English

• 0.   Introduction

  Binuclear copper(Ⅱ) complexes are of ongoing interest due to their interesting magnetic, catalytic, electrochemical properties and a wide variety of biolo-gical applications as catechol oxidase, antibacterial species, DNA binding and cleaving agents^[1-11]. Among these binuclear complexes, the phenolate bridged binuclear copper complexes with tunable stereochem-istry are often five-coordinated in which Cu(Ⅱ) ions are in distorted square pyramid with different Addison parameter (τ). Structural properties of the Cu₂O₂ core, such as the coordination geometry of the copper ions, the Cu…Cu distances, Addison parameter (τ) and torsion angles have been postulated to influence the spectral and electrochemical properties of the binuclear copper complexes, which offer a great scope of design for species that are suitable for magnetic, catalytic properties and biological activities^{[3-4, 12-14]}. Hence, it would be interesting to find a relationship between the geometries and properties of newly designed phenoxo bridged binuclear copper complexes.

  Herein, we report the synthesis, crystal structures, and electrochemical properties of two binuclear copper complexes [CuL(CH₃OH)]₂(BF₄)₂ (1) and [CuL(NO₃)₂]₂ (2) of the newly designed reduced Schiff base ligand HL(HL=2-(((2-(2-benzimidazyl) ethyl)aimino)methyl)phenol). The ligand HL is considered to be more flexible compared to the Schiff base due to the reduction of the rigid azomethine (-CH=N-) fragment to less constrained -CH₂-NH- moiety^[15] and therefore has the potential to form binuclear complexes through a bridging phenolate group.

  1.   Experimental

  1.1   Materials and physical measurement

  All chemicals were of reagent grade and used as received. 2-(Aminoethyl)-benzimidazole dihydrochlor-ide was performed by a method described by Cescon et al^[16]. FT-IR spectra (KBr pellet) were obtained on a FT-IR 170 SX (Nicolet) spectrometer in the range of 4 000～400 cm^-1. Elemental analyses were taken using a Perkin-Elmer 240C analyzer. ¹H NMR was performed on a Brucker Avance 500MHz spectrometer using trimethyl silicon as internal standard. The electronic absorption spectra UV-Vis spectroscopy were recorded on a spectrophotometer using DMF as solvent. Cyclic voltammograms were run on a CHI model 750B electrochemical analyzer in a DMF solution containing tetrabutylammonium perchlorate (TBAP) as the supporting electrolyte. A three-electrode cell was used, which was equipped with a glassy carbon-working electrode, a platinum wire as the counter electrode and a saturated Ag/AgCl electrode as the reference electrode.

  1.2   Synthesis of HL

  The ligand was synthesized by a condensation reaction between 2-(aminoethyl)-benzimidazole dihy-drochloride (3.16 g, 13.5 mmol), previously neutralized with NaOH (1.08 g, 27 mmol), and salicylaldehyde (1.4 mL, 13.5 mmol) in 75 mL of methanol. The reaction mixture was refluxed for approximately two hours and then reduced by slow addition of NaBH₄ (0.5 g, 13.5 mmol) at 0 ℃. The reaction mixture was concentrated under reduced pressure and the product was extracted with three portions of CHCl₃ (60 mL). The organic extracts were combined, washed with brine, dried over Na₂SO₄, filtered and concentrated under reduced pressure resulting in a white powder. Yield (2.56 g, 68%). m.p. 147～149 ℃. Anal. Calcd. for C₁₆H₁₇N₃O(%): C, 71.89; H, 6.41; N, 15.72. Found(%): C, 71.52; H, 6.37; N, 15.96. ¹H NMR: δ 7.21～7.55 (4H, CH_benzim), 6.76～7.20 (4H, CH_ar), 3.99～4.04 (2H, N-CH₂), 3.08～3.19 (2H, CH₂). IR (KBr, cm^-1): 3 316(m), 2 855(w), 1 598(s), 1 455(s), 1 275(s), 1 094(m), 1 031(m), 922(m), 751(s), 617(w).

  1.3   Syntheses of the complexes

  1.3.1   Synthesis of [CuL(CH₃OH)]₂(BF₄)₂ (1)

  A solution of HL (26.6 mg, 0.1 mmol) and NEt₃ (0.014 mL, 0.1 mmol) in 7 mL methanol was added to a solution of Cu(BF₄)₂·6H₂O (34.5 mg, 0.1 mmol) in 3 mL water. The resulting dark green solution was stirred for two hours at room temperature. Crystals suitable for X-ray structural analysis were obtained by slow evaporation of the solvent at 4 ℃. Yield: 65%. Anal. Calcd. for C₁₇H₂₀BCuF₄N₃O₂(%): C, 45.51; H, 4.49; N, 9.36. Found(%): C, 45.62; H, 4.52; N, 9.49. IR (KBr, cm^-1): 3 647(m), 3 120(w), 1 599(s), 1 545(m), 1 483(s), 1 457(s), 1 419(w), 1 394(w), 1 293(s), 1 251(s), 1 083(s), 880(m), 854(m), 764(s), 753(s).

  1.3.2   Synthesis of [CuL(NO₃)₂]₂ (2)

  A solution of HL (26.6 mg, 0.1 mmol) and NEt₃ (0.014 mL, 0.1 mmol) in 5 mL methanol was added to a solution of Cu(NO₃)₂·3H₂O (24.1 mg, 0.1 mmol) in 5 mL methanol. The resulting dark green solution was stirred for two hours at room temperature. Crystals suitable for X-ray structural analysis were obtained by slow evaporation of the solvent at room temperature. Yield: 47%. Anal. Calcd. for C₁₆H₁₆CuN₄O₄(%): C, 49.05; H, 4.12; N, 14.30. Found(%): C, 49.39; H, 4.06, N, 14.21. IR (KBr, cm^-1): 3 119(w), 1 598(s), 1 484(m), 1 456(m), 1 384(s), 1 256(m), 1 025(w), 857(w), 751(s).

  1.4   X-ray crystallography

  Diffraction intensities for complexes 1 and 2 were collected on a Bruker Smart 1000 CCD area detector using graphite-monochromatized Mo Kα radiation (λ=0.071 073 nm) with φ-ω scan mode at 293(2) K. Unit cell dimensions were obtained with least-squares refinements and semi-empirical absorption corrections were applied using SADABS program^[17]. For complex 1 all fluorine atoms from BF₄^- are disordered and were refined isotropically with occupancy with 0.6 and 0.4. All the structures were solved by direct method and non-hydrogen atoms were obtained in successive difference Fourier syntheses. All the structures were solved by direct method and the refinements were performed by full-matrix least-squares methods on F² with SHELXTL program package^[18]. Hydrogen atoms were included in calculated positions and refined with fixed thermal parameters riding on their parent atoms. The crystal data and structure refinement parameters of complexes are listed in Table 1 while Table 2 lists selected bond distances and angles.

  Table 1

  

  Table 1.  Crystal data and structural refinement parameters for complexes 1 and 2

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  Complex	1	2
  Formula	C17H20BCuF4N3O2	C16H16CuN4O4
  Formula weight	448.71	391.87
  Crystal system	Monoclinic	Monoclinic
  Space group	P21/c	P21/c
  a/nm	0.845 7(6)	0.809 6(4)
  b/nm	1.738 4(11)	1.058 2(5)
  c/nm	1.311 0(8)	1.929 1(10)
  β/(°)	99.443(12)	94.756(9)
  V/nm3	1.901(2)	1.647 1(15)
  Dc/(g·cm-3)	1.567	1.580
  Z	4	4
  Absorption coefficient/mm-1	1.204	1.356
  F(000)	916	804
  Crystal size/mm	0.28×0.20×0.16	0.24×0.20×0.18
  θ range/(°)	1.96-25.01	2.12-26.42
  Limiting indices	-10 ≤ h≤ 9, -18 ≤ k ≤20, -14≤l≤15	-10≤h ≤ 9, -12≤ k≤13, -15≤l≤24
  Reflection collected, unique	9 642, 3 343 (Rint=0.086 0)	9 229, 3 351 (Rint=0.035 8)
  Reflection with I > 2σ(I)	2 009	2 467
  Data, restraint, parameter	3 343, 68, 291	3 351, 2, 234
  Goodness of fit on F2	1.005	1.010
  Final R indices [I > 2σ(I)]	R1=0.069 9, wR2=0.174 5	R1=0.035 5, wR2=0.077 3
  R indices (all data)	R1=0.125 0, wR22=0.209 4	R1=0.060 4, wR2=0.086 9
  Largest diff. peak and hole / (e·nm-3)	793 and -991	336 and -422
  Complex 1:w=1/[σ2(Fo2)+(0.123 5P)2], with P=(Fo2+2Fc2)/3; Complex 2: w=1/[σ2(Fo2)+(0.041 6P)2+0.447 0P], with P=(Fo2+2Fc2)/3.

  Table 2

  

  Table 2.  Selected bond distances (nm) and angles (°) for 1 and 2

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  Complex 1
  Cu1-N1	0.195 2(6)	Cu1-N3	0.202 0(5)	Cu1-01	0.195 3(4)
  Cu1-02	0.228 0(6)	Cu1-O1ⅰ	0.197 4(4)
  N1-Cu1-N3	91.8(2)	N1-Cu1-O1	175.3(2)	N1-Cu1-O1ⅰ	99.7(2)
  N1-Cu1-O2	88.3(2)	N3-Cu1-O2	101.5(2)	O1-Cu1-N3	92.6(2)
  O1-Cu1-O1A	76.83(19)	O1-Cu1-O2	89.1(2)	O1A-Cu1-N3	156.0(2)
  O1A-Cu1-O2	99.7(2)	Cu1-O1-Cu1ⅰ	103.17(19)
  Complex 2
  Cu1-N1	0.202 0(2)	Cu1-N2	0.195 5(2)	Cu1-O1	0.192 29(18)
  Cu1-O2	0.258 0(3)	Cu1-O1ⅱ	0.198 20(19)
  N2-Cu1-N1	92348(9)	N2-Cu1-O1ⅱ	98.75(8)	O1-Cu1-N1	93.10(9)
  O1-Cu1-N2	174.05(8)	O1-Cu1-O1ⅱ	77.03(8)	O1A-Cu1-N1	153.25(8)
  O2-Cu1-N1	103.036(80)	O2-Cu1-N2	93.199(80)	O2-Cu1-O1	83.544(70)
  O2-Cu1-O2ⅱ	100.494(74)	Cu1-O1-Cu1ⅱ	102.97(8)
  Symmetry codes: ⅰ -x+1, -y+1, -z+2 for 1; ⅱ -x, -y+1, -z+1 for 2.

  CCDC: 2276305, 1; 2276307, 2.

  2.   Results and discussion

  2.1   Synthesis and characterization

  The condensation of 2-(aminoethyl)-benzimidazole dihydrochloride in 1: 1 molar ratio with salicylaldehyde afforded the Schiff bases, N-salicylidine-2-aminoethy-lbenzimidazole which on reduction with sodium boro-hydride readily produced the reduced Schiff base, HL. HL on reaction with copper(Ⅱ) tetrafluoroborate hexa-hydrate and copper(Ⅱ) nitrate trihydrate in 1:1 molar ratios yielded complexes 1 and 2, respectively (Scheme 1). Unlike its Schiff base counterpart, the reduced Schiff base has flexible backbones. Two phenolic oxygen atoms bind two metals to form a dimer, in which one four-membered ring, four six-membered rings are formed as shown in Scheme 1.

  Scheme 1

  

  Scheme 1.  Synthesis of the reduced Schiff base ligand and the complexes 1 and 2

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  The characteristic IR bands (4 000～400 cm^-1) for the free ligand, when compared with those of its copper(Ⅱ) complexes, provided positive indications with regard to the bonding sites of the ligand. The presence of one medium intensity broad band between 2 500 and 3 200 cm^-1 in the free ligand hints toward the existence of hydrogen bonding between NH of benzimidazole and other electronegative atoms^[19]. The broad bond remains almost unchanged in the two complexes, indicating that the N-H of benzimidazole ring does not participate in the coordination^[20]. In the spectrum of the free ligand the band of the stretching vibrational modes of the phenolic OH around 3 316 cm^-1, disappeared from the spectra of the two complexes indicating the deprotonation of the ligand. Additionally, the bands originating from the C-O stretching vibrations at 1 205 cm^-1, in the complexes exhibited positive shifts at 1 251 cm^-1 for complex 1 and 1 256 cm^-1 for complex 2, respectively, denoting coordination through the phenolic oxygen of the ligand^[21]. Furthermore, the reduction of the imine group is very clearly indicated by the absence of the strong band due to imine vibration which appeared in the region of 1 620～1 650 cm^-1 for the free ligand and the two complexes^[22]. Several new bands presented in the region 400～600 cm^-1 in the spectra of the complexes were assigned to the Cu-N and Cu-O stretching vibrations^[23].

  Characteristic stretching frequencies for the anions are observed. The presence of the bands at near 1 100 and 522 cm^-1 in complex 1 confirmed the presence of non-coordinated tetrafluoroborate anions and point to a lack of strong deviation from tetrahedral symmetry^[24]. Furthermore, the BF₄^- group vibration near 1 083 cm^-1 splitting into a peak at 1 083 cm^-1 and a shoulder at 1 063 cm^-1 approximately, indicated BF₄^- anions involved hydrogen bonding, which is consistent with the crystal structures^[25]. Appearance of a strong sharp band at 1 384 cm^-1 demonstrated the presence of nitrate in complex 2^[26].

  The electronic absorption spectra of the ligand HL and the two complexes in DMF were recorded at room temperature. UV bands at 275 and 285 nm were observed for the free ligand HL, which are character-istic of the benzimidazole group and arise from a π-π^* transition. These were blue-shifted upon coordina-tion and were observed at 272 and 278 nm for the two complexes^[27], respectively. The complexes display a broad d-d band in the region of 560～680 nm. The position of this band suggests that the geometry about each Cu(Ⅱ) atom is best described as square pyra-midal^[28]. In addition, one charger transfer band due to a LMCT transition between the bridging phenoxo and Cu(Ⅱ) atoms in the region of 400～420 nm was also observed. Similar UV-Vis features have been previously observed for several related phenolate bridged binuclear copper(Ⅱ) complexes^[29].

  2.2   Crystal structure

  Fig. 1 gives the crystal structures of 1 and 2 with atomic labeling scheme, respectively. X-ray diffraction studies revealed that both complexes 1 and 2 crystallize in monoclinic system with P2₁/c space group. In complexes 1 and 2, two phenoxo groups bridge two Cu(Ⅱ) atoms giving the binuclear structure, containing an exactly planar Cu₂O₂ core owing to the crystallogra-phic inversion symmetry. The stereochemistry around each Cu(Ⅱ) is best described as a distorted square pyramidal with a value of τ being 0.31 for 1 and 0.35 for 2, respectively. The equatorial positions are occupied by benzimidazolyl nitrogen atom, the amine nitrogen atom, phenolate oxygen atom and the bridging phenoxo oxygen atom from the symmetry related molecule. The Cu-O bridge distances are in the range of 0.192 29(18)～0.198 20(19) nm, with Cu1-O1-Cu1^ⅰ bridging angles of 103.17(19)° for 1 and Cu1-O1-Cu1^ⅱ of 102.97(8)° for 2, falling within the normal range for diphenoxo-bridged copper(Ⅱ) complexes^{[3-4, 12-14]}. The average Cu-N_imine and Cu-N_{benzimidazole} bond lengths are 0.202 0 and 0.195 4 nm, which are similar to the Cu-N bond distance found for similar copper/reduced Schiff system and copper/benzimidazole system, respe-ctively^{[27, 30]}. In 1, the axial position is occupied by oxygen O₂ of the monodentate coordinating methanol molecule with the Cu-O2 distance of 0.228 0(6) nm, suggesting a weak axial interaction. While in 2, the fifth position is occupied by a nitrate oxygen at a semi-coordination distance of 0.258 0 nm for Cu1-O2, Equatorial bond angles deviate from the expected value of 90°, the largest deviation being 13.17°, and the sum of the equatorial angles at Cu(Ⅱ) are nearly 360° for both 1 and 2. The Cu…Cu distances between the two metal ions are 0.308 5 nm for 1 and 0.305 6 nm for 2, which are almost close to other symmetric bis(μ-phenoxo) bridged binuclear copper(Ⅱ) complexes^{[3-4, 12-14]}.

  Figure 1

  

  Figure 1.  Molecular structures of 1 (a) and 2 (b) with 30% probability level along with the atom numbering scheme

  H atoms are omitted for clarity; Symmetry codes: ^ⅰ-x+1, -y+1, -z+2 for 1; ^ⅱ -x, -y+1, -z+1 for 2

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  In complex 1, the binuclear moieties are linked with pairs of tetrafluoroborate anions by hydrogen bonds into 1D chain (Fig. 2). Each tetrafluoroborate acts as hydrogen bond acceptor and forms two hydrogen bonds with one methanol molecule and one benzi-midazole NH group (N2-H2A…F4 and O2-H2…F1^ⅲ, Symmetry codes: ^ⅲ x, -y+1, -z+1). The interatomic distances of N2…F4 and O2…F1^ⅲ are 0.280 5 and 0.288 9 nm, respectively, both being in the range of moderate hydrogen bond distances. The H…F separa-tions are 0.212 3 and 0.213 1 nm and hydrogen bond angles are 135.89° and 137.96°, respectively.

  Figure 2

  

  Figure 2.  One dimensional chain in 1 formed through N-H…F and O-H…F hydrogen-bonding interactions along the a-axis

  Symmetry codes: ^ⅲ-x, -y+1, -z+1

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  In complex 2, each nitrate acts as hydrogen bond acceptor and forms two hydrogen bonds with one amine group (N1-H1…O2^ⅳ, Symmetry codes: ^ⅳ -x+1, -y+1, z+1) and one benzimidazole NH group (N3-H3A…O4^ⅴ, Symmetry codes: ^ⅴx, 0.5-y, z-0.5) (Fig. 3a). The interatomic distances of N1…O2^ⅳ and N3…O4^ⅴ are 0.315 6 and 0.288 5 nm, respectively. The H…O separations are 0.238 2 and 0.204 9 nm and hydrogen bond angles are 151.03° and 165.33°, resp-ectively. As a result, a 3D hydrogen-bonded network is formed (Fig. 3b).

  Figure 3

  

  Figure 3.  (a) Packing diagram showing the hydrogen-bonded interactions in 2; (b) 3D framework for 2 built by hydrogen bond

  Symmetry codes: ^ⅳ-x+1, -y+1, z+1; ^ⅴx, 0.5-y, z-0.5

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  2.3   Electrochemical characterization

  Cyclic voltammetric studies were carried out for the copper(Ⅱ) complexes at 1 mmol·L^-1 concentration, dissolved in DMF containing 0.1 mol·L^-1 TBAP as a supporting electrolyte. The cyclic voltammetric data for the binuclear complexes 1 and 2 are shown in Table 3. The cyclic voltammograms (CV) of 1 and 2 were almost identical, suggesting similar environments around the Cu(Ⅱ) ions in 1 and 2 (Fig. 4). This is consistent with the single crystal X-ray diffraction results. The CV of the two complexes showed two quasi-reversible reduction waves at E_1/2¹=-0.41 V and E_1/2²=-0.85 V for 1 and E_1/2¹=-0.38 V and E_1/2²=-0.85 V for 2. The first process corresponds to the Cu^ⅡCu^Ⅱ ⇄ Cu^ⅡCu^Ⅰ reduction couple and the second process corresponds to the Cu^ⅡCu^Ⅰ ⇄ Cu^ⅠCu^Ⅰ reduction couple. The negative potentials observed in 1 and 2 are due to the factors such as the steric hindrance of the benzimidazole ring and the hard nature of the phenoxide atoms in the ligand, which will stabilize the copper(Ⅱ) oxidation state, making the Cu(Ⅱ) to Cu(Ⅰ) conversion difficult. Similar observations are also reported for benzimidazole copper complexes and phenoxo copper complexes, which reduced in the range of -0.87～-1.40 V^[31-33].

  Table 3

  

  Table 3.  Cyclic voltammetric data for 1 mmol·L^-1 solution of 1 and 2 in DMF containing 0.1 mol·L^-1 TBAP as supporting electrolyte

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  Complex	Epc1/V	Epa1/JV	E1/21/V	△E1/mV	Epc2/V	Epa2/V	E1/22/V	△E2/mV	Kcon
  1	-0.47	-0.35	-0.41	120	-0.91	-0.78	-0.85	130	2.73×107
  2	-0.41	-0.36	-0.38	50	-0.92	-0.78	-0.85	140	1.91×108

  Figure 4

  

  Figure 4.  CV of the complexes 1 and 2 in DMF

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  The observed two well-separated one electron reductions for 1 and 2 can be substantiated from a stability consideration of the mixed-valence species, Cu^ⅡCu^Ⅰ. The stability of mixed valance form can be quantified by the conproportionation equilibrium constant (K_con), lgK_con=16.9(ΔE_1/2), where ΔE_1/2=(E_1/2¹-E_1/2²)^[34]. It is observed that the larger ΔE_1/2 is, the greater is the stability of the mixed-valence species with respect to conproportionation. The magnitude of the constant, K_con was determined to be 2.73×10⁷ for 1 and 1.91×10⁸ for 2, respectively, which can be comp-ared to the value of K_con for phenoxo bridge copper(Ⅱ) complexes^[32]. The large K_con values indicated that the addition of a second electron is more difficult than of the first electron and the Cu^ⅡCu^Ⅰ mixed valence species is stable with respect to conproportionation^[35].

  3.   Conclusions

  In this work, one unsymmetrical tridentate Schiff base ligand has been reduced by NaBH₄. The reduced ligand was more flexible compared to the Schiff base and used to form two phenoxo bridged binuclear copper complexes, which differ by the anions. The Addison parameters (τ) of both complexes indicated that the environment around the copper ions is a distorted square pyramidal geometry. The binuclear moieties are linked with pairs of tetrafluoroborate anions by the N2-H2A…F4 and O₂-H2…F1^ⅲ hydrogen bonds in complex 1 while in complex 2 a 3D hydrogen-bonded network is formed by the N1-H1…O₂^ⅳ and N3-H3A…O4^ⅴ hydrogen bonds. The two complexes show two quasi-reversible one electron reduction processes in cyclic voltammetry.

• 1. [1]

     Koohzad S, Golchoubian H, Jaglii Z. Inorg. Chim. Acta, 2018, 473:60-69 doi: 10.1016/j.ica.2017.12.026

  2. [2]

     Chai D F, Wang M, Zhang C J, et al. Inorg. Chem. Commun., 2017, 83:16-19 doi: 10.1016/j.inoche.2017.05.028

  3. [3]

     Pattanayak P, Pratihar J L, Patra D, et al. Polyhedron, 2013, 59:23-28 doi: 10.1016/j.poly.2013.04.034

  4. [4]

     Hazra S, Karmakar A, da Silva M F C G, et al. Inorg. Chem. Commun., 2014, 46:113-117 doi: 10.1016/j.inoche.2014.05.025

  5. [5]

     Chai L Q, Li Y X, Chen L C, et al. Inorg. Chim. Acta, 2016, 444:193-201 doi: 10.1016/j.ica.2016.01.038

  6. [6]

     杨永生, 陈博庸, 琚海燕, 等.无机化学学报, 2017, 33(12):2338-2344 doi: 10.11862/CJIC.2017.262YANG Yong-Sheng, CHEN Bo-Yong, JU Hai-Yan, et al. Chinese J. Inorg. Chem., 2017, 33(12):2338-2344 doi: 10.11862/CJIC.2017.262

  7. [7]

     林龙, 李先宏, 张波, 等.无机化学学报, 2017, 33(1):143-148 http://www.wjhxxb.cn/wjhxxbcn/ch/reader/view_abstract.aspx?file_no=20170117&flag=1LIN Long, LI Xian-Hong, ZHANG Bo, et al. Chinese J. Inorg. Chem., 2017, 33(1):143-148 http://www.wjhxxb.cn/wjhxxbcn/ch/reader/view_abstract.aspx?file_no=20170117&flag=1

  8. [8]

     杨红, 郭利君.无机化学学报, 2017, 33(6):1059-1064 http://www.wjhxxb.cn/wjhxxbcn/ch/reader/view_abstract.aspx?file_no=20180620&flag=1YANG Hong, GUO Li-Jun. Chinese J. Inorg. Chem., 2017, 33(6):1059-1064 http://www.wjhxxb.cn/wjhxxbcn/ch/reader/view_abstract.aspx?file_no=20180620&flag=1

  9. [9]

     Ferreira B J M L, BrandO P, Meiriles M, et al. J. Inorg. Biochem., 2016, 161:9-17 doi: 10.1016/j.jinorgbio.2016.04.026

  10. [10]

      Ghosh A K, Ali A, Singh Y, et al. Inorg. Chim. Acta, 2018, 474:156-163 doi: 10.1016/j.ica.2018.02.004

  11. [11]

      Arthi P, Haleel A, Srinivasan P, et al. Spectrochim. Acta A, 2014, 129:400-414 doi: 10.1016/j.saa.2014.03.058

  12. [12]

      You X L, Wei Z H. Inorg. Chim. Acta, 2014, 423:332-339 doi: 10.1016/j.ica.2014.08.051

  13. [13]

      Sadhukhan D, Ray A, Butcher R J, et al. Inorg. Chim. Acta, 2011, 376:245-254 doi: 10.1016/j.ica.2011.06.024

  14. [14]

      Biswas A, Drew M G B, Ribas J, et al. Inorg. Chim. Acta, 2011, 379:28-33 doi: 10.1016/j.ica.2011.09.026

  15. [15]

      Biswas A, Drew M G B, Ghosh A. Polyhedron, 2010, 29:1029-1034 doi: 10.1016/j.poly.2009.12.006

  16. [16]

      Cescon L A, Day A R. J. Org. Chem., 1962, 27:581-586 doi: 10.1021/jo01049a056

  17. [17]

      Sheldrick G M. SADABS, Program for Empirical Absorption Correction of Area Detector Data, University of Göttingen, Germany, 1996.

  18. [18]

      Sheldrick G M. SHELXL-97, Program for X-ray Crystal Structure Solution, Göttingen University, Germany, 1997.

  19. [19]

      Maurya M R, Kumar A, Ebel M, et al. Inorg. Chem., 2006, 45:5924-5937 doi: 10.1021/ic0604922

  20. [20]

      Nath M, Saini P K, Kumar A. Appl. Organometal. Chem., 2009, 23:434-445 doi: 10.1002/aoc.v23:11

  21. [21]

      Zianna A, Psomas G, Hatzidimitriou A, et al. J. Inorg. Biochem., 2013, 127:116-126 doi: 10.1016/j.jinorgbio.2013.07.031

  22. [22]

      Muppidi V K, Das M S, Raghavaiah P, et al. Inorg. Chem. Commun., 2007, 10:234-238 doi: 10.1016/j.inoche.2006.10.011

  23. [23]

      Creaven B S, Devereux M, Karcz D, et al. J. Inorg. Biochem., 2009, 103:196-1203

  24. [24]

      Bronisz R. Inorg. Chim. Acta, 2004, 357:396-404 doi: 10.1016/j.ica.2003.05.002

  25. [25]

      Youngme S, van Albada G A, Chaichit N, et al. Inorg. Chim. Acta, 2003, 353:119-128 doi: 10.1016/S0020-1693(03)00207-X

  26. [26]

      Keypour H, Shayesteh M, Rezaeivala M, et al. Spectrochim. Acta A, 2013, 101:59-66 doi: 10.1016/j.saa.2012.09.048

  27. [27]

      Yang J, Ma J F, Liu Y C, et al. J. Mol. Struct., 2003, 646:55-60 doi: 10.1016/S0022-2860(02)00591-4

  28. [28]

      McLachlan G A, Fallon G D, Martin R L, et al. Inorg. Chem., 1995, 34:254-261 doi: 10.1021/ic00105a041

  29. [29]

      Gupta S, Pal S, Barik A K, et al. Polyhedron, 2008, 27:2519-2528 doi: 10.1016/j.poly.2008.05.009

  30. [30]

      Sreenivasulu B, Zhao F, Gao S, et al. Eur. J. Inorg. Chem., 2006:2656-2670

  31. [31]

      Amudha P, Akilan P, Kandaswam M. Polyhedron, 1999, 18:1355-1362 doi: 10.1016/S0277-5387(98)00401-X

  32. [32]

      Thirumavalavan M, Akilan P, Amudha P, et al. Polyhedron, 2004, 23:519-527 doi: 10.1016/j.poly.2003.09.032

  33. [33]

      Sreedaran S, Bharathi K S, Rahiman A K, et al. Polyhedron, 2008, 27:2931-2938 doi: 10.1016/j.poly.2008.06.025

  34. [34]

      Sundaravadivel E, Kandaswamy M, Varghese B. Polyhedron, 2013, 61:33-44 doi: 10.1016/j.poly.2013.04.057

  35. [35]

      Patel R N, Patel D K, Sondhiya V P, et al. Inorg. Chim. Acta, 2013, 405:209-217 doi: 10.1016/j.ica.2013.05.024

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  Scheme 1  Synthesis of the reduced Schiff base ligand and the complexes 1 and 2

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  Figure 1  Molecular structures of 1 (a) and 2 (b) with 30% probability level along with the atom numbering scheme

  H atoms are omitted for clarity; Symmetry codes: ^ⅰ-x+1, -y+1, -z+2 for 1; ^ⅱ -x, -y+1, -z+1 for 2

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  Figure 2  One dimensional chain in 1 formed through N-H…F and O-H…F hydrogen-bonding interactions along the a-axis

  Symmetry codes: ^ⅲ-x, -y+1, -z+1

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  Figure 3  (a) Packing diagram showing the hydrogen-bonded interactions in 2; (b) 3D framework for 2 built by hydrogen bond

  Symmetry codes: ^ⅳ-x+1, -y+1, z+1; ^ⅴx, 0.5-y, z-0.5

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  Figure 4  CV of the complexes 1 and 2 in DMF

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  Table 1.  Crystal data and structural refinement parameters for complexes 1 and 2

  Complex	1	2
  Formula	C17H20BCuF4N3O2	C16H16CuN4O4
  Formula weight	448.71	391.87
  Crystal system	Monoclinic	Monoclinic
  Space group	P21/c	P21/c
  a/nm	0.845 7(6)	0.809 6(4)
  b/nm	1.738 4(11)	1.058 2(5)
  c/nm	1.311 0(8)	1.929 1(10)
  β/(°)	99.443(12)	94.756(9)
  V/nm3	1.901(2)	1.647 1(15)
  Dc/(g·cm-3)	1.567	1.580
  Z	4	4
  Absorption coefficient/mm-1	1.204	1.356
  F(000)	916	804
  Crystal size/mm	0.28×0.20×0.16	0.24×0.20×0.18
  θ range/(°)	1.96-25.01	2.12-26.42
  Limiting indices	-10 ≤ h≤ 9, -18 ≤ k ≤20, -14≤l≤15	-10≤h ≤ 9, -12≤ k≤13, -15≤l≤24
  Reflection collected, unique	9 642, 3 343 (Rint=0.086 0)	9 229, 3 351 (Rint=0.035 8)
  Reflection with I > 2σ(I)	2 009	2 467
  Data, restraint, parameter	3 343, 68, 291	3 351, 2, 234
  Goodness of fit on F2	1.005	1.010
  Final R indices [I > 2σ(I)]	R1=0.069 9, wR2=0.174 5	R1=0.035 5, wR2=0.077 3
  R indices (all data)	R1=0.125 0, wR22=0.209 4	R1=0.060 4, wR2=0.086 9
  Largest diff. peak and hole / (e·nm-3)	793 and -991	336 and -422
  Complex 1:w=1/[σ2(Fo2)+(0.123 5P)2], with P=(Fo2+2Fc2)/3; Complex 2: w=1/[σ2(Fo2)+(0.041 6P)2+0.447 0P], with P=(Fo2+2Fc2)/3.

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  Table 2.  Selected bond distances (nm) and angles (°) for 1 and 2

  Complex 1
  Cu1-N1	0.195 2(6)	Cu1-N3	0.202 0(5)	Cu1-01	0.195 3(4)
  Cu1-02	0.228 0(6)	Cu1-O1ⅰ	0.197 4(4)
  N1-Cu1-N3	91.8(2)	N1-Cu1-O1	175.3(2)	N1-Cu1-O1ⅰ	99.7(2)
  N1-Cu1-O2	88.3(2)	N3-Cu1-O2	101.5(2)	O1-Cu1-N3	92.6(2)
  O1-Cu1-O1A	76.83(19)	O1-Cu1-O2	89.1(2)	O1A-Cu1-N3	156.0(2)
  O1A-Cu1-O2	99.7(2)	Cu1-O1-Cu1ⅰ	103.17(19)
  Complex 2
  Cu1-N1	0.202 0(2)	Cu1-N2	0.195 5(2)	Cu1-O1	0.192 29(18)
  Cu1-O2	0.258 0(3)	Cu1-O1ⅱ	0.198 20(19)
  N2-Cu1-N1	92348(9)	N2-Cu1-O1ⅱ	98.75(8)	O1-Cu1-N1	93.10(9)
  O1-Cu1-N2	174.05(8)	O1-Cu1-O1ⅱ	77.03(8)	O1A-Cu1-N1	153.25(8)
  O2-Cu1-N1	103.036(80)	O2-Cu1-N2	93.199(80)	O2-Cu1-O1	83.544(70)
  O2-Cu1-O2ⅱ	100.494(74)	Cu1-O1-Cu1ⅱ	102.97(8)
  Symmetry codes: ⅰ -x+1, -y+1, -z+2 for 1; ⅱ -x, -y+1, -z+1 for 2.

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  Table 3.  Cyclic voltammetric data for 1 mmol·L^-1 solution of 1 and 2 in DMF containing 0.1 mol·L^-1 TBAP as supporting electrolyte

  Complex	Epc1/V	Epa1/JV	E1/21/V	△E1/mV	Epc2/V	Epa2/V	E1/22/V	△E2/mV	Kcon
  1	-0.47	-0.35	-0.41	120	-0.91	-0.78	-0.85	130	2.73×107
  2	-0.41	-0.36	-0.38	50	-0.92	-0.78	-0.85	140	1.91×108

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