metal-organic compounds\(\def\hfill{\hskip 5em}\def\hfil{\hskip 3em}\def\eqno#1{\hfil {#1}}\)

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catena-Poly[[di­chloridozinc(II)]-μ-1,1′-(butane-1,4-di­yl)di­imidazole-κ2N3:N3′]

aThe State Key Laboratory of Electroanalytical Chemistry, Changchun Institute of Applied Chemistry, Chinese Academy of Sciences, Changchun 130022, People's Republic of China
*Correspondence e-mail: jwxu@ciac.jl.cn

(Received 2 February 2010; accepted 17 May 2010; online 5 June 2010)

The title compound, [ZnCl2(C10H14N4)]n, is a coordination polymer consisting of zigzag chains propagating in [001], in which the metal cation exhibits a distorted tetrahedral ZnCl2N2 coordination. Adjacent chains are linked by inter­molecular C—H⋯Cl hydrogen bonds, forming a three-dimensional supra­molecular network.

Related literature

For general background to metal complexes of N-heterocyclic compounds, see: Hu et al. (2003[Hu, X.-L., Tang, Y.-J., Gantzel, P. & Meyer, K. (2003). J. Am. Chem. Soc. 22, 612-614.]); Ohmori et al. (2005[Ohmori, O., Kawano, M. & Fujita, M. (2005). Angew. Chem. Int. Ed. 44, 1962-1964.]); Chen et al. (2004[Chen, Y.-B., Kang, Y., Qin, Y.-Y., Li, Z.-J., Cheng, J.-K., Hu, R.-F., Wen, Y.-H. & Yao, Y.-G. (2004). Acta Cryst. C60, m168-m169.]); Hu et al. (2005[Hu, S., Chen, J.-C., Tong, M.-L., Wang, B., Yan, Y.-X. & Batten, S. R. (2005). Angew. Chem. Int. Ed. 44, 5471-5475.]). For related structures, see: Li et al. (2006[Li, F.-F., Ma, J.-F., Song, S.-Y., Yang, J., Jia, H. Q. & Hu, N.-H. (2006). Cryst. Growth Des. 6, 209-215.]); Liu et al. (2007[Liu, Y.-Y., Ma, J.-F. & Zhang, L.-P. (2007). Acta Cryst. E63, m2317.]); Jin et al. (2007[Jin, S.-W., Wang, D.-Q. & Chen, W.-Z. (2007). Inorg. Chem. Commun. 10, 685-689.]); Yang et al. (2009[Yang, J., Ma, J.-F., Liu, Y.-Y. & Batten, S. R. (2009). CrystEngComm, 11, 151-159.]); Qi et al. (2008[Qi, Y., Luo, F., Batten, S. R., Che, Y.-X. & Zheng, J.-M. (2008). Cryst. Growth Des. 8, 2806-2813.]).

[Scheme 1]

Experimental

Crystal data
  • [ZnCl2(C10H14N4)]

  • Mr = 326.52

  • Monoclinic, P 21 /c

  • a = 7.8090 (9) Å

  • b = 11.6001 (13) Å

  • c = 15.8047 (18) Å

  • β = 92.908 (2)°

  • V = 1429.8 (3) Å3

  • Z = 4

  • Mo Kα radiation

  • μ = 2.08 mm−1

  • T = 185 K

  • 0.29 × 0.22 × 0.15 mm

Data collection
  • Bruker SMART APEX CCD diffractometer

  • Absorption correction: multi-scan (SADABS; Sheldrick, 1996[Sheldrick, G. M. (1996). SADABS. University of Göttingen, Germany.]) Tmin = 0.585, Tmax = 0.742

  • 7827 measured reflections

  • 2820 independent reflections

  • 2174 reflections with I > 2σ(I)

  • Rint = 0.054

Refinement
  • R[F2 > 2σ(F2)] = 0.051

  • wR(F2) = 0.107

  • S = 1.06

  • 2820 reflections

  • 154 parameters

  • H-atom parameters constrained

  • Δρmax = 0.68 e Å−3

  • Δρmin = −0.36 e Å−3

Table 1
Hydrogen-bond geometry (Å, °)

D—H⋯A D—H H⋯A DA D—H⋯A
C3—H3⋯Cl1i 0.93 2.63 3.538 (2) 166
C5—H5⋯Cl2ii 0.93 2.78 3.599 (5) 147
Symmetry codes: (i) [-x+1, y+{\script{1\over 2}}, -z+{\script{1\over 2}}]; (ii) [x, -y+{\script{3\over 2}}, z+{\script{1\over 2}}].

Data collection: SMART (Bruker, 2007[Bruker (2007). SMART and SAINT. Bruker AXS Inc., Madison, Wisconsin, USA.]); cell refinement: SAINT (Bruker, 2007[Bruker (2007). SMART and SAINT. Bruker AXS Inc., Madison, Wisconsin, USA.]); data reduction: SAINT; program(s) used to solve structure: SHELXS97 (Sheldrick, 2008[Sheldrick, G. M. (2008). Acta Cryst. A64, 112-122.]); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008[Sheldrick, G. M. (2008). Acta Cryst. A64, 112-122.]); molecular graphics: SHELXTL (Sheldrick, 2008[Sheldrick, G. M. (2008). Acta Cryst. A64, 112-122.]) and Mercury (Macrae et al., 2006[Macrae, C. F., Edgington, P. R., McCabe, P., Pidcock, E., Shields, G. P., Taylor, R., Towler, M. & van de Streek, J. (2006). J. Appl. Cryst. 39, 453-457.]); software used to prepare material for publication: SHELXTL.

Supporting information


Comment top

N-heterocyclic compounds have been extensively studied in coordination chemistry research for their excellent bridging ability (Hu et al., 2003; Ohmori et al., 2005; Chen et al., 2004; Hu et al., 2005). The compound 1,1'-(1,4-butanediyl)bis(imidazole) (bbi), as a flexible nitrogenous ligand with a long -CH2CH2CH2CH2- spacer, can link discrete clusters into an extended network and is a good candidate to form highly connected 3D frameworks. A number of metal-bbi coordination polymers have been reported (Li et al., 2006; Liu et al., 2007; Jin et al., 2007; Yang et al., 2009; Qi et al., 2008). Here we present a new polymeric compound, [ZnCl2(bbi)]n, (I), with a zigzag chain structure, synthesized under solvothermal conditions.

In the title compound, (I), the Zn centers are four-coordinated by two N atoms from two bbi ligands [Zn(1)—N(1) = 2.005 (3) Å and Zn(1)—N(3) = 2.013 (3) Å] and two Cl atoms [Zn(1)—Cl(1) = 2.2557 (11) Å and Zn(1)—Cl(2) =2.2321 (12) Å], resulting in a distorted tetrahedral geometry (Fig. 1). Each bbi coordinates to two Zn atoms through its two aromatic N atoms and acts as a bridging bidentate ligand to form a one-dimensional zigzag chain (Fig. 2). The adjacent Zn···Zn distance is 14.290 Å, which is similar to that observed in [Cu2(bbi)2Cl2] (Qi et al., 2008). In addition, these one-dimensional chains are further connected by weak intermolecular C—H···Cl hydrogen bonds to construct a three-dimensional supramolecular network (Fig. 2).

Related literature top

For general background to metal complexes of N-heterocyclic compounds, see: Hu et al. (2003); Ohmori et al. (2005); Chen et al. (2004); Hu et al. (2005). For related structures, see: Li et al. (2006); Liu et al. (2007); Jin et al. (2007); Yang et al. (2009); Qi et al. (2008).

Experimental top

The title compound was solvothermally prepared from a reaction mixture of ZnCl2 (0.3 mmol), bbi (0.1 mmol), ethanol (3 ml) and distilled water (7 ml); the pH value was adjusted to 4.5 with triethylamine and acetic acid. The mixture was stirred for 20 min at room temperature, then sealed in a 20 ml teflon-lined stainless steel autoclave and heated at 433 K for 72 h under autogenous pressure. After cooling to room temperature, colorless block crystals were obtained (yield 83% based on Zn).

Refinement top

H atoms were positioned geometrically and refined with fixed individual displacement parameters [Uiso(H) = 1.2Ueq(C)], using a riding model, with C—H distances of 0.93 Å for Csp2 and 0.97 Å for CH2.

Computing details top

Data collection: SMART (Bruker, 2007); cell refinement: SAINT (Bruker, 2007); data reduction: SAINT (Bruker, 2007); program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: SHELXTL (Sheldrick, 2008) and Mercury (Macrae et al., 2006); software used to prepare material for publication: SHELXTL (Sheldrick, 2008).

Figures top
[Figure 1] Fig. 1. Partial molecular structure of the title compound showing the atom numbering scheme. Displacement ellipsoids are drawn at the 30% probability level. Atoms marked with i or ii are at the symmetry positions (x+2, y+5/2, 3/2-z) and (x, y+5/2, 1/2-z) respectively.
[Figure 2] Fig. 2. The zigzag polymeric chain structure of the title compound. Dashed lines denote hydrogen bonds.
catena-Poly[[dichloridozinc(II)]-µ-1,1'-(butane-1,4-diyl)diimidazole- κ2N3:N3'] top
Crystal data top
[ZnCl2(C10H14N4)]F(000) = 664
Mr = 326.52Dx = 1.517 Mg m3
Monoclinic, P21/cMo Kα radiation, λ = 0.71073 Å
Hall symbol: -P 2ybcCell parameters from 2763 reflections
a = 7.8090 (9) Åθ = 2.2–26.1°
b = 11.6001 (13) ŵ = 2.08 mm1
c = 15.8047 (18) ÅT = 185 K
β = 92.908 (2)°Block, colorless
V = 1429.8 (3) Å30.29 × 0.22 × 0.15 mm
Z = 4
Data collection top
Bruker SMART APEX CCD
diffractometer
2820 independent reflections
Radiation source: fine-focus sealed tube2174 reflections with I > 2σ(I)
Graphite monochromatorRint = 0.054
ϕ and ω scansθmax = 26.1°, θmin = 2.2°
Absorption correction: multi-scan
(SADABS; Sheldrick, 1996)
h = 99
Tmin = 0.585, Tmax = 0.742k = 1114
7827 measured reflectionsl = 1919
Refinement top
Refinement on F2Primary atom site location: structure-invariant direct methods
Least-squares matrix: fullSecondary atom site location: difference Fourier map
R[F2 > 2σ(F2)] = 0.051Hydrogen site location: inferred from neighbouring sites
wR(F2) = 0.107H-atom parameters constrained
S = 1.06 w = 1/[σ2(Fo2) + (0.0437P)2 + 0.2952P]
where P = (Fo2 + 2Fc2)/3
2820 reflections(Δ/σ)max < 0.001
154 parametersΔρmax = 0.68 e Å3
0 restraintsΔρmin = 0.36 e Å3
Crystal data top
[ZnCl2(C10H14N4)]V = 1429.8 (3) Å3
Mr = 326.52Z = 4
Monoclinic, P21/cMo Kα radiation
a = 7.8090 (9) ŵ = 2.08 mm1
b = 11.6001 (13) ÅT = 185 K
c = 15.8047 (18) Å0.29 × 0.22 × 0.15 mm
β = 92.908 (2)°
Data collection top
Bruker SMART APEX CCD
diffractometer
2820 independent reflections
Absorption correction: multi-scan
(SADABS; Sheldrick, 1996)
2174 reflections with I > 2σ(I)
Tmin = 0.585, Tmax = 0.742Rint = 0.054
7827 measured reflections
Refinement top
R[F2 > 2σ(F2)] = 0.0510 restraints
wR(F2) = 0.107H-atom parameters constrained
S = 1.06Δρmax = 0.68 e Å3
2820 reflectionsΔρmin = 0.36 e Å3
154 parameters
Special details top

Geometry. All esds (except the esd in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell esds are taken into account individually in the estimation of esds in distances, angles and torsion angles; correlations between esds in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell esds is used for estimating esds 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 (Å2) top
xyzUiso*/Ueq
Zn10.46384 (6)0.61215 (4)0.27801 (3)0.02355 (16)
Cl10.33311 (13)0.46729 (9)0.34476 (7)0.0299 (3)
Cl20.67102 (14)0.55460 (11)0.19540 (7)0.0370 (3)
N20.1432 (4)0.8426 (3)0.1480 (2)0.0244 (8)
N10.2770 (4)0.6993 (3)0.2141 (2)0.0249 (8)
N30.5563 (4)0.7158 (3)0.3717 (2)0.0289 (9)
N40.6711 (5)0.8617 (3)0.4421 (2)0.0341 (10)
C10.1030 (5)0.6818 (4)0.2160 (3)0.0319 (11)
H10.05090.61950.24130.038*
C20.0202 (6)0.7689 (4)0.1755 (3)0.0342 (11)
H20.09800.77760.16760.041*
C30.2941 (5)0.7974 (4)0.1726 (3)0.0283 (10)
H30.39920.83070.16200.034*
C60.5363 (6)0.6995 (4)0.4562 (3)0.0384 (12)
H60.48150.63680.47960.046*
C50.6077 (6)0.7875 (4)0.5003 (3)0.0423 (13)
H50.61310.79650.55890.051*
C40.6379 (6)0.8141 (4)0.3661 (3)0.0359 (11)
H40.66880.84680.31530.043*
C70.1145 (6)0.9520 (4)0.1043 (3)0.0302 (11)
H7A0.22430.98900.09740.036*
H7B0.04781.00180.13930.036*
C80.0227 (5)0.9402 (4)0.0186 (3)0.0261 (10)
H8A0.08140.89570.02380.031*
H8B0.09520.89930.01940.031*
C90.7655 (6)0.9682 (4)0.4623 (3)0.0438 (13)
H9A0.71321.00700.50890.053*
H9B0.75741.01920.41360.053*
C100.9514 (6)0.9456 (4)0.4862 (3)0.0423 (13)
H10A1.00550.91210.43800.051*
H10B0.95910.88990.53200.051*
Atomic displacement parameters (Å2) top
U11U22U33U12U13U23
Zn10.0249 (3)0.0224 (3)0.0230 (3)0.0008 (2)0.00252 (19)0.0021 (2)
Cl10.0288 (6)0.0250 (6)0.0366 (6)0.0026 (5)0.0069 (5)0.0052 (5)
Cl20.0349 (6)0.0457 (8)0.0311 (6)0.0052 (6)0.0072 (5)0.0077 (5)
N20.0253 (19)0.024 (2)0.0237 (18)0.0029 (16)0.0019 (15)0.0046 (15)
N10.0265 (19)0.023 (2)0.0247 (19)0.0014 (16)0.0006 (15)0.0043 (16)
N30.031 (2)0.028 (2)0.027 (2)0.0034 (17)0.0035 (16)0.0027 (16)
N40.039 (2)0.031 (2)0.031 (2)0.0085 (18)0.0086 (18)0.0007 (17)
C10.028 (2)0.034 (3)0.034 (3)0.001 (2)0.002 (2)0.015 (2)
C20.022 (2)0.038 (3)0.043 (3)0.002 (2)0.003 (2)0.012 (2)
C30.026 (2)0.031 (3)0.028 (2)0.003 (2)0.0038 (18)0.004 (2)
C60.048 (3)0.040 (3)0.028 (3)0.018 (3)0.000 (2)0.001 (2)
C50.054 (3)0.048 (3)0.024 (2)0.011 (3)0.001 (2)0.001 (2)
C40.045 (3)0.035 (3)0.027 (2)0.007 (2)0.006 (2)0.005 (2)
C70.036 (3)0.022 (3)0.032 (3)0.001 (2)0.002 (2)0.005 (2)
C80.024 (2)0.030 (3)0.025 (2)0.005 (2)0.0043 (18)0.0050 (19)
C90.057 (3)0.037 (3)0.037 (3)0.018 (3)0.007 (2)0.003 (2)
C100.052 (3)0.034 (3)0.039 (3)0.017 (3)0.008 (2)0.002 (2)
Geometric parameters (Å, º) top
Zn1—N12.005 (3)C3—H30.9300
Zn1—N32.013 (3)C6—C51.342 (7)
Zn1—Cl22.2321 (12)C6—H60.9300
Zn1—Cl12.2557 (11)C5—H50.9300
N2—C31.330 (5)C4—H40.9300
N2—C21.373 (5)C7—C81.506 (6)
N2—C71.457 (5)C7—H7A0.9700
N1—C31.323 (5)C7—H7B0.9700
N1—C11.375 (5)C8—C8i1.540 (8)
N3—C41.312 (6)C8—H8A0.9700
N3—C61.364 (5)C8—H8B0.9700
N4—C41.336 (5)C9—C101.504 (6)
N4—C51.369 (6)C9—H9A0.9700
N4—C91.466 (6)C9—H9B0.9700
C1—C21.344 (6)C10—C10ii1.524 (9)
C1—H10.9300C10—H10A0.9700
C2—H20.9300C10—H10B0.9700
N1—Zn1—N3107.13 (14)C6—C5—N4106.5 (4)
N1—Zn1—Cl2112.74 (10)C6—C5—H5126.8
N3—Zn1—Cl2111.43 (11)N4—C5—H5126.8
N1—Zn1—Cl1106.02 (10)N3—C4—N4111.7 (4)
N3—Zn1—Cl1104.75 (11)N3—C4—H4124.1
Cl2—Zn1—Cl1114.17 (5)N4—C4—H4124.1
C3—N2—C2106.6 (4)N2—C7—C8113.7 (4)
C3—N2—C7126.6 (4)N2—C7—H7A108.8
C2—N2—C7126.8 (4)C8—C7—H7A108.8
C3—N1—C1105.2 (4)N2—C7—H7B108.8
C3—N1—Zn1126.4 (3)C8—C7—H7B108.8
C1—N1—Zn1127.5 (3)H7A—C7—H7B107.7
C4—N3—C6105.5 (4)C7—C8—C8i110.6 (5)
C4—N3—Zn1128.8 (3)C7—C8—H8A109.5
C6—N3—Zn1125.6 (3)C8i—C8—H8A109.5
C4—N4—C5106.5 (4)C7—C8—H8B109.5
C4—N4—C9128.0 (4)C8i—C8—H8B109.5
C5—N4—C9125.3 (4)H8A—C8—H8B108.1
C2—C1—N1109.3 (4)N4—C9—C10112.1 (4)
C2—C1—H1125.3N4—C9—H9A109.2
N1—C1—H1125.3C10—C9—H9A109.2
C1—C2—N2106.9 (4)N4—C9—H9B109.2
C1—C2—H2126.5C10—C9—H9B109.2
N2—C2—H2126.5H9A—C9—H9B107.9
N1—C3—N2112.0 (4)C9—C10—C10ii112.8 (5)
N1—C3—H3124.0C9—C10—H10A109.0
N2—C3—H3124.0C10ii—C10—H10A109.0
C5—C6—N3109.7 (4)C9—C10—H10B109.0
C5—C6—H6125.1C10ii—C10—H10B109.0
N3—C6—H6125.1H10A—C10—H10B107.8
Symmetry codes: (i) x, y+2, z; (ii) x+2, y+2, z+1.
Hydrogen-bond geometry (Å, º) top
D—H···AD—HH···AD···AD—H···A
C3—H3···Cl1iii0.932.633.538 (2)166
C5—H5···Cl2iv0.932.783.599 (5)147
Symmetry codes: (iii) x+1, y+1/2, z+1/2; (iv) x, y+3/2, z+1/2.

Experimental details

Crystal data
Chemical formula[ZnCl2(C10H14N4)]
Mr326.52
Crystal system, space groupMonoclinic, P21/c
Temperature (K)185
a, b, c (Å)7.8090 (9), 11.6001 (13), 15.8047 (18)
β (°) 92.908 (2)
V3)1429.8 (3)
Z4
Radiation typeMo Kα
µ (mm1)2.08
Crystal size (mm)0.29 × 0.22 × 0.15
Data collection
DiffractometerBruker SMART APEX CCD
diffractometer
Absorption correctionMulti-scan
(SADABS; Sheldrick, 1996)
Tmin, Tmax0.585, 0.742
No. of measured, independent and
observed [I > 2σ(I)] reflections
7827, 2820, 2174
Rint0.054
(sin θ/λ)max1)0.618
Refinement
R[F2 > 2σ(F2)], wR(F2), S 0.051, 0.107, 1.06
No. of reflections2820
No. of parameters154
H-atom treatmentH-atom parameters constrained
Δρmax, Δρmin (e Å3)0.68, 0.36

Computer programs: SMART (Bruker, 2007), SAINT (Bruker, 2007), SHELXS97 (Sheldrick, 2008), SHELXL97 (Sheldrick, 2008), SHELXTL (Sheldrick, 2008) and Mercury (Macrae et al., 2006), SHELXTL (Sheldrick, 2008).

Hydrogen-bond geometry (Å, º) top
D—H···AD—HH···AD···AD—H···A
C3—H3···Cl1i0.932.633.538 (2)166
C5—H5···Cl2ii0.932.783.599 (5)147
Symmetry codes: (i) x+1, y+1/2, z+1/2; (ii) x, y+3/2, z+1/2.
 

Acknowledgements

The authors thank Changchun Institute of Applied Chemistry for supporting this work.

References

First citationBruker (2007). SMART and SAINT. Bruker AXS Inc., Madison, Wisconsin, USA.
First citationChen, Y.-B., Kang, Y., Qin, Y.-Y., Li, Z.-J., Cheng, J.-K., Hu, R.-F., Wen, Y.-H. & Yao, Y.-G. (2004). Acta Cryst. C60, m168–m169.  Web of Science CSD CrossRef CAS IUCr Journals
First citationHu, S., Chen, J.-C., Tong, M.-L., Wang, B., Yan, Y.-X. & Batten, S. R. (2005). Angew. Chem. Int. Ed. 44, 5471–5475.  Web of Science CSD CrossRef CAS
First citationHu, X.-L., Tang, Y.-J., Gantzel, P. & Meyer, K. (2003). J. Am. Chem. Soc. 22, 612–614.  CAS
First citationJin, S.-W., Wang, D.-Q. & Chen, W.-Z. (2007). Inorg. Chem. Commun. 10, 685–689.  Web of Science CSD CrossRef CAS
First citationLi, F.-F., Ma, J.-F., Song, S.-Y., Yang, J., Jia, H. Q. & Hu, N.-H. (2006). Cryst. Growth Des. 6, 209–215.  Web of Science CSD CrossRef CAS
First citationLiu, Y.-Y., Ma, J.-F. & Zhang, L.-P. (2007). Acta Cryst. E63, m2317.  Web of Science CSD CrossRef IUCr Journals
First citationMacrae, C. F., Edgington, P. R., McCabe, P., Pidcock, E., Shields, G. P., Taylor, R., Towler, M. & van de Streek, J. (2006). J. Appl. Cryst. 39, 453–457.  Web of Science CrossRef CAS IUCr Journals
First citationOhmori, O., Kawano, M. & Fujita, M. (2005). Angew. Chem. Int. Ed. 44, 1962–1964.  Web of Science CSD CrossRef CAS
First citationQi, Y., Luo, F., Batten, S. R., Che, Y.-X. & Zheng, J.-M. (2008). Cryst. Growth Des. 8, 2806–2813.  Web of Science CSD CrossRef CAS
First citationSheldrick, G. M. (1996). SADABS. University of Göttingen, Germany.
First citationSheldrick, G. M. (2008). Acta Cryst. A64, 112–122.  Web of Science CrossRef CAS IUCr Journals
First citationYang, J., Ma, J.-F., Liu, Y.-Y. & Batten, S. R. (2009). CrystEngComm, 11, 151–159.  Web of Science CSD CrossRef CAS

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