Poly­[lead(II)-[mu]-4,4-bi­pyridine-N:N'-di-[mu]-bromo]

The title complex, [PbBr₂(bipy)]_n (bipy is 4,4'-bi­pyridine, C₁₀H₈N₂), was obtained by hydro­thermal reaction of Pb(O₂CCH₃), NaBr and bipy. The bipy group acts as a linear bifunctional bridge forming a planar {-[Pb(bipy)]-}_n belt in the direction of the b axis. The remaining lead coordination sites are occupied by Br ions which link Pb centres in adjacent belts through double bridges to form extended two-dimensional layers.

S1. Comment

In recent years, an increasing interest has been given to low-dimensional organic–inorganic hybrid compounds owing to their special magnetic, electronic and optoelectronic properties (Lacroix et al., 1994; Chakravarthy & Guloy, 1997). Studies suggest that complex systems consisting of organic and inorganic components have great potential for the creation of functional materials utilizing the wide variety of properties associated with each component. Lead halide-based (PbX₃, PbX₄ and PbX₅) molecules with ionic-type hybrid compounds have been extensively studied (Conadi et al., 1997; Chakravarthy & Guloy, 1997), because they form a stable exciton with a large binding energy of several hundred meV and exhibit attractive optical properties such as strong and sharp photoluminescence (Papavassiliou & Kontselas, 1995) and electroluminescence (Hattori et al., 1996), and highly efficient non-linear optical effects (Kondo et al., 1998). However, the lead halide adducts Pb(L)X₂ (X = halide and L = ligand) with ligands coordinatively linked to the inorganic backbone have received little attention and structural information on this type of compounds is still rather scarce (Zhu et al., 1999). Herein, the hydrothermal growth and crystal structure of the two-dimensional lead coordination polymer [PbBr₂(bpy)]_n (bpy is 4,4'-bipyridine), (I), is reported. \scheme

Structural analysis of (I) reveals that the Pb centre has a distorted octahedral coordination with four µ₂-Br and two bridging 4,4'-bpy at trans positions. The Pb—Br bond lengths of 2.999 (2) and 3.008 (2) Å are comparable with those in the reported lead bromides (Klapotke et al., 1999), while the Pb—N bond length of 2.659 (14) Å is significantly longer than those in [PbI₂(L)]_n [L is 2,2'-bipyridine; Pb—N = 2.516; L is 1,10-phenanthroline, Pb—N = 2.518 (8); Zhu et al., 1999]. The crystal structure of compound (I) consists of two-dimensional [PbBr₂(bpy)] networks built upon PbBr₄(bpy)₂ building blocks. The two-dimensional layers are formed in the bc plane by connecting metal centres through bridging Br and 4,4'-bpy ligands. The adjacent bpy ligands are parallel to each other at a distance of 3.74 Å. These layers stack on top of each other along the c axis at a distance of c/2 to complete the three dimensional structure. Therefore, the present crystal structure is very similar to those observed for [MCl₂(bpy)]_n (M = Fe, Co; Lawandy et al., 1999) and [HgBr₂(bpy)]_n (Pan et al., 1999).

S2. Experimental

A solution of Pb(O₂CCH₃) (1 mmol), NaBr (2 mmol), bipy (1 mmol) and water (10 ml) was heated at 393 K for 3 d in a 23 ml acid digestion bomb. After cooling to room temperature, triangular prismatic crystals of (I) were isolated.

S3. Refinement

Data collection was curtailed after 93% completion, since the data at the end were very weak. The largest positive and negative features in the final difference synthesis are close to Pb.

Computing details

Data collection: CAD-4 Software (Enraf-Noinus, 1989); cell refinement: CAD-4 Software; data reduction: MolEN (Fair, 1990); program(s) used to solve structure: SHELXS97 (Sheldrick, 1990); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997); software used to prepare material for publication: SHELXL97 (Sheldrick, 1997).

(I)

Crystal data

[PbBr2(C10H8N2)]	F(000) = 468
Mr = 523.19	Dx = 2.715 Mg m^−3
Monoclinic, C2/m	Mo Kα radiation, λ = 0.71073 Å
a = 12.282 (3) Å	Cell parameters from 25 reflections
b = 12.407 (3) Å	θ = 2.3–27.5°
c = 4.2191 (8) Å	µ = 19.40 mm^−1
β = 95.55 (3)°	T = 293 K
V = 639.9 (2) Å^3	Triangular prism, colourless
Z = 2	0.10 × 0.10 × 0.08 mm

Data collection

Enraf-Nonius CAD-4 diffractometer	709 reflections with I > 2σ(I)
Radiation source: fine-focus sealed tube	Rint = 0.000
Graphite monochromator	θmax = 27.5°, θmin = 2.3°
ω scans	h = −15→15
Absorption correction: ψ scan (Fair, 1990)	k = −16→0
Tmin = 0.179, Tmax = 0.212	l = −5→0
721 measured reflections	3 standard reflections every 265 reflections
721 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)] = 0.048	Hydrogen site location: inferred from neighbouring sites
wR(F^2) = 0.128	H-atom parameters constrained
S = 1.11	w = 1/[σ^2(Fo^2) + (0.0797P)^2 + 7.2192P] where P = (Fo^2 + 2Fc^2)/3
721 reflections	(Δ/σ)max < 0.001
39 parameters	Δρmax = 1.56 e Å^−3
0 restraints	Δρmin = −3.85 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
Pb	−0.5000	1.0000	0.5000	0.0364 (3)
Br	−0.67493 (13)	1.0000	0.9492 (4)	0.0541 (5)
C1	−0.4173 (11)	0.7290 (11)	0.396 (5)	0.066 (4)
H1A	−0.3597	0.7664	0.3195	0.079*
C2	−0.4141 (10)	0.6196 (10)	0.397 (4)	0.058 (3)
H2A	−0.3538	0.5845	0.3290	0.070*
C3	−0.5000	0.5590 (12)	0.5000	0.042 (3)
N	−0.5000	0.7857 (11)	0.5000	0.060 (4)

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
Pb	0.0375 (4)	0.0303 (4)	0.0426 (5)	0.000	0.0105 (3)	0.000
Br	0.0389 (8)	0.0713 (12)	0.0536 (9)	0.000	0.0122 (6)	0.000
C1	0.055 (7)	0.035 (6)	0.112 (11)	0.004 (5)	0.031 (7)	0.014 (7)
C2	0.049 (7)	0.041 (6)	0.089 (9)	0.006 (5)	0.030 (6)	0.011 (6)
C3	0.039 (7)	0.033 (8)	0.054 (8)	0.000	0.007 (6)	0.000
N	0.051 (8)	0.033 (7)	0.095 (12)	0.000	0.011 (7)	0.000

Geometric parameters (Å, º)

Pb—N	2.659 (14)	C1—N	1.343 (15)
Pb—N^i	2.659 (14)	C1—C2	1.358 (18)
Pb—Br	2.9992 (18)	C2—C3	1.398 (14)
Pb—Br^i	2.9992 (18)	C3—C2^v	1.398 (14)
Pb—Br^ii	3.008 (2)	C3—C3^vi	1.46 (3)
Pb—Br^iii	3.008 (2)	N—C1^v	1.343 (15)
Br—Pb^iv	3.008 (2)
N—Pb—N^i	180.0	Br—Pb—Br^iii	89.22 (4)
N—Pb—Br	90.0	Br^i—Pb—Br^iii	90.78 (4)
N^i—Pb—Br	90.0	Br^ii—Pb—Br^iii	180.0
N—Pb—Br^i	90.0	Pb—Br—Pb^iv	89.22 (4)
N^i—Pb—Br^i	90.0	N—C1—C2	122.9 (13)
Br—Pb—Br^i	180.0	C1—C2—C3	121.2 (12)
N—Pb—Br^ii	90.0	C2^v—C3—C2	114.8 (14)
N^i—Pb—Br^ii	90.0	C2^v—C3—C3^vi	122.6 (7)
Br—Pb—Br^ii	90.78 (4)	C2—C3—C3^vi	122.6 (7)
Br^i—Pb—Br^ii	89.22 (4)	C1^v—N—C1	116.9 (15)
N—Pb—Br^iii	90.0	C1^v—N—Pb	121.5 (8)
N^i—Pb—Br^iii	90.0	C1—N—Pb	121.5 (8)

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