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The title compound, [HgCl2(C10H8N2)]n, features two-dimensional [HgCl2(4,4′-bipy)]n neutral networks (4,4′-bipy is 4,4′-bipyridine), based on an octa­hedral Hg atom coordinated by four μ2-Cl atoms and two μ2-4,4′-bipy ligands in trans positions, yielding a HgCl4N2 octa­hedron. The structure has mmm symmetry about the Hg atoms, with most of the atoms on at least one mirror plane, but the unsubstituted C atoms of the 4,4′-bipy rings are disordered across a mirror plane. Photoluminescent investigations reveal that the title compound displays a strong emission in the green region, which probably originates from a ligand-to-ligand charge-transfer transition.

Supporting information

cif

Crystallographic Information File (CIF) https://doi.org/10.1107/S0108270107016800/ln3048sup1.cif
Contains datablocks global, I

hkl

Structure factor file (CIF format) https://doi.org/10.1107/S0108270107016800/ln3048Isup2.hkl
Contains datablock I

CCDC reference: 628368

Comment top

Being an important class of inorganic–organic hybrid materials, metal halide–bipy systems (bipy is bipyridine) have attracted increasing attention in recent years, not only for their intrinsic aesthetic appeal, but also for their various potential applications. 4,4'-Bipy is a common linear synthon used in supramolecular syntheses. Many structures of metal halide–bipy materials have been reported (Figgis et al., 1983; Hu et al., 2003; Lu et al., 1998). However, group 12 (IIB) metal halide–bipy materials are relatively rare. We describe here the synthesis and characterization of [HgCl2(4,4'-bipy)]n, (I).

X-ray diffraction analysis reveals that the title compound features two-dimensional [HgCl2(4,4'-bipy)]n neutral networks, as shown in Fig. 1. The structure has high symmetry, with most of the atoms (except for atoms C1 and C2) lying on at least one mirror plane. The divalent metal center HgII, which is on an mmm site, has a slightly distorted octahedral coordination with four µ2-Cl atoms and two bridging 4,4'-bipy ligands in trans positions, yielding edge-shared HgCl4N2 octahedra. Each 4,4'-bipy ligand also has crystallographic mmm symmetry about its mid-point. The unsubstituted C atoms of the 4,4'-bipy rings, C1 and C2, sit slightly off a mirror plane and so are disordered about it. Thus the 4,4'-bipy ligand is twisted with an angle between the planes of the rings of 33.69 (19)°. The HgCl4N2 octahedra interconnect to each other via two µ2-Cl atoms, forming a linear inorganic chain running along the [001] direction. These chains are bridged by µ2-4,4'-bipy ligands to form inorganic–organic hybrid two-dimensional layers, which lie parallel to the (010) plane (Fig. 1). The atoms in adjacent layers are offset from one another by one-half of the length of the a axis. In this way, the layers stack in an –ABAB– mode along the b axis to yield the three-dimensional structure (Fig. 2).

It is noteworthy that group 12 (IIB) metal halide–bipy materials are relatively rare and, to our knowledge, only two halide–4,4'-bipy compounds have been reported, viz. HgI2–4,4'-bipy (Niu et al., 2003; Morsali & Zhu, 2006) and ZnI2–4,4'-bipy (Fan & Wu, 2006). Both of these compounds exhibit a one-dimensional structure, in contrast to the two-dimensional structure of the title compound. For HgI2–4,4'-bipy and ZnI2–4,4'-bipy, each 4,4'-bipy ligand bridges two HgI2 or ZnI2 groups to form a one-dimensional zigzag single chain. In both structures, the I atoms are terminally coordinated to the metal centers, while in the title compound the Cl atoms act as bridging atoms. For the title compound, the Hg atom is in an octahedral coordination environment, while in the two diiodide compounds, the metal atoms are in tetrahedral coordination environments.

The solid-state emission spectrum of the title compound was investigated at room temperature (Fig. 3). The fluorescence spectrum shows that the title compound exhibits a broad and strong emission with a maximum wavelength of 492 nm upon photo-excitation at 398 nm, which is red-shifted by 54 nm compared with that of pure 4,4'-bipy (Fig. 3). The emission of (I) can probably be assigned to the ligand-to-ligand charge-transfer transition from the highest occupied molecular orbital of the Cl atom to the lowest occupied molecular orbital of the 4,4'-bipy moiety. Thus, this compound may be a candidate in green-light luminescent materials.

Related literature top

For related literature, see: Fan & Wu (2006); Figgis et al. (1983); Hu et al. (2003); Lu et al. (1998); Morsali & Zhu (2006); Niu et al. (2003).

Experimental top

HgCl2 (0.1 mmol, 27 mg), 4,4'-bipyridine (0.2 mmol, 31 mg), ethanol (1 ml) and distilled water (3 ml) were loaded into a Teflon-lined stainless steel autoclave (25 ml) and kept at 473 K for 3 d. After the mixture had been slowly cooled to room temperature at a rate of 8 K h-1, colorless crystals suitable for X-ray analysis were obtained.

Refinement top

All H atoms were placed geometrically and refined using a riding model, with C—H distances of 0.93 Å and with Uiso(H) values of 1.2Ueq(C).

Computing details top

Data collection: WinAFC (Rigaku Corporation, 2002); cell refinement: WinAFC; data reduction: CrystalStructure (Rigaku Corporation, 2002); program(s) used to solve structure: SHELXTL (Siemens, 1994); program(s) used to refine structure: SHELXTL; molecular graphics: SHELXTL; software used to prepare material for publication: SHELXTL.

Figures top
[Figure 1] Fig. 1. The layered structure of the title compound, showing the atom labels for the asymmetric unit and only one of the possible orientations of the disordered 4,4'-bipy rings. Displacement ellipsoids are drawn at the 30% probability level. H atoms have been omitted for clarity.
[Figure 2] Fig. 2. The packing of (I), showing the stacks of layers. H atoms have been omitted for clarity.
[Figure 3] Fig. 3. Solid-state emission and excitation spectra of (I) (red lines) and pure 4,4'-bipyridine (green lines) at room temperature. Solid lines: emission spectra; dashed lines: excitation spectra.
poly[µ2-4,4'-bipyridyl-di-µ2-chloro-mercury(II)] top
Crystal data top
[HgCl2(C10H8N2)]Dx = 2.602 Mg m3
Mr = 427.67Mo Kα radiation, λ = 0.71073 Å
Orthorhombic, CmmmCell parameters from 24 reflections
a = 11.6289 (17) Åθ = 4.8–61.0°
b = 12.179 (2) ŵ = 14.55 mm1
c = 3.8538 (7) ÅT = 293 K
V = 545.81 (16) Å3Block, colorless
Z = 20.16 × 0.09 × 0.05 mm
F(000) = 392
Data collection top
Rigaku AFC-7R
diffractometer
323 reflections with I > 2σ(I)
Radiation source: rotating-anode generatorRint = 0.021
Graphite monochromatorθmax = 25.4°, θmin = 3.4°
ω–2θ scansh = 414
Absorption correction: ψ scan
(Psi in WinAFC; Rigaku Corporation, 2002)
k = 014
Tmin = 0.571, Tmax = 1.000l = 14
338 measured reflections30 standard reflections every 5 reflections
323 independent reflections intensity decay: none
Refinement top
Refinement on F2Secondary atom site location: difference Fourier map
Least-squares matrix: fullHydrogen site location: inferred from neighbouring sites
R[F2 > 2σ(F2)] = 0.019H-atom parameters constrained
wR(F2) = 0.045 w = 1/[σ2(Fo2) + (0.0286P)2]
where P = (Fo2 + 2Fc2)/3
S = 1.09(Δ/σ)max = 0.001
323 reflectionsΔρmax = 0.90 e Å3
35 parametersΔρmin = 1.11 e Å3
0 restraintsExtinction correction: SHELXTL, Fc*=kFc[1+0.001xFc2λ3/sin(2θ)]-1/4
Primary atom site location: structure-invariant direct methodsExtinction coefficient: 0.0066 (3)
Crystal data top
[HgCl2(C10H8N2)]V = 545.81 (16) Å3
Mr = 427.67Z = 2
Orthorhombic, CmmmMo Kα radiation
a = 11.6289 (17) ŵ = 14.55 mm1
b = 12.179 (2) ÅT = 293 K
c = 3.8538 (7) Å0.16 × 0.09 × 0.05 mm
Data collection top
Rigaku AFC-7R
diffractometer
323 reflections with I > 2σ(I)
Absorption correction: ψ scan
(Psi in WinAFC; Rigaku Corporation, 2002)
Rint = 0.021
Tmin = 0.571, Tmax = 1.00030 standard reflections every 5 reflections
338 measured reflections intensity decay: none
323 independent reflections
Refinement top
R[F2 > 2σ(F2)] = 0.0190 restraints
wR(F2) = 0.045H-atom parameters constrained
S = 1.09Δρmax = 0.90 e Å3
323 reflectionsΔρmin = 1.11 e Å3
35 parameters
Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å2) top
xyzUiso*/UeqOcc. (<1)
Hg10.00000.00000.00000.02671 (7)
Cl10.00000.16166 (10)0.50000.0309 (3)
N10.1961 (3)0.00000.00000.0268 (10)
C10.2552 (4)0.0908 (4)0.0875 (12)0.0359 (18)0.50
H1A0.21510.15390.14920.043*0.50
C20.3741 (4)0.0925 (3)0.0879 (13)0.0334 (19)0.50
H2A0.41280.15660.14800.040*0.50
C30.4359 (4)0.00000.00000.0263 (12)
Atomic displacement parameters (Å2) top
U11U22U33U12U13U23
Hg10.01574 (11)0.02877 (13)0.03562 (15)0.0000.0000.000
Cl10.0344 (6)0.0228 (5)0.0355 (6)0.0000.0000.000
N10.0184 (18)0.0245 (19)0.037 (2)0.0000.0000.000
C10.0251 (18)0.029 (2)0.053 (5)0.0024 (18)0.006 (2)0.007 (2)
C20.0234 (18)0.0234 (19)0.053 (5)0.0026 (17)0.001 (2)0.005 (2)
C30.024 (2)0.026 (2)0.029 (2)0.0000.0000.000
Geometric parameters (Å, º) top
Hg1—N12.280 (4)C1—H1A0.9300
Hg1—Cl12.7549 (9)C2—C31.379 (5)
N1—C11.345 (5)C2—H2A0.9300
C1—C21.383 (6)C3—C3i1.491 (10)
N1ii—Hg1—N1180N1—C1—C2121.6 (4)
Cl1ii—Hg1—Cl1180N1—C1—H1A119.2
Cl1iii—Hg1—Cl191.23 (4)C2—C1—H1A119.2
Cl1iv—Hg1—Cl188.77 (4)C3—C2—C1120.5 (4)
N1—Hg1—Cl190C3—C2—H2A119.7
Hg1v—Cl1—Hg188.77 (4)C1—C2—H2A119.7
C1—N1—C1vi118.5 (5)C2vi—C3—C2117.2 (5)
C1—N1—Hg1120.7 (3)C2—C3—C3i121.4 (2)
N1ii—Hg1—Cl1—Hg1v90.0Cl1—Hg1—N1—C1viii118.7 (2)
N1—Hg1—Cl1—Hg1v90.0Cl1iii—Hg1—N1—C1vi61.3 (2)
Cl1iii—Hg1—Cl1—Hg1v0.0Cl1iv—Hg1—N1—C1vi118.7 (2)
Cl1iv—Hg1—Cl1—Hg1v180.0Cl1ii—Hg1—N1—C1vi27.4 (2)
Cl1iii—Hg1—N1—C1vii152.6 (2)Cl1—Hg1—N1—C1vi152.6 (2)
Cl1iv—Hg1—N1—C1vii27.4 (2)C1vii—N1—C1—C280.9 (4)
Cl1ii—Hg1—N1—C1vii118.7 (2)C1viii—N1—C1—C231.1 (7)
Cl1—Hg1—N1—C1vii61.3 (2)C1vi—N1—C1—C20.2 (3)
Cl1iii—Hg1—N1—C1118.7 (2)Hg1—N1—C1—C2179.8 (3)
Cl1iv—Hg1—N1—C161.3 (2)N1—C1—C2—C30.5 (7)
Cl1ii—Hg1—N1—C1152.6 (2)C1—C2—C3—C2viii29.8 (7)
Cl1—Hg1—N1—C127.4 (2)C1—C2—C3—C2vi0.2 (3)
Cl1iii—Hg1—N1—C1viii27.4 (2)C1—C2—C3—C2vii81.3 (4)
Cl1iv—Hg1—N1—C1viii152.6 (2)C1—C2—C3—C3i179.8 (3)
Cl1ii—Hg1—N1—C1viii61.3 (2)
Symmetry codes: (i) x1, y, z; (ii) x, y, z; (iii) x, y, z+1; (iv) x, y, z1; (v) x, y, z+1; (vi) x, y, z; (vii) x, y, z; (viii) x, y, z.

Experimental details

Crystal data
Chemical formula[HgCl2(C10H8N2)]
Mr427.67
Crystal system, space groupOrthorhombic, Cmmm
Temperature (K)293
a, b, c (Å)11.6289 (17), 12.179 (2), 3.8538 (7)
V3)545.81 (16)
Z2
Radiation typeMo Kα
µ (mm1)14.55
Crystal size (mm)0.16 × 0.09 × 0.05
Data collection
DiffractometerRigaku AFC-7R
diffractometer
Absorption correctionψ scan
(Psi in WinAFC; Rigaku Corporation, 2002)
Tmin, Tmax0.571, 1.000
No. of measured, independent and
observed [I > 2σ(I)] reflections
338, 323, 323
Rint0.021
(sin θ/λ)max1)0.602
Refinement
R[F2 > 2σ(F2)], wR(F2), S 0.019, 0.045, 1.09
No. of reflections323
No. of parameters35
H-atom treatmentH-atom parameters constrained
Δρmax, Δρmin (e Å3)0.90, 1.11

Computer programs: WinAFC (Rigaku Corporation, 2002), WinAFC, CrystalStructure (Rigaku Corporation, 2002), SHELXTL (Siemens, 1994), SHELXTL.

Selected geometric parameters (Å, º) top
Hg1—N12.280 (4)Hg1—Cl12.7549 (9)
N1i—Hg1—N1180Cl1iii—Hg1—Cl188.77 (4)
Cl1i—Hg1—Cl1180N1—Hg1—Cl190
Cl1ii—Hg1—Cl191.23 (4)Hg1iv—Cl1—Hg188.77 (4)
Symmetry codes: (i) x, y, z; (ii) x, y, z+1; (iii) x, y, z1; (iv) x, y, z+1.
 

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