catena-Poly­[[bis­(thio­cyanato-[kappa]N)cadmium(II)]-di-[mu]-thio­urea-[kappa]⁴S:S]

The Cd^II ion in the title complex, [Cd(SCN)₂{SC(NH₂)₂}₂]_[infinity], is situated at a centre of symmetry, and is bound to two N atoms belonging to thio­cyanate groups and to four S atoms of bridging thio­urea ligands. The structure consists of infinite chains of slightly distorted edge-shared Cd-centred octahedra. The bridging S atoms of two thio­urea ligands comprise the common edge. Some thermal properties are described.

S1. Comment

From a chemical and structural point of view, cadmium complexes have been extensively studied due to the ability of cadmium to adopt different modes of coordination determined by considerations of size, as well as electrostatic and covalent bonding forces. The presence of the thiocyanate (SCN^-) ion as a ligand introduces some additional degrees of freedom, because of its versatility in acting as a monodentate, bidentate or bridging ligand. Recently, coordination compounds formed by thiourea and cadmium have received renewed attention (Alia et al., 1999). This interest arises for two main reasons: (I) the non-linear optical (NLO) properties of these compounds (Yu et al., 2001) and (ii) the convenient preparation of semiconducting materials through the thermal decomposition of these complexes (Krunks et al., 1997; Semenov & Naumov, 2001). As part of these investigations, the title complex, catena-poly[[bis(thiocyanate-κN)cadmium(II)]-di-µ-thiourea-κ²S:S] (abbreviated as BTCT, hereinafter), has been prepared and its thermal properties have been described.

The Cd^II atom, which is situated at a centre of symmetry, is bound to two thiocyanate N atoms and to four thiourea S atoms. The structure consists of infinite chains of edge-shared Cd-centred slightly distorted octahedra. The bridging S atoms of two thiourea ligands comprise the common edge. The Cd—S distances [2.7217 (5) and 2.7985 (6) Å] are much longer that the sum (2.52 Å) of the single-bond covalent radii (Pauling, 1960), indicating a relatively weak covalent interaction. The Cd—N bond lengths [2.258 (2) Å] are much shorter than the sum of Shannon's ionic radii (2.41 Å; Shannon, 1976), which is probably because the assumed valences of the N and S atoms are not appropriate, for the charges on the SCN^- ions are delocalized. The N—Cd—S and S—Cd—S angles (between adjacent atoms) are in the ranges 84.15 (6)–95.85 (6) and 86.023 (16)–93.977 (16)°, respectively, which are somewhat different from the typical octahedral angles. The thermal decomposition results (under nitrogen flux) indicate that two thiourea molecules are lost initially; the decomposition of Cd(SCN)₂ occurs subsequently, and the final product is CdS crystalline powder.

S2. Experimental

Cd(SCN)₂ was prepared by the reaction of CdX₂ (where X = Cl, NO₃ or CH₃COO) and ASCN (where A = K, Na or NH₄) (molar ratio 1:2) in water. The crystalline powders of Cd(SCN)₂ and thiourea were dissolved in water in stoichiometric proportions at about 313 K. The mixture was left standing at room temperature, from which the colorless crystals of BTCT used for the X-ray structure determination were obtained.

S3. Refinement

All H atoms were refined and N—H distances were in the range 0.81 (4)–0.92 (4) Å.

Computing details

Data collection: XSCANS (Siemens, 1996); cell refinement: XSCANS; data reduction: XSCANS; program(s) used to solve structure: SHELXTL (Bruker, 1997); program(s) used to refine structure: SHELXTL; molecular graphics: SHELXTL.

Figures

Fig. 1. The molecular structure of BTCT showing 50% probability displacement ellipsoids. H atoms have been omitted for clarity.

(BTCT)

Crystal data

[Cd(SCN)2(CH4N2S)2]	Z = 1
Mr = 380.85	F(000) = 186
Triclinic, P1	Dx = 2.099 Mg m^−3
Hall symbol: -p 1	Mo Kα radiation, λ = 0.71073 Å
a = 4.0368 (3) Å	Cell parameters from 37 reflections
b = 7.7237 (4) Å	θ = 5.9–15.5°
c = 10.1355 (5) Å	µ = 2.48 mm^−1
α = 84.607 (4)°	T = 293 K
β = 80.825 (5)°	Prism, colourless
γ = 75.318 (5)°	0.18 × 0.15 × 0.10 mm
V = 301.31 (3) Å^3

Data collection

Bruker P4 diffractometer	1637 reflections with I > 2σ(I)
Radiation source: fine-focus sealed tube	Rint = 0.015
Graphite monochromator	θmax = 30.0°, θmin = 2.0°
θ/2θ scans	h = −1→5
Absorption correction: ψ scan (XSCANS; Siemens, 1996)	k = −10→10
Tmin = 0.640, Tmax = 0.782	l = −14→14
2433 measured reflections	3 standard reflections every 97 reflections
1757 independent reflections	intensity decay: none

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)] = 0.022	Hydrogen site location: inferred from neighbouring sites
wR(F^2) = 0.065	All H-atom parameters refined
S = 1.14	w = 1/[σ^2(Fo^2) + (0.0253P)^2 + 0.1999P] where P = (Fo^2 + 2Fc^2)/3
1757 reflections	(Δ/σ)max < 0.001
86 parameters	Δρmax = 0.60 e Å^−3
0 restraints	Δρmin = −0.66 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
Cd	1.0000	0.0000	0.0000	0.02530 (8)
S2	0.38123 (14)	0.24618 (7)	0.03097 (5)	0.02272 (11)
S1	1.28382 (19)	−0.29833 (11)	0.42963 (7)	0.04088 (17)
N1	0.9855 (6)	−0.0947 (3)	0.2180 (2)	0.0327 (4)
C2	0.2265 (6)	0.3052 (3)	0.1950 (2)	0.0249 (4)
N2	0.3572 (7)	0.2102 (3)	0.2975 (2)	0.0359 (5)
C1	1.1093 (6)	−0.1789 (3)	0.3062 (2)	0.0253 (4)
N3	−0.0306 (7)	0.4492 (3)	0.2142 (3)	0.0398 (6)
H2B	0.276 (10)	0.234 (5)	0.384 (4)	0.040 (9)*
H2A	0.558 (11)	0.122 (5)	0.286 (4)	0.044 (10)*
H3B	−0.095 (11)	0.490 (6)	0.287 (4)	0.052 (11)*
H3A	−0.099 (13)	0.506 (7)	0.145 (5)	0.076 (15)*

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
Cd	0.02309 (12)	0.03219 (13)	0.01756 (11)	−0.00200 (9)	−0.00363 (8)	0.00240 (8)
S2	0.0225 (2)	0.0235 (2)	0.0199 (2)	−0.0010 (2)	−0.00307 (19)	−0.00228 (18)
S1	0.0326 (3)	0.0579 (4)	0.0249 (3)	0.0000 (3)	−0.0078 (2)	0.0103 (3)
N1	0.0388 (11)	0.0361 (10)	0.0213 (9)	−0.0071 (9)	−0.0054 (8)	0.0042 (8)
C2	0.0263 (10)	0.0244 (9)	0.0235 (10)	−0.0055 (8)	−0.0009 (8)	−0.0045 (7)
N2	0.0431 (13)	0.0387 (11)	0.0220 (9)	−0.0013 (10)	−0.0055 (9)	−0.0039 (8)
C1	0.0257 (10)	0.0291 (10)	0.0207 (9)	−0.0069 (8)	−0.0010 (8)	−0.0022 (8)
N3	0.0459 (14)	0.0338 (11)	0.0296 (11)	0.0079 (10)	0.0009 (10)	−0.0097 (9)

Geometric parameters (Å, º)

Cd—N1	2.258 (2)	C2—N2	1.316 (3)
Cd—S2	2.7217 (5)	C2—N3	1.320 (3)
Cd—S2^i	2.7985 (6)	N2—H2B	0.90 (4)
S2—C2	1.740 (2)	N2—H2A	0.92 (4)
S1—C1	1.627 (2)	N3—H3B	0.81 (4)
N1—C1	1.158 (3)	N3—H3A	0.84 (5)
N1—Cd—S2	95.85 (6)	N2—C2—N3	120.4 (2)
N1—Cd—S2^ii	84.15 (6)	N2—C2—S2	121.80 (19)
N1—Cd—S2^i	88.28 (6)	N3—C2—S2	117.77 (19)
S2—Cd—S2^i	86.023 (16)	C2—N2—H2B	124 (2)
N1—Cd—S2^iii	91.72 (6)	C2—N2—H2A	122 (2)
S2—Cd—S2^iii	93.977 (16)	H2B—N2—H2A	114 (3)
C2—S2—Cd	114.67 (8)	N1—C1—S1	179.6 (2)
C2—S2—Cd^iv	101.74 (8)	C2—N3—H3B	122 (3)
Cd—S2—Cd^iv	93.977 (16)	C2—N3—H3A	116 (4)
C1—N1—Cd	152.1 (2)	H3B—N3—H3A	121 (4)

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

Hydrogen-bond geometry (Å, º)

D—H···A	D—H	H···A	D···A	D—H···A
N2—H2A···N1	0.92 (4)	2.15 (4)	3.051 (3)	166 (3)
N2—H2B···S1^v	0.90 (4)	2.94 (4)	3.513 (3)	123 (3)
N3—H3A···S2^vi	0.84 (5)	2.66 (5)	3.471 (3)	165 (5)

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