Two copper complexes with imidazole ligands: Syntheses, crystal structures and fluorescence

ISSN 0036�0236, Russian Journal of Inorganic Chemistry, 2010, Vol. 55, No. 3, pp. 384–389. © Pleiades Publishing, Ltd., 2010.

384

1 1. INTRODUCTION

The study of imidazole as a complexing agent hasbeen a matter of active interest for years, mainlybecause imidazole is involved in important biologicalprocesses [1–3]. There are two nitrogen atoms in oneimidazole molecule. The deprotonated nitrogen atomis a good resource to coordinate with metal ion and aserial of compounds based on imidazole and differentmetal ions have been reported [4–8]. On the otherhand, the protonated nitrogen atom in imidazole mol�ecule is a good hydrogen bonding donor and multi�dimensional supramolecular assembly can be obtainedvia hydrogen bonding interaction [9–14]. The presentpaper describes the synthesis, structure and propertiesof the copper complex with imidazole ligand.

2. EXPERIMENTAL

2.1. Synthesis of [Cu(im)6]Cl2 · 4H2O (1)

All the reagents were of AR grade and used withoutfurther purification, imidazole (0.0681 g, 1 mmol) wasdissolved in 10 mL EtOH/H2O (V : V = 1 : 1) solution,and then the resultant solution was added in 10 mLdouble�distilled water containing CuCl2 · 2H2O(0.170 g, 1 mmol). The resulting solution was heatedat 373 K for 96 h. After cooling to room temperature,blue crystals were obtained in a yield up to 37.65%.

1 The article is published in the original.

Elemental analysis Calcd. for 1: C, 35.12; H, 5.20; N,27.31 %. Found: C, 35.61; H, 5.23, N, 27.43%.

2.2. Synthesis of [Cu(im)6]Cl2 · 2H2O (2).

The procedure was similar to that for 1 except thatthe imidazole was dissolved in 10 mL H2O solution,(43% yield). Calcd. for 2: C, 37.31; H, 4.84; N,29.16%. Found: C, 37.16; H, 4.75; N, 29.13%

2.3. Structure Determination of 1 and 2

Suitable single crystals of 1 and 2 were carefullyselected under an optical microscope and glued to thinglass fibers. The diffraction data were collected on asiemens SMART CCD diffractometer with graphite�monochromated MoK

α radiation (λ = 0.71073 Å) at

291 K. An empirical absorption correction was appliedusing the SADABS program [15]. The structures weresolved by direct methods and refined by full�matrixleast�squares methods on F2 by using the SHELX�97program package [16]. All non�hydrogen atoms wererefined anisotropically.

Hydrogen atoms of imidazole and water were gen�erated geometrically. The crystallography details forthe structures determination of 1 and 2 are presentedin Table 1. Selected bond distances and bond anglesare listed in Table 2.

Two Copper Complexes with Imidazole Ligands: Syntheses, Crystal Structures and Fluorescence1

Wu Wen, Xie Jimin, and Xie DongpoDepartment of Chemistry, Zhou Kou Normal University 466001, P. R. China

e�mail: [email protected]

Received April 27, 2007

Abstract—Two copper (imidazole) complexes, namely, [Cu(im)6]Cl2 · 4H2O (1), and [Cu(im)6]Cl2 · 2H2O (2)(im—imidazole) have been synthesized by hydrothermal method. Single�crystal X�ray analysis revealed thatthe complex 1 belongs to triclinic system, space group P with a = 8.8097(18) Å, b = 9.0812(18) Å, c = 10.586(2) Å;

= 75.08(3)°, = 83.14(2)°, = 61.84(3)°; R1 = 0.0562, wR2 = 0.1607. In compound 1, [Cu(im)6]2+ cation

and counter anions Cl– alternatively array in an ABAB fashion via N–H···Cl hydrogen bonding. Compound2 falls into monoclinic system, space group P21/n with a = 8.073(2) Å, b = 13.239(2) Å, c = 15.0810(10) Å;

= 97.940(10)°; R1 = 0.0434, wR2 = 0.1243. The equatorial ligands are involved into a complex hydrogenbond network that involves the chloride anions and uncoordinated water molecules. We report there synthe�sis, crystal structure, thermal stability, IR spectrum and fluorescent property.

Key words: copper complex; imidazole; fluorescent property.

DOI: 10.1134/S0036023610030149

1

α β γ

β

COORDINATION COMPOUNDS

RUSSIAN JOURNAL OF INORGANIC CHEMISTRY Vol. 55 No. 3 2010

TWO COPPER COMPLEXES 385

3. RESULTS AND DISCUSSION

3.1. Description of Structures

The complex 1 crystallizes as blue irregular crystalswith the copper(II) ion located on an inversion center.The complex consists of a hexakis (imidazole) cop�per(II) cation, two non�coordinated Cl– anions andfour water molecules (Fig. 1). In the [Cu(im)6]

2+ cat�ion, copper ion is coordinated by six imidazole, exhib�iting nontrivially regular octahedron. The four shortCu–N distances in the equatorial plane; Cu–N(1) is2.127(3) Å and Cu–N(5) is 2.135(3) Å, and are com�parable to inner sphere Cu–N distances found in otherimidazole copper(II) carboxylate complexes [17–20], theother two imidazole ligands ions: Cu–N(3) 2.144(3) Å, lieon the axial positions which deviate only trivially fromequivalence. The CuN4 is co�planar, but the imidazoleligands are oriented in two sets: perpendicular andparallel.

In compound 1, each [Cu(im)6]2+ cation arrays

orderly in the middle of crystal cell and links Cl– in abcell plane via N–H···Cl hydrogen bonding alterna�tively array in the solid state and crystal plane in anABAB fashion. Water molecules (their oxygen atomsare in ab plane) connect each other or link Cl– viaO⎯H···O or O–H···Cl hydrogen bonding interactions(Table 3).

The complex 2 again is formed of discrete[Cu(im)6]

2+ cation and Cl– anions as shown in Fig. 3.

The Cu atom is in an octahedral environment formedby N atoms of imidazole moieties. The bond distancesinvolved in this octahedral geometry, (Cu–N1, Cu–N2and Cu–N3) are the most close to regular octahedronranging from 2.122(12) to 2.161(12) Å. The equatorial

Table 1. Crystal data and structure refinement parameters for complexes 1, 2

1 2

Formula C18H32Cl2CuN12O4 C18H28Cl2CuN12 O2

Molecular mass 615.00 578.97

Crystal system Triclinic Monoclinic

Space group P�1 P 21/n

a (Å) 8.8097(18) 8.072(1)

b (Å) 9.0812(18) 13.239(2)

c (Å) 10.586(2) 15.0810(10)

α (o ) 75.08(3) 90

β (o ) 83.14(3) 97.940(10)

γ (o ) 61.84(3) 90

V (Å3) 721.5(3) 1596.4(5)

Z 1 2

T, K 291(2) 291(2)

Dcalc (g cm–3) 1.415 1.204

F(000) 319 598

Goodness�of�fit on F2 1.067 1.081

Final R indices [I > 2sigma(I)]a

R1 = 0.0562, wR2 = 0.1557

R1= 0.0434, wR2 = 0.1221

R indices (all data) R1 = 0.0610, wR2 = 0.1607 R1 =0.0486, wR2 = 0.1243

R1 = Σ (|F0| – |FC|) / Σ|F0, wR2 = [Σw( – /Σw 0.5F02 FC

2)

2F0

2( )

2

Table 2. Selected bond lengths (Å) and angles (o) for 1, 2

Complex 1

Cu(1)–N(1) 2.127(3) N(1)Cu(1)N(5) 98.81(13)

Cu(1)–N(5) 2.136(3) N(5)#1Cu(1)N(3)#1 90.52(12)

Cu(1)–N(3)#1 2.144(3) N(1)–Cu(1)–N(3) 90.28(13)

N(1)–C(1) 1.376(6)

N(2)–C(3) 1.332(6)

N(5)–C(7) 1.317(5)

Complex 2

Cu–N(2)#1 2.1355(13) N(1)#1CuN(2) 92.34(5)

Cu–N(1) 2.1221(12) N(2)CuN(3)#1 91.744(5)

Cu–N(3) 2.1605(12) N(1)#1Cu�N(3) 87.16(5)

N(1)–C(4) 1.3143(19) N(2)–Cu–N(3) 88.56(5)

N(1)–C(6) 1.381(2)

N(5)–C(7) 1.3549(19)

C(6)–C(5) 1.355(3)

N(6)–C(9) 1.371(7)

N(6)–C(3) 1.346(2)

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WEN et al.

ligands are involved into a complex hydrogen bondnetwork that involves the chloride anions and uncoor�dinated water molecules.

An interesting aspect of this crystal structure is thehydrogen�bonding pattern. The Cl– ion does not coor�dinate to the metal atom, but forms hydrogen bondswith the [Cu(im)6]

2+ ins and water molecules Fig. 4.There are no unusual features in either the bondlengths or the bond angles in the anion (see Table 2).

The complexes 1 and 2 form a three�dimensionalnetwork through intermolecular hydrogen bonds withthe counter anions and water molecules. Details of the

complex hydrogen�bonding scheme can be createdfrom the deposited cif�files. All the imidazole rings areindividually planar. The largest deviations from the meanplane are –0.0027 Å at C6 atom for 1 and 0.0046 Å at C7atom for 2, respectively. Bond lengths and angleswithin the imidazole rings are in good agreement withthe parameters reported for the structure of imidazoleitself [21]. In compound 1, the least�squares plane ofthe imidazole ligands that contain N1, N2, C1, C2,C3 (A); N5, N6, C7, C8, C9 (B) and N3, N4, C4, C5,C6 (D) makes a dihedral angle: 85.0° (A/B), 85.6°(A/D), 91.2° (B/D). In compound 2, the least�squares

O(1A)

O(2A)

Cl(1A) N(3A)

C(6A)

N(4A)C(5A)

C(9)

N(6)

C(8)

C(7)

N(5)C(4A)

Cu(1)C(1A)

C(2A)

N(2A)

C(3A)

N(1A)

O(2)

Cl(1) O(1)

N(2)

C(2)C(1)

N(1)

C(3)

N(3)

N(5A)C(4)

C(7A)

C(8A)

N(6A)

C(9A)C(5)

N(4)

C(6)

Fig. 1. A view of 1 with 30% probability ellipsoid.

Table 3. Hydrogen�bonding geometry and close contacts (Å, °) for 1, 2

D�H…A d(D–H) d(H···A) d(D···A) d(D–H···A)

Complex 1a

N(4)–H(4B)···Cl(1)#2 0.86 2.52 3.342(4) 161

N(2)–H(2B)···Cl(1)#3 0.86 2.39 3.238(4) 170

O(2)–H(2F)···Cl(1)#3 0.86 2.55 3.203(4) 134

O(1)–H(1F)···O(1)#4 0.88 1.85 2.712(8) 168

O(2)–H(2G)···O(1) 0.83 1.96 2.743(6) 159

O(1)–H(1E)···Cl(1) 0.87 2.33 3.171(4) 160

Complex 2b

O(1)–H(1W)···Cl #1 0.79 2.41 3.196(2) 172

O(1)–H(2W)···Cl #2 0.76 2.47 3.209(2) 166

C(4)–H(4)···Cl #3 0.93 2.73 3.4816(16) 139

C(5)–H(5)···Cl0.93 0.93 2.75 3.6277(19) 157

Symmetry transformations used to generate equivalent atoms: a #1 –x + 2, –y + 2, –z; #2 –x + 1, –y + 2, –z + 1; #3 –x + 2, –y + 1, –z + 1; #4 –x + 1, –y + 1, –z + 1. b #1 1/2 – x, 1/2 + y, 1/2 – z; #2 x, y, 1 + z; #3 1– x, –y, 1 – z.



Fig. 2. Unit cell packing of 1 showing hydrogen�bonding interactions.

Cl C(9A)C(8A)

N(5A)

C(7A)N(2A)

C(3)

N(6)

C(2) C(1)

C(6A)

N(3)

C(5A)

N(4A)

C(4A)

N(1A)C(9) C(8) N(5)

Cu N(2)C(7)

C(3A)

N(6A)

C(2A)C(1A)

C(6)

N(3A)N(1)

C(4)

N(4)C(5)

O(1)

Fig. 3. A view of 2 with 30% probability ellipsoid.

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WEN et al.

plane that contain N1, N4, C4, C5, C6 (A); N3, N6,C1, C2, C3 (B) and N5, N2, C7, C8, C9 (D) makes adihedral angle of 65.9° (A/B), 102.5° (A/D), 71.6°(B/D) with the plane defined by, respectively.

3.2. TGA Properties

The TGA diagrams show these complexes havesimilar stability and behavior in the range of 100–600°C, all displaying three steps of weight loss corre�sponding to the release of solvent water, chlorine andorganic coordination ligands. Complex 1 exhibits loss

of four lattice water and two chlorine in two stepsbetween 80–270°C (11.7 and 11.6% weight lossobserved; 11.8 and 11.9% calculated). In contrast,complex 2 exhibits loss of two water molecules and twochlorine between 74–203°C (6.3 and 12.28% weightloss observed; 6.6 and 12.5% calculated). These com�plexes exhibit sharp weight losses between approxi�mately 270–480°C in two steps, followed by slowweight losses. The common behavior of the two spe�cies suggests that there might exist a common series ofintermediates.

3.3. IR Spectrum

In the IR spectrum of compound 1, the peak at749, 848, 1072, 1325, 1534 cm–1 are attributed to thecharacteristic peaks of imidazole. These characteristicpeaks shift to 749, 839, 1067, 1386, 1537 cm–1 in 2 dueto the influence of water molecules in the two com�plexes. The peak at 3207 and 3212 cm–1 of 1 and 2 isattributed to vO–H of the water molecules respectively.

3.4. Fluorescent Properties

Complexes 1, 2 and free imidazole ligand exhibitphotoluminescence in solid state at room tempera�ture. The emission spectra are shown in Fig. 5. Theweak emission of free imidazole with energy from400–650 nm (max = 488 nm) upon excitation at 367 nm,might be assigned to intra�ligand charge�transfer(LCT). Samples of 1 at λ = 460 nm produce an intenseluminescence with the peak maximum at 548 nm.Excitation of solid samples of 2 at λ = 460 nm pro�duces an intense luminescence with maximum peak at

Fig. 4. Unit cell packing of 2 showing hydrogen�bonding interactions.

750700650600550500400 800450

1 2Inte

nsi

ty

Wavelength, nm

imidazole

Fig. 5. Emission spectra of free imidazole and complexes1, 2 at room temperature.



578 nm and 659 nm. Such low energy might comefrom the metal�to�ligand charge�transfer.

4. CONCLUSIONS

We have successfully synthesized and characterizedtwo novel supramolecular assemblies, it is worth tonote that although the reaction conditions are thesame except different solvent, the structures of 1 and 2are completely different. There are two kinds of hydro�gen bonds: inter� and intramolecular hydrogen bond�ing interactions which form 2�D sheets. But onlyintramolecular hydrogen bonding interactions exits incompound 2, which is 0�D. From these examples weknow hydrogen bonding will play a more importantrole in defining the overall supramolecular architec�ture.

ACKNOWLEDGMENTS

We thank the Natural Science Foundation ofHenan Province and the Key Discipline Foundationof Zhoukou Normal University for financial supportof this research.

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Appendix A. Supplementary data

Crystallographic data for the structural analysishave been deposited with the Cambridge Crystallo�graphic Data Centre CCDC: (1) 660809; (2) 669533Copies of this information may be obtained free ofcharge from The Director, 12 Union Road, Cam�bridge, CB2 1EZ, UK(Fax:+44�1223�336033; e�mail:[email protected] or www:http:// www.ccdc.cam.ac.uk

Two copper complexes with imidazole ligands: Syntheses, crystal structures and fluorescence

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