2000); cell refinement: SAINT-Plus (Bruker, 1999); data reduction: SAINT-Plus; program(s) used to solve structure: SHELXS97 (Sheldrick, 1997); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997); molecular graphics: XP in SHELXTL (Bruker, 2000); software used to prepare material for publication: XCIF in SHELXTL.

Figures

Fig. 1. A view of the structure of the Ag2(S2COEt)2 moieties of (I), showing the coordination geometry and the atom-numbering scheme. Displacement ellipsoids are drawn at the 50% probability level and H atoms are shown as small spheres of arbitrary radii. [Symmetry codes: (') 1 − x, −y, 1 − z; (") 1 − x, −1/2 + y, 1/2 − z; ('") 1 − x, 1/2 + y, 1/2 − z; (*) x, 1/2 − y, −1/2 + z; (**) 1 − x, −1/2 + y, 3/2 − z; (#) x, −1/2 − y, −1/2 + z;(##) 1 − x, 1/2 + y, 3/2 − z.]

Fig. 2. Packing diagram of (I), viewed along the c axis.

(O-ethyl dithiocarbonato)silver(I)

Crystal data

[Ag(C3H5OS2)]	F(000) = 440
Mr = 229.06	Dx = 2.565 Mg m^−3
Monoclinic, P21/c	Mo Kα radiation, λ = 0.71073 Å
Hall symbol: -P 2ybc	Cell parameters from 1495 reflections
a = 12.6929 (12) Å	θ = 3.3–26.3°
b = 6.1566 (6) Å	µ = 3.97 mm^−1
c = 7.8385 (7) Å	T = 100 K
β = 104.419 (2)°	Thin plate, yellow
V = 593.25 (10) Å^3	0.36 × 0.18 × 0.02 mm
Z = 4

Data collection

Bruker SMART APEX CCD system diffractometer	1211 independent reflections
Radiation source: fine-focus sealed tube	1042 reflections with I > 2σ(I)
Graphite monochromator	Rint = 0.032
Detector resolution: 8.26 pixels mm^-1	θmax = 26.4°, θmin = 1.7°
ω rotations scans	h = −15→11
Absorption correction: multi-scan SADABS (Sheldrick, 1996)	k = −7→7
Tmin = 0.329, Tmax = 0.925	l = −9→9
3390 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)] = 0.039	Hydrogen site location: inferred from neighbouring sites
wR(F^2) = 0.092	H-atom parameters constrained
S = 1.03	w = 1/[σ^2(Fo^2) + (0.0546P)^2] where P = (Fo^2 + 2Fc^2)/3
1211 reflections	(Δ/σ)max < 0.001
64 parameters	Δρmax = 2.08 e Å^−3
0 restraints	Δρmin = −1.25 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.

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

	x	y	z	Uiso*/Ueq
Ag	0.58119 (4)	0.11710 (6)	0.41750 (5)	0.01792 (18)
S1	0.69503 (12)	0.1153 (2)	0.72880 (18)	0.0164 (3)
S2	0.59321 (11)	−0.3311 (2)	0.68641 (17)	0.0151 (3)
O	0.7641 (3)	−0.2338 (6)	0.9211 (5)	0.0161 (8)
C1	0.6899 (4)	−0.1490 (8)	0.7896 (7)	0.0139 (11)
C2	0.8462 (5)	−0.0964 (9)	1.0352 (8)	0.0205 (13)
H2A	0.8144	−0.0155	1.1195	0.025*
H2B	0.8763	0.0090	0.9646	0.025*
C3	0.9331 (5)	−0.2499 (10)	1.1310 (7)	0.0214 (13)
H3A	0.9913	−0.1673	1.2102	0.032*
H3B	0.9630	−0.3294	1.0455	0.032*
H3C	0.9017	−0.3531	1.1998	0.032*

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
Ag	0.0261 (3)	0.0102 (2)	0.0177 (3)	0.00193 (16)	0.00590 (18)	0.00054 (16)
S1	0.0258 (8)	0.0072 (6)	0.0174 (7)	−0.0004 (5)	0.0073 (6)	0.0011 (5)
S2	0.0210 (7)	0.0070 (6)	0.0174 (7)	0.0006 (5)	0.0050 (6)	−0.0002 (5)
O	0.022 (2)	0.0052 (17)	0.0198 (19)	−0.0019 (15)	0.0030 (17)	0.0008 (15)
C1	0.019 (3)	0.011 (2)	0.014 (3)	0.000 (2)	0.008 (2)	−0.003 (2)
C2	0.024 (3)	0.015 (3)	0.021 (3)	−0.004 (2)	0.004 (3)	−0.004 (2)
C3	0.027 (3)	0.019 (3)	0.020 (3)	0.000 (2)	0.009 (3)	0.001 (2)

Geometric parameters (Å, º)

Ag—S1	2.5073 (15)	S2—Ag^v	2.5578 (14)
Ag—S2^i	2.5302 (15)	O—C1	1.318 (6)
Ag—S2^ii	2.5578 (14)	O—C2	1.462 (6)
Ag—S1^iii	2.8379 (14)	C2—C3	1.504 (8)
Ag—Ag^i	3.0540 (8)	C2—H2A	0.9900
S1—C1	1.701 (5)	C2—H2B	0.9900
S1—Ag^iv	2.8379 (14)	C3—H3A	0.9800
S2—C1	1.710 (5)	C3—H3B	0.9800
S2—Ag^i	2.5302 (15)	C3—H3C	0.9800
S1—Ag—S2^i	124.16 (5)	C1—O—C2	120.7 (4)
S1—Ag—S2^ii	124.38 (5)	O—C1—S1	121.9 (4)
S2^i—Ag—S2^ii	109.40 (3)	O—C1—S2	113.5 (4)
S1—Ag—S1^iii	105.36 (5)	S1—C1—S2	124.6 (3)
S2^i—Ag—S1^iii	92.76 (4)	O—C2—C3	105.3 (4)
S2^ii—Ag—S1^iii	84.41 (4)	O—C2—H2A	110.7
S1—Ag—Ag^i	82.64 (4)	C3—C2—H2A	110.7
S2^i—Ag—Ag^i	75.73 (4)	O—C2—H2B	110.7
S2^ii—Ag—Ag^i	98.08 (4)	C3—C2—H2B	110.7
S1^iii—Ag—Ag^i	168.43 (4)	H2A—C2—H2B	108.8
C1—S1—Ag	102.94 (19)	C2—C3—H3A	109.5
C1—S1—Ag^iv	110.46 (18)	C2—C3—H3B	109.5
Ag—S1—Ag^iv	105.06 (5)	H3A—C3—H3B	109.5
C1—S2—Ag^i	106.17 (19)	C2—C3—H3C	109.5
C1—S2—Ag^v	106.19 (18)	H3A—C3—H3C	109.5
Ag^i—S2—Ag^v	112.63 (5)	H3B—C3—H3C	109.5
S2^i—Ag—S1—C1	117.42 (19)	Ag—S1—C1—O	158.7 (4)
S2^ii—Ag—S1—C1	−44.5 (2)	Ag^iv—S1—C1—O	−89.6 (4)
S1^iii—Ag—S1—C1	−138.29 (18)	Ag—S1—C1—S2	−19.5 (4)
Ag^i—Ag—S1—C1	50.25 (19)	Ag^iv—S1—C1—S2	92.2 (3)
S2^i—Ag—S1—Ag^iv	1.75 (7)	Ag^i—S2—C1—O	147.6 (3)
S2^ii—Ag—S1—Ag^iv	−160.20 (4)	Ag^v—S2—C1—O	27.5 (4)
S1^iii—Ag—S1—Ag^iv	106.04 (7)	Ag^i—S2—C1—S1	−34.1 (4)
Ag^i—Ag—S1—Ag^iv	−65.43 (4)	Ag^v—S2—C1—S1	−154.2 (3)
C2—O—C1—S1	8.1 (6)	C1—O—C2—C3	−163.8 (5)
C2—O—C1—S2	−173.6 (4)

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