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Influence of anions on decomposition of Schiff base ligand determines the structure and magnetic property of dinuclear copper(II) complexes
Accepted Manuscript Influence of Anions on Decomposition of Schiff base Ligand Determines the Structure and Magnetic Property of Dinuclear Copper (II) Complexes Lianke Wang, Yuanyuan Zhu, Zongquan Wu, Zirong Li, Hongping Zhou, Jieying Wu, Yupeng Tian PII: DOI: Reference:
S0277-5387(15)00458-1 http://dx.doi.org/10.1016/j.poly.2015.08.021 POLY 11489
To appear in:
Polyhedron
Received Date: Accepted Date:
31 May 2015 5 August 2015
Please cite this article as: L. Wang, Y. Zhu, Z. Wu, Z. Li, H. Zhou, J. Wu, Y. Tian, Influence of Anions on Decomposition of Schiff base Ligand Determines the Structure and Magnetic Property of Dinuclear Copper (II) Complexes, Polyhedron (2015), doi: http://dx.doi.org/10.1016/j.poly.2015.08.021
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Influence of Anions on Decomposition of Schiff base Ligand Determines the Structure and Magnetic Property of Dinuclear Copper (II) Complexes Lianke Wanga, Yuanyuan Zhuc, Zongquan Wuc, Zirong Lib*, Hongping Zhoua*, Jieying Wua, Yupeng Tiana a
College of Chemistry and Chemical Engineering, Anhui University, Hefei 230601, P. R. China. Corresponding author Tel.: +86-551-63861259, Fax: +86-551-63861259. E-mail address: [email protected].
b
College of Food and Drug, Anhui Science and Technology University, Fengyang 233100, P. R. China. Tel: +86-550-6733103, Fax: +86-550-6733103. E-mail: [email protected].
c
College of Chemistry and Chemical Engineering, Hefei University of Technology, Hefei 230009, P. R. China.
Abstract Two dinuclear copper (II) complexes (1 and 2) with similar coordination modes, supported by the phenylbenzoxazole system, were synthesized by the self-assembly of the (E) 2-hydroxy-4-[4'-(benzoxazolyl)]benzylideneimine (L) with cupric acetate and cupric chloride, respectively. The X-ray single crystal analysis demonstrates that the copper atom both in 1 and 2 is five-coordinated and features a distorted pyramidal geometry. 2 show a novel dicopper-dichlorine two dimensional coordination polymer with the CuII-Cl-CuII structural motif, while 1 is dicopper-dioxygen complex with the CuII-O-CuII substrate. Magnetic property of 2 indicates antiferromagnetic (AF) coupling between two identical Cu2+ ions and provides satisfactory fits for 2 in the temperature range 2-300 K with the following parameters: J = -2.68 cm-1, g1 = g2 = 2.15. These results indicate that the anion will influence the stability of Schiff base ligand, which further influence the various architectures and magnetic property of coordination complexes. Keywords: Schiff bases, Dinuclear copper complex, Crystal structure, Magnetic property
1. Introduction
Investigation of multinuclear copper complexes or coordination polymers has grown into an intense area of research in coordination chemistry, in a large part because of their interesting network topologies and diverse structures, as well as their potential applications as materials.[1] So far, many supramolecular 1
copper complexes with specific topologies and excellent properties have been synthesized by assembly of copper salts and organic ligands.[2,4,5] The copper (II) ion with soft Lewis acid[3], adopts different coordination modes, such as three-[4], four-[1e,5,8], five-[4b,5b,6,8] or six-coordination[2c,7,8] modes according to the specific structures. Organic ligands with N- or O-donors, as effective building blocks, are also play important roles in the construction of copper complexes.[6b,10] Among the N-donors, imidazolyl, triazolyl and pyridyl ligands have been intensively engaged in the formation of complexes associated with interesting structures, topologies and properties in our systematic studies.[8,10a,11] Benzoxazolecontaining ligands with pyridyl group have been used to construct complexes with excellent properties.[12] Phenylbenzoxazole systems often were used to coordinate with iridium (III), ruthenium (II) and rhenium (II) ions,[13] and rarely coordinate with copper (II) ions. The introduction of different anions can also have a significant effect on the structural construction and properties of complexes.[8] Acetate and halogen ions have been widely used in the construction of copper complexes because they can adjust the topologies of complexes
through
different
coordination
modes
and
non-covalent
interactions.[6b,9]
Scheme 1. The molecular structure of ligand L and Lʹ. According to our previous work,[14] we develop the ligand L coordinate with different copper (II) salts to construct new phenylbenzoxazole-based coordination complexes with fascinating structure and properties (Scheme 1). In this study, we report the crystal structures and magnetic properties of two novel
dinuclear
copper
(II)
coordination
complexes
based
on
phenylbenzoxazole system and illustrate the importance of anions in the crystal structure and property of copper complexes. The detailed structure and 2
properties are discussed as follow. 2. Experimental 2.1. Material and Methods All starting materials, including chemicals and solvents, are commercially available at analytical grade and were used as received without further purification. Elemental analyses were carried out on Vario EL III element analyzer. IR spectra were recorded with a Nicolet NEXUS-870 FT-IR spectrometer (KBr discs) in the 4000-400 cm-1 region. The magnetic data of compounds were measured with a Quantum Design MPMS-XL5 SQUID system. The experimental susceptibility data were corrected for diamagnetism (Pascal’s parameters) and background by experimental measurement on the sample holder. 2.2 Crystal structure determinations The X-ray diffraction measurements were performed on a Bruker SMART CCD area detector using graphite monochromated MoK radiation (λ = 0.71069 Å) at 296 (2) K. Intensity data were collected in the variable ω-scan mode. The structures were solved by direct methods and difference Fourier syntheses. The non-hydrogen atoms were refined anisotropically and hydrogen atoms were introduced geometrically. Calculations were performed with SHELXTL-97 program package. Crystallographic data (excluding structure factors) for the structures reported in this paper have been deposited with the Cambridge Crystallographic Data Centre as supplementary publication no. CCDC: 1020487-1020488. 2.3 Synthesis The ligands were prepared according to our previous work [14]. 1. The methanol solution (10 mL) of Cu(OAc)2·H2O (0.10 g, 0.5 mmol) was slowly added into the solution of ligand L (0.15 g, 0.5 mmol) in dichloromethane (10 mL) and the product was obtained by slow interlayer diffusion at room temperature, respectively. We single out the black block single crystals of 1 under microscope and the crystals are characterized by single crystal X-ray diffraction analyses. Yield: 0.08 g (46.38%). C80H52Cu2N8O8 (1380.38): calcd. C 69.55, H 3.77, O 9.27, N 8.11. Found: C 69.78, H 3.52, O 9.45, N 8.28. IR ν (cm-1): 3046.55 (w), 3018.24 (w), 3
2927.13 (w), 1607.01 (vs), 1585.2 (s), 1540.31 (s), 1493.23 (m), 1466.36 (vs), 1446.39 (vs), 1417.56 (m), 1377.01 (m), 1348.05 (m), 1326.58 (s), 1242.73 (m), 1177.05 (s), 1155.35 (m), 1126.05 (w), 1061.85 (m), 1032.08 (w), 1013.17 (w), 861.43 (m), 850.75 (m), 761.73 (s), 739.23 (s), 702.38 (m). 2. The black block crystal 2 was prepared according to a similar procedure of complex 1 using CuCl2·2H2O (0.09 g, 0.5 mmol) instead of Cu(OAc)2·H2O. Yield: 0.09 g (52.22%). C13H10Cl2CuN2O (344.67): calcd. C 45.26, H 2.90, O 4.64, N 8.12. Found: C 45. 43, H 2.67, O 4.83, N 8.33. IR ν (cm-1): 3314.43 (s), 3243.01(s), 3143.79 (m), 2923.84 (w), 1607.76 (vs), 1583.20 (m), 1552.04 (m), 1550.95 (s), 1477.08 (m), 1459.05 (s), 1437.24 (m), 1349.44 (m), 1327.83 (w), 1295.06 (w), 1281.94 (w), 1254.48 (m), 1240.14 (m), 1181.90 (m), 1091.12 (s), 1028.51 (vs), 865.18 (w), 833.45 (w), 799.53 (m), 765.03 (vs), 693.77 (m). 3. Results and Discussion The reaction of ligand L with CuX2 (CuCl2 and Cu(OAc)2) lead to the formation of two different complex 1 and 2. Single crystals for X-ray crystallography were obtained by slow interlayer diffusion at room temperature for a couple of days. The crystallographic data and the geometrical parameters of the hydrogen bonds of 1-2 are summarized in Table 1 and 3, respectively. The selected bond lengths and angles data are tabulated in Table 2, which includes the τ5 value (Table 4), which provides an easy determination of the coordination mode around the metal centre.[15] 3.1 Structure of Dicopper-dioxygen complex (1). Complex 1 crystalizes in the monoclinic system, space group P21/a, with one independent molecule in the unit cell, and its single-crystal X-ray analysis reveals that it is a neoteric oxygen-bridged dinuclear Cu(II) complex formulated as [Cu2[L-H]4], where the metal ion Cu(II) bridged by two deprotonated ligand [L-H]¯. The distance of dinuclear center is 3.336 Å. The molecular structure of the complex 1 is shown in Figure 1a, the copper (II) center is five-coordinated to three oxygen atoms from four phenolic hydroxyl groups and two nitrogen atoms from two azomethine groups. In 4
addition, the oxygen atoms in two ligands as bridged auxiliary ligand are two-coordinated by two copper atoms, where the two Cu (II) and two oxygen atoms compose of a parallelogram, the oxygen atoms in other two ligands are one-coordinated with one Cu (II) ion. The bond lengths of Cu-N (Cu1-N2 2.040(4) Å, Cu1-N3 2.047(4) Å,) and Cu-O (Cu1-O3 1.881(3) Å, Cu1-O2 1.919(3) Å, Cu1-O2#1 2.431(3) Å, O2-Cu1#1 2.431(3) Å) are analogous to that of other copper complex systems.[6,9,16] According to the angles around copper centers, τ5 values is 0.10, thereby resulting in a very slightly distorted square pyramidal geometry. Table 1. Crystallographic data for 1-2. compound empirical formula formula weight crystal system space group a [Å] b [Å] c [Å] α [°] β [°] γ [°] V [Å3] Z T [K] Dcalcd[g ·cm-3 ] µ [mm-1] θ range [°] total no. data no.unique data no. params refined R1 wR2 GOF
1 C80H52Cu2N8O8 1380.38 Monoclinic P 21/c 17.333(5) 11.673(5) 15.570(5) 90.000(5) 100.280(5) 90.000(5) 3099.7(19) 2 296(2) 1.479 0.757 1.19-25.00 21818 5455 442 0.0536 0.1437 1.012
2 C13H10Cl2CuN2O 344.67 Monoclinic P 21/n 11.432(5) 6.702(5) 16.473(5) 90.000(5) 92.932(5) 90.000(5) 1260.5(12) 4 296(2) 1.816 2.146 2.12-25.00 8420 2211 172 0.0246 0.0668 1.027
As shown in Figure 1b, the neighbouring complex molecules are linked by C-H···N hydrogen bonds (H36···N2 2.887(4) Å, H22···N1 2.614(4) Å) to form two dimensional supramolecular structures. The resulting two dimensional structures are joined into the three dimensional packing framework connected by many C-H···N 5
hydrogen bonds (H25···N4 2.894(4) Å, H22···N1 2.614(4) Å) and π···π (d = 3.275 Å) stacking interactions, as shown in Figure 1c. Table 2. Selected bond lengths (Å) and angles (°) for 1-2. C80H52Cu2N8O8 (1) Cu1-O3 1.881(3) Cu1-O2 1.919(3) Cu1-N2 2.040(4) Cu1-N3 2.047(4) #1 #1 Cu1-O2 2.431(3) O2-Cu1 2.431(3) O3-Cu1-O2 174.30(13) O3-Cu1-N2 85.62(15) O2-Cu1-N2 90.49(14) O3-Cu1-N3 89.54(15) O2-Cu1-N3 93.47(14) N2-Cu1-N3 167.95(15) #1 #1 O3-Cu1-O2 104.09(13) O2-Cu1-O2 80.51(12) N3-Cu1-O2#1 94.68(13) N2-Cu1-O2#1 97.20(12) C13H10Cl2CuN2O (2) Cu1-N2 2.022(2) Cu1-N1 2.064(2) Cu1-Cl2 2.2635(13) Cu1-Cl1 2.3148(12) N2-Cu1-N1 159.01(8) N2-Cu1-Cl2 90.64(7) N1-Cu1-Cl2 87.42(8) N2-Cu1-Cl1 91.65(7) Cl2-Cu1-Cl1 175.31(3) N1-Cu1-Cl1 91.90(8) a Symmetry transformations used to generate equivalent atoms: #1: -x+1, -y, -z+2 . 3.2 Structure of Dicopper-dichlorine coordination polymer (2). When ligand L reacts with CuCl2, a new product may be crystallized in the form of black colored block 2. The single-crystal diffraction analysis reveals that complex 2 crystalizes in a monoclinic system and space group P21/n. The molecular structure with numbering scheme of 2 is given in Figure 2a, which shows that the azomethine groups decompose into amino, and the copper (II) center is five-coordinated, bound with amino and benzoxazolyl nitrogen atoms from different ligands. At the same time, the two copper (II) centers are bridged by two chlorine atoms that act as bridged auxiliary ligands to form a rhombus-like diagram, and the distance of dinuclear center is 3.919 Å. The bond angles of N-Cu-N, N-Cu-Cl and Cl-Cu-Cl (Table 2) demonstracte that the τ5 values is 0.27, which indicate the copper center and coordination atoms generate a distorted square pyramidal geometry. The bond lengths of Cu-N (Cu1-N1 2.064(2) Å, Cu1-N2 2.022(2) Å) and Cu-Cl (Cu1-Cl1 2.3148(12) Å, Cu1-Cl2 2.2635(13) Å) and bond angles around copper centers are within the range of
6
values previously observed for related copper coordination compounds.[17] In a word, complex 2 features a specific dicopper-dichlorine coordination complex. (a)
(b)
(c)
Figure 1. (a) Molecular structure of 1, (b) Two dimensional supramolecular structure of 1, (c) Three dimensional supramolecular structure of 1. The colorized dotted lines represent the weak interactions and hydrogen atoms not participating in hydrogen bonds are omitted for clarity. 7
(a)
(b)
(c)
Figure 2. (a) Molecular dinuclear units diagram of a representative part of the chain structure in 2, (b) the two dimensional polymeric structure of 2, (c) the three dimensional network of 2. The colorized dotted lines represent the weak interactions and hydrogen atoms not participating in hydrogen bonds are omitted for clarity. As depicted in Figure 2b, the decomposed p-benzoxazolyl-phenylamine (L′) acts as head-to-tail linker bridging two identical copper (II). Such a connection between dimetallic units produces a two dimensional polymeric structure through the coordination bonds Cu-O and Cu-Cl. In addition, there exists multiple intramolecular 8
hydrogen bonds, such as C-H···Cl (H1···Cl1 2.934(1) Å, H13···Cl1 2.919(1) Å), C-H···O (H9···O1 2.326(2) Å), N-H···Cl (H1A···Cl1 2.750(2) Å, H1A···Cl2 2.667(1) Å) and C-H···N (H13···N2 2.870(2) Å), which are also in favor of the formation of the two dimensional polymeric structure. These two dimensional structures are further packed together to form three dimensional supramolecular network structure (Figure 2c) through intermolecular π···π weak interaction (d = 3.310 Å) between two different oxazolyl groups. Table 3. The intermolecular and intramolecular bond lengths (Å) and angles (°) for 1-2. D-H···A C31-H31···O2 C12-H12···O3 C9-H9···O1 C30-H30···N4 C29-H29···O4 C13-H13···N1 C12-H12···O2 C25-H25···N4 C22-H22···N1 C36-H36···N2 N1-H1A···Cl2 C1-H1···Cl1 N1-H1A···Cl1 C13-H13···N2 C9-H9···O1 C13-H13···Cl1
d(D-H) Å
d(D-A) Å C80H52Cu2N8O8 (1) 0.930(.005) 2.964(.005) 0.930(.005) 2.908(.005) 0.930(.005) 2.852(.007) 0.930(.005) 2.894(.007) 0.930(.005) 2.889(.006) 0.930(.005) 2.915(.007) 0.930(.005) 3.700(.006) 0.930(.005) 3.820(.007) 0.930(.005) 3.539(.007) 0.930(.005) 3.706(.006) C13H10Cl2CuN2O (2) 0.900(.002) 2.994(.002) 0.930(.003) 3.722(.003) 0.900(.002) 3.564(.003) 0.930(.002) 3.111(.003) 0.930(.002) 2.686(.003) 0.930(.003) 3.560(.003)
d(H···A) Å
∠DHA °
2.665(.003) 2.874(.003) 2.549(.004) 2.603(.004) 2.590(.004) 2.628(.004) 2.898(.003) 2.894(.004) 2.614(.004) 2.887(.004)
99.48(0.32) 82.82( 0.31) 99.38( 0.34) 98.73( 0.32) 99.19( 0.33) 98.50( 0.33) 145.19( 0.30) 173.90( 0.35) 173.14( 0.37) 147.57( 0.34)
2.667(.001) 2.934(.001) 2.750(.002) 2.870(.002) 2.326(.002) 2.919(.001)
102.55( 0.13) 143.35( 0.16) 151.02( 0.13) 96.25( 0.15) 102.54( 0.16) 127.24( 0.15)
3.3 Reaction Mechanism and Structural Comparison. According to the above mentioned discussion of crystal structure of 1-2, we speculate and summarize the reaction mechanism. The formation of 1 shows that the phenolic hydroxyl group of L lose a proton under the help of strongly basic acetate ion, and the resulting [L-H]¯ coordinates with Lewis acidic Cu2+ ion to produce complex 1. The synthetic routes are shown in equilibrium equation (1) in Scheme 2. Different from Cu(OAc)2, the solution of CuCl2 shows weakly acidic, which lead to 9
the formation of hydronium ions (H3O+). The processes of electrophilic attack of H3O+ ions to the azomethine groups and the deprotonation in ligand L generate the intermediate hydramine C through the transformation of intermediate A and B, as depicted in equation (2) in Scheme 2. The intermediate hydramine C is easy to combine H+ ion to further decompose to p-benzoxazolyl-phenylamine(L') and salicylaldehyde through the intramolecular charge transfer and deprotonation in intermediate D. Then the new ligand L' coordinates with CuCl2 yielded coordination polymer 2. We obtained the same coordination mode and crystal structure comparing with complex 2 in the coordination process of L' with CuCl2, which proves the fact that two-dimensional coordination polymer 2 was obtained through the ligand L' coordinates with CuCl2 in the self-assembly reaction of ligand L with CuCl2 at the room temperature. Table 4. Five-coordinate geometry indices for 1-2 Compound 1 2
τ5[15] 0.10 0.27
Geometry square pyramidal square pyramidal
τ5 : Addison and Reedijk’s five-coordinate structural index.[15] ߬ହ =
ఉି
.
α, β : the two largest bond angles in the five-coordinate complex.
Scheme 2. The synthetic routes and reaction mechanism of 1-2. According to the crystal structures of complexes, the dinuclear center in complex
10
1 and 2 displays similar coordination mode, but 2 exhibits two dimensional coordination polymer complex that is more fascinating than 1. Firstly, the metallic coordinated polymer itself is more interesting than metal complex. Meanwhile, the nitrogen atoms in new ligand L' both coordinate with copper atoms, which improves the utilization ratio of nitrogen atoms of ligand. Finally, complex 2 provide a more stable two dimensional structure, which offer a better foundation in some potential application areas. In addition, the distance of dicopper center in 2 is larger than that in 1, which is caused by the bigger radius of auxiliary chlorine atoms than oxygen atoms. Consequently, the acidity of system will influence the stability of Schiff base ligand and further the various structures of the resulting complexes.
Figure 3. Plots of temperature dependence of χMT and χM under 1 kOe dc field of 2. Blue and red solid line is the best fit by PHI from 2-300 K.
Figure 4. Plots of temperature dependence of χM-1 under 1 kOe dc field of 2. The solid red lines are the linear fitted results. 11
Figure 5. Isothermal magnetization for 2 from 0 to 5 T at 2.0 K. 3.4 Magnetic Property. The magnetic measurements were performed on polycrystalline sample of complexes of 1 and 2 using Quantum-Design MPMS XL-5 SQUID magnetometer. Variable-temperature magnetic susceptibility measurement was performed from 2 to 300 K. Complex 2 performs obvious magnetic property. The χMT and χM versus T plot of 2 under an applied static field of 1000 Oe is shown in Figure 3 (χM is the molar magnetic susceptibility per binuclear molecule). The χMT value at room temperature is equal to 0.87 cm3 mol-1 K, which is slightly higher than that expected for two uncoupled Cu2+ ions (χMT = 0.375 cm3 mol-1 K for an S = 1/2 ion with g = 2.00). The χMT value decreases upon cooling and drops very qiuckly below 25 K. It downs to 0.18 cm3 mol-1 K at 2 K. The magnetic susceptibility data in the range of 5-300 K obeys the Curie-Weiss law, χM = C/(T − θ). The linear fitting of the χM-1 versus T plots gives the Curie constant C = 0.88 cm3 mol-1 K and Weiss constant θ = −4.00 K (Figure 4). The negative Weiss value indicated the antiferromagnetic (AF) coupling between two identical Cu2+ ions. The χM value increases continuously upon cooling and a peak is observed at 3.5 K. It suggests the presence of possible antiferromagnetic ordering in the low temperature (Figure 3). The field dependence of the magnetization measured at 2.0 K increases linearly with the increased dc field. The molar magnetization at 50 kOe is only 0.85 Nβ (the unit of magnetization) (Figure 5), far from the saturation value (2 Nβ for S = 1 when g factor is taken equal to 2.00). It is also the evidence of antiferromagnetic interaction existing in this complex. The 12
magnetic data fitted by PHI program [18] in the temperature range 2-300 K gives J = -2.68 cm-1, g1 = g2 = 2.15. Overall, the Cl-bridge in 2 leads to an antimagnetic coupling interaction, which is identical to some reported bi- and polynuclear copper complexes with Cl anion as bridge.[19] 4 Conclusions In this paper, we present two novel dicopper(II) center coordination complexes with five coordination mode based on benzoxazolyl system. Complex 2 is a very rare dicopper-dichlorine two dimensional coordination polymer with the CuII-Cl-CuII structural motif and 1 is a dicopper-dioxygen complex with CuII-O-CuII substrate, which demonstrates that the anion induces the diverse architectures of copper complexes. Magnetic studies indicate that there exists the antiferromagnetic interaction in 2. The magnetic susceptibility data in the range of 5-300 K obeys the Curie-Weiss law and the magnetic data fitted by PHI program in the 2-300 K range provides the following parameters : J = -2.68 cm-1, g1 = g2 = 2.15. These results demonstrate that the anion will influence the structure of Schiff base ligand, which further influence the various architectures and magnetic property of resulting complexes. Acknowledgements This work was supported by the Program for New Century Excellent Talents in University (China), the Doctoral Program Foundation of the Ministry of Education of China (20113401110004), the National Natural Science Foundation of China (21271003, 21271004, 51432001 and 51472002), the 211 Project of Anhui University, Higher Education Revitalization Plan Talent Project of (2013) and the Ministry of Education Funded Projects Focus on Returned Overseas Scholar. Appendix A. Supplementary data CCDC 1020487 and 1020488 contain the supplementary crystallographic data for the complexes 1 and 2. These data can be obtained free of charge via http://www.ccdc.cam.ac.uk/conts/retrieving.html,
or
from
the
Cambridge
Crystallographic Data Centre, 12 Union Road, Cambridge CB2 1EZ, UK; fax: (+44) 1223-336-033; or e-mail: [email protected]. 13
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[19](a) R. J. Butcher, J. W. Overman, E. Sinn, J. Am. Chem. Soc., 102 (1980), 3276-3278. (b) S. Mondal, S. Naskar, A. K. Dey, E. Sinn, C. Eribal, S. R. Herron and S. K. Chattopadhyay, Inorg. Chim. Acta, 398 (2013), 98-105.
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Highlights 1. Microwave irradiation was classified into atmospheric and high pressure treatment 2. Microwave pretreatment reactors were introduced 3. Advantage, disadvantage and prospect on microwave treatment were summarized
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Graphical abstract
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S0277-5387(15)00458-1 http://dx.doi.org/10.1016/j.poly.2015.08.021 POLY 11489
To appear in:
Polyhedron
Received Date: Accepted Date:
31 May 2015 5 August 2015
Please cite this article as: L. Wang, Y. Zhu, Z. Wu, Z. Li, H. Zhou, J. Wu, Y. Tian, Influence of Anions on Decomposition of Schiff base Ligand Determines the Structure and Magnetic Property of Dinuclear Copper (II) Complexes, Polyhedron (2015), doi: http://dx.doi.org/10.1016/j.poly.2015.08.021
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Influence of Anions on Decomposition of Schiff base Ligand Determines the Structure and Magnetic Property of Dinuclear Copper (II) Complexes Lianke Wanga, Yuanyuan Zhuc, Zongquan Wuc, Zirong Lib*, Hongping Zhoua*, Jieying Wua, Yupeng Tiana a
College of Chemistry and Chemical Engineering, Anhui University, Hefei 230601, P. R. China. Corresponding author Tel.: +86-551-63861259, Fax: +86-551-63861259. E-mail address: [email protected].
b
College of Food and Drug, Anhui Science and Technology University, Fengyang 233100, P. R. China. Tel: +86-550-6733103, Fax: +86-550-6733103. E-mail: [email protected].
c
College of Chemistry and Chemical Engineering, Hefei University of Technology, Hefei 230009, P. R. China.
Abstract Two dinuclear copper (II) complexes (1 and 2) with similar coordination modes, supported by the phenylbenzoxazole system, were synthesized by the self-assembly of the (E) 2-hydroxy-4-[4'-(benzoxazolyl)]benzylideneimine (L) with cupric acetate and cupric chloride, respectively. The X-ray single crystal analysis demonstrates that the copper atom both in 1 and 2 is five-coordinated and features a distorted pyramidal geometry. 2 show a novel dicopper-dichlorine two dimensional coordination polymer with the CuII-Cl-CuII structural motif, while 1 is dicopper-dioxygen complex with the CuII-O-CuII substrate. Magnetic property of 2 indicates antiferromagnetic (AF) coupling between two identical Cu2+ ions and provides satisfactory fits for 2 in the temperature range 2-300 K with the following parameters: J = -2.68 cm-1, g1 = g2 = 2.15. These results indicate that the anion will influence the stability of Schiff base ligand, which further influence the various architectures and magnetic property of coordination complexes. Keywords: Schiff bases, Dinuclear copper complex, Crystal structure, Magnetic property
1. Introduction
Investigation of multinuclear copper complexes or coordination polymers has grown into an intense area of research in coordination chemistry, in a large part because of their interesting network topologies and diverse structures, as well as their potential applications as materials.[1] So far, many supramolecular 1
copper complexes with specific topologies and excellent properties have been synthesized by assembly of copper salts and organic ligands.[2,4,5] The copper (II) ion with soft Lewis acid[3], adopts different coordination modes, such as three-[4], four-[1e,5,8], five-[4b,5b,6,8] or six-coordination[2c,7,8] modes according to the specific structures. Organic ligands with N- or O-donors, as effective building blocks, are also play important roles in the construction of copper complexes.[6b,10] Among the N-donors, imidazolyl, triazolyl and pyridyl ligands have been intensively engaged in the formation of complexes associated with interesting structures, topologies and properties in our systematic studies.[8,10a,11] Benzoxazolecontaining ligands with pyridyl group have been used to construct complexes with excellent properties.[12] Phenylbenzoxazole systems often were used to coordinate with iridium (III), ruthenium (II) and rhenium (II) ions,[13] and rarely coordinate with copper (II) ions. The introduction of different anions can also have a significant effect on the structural construction and properties of complexes.[8] Acetate and halogen ions have been widely used in the construction of copper complexes because they can adjust the topologies of complexes
through
different
coordination
modes
and
non-covalent
interactions.[6b,9]
Scheme 1. The molecular structure of ligand L and Lʹ. According to our previous work,[14] we develop the ligand L coordinate with different copper (II) salts to construct new phenylbenzoxazole-based coordination complexes with fascinating structure and properties (Scheme 1). In this study, we report the crystal structures and magnetic properties of two novel
dinuclear
copper
(II)
coordination
complexes
based
on
phenylbenzoxazole system and illustrate the importance of anions in the crystal structure and property of copper complexes. The detailed structure and 2
properties are discussed as follow. 2. Experimental 2.1. Material and Methods All starting materials, including chemicals and solvents, are commercially available at analytical grade and were used as received without further purification. Elemental analyses were carried out on Vario EL III element analyzer. IR spectra were recorded with a Nicolet NEXUS-870 FT-IR spectrometer (KBr discs) in the 4000-400 cm-1 region. The magnetic data of compounds were measured with a Quantum Design MPMS-XL5 SQUID system. The experimental susceptibility data were corrected for diamagnetism (Pascal’s parameters) and background by experimental measurement on the sample holder. 2.2 Crystal structure determinations The X-ray diffraction measurements were performed on a Bruker SMART CCD area detector using graphite monochromated MoK radiation (λ = 0.71069 Å) at 296 (2) K. Intensity data were collected in the variable ω-scan mode. The structures were solved by direct methods and difference Fourier syntheses. The non-hydrogen atoms were refined anisotropically and hydrogen atoms were introduced geometrically. Calculations were performed with SHELXTL-97 program package. Crystallographic data (excluding structure factors) for the structures reported in this paper have been deposited with the Cambridge Crystallographic Data Centre as supplementary publication no. CCDC: 1020487-1020488. 2.3 Synthesis The ligands were prepared according to our previous work [14]. 1. The methanol solution (10 mL) of Cu(OAc)2·H2O (0.10 g, 0.5 mmol) was slowly added into the solution of ligand L (0.15 g, 0.5 mmol) in dichloromethane (10 mL) and the product was obtained by slow interlayer diffusion at room temperature, respectively. We single out the black block single crystals of 1 under microscope and the crystals are characterized by single crystal X-ray diffraction analyses. Yield: 0.08 g (46.38%). C80H52Cu2N8O8 (1380.38): calcd. C 69.55, H 3.77, O 9.27, N 8.11. Found: C 69.78, H 3.52, O 9.45, N 8.28. IR ν (cm-1): 3046.55 (w), 3018.24 (w), 3
2927.13 (w), 1607.01 (vs), 1585.2 (s), 1540.31 (s), 1493.23 (m), 1466.36 (vs), 1446.39 (vs), 1417.56 (m), 1377.01 (m), 1348.05 (m), 1326.58 (s), 1242.73 (m), 1177.05 (s), 1155.35 (m), 1126.05 (w), 1061.85 (m), 1032.08 (w), 1013.17 (w), 861.43 (m), 850.75 (m), 761.73 (s), 739.23 (s), 702.38 (m). 2. The black block crystal 2 was prepared according to a similar procedure of complex 1 using CuCl2·2H2O (0.09 g, 0.5 mmol) instead of Cu(OAc)2·H2O. Yield: 0.09 g (52.22%). C13H10Cl2CuN2O (344.67): calcd. C 45.26, H 2.90, O 4.64, N 8.12. Found: C 45. 43, H 2.67, O 4.83, N 8.33. IR ν (cm-1): 3314.43 (s), 3243.01(s), 3143.79 (m), 2923.84 (w), 1607.76 (vs), 1583.20 (m), 1552.04 (m), 1550.95 (s), 1477.08 (m), 1459.05 (s), 1437.24 (m), 1349.44 (m), 1327.83 (w), 1295.06 (w), 1281.94 (w), 1254.48 (m), 1240.14 (m), 1181.90 (m), 1091.12 (s), 1028.51 (vs), 865.18 (w), 833.45 (w), 799.53 (m), 765.03 (vs), 693.77 (m). 3. Results and Discussion The reaction of ligand L with CuX2 (CuCl2 and Cu(OAc)2) lead to the formation of two different complex 1 and 2. Single crystals for X-ray crystallography were obtained by slow interlayer diffusion at room temperature for a couple of days. The crystallographic data and the geometrical parameters of the hydrogen bonds of 1-2 are summarized in Table 1 and 3, respectively. The selected bond lengths and angles data are tabulated in Table 2, which includes the τ5 value (Table 4), which provides an easy determination of the coordination mode around the metal centre.[15] 3.1 Structure of Dicopper-dioxygen complex (1). Complex 1 crystalizes in the monoclinic system, space group P21/a, with one independent molecule in the unit cell, and its single-crystal X-ray analysis reveals that it is a neoteric oxygen-bridged dinuclear Cu(II) complex formulated as [Cu2[L-H]4], where the metal ion Cu(II) bridged by two deprotonated ligand [L-H]¯. The distance of dinuclear center is 3.336 Å. The molecular structure of the complex 1 is shown in Figure 1a, the copper (II) center is five-coordinated to three oxygen atoms from four phenolic hydroxyl groups and two nitrogen atoms from two azomethine groups. In 4
addition, the oxygen atoms in two ligands as bridged auxiliary ligand are two-coordinated by two copper atoms, where the two Cu (II) and two oxygen atoms compose of a parallelogram, the oxygen atoms in other two ligands are one-coordinated with one Cu (II) ion. The bond lengths of Cu-N (Cu1-N2 2.040(4) Å, Cu1-N3 2.047(4) Å,) and Cu-O (Cu1-O3 1.881(3) Å, Cu1-O2 1.919(3) Å, Cu1-O2#1 2.431(3) Å, O2-Cu1#1 2.431(3) Å) are analogous to that of other copper complex systems.[6,9,16] According to the angles around copper centers, τ5 values is 0.10, thereby resulting in a very slightly distorted square pyramidal geometry. Table 1. Crystallographic data for 1-2. compound empirical formula formula weight crystal system space group a [Å] b [Å] c [Å] α [°] β [°] γ [°] V [Å3] Z T [K] Dcalcd[g ·cm-3 ] µ [mm-1] θ range [°] total no. data no.unique data no. params refined R1 wR2 GOF
1 C80H52Cu2N8O8 1380.38 Monoclinic P 21/c 17.333(5) 11.673(5) 15.570(5) 90.000(5) 100.280(5) 90.000(5) 3099.7(19) 2 296(2) 1.479 0.757 1.19-25.00 21818 5455 442 0.0536 0.1437 1.012
2 C13H10Cl2CuN2O 344.67 Monoclinic P 21/n 11.432(5) 6.702(5) 16.473(5) 90.000(5) 92.932(5) 90.000(5) 1260.5(12) 4 296(2) 1.816 2.146 2.12-25.00 8420 2211 172 0.0246 0.0668 1.027
As shown in Figure 1b, the neighbouring complex molecules are linked by C-H···N hydrogen bonds (H36···N2 2.887(4) Å, H22···N1 2.614(4) Å) to form two dimensional supramolecular structures. The resulting two dimensional structures are joined into the three dimensional packing framework connected by many C-H···N 5
hydrogen bonds (H25···N4 2.894(4) Å, H22···N1 2.614(4) Å) and π···π (d = 3.275 Å) stacking interactions, as shown in Figure 1c. Table 2. Selected bond lengths (Å) and angles (°) for 1-2. C80H52Cu2N8O8 (1) Cu1-O3 1.881(3) Cu1-O2 1.919(3) Cu1-N2 2.040(4) Cu1-N3 2.047(4) #1 #1 Cu1-O2 2.431(3) O2-Cu1 2.431(3) O3-Cu1-O2 174.30(13) O3-Cu1-N2 85.62(15) O2-Cu1-N2 90.49(14) O3-Cu1-N3 89.54(15) O2-Cu1-N3 93.47(14) N2-Cu1-N3 167.95(15) #1 #1 O3-Cu1-O2 104.09(13) O2-Cu1-O2 80.51(12) N3-Cu1-O2#1 94.68(13) N2-Cu1-O2#1 97.20(12) C13H10Cl2CuN2O (2) Cu1-N2 2.022(2) Cu1-N1 2.064(2) Cu1-Cl2 2.2635(13) Cu1-Cl1 2.3148(12) N2-Cu1-N1 159.01(8) N2-Cu1-Cl2 90.64(7) N1-Cu1-Cl2 87.42(8) N2-Cu1-Cl1 91.65(7) Cl2-Cu1-Cl1 175.31(3) N1-Cu1-Cl1 91.90(8) a Symmetry transformations used to generate equivalent atoms: #1: -x+1, -y, -z+2 . 3.2 Structure of Dicopper-dichlorine coordination polymer (2). When ligand L reacts with CuCl2, a new product may be crystallized in the form of black colored block 2. The single-crystal diffraction analysis reveals that complex 2 crystalizes in a monoclinic system and space group P21/n. The molecular structure with numbering scheme of 2 is given in Figure 2a, which shows that the azomethine groups decompose into amino, and the copper (II) center is five-coordinated, bound with amino and benzoxazolyl nitrogen atoms from different ligands. At the same time, the two copper (II) centers are bridged by two chlorine atoms that act as bridged auxiliary ligands to form a rhombus-like diagram, and the distance of dinuclear center is 3.919 Å. The bond angles of N-Cu-N, N-Cu-Cl and Cl-Cu-Cl (Table 2) demonstracte that the τ5 values is 0.27, which indicate the copper center and coordination atoms generate a distorted square pyramidal geometry. The bond lengths of Cu-N (Cu1-N1 2.064(2) Å, Cu1-N2 2.022(2) Å) and Cu-Cl (Cu1-Cl1 2.3148(12) Å, Cu1-Cl2 2.2635(13) Å) and bond angles around copper centers are within the range of
6
values previously observed for related copper coordination compounds.[17] In a word, complex 2 features a specific dicopper-dichlorine coordination complex. (a)
(b)
(c)
Figure 1. (a) Molecular structure of 1, (b) Two dimensional supramolecular structure of 1, (c) Three dimensional supramolecular structure of 1. The colorized dotted lines represent the weak interactions and hydrogen atoms not participating in hydrogen bonds are omitted for clarity. 7
(a)
(b)
(c)
Figure 2. (a) Molecular dinuclear units diagram of a representative part of the chain structure in 2, (b) the two dimensional polymeric structure of 2, (c) the three dimensional network of 2. The colorized dotted lines represent the weak interactions and hydrogen atoms not participating in hydrogen bonds are omitted for clarity. As depicted in Figure 2b, the decomposed p-benzoxazolyl-phenylamine (L′) acts as head-to-tail linker bridging two identical copper (II). Such a connection between dimetallic units produces a two dimensional polymeric structure through the coordination bonds Cu-O and Cu-Cl. In addition, there exists multiple intramolecular 8
hydrogen bonds, such as C-H···Cl (H1···Cl1 2.934(1) Å, H13···Cl1 2.919(1) Å), C-H···O (H9···O1 2.326(2) Å), N-H···Cl (H1A···Cl1 2.750(2) Å, H1A···Cl2 2.667(1) Å) and C-H···N (H13···N2 2.870(2) Å), which are also in favor of the formation of the two dimensional polymeric structure. These two dimensional structures are further packed together to form three dimensional supramolecular network structure (Figure 2c) through intermolecular π···π weak interaction (d = 3.310 Å) between two different oxazolyl groups. Table 3. The intermolecular and intramolecular bond lengths (Å) and angles (°) for 1-2. D-H···A C31-H31···O2 C12-H12···O3 C9-H9···O1 C30-H30···N4 C29-H29···O4 C13-H13···N1 C12-H12···O2 C25-H25···N4 C22-H22···N1 C36-H36···N2 N1-H1A···Cl2 C1-H1···Cl1 N1-H1A···Cl1 C13-H13···N2 C9-H9···O1 C13-H13···Cl1
d(D-H) Å
d(D-A) Å C80H52Cu2N8O8 (1) 0.930(.005) 2.964(.005) 0.930(.005) 2.908(.005) 0.930(.005) 2.852(.007) 0.930(.005) 2.894(.007) 0.930(.005) 2.889(.006) 0.930(.005) 2.915(.007) 0.930(.005) 3.700(.006) 0.930(.005) 3.820(.007) 0.930(.005) 3.539(.007) 0.930(.005) 3.706(.006) C13H10Cl2CuN2O (2) 0.900(.002) 2.994(.002) 0.930(.003) 3.722(.003) 0.900(.002) 3.564(.003) 0.930(.002) 3.111(.003) 0.930(.002) 2.686(.003) 0.930(.003) 3.560(.003)
d(H···A) Å
∠DHA °
2.665(.003) 2.874(.003) 2.549(.004) 2.603(.004) 2.590(.004) 2.628(.004) 2.898(.003) 2.894(.004) 2.614(.004) 2.887(.004)
99.48(0.32) 82.82( 0.31) 99.38( 0.34) 98.73( 0.32) 99.19( 0.33) 98.50( 0.33) 145.19( 0.30) 173.90( 0.35) 173.14( 0.37) 147.57( 0.34)
2.667(.001) 2.934(.001) 2.750(.002) 2.870(.002) 2.326(.002) 2.919(.001)
102.55( 0.13) 143.35( 0.16) 151.02( 0.13) 96.25( 0.15) 102.54( 0.16) 127.24( 0.15)
3.3 Reaction Mechanism and Structural Comparison. According to the above mentioned discussion of crystal structure of 1-2, we speculate and summarize the reaction mechanism. The formation of 1 shows that the phenolic hydroxyl group of L lose a proton under the help of strongly basic acetate ion, and the resulting [L-H]¯ coordinates with Lewis acidic Cu2+ ion to produce complex 1. The synthetic routes are shown in equilibrium equation (1) in Scheme 2. Different from Cu(OAc)2, the solution of CuCl2 shows weakly acidic, which lead to 9
the formation of hydronium ions (H3O+). The processes of electrophilic attack of H3O+ ions to the azomethine groups and the deprotonation in ligand L generate the intermediate hydramine C through the transformation of intermediate A and B, as depicted in equation (2) in Scheme 2. The intermediate hydramine C is easy to combine H+ ion to further decompose to p-benzoxazolyl-phenylamine(L') and salicylaldehyde through the intramolecular charge transfer and deprotonation in intermediate D. Then the new ligand L' coordinates with CuCl2 yielded coordination polymer 2. We obtained the same coordination mode and crystal structure comparing with complex 2 in the coordination process of L' with CuCl2, which proves the fact that two-dimensional coordination polymer 2 was obtained through the ligand L' coordinates with CuCl2 in the self-assembly reaction of ligand L with CuCl2 at the room temperature. Table 4. Five-coordinate geometry indices for 1-2 Compound 1 2
τ5[15] 0.10 0.27
Geometry square pyramidal square pyramidal
τ5 : Addison and Reedijk’s five-coordinate structural index.[15] ߬ହ =
ఉି
.
α, β : the two largest bond angles in the five-coordinate complex.
Scheme 2. The synthetic routes and reaction mechanism of 1-2. According to the crystal structures of complexes, the dinuclear center in complex
10
1 and 2 displays similar coordination mode, but 2 exhibits two dimensional coordination polymer complex that is more fascinating than 1. Firstly, the metallic coordinated polymer itself is more interesting than metal complex. Meanwhile, the nitrogen atoms in new ligand L' both coordinate with copper atoms, which improves the utilization ratio of nitrogen atoms of ligand. Finally, complex 2 provide a more stable two dimensional structure, which offer a better foundation in some potential application areas. In addition, the distance of dicopper center in 2 is larger than that in 1, which is caused by the bigger radius of auxiliary chlorine atoms than oxygen atoms. Consequently, the acidity of system will influence the stability of Schiff base ligand and further the various structures of the resulting complexes.
Figure 3. Plots of temperature dependence of χMT and χM under 1 kOe dc field of 2. Blue and red solid line is the best fit by PHI from 2-300 K.
Figure 4. Plots of temperature dependence of χM-1 under 1 kOe dc field of 2. The solid red lines are the linear fitted results. 11
Figure 5. Isothermal magnetization for 2 from 0 to 5 T at 2.0 K. 3.4 Magnetic Property. The magnetic measurements were performed on polycrystalline sample of complexes of 1 and 2 using Quantum-Design MPMS XL-5 SQUID magnetometer. Variable-temperature magnetic susceptibility measurement was performed from 2 to 300 K. Complex 2 performs obvious magnetic property. The χMT and χM versus T plot of 2 under an applied static field of 1000 Oe is shown in Figure 3 (χM is the molar magnetic susceptibility per binuclear molecule). The χMT value at room temperature is equal to 0.87 cm3 mol-1 K, which is slightly higher than that expected for two uncoupled Cu2+ ions (χMT = 0.375 cm3 mol-1 K for an S = 1/2 ion with g = 2.00). The χMT value decreases upon cooling and drops very qiuckly below 25 K. It downs to 0.18 cm3 mol-1 K at 2 K. The magnetic susceptibility data in the range of 5-300 K obeys the Curie-Weiss law, χM = C/(T − θ). The linear fitting of the χM-1 versus T plots gives the Curie constant C = 0.88 cm3 mol-1 K and Weiss constant θ = −4.00 K (Figure 4). The negative Weiss value indicated the antiferromagnetic (AF) coupling between two identical Cu2+ ions. The χM value increases continuously upon cooling and a peak is observed at 3.5 K. It suggests the presence of possible antiferromagnetic ordering in the low temperature (Figure 3). The field dependence of the magnetization measured at 2.0 K increases linearly with the increased dc field. The molar magnetization at 50 kOe is only 0.85 Nβ (the unit of magnetization) (Figure 5), far from the saturation value (2 Nβ for S = 1 when g factor is taken equal to 2.00). It is also the evidence of antiferromagnetic interaction existing in this complex. The 12
magnetic data fitted by PHI program [18] in the temperature range 2-300 K gives J = -2.68 cm-1, g1 = g2 = 2.15. Overall, the Cl-bridge in 2 leads to an antimagnetic coupling interaction, which is identical to some reported bi- and polynuclear copper complexes with Cl anion as bridge.[19] 4 Conclusions In this paper, we present two novel dicopper(II) center coordination complexes with five coordination mode based on benzoxazolyl system. Complex 2 is a very rare dicopper-dichlorine two dimensional coordination polymer with the CuII-Cl-CuII structural motif and 1 is a dicopper-dioxygen complex with CuII-O-CuII substrate, which demonstrates that the anion induces the diverse architectures of copper complexes. Magnetic studies indicate that there exists the antiferromagnetic interaction in 2. The magnetic susceptibility data in the range of 5-300 K obeys the Curie-Weiss law and the magnetic data fitted by PHI program in the 2-300 K range provides the following parameters : J = -2.68 cm-1, g1 = g2 = 2.15. These results demonstrate that the anion will influence the structure of Schiff base ligand, which further influence the various architectures and magnetic property of resulting complexes. Acknowledgements This work was supported by the Program for New Century Excellent Talents in University (China), the Doctoral Program Foundation of the Ministry of Education of China (20113401110004), the National Natural Science Foundation of China (21271003, 21271004, 51432001 and 51472002), the 211 Project of Anhui University, Higher Education Revitalization Plan Talent Project of (2013) and the Ministry of Education Funded Projects Focus on Returned Overseas Scholar. Appendix A. Supplementary data CCDC 1020487 and 1020488 contain the supplementary crystallographic data for the complexes 1 and 2. These data can be obtained free of charge via http://www.ccdc.cam.ac.uk/conts/retrieving.html,
or
from
the
Cambridge
Crystallographic Data Centre, 12 Union Road, Cambridge CB2 1EZ, UK; fax: (+44) 1223-336-033; or e-mail: [email protected]. 13
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Highlights 1. Microwave irradiation was classified into atmospheric and high pressure treatment 2. Microwave pretreatment reactors were introduced 3. Advantage, disadvantage and prospect on microwave treatment were summarized
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Graphical abstract
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