An unusual chain cadmium(II) ­coordination polymer: catena-poly[[(2,2′-bipyridyl-κ²N,N′)cadmium(II)]-di-μ-chlorido-[(2,2′-bipyridyl-κ²N,N′)cadmium(II)]-di-μ-thiocyanato-κ²N:S;κ²S:N]

The title complex, [CdCl(NCS)(C₁₀H₈N₂)]_n, represents an unusual Cd^II coordination polymer constructed by two types of anionic bridges and 2,2′-bipyridyl (bipy) terminal ligands. These two types of bridges are arranged around inversion centers. The distorted octa­hedral coordination of the Cd^II center is provided by two chloride ions, one N- and one S-donor atom from two thio­cyanate ions, and a pair of N atoms from the chelating bipy ligand. Inter­estingly, adjacent Cd^II ions are inter­connected alternately by paired chloride [Cd...Cd = 3.916 (1) Å] and thio­cyanate bridges [Cd...Cd = 5.936 (1) Å] to generate an infinite one-dimensional coordination chain. Furthermore, weak inter­chain C—H...S inter­actions between the bipy components and thio­cyanate ions lead to the formation of a layered supra­molecular structure.

S1. Comment

Currently, metallosupramolecular crystalline architectures with the incorporation of the 2,2'-bipyridyl (bipy) ligand have attracted considerable research interest for their interesting structural features and physicochemical properties (Kaes et al., 2000; Ye et al., 2005, and references therein; Liu et al., 2006). With regard to the Cd^II species, quite a few coordination arrays with extended structures have been addressed, in which the metal centers are commonly connected by small anionic bridging ligands such as SCN^- (Yang & Ng, 2004), Cl^- (Zhou et al., 2003), CN^- (Kim & Kim, 2000), N₃^- (Abu-Youssef, 2005), SO₄^2- (Harvey et al., 2003), CH₃COO^- (Ye et al., 2000) and C₂O₄^2- (Xia et al., 2004), as well as various polycarboxylate linkers (Ye et al., 2005, and references therein). Within this family, two similar one-dimensional chain complexes with bis-chloride (Zhou et al., 2003) or bis-thiocyanate (Yang & Ng, 2004) bridges constitute a pair of interesting examples. In this context, we preesnt here a relevant Cd^II coordination polymer, [Cd(µ₂-Cl)(µ₂-SCN)(bipy)]_n, (I), which shows an unusual chain array derived from alternate anionic bridges of chloride and thiocyanate ligands. Complex (I) was obtained by using a diffusion method; notably, a concomitant crystalline phase that has been confirmed to be a known mononuclear complex [Cd(SCN)₂(bipy)₂], (II) (Rodesiler et al., 1984), was also afforded.

X-ray structural analysis of (I) reveals a neutral polymeric coordination compound, in which each Cd^II center is surrounded by a pair of N-atom donors from bipy, a pair of chloride anions, and one N and one S donor atoms from two thiocyanate anions (Fig. 1) to constitute a distorted octahedral coordination (Table 1). The two Cd—Cl bond lengths differ significantly [2.750 (1) and 2.552 (1) Å], and the Cd—N_thiocyanate bond distance [2.319 (2) Å] is slightly shorter than the Cd—N_py bonds [2.358 (2) and 2.359 (2) Å]. The Cd^II ion lies 0.176 Å out of the least-square basal plane, N1/N2/Cl1B/S1. The bipy ligand forms a five-membered chelate ring with the Cd^II ion, and the resulting N—Cd—N bite angle is 69.92 (7)°. The N1—C1—C6—N2 torsion angle within the bipy ligand is -2.6 (3)°, and the two conjugated pyridyl rings make a dihedral angle of 8.5 (1)°.

Both the chloride and the thiocyanate anions act as bridging ligands, which connect metal centers to generate a one-dimensional infinite chain along the [010] direction (Fig. 1). Each linear thiocyanate ligand [S—C—N = 178.0 (2)°] adopts a bidentate µ_N,_S linking mode, with a Cd···Cd separation of 5.936 (1) Å, which is significantly longer than the Cd···Cd separation [3.916 (1) Å] bridged by the chloride anion. Notably, polymeric complexes supported by two such anionic bridges are rare; a survey of the Cambridge Structural Database (CSD; Version 5.28; Allen, 2002) revealed only five hits (refcodes EQUHAZ, LOLWOY, LEMPIC, VEJREH and ZASLOU). The most fascinating structural feature of complex (I) is that the adjacent Cd^II ions in each chain are combined alternately by paired chloride and thiocyanate ligands, and so far only one such structural example has been observed in an inorganic [Hg(µ₂-Cl)(µ₂-SCN)(SCN)]^- chain (CSD refcode ZASLOU).

Further analysis of the crystal packing of (I) reveals the existence of a weak C5—H5···S1 interaction between the pyridyl and thiocyanate ligands (Table 2). Such interchain contacts extend the one-dimensional coordination arrays to result in a hydrogen-bonded supramolecular layer along the (100) plane (Fig. 2). Moreover, these layers are stacked in a parallel fashion along [100] without significant interlayer interactions.

Related literature

For related literature, see: Abu-Youssef (2005); Harvey et al. (2003); Kaes et al. (2000); Kim & Kim (2000); Liu et al. (2006); Rodesiler et al. (1984); Xia et al. (2004); Yang & Ng (2004); Ye et al. (2000, 2005); Zhou et al. (2003).

S2. Experimental

A methanol solution (5 ml) of 2,2'-bipyridyl (16 mg, 0.1 mmol) was carefully layered onto a buffer of methanol (2 ml), below which an aqueous solution (5 ml) containing a mixture of cadmium(II) dichloride hemipentahydrate (24 mg, 0.1 mmol) and ammonium thiocyanate (16 mg, 0.2 mmol) was placed in a straight glass tube. Colorless block-shaped crystals of (I) and colorless prismatic crystals of (II) were obtained simultaneously on the tube wall after several days, and were separated manually under a microscope [yield 45–50% for (I) and 10–15% for (II)]. IR (KBr pellet, cm^-1) for (I): 2104 (vs), 1592 (w), 1471 (w), 1433 (m), 1310 (w), 1244 (w), 1155 (s), 1058 (w), 1013 (m), 764 (m), 733 (w), 647 (w).

S3. Refinement

There was no evidence of crystal decay during data collection. All H atoms were placed at the calculated positions, with C—H distance of 0.93 Å, and treated as riding. The U_iso(H) values were set to 1.2U_eq with regard to their parent carbon atoms.

Computing details

Data collection: APEX2 (Bruker, 2003); cell refinement: SAINT (Bruker, 2001); data reduction: SAINT (Bruker, 2001); program(s) used to solve structure: SHELXS97 (Sheldrick, 1997); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997); molecular graphics: ORTEPIII (Burnett & Johnson, 1996), ORTEP-3 (Farrugia, 1997) and Diamond (Brandenburg, 2005); software used to prepare material for publication: SHELXTL (Bruker, 2001).

Figures

	Fig. 1. Part of the polymeric chain of (I), with the atom-labelling scheme. Displacement ellipsoids are drawn at the 30% probability level. H atoms have been omitted for clarity. [Symmetry codes: (i) -x, -y + 2, -z; (ii) -x, -y + 1, -z.]
	Fig. 2. A perspective view of (I), showing the interchain C—H···S weak interactions. All irrelevant H atoms have been omitted for clarity.

catena-poly[[(2,2-bipyridyl-κ²N,N')cadmium(II)]-di- µ-chlorido-cadmium(II)-di-µ-thiocyanato-κ²N:S;κ²S:N]

Crystal data

[CdCl(NCS)(C10H8N2)]	Z = 2
Mr = 362.11	F(000) = 352
Triclinic, P1	Dx = 1.962 Mg m^−3
Hall symbol: -P 1	Mo Kα radiation, λ = 0.71073 Å
a = 8.0149 (7) Å	Cell parameters from 2556 reflections
b = 9.2527 (8) Å	θ = 2.4–27.8°
c = 9.5534 (8) Å	µ = 2.15 mm^−1
α = 103.031 (1)°	T = 294 K
β = 106.938 (1)°	Block, colorless
γ = 106.303 (1)°	0.32 × 0.26 × 0.20 mm
V = 612.98 (9) Å^3

Data collection

Bruker APEXII CCD area-detector diffractometer	2126 independent reflections
Radiation source: fine-focus sealed tube	2000 reflections with I > 2σ(I)
Graphite monochromator	Rint = 0.016
ϕ and ω scans	θmax = 25.0°, θmin = 2.4°
Absorption correction: multi-scan (SADABS; Sheldrick, 1996)	h = −9→6
Tmin = 0.523, Tmax = 0.724	k = −10→10
3325 measured reflections	l = −9→11

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)] = 0.018	Hydrogen site location: inferred from neighbouring sites
wR(F^2) = 0.045	H-atom parameters constrained
S = 1.04	w = 1/[σ^2(Fo^2) + (0.0233P)^2 + 0.1701P] where P = (Fo^2 + 2Fc^2)/3
2126 reflections	(Δ/σ)max < 0.001
154 parameters	Δρmax = 0.21 e Å^−3
0 restraints	Δρmin = −0.50 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
Cd1	−0.01334 (2)	0.708160 (18)	0.083907 (17)	0.03188 (7)
Cl1	0.21650 (8)	0.54146 (7)	0.15382 (6)	0.03779 (14)
S1	0.24401 (10)	0.85341 (8)	−0.01728 (8)	0.04239 (16)
N1	0.1456 (3)	0.8904 (2)	0.3396 (2)	0.0339 (4)
N2	−0.1540 (3)	0.6170 (2)	0.2488 (2)	0.0338 (4)
N3	0.1891 (3)	1.1390 (3)	−0.0190 (3)	0.0433 (5)
C1	0.1040 (3)	0.8435 (3)	0.4520 (3)	0.0313 (5)
C2	0.2818 (4)	1.0323 (3)	0.3798 (3)	0.0432 (6)
H2	0.3098	1.0653	0.3015	0.052*
C3	0.3825 (4)	1.1320 (3)	0.5309 (3)	0.0465 (6)
H3	0.4745	1.2309	0.5541	0.056*
C4	0.3443 (4)	1.0821 (3)	0.6458 (3)	0.0483 (7)
H4	0.4121	1.1456	0.7494	0.058*
C5	0.2046 (4)	0.9373 (3)	0.6070 (3)	0.0463 (6)
H5	0.1773	0.9019	0.6843	0.056*
C6	−0.0585 (3)	0.6910 (3)	0.4026 (3)	0.0329 (5)
C7	−0.3088 (4)	0.4864 (3)	0.2000 (3)	0.0432 (6)
H7	−0.3752	0.4357	0.0937	0.052*
C8	−0.3741 (4)	0.4236 (3)	0.2989 (4)	0.0539 (7)
H8	−0.4840	0.3336	0.2606	0.065*
C9	−0.2746 (4)	0.4957 (4)	0.4556 (4)	0.0543 (7)
H9	−0.3144	0.4539	0.5253	0.065*
C10	−0.1153 (4)	0.6307 (3)	0.5087 (3)	0.0452 (6)
H10	−0.0462	0.6812	0.6147	0.054*
C11	0.2091 (3)	1.0209 (3)	−0.0175 (3)	0.0329 (5)

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
Cd1	0.04384 (12)	0.02413 (10)	0.02389 (10)	0.00995 (8)	0.01088 (7)	0.00719 (7)
Cl1	0.0433 (3)	0.0287 (3)	0.0284 (3)	0.0124 (2)	0.0012 (2)	0.0036 (2)
S1	0.0589 (4)	0.0367 (3)	0.0496 (4)	0.0252 (3)	0.0312 (3)	0.0234 (3)
N1	0.0422 (11)	0.0292 (10)	0.0276 (10)	0.0103 (9)	0.0130 (8)	0.0088 (8)
N2	0.0384 (11)	0.0295 (10)	0.0311 (10)	0.0118 (9)	0.0116 (8)	0.0090 (8)
N3	0.0524 (13)	0.0357 (12)	0.0463 (13)	0.0191 (10)	0.0187 (10)	0.0185 (10)
C1	0.0363 (12)	0.0342 (12)	0.0279 (11)	0.0178 (10)	0.0130 (9)	0.0114 (10)
C2	0.0523 (15)	0.0326 (13)	0.0360 (13)	0.0055 (12)	0.0167 (11)	0.0087 (11)
C3	0.0465 (15)	0.0339 (14)	0.0427 (15)	0.0052 (11)	0.0113 (12)	0.0027 (12)
C4	0.0485 (15)	0.0468 (16)	0.0294 (13)	0.0122 (13)	0.0033 (11)	−0.0014 (12)
C5	0.0567 (16)	0.0518 (16)	0.0265 (12)	0.0165 (13)	0.0145 (11)	0.0124 (12)
C6	0.0395 (12)	0.0356 (13)	0.0313 (12)	0.0190 (10)	0.0162 (10)	0.0149 (10)
C7	0.0435 (14)	0.0361 (14)	0.0429 (14)	0.0101 (11)	0.0133 (11)	0.0103 (12)
C8	0.0477 (15)	0.0465 (16)	0.066 (2)	0.0068 (13)	0.0253 (14)	0.0239 (15)
C9	0.0583 (17)	0.0597 (18)	0.0569 (18)	0.0172 (15)	0.0321 (15)	0.0336 (15)
C10	0.0506 (15)	0.0525 (16)	0.0388 (14)	0.0196 (13)	0.0201 (12)	0.0222 (12)
C11	0.0383 (12)	0.0336 (13)	0.0263 (11)	0.0105 (10)	0.0121 (9)	0.0128 (10)

Geometric parameters (Å, º)

Cd1—N3^i	2.319 (2)	C2—C3	1.374 (4)
Cd1—N1	2.3576 (19)	C2—H2	0.9300
Cd1—N2	2.3592 (19)	C3—C4	1.363 (4)
Cd1—Cl1^ii	2.5519 (6)	C3—H3	0.9300
Cd1—S1	2.6807 (7)	C4—C5	1.370 (4)
Cd1—Cl1	2.7498 (6)	C4—H4	0.9300
S1—C11	1.651 (2)	C5—H5	0.9300
N1—C2	1.337 (3)	C6—C10	1.388 (3)
N1—C1	1.338 (3)	C7—C8	1.368 (4)
N2—C7	1.336 (3)	C7—H7	0.9300
N2—C6	1.345 (3)	C8—C9	1.370 (4)
N3—C11	1.150 (3)	C8—H8	0.9300
N3—Cd1^i	2.319 (2)	C9—C10	1.375 (4)
C1—C5	1.388 (3)	C9—H9	0.9300
C1—C6	1.490 (3)	C10—H10	0.9300
N3^i—Cd1—N1	90.77 (7)	N1—C2—H2	118.3
N3^i—Cd1—N2	96.76 (7)	C3—C2—H2	118.3
N1—Cd1—N2	69.92 (7)	C4—C3—C2	118.3 (2)
N3^i—Cd1—Cl1^ii	96.36 (6)	C4—C3—H3	120.8
N1—Cd1—Cl1^ii	164.01 (5)	C2—C3—H3	120.8
N2—Cd1—Cl1^ii	94.97 (5)	C3—C4—C5	119.2 (2)
N3^i—Cd1—S1	92.03 (6)	C3—C4—H4	120.4
N1—Cd1—S1	93.69 (5)	C5—C4—H4	120.4
N2—Cd1—S1	161.41 (5)	C4—C5—C1	120.0 (2)
Cl1^ii—Cd1—S1	100.31 (2)	C4—C5—H5	120.0
N3^i—Cd1—Cl1	175.34 (6)	C1—C5—H5	120.0
N1—Cd1—Cl1	89.18 (5)	N2—C6—C10	121.0 (2)
N2—Cd1—Cl1	87.60 (5)	N2—C6—C1	116.7 (2)
Cl1^ii—Cd1—Cl1	84.858 (19)	C10—C6—C1	122.2 (2)
S1—Cd1—Cl1	83.32 (2)	N2—C7—C8	123.1 (3)
Cd1^ii—Cl1—Cd1	95.142 (19)	N2—C7—H7	118.4
C11—S1—Cd1	102.74 (9)	C8—C7—H7	118.4
C2—N1—C1	118.4 (2)	C7—C8—C9	118.7 (3)
C2—N1—Cd1	124.12 (16)	C7—C8—H8	120.7
C1—N1—Cd1	117.34 (15)	C9—C8—H8	120.7
C7—N2—C6	118.5 (2)	C8—C9—C10	119.2 (3)
C7—N2—Cd1	124.02 (17)	C8—C9—H9	120.4
C6—N2—Cd1	116.96 (15)	C10—C9—H9	120.4
C11—N3—Cd1^i	154.0 (2)	C9—C10—C6	119.4 (3)
N1—C1—C5	120.7 (2)	C9—C10—H10	120.3
N1—C1—C6	117.1 (2)	C6—C10—H10	120.3
C5—C1—C6	122.2 (2)	N3—C11—S1	178.0 (2)
N1—C2—C3	123.3 (3)
N1—Cd1—Cl1—Cd1^ii	165.14 (5)	Cl1—Cd1—N2—C6	77.48 (16)
N2—Cd1—Cl1—Cd1^ii	95.21 (5)	C2—N1—C1—C5	−2.3 (3)
Cl1^ii—Cd1—Cl1—Cd1^ii	0.0	Cd1—N1—C1—C5	173.52 (18)
S1—Cd1—Cl1—Cd1^ii	−101.04 (2)	C2—N1—C1—C6	175.2 (2)
N3^i—Cd1—S1—C11	19.90 (10)	Cd1—N1—C1—C6	−8.9 (3)
N1—Cd1—S1—C11	−71.00 (10)	C1—N1—C2—C3	0.6 (4)
N2—Cd1—S1—C11	−98.47 (17)	Cd1—N1—C2—C3	−175.0 (2)
Cl1^ii—Cd1—S1—C11	116.75 (8)	N1—C2—C3—C4	1.4 (4)
Cl1—Cd1—S1—C11	−159.74 (8)	C2—C3—C4—C5	−1.6 (4)
N3^i—Cd1—N1—C2	−76.3 (2)	C3—C4—C5—C1	−0.1 (4)
N2—Cd1—N1—C2	−173.3 (2)	N1—C1—C5—C4	2.1 (4)
Cl1^ii—Cd1—N1—C2	166.96 (16)	C6—C1—C5—C4	−175.3 (2)
S1—Cd1—N1—C2	15.7 (2)	C7—N2—C6—C10	2.0 (3)
Cl1—Cd1—N1—C2	99.0 (2)	Cd1—N2—C6—C10	−170.08 (18)
N3^i—Cd1—N1—C1	108.05 (17)	C7—N2—C6—C1	−175.1 (2)
N2—Cd1—N1—C1	11.13 (15)	Cd1—N2—C6—C1	12.8 (3)
Cl1^ii—Cd1—N1—C1	−8.7 (3)	N1—C1—C6—N2	−2.6 (3)
S1—Cd1—N1—C1	−159.86 (16)	C5—C1—C6—N2	174.9 (2)
Cl1—Cd1—N1—C1	−76.61 (16)	N1—C1—C6—C10	−179.7 (2)
N3^i—Cd1—N2—C7	87.6 (2)	C5—C1—C6—C10	−2.2 (4)
N1—Cd1—N2—C7	175.9 (2)	C6—N2—C7—C8	−0.4 (4)
Cl1^ii—Cd1—N2—C7	−9.48 (19)	Cd1—N2—C7—C8	171.1 (2)
S1—Cd1—N2—C7	−154.77 (15)	N2—C7—C8—C9	−1.4 (4)
Cl1—Cd1—N2—C7	−94.10 (19)	C7—C8—C9—C10	1.6 (5)
N3^i—Cd1—N2—C6	−100.87 (17)	C8—C9—C10—C6	0.0 (4)
N1—Cd1—N2—C6	−12.53 (16)	N2—C6—C10—C9	−1.8 (4)
Cl1^ii—Cd1—N2—C6	162.10 (16)	C1—C6—C10—C9	175.2 (2)
S1—Cd1—N2—C6	16.8 (3)

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

Hydrogen-bond geometry (Å, º)

D—H···A	D—H	H···A	D···A	D—H···A
C5—H5···S1^iii	0.93	2.90	3.785 (3)	158

Symmetry code: (iii) x, y, z+1.