The chain structure of catena-poly[[(2,2′-bipyridine)cadmium(II)]-di-μ-chloro]

In the title compound, [CdCl₂(C₁₀H₈N₂)]_n, the Cd^II ion is six-coordinate and has a distorted octahedral geometry. The basal plane is formed by the two N atoms of the 2,2′-bi­pyridine ligand [Cd—N 2.352 (3) Å] and two Cl atoms [Cd—Cl 2.5519 (8) Å]. The apical sites are occupied by Cl atoms from neighbouring monomeric units [Cd—Cl 2.7517 (9) Å]. All the Cl atoms act as bridging ligands. The adjacent Cd coordination polyhedra share Cl—Cl edges, thus giving rise to a polymeric chain along the c axis. The Cd^II ion is positioned on a twofold axis.

Key indicators

• Single-crystal X-ray study
• T = 293 K
• Mean [sigma](C-C) = 0.006 Å
• R factor = 0.025
• wR factor = 0.065
• Data-to-parameter ratio = 13.6

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S1. Comment

Polynuclear d¹⁰ metal complexes have been found to exhibit intriguing structural and photoluminescent properties. Chloride-bridged cadmium(II) polymeric complexes are of considerable interest, because they may act as photoactive materials. Structural studies of chloride-bridged Cd^II polymeric complexes are common (Bell et al., 1982; Griffith et al., 1982; Bigoli et al., 1983; Huang et al., 1998). However, Cd^II polymeric complexes with a CdCl₂N₂ coordination polydedron have rarely been reported (Bonomo et al., 1989). We have introduced 2,2'-bipyridine as a terminal ligand which favours crystal growth of the product. Through a hydrothermal reaction, we have successfully synthesized the title crystalline chloride-bridged Cd complex [CdCl₂(bpy)]_n (bpy is 2,2'-bipyridine), (I).

Single crystal X-ray diffraction analysis reveals that compound (I) crystallizes in space group C2/c and consists of one-dimensional chains along the c axis. It is isostructural with an analogous bromide-bridged Cu^II complex (Garland et al., 1988). The Cd^II ion is positioned on the 2₁ axis, so the primarily monomeric unit is generated by symmetry (Fig. 1).

The Cd^II ion in (I) is coordinated by two N atoms from one chelating bpy ligand and by four Cl atoms, to furnish a distorted coordination octahedron, as depicted in Fig. 2. The basal plane is formed by the two cis N atoms from the bpy ligand [Cd—N 2.352 (3) Å] and the two cis Cl atoms [Cd—Cl 2.5519 (8) Å]. The axial positions of the octahedron are occupied by Cl atoms from neighbouring monomeric units [Cd—Cl 2.7517 (9) Å]. Adjacent Cd coordination octahedra share Cl—Cl edges, thus forming a one-dimensional chain along the c axis. All bpy ligands are coordinated in a chelating mode and they lie on alternate sides of the chain. The Cd···Cd distance between neighbouring Cd^II ions in the chain is 3.931 (9) Å, which is shorter than that of the Cu^II isomorph [3.974 (1) Å]. The closest distance between the pyridyl rings of two bpy ligands in neighbouring chains is 3.342 (3) Å, indicating the existence of π–π interactions between the adjacent chains. Thus the chains are connected to each other via π–π interactions to form two-dimensional layers parallel to the bc plane.

The packing of (I) (Fig. 3) is determined by van der Waals interactions and possible hydrogen bonds involving the C atoms of the bpy ligand and Cl atoms of the same [C4—H4A···Clⁱ 3.534 (5) Å] or adjacent [C2—H2A···Clⁱⁱ 3.751 (5) Å] chains [symmetry codes: (i) 1 − x, 1 + y, 3/2 − z; (ii) x − 1/2, 1/2 + y, z − 1].

S2. Experimental

The hydrothermal reaction of cadmium chloride (0.06 g, 0.26 mmol), 2,2'-bipyridine (0.04 g, 0.25 mmol) and water (15.0 ml) was carried out at 433 K for 4 d. After cooling to room temperature at 5 K h⁻¹, the crystalline complex, (I), was isolated in 63% yield (based on Cd). IR (KBr, ν, cm⁻¹): 3417, 1604, 1558, 1439, 1375, 1171, 1016, 771, 735. Elemental analysis, calculated for C₁₀H₈N₂CdCl₂: C 35.38, H 2.38, N 8.25%; found: C 35.16, H 2.17, N 8.23%.

S3. Refinement

All H atoms were located in a difference Fourier map but were introduced in idealized positions (C—H = 0.93 Å) and treated as riding, with displacement parameters fixed at 120% of those of their parent atoms. The maximum residual electron-density peak is 0.84 Å from the Cd atom.

Computing details

Data collection: SMART (Siemens, 1996); cell refinement: SMART; data reduction: SAINT (Siemens, 1994); program(s) used to solve structure: SHELXTL (Siemens, 1994); program(s) used to refine structure: SHELXTL; molecular graphics: XPREP (Bruker, 1997); software used to prepare material for publication: SHELXL97 (Sheldrick 1997).

Figures

	Fig. 1. A view of the molecule of (I), showing the atom-labelling scheme. Displacement ellipsoids are drawn at the 50% probability level and H atoms are represented by circles of arbitrary size.
	Fig. 2. A view of the one-dimensional chain of chloride-bridged Cd^II ions in (I), along the a axis.
	Fig. 3. A packing diagram for (I), viewed down the c axis.

catena-poly[[(2,2'-bipyridine)cadmium(II)]-di-µ-chloro]

Crystal data

[CdCl2(C10H8N2)]	F(000) = 656
Mr = 339.49	Dx = 2.058 Mg m^−3
Monoclinic, C2/c	Mo Kα radiation, λ = 0.71073 Å
Hall symbol: -C 2yc	Cell parameters from 35 reflections
a = 17.5517 (6) Å	θ = 2.5–25.0°
b = 9.3166 (6) Å	µ = 2.44 mm^−1
c = 7.1710 (4) Å	T = 293 K
β = 110.860 (2)°	Prism, colourless
V = 1095.76 (10) Å^3	0.56 × 0.22 × 0.20 mm
Z = 4

Data collection

Siemens SMART CCD area-detector diffractometer	954 independent reflections
Radiation source: fine-focus sealed tube	885 reflections with I > 2σ(I)
Graphite monochromator	Rint = 0.019
ω scans	θmax = 25.0°, θmin = 2.5°
Absorption correction: multi-scan (SADABS; Sheldrick, 1996)	h = −20→10
Tmin = 0.494, Tmax = 0.613	k = −11→6
1693 measured reflections	l = −8→8

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)] = 0.025	H-atom parameters constrained
wR(F^2) = 0.065	w = 1/[σ^2(Fo^2) + (0.0528P)^2 + 0.4415P] where P = (Fo^2 + 2Fc^2)/3
S = 1.12	(Δ/σ)max = 0.001
954 reflections	Δρmax = 0.43 e Å^−3
70 parameters	Δρmin = −0.53 e Å^−3
0 restraints	Extinction correction: SHELXL97 (Sheldrick, 1997), Fc^*=kFc[1+0.001xFc^2λ^3/sin(2θ)]^-1/4
Primary atom site location: structure-invariant direct methods	Extinction coefficient: 0.0037 (4)

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	0.5000	0.58652 (3)	0.7500	0.03294 (18)
Cl	0.59307 (5)	0.41676 (9)	1.01188 (13)	0.0381 (2)
C1	0.3487 (2)	0.7879 (5)	0.4744 (6)	0.0440 (9)
H1A	0.3263	0.6989	0.4264	0.053*
C2	0.3018 (2)	0.9094 (5)	0.4072 (6)	0.0504 (11)
H2A	0.2486	0.9023	0.3172	0.060*
C3	0.3354 (3)	1.0404 (5)	0.4758 (6)	0.0526 (11)
H3A	0.3051	1.1238	0.4319	0.063*
C4	0.4139 (3)	1.0482 (4)	0.6096 (6)	0.0427 (9)
H4A	0.4377	1.1366	0.6560	0.051*
C5	0.4574 (2)	0.9218 (3)	0.6747 (5)	0.0309 (7)
N	0.42536 (16)	0.7934 (3)	0.6064 (4)	0.0335 (6)

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
Cd	0.0349 (3)	0.0249 (2)	0.0302 (2)	0.000	0.00078 (15)	0.000
Cl	0.0374 (5)	0.0361 (5)	0.0362 (5)	0.0098 (3)	0.0073 (4)	0.0075 (3)
C1	0.0324 (18)	0.047 (2)	0.046 (2)	−0.0018 (16)	0.0052 (16)	0.0092 (17)
C2	0.031 (2)	0.068 (3)	0.047 (2)	0.0070 (19)	0.0070 (17)	0.020 (2)
C3	0.056 (3)	0.056 (3)	0.050 (2)	0.024 (2)	0.023 (2)	0.021 (2)
C4	0.055 (2)	0.0303 (18)	0.046 (2)	0.0075 (17)	0.0225 (19)	0.0080 (16)
C5	0.0347 (19)	0.0278 (17)	0.0335 (17)	0.0011 (14)	0.0162 (15)	0.0030 (13)
N	0.0283 (14)	0.0347 (16)	0.0344 (15)	−0.0014 (12)	0.0075 (12)	0.0052 (12)

Geometric parameters (Å, º)

Cd—N^i	2.352 (3)	C1—H1A	0.9300
Cd—N	2.352 (3)	C2—C3	1.368 (7)
Cd—Cl^i	2.5519 (8)	C2—H2A	0.9300
Cd—Cl	2.5519 (8)	C3—C4	1.373 (6)
Cd—Cl^ii	2.7517 (9)	C3—H3A	0.9300
Cd—Cl^iii	2.7517 (9)	C4—C5	1.390 (5)
Cl—Cd^ii	2.7517 (9)	C4—H4A	0.9300
C1—N	1.342 (4)	C5—N	1.338 (4)
C1—C2	1.381 (6)	C5—C5^i	1.502 (7)
N^i—Cd—N	69.93 (14)	N—C1—H1A	118.7
N^i—Cd—Cl^i	160.22 (7)	C2—C1—H1A	118.7
N—Cd—Cl^i	94.29 (7)	C3—C2—C1	118.6 (4)
N^i—Cd—Cl	94.29 (7)	C3—C2—H2A	120.7
N—Cd—Cl	160.22 (7)	C1—C2—H2A	120.7
Cl^i—Cd—Cl	103.40 (4)	C2—C3—C4	119.7 (4)
N^i—Cd—Cl^ii	95.66 (7)	C2—C3—H3A	120.2
N—Cd—Cl^ii	85.39 (7)	C4—C3—H3A	120.2
Cl^i—Cd—Cl^ii	94.81 (3)	C3—C4—C5	118.9 (4)
Cl—Cd—Cl^ii	84.40 (3)	C3—C4—H4A	120.5
N^i—Cd—Cl^iii	85.39 (7)	C5—C4—H4A	120.5
N—Cd—Cl^iii	95.66 (7)	N—C5—C4	121.7 (4)
Cl^i—Cd—Cl^iii	84.40 (3)	N—C5—C5^i	116.37 (19)
Cl—Cd—Cl^iii	94.81 (3)	C4—C5—C5^i	121.9 (2)
Cl^ii—Cd—Cl^iii	178.73 (4)	C5—N—C1	118.5 (3)
Cd—Cl—Cd^ii	95.60 (3)	C5—N—Cd	118.5 (2)
N—C1—C2	122.6 (4)	C1—N—Cd	122.7 (3)
N^i—Cd—Cl—Cd^ii	95.28 (7)	C5^i—C5—N—Cd	5.7 (5)
N—Cd—Cl—Cd^ii	59.2 (2)	C2—C1—N—C5	−0.1 (6)
Cl^i—Cd—Cl—Cd^ii	−93.63 (3)	C2—C1—N—Cd	172.6 (3)
Cl^ii—Cd—Cl—Cd^ii	0.0	N^i—Cd—N—C5	−2.15 (18)
Cl^iii—Cd—Cl—Cd^ii	−179.00 (3)	Cl^i—Cd—N—C5	−169.9 (2)
N—C1—C2—C3	1.0 (6)	Cl—Cd—N—C5	36.5 (4)
C1—C2—C3—C4	−0.5 (6)	Cl^ii—Cd—N—C5	95.6 (2)
C2—C3—C4—C5	−0.9 (6)	Cl^iii—Cd—N—C5	−85.1 (2)
C3—C4—C5—N	1.8 (5)	N^i—Cd—N—C1	−174.9 (4)
C3—C4—C5—C5^i	−178.3 (4)	Cl^i—Cd—N—C1	17.4 (3)
C4—C5—N—C1	−1.3 (5)	Cl—Cd—N—C1	−136.2 (3)
C5^i—C5—N—C1	178.8 (4)	Cl^ii—Cd—N—C1	−77.1 (3)
C4—C5—N—Cd	−174.3 (3)	Cl^iii—Cd—N—C1	102.1 (3)

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

Hydrogen-bond geometry (Å, º)

D—H···A	D—H	H···A	D···A	D—H···A
C2—H2A···Cl^iv	0.93	2.83	3.751 (5)	171
C4—H4A···Cl^v	0.93	2.84	3.534 (5)	132

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