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Crystal structure and fluorescence properties of catena-poly[[(2,2′-bi-1H-imidazole-κ2N,N′)cadmium]-di-μ-chlorido]

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aKey Laboratory of Functional Organometallic Materials, Department of Chemistry and Materials Science, Hengyang Normal University, Hengyang 421008, People's Republic of China, and bDepartment of Chemistry and Materials Science, Hengyang Normal University, Hengyang 421008, People's Republic of China
*Correspondence e-mail: 275810051@qq.com

Edited by M. Weil, Vienna University of Technology, Austria (Received 18 August 2016; accepted 27 August 2016; online 9 September 2016)

In the polymeric title compound, [CdCl2(C6H6N4)]n, the central CdII atom is coordinated by four chloride ligands and two N atoms from a chelating 2,2′-bi-1H-imidazole mol­ecule, leading to a distorted octa­hedral Cl4N2 coordination set. As a result of the μ2-bridging character of the Cl ligands, chains parallel to the c axis are formed, with the chelating 2,2′-bi-1H-imidazole ligands decorated on both sides of the chain. The luminescence properties of the complex dispersed in di­methyl­formamide shows that the emission intensities are significantly quenched by nitro­benzene.

1. Chemical context

In recent years, great efforts have been devoted to the design and assembly of coordination polymers, not only because of the aesthetic beauty of their structures but also their potential applications in the fields of gas storage, separation, magnetism or their optical properties (Thangavelu et al., 2015[Thangavelu, S. G., Butcher, R. J. & Cahill, C. L. (2015). Cryst. Growth Des. 15, 3481-3492.]; Zhao et al., 2014[Zhao, X., Wong, M., Mao, C., Trieu, T. X., Zhang, J., Feng, P. & Bu, X. (2014). J. Am. Chem. Soc. 136, 12572-12575.]; Erer et al., 2015[Erer, H., Yeşilel, O. Z. & Arıcı, M. (2015). Cryst. Growth Des. 15, 3201-3211.]; Eddaoudi et al., 2015[Eddaoudi, M., Sava, D. F., Eubank, J. F., Adil, K. & Guillerm, V. (2015). Chem. Soc. Rev. 44, 228-249.]; O'Keeffe, 2009[O'Keeffe, M. (2009). Chem. Soc. Rev. 38, 1215-1217.]). The structural chemistry of transition metal halides with neutral N-donor co-ligands has been investigated thoroughly, leading to a multitude of complexes with new topologies and functionalities. Such N-donor ligands include, for example, tethering ligands such as bis­(4-pyridyl­meth­yl)piperazine (Low & LaDuca, 2015[Low, E. M. & LaDuca, R. L. (2015). Inorg. Chim. Acta, 425, 221-232.]), 4,4′-di­pyridyl­amine (Brown et al., 2008[Brown, K. A., Martin, D. P., Supkowski, R. M. & LaDuca, R. L. (2008). CrystEngComm, 10, 846-855.]) or 4,4′-bi­pyridine (Lyons et al., 2008[Lyons, E. M., Braverman, M. A., Supkowski, R. M. & LaDuca, R. L. (2008). Inorg. Chem. Commun. 11, 855-858.]). We are also inter­ested in conjugated terminal N-heterocyclic mol­ecules as ligands, which can endow the resulting structures with photoluminescent properties. 2,2′-Bi-1H-imidazole is used as such an important terminal N-donor co-ligand, which can not only direct the structural properties with hydrogen-bonding networks, but also can be used as a suitable fragment for ππ inter­actions through the imidazole rings.

We have explored the self-assembly of CdCl2 and 2,2′-bi-1H-imidazole in the presence of 2,2-di­methyl­succinic acid and obtained a new polymeric cadmium complex, [Cd(2,2′-bi-1H-imidazole)Cl2]n. Its crystal structure and luminescence sensing of solvent mol­ecules are reported in this communication.

2. Structural commentary

The asymmetric unit of the title compound is shown in Fig. 1[link]. The central CdII atom is coordinated by four chloride ligands and two nitro­gen atoms from a chelating 2,2′-bi-1H-imidazole ligand, forming a distorted Cl4N2 octa­hedral coordination set (Fig. 2[link]). The Cd—Cl and Cd—N bond lengths range from 2.5271 (11)–2.8150 (14) and 2.323 (3)–2.342 (4) Å, respectively. The five-membered Cd1/N1/C1/C2/N2 chelate ring is characterized by a bite angle of 72.6 (1)°. The two imidazole rings of the 2,2′-bi-1H-imidazole ligand are nearly parallel to each other, making a dihedral angle of 0.8 (5)°. The μ2-bridg­ing character of the four Cl ligands leads to the formation of a chain expanding parallel to the c axis (Fig. 2[link]).

[Scheme 1]
[Figure 1]
Figure 1
The asymmetric unit of the title compound, with anisotropic displacement parameters drawn at the 30% probability level.
[Figure 2]
Figure 2
The supra­molecular structure showing the inter­actions between neighbouring chains. N—H⋯Cl hydrogen bonds are shown as dashed lines.

3. Supra­molecular features

In the presence of the chelating 2,2′-bi-1H-imidazole ligands that decorate the chains on both sides, the chains are directed by weak ππ inter­actions into zipper-like double-stranded chains with centroid-to-centroid distances of 3.6538 (15) and 3.9452 (14) Å, respectively. In addition, there are inter­molecular hydrogen bonds between the imidazole N atoms and coordinating Cl atoms of neighboring chains (Table 1[link]). The ππ stacking inter­actions together with N—H⋯Cl hydrogen-bonding inter­actions expand the [CdCl4/2]n chains to supra­molecular sheets parallel to the bc plane (Fig. 2[link]).

Table 1
Hydrogen-bond geometry (Å, °)

D—H⋯A D—H H⋯A DA D—H⋯A
N2—H7⋯Cl2i 0.86 2.32 3.174 (4) 172
N4—H8⋯Cl1i 0.86 2.63 3.237 (4) 129
Symmetry code: (i) x, y+1, z.

4. Luminescence properties

Coordination polymers based on d10 metal ions and conjugated organic ligands are promising candidates for potential photoactive materials with applications in chemical sensoring or in photochemistry. In particular, solvent-dependent quenching behaviour is of inter­est for the development of luminescent probes for chemical species (Liu et al., 2015[Liu, F.-H., Qin, C., Ding, Y., Wu, H., Shao, K.-Z. & Su, Z.-M. (2015). Dalton Trans. 44, 1754-1760.]). Hence the luminescence properties of the title compound in different solvent emulsions were investigated. The luminescent intensities had no distinct differences if di­chloro­methane, aceto­nitrile, ethanol, ethyl acetate or benzene were selected as dispersing agents. However, the intensity had an abrupt decrease when the powdered samples of the title compound were dispersed in nitro­benzene. When the nitro­benzene solvent was gradually and increasingly added to the standard emulsions, the fluorescence intensities of the standard emulsions gradually decreased with increasing addition of nitro­benzene (Fig. 3[link]). The fluorescence decrease was nearly proportional to the nitro­benzene concentration and intensity ultimately was found to be negligible. The efficient quenching of nitro­benzene in this system can be ascribed to the physical inter­action of the solute and solvent, which induces the electron transfer from the excited title compound to the electron-deficient nitro­benzene (Hao et al., 2013[Hao, Z., Song, X., Zhu, M., Meng, X., Zhao, S., Su, S., Yang, W., Song, S. & Zhang, H. (2013). J. Mater. Chem. A, 1, 11043-11050.]). These results have given us the impetus to carry out more detailed investigations on the sensing behaviour of the title compound.

[Figure 3]
Figure 3
Fluorescence intensity of the title complex at different nitro­benzene concentrations in DMF.

5. Database survey

A search of the Cambridge Structure Database (Version 5.35; last update May 2015; Groom et al., 2016[Groom, C. R., Bruno, I. J., Lightfoot, M. P. & Ward, S. C. (2016). Acta Cryst. B72, 171-179.]) for related Cd-based complexes with 2,2′-bi-1H-imidazole gave 41 hits. In most cases, 2,2′-bi-1H-imidazole serves as an ancillary ligand to be incorporated in carboxyl­ate coordination polymer systems. [Cd(2,2′-bi-1H-imidazole)Br2]n has a very similar composition to the title compound and also shows an arrangement of polymeric chains constructed from the bridging behaviour of the Br ligand (Hester et al., 1996[Hester, C. A., Collier, H. L. & Baughman, R. G. (1996). Polyhedron, 15, 4255-4258.]); however, the space group is different (C2/c).

6. Synthesis and crystallization

A mixture of CdCl2·2.5H2O (0.5 mmol, 0.114 g), 2,2-di­methyl­succinic acid (0.5 mmol, 0.073 g), 2,2′-bi-1H-imidazole (0.5 mmol, 0.067 g) in water (8 ml) was stirred vigorously for 1 h at 333 K. Slow evaporation of the clear solution resulted in the separation of block-like colorless crystals as a pure phase. The crystals were washed with ethanol, and dried at room temperature. Calculated: C, 22.70; H, 1.90; N, 17.65; found: C, 22.51; H, 2.58; N, 17.49%.

7. Refinement

Crystal data, data collection and structure refinement details are summarized in Table 2[link]. C-bound H atoms were positioned geometrically and constrained using a riding-model approximation, with C—H = 0.93 Å and Uiso(H) = 1.2Ueq(C). H atoms attached to the N atoms were found from difference maps but constrained with N—H = 0.86 Å and Uiso(H) = 1.2Ueq(N).

Table 2
Experimental details

Crystal data
Chemical formula [CdCl2(C6H6N4)]
Mr 317.45
Crystal system, space group Monoclinic, P21/c
Temperature (K) 296
a, b, c (Å) 14.977 (5), 8.777 (3), 7.160 (3)
β (°) 97.900 (5)
V3) 932.3 (6)
Z 4
Radiation type Mo Kα
μ (mm−1) 2.87
Crystal size (mm) 0.26 × 0.21 × 0.17
 
Data collection
Diffractometer Bruker APEXII CCD area-detector
Absorption correction Multi-scan (SADABS; Bruker, 2012[Bruker (2012). APEX2, SAINT and SADABS. Bruker AXS Inc. Madison, Wisconsin, USA.])
Tmin, Tmax 0.523, 0.641
No. of measured, independent and observed [I > 2σ(I)] reflections 5643, 2229, 1997
Rint 0.042
(sin θ/λ)max−1) 0.667
 
Refinement
R[F2 > 2σ(F2)], wR(F2), S 0.043, 0.113, 1.10
No. of reflections 2229
No. of parameters 119
H-atom treatment H-atom parameters constrained
Δρmax, Δρmin (e Å−3) 1.50, −1.62
Computer programs: APEX2 and SAINT (Bruker, 2012[Bruker (2012). APEX2, SAINT and SADABS. Bruker AXS Inc. Madison, Wisconsin, USA.]), SHELXS97, SHELXL97 and SHELXTL (Sheldrick, 2008[Sheldrick, G. M. (2008). Acta Cryst. A64, 112-122.]).

Supporting information


Computing details top

Data collection: APEX2 (Bruker, 2012); cell refinement: SAINT (Bruker, 2012); data reduction: SAINT (Bruker, 2012); program(s) used to solve structure: SHELXS97 (Sheldrick, 2008); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008); molecular graphics: SHELXTL (Sheldrick, 2008); software used to prepare material for publication: SHELXTL (Sheldrick, 2008).

catena-Poly[[(2,2'-bi-1H-imidazole-κ2N,N')cadmium]-di-µ-chlorido] top
Crystal data top
[CdCl2(C6H6N4)]F(000) = 608
Mr = 317.45Dx = 2.262 Mg m3
Monoclinic, P21/cMo Kα radiation, λ = 0.71073 Å
Hall symbol: -P 2ybcCell parameters from 3238 reflections
a = 14.977 (5) Åθ = 2.7–28.3°
b = 8.777 (3) ŵ = 2.87 mm1
c = 7.160 (3) ÅT = 296 K
β = 97.900 (5)°Block, colorless
V = 932.3 (6) Å30.26 × 0.21 × 0.17 mm
Z = 4
Data collection top
Bruker APEXII CCD area-detector
diffractometer
2229 independent reflections
Radiation source: fine-focus sealed tube1997 reflections with I > 2σ(I)
Graphite monochromatorRint = 0.042
phi and ω scansθmax = 28.3°, θmin = 2.7°
Absorption correction: multi-scan
(SADABS; Bruker, 2012)
h = 1219
Tmin = 0.523, Tmax = 0.641k = 1111
5643 measured reflectionsl = 97
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)] = 0.043H-atom parameters constrained
wR(F2) = 0.113 w = 1/[σ2(Fo2) + (0.0676P)2 + 0.4551P]
where P = (Fo2 + 2Fc2)/3
S = 1.10(Δ/σ)max < 0.001
2229 reflectionsΔρmax = 1.50 e Å3
119 parametersΔρmin = 1.62 e Å3
0 restraintsExtinction correction: SHELXL97 (Sheldrick, 2008), Fc*=kFc[1+0.001xFc2λ3/sin(2θ)]-1/4
Primary atom site location: structure-invariant direct methodsExtinction coefficient: 0.044 (3)
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 > 2sigma(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
Cd10.23613 (2)0.15121 (3)0.09150 (4)0.02900 (17)
Cl10.13506 (7)0.32441 (12)0.12634 (15)0.0334 (2)
Cl20.33418 (8)0.35735 (11)0.28324 (18)0.0385 (3)
N10.3334 (2)0.0418 (4)0.2122 (5)0.0313 (7)
N20.3617 (3)0.2854 (4)0.2529 (6)0.0381 (8)
H70.35450.38260.24920.046*
N30.1636 (2)0.0810 (4)0.0127 (5)0.0317 (7)
N40.1669 (3)0.3302 (4)0.0271 (6)0.0403 (9)
H80.18630.42130.05150.048*
C10.3014 (3)0.1809 (4)0.1799 (6)0.0271 (8)
C20.4183 (3)0.0601 (6)0.3068 (7)0.0415 (10)
H20.45770.01890.34680.050*
C30.4364 (3)0.2096 (6)0.3338 (7)0.0455 (11)
H30.48930.25220.39520.055*
C40.2120 (3)0.2008 (5)0.0758 (6)0.0297 (8)
C50.0842 (3)0.1383 (6)0.0763 (7)0.0410 (11)
H50.03650.08010.13460.049*
C60.0854 (3)0.2916 (7)0.0671 (7)0.0489 (13)
H60.03950.35770.11570.059*
Atomic displacement parameters (Å2) top
U11U22U33U12U13U23
Cd10.0339 (2)0.0185 (2)0.0330 (2)0.00127 (9)0.00124 (13)0.00016 (9)
Cl10.0291 (5)0.0343 (5)0.0368 (5)0.0095 (4)0.0048 (4)0.0071 (4)
Cl20.0386 (6)0.0319 (5)0.0468 (6)0.0149 (4)0.0129 (5)0.0112 (4)
N10.0334 (17)0.0234 (15)0.0358 (18)0.0003 (13)0.0009 (13)0.0044 (13)
N20.044 (2)0.0264 (18)0.047 (2)0.0092 (15)0.0150 (16)0.0079 (16)
N30.0334 (17)0.0297 (17)0.0320 (17)0.0002 (14)0.0049 (13)0.0043 (14)
N40.048 (2)0.0257 (17)0.052 (2)0.0143 (15)0.0236 (19)0.0099 (16)
C10.0300 (18)0.0227 (16)0.031 (2)0.0048 (15)0.0129 (15)0.0025 (15)
C20.031 (2)0.047 (3)0.044 (2)0.0051 (19)0.0024 (17)0.008 (2)
C30.037 (2)0.053 (3)0.046 (3)0.015 (2)0.0044 (18)0.010 (2)
C40.0311 (19)0.0236 (19)0.037 (2)0.0067 (16)0.0151 (15)0.0047 (16)
C50.030 (2)0.054 (3)0.038 (2)0.0056 (18)0.0020 (17)0.0118 (19)
C60.043 (3)0.057 (3)0.048 (3)0.023 (2)0.013 (2)0.019 (2)
Geometric parameters (Å, º) top
Cd1—N12.323 (3)N3—C51.365 (5)
Cd1—N32.342 (4)N4—C41.343 (5)
Cd1—Cl12.5271 (11)N4—C61.354 (7)
Cd1—Cl22.6001 (12)N4—H80.8600
Cd1—Cl1i2.6944 (13)C1—C41.450 (6)
Cd1—Cl2ii2.8150 (14)C2—C31.348 (8)
N1—C11.320 (5)C2—H20.9300
N1—C21.365 (5)C3—H30.9300
N2—C11.342 (5)C5—C61.348 (7)
N2—C31.360 (7)C5—H50.9300
N2—H70.8600C6—H60.9300
N3—C41.321 (6)
N1—Cd1—N372.61 (11)C4—N3—Cd1113.3 (3)
N1—Cd1—Cl1163.82 (9)C5—N3—Cd1141.1 (3)
N3—Cd1—Cl198.98 (9)C4—N4—C6107.8 (4)
N1—Cd1—Cl291.80 (9)C4—N4—H8126.1
N3—Cd1—Cl2160.47 (9)C6—N4—H8126.1
Cl1—Cd1—Cl298.87 (5)N1—C1—N2110.7 (4)
N1—Cd1—Cl1i99.64 (9)N1—C1—C4119.3 (3)
N3—Cd1—Cl1i87.70 (8)N2—C1—C4130.0 (4)
Cl1—Cd1—Cl1i93.69 (4)C3—C2—N1109.9 (4)
Cl2—Cd1—Cl1i83.31 (4)C3—C2—H2125.0
N1—Cd1—Cl2ii84.49 (9)N1—C2—H2125.0
N3—Cd1—Cl2ii93.59 (8)C2—C3—N2106.1 (4)
Cl1—Cd1—Cl2ii82.24 (4)C2—C3—H3127.0
Cl2—Cd1—Cl2ii96.60 (4)N2—C3—H3127.0
Cl1i—Cd1—Cl2ii175.87 (3)N3—C4—N4110.5 (4)
Cd1—Cl1—Cd1ii99.20 (4)N3—C4—C1120.3 (3)
Cd1—Cl2—Cd1i94.46 (4)N4—C4—C1129.1 (4)
C1—N1—C2105.6 (4)C6—C5—N3109.9 (5)
C1—N1—Cd1114.5 (3)C6—C5—H5125.1
C2—N1—Cd1139.8 (3)N3—C5—H5125.1
C1—N2—C3107.6 (4)C5—C6—N4106.2 (4)
C1—N2—H7126.2C5—C6—H6126.9
C3—N2—H7126.2N4—C6—H6126.9
C4—N3—C5105.6 (4)
N1—Cd1—Cl1—Cd1ii41.8 (3)Cl2—Cd1—N3—C5140.3 (4)
N3—Cd1—Cl1—Cd1ii99.06 (9)Cl1i—Cd1—N3—C577.8 (4)
Cl2—Cd1—Cl1—Cd1ii88.90 (4)Cl2ii—Cd1—N3—C598.2 (4)
Cl1i—Cd1—Cl1—Cd1ii172.70 (4)C2—N1—C1—N21.1 (5)
Cl2ii—Cd1—Cl1—Cd1ii6.62 (3)Cd1—N1—C1—N2179.6 (2)
N1—Cd1—Cl2—Cd1i93.14 (9)C2—N1—C1—C4178.4 (4)
N3—Cd1—Cl2—Cd1i56.8 (3)Cd1—N1—C1—C40.2 (4)
Cl1—Cd1—Cl2—Cd1i99.06 (4)C3—N2—C1—N10.8 (5)
Cl1i—Cd1—Cl2—Cd1i6.35 (3)C3—N2—C1—C4178.6 (4)
Cl2ii—Cd1—Cl2—Cd1i177.80 (3)C1—N1—C2—C31.0 (5)
N3—Cd1—N1—C10.5 (3)Cd1—N1—C2—C3178.9 (3)
Cl1—Cd1—N1—C161.0 (5)N1—C2—C3—N20.5 (5)
Cl2—Cd1—N1—C1167.6 (3)C1—N2—C3—C20.1 (5)
Cl1i—Cd1—N1—C184.0 (3)C5—N3—C4—N41.1 (4)
Cl2ii—Cd1—N1—C196.0 (3)Cd1—N3—C4—N4179.7 (3)
N3—Cd1—N1—C2177.4 (5)C5—N3—C4—C1179.6 (4)
Cl1—Cd1—N1—C2116.8 (4)Cd1—N3—C4—C10.9 (4)
Cl2—Cd1—N1—C214.6 (4)C6—N4—C4—N31.5 (5)
Cl1i—Cd1—N1—C298.1 (4)C6—N4—C4—C1179.2 (4)
Cl2ii—Cd1—N1—C281.9 (4)N1—C1—C4—N30.5 (6)
N1—Cd1—N3—C40.7 (2)N2—C1—C4—N3178.8 (4)
Cl1—Cd1—N3—C4166.5 (2)N1—C1—C4—N4179.8 (4)
Cl2—Cd1—N3—C437.6 (4)N2—C1—C4—N40.5 (7)
Cl1i—Cd1—N3—C4100.1 (3)C4—N3—C5—C60.3 (5)
Cl2ii—Cd1—N3—C483.8 (3)Cd1—N3—C5—C6178.3 (3)
N1—Cd1—N3—C5178.7 (5)N3—C5—C6—N40.6 (6)
Cl1—Cd1—N3—C515.5 (5)C4—N4—C6—C51.2 (5)
Symmetry codes: (i) x, y1/2, z+1/2; (ii) x, y1/2, z1/2.
Hydrogen-bond geometry (Å, º) top
D—H···AD—HH···AD···AD—H···A
N2—H7···Cl2iii0.862.323.174 (4)172
N4—H8···Cl1iii0.862.633.237 (4)129
Symmetry code: (iii) x, y+1, z.
 

Acknowledgements

This work was supported by the Open Research Fund of the Key Laboratory in Hunan Province (grant No. GN15K03). We also thank the Aid programs for Science and Technology Innovative Research Team in Higher Educational Institutions of Hunan Province and the Key Discipline of Hunan Province for support.

References

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COMMUNICATIONS
ISSN: 2056-9890
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