Bis(O-methyl­di­thio­carbonato)­cadmium(II)

To a first approximation, the cadmium centre in the centrosymmetric title compound, [Cd(S₂COCH₃)₂], exists within an S₄ donor set which defines a distorted square planar geometry. Molecules associate in the crystal structure via Cd-S interactions above and below the square plane, so as to form stacks that might be considered as edge-shared, tetragonally distorted octahedra.

Key indicators

• Single-crystal synchrotron study
• T = 123 K
• Mean [sigma](O-C) = 0.003 Å
• R factor = 0.030
• wR factor = 0.073
• Data-to-parameter ratio = 18.1

checkCIF results

No syntax errors found

ADDSYM reports no extra symmetry


 Alert Level C:



HYDTR_01  Alert C The hydrogen treatment should only be one of the following
          keywords
          *  refall
          *  refxyz
          *  refU
          *  noref
          *  undef
          *  constr
          *  none
          *  mixed
          Hydrogen treatment given as see experimental section

General Notes



ABSMU_01  Radiation type not identified. Calculation of
          _exptl_absorpt_correction_mu not performed.


 0 Alert Level A = Potentially serious problem

 0 Alert Level B = Potential problem

 1 Alert Level C = Please check

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S1. Comment

As highlighted in a bibliographic review of the binary 1,1-dithiolates, e.g. dithiocarbamate (⁻S₂CNR₂), xanthate (⁻S₂COR), and dithiophosphate (⁻S₂P(OR)₂) anions, the structural chemistry of this class of ligands is extraordinarily diverse (Cox & Tiekink, 1997). Particularly interesting is the observation that very different structural types may be found even when there has only been a minor change in the nature of the organic substituent. Pertinent to the present paper are the structures of the cadmium bis(xanthate)s.

The structure of the butylxanthate, i.e. Cd(S₂COnBu)₂, features tetrahedral cadmium centres and bridging xanthate ligands so that a layer structure is formed (Rietveld & Maslen, 1965). A similar motif is found for the ethyl- (Iimura, Ito & Hagihara, 1972) and isopropyl-xanthates (Iimura, 1973; Tomlin et al., 1999; Tiekink, 2000). Incredibly, exchanging the γ-methylene group in Cd(S₂COnBu)₂ for an O atom, giving Cd(S₂COCH₂CH₂OMe)₂, leads to an entirely different motif based on a square planar geometry (Abrahams et al., 1988). The challenge remains to rationalize the diverse structures found in the solid state.

Systematic studies in this field have been hampered by the inability to grow suitable crystals for X-ray analysis. In the case of the title compound, Cd(S₂COMe)₂, (I), this difficulty has been overcome by the utilization of synchrotron radiation that has enabled a full structure determination on a microcrystal with dimensions 0.01 x 0.025 x 0.025 mm. As described, the structure of (I) resembles that reported earlier for Cd(S₂COCH₂CH₂OMe)₂ (Abrahams et al., 1988).

The molecular structure of (I) (Fig. 1 & Table 1) is centrosymmetric and features two almost symmetrically chelating xanthate ligands that define an S₄ donor set leading, to a first approximation, to a square planar geometry. The variation of the parameters associated with the independent xanthate ligand are as expected; see Table 1. Molecules associate in the crystal structure to form stacks between translationally related molecules aligned along b; one such stack is illustrated in Fig. 2. These are held in place by close Cd···S interactions occurring above and below the square plane. The Cd···S1ⁱ (i: x, y − 1, z) distance of 2.8881 (6) Å is at least 0.24 Å longer than the weaker of the Cd—S bonds defining the square plane. The comparable intermolecular Cd—S interaction in the structure of Cd(S₂COCH₂CH₂OMe)₂ was reported to be significantly longer at 3.0225 (8) Å (Abrahams et al., 1988). If the Cd—S1ⁱ interaction in (I) was considered significant, the coordination geometry could be considered as tetragoanlly distorted octahedral and the crystal structure thought of being comprised of edge-shared octahedra.

S2. Experimental

Pale-yellow crystals were obtained from the slow evaporation of an acetone solution of the compound that had been prepared following the literature procedure (Abrahams et al., 1988).

S3. Refinement

The methyl group was placed torsionally from the Fourier. Isotropic displacement parameters for all three H atoms were refined and the methyl group was allowed to rotate but not to tip.

Computing details

Data collection: SMART-KAPPA (Bruker, 1998); cell refinement: SAINT (Bruker, 2000); data reduction: SHELXTL (Bruker, 2000); program(s) used to solve structure: SHELXS86 (Sheldrick, 1986); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997); molecular graphics: ORTEPII (Johnson, 1976); software used to prepare material for publication: SHELXL97.

Figures

	Fig. 1. The molecular structure and crystallographic numbering scheme for (I). Displacement ellipsoids are shown at the 70% probability level (Johnson, 1976). Symmetry operator for generating eqivalent atoms: 1/2 − x, 1/2 − y, −z.
	Fig. 2. View of the molecular aggregation in (I).

(I)

Crystal data

[Cd(S2C2H3O)2]	F(000) = 632
Mr = 326.73	Dx = 2.415 Mg m^−3
Monoclinic, C2/c	Synchrotron radiation, λ = 0.56357 Å
Hall symbol: -C 2yc	Cell parameters from 2655 reflections
a = 19.006 (2) Å	θ = 2.7–21.4°
b = 3.9728 (3) Å	µ = 1.72 mm^−1
c = 12.5126 (14) Å	T = 123 K
β = 107.993 (4)°	Plate, yellow
V = 898.59 (17) Å^3	0.03 × 0.03 × 0.01 mm
Z = 4

Data collection

Bruker Mosaic KappaCCD diffractometer	1031 independent reflections
Radiation source: APS 15-ID-C synchrotron	992 reflections with I > 2σ(I)
Silicon monochromator	Rint = 0.084
ϕ scans	θmax = 21.4°, θmin = 1.8°
Absorption correction: multi-scan (SADABS; Blessing, 1995)	h = −24→23
Tmin = 0.958, Tmax = 0.998	k = 0→5
6696 measured reflections	l = 0→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	See experimental section
wR(F^2) = 0.073	w = 1/[σ^2(Fo^2) + (0.0667P)^2] where P = (Fo^2 + 2Fc^2)/3
S = 1.01	(Δ/σ)max < 0.001
1031 reflections	Δρmax = 0.72 e Å^−3
57 parameters	Δρmin = −1.22 e Å^−3
0 restraints	Extinction correction: SHELXL, Fc^*=kFc[1+0.001xFc^2λ^3/sin(2θ)]^-1/4
Primary atom site location: structure-invariant direct methods	Extinction coefficient: 0.0301 (16)

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
Cd	0.2500	0.2500	0.0000	0.01603 (16)
S1	0.35350 (3)	0.70595 (14)	0.08140 (5)	0.01264 (17)
S2	0.31582 (2)	0.41115 (11)	−0.15051 (3)	0.01345 (18)
C1	0.37211 (9)	0.6362 (5)	−0.04373 (14)	0.0118 (4)
O1	0.43460 (12)	0.7738 (3)	−0.04763 (15)	0.0149 (4)
C2	0.45575 (14)	0.7352 (5)	−0.1491 (2)	0.0172 (5)
H2a	0.4582	0.4954	−0.1659	0.021 (6)*
H2b	0.5043	0.8385	−0.1379	0.025 (6)*
H2c	0.4190	0.8459	−0.2120	0.014 (5)*

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
Cd	0.0175 (2)	0.0159 (2)	0.0174 (2)	−0.00469 (6)	0.00938 (13)	−0.00186 (6)
S1	0.0144 (3)	0.0155 (3)	0.0083 (3)	−0.00119 (16)	0.0041 (2)	−0.00103 (16)
S2	0.0144 (3)	0.0166 (3)	0.0092 (2)	−0.00256 (14)	0.00337 (17)	−0.00170 (15)
C1	0.0125 (8)	0.0123 (9)	0.0101 (8)	0.0015 (6)	0.0030 (6)	0.0025 (7)
O1	0.0135 (7)	0.0202 (10)	0.0124 (8)	−0.0029 (4)	0.0058 (6)	−0.0013 (4)
C2	0.0170 (11)	0.0238 (13)	0.0146 (11)	−0.0017 (6)	0.0102 (9)	−0.0014 (6)

Geometric parameters (Å, º)

Cd—S1	2.6364 (6)	C1—O1	1.322 (3)
Cd—S2	2.6413 (5)	O1—C2	1.454 (3)
Cd—S1^i	2.8881 (6)	C2—H2a	0.9800
S1—C1	1.7307 (18)	C2—H2b	0.9800
S2—C1	1.6871 (19)	C2—H2c	0.9800
S1—Cd—S2	69.373 (17)	S2—C1—O1	123.17 (14)
S1—Cd—S2^ii	110.627 (17)	S1—C1—S2	122.99 (11)
S1—Cd—S1^iii	88.150 (19)	C1—O1—C2	118.87 (17)
S2—Cd—S1^iii	89.322 (16)	O1—C2—H2A	109.5
S2—Cd—S1^i	90.679 (16)	O1—C2—H2B	109.5
Cd—S1—C1	82.94 (7)	H2A—C2—H2B	109.5
Cd—S2—C1	83.57 (6)	O1—C2—H2C	109.5
C1—S1—Cd^iv	96.20 (6)	H2A—C2—H2C	109.5
Cd—S1—Cd^iv	91.850 (19)	H2B—C2—H2C	109.5
S1—C1—O1	113.84 (14)

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