Supramolecular interaction in copper(ll) complexes ...scijournal.hcu.ac.th/data/Supramolecular.pdfTable 1. Crystal data and structure refinements for complexes 1 and 2. Compound 1

ว. วิทย. เทคโน. หัวเฉียวเฉลิมพระเกียรติ 33ปีที่ 1 ฉบับที่ 1 มกราคม - มิถุนายน 2558

Supramolecular interaction in copper(ll) complexes containing schiff base ligands

Phailyn Khemthong1, Chatphorn Theppitak1, Filip Kielar1 and Kittipong Chainok2*

1 Department of Chemistry, Faculty of Science, Naresuan University, Mueang, Phitsanulok 65000 2 Department of Physics, Faculty of Science and Technology,

Thammasat University, Khlong Luang, Pathum Thani 12120

AbstractTwo new dinuclear copper(II) complexes containing 4-bromo-N-(2-pyridylmethylene)aniline

(C12H

9BrN

2) or 4-chloro-3,5-dimethyl-N-(2-pyridylmethylene)aniline (C

14H

13ClN

2) Schiff base ligands,

[Cu(C12H

9BrN

2)Cl

2] (1) or [Cu(C

14H

13ClN

2)Cl

2] (2), were synthesized. Single crystal X-ray analysis at room

temperature revealed that complex 1 crystallizes in the monoclinic space group P21/n and the molecular

structure consists of a dichloro-bridged dinuclear Cu(II) species [Cu···Cu = 3.4678(6) Å]. Whereas, complex 2 also crystallizes the monoclinic system with P2

1/c space group in which the two Cu(II) atoms are linked

by weak electrostatic Cu···Cl interactions [3.021(1) Å] to form a dinuclear complex [Cu···Cu separation = 3.468(1) Å]. The different of supramolecular artchitecture of complexes is the result of combination of intermolecular forces including electrostatic Cu···Cl, halogen···π, π–π, C–H···π and C–H···Cl interactions.

Keywords: Copper(II), Noncovalent interactions, Schiff base, Supramolecule, X-ray crystallography

บทคัดย่อในงานวิจัยนี้ท�าการสังเคราะห์สารประกอบเชิงซ้อน 2 ชนิด สารนี้ประกอบด้วยไอออนของโลหะคอปเปอร์ (Cu)2+

และลิแกนด์ประเภทชิพพ์เบส 4-โบรโม-N-(2-ไพริดิลเมทิลลีน)อนิลิน (C12H

9BrN

2) หรือ 4-คลอโร-3,5-ไดเมทิล-N-(2-

ไพริดิลเมทิลลีน)อนิลิน (C14H

13ClN

2), [Cu(C

12H

9BrN

2)Cl

2] (1) หรือ [Cu(C

14H

13ClN

2)Cl

2] (2) ได้ถูกสังเคราะห์ขึ้น เมื่อ

ศึกษาโครงสร้างด้วยเทคนิคการเลี้ยวเบนรังสีเอ็กซ์ผ่านผลึกเดี่ยวที่อุณหภูมิห้องพบว่า สารประกอบเชิงซ้อน 1 อยู่ในระบบผลึกแบบโมโนคลินิคของหมู่ปริภูมิ P2

1/n โครงสร้างเป็นแบบไดนิวเคลียร์เกิดจากคลอไรด์ไอออน (Cl-) สองไอออนเชื่อมกับ

ไอออนของโลหะคอบเปอร์ จ�านวนสองไอออนด้วยพันธะโควาเลนต์ [ระยะห่างระหว่างไอออนของโลหะคอปเปอร์เท่ากับ 3.4678(6) อังสตรอม] สารประกอบเชิงซ้อน 2 มีระบบผลึกแบบโมโนคลินิคเช่นเดียวกับสารประกอบเชิงซ้อน 1 แต่อยู่ในหมู่ปริภูมิ P2

1/c ซึ่งโครงสร้างแบบไดนิวเคลียร์เกิดจากไอออนของโลหะคอบเปอร์ มีอันตรกิริยากับคลอไรด์ไอออนด้วยแรง

ไฟฟ้าสถิตอย่างอ่อน [ระยะห่างระหว่างไอออนของโลหะคอปเปอร์และคลอไรด์ไอออนเท่ากับ 3.468(1) อังสตรอม] ความแตกต่างทางโครงสร้างซูปราโมเลกุลระหว่างสารประกอบเชิงซ้อนทั้งสอง เป็นผลเนื่องมาจากแรงระหว่างโมเลกุลซึ่งได้แก่ แรงไฟฟ้าสถิตย์ Cu···Cl, ฮาโลเจน···π, π–π, C–H···π และ C–H···Cl

ค�าส�าคัญ: คอปเปอร์(II) อันตรกิริยาระหว่างโมเลกุล ชิพพ์เบส ซูปราโมเลกุล ผลึกศาสตร์

Corresponding author: [email protected]

ปีที่ 1 ฉบับที่ 1 มกราคม - มิถุนายน 255834 ว. วิทย. เทคโน. หัวเฉียวเฉลิมพระเกียรติ

IntroductionSupramolecular interactions or noncovalent

bonding such as hydrogen bonding, π-π stacking and van der Waals forces have been used extensively in molecular recognition applications (1). Exploration to understanding the mechanistic consequences of such interactions is essentially contemporary in research area of chemistry because these interactions play a major role in determining the supramolecular arrangement and control the packing in neutral molecular crystals architectures (2-4). These interactions also play an important role in biology due to the presence of a great number of cation–π and π-π interactions in biological systems (5). It should also be taken into account in the supramolecular chemistry of the crystal engineering field, the design of new solids with desired physical and chemical properties (6).

The purpose of the present work is to study types of intermolecular forces which may lead to new supramolecular architectures. The reaction of the N-donor bidentate Schiff base ligands and Cu(II) ions was investigated. The coordination sphere of Cu(II) can adopt coordination numbers between four and six and various geometries from square planar through square pyramid or trigonal bipyramid to octahedron. The ligands are chosen in the present study also able to form noncovalent interactions. It is anticipated that weak association of interactions such as C−H···halogen, C−H···π or π···π interactions will help to provide diversity to the architectures of supramolecular formed. This study will advance understanding of the development of supramolecular chemistry and the tuning and prediction of the crystal structures.

Materials and MethodsSynthesis and crystallization

[Cu(C12H

9BrN

2)Cl

2] (1). To a CH

3CN solution

(5 mL) of CuCl2·3H

2O (37.7 mg, 0.2 mmol) in a

20 mL capacity of test tube was carefully layered by a CH

2Cl

2 (5 mL) solution of 4-bromo-

N-(2-pyridylmethylene)aniline (52.2 mg, 0.2 mmol). Upon slow diffusion for 5 days, brown-green block crystals of 1 were obtained in 59.9% (22.6 mg) yield base on Cu(II) source.

[Cu(C14

H13

ClN2)Cl

2] (2). This compound

was prepared following the procedure described above for 1, except that 3,5-dimethyl-N-(2-py r i d y lme thy lene ) an i l i ne ( 42 . 0 mg , 0.2 mmol) was used instead of 4-bromo-N-(2-pyridylmethylene)aniline. Green block crystals of 2 were obtained in 68.4% (25.8 mg) yield base on Cu (II) source.

X-ray crystallographySuitable single crystals of complexes 1 and

2 were carefully picked under an optical microscope and then glued to thin glass fibers. Crystallographic data collections for both complexes were performed on a Bruker D8 QUEST CMOS diffractometer with graphite-monochromated MoKα radiation (λ = 0.71073 Å) at 296(2) K. Empirical absorption corrections were made using the SADABS program (7). The structures were solved using direct methods and refined on F2 using the SHELXTL (8). All non-hydrogen atoms were refined anisotropically, and hydrogen atoms attached to carbon atoms were fixed at their ideal positions. The crystal data of 1 and 2 are summarized in Table 1, and selected bond lengths and angles are listed in Table 2.


Crystallographic data (excluding structure factors) of both complexes have been deposited with the Cambridge Crystallographic Data Centre, CCDC, 12 Union Road, Cambridge CB21EZ, UK. Copies of the data can be obtained free of charge

Table 1. Crystal data and structure refinements for complexes 1 and 2.Compound 1 2

Empirical formula C12H

9BrCl

2CuN

2C

14H

13Cl

3CuN

2Formula weight 395.56 373.11Temperature (K) 296(2) 296(2)Crystal habit/color Block/brown-green Block/greenCrystal size (mm) 0.24 × 0.24 × 0.24 0.18 × 0.30 × 0.30Crystal system Monoclinic MonoclinicSpace group P2

1/n P2

1/c

a (Å) 7.5632(4) 8.2533(3)b (Å) 13.6555(8) 23.8266(10)c (Å) 13.3348(8) 7.8807(4)β (°) 97.691(2) 100.4563(13)V (Å3) 1364.82(14) 1523.99(11)Z 4 4D

calc (Mg/m3) 1.925 1.626

µ (mm–1) 4.90 1.95Absorption correction Multi-scan Multi-scanT

min, T

max0.586, 0.746 0.617, 0.745

Reflections collected 18433 19251Independent reflections 3389 2902R

int0.028 0.056

Observed reflections [I > 2σ(I)] 2817 2322Restraints/parameters 0/163 0/183GOF on F2 1.03 1.05R

1, wR

2 [I > 2σ(I)] 0.031, 0.076 0.037, 0.089

R1, wR

2 [all data] 0.041, 0.072 0.053, 0.083

Δρmax

, Δρmin

(e Å−3) 0.86, −0.76 0.40, −0.37

on quoting the depository numbers CCDC 1055348 (1) and CCDC 1055349 (2) (Fax: +44-1223-336-033; E-Mail: [email protected], http://www.ccdc.cam.ac.uk).

Results and Discussion The complex 1 was prepared as brown-green block shaped crystal from the 1:1 reaction of CuCl

2 and 4-bromo-N-(2-pyridylmethylene)

aniline ligand in a mixture CH3CN/CH

2Cl

2 (1:1)

solution at room temperature. X-ray crystal

structure analysis at 296(2) K reveals that complex 1 belongs to the monoclinic system with a space group P2

1/n and features a dinuclear structure. As

shown in Figure 1a, the asymmetric unit of 1 contains one Cu(II) ion, one 4-bromo-N-(2-pyridylmethylene)aniline ligand and two


coordinated Cl atoms. The Cu1 center adopts a trigonal bipyramidal five coordinate geometry with two nitrogen atoms from Schiff base ligand and two chloride anions. The geometry is evaluated by the parameter, t = (β – α)/60, where α and β are the angles between the nitrogen and chloride ions forming the basal plane in trigonal bipyramidal geometry (N

1, Cl

1 and Cl

2, see Figure 1). Ideally,

(a) (b)Figure 1. Thermal ellipsoid plot of a fragment at the 50% probability level containing the asymmetric unit with atom numbering and coordination environments of the metal centers in 1 (a) and 2 (b). The labeling scheme A B C and D, applied for the phenyl rings are used to identify the rings in subsequent discussion. Symmetry codes: (i) −x, 1−y, 1−z.

The intra ligand N–C and C–C bond lengths have typical values, and are in agreement with those reported for related complexes of the 4-bromo-N-(2-pyridylmethylene)aniline ligand (11,12). The pyridine ring A and the phenyl ring B of the ligand are coplanar. The dihedral angle between two rings is 19.4(1)°. In the dinulclear unit, the separation

square pyramidal and trigonal bipyramidal geometries t are equal to 0 and 1, respectively (9). The calculated values of the t parameter for the Cu1 ion is equal to 0.8, suggesting that Cu1 geometry in 1 is trigonal bipyramidal. The bond lengths and bond angles in 1 (Table 2) are comparable to that found in the trigonal bipyramidal geometry of related copper(II) complex such as [Cu

2(C

14H

14N

2)2Cl

4]

(10).

between the two CuII atoms in 1 is 3.4678(6) Å. The self-assembly of the supramolecular structure 1 is the result of combinations of intermolecular forces including C−H···Cl and C−H···π interaction along with π–π stacking. These supramolecular interactions help to stabilize the assembly as well as increase the dimensionality of the structure.


Table 2. Selected bond lengths (Å) and bond angles (°) for complexes 1 and 2.1 2

Cu1–Cl1 2.2847(7) 2.2139(9)Cu1–Cl2 2.3085(6) 2.2095(9)Cu1–Cl2i 2.4155(7) 3.459(1)‡

Cu1–N1 2.066(2) 2.009(2)Cu1–N2 2.046(1) 2.026(2)Cu1···Cu1i 3.4678(6) 4.3443(8)

Cl1–Cu1–Cl2 93.83(3) 100.79(4)

Cl1–Cu1–Cl2i 120.29(3) 128.76(4)Cl1–Cu1–N1 118.89(6) 137.88(8)

Cl1–Cu1–N2 96.20(6) 97.85(7)Cl2–Cu1–Cl2i 85.57(2) 82.38(7)

Cl2–Cu1–N1 93.41(6) 96.89(7)

Cl2–Cu1–N2 169.92(6) 153.26(7)

Cl2i–Cu1–N1 120.75(6) 91.17(8)

Cl2i–Cu1–N2 90.22(6) 71.00(7)

N1–Cu1–N2 93.83(3) 81.58(9)

‡Intermolecular contact. Symmetry code: –x, 1–y, 1–z.

As shown in Figure 2, adjacent dinuclear complex is connected via weak C−H···Cl [C6···Cl1 = 3.717(3) Å; symmetry code: 1–x, 1–y, 1–z] and C−H···π hydrogen bonds [C···ring A = 3.402 Å; symmetry code: 1/2–x, 1/2+y, 3/2–z], leading to the formation of a two-dimensional supramolecular sheet along a axis. Further investigation of the packing structure found that there is significant weak π–π stacking between pyridine ring A and phenyl

ring B of ligands from neighboring dinuclear complex, Figure 3. The centroid-to-centroid distance and dihedral angle between the two aromatic rings is 3.854 Å and 19.4(1)°, respectively. This interaction plays important role to increase the dimensionality of the structure by connect the two-dimensional sheet into the three-dimensional supramolecular artchitectures.


Figure 3. View of the one-dimensional supramolecular chain of 1 generated by π···π interactions (dotted lines).

Figure 2. View of the two-dimensional supramolecular sheet of 1 showing two kinds of C−H···Cl and C−H···π interactions (dotted lines).


Using the same stoichiometric ratio of reactants and solvent as in 1, but with the ligand changed from 4-bromo-N-(2-pyridylmethylene)aniline to 3,5-dimethyl-N-(2-pyridylmethylene)aniline, green block shaped crystal of 2 was obtained. Surprisingly, aromatic halogenation of benzene ring at the 4’ position with chloride of 3,5-dimethyl-N-(2-pyridylmethy-lene)aniline ligand was observed. Complex 2 crystallize in the monoclinic system with P2

1/c. space group The

asymmetric unit contains one Cu(II) ion, one 4-chloro-3,5-dimethyl-N-(2-pyridylmethylene)aniline ligand and two coordinated Cl anions (Figure 1b). The Cu1 center has a four coordinate geometry formed by two N atoms of ligand and two Cl atoms. However, Cu1 center also weakly bonded by another Cl anion from adjacent molecule [Cu1···Cl2 = 3.021(1) Å] to give a dinuclear complex with a Cu···Cu separation of 3.468(1) Å. Therefore, each Cu1 center of the dinuclear fragment in 2 can be

described as a pseudo trigonal bipyramidal arrangement (t = 1.03). The bond lengths and bond angles around Cu1 center in 2 are in the normal range and comparable to those found in 1.

As shown in Figure 4, a one-dimensional supramolecular structure along the c axis of 2 is generated by C−H···Cl hydrogen bonding interactions between the C imine ligand and Cl atom [C6···Cl2 = 3.520(3) Å; symmetry code: 1+x, y, z], π···π stacking interactions between rings C and D of ligands [centroid–centroid distance = 3.989 Å, dihedral angle = 17.0(1)°], along with weak electrostatic Cu···Cl interactions [Cu1···Cl2 = 3.021(1) Å; symmetry code: –x, 1–y, 1–z]. Interestingly, as illustrated in Figure 5, the Cl···π interactions between Cl atom at the 4’ position on phenyl ligand [Cl3···ring D = 3.148(1) Å; symmetry code: x, 1/2–y, 1/2+z] are observed in 2. This interaction appears to provide some support to link the above mentioned chains into a three-dimensional network.

Figure 4. View of the one-dimensional supramolecular chain of 2 formed by C−H···Cl hydrogen bonds, π···π stacking and electrostatic Cu···Cl interactions (dotted lines).


Figure 5. View of Cl···π interaction between adjacent molecules in 2 which serve to connect the chains into a three-dimensional architecture.

ConclusionThe packing of complexes 1 and 2 show

that the presence of different functional groups on phenyl ring of the N-(2-pyridylmethylene)aniline backbone plays an active role in the intermolecular interactions. Nonclassical interactions involving C−H···Cl hydrogen bonding and π···π stacking interactions, contribute to the packing pattern for both complexes. Weak electrostatic Cu···Cl and Cl···π interactions are only observed in 2.

AcknowledgementsThis research was financially supported by

research career development grant (No. RSA5780056) from the Thailand Research Fund.


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Supramolecular interaction in copper(ll) complexes ...scijournal.hcu.ac.th/data/Supramolecular.pdfTable 1. Crystal data and structure refinements for complexes 1 and 2. Compound 1