ORIGINAL PAPER Synthesis, crystal structure, and

Chemical Papers 65 (1) 23–28 (2011) DOI: 10.2478/s11696-010-0087-6

ORIGINAL PAPER

Synthesis, crystal structure, and thermal analysis of a copper(II) complex with imidazo[4,5- ]1,10-phenantroline Fushan Yu, Lingling Zhang, Jinting Tan, Xia Li, Lijun Wang, Fei Liu, Xuwu Yang* Key Laboratory of Synthetic and Natural Functional Molecule Chemistry of Ministry of Education, Shaanxi Key Laboratory of Physico-Inorganic Chemistry, College of Chemistry and Materials Science, Northwest University, Xi’an, 710069, China Received 12 June 2010; Revised 8 September 2010; Accepted 30 September 2010

A new complex, [Cu2 (µ2 -Cl)2 (IP)2 Cl2 ] · 4H2 O (IP = imidazo[4,5-f ]1,10-phenathroline), was synthesised and characterised by elemental analysis, thermal analysis, IR spectra, and X-ray crystallography. The results showed that the complex crystallises in the monoclinic space group P ¯ 1; a = 7.880 (2) ˚ A, b = 9.227(2) ˚ A, c = 10.694(2) ˚ A; α = 97.788(4)◦ , β = 100.637(4)◦ , γ = 95.841(3)◦ ; V = 750.7(3) ˚ A3 , and Z = 1. The complex is further stabilised by H-bonds and a π–π stacking interaction between the pyridine and benzene rings of two neighbouring molecules with the centroid–centroid distance of 3.498(3) ˚ A, leading to a 3D supramolecular architecture. Thermal decomposition procedure of the complex explored by TG-DTG has three stages, and the final product is Cu in residual rate of 16.18 % (calculated to be 16.26 %). c 2011 Institute of Chemistry, Slovak Academy of Sciences Keywords: imidazo[4,5-f ]1,10-phenathroline, copper(II) complex, crystal structure, thermal analysis

Introduction Transition metal complexes containing electronrich ligands have been the focus of recent studies in the field of organometallic chemistry (Ng & Das, 1996; Miklovič et al., 2008; Siddiqi et al., 2009; Ondrejovič et al., 2008, 2010). Very strong σ-donor ligands, 2,2 bipyridyl (bipy) and 1,10-phenanthroline (phen), have been extensively used in the coordination chemistry (Gorelsky et al., 1998; Juris et al., 1988; Chen et al., 1998; Sariego et al., 1997; Hage et al., 1997; Ma et al., 2006). These ligands have been applied in homogeneous catalysis either as reducible “electron reservoirs” in metal complexes or as promoters of catalytic reactions (Maruyama et al., 1995; Ooyama et al., 1995; Zaleski et al., 2005). Many Cu(II) complexes with bidentate pyridyl ligands such as 2,2 -bipyridyl and 1,10-phenanthroline have been reported, and much attention has been focused on the photochemistry and electrochemistry of these complexes (Balzani et al., 1998; Server-Carrió et al., 1998).

It is well known that the most obvious synthetic pathway for the preparation of supra-molecular frameworks is via direct chemical combination of functional inorganic and organic components. 1,10Phenanthroline (phen) and its derivatives are widely employed as metal-binding components in the field of coordination chemistry (Joniaková et al., 2006; Yin & Zhai, 2009; Pan et al., 2009; Zhang et al., 2001; Nagababu & Satyanarayana, 2007; Wang et al., 2008). With this background in mind, our research focused on a new phen derivative of imidazo[4,5-f ]1,10phenanthroline (IP) which possesses a multifunctional aromatic system. In this paper, a new copper complex with imidazo[4,5-f ]1,10-phenanthroline was synthesised and characterised. Using the TG-DTG technique, the thermal decomposition procedure was explored.

Experimental All reagents and solvents employed were commer-

*Corresponding author, e-mail: [email protected]

Unauthenticated Download Date | 9/25/15 7:02 AM

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F. Yu et al./Chemical Papers 65 (1) 23–28 (2011)

cially available and used as received without further purification. The C, H, and N contents were measured by a Vario EL III elemental analyser (Elementar Analysensysteme GmbH, Germany). FT-IR spectra (in KBr pellets) were recorded in the range of 4000– 400 cm−1 on a Bruker EQUINOX-55 spectrometer. The thermal analysis, TG-DTG measurements were carried out under nitrogen atmosphere at the flow rate of 60 cm3 min−1 and heating rate of 10 ◦C min−1 . CuCl2 · 2H2 O (1 mmol, 170.48 mg) and IP (1 mmol, 220.23 mg) were dissolved in 20 mL of deionised water. pH of the mixture was adjusted to 2–3 with HCl (2.0 mol mL−1 ) and the solution was stirred at room temperature for 2 h. Then, it was filtered and the filtrate was allowed to evaporate very slowly. After two weeks, some green, block single crystals of the complex appeared in the mother liquid. These crystals were isolated, washed with deionised water and acetone to yield 47 % of the product. For C13 H12 Cl2 CuN4 O2 (Mr = 781.43) wi /mass % calculated: C, 39.96; H, 3.10; N, 14.34; found: C, 39.52; H, 3.03; N, 13.98. Single-crystal X-ray diffraction of the complex was performed on a Bruker SMART 1000 CCD diffractometer equipped with a graphite crystal monochromator situated in the incident beam for data collection. Crystallographic data were collected using Mo Kα radiation at λ = 0.71073 ˚ A for the complex at 296(2) K, and the data reduction was performed using the Bruker SAINT software (SMART and SAINT programs) (Siemens AXS, 1998). Empirical absorption corrections were applied using the SADABS program (Sheldrick, 2003). The structure was solved by direct methods and refined with full-matrix least-squares on F 2 with the SHELXL-97 program package (Bruker AXS, 1997). All non-hydrogen atoms were located applying difference Fourier synthesis, and the hydrogen atoms were generated geometrically. Water H atoms were located in different Fourier maps and refined with restrained O—H bond lengths (0.85(2) ˚ A); isotropic displacement parameters (0.080 ˚ A) in the complex were fixed. Crystal data collection and refinement parameters for the complex are shown in Table 1; se-

Table 1. Crystal data and structure refinement for complex [Cu2 (µ2 -Cl)2 (IP)2 Cl2 ] · 4H2 Oa Empirical formula Formula mass Temperature, T (K) Crystal system, space group a (˚ A) b (˚ A) c (˚ A) α (◦ ) β (◦ ) γ (◦ ) Unit-cell volume, V (˚ A3 ) Formula per unit cell, Z Density, Dcalcd (g cm−3 ) Absorption coefficient, µ (mm−1 ) F(000) Crystal size (mm) θ range for data collection (◦ ) Index ranges

C26 H24 Cl4 Cu2 N8 O4 781.43 296(2) Triclinic, P ¯ 1 7.880(2) 9.227(2) 10.694(2) 97.788(4) 100.637(4) 95.841(3) 750.7(3) 1 1.729 1.821 394.0 0.28 × 0.21 × 0.14 1.96–25.10 −6 ≤ h ≤ 9 −10 ≤ k ≤ 11 −12 ≤ l ≤ 10 Reflections collected/unique 3786/2675 0.0445 Independent reflections (Rint ) Refinement method Full-matrix least-squares on F 2 Maximal and minimal transmission 0.775 and 0.638 0.997 Goodness-of-fit on F2 Final R indices [I > 2σ(I)] R1 = 0.0445, wR2 = 0.1208 R indices (all data) R1 = 0.0671, wR2 = 0.1561 a) Standard deviations in parentheses.

lected bond lengths and angles are listed in Table 2.

Results and discussion The title complex crystallises in the centrosymmetric P ¯1 space group of the triclinic crystal system. As seen in Fig. 1, the complex exists as a dimer consisting of two copper(II) ions, two IP ligands, four chlorine anions, and four lattice water molecules in its molecular structure. There are two crystallographically unique Cu(II) in the asymmetrical structural unit. According to Addison et al. (1984),

Table 2. Selected bond lengths and bond angles for complex [Cu2 (µ2 -Cl)2 (IP)2 Cl2 ] · 4H2 Oa Bond length

Bond angle Bond

Bond ˚ A Cu1—N1 Cu1—N2 Cu1—Cl2 Cu1—Cl1 Cu1—Cl1b Cl1—Cu1b – –

2.037(4) 2.035(4) 2.258(2) 2.273(2) 2.705(2) 2.705(2) – –

C12—N2—Cu1 C11—N2—Cu1 C13—N1—Cu1 C1—N1—Cu1 Cu1—Cl1—Cu1b N1—Cu1—N2 N1—Cu1—Cl2 –

◦

112.7(3) 128.3(4) 112.9(4) 128.3(4) 88.0(5) 81.3(2) 166.6(1) –

Bond angle Bond

N2—Cu1—Cl2 N1—Cu1—Cl1 N2—Cu1—Cl1 Cl2—Cu1—Cl1 N1—Cu1—Cl1b N2—Cu1—Cl1b Cl2—Cu1—Cl1b Cl1—Cu1—Cl1b

◦

92.9(1) 92.9(1) 173.7(1) 92.3(6) 89.0(1) 90.3(1) 103.3(6) 92.0(5)

a) Standard deviations in parentheses; b) symmetry transformations used to generate equivalent atoms: −x + 2, −y + 1, z + 2.



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Fig. 1. Molecular structure (ORTEP drawing) of [Cu2 (µ2 -Cl)2 (IP)2 Cl2 ] · 4H2 O. Thermal ellipsoids are set at the 30 % probability level. A part of hydrogen atoms are omitted and the others are not labelled for clarity.

Fig. 2. 3D framework of the title complex viewed along the b axis.

Fig. 3. π–π stacking interactions between two neighbouring molecules. Water molecules are omitted for clarity.

when τ is close to 0, the coordination is squarepyramidal, when it is close to 1, the coordination is trigonal-bipyramidal. The value of τ was calculated as 0.12 which is close to 0, so Cu(II) displays distorted square-pyramidal coordination geometry. Each Cu(II) particle is coordinated by two nitrogen atoms from imidazo[4,5-f ]1,10-phenanthroline [Cu1—N1, 2.037(4) ˚ A; Cu1—N2, 2.035(4) ˚ A; N1—Cu1—N2, 81.3(2)◦ ], two bridged chlorine anions [Cu1—Cl1, 2.273(2) ˚ A; Cu1—Cl1, 2.705(2) ˚ A] and a non-bridged chlorine anion [Cu1—Cl2, 2.258(2) ˚ A]. In the dimer, two Cu(II) are connected by two bridged chlorine anions forming a parallelogram. The part bond angles Cl1—Cu1—Cl1 and Cu1—Cl1—Cu1 are 92.0(5)◦ and 88.0(5)◦ , respectively. Compared with the complex [Cu2 Cl4 (C10 H8 N2 )2 ] reported by Kostakis et al. (2006) and the complex [Cu2 (Phen)2 (µ2 -Cl)2 Cl2 ] re-

ported by Lan et al. (2007), when the π–π conjugated system is larger, the bond lengths of Cu—Cl shorten and the plane formed by the unit Cu2 Cl2 becomes gradually almost vertical to the plane of the ligand, and the dihedral angle formed by Cu2 Cl2 and the plane of IP ligand is 88.95◦. Fig. 2 shows the packing view of a unit cell of the title complex. The supramolecular structure depends on two kinds of interactions: π–π stacking interactions and hydrogen bonds. The π–π stacking interactions occur between two neighbouring molecules (Fig. 3). All π–π stacking interactions are listed in Table 3. Geometrical determination of the stacking parameters was calculated by the program PLATON. Intermolecular interactions occur between ring i (N1/C1/C2/C3/C4/C13) and ring j (C4/C5/C7/C8/C12/C13). Distances between the


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Table 3. π–π stacking interactions parameters between two neighbouring moleculesa Distance/˚ A Ring i

Angle α/◦

Ring j

Cg3 Cg3 Cg3 Cg4

Cg4 Cg5 Cg6 Cg6

dc–c

CgI Perp

CgJ Perp

3.683(3) 3.582(3) 3.926(3) 3.498(3)

3.263(2) 3.390(2) 3.426(2) 3.349(2)

3.363(2) 3.444(2) 3.401(2) 3.359(2)

3.7(3) 3.2(3) 2.1(3) 1.6(3)

a) Standard deviations in parentheses; ring i and ring j represent two rings which come from two neighbouring molecules with π–π stacking interaction; dc–c stands for centroid–centroid distances of ring i and ring j; CgI Perp is the perpendicular distance of Cg(I) on ring j; CgJ Perp is the perpendicular distance of Cg(J) on ring i; α is the dihedral angle formed by the plane i and plane j. Cg3, Cg4, Cg5, and Cg6 represent the (N3/C5/C7/N4/C6), (N1/C1/C2/C3/C4/C13), (N2/C11/C10/C9/C8/C12), and (C4/C5/C7/C8/C12/C13) rings, respectively. Table 4. Hydrogen bonding geometry for complex [Cu2 (µ2 -Cl)2 (IP)2 Cl2 ] · 4H2 O Bond angle/◦

Bond length/˚ A D—H · · ·A O2—H1w2· · ·N3 O1w—H1w1· · ·Cl2 N4—H4· · ·O1w O1w—H2w1· · ·O2w

D—H

H· · ·A

D· · ·A

D—H· · ·A

0.850 0.850 0.860 0.850

2.001 2.400 1.912 1.930

2.848 3.248 2.754 2.780

174.28 175.48 165.55 179.96

ring centroids and the perpendicular distance from ring i to ring j (symmetry code: (i) 1 − x, 1 − y, 1 − z; (j) x, y, z) are 3.498(3) ˚ A and 3.349(2) ˚ A, respectively. Dihedral angle between the planes of the two rings is 1.6(3)◦ . The hydrogen bond depends on the lattice water molecules, N atoms of the IP ligands, and non-bridged chlorine anions as the acceptors. Existing intermolecular hydrogen bonds presented in the structure are as follows: one is the hydrogen bond between oxygen atoms of lattice water molecules and the imidazole rings N atom of the ligand or nonbridged chlorine anions, the bond lengths of which are 2.754 ˚ A (O2—H1w2· · ·N3) and 3.248 ˚ A (O1w— H1w1· · ·Cl2), and the bond angles are 174.28◦ (O2— H1w2—N3) and 175.48◦ (O1w—H1w1—Cl2), respectively; another one is N4—H4· · ·O1w from nitrogen atom of the imidazole ring as the donor and the oxygen atom of lattice water molecule as the acceptor, hydrogen bond length in this case is 2.754 ˚ A, and the bond angle is 165.55◦; the last one is the O— H· · ·O hydrogen bond between oxygen atoms of lattice water molecules, hydrogen bond length of O1w— H2w1· · ·O2w is 2.780 ˚ A, and the bond angle is 179.96◦. All hydrogen bonds data are listed in Table 4. Packing is further stabilised by H-bonds and π–π stacking interactions along the b axis. Intermolecular hydrogen bonds are in a framework fashion and consolidate the stacked arrangement leading to a three-dimensional supramolecular architecture. As seen in Fig. 4, infrared spectra of the complex show a strong and broad band at 3444 cm−1 which is ascribed to the stretching modes of the lattice water

Fig. 4. FTIR spectra of 1-IP (1) and the title complex (2).

Fig. 5. TG-DTG curves for the title complex.

molecule. The bands at 1445 cm−1 and 1577 cm−1 originate in the skeleton vibration of aromatic rings.


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[Cu 2( µ 2-Cl)2 (IP)2Cl2 ] · 4H2O

30 ~ 86 ~ 110 °C

[Cu2 (µ 2-Cl) 2(IP) 2Cl2]

9.28 % (9.22 %) 110 ~ 205 ~ 360 °C

[Cu2(µ 2-Cl) 2(IP)Cl2]

360 ~ 593 ~ 865 °C 2Cu 46.41 % (46.34 %)

28.13 % (28.18 %) Fig. 6. Thermal decomposed procedure for the title complex.

The peaks at 1653 cm−1 and 1527 cm−1 were assigned to the skeleton vibration of C—N in the complex, and display certain shifts in contrast with 1607 cm−1 and 1505 cm−1 in the ligand. It is thus assumed that two nitrogen atoms of the ligand coordinate with copper atoms. To obtain more information on the thermal decomposition behaviour of the title complex, thermal analysis of the complex was measured by TG-DTG from 30 ◦C to 900 ◦C under nitrogen atmosphere (Fig. 5) and the decomposition procedure was deduced (Fig. 6). According to the TG-DTG curve, thermal decomposition procedure of the complex has three stages. In the first stage, in the range of 30–110 ◦C, the loss of four lattice water molecules was observed (experimental mass loss was 9.28 %, calculated mass loss was 9.22 %). In the second stage, from 110 ◦C to 360 ◦C, the break of IP occurred with the mass loss of 28.13 % (calculated value is 28.18 %). In the temperature range of 360–865 ◦C, the third stage, the complex undergoes a large mass loss of 46.41 % which represents the mass losses of the rest IP and four coordinated chlorine anions (calculated to be 46.34 %). The DTG curve shows a peak at 593 ◦C, and the final product is Cu with the residual rate of 16.18 % (calculated to be 16.26 %).

Conclusions In summary, a new supramolecular architecture has been successfully designed and synthesised by the combination of coordination bonds, hydrogen bonds, π–π interactions. In the title complex, each copper(II) is five-coordinated. There exist strong π–π interactions with the centroid–centroid distance of 3.498(3) ˚ A between the pyridine and benzene rings of two neighbouring molecules. In the complex, lattice water molecules act as hydrogen bond donors/acceptors forming hydrogen bonds with N atoms of IP and chlorine anions, to form a supramolecular architecture. Thermal analysis shows that the thermal decomposition procedure of the complex has three stages.

Supplementary data Crystallographic data for the structure reported in this article have been deposited with the Cambridge Crystallographic Data Centre, CCDC No. 689127.

Copies of this information may be obtained free of charge from The Director, CCDC, 12 Union Road, Cambridge CB2 1EZ, UK (fax: 0044-1223-336-033; e-mail: [email protected] or http://www.ccdc. cam.ac.uk). Acknowledgements. The authors are thankful for the “13115” S&T innovation program of Shaanxi province (No. 2008ZDKG-22).

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