New complexes of Ni(II) and Cu(II) with tridentate ONO Schiff base ligand: synthesis, crystal structures, electrochemical and theoretical investigation

New complexes of Ni(II) and Cu(II) with tridentate ONO Schiff base ligand: synthesis, crystal... In this research, we prepared a new series of the Cu(II) (1) and Ni(II) (2) metal complexes of a tridentate Schiff base ligand, (E)-2-(5-bromo-2-hydroxybenzylideneamino) phenol (H L). These complexes were characterized by elemental analysis, FT-IR, UV–Vis, and H-NMR spectroscopy. The crystal structures of (1) and (2) were determined by X-ray diffraction studies. The single crystal X-ray diffraction analyses revealed that copper(II) cation is five-coordinated and the coordination polyhedron is a slightly distorted square pyramid. Nickel(II), on the other hand, is four-coordinated, and has a regular, square planar geometry. Further discussed were the electrochemical reduction of these complexes. We also analyzed the nature of the metal–ligand bond in the complexes through NBO and EDA analysis. Besides, vibrational sample magnetometer (VSM) revealed complex (1) was ferromagnetic. Keywords Schiff base · Copper(II) complex · Nickel(II) complex · Crystal structure · Theoretical investigation · Electrochemical studies Introduction modeling, and catalytic activity and their function as anti- microbial, antifungal and antitumor agents [11–15]. It has Schiff bases, whose metal complexes are of great interest, been demonstrated that biological activities of these com- have often been employed as chelating ligands in the field pounds are influenced significantly by metal coordination of coordination chemistry [1–3]. They are able to coordi- [16, 17]. There is also some evidence suggesting that these nate metals through imine nitrogen and another group, drugs interact directly with DNA, blocking the activity of more often than not, linked to aldehyde or ketone [4]. Schiff DNA–gyrase repair enzymes [18–20]. Schiff bases facili- base metal complexes also find diverse and fruitful applica- tate the process of inducing substrate chirality, tuning the tions in industry and daily life [5–10]. There exist myriad metal-centered electronic factor, enhancing solubility and reports on the biological activities of Schiff base ligands performing either homogeneous or heterogeneous catalysts and their metal complexes, including their use for enzyme [21]. Furthermore, recent studies have witnessed a great deal of interest in the synthesis and characterization of transition metal complexes containing Schiff bases as ligands due to Electronic supplementary material The online version of this their applications in pharmaceutical fields. article (https ://doi.org/10.1007/s1373 8-018-1412-1) contains Since the synthesis of new compounds with new proper- supplementary material, which is available to authorized users. ties are important in inorganic chemistry, we have focused * Mehdi Salehi on the synthesis and characterization of new Schiff base msalehi@semnan.ac.ir ligands and their complexes to check out their applica- 1 tions in the future. Considering the remarkable importance Department of Chemistry, College of Science, Semnan of Schiff base complexes and so as to continue our previ- University, Semnan, Iran 2 ous work [22–25], we found it worthwhile to synthesize Faculty of Chemistry, Adam Mickiewicz University, and characterize new complexes of Ni(II) and Cu(II) with Umultowska 89b, 61-614 Poznan, Poland 3 1-methyl-imidazole and a tridentate Schiff base ligand, Department of Inorganic Chemistry, Faculty of Chemistry, obtained by the condensation of 2-aminophenol with Bu-Ali Sina University, Hamedan 65167, Iran Vol.:(0123456789) 1 3 Journal of the Iranian Chemical Society II 5-bromo-2- hydroxybenzaldehyde (Scheme  1). In addi-Synthesis of  [Ni (L)(MeIm)] (2) tion, a theoretical study was conducted on the structure and nature of the metal–ligand bond in complexes at the BP86/ This complex was prepared by the same procedure TZ2P(ZORA)//BP86/def2-SVP level of theory. applied to complex (1), with the exception that instead of Cu(CH COO) .H O, 0.5  mmol (0.124  g) of the 3 2 2 Ni(CH COO) .4H O was used. The red crystals, suitable for 3 2 2 Experimental X-ray data collection, were obtained by slow evaporation of the methanol solution after 4 days. Yield: 70%. Anal. Calcd. Materials and methodsfor C H BrN NiO (%): C, 47.38; H, 3.27; N, 9.75. Found 17 14 3 2 −1 (%): C, 47.22; H, 3.18; N, 9.70%. FT-IR: ν (cm ) (KBr): max −1 −1 All starting materials and solvents were purchased from 1596 (ν ). UV–Vis in CH CN: λ (nm) (ɛ, M cm ): C=N 3 max commercial sources and used without further purification. 238 (43,500), 275 (22,650), 312 (8500), 330 (19,500), 444 The elemental analyses of carbon, nitrogen and hydrogen (16,200). H-NMR (CDCl , 400 MHz): 8.04 (s, 1H, H ), 3 l atoms were done through the use of a Perkin-Elmer 2400II 7.65 (s, 1H, H ), 7.53 (dd, 1H, J = 1.2, J = 8.4 Hz, H ), 7.48 k 1 1 j CHNS-O elemental analyzer. FT-IR spectra were recorded (d, 1H, J = 2.4 Hz, H ), 7.25 (dd, H, J = 2.4, J = 9 Hz, H ), i 1 2 h −1 in the range of 4000–400 cm on a FT-IR SHIMADZU 8.61 (s, 1H, H ), 7.00 (t, 1H, J = 1.2, J = 7.4 Hz, H ), 6.84 g 1 2 f spectrophotometer from KBr pellet. UV–Vis spectra were (t, 1H, J = 1.6 Hz, H ), 6.81 (d, 1H, J = 9.2 Hz, H ), 6.74 (dd, e d recorded on a UV-1650 PC SHIMADZU spectrophotom- 1H, J = 1.2, J = 8.4 Hz, H ), 6.53 (t, 1H, J = 1.2, J = 8 Hz, 1 2 c 1 2 eter in acetonitrile solution. Using CDCl as the solvent, H ), 3.74 (s, 3H, H ). 3 b a H-NMR measurements were performed on NMR BRUKER 400 MHZ spectrometer, at 25 °C. The Schiff base ligand X‑ray crystallography analyses was prepared according to the literature [26]. Also, magnetic measurements were carried out with a vibrating sampling The X-ray single crystal data for complexes 1 and 2 were magnetometer (VSM, Model 7400- LakeShore). collected at 100(1) K by the ω-scan technique on an Agilent Technologies Xcalibur four-circle diffractometer with Eos Synthesis of the complexes CCD detector, equipped with graphite-monochromatized MoK radiation source (λ = 0.71073 Å). The data were cor- II Synthesis of  [Cu (L)(MeIm)(H O)] (1) rected for Lorentz-polarization as well as for absorption effects [27]. Precise unit-cell parameters were determined In a typical experiment, a methanolic solution (10  mL) by a least-squares fit of 2189 (1 ) and 1478 (2) reflections of of 0.5 mmol (0.099 g) Cu(CH COO) .H O was added to the highest intensity, chosen from the whole experiment. The 3 2 2 0.5 mmol (0.146 g) methanolic solution of ligand. The mix- structures were solved with S FT-IR 92 [28] and refined with ture color turned green. After that, N-methyl imidazole was the full-matrix least-squares procedure on F by SHELXL97 added dropwise. The reaction mixture was refluxed for 3 h. [29]. All non-hydrogen atoms were refined anisotropically. The green-colored single crystals suitable for X-ray data Hydrogen atoms were found from water molecule in 1 in the collection were obtained by slow evaporation of the solu- different Fourier map, all other ones were positioned geo- tion. Yield: 58%. Anal. Calcd. for C H BrCuN O (%): metrically and refined with a riding model approximation 17 16 3 3 C, 44.99; H, 3.55; N, 9.26. Found (%): C, 44.75; H, 3.38; with their displacement parameters constrained to the parent −1 N, 9.25. FT-IR: ν (cm ) (KBr): 1608 (ν ). UV–Vis atom with U (H) = 1.2 (CH, CH, H O) or 1.5 (CH ) U max C=N iso 2 2 3 eq −1 −1 in CH CN: λ (nm) (ɛ, M   cm ): 249 (26,000), 277 (C). The summary of crystal data and refinement for (1) and 3 max (16,100), 304 (8900), 318 (15,050), 427 (13,280). (2) are given in Table 1. Scheme 1 Synthetic procedure for the preparation of complexes 1 3 Journal of the Iranian Chemical Society Table 1 Crystal data and Compound (1) (2) structure refinement parameters for complexes (1) and (2) Empirical formula C H Br Cu N O C H Br N Ni O 17 16 3 3 17 14 3 2 Formula weight 453.78 430.90 Temperature (K) 293 293 Wavelength λ (Å) 0.71073 0.71073 Crystal system Monoclinic Orthorhombic Space group P2 /n P2 2 2 1 1 1 1 Unit cell dimensions  a (Å) 15.0867 (6) 5.8913 (6)  b (Å) 5.4040 (2) 15.715 (2)  c (Å) 20.1813 (10) 16.8121 (18)  β (◦) 91.082 (4) Volume (Å ), Z 1645.06 (12), 4 1556.5 (3), 4 Calculated density (g/cm ) 1.83 1.84 θ ranges for data collection (◦) 3.3–28.2 3.5–28.0 F(000) 908 864 −1 ) 3.78 1.34 Absorption coefficient (mm Total reflections 6905 4348 Unique reflections (R ) 3409 (0.037) 2718 (0.034) int Observed data [I > 2σ(I)] 2554 2359 Number of parameters 227 218 Final R index [I > 2σ(I)] R1 = 0.0360, wR2 = 0.0710 R1 = 0.0358, wR = 0.0700 R index (all data) R1 = 0.0587, wR2 = 0.0769 R1 = 0.0460, wR = 0.0750 Goodness-of-fit on F 0.97 0.95 −3 Δρ /Δρ (e˚A ) 0.64, − 0.60 0.62, − 0.58 max min without any imaginary frequency. The bonding analyses Electrochemistry pertaining to energy decomposition, were carried out at BP86/TZ2P(ZORA)//BP86/def2-SVP with C symmetry. Cyclic voltammograms were recorded employing a SAMA The basis sets for all elements had triple-f quality aug- Research Analyzer M-500. Three electrodes are utilized in mented by one set of polarization functions (ADF basis set this system, a glassy carbon working electrode, a platinum TZ2P(ZORA)) with the program package ADF2013.01. disk auxiliary electrode and Ag wire as reference elec- EDA calculations were performed to analyse the nature of trode. The glassy carbon working electrode was manu- 2+ 2+ bonds between the [Ni(MeIm)] and [Cu(MeIm)(H O)] ally cleaned with 1 µm alumina polish prior to each scan. 2− fragments and L ligand (Schiff base ligand) in the forego - Tetrabutylammonium hexafluorophosphate (TBAH) was ing complexes. used as the supporting electrolyte. Acetonitrile was dried over CaH . The solutions were deoxygenated for 5 min via purging with Ar. All electrochemical potentials were Results and discussions calibrated against ferrocene–ferrocenium couple under the same conditions [30]. Synthesis Computational details (theoretical studies) The new metal complexes were synthesized and character- ized by elemental analysis, FT-IR, H-NMR, UV–Vis and The geometries of the compounds were optimized without X-Ray diffraction. All complexes were stable at room tem- symmetry constraints at the BP86 [1, 2]/def2-SVP [31] level perature in the solid state and soluble in common organic of theory using the Gaussian 03 [32]. It has been shown that solvents (CH Cl , EtOH and CH CN). The spectroscopic BP86 is a suitable level for the calculation of the bonding 2 2 3 data concerning ligand and metal complexes in the “Experi- situation between the M ← L in complexes such as these mental” section are in good agreement with the expected [33–50]. Vibrational frequency analyses, done at the same values. level of theory, indicated that the optimized structures are at the stationary points corresponding to the local minima 1 3 Journal of the Iranian Chemical Society IR spectra of these ligands further showed a strong band at Spectroscopic characterizations of the complexes −1 1627 cm attributable to υ(C = N). This band, in the FT-IR spectra of the complexes, shifted to lower frequencies almost To clarify the mode of complexation and the effect of the −1 metal ion on the ligand, the FT-IR spectra of the free ligand between 10 and 30 cm probably indicating the involvement of nitrogen in coordination to the metal ions [23]. and their Ni(II) and Cu(II) complexes were compared and assigned on the basis of careful and minute comparison. In The electronic spectra of Schif base ligand and its com- plexes were recorded in CH CN (Fig. 1). As seen, the Schiff the IR spectrum of H L exhibited a broad band characteristic 2 3 −1 of the OH group at 3300–3500 cm . The disappearance base ligand shows a strong band at 362 nm which can be associated to n → π* transition of the azomethine chromo- of this band in the IR spectra of complexes is indicative of the fact that the Schiff base ligand is coordinated [26]. The phore. This band disappears in complexes after bonding Schiff base ligand to metal center [51]. All the bands in the 200–300 nm region are attributed to the π → π* transitions of the aromatic rings and the azomethine group. The ligand bands shift to longer wavelengths in the metal complexes as compared to their position in the free ligand which indi- cates the bond between Schiff base and metal center [ 52]. Complexes (1) and (2) show bands in 410–470 nm region assigned to the CT transition. As shown in Fig.  2, the H-NMR spectral data of the complex was recorded in CDCl with the chemical shifts expressed in ppm downfield from tetramethylsilane and presented in “Experimental” section. The H-NMR spectra of complex 2 indicate sharp singlet signals (s) at around 8.03 ppm due to the presence of azomethine protons, H . Moreover, the singlets at 3.74 ppm are assigned to CH pro- tons of N-methyl-imidazole, H . The aromatic protons of coordinated Schiff base and the amine ligands, H , b,c,d,e,f,g,h,i,j,k appear in the appropriate region of 6.51–7.65 ppm in com- Fig. 1 The electronic spectra of the free Schiff base ligand and the plex 2. related complexes in CH CN solution Fig. 2 H NMR spectrum of (2) in CDCl 1 3 Journal of the Iranian Chemical Society Table 2 Selected geometrical 1 (M = Cu) 2 (M = Ni) 1 (M = Cu) 2 (M = Ni) parameters (Å, °) with s.u.’s in parentheses M–O1 1.969 (2) 1.844 (4) M–O10 1.910 (2) 1.818 (4) M–N7 1.962 (3) 1.864 (5) M–N15 1.987 (3) 1.906 (5) M–O1W 2.335 (2) O1–M–O10 176.34 (10) 175.4 (2) N7–M–N15 168.03 (11) 174.8 (2) O1–M–N7 83.89 (11) 87.37 (19) N7–M–O1W 95.29 (10) O1–M–N15 94.66 (11) 89.81 (19) O10–M–N15 88.62 (11) 87.74 (19) O1–M–O1W 91.81 (9) O10–M–O1W 89.41 (9) N7–M–O10 92.56 (11) 95.4 (2) N15–M–O1W 96.63 (10) basal Cu1–O1 and Cu1–O10 bond distances of 1.969(2) and Description of the crystal structures 1.910(2) Å, respectively. The Cu–N and Cu–O bond dis- tances (Table 3) agree well with similar other square pyrami- The perspective views of the complexes 1 and 2 are shown dal Schiff base complexes of copper(II) [53, 54]. in Figs.  3 and 4, respectively. Selected bond lengths and The coordination number of Ni(II) ion in 2 is 4 (one angles for both complexes are listed in Table  2. In 1, Cu(II) nitrogen and two phenolic oxygen atoms from the tri- center is in a five-coordinate environment. The coordination dentate ligands, plus one nitrogen atoms from N-methyl polyhedron is a distorted square pyramid, with two oxygen imidazole molecules) and the geometry is square-planar. and nitrogen atoms from the Schiff base ligand and N atom Maximum deviation from the least-squares plane defined from N-methyl imidazole creating the base, and oxygen atom by four coordination centers is as small as 0.066(2)  Å from a water molecule at the axial position. The four basal and the Ni ion lies exactly in this plane (deviation of atoms are making quite a good plane (maximum deviation of 0.004(2) Å). Table 3 shows that the angles within coordi- 0.095(2) Å), and the Cu–O1W direction is almost perfectly nation square are slightly different—in fact, such a slightly perpendicular to this plane (88.5°). The axial Cu1–O1W distorted square planar geometry is similar to previously bond distance of 2.335(2) Å is significantly larger than the reported analogs [55, 56]. In both complexes, the Schiff base ligand molecule is almost planar, the dihedral angle between the planes of ter- minal rings is 8.0(3)° in 1 and 7.7(4)º in 2. In the crystal structure of 1—thanks to the presence of water molecule—O–H(water)···O(ligand) hydrogen bonds Fig. 3 The molecular structure of (1) with labeling scheme Fig. 4 The molecular structure of (2) with labeling scheme 1 3 Journal of the Iranian Chemical Society Table 3 Hydrogen bond data for D H A D–H H···A D···A D–H···A 1 (symmetry codes: x, − 1 + y, ii z; 3/2 − x, − 1/2 + y, 1.2 − z) O1W H1WA O1 0.90 1.91 2.796 (3) 166 ii O1W H1WB O1 0.88 1.93 2.796 (3) 171 Fig. 5 The fragment of hydrogen-bonded chain in (1) Fig. 7 µ Cyclic voltammogram of (1) in CH CN at 298  K, scan rate = 100 mV/S copper complex, the redox couple Cu(II)/Cu(I) is important and is known to be influenced by such ligand factors as the nature of donor atoms and their structural arrangements around the copper ion [57]. The copper complex (Fig. 7) shows an irreversible redox couple with a cathodic and anodic peak potential at − 1.08 and − 0.93 V, respectively [58]. The cyclic voltammogram of Ni(II) complex (Fig. 8) shows an anodic peak at E = 0.82  V cor responding to pa II III Ni → Ni [59–62]. Theoretical studies Fig. 6 The crystal packing of (2) The geometry of the metal complexes of both [Cu(L)(MeIm) (H O)] (1) and [Ni(L)(MeIm)] (2) complexes was specified connect molecules into infinite chains along y-direction by the X-ray crystal structure analysis, and fully optimized (Table 3; Fig. 5). Structure of 2 lacks strong hydrogen bond at BP86/def2-SVP level of theory. The obtained optimized donors, so the complex molecules create the layers, only geometry of both above complexes were similar to those very loosely interacting with one another (Fig. 6). derived by X-ray crystal structures (See Fig. 9). Table  4 shows the selected calculated bond lengths and bond angles Electrochemical studies of both complexes. With the help of NBO analysis, we fur- ther investigated the nature of bonds between two interact- 2+ 2+ The cyclic voltammetry of the complexes (1, 2) was con- ing fragments, [Cu(MeIm)(H O)] and [Ni(MeIm)] and 2− ducted at 25 °C under an argon atmosphere using acetoni- L ligand (the studied Schiff base ligand). The Wiberg bond −3 2+ 2+ trile solvent containing 0.1 mol dm TBAH as the sup- indices (WBIs) for M → L (M = Cu ,Ni ) bonds were cal- porting electrolyte and complex concentrations of about culated, which corresponding values are given in Table  4. −3 −3 4 × 10  mol dm . In general, redox data are used to iden- The values of WBIs for M → N bonds in the complexes are tify the model system among the synthetic complexes. In the almost similar, yet those of M → O bond lengths obtained 1 3 Journal of the Iranian Chemical Society Table 4 The important bond lengths (Å) and bond angles (˚) and Wiberg bond indices (WBI) of [Cu(L)(MeIm)(H2O)] (1) and [Ni(L) (MeIm)] (2) complexes at BP86/def2-SVP level of theory [Cu(L)(MeIm)(H O)] [Ni(L)(MeIm)] Bond lengths (Å) WBI Bond lengths (Å) WBI M–N13 1.97 (1.96) 0.3404 1.98 (1.86) 0.3382 M–N27 1.98 (1.99) 0.2831 2.02 (1.90) 0.2913 M–O3 2.03 (1.97) 0.3626 1.92 (1.84) 0.4270 M–O18 1.97 (1.91) 0.3302 1.92 (1.82) 0.4135 M–O39(H O) 2.49 (2.33) 0.1353 − Bond angels (˚) Bond angels (˚) N13–M–O18 94.30 (92.59) 93.94 (95.37) N13–M–N27 161.18 (168.03) 175.44 (174.79) N13–M–O3 85.01 (83.89) 84.99 (87.33) O18–M–N27 91.36 (88.60) 90.61 (87.72) O18–M–O3 177.85 (176.37) 178.93 (175.41) Fig. 8 Cyclic voltammogram of (2) in CH CN at 298  K, scan N27–M–O3 89.92 (94.65) 90.44 (89.86) −4 rate = 100 mV/S, c = 5.6 × 10 M The experimental data are given in parenthesis for [Ni(L)(MeIm)] complex are greater than the correspond- Morokuma [63] and Ziegler et al. [64] have recently pre- ing values of [Cu(L)(MeIm)(H O)] complex. Also, in the sented the “energy decomposition analysis” (EDA) method, complexes, the value of M → N bonds obtained from Schiff where a quantitative computational pattern explains the base ligand are slightly higher than that obtained from imi- strength of M ← L σ donation and M → L back bonding in dazole ligand. the main group and transition metal complexes with different Further studied were the values of natural charges on M types of ligands [33–50, 65–69]. metal ions and N and O atoms in Schiff base ligand (L) and To better fathom the nature of the bonding situation imidazole ligands (see Table  5). 2+ 2+ between [Cu(MeIm)(H O)] and [Ni(MeIm)] fragments 2− 2 Also, the values of charge transfer from L ligand (Schiff and Schiff base ligand L in the complexes, the energy- 2+ 2+ base ligand) to [Cu(MeIm)(H O)] and [Ni(MeIm)] frag- decomposition analysis (EDA) was carried out at BP86/ ments in the latter complexes are about − 0.96 and − 0.93 TZ2P(ZORA)//BP86/def2-SVP with C symmetry. The e, respectively. results indicated that the ∆E for [Ni(L)(MeIm)] complex int −1 is about 545.8 kcal mol and more than the corresponding Fig. 9 Optimized geometries of [Ni(L)(MeIm)] and [Cu(L)(MeIm)(H O)] complexes at BP86/def2-SVP level of theory 1 3 Journal of the Iranian Chemical Society Table 5 Natural charges of M, N and O atoms of [Cu(L)(MeIm) value for [Cu(L)(MeIm)H O] complex (see Table  6). The (H2O)] (1) and [Ni(L)(MeIm)] (2) complexes at BP86/def2-SVP breakdown of the ΔE values into the Pauli repulsion, int level of theory ΔE and the three attractive components shows that Pauli Natural charge [Cu(L)(MeIm) [Ni(L)(MeIm)] roughly 65% come from the electrostatic attraction (ΔE ) elstat (H O)] while ~ 34% come from the orbital term ΔE in [Cu(L) orb (MeIm)(H O)] and[Ni(L)(MeIm)] complexes. In addition, NPA (M) 0.417 0.553 2 the values of ∆E show that the nature of M → N bonds NPA (O3) − 0.354 − 0.384 elstat in the complexes is more electrostatic. The covalent bonding NPA (N13) − 0.152 − 0.179 2+ between the two interacting fragments, [Cu(MeIm)(H O)] NPA (O18) − 0.369 − 0.363 2 2− 2+ and L in [Cu(L)(MeIm)(H O)] complex and [Ni(MeIm)] NPA (N27) − 0.217 − 0.235 2 2− and L in [Ni(L)(MeIm)] complex becomes visible by the NPA (O39(H O)) − 0.245 2− calculated deformation densities Δρ, which are associated NPA L (Schiff base ligand) − 1.04 − 1.07 with the significant orbital interactions between the cor - responding fragments. Figures 10 and 11 show important Fig. 10 Deformation densities Δρ associated with the most important orbital interactions in [Cu(L)(MeIm)(H O)] complex Δρ1α: ΔE= -17.45 (kcal/mol), ν= 0.25 Δρ1β: ΔE= -94.74 (kcal/mol),ν= 0.96 Δρ2β: ΔE= -15.96 (kcal/mol),ν= 0.23 Counter =0.001 Counter =0.0007 Counter =0.0005 Δρ4β: ΔE= -6.87 (kcal/mol), ν= 0.17 Δρ4α: ΔE= -5.14 (kcal/mol), ν= 0.13 Δρ3β: ΔE= -9.12 (kcal/mol), ν= 0.20 Counter=0.0001 Counter =0.0001 Counter =0.0001 Δρ5β: ΔE= -4.86 (kcal/mol), ν= 0.13 Δρ6α: ΔE= -6.53 (kcal/mol), ν= 0.12 Δρ5α: ΔE= -5.42 (kcal/mol), ν= 0.12 Counter =0.0001 Counter =0.0001 Counter =0.0001 Δρ6β: ΔE= -6.65 (kcal/mol), ν= 0.12 Δρ7β: ΔE= -3.58 (kcal/mol), ν= 0.12 Counter =0.0001 Counter =0.0001 1 3 Journal of the Iranian Chemical Society Fig. 11 Deformation densities Δρ associated with the most important orbital interactions in [Ni(L)(MeIm)] complex Δρ1α: ΔE= -17.49 (kcal/mol), ν= 0.25 Δρ1β: ΔE= -71.44 (kcal/mol),ν= Δρ3β: ΔE= -6.75 (kcal/mol), ν= 0.17 Counter =0.0007 0.93 Counter =0.0001 Counter =0.001 Δρ4β: ΔE= -14.35 (kcal/mol), ν= 0.20 Δρ3β: ΔE= -7.61 (kcal/mol), ν= 0.21 Δρ4α: ΔE= -5.01 (kcal/mol), ν= Counter =0.0001 Counter =0.0001 0.13 Counter =0.0001 Δρ5α: ΔE= -6.25 (kcal/mol), ν= 0.12 Δρ5β: ΔE= -7.61 (kcal/mol), ν= Δρ6α: ΔE= -6.52 (kcal/mol), ν= 0.11 Counter =0.0001 0.20 Counter =0.0001 Counter =0.0001 Δρ6β: ΔE= -4.41 (kcal/mol),ν= 0.13 Δρ8α: ΔE= -3.76 (kcal/mol),ν= 0.09 Δρ7β: ΔE= -6.85 (kcal/mol), ν= Counter =0.0001 Counter =0.0001 0.11 Counter =0.0001 Δρ8β: ΔE= -4.25 (kcal/mol), ν= 0.10 Counter =0.0001 1 3 Journal of the Iranian Chemical Society Table 6 EDA analysis (BP86/TZ2P(ZORA)//BP86/def2-TZVP) of Magnetic measurement the [Cu(L)(MeIm)(H O)] (1) and [Ni(L)(MeIm)] (2) complexes with the C1 symmetry The magnetic characterization of [Cu(L)(MeIm)(H O)] (1) [Cu(L)(MeIm)(H O)] [Ni(L)(MeIm)] complex was examined using vibration sampling magnetom- eter (VSM). The magnetic behavior of the complex in the ∆E − 512.50 − 545.83 int M–H [M—magnetization (memu/g) and H—magnetic field ∆E 209.94 228.21 Pauli (Gouss)] curve are shown in Fig. 12. The fine shape of the ∆E − 474.71 (65.72%) − 501.59 (64.80%) elstat hysteresis loop is a characteristic of a weak ferromagnetic ∆E − 239.67 (33.18%) − 267.00 (34.50%) orb behavior. ∆E − 7.96 (1.10%) − 5.45 (0.7%) disp deformation densities (Δρ) and related energy values, pro- Conclusions viding around 61 and 73.5% of the overall orbital interac- tions for both [Cu(L)(MeIm)(H O)] and [Ni(L)(MeIm)] Two new Schiff base complexes were synthesized and char - complexes, respectively. Figure 10 illustrates the deforma- acterized by the spectral and analytical techniques. The tion densities Δρ1α and 1β, Δρ2β, Δρ3β, Δρ5α, Δρ6α and crystal structures of complexes (1) and (2) were specified 6β, and Δρ7β,which come from M ← L σ donation from the by X-ray crystallography. The electrochemical reduction 2− lone pair of N and O atoms of L ligand (Schiff base ligand) of these complexes at a carbon glass electrode in CH CN to Cu metal ion in [Cu(L)(MeIm)(H O)] complex. In the last solution indicates that the redox reaction of Ni(III)/Ni(II) figure, the deformation densities, Δρ3β, and Δρ4β represent and Cu(II)/Cu(I) is irreversible. The bonding situation 2+ the M ← L π donation and Δρ4α and Δρ5β represent the π between the two interacting fragments, [Ni(MeIm)] and 2− 2+ back-donation, respectively (See Fig. 8). On the other hand, L in [Ni(L)(MeIm)] complex and [Cu(MeIm)(H O)] and 2− the visual inspection of Fig. 11 indicates that Δρ1α and 1β, L in [Cu(L)(MeIm)(H O)] complex was analyzed by NBO Δρ4β, Δρ5α, Δρ6α, Δρ7β, Δρ8α and Δρ8β come from the and energy-decomposition analysis (EDA), and its natural M ← L σ donation from the lone pair of N and O atoms of orbitals for chemical valence variation (EDA–NOCV). 2− L ligand (Schiff base ligand) to Ni metal ion in [Ni(L) The findings indicated that the values of WBIs for M → N (MeIm)] complex. Furthermore, the deformation densities bonds in the complexes are almost similar but the values Δρ3α, Δρ3β, and Δρ5β represent the M ← L π donation and of M → O bond lengths obtained for [Ni(L)(MeIm)] com- Δρ4β indicates the π back-donation. Note that the colour in plex are slightly more than the corresponding values for Figs. 8 and 9 denotes the charge flow, which is from red to [Cu(L)(MeIm)(H O)] complex. 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Dis. 124, Trans. 46, 207–220 (2017) 365–378 (2003) 66. M. Lein, G. Frenking, Chap. 13 (Elsevier, Amsterdam, 2005), pp. 291–372 1 3 http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png Journal of the Iranian Chemical Society Springer Journals

New complexes of Ni(II) and Cu(II) with tridentate ONO Schiff base ligand: synthesis, crystal structures, electrochemical and theoretical investigation

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Chemistry; Analytical Chemistry; Inorganic Chemistry; Physical Chemistry; Biochemistry, general; Organic Chemistry
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10.1007/s13738-018-1412-1
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Abstract

In this research, we prepared a new series of the Cu(II) (1) and Ni(II) (2) metal complexes of a tridentate Schiff base ligand, (E)-2-(5-bromo-2-hydroxybenzylideneamino) phenol (H L). These complexes were characterized by elemental analysis, FT-IR, UV–Vis, and H-NMR spectroscopy. The crystal structures of (1) and (2) were determined by X-ray diffraction studies. The single crystal X-ray diffraction analyses revealed that copper(II) cation is five-coordinated and the coordination polyhedron is a slightly distorted square pyramid. Nickel(II), on the other hand, is four-coordinated, and has a regular, square planar geometry. Further discussed were the electrochemical reduction of these complexes. We also analyzed the nature of the metal–ligand bond in the complexes through NBO and EDA analysis. Besides, vibrational sample magnetometer (VSM) revealed complex (1) was ferromagnetic. Keywords Schiff base · Copper(II) complex · Nickel(II) complex · Crystal structure · Theoretical investigation · Electrochemical studies Introduction modeling, and catalytic activity and their function as anti- microbial, antifungal and antitumor agents [11–15]. It has Schiff bases, whose metal complexes are of great interest, been demonstrated that biological activities of these com- have often been employed as chelating ligands in the field pounds are influenced significantly by metal coordination of coordination chemistry [1–3]. They are able to coordi- [16, 17]. There is also some evidence suggesting that these nate metals through imine nitrogen and another group, drugs interact directly with DNA, blocking the activity of more often than not, linked to aldehyde or ketone [4]. Schiff DNA–gyrase repair enzymes [18–20]. Schiff bases facili- base metal complexes also find diverse and fruitful applica- tate the process of inducing substrate chirality, tuning the tions in industry and daily life [5–10]. There exist myriad metal-centered electronic factor, enhancing solubility and reports on the biological activities of Schiff base ligands performing either homogeneous or heterogeneous catalysts and their metal complexes, including their use for enzyme [21]. Furthermore, recent studies have witnessed a great deal of interest in the synthesis and characterization of transition metal complexes containing Schiff bases as ligands due to Electronic supplementary material The online version of this their applications in pharmaceutical fields. article (https ://doi.org/10.1007/s1373 8-018-1412-1) contains Since the synthesis of new compounds with new proper- supplementary material, which is available to authorized users. ties are important in inorganic chemistry, we have focused * Mehdi Salehi on the synthesis and characterization of new Schiff base msalehi@semnan.ac.ir ligands and their complexes to check out their applica- 1 tions in the future. Considering the remarkable importance Department of Chemistry, College of Science, Semnan of Schiff base complexes and so as to continue our previ- University, Semnan, Iran 2 ous work [22–25], we found it worthwhile to synthesize Faculty of Chemistry, Adam Mickiewicz University, and characterize new complexes of Ni(II) and Cu(II) with Umultowska 89b, 61-614 Poznan, Poland 3 1-methyl-imidazole and a tridentate Schiff base ligand, Department of Inorganic Chemistry, Faculty of Chemistry, obtained by the condensation of 2-aminophenol with Bu-Ali Sina University, Hamedan 65167, Iran Vol.:(0123456789) 1 3 Journal of the Iranian Chemical Society II 5-bromo-2- hydroxybenzaldehyde (Scheme  1). In addi-Synthesis of  [Ni (L)(MeIm)] (2) tion, a theoretical study was conducted on the structure and nature of the metal–ligand bond in complexes at the BP86/ This complex was prepared by the same procedure TZ2P(ZORA)//BP86/def2-SVP level of theory. applied to complex (1), with the exception that instead of Cu(CH COO) .H O, 0.5  mmol (0.124  g) of the 3 2 2 Ni(CH COO) .4H O was used. The red crystals, suitable for 3 2 2 Experimental X-ray data collection, were obtained by slow evaporation of the methanol solution after 4 days. Yield: 70%. Anal. Calcd. Materials and methodsfor C H BrN NiO (%): C, 47.38; H, 3.27; N, 9.75. Found 17 14 3 2 −1 (%): C, 47.22; H, 3.18; N, 9.70%. FT-IR: ν (cm ) (KBr): max −1 −1 All starting materials and solvents were purchased from 1596 (ν ). UV–Vis in CH CN: λ (nm) (ɛ, M cm ): C=N 3 max commercial sources and used without further purification. 238 (43,500), 275 (22,650), 312 (8500), 330 (19,500), 444 The elemental analyses of carbon, nitrogen and hydrogen (16,200). H-NMR (CDCl , 400 MHz): 8.04 (s, 1H, H ), 3 l atoms were done through the use of a Perkin-Elmer 2400II 7.65 (s, 1H, H ), 7.53 (dd, 1H, J = 1.2, J = 8.4 Hz, H ), 7.48 k 1 1 j CHNS-O elemental analyzer. FT-IR spectra were recorded (d, 1H, J = 2.4 Hz, H ), 7.25 (dd, H, J = 2.4, J = 9 Hz, H ), i 1 2 h −1 in the range of 4000–400 cm on a FT-IR SHIMADZU 8.61 (s, 1H, H ), 7.00 (t, 1H, J = 1.2, J = 7.4 Hz, H ), 6.84 g 1 2 f spectrophotometer from KBr pellet. UV–Vis spectra were (t, 1H, J = 1.6 Hz, H ), 6.81 (d, 1H, J = 9.2 Hz, H ), 6.74 (dd, e d recorded on a UV-1650 PC SHIMADZU spectrophotom- 1H, J = 1.2, J = 8.4 Hz, H ), 6.53 (t, 1H, J = 1.2, J = 8 Hz, 1 2 c 1 2 eter in acetonitrile solution. Using CDCl as the solvent, H ), 3.74 (s, 3H, H ). 3 b a H-NMR measurements were performed on NMR BRUKER 400 MHZ spectrometer, at 25 °C. The Schiff base ligand X‑ray crystallography analyses was prepared according to the literature [26]. Also, magnetic measurements were carried out with a vibrating sampling The X-ray single crystal data for complexes 1 and 2 were magnetometer (VSM, Model 7400- LakeShore). collected at 100(1) K by the ω-scan technique on an Agilent Technologies Xcalibur four-circle diffractometer with Eos Synthesis of the complexes CCD detector, equipped with graphite-monochromatized MoK radiation source (λ = 0.71073 Å). The data were cor- II Synthesis of  [Cu (L)(MeIm)(H O)] (1) rected for Lorentz-polarization as well as for absorption effects [27]. Precise unit-cell parameters were determined In a typical experiment, a methanolic solution (10  mL) by a least-squares fit of 2189 (1 ) and 1478 (2) reflections of of 0.5 mmol (0.099 g) Cu(CH COO) .H O was added to the highest intensity, chosen from the whole experiment. The 3 2 2 0.5 mmol (0.146 g) methanolic solution of ligand. The mix- structures were solved with S FT-IR 92 [28] and refined with ture color turned green. After that, N-methyl imidazole was the full-matrix least-squares procedure on F by SHELXL97 added dropwise. The reaction mixture was refluxed for 3 h. [29]. All non-hydrogen atoms were refined anisotropically. The green-colored single crystals suitable for X-ray data Hydrogen atoms were found from water molecule in 1 in the collection were obtained by slow evaporation of the solu- different Fourier map, all other ones were positioned geo- tion. Yield: 58%. Anal. Calcd. for C H BrCuN O (%): metrically and refined with a riding model approximation 17 16 3 3 C, 44.99; H, 3.55; N, 9.26. Found (%): C, 44.75; H, 3.38; with their displacement parameters constrained to the parent −1 N, 9.25. FT-IR: ν (cm ) (KBr): 1608 (ν ). UV–Vis atom with U (H) = 1.2 (CH, CH, H O) or 1.5 (CH ) U max C=N iso 2 2 3 eq −1 −1 in CH CN: λ (nm) (ɛ, M   cm ): 249 (26,000), 277 (C). The summary of crystal data and refinement for (1) and 3 max (16,100), 304 (8900), 318 (15,050), 427 (13,280). (2) are given in Table 1. Scheme 1 Synthetic procedure for the preparation of complexes 1 3 Journal of the Iranian Chemical Society Table 1 Crystal data and Compound (1) (2) structure refinement parameters for complexes (1) and (2) Empirical formula C H Br Cu N O C H Br N Ni O 17 16 3 3 17 14 3 2 Formula weight 453.78 430.90 Temperature (K) 293 293 Wavelength λ (Å) 0.71073 0.71073 Crystal system Monoclinic Orthorhombic Space group P2 /n P2 2 2 1 1 1 1 Unit cell dimensions  a (Å) 15.0867 (6) 5.8913 (6)  b (Å) 5.4040 (2) 15.715 (2)  c (Å) 20.1813 (10) 16.8121 (18)  β (◦) 91.082 (4) Volume (Å ), Z 1645.06 (12), 4 1556.5 (3), 4 Calculated density (g/cm ) 1.83 1.84 θ ranges for data collection (◦) 3.3–28.2 3.5–28.0 F(000) 908 864 −1 ) 3.78 1.34 Absorption coefficient (mm Total reflections 6905 4348 Unique reflections (R ) 3409 (0.037) 2718 (0.034) int Observed data [I > 2σ(I)] 2554 2359 Number of parameters 227 218 Final R index [I > 2σ(I)] R1 = 0.0360, wR2 = 0.0710 R1 = 0.0358, wR = 0.0700 R index (all data) R1 = 0.0587, wR2 = 0.0769 R1 = 0.0460, wR = 0.0750 Goodness-of-fit on F 0.97 0.95 −3 Δρ /Δρ (e˚A ) 0.64, − 0.60 0.62, − 0.58 max min without any imaginary frequency. The bonding analyses Electrochemistry pertaining to energy decomposition, were carried out at BP86/TZ2P(ZORA)//BP86/def2-SVP with C symmetry. Cyclic voltammograms were recorded employing a SAMA The basis sets for all elements had triple-f quality aug- Research Analyzer M-500. Three electrodes are utilized in mented by one set of polarization functions (ADF basis set this system, a glassy carbon working electrode, a platinum TZ2P(ZORA)) with the program package ADF2013.01. disk auxiliary electrode and Ag wire as reference elec- EDA calculations were performed to analyse the nature of trode. The glassy carbon working electrode was manu- 2+ 2+ bonds between the [Ni(MeIm)] and [Cu(MeIm)(H O)] ally cleaned with 1 µm alumina polish prior to each scan. 2− fragments and L ligand (Schiff base ligand) in the forego - Tetrabutylammonium hexafluorophosphate (TBAH) was ing complexes. used as the supporting electrolyte. Acetonitrile was dried over CaH . The solutions were deoxygenated for 5 min via purging with Ar. All electrochemical potentials were Results and discussions calibrated against ferrocene–ferrocenium couple under the same conditions [30]. Synthesis Computational details (theoretical studies) The new metal complexes were synthesized and character- ized by elemental analysis, FT-IR, H-NMR, UV–Vis and The geometries of the compounds were optimized without X-Ray diffraction. All complexes were stable at room tem- symmetry constraints at the BP86 [1, 2]/def2-SVP [31] level perature in the solid state and soluble in common organic of theory using the Gaussian 03 [32]. It has been shown that solvents (CH Cl , EtOH and CH CN). The spectroscopic BP86 is a suitable level for the calculation of the bonding 2 2 3 data concerning ligand and metal complexes in the “Experi- situation between the M ← L in complexes such as these mental” section are in good agreement with the expected [33–50]. Vibrational frequency analyses, done at the same values. level of theory, indicated that the optimized structures are at the stationary points corresponding to the local minima 1 3 Journal of the Iranian Chemical Society IR spectra of these ligands further showed a strong band at Spectroscopic characterizations of the complexes −1 1627 cm attributable to υ(C = N). This band, in the FT-IR spectra of the complexes, shifted to lower frequencies almost To clarify the mode of complexation and the effect of the −1 metal ion on the ligand, the FT-IR spectra of the free ligand between 10 and 30 cm probably indicating the involvement of nitrogen in coordination to the metal ions [23]. and their Ni(II) and Cu(II) complexes were compared and assigned on the basis of careful and minute comparison. In The electronic spectra of Schif base ligand and its com- plexes were recorded in CH CN (Fig. 1). As seen, the Schiff the IR spectrum of H L exhibited a broad band characteristic 2 3 −1 of the OH group at 3300–3500 cm . The disappearance base ligand shows a strong band at 362 nm which can be associated to n → π* transition of the azomethine chromo- of this band in the IR spectra of complexes is indicative of the fact that the Schiff base ligand is coordinated [26]. The phore. This band disappears in complexes after bonding Schiff base ligand to metal center [51]. All the bands in the 200–300 nm region are attributed to the π → π* transitions of the aromatic rings and the azomethine group. The ligand bands shift to longer wavelengths in the metal complexes as compared to their position in the free ligand which indi- cates the bond between Schiff base and metal center [ 52]. Complexes (1) and (2) show bands in 410–470 nm region assigned to the CT transition. As shown in Fig.  2, the H-NMR spectral data of the complex was recorded in CDCl with the chemical shifts expressed in ppm downfield from tetramethylsilane and presented in “Experimental” section. The H-NMR spectra of complex 2 indicate sharp singlet signals (s) at around 8.03 ppm due to the presence of azomethine protons, H . Moreover, the singlets at 3.74 ppm are assigned to CH pro- tons of N-methyl-imidazole, H . The aromatic protons of coordinated Schiff base and the amine ligands, H , b,c,d,e,f,g,h,i,j,k appear in the appropriate region of 6.51–7.65 ppm in com- Fig. 1 The electronic spectra of the free Schiff base ligand and the plex 2. related complexes in CH CN solution Fig. 2 H NMR spectrum of (2) in CDCl 1 3 Journal of the Iranian Chemical Society Table 2 Selected geometrical 1 (M = Cu) 2 (M = Ni) 1 (M = Cu) 2 (M = Ni) parameters (Å, °) with s.u.’s in parentheses M–O1 1.969 (2) 1.844 (4) M–O10 1.910 (2) 1.818 (4) M–N7 1.962 (3) 1.864 (5) M–N15 1.987 (3) 1.906 (5) M–O1W 2.335 (2) O1–M–O10 176.34 (10) 175.4 (2) N7–M–N15 168.03 (11) 174.8 (2) O1–M–N7 83.89 (11) 87.37 (19) N7–M–O1W 95.29 (10) O1–M–N15 94.66 (11) 89.81 (19) O10–M–N15 88.62 (11) 87.74 (19) O1–M–O1W 91.81 (9) O10–M–O1W 89.41 (9) N7–M–O10 92.56 (11) 95.4 (2) N15–M–O1W 96.63 (10) basal Cu1–O1 and Cu1–O10 bond distances of 1.969(2) and Description of the crystal structures 1.910(2) Å, respectively. The Cu–N and Cu–O bond dis- tances (Table 3) agree well with similar other square pyrami- The perspective views of the complexes 1 and 2 are shown dal Schiff base complexes of copper(II) [53, 54]. in Figs.  3 and 4, respectively. Selected bond lengths and The coordination number of Ni(II) ion in 2 is 4 (one angles for both complexes are listed in Table  2. In 1, Cu(II) nitrogen and two phenolic oxygen atoms from the tri- center is in a five-coordinate environment. The coordination dentate ligands, plus one nitrogen atoms from N-methyl polyhedron is a distorted square pyramid, with two oxygen imidazole molecules) and the geometry is square-planar. and nitrogen atoms from the Schiff base ligand and N atom Maximum deviation from the least-squares plane defined from N-methyl imidazole creating the base, and oxygen atom by four coordination centers is as small as 0.066(2)  Å from a water molecule at the axial position. The four basal and the Ni ion lies exactly in this plane (deviation of atoms are making quite a good plane (maximum deviation of 0.004(2) Å). Table 3 shows that the angles within coordi- 0.095(2) Å), and the Cu–O1W direction is almost perfectly nation square are slightly different—in fact, such a slightly perpendicular to this plane (88.5°). The axial Cu1–O1W distorted square planar geometry is similar to previously bond distance of 2.335(2) Å is significantly larger than the reported analogs [55, 56]. In both complexes, the Schiff base ligand molecule is almost planar, the dihedral angle between the planes of ter- minal rings is 8.0(3)° in 1 and 7.7(4)º in 2. In the crystal structure of 1—thanks to the presence of water molecule—O–H(water)···O(ligand) hydrogen bonds Fig. 3 The molecular structure of (1) with labeling scheme Fig. 4 The molecular structure of (2) with labeling scheme 1 3 Journal of the Iranian Chemical Society Table 3 Hydrogen bond data for D H A D–H H···A D···A D–H···A 1 (symmetry codes: x, − 1 + y, ii z; 3/2 − x, − 1/2 + y, 1.2 − z) O1W H1WA O1 0.90 1.91 2.796 (3) 166 ii O1W H1WB O1 0.88 1.93 2.796 (3) 171 Fig. 5 The fragment of hydrogen-bonded chain in (1) Fig. 7 µ Cyclic voltammogram of (1) in CH CN at 298  K, scan rate = 100 mV/S copper complex, the redox couple Cu(II)/Cu(I) is important and is known to be influenced by such ligand factors as the nature of donor atoms and their structural arrangements around the copper ion [57]. The copper complex (Fig. 7) shows an irreversible redox couple with a cathodic and anodic peak potential at − 1.08 and − 0.93 V, respectively [58]. The cyclic voltammogram of Ni(II) complex (Fig. 8) shows an anodic peak at E = 0.82  V cor responding to pa II III Ni → Ni [59–62]. Theoretical studies Fig. 6 The crystal packing of (2) The geometry of the metal complexes of both [Cu(L)(MeIm) (H O)] (1) and [Ni(L)(MeIm)] (2) complexes was specified connect molecules into infinite chains along y-direction by the X-ray crystal structure analysis, and fully optimized (Table 3; Fig. 5). Structure of 2 lacks strong hydrogen bond at BP86/def2-SVP level of theory. The obtained optimized donors, so the complex molecules create the layers, only geometry of both above complexes were similar to those very loosely interacting with one another (Fig. 6). derived by X-ray crystal structures (See Fig. 9). Table  4 shows the selected calculated bond lengths and bond angles Electrochemical studies of both complexes. With the help of NBO analysis, we fur- ther investigated the nature of bonds between two interact- 2+ 2+ The cyclic voltammetry of the complexes (1, 2) was con- ing fragments, [Cu(MeIm)(H O)] and [Ni(MeIm)] and 2− ducted at 25 °C under an argon atmosphere using acetoni- L ligand (the studied Schiff base ligand). The Wiberg bond −3 2+ 2+ trile solvent containing 0.1 mol dm TBAH as the sup- indices (WBIs) for M → L (M = Cu ,Ni ) bonds were cal- porting electrolyte and complex concentrations of about culated, which corresponding values are given in Table  4. −3 −3 4 × 10  mol dm . In general, redox data are used to iden- The values of WBIs for M → N bonds in the complexes are tify the model system among the synthetic complexes. In the almost similar, yet those of M → O bond lengths obtained 1 3 Journal of the Iranian Chemical Society Table 4 The important bond lengths (Å) and bond angles (˚) and Wiberg bond indices (WBI) of [Cu(L)(MeIm)(H2O)] (1) and [Ni(L) (MeIm)] (2) complexes at BP86/def2-SVP level of theory [Cu(L)(MeIm)(H O)] [Ni(L)(MeIm)] Bond lengths (Å) WBI Bond lengths (Å) WBI M–N13 1.97 (1.96) 0.3404 1.98 (1.86) 0.3382 M–N27 1.98 (1.99) 0.2831 2.02 (1.90) 0.2913 M–O3 2.03 (1.97) 0.3626 1.92 (1.84) 0.4270 M–O18 1.97 (1.91) 0.3302 1.92 (1.82) 0.4135 M–O39(H O) 2.49 (2.33) 0.1353 − Bond angels (˚) Bond angels (˚) N13–M–O18 94.30 (92.59) 93.94 (95.37) N13–M–N27 161.18 (168.03) 175.44 (174.79) N13–M–O3 85.01 (83.89) 84.99 (87.33) O18–M–N27 91.36 (88.60) 90.61 (87.72) O18–M–O3 177.85 (176.37) 178.93 (175.41) Fig. 8 Cyclic voltammogram of (2) in CH CN at 298  K, scan N27–M–O3 89.92 (94.65) 90.44 (89.86) −4 rate = 100 mV/S, c = 5.6 × 10 M The experimental data are given in parenthesis for [Ni(L)(MeIm)] complex are greater than the correspond- Morokuma [63] and Ziegler et al. [64] have recently pre- ing values of [Cu(L)(MeIm)(H O)] complex. Also, in the sented the “energy decomposition analysis” (EDA) method, complexes, the value of M → N bonds obtained from Schiff where a quantitative computational pattern explains the base ligand are slightly higher than that obtained from imi- strength of M ← L σ donation and M → L back bonding in dazole ligand. the main group and transition metal complexes with different Further studied were the values of natural charges on M types of ligands [33–50, 65–69]. metal ions and N and O atoms in Schiff base ligand (L) and To better fathom the nature of the bonding situation imidazole ligands (see Table  5). 2+ 2+ between [Cu(MeIm)(H O)] and [Ni(MeIm)] fragments 2− 2 Also, the values of charge transfer from L ligand (Schiff and Schiff base ligand L in the complexes, the energy- 2+ 2+ base ligand) to [Cu(MeIm)(H O)] and [Ni(MeIm)] frag- decomposition analysis (EDA) was carried out at BP86/ ments in the latter complexes are about − 0.96 and − 0.93 TZ2P(ZORA)//BP86/def2-SVP with C symmetry. The e, respectively. results indicated that the ∆E for [Ni(L)(MeIm)] complex int −1 is about 545.8 kcal mol and more than the corresponding Fig. 9 Optimized geometries of [Ni(L)(MeIm)] and [Cu(L)(MeIm)(H O)] complexes at BP86/def2-SVP level of theory 1 3 Journal of the Iranian Chemical Society Table 5 Natural charges of M, N and O atoms of [Cu(L)(MeIm) value for [Cu(L)(MeIm)H O] complex (see Table  6). The (H2O)] (1) and [Ni(L)(MeIm)] (2) complexes at BP86/def2-SVP breakdown of the ΔE values into the Pauli repulsion, int level of theory ΔE and the three attractive components shows that Pauli Natural charge [Cu(L)(MeIm) [Ni(L)(MeIm)] roughly 65% come from the electrostatic attraction (ΔE ) elstat (H O)] while ~ 34% come from the orbital term ΔE in [Cu(L) orb (MeIm)(H O)] and[Ni(L)(MeIm)] complexes. In addition, NPA (M) 0.417 0.553 2 the values of ∆E show that the nature of M → N bonds NPA (O3) − 0.354 − 0.384 elstat in the complexes is more electrostatic. The covalent bonding NPA (N13) − 0.152 − 0.179 2+ between the two interacting fragments, [Cu(MeIm)(H O)] NPA (O18) − 0.369 − 0.363 2 2− 2+ and L in [Cu(L)(MeIm)(H O)] complex and [Ni(MeIm)] NPA (N27) − 0.217 − 0.235 2 2− and L in [Ni(L)(MeIm)] complex becomes visible by the NPA (O39(H O)) − 0.245 2− calculated deformation densities Δρ, which are associated NPA L (Schiff base ligand) − 1.04 − 1.07 with the significant orbital interactions between the cor - responding fragments. Figures 10 and 11 show important Fig. 10 Deformation densities Δρ associated with the most important orbital interactions in [Cu(L)(MeIm)(H O)] complex Δρ1α: ΔE= -17.45 (kcal/mol), ν= 0.25 Δρ1β: ΔE= -94.74 (kcal/mol),ν= 0.96 Δρ2β: ΔE= -15.96 (kcal/mol),ν= 0.23 Counter =0.001 Counter =0.0007 Counter =0.0005 Δρ4β: ΔE= -6.87 (kcal/mol), ν= 0.17 Δρ4α: ΔE= -5.14 (kcal/mol), ν= 0.13 Δρ3β: ΔE= -9.12 (kcal/mol), ν= 0.20 Counter=0.0001 Counter =0.0001 Counter =0.0001 Δρ5β: ΔE= -4.86 (kcal/mol), ν= 0.13 Δρ6α: ΔE= -6.53 (kcal/mol), ν= 0.12 Δρ5α: ΔE= -5.42 (kcal/mol), ν= 0.12 Counter =0.0001 Counter =0.0001 Counter =0.0001 Δρ6β: ΔE= -6.65 (kcal/mol), ν= 0.12 Δρ7β: ΔE= -3.58 (kcal/mol), ν= 0.12 Counter =0.0001 Counter =0.0001 1 3 Journal of the Iranian Chemical Society Fig. 11 Deformation densities Δρ associated with the most important orbital interactions in [Ni(L)(MeIm)] complex Δρ1α: ΔE= -17.49 (kcal/mol), ν= 0.25 Δρ1β: ΔE= -71.44 (kcal/mol),ν= Δρ3β: ΔE= -6.75 (kcal/mol), ν= 0.17 Counter =0.0007 0.93 Counter =0.0001 Counter =0.001 Δρ4β: ΔE= -14.35 (kcal/mol), ν= 0.20 Δρ3β: ΔE= -7.61 (kcal/mol), ν= 0.21 Δρ4α: ΔE= -5.01 (kcal/mol), ν= Counter =0.0001 Counter =0.0001 0.13 Counter =0.0001 Δρ5α: ΔE= -6.25 (kcal/mol), ν= 0.12 Δρ5β: ΔE= -7.61 (kcal/mol), ν= Δρ6α: ΔE= -6.52 (kcal/mol), ν= 0.11 Counter =0.0001 0.20 Counter =0.0001 Counter =0.0001 Δρ6β: ΔE= -4.41 (kcal/mol),ν= 0.13 Δρ8α: ΔE= -3.76 (kcal/mol),ν= 0.09 Δρ7β: ΔE= -6.85 (kcal/mol), ν= Counter =0.0001 Counter =0.0001 0.11 Counter =0.0001 Δρ8β: ΔE= -4.25 (kcal/mol), ν= 0.10 Counter =0.0001 1 3 Journal of the Iranian Chemical Society Table 6 EDA analysis (BP86/TZ2P(ZORA)//BP86/def2-TZVP) of Magnetic measurement the [Cu(L)(MeIm)(H O)] (1) and [Ni(L)(MeIm)] (2) complexes with the C1 symmetry The magnetic characterization of [Cu(L)(MeIm)(H O)] (1) [Cu(L)(MeIm)(H O)] [Ni(L)(MeIm)] complex was examined using vibration sampling magnetom- eter (VSM). The magnetic behavior of the complex in the ∆E − 512.50 − 545.83 int M–H [M—magnetization (memu/g) and H—magnetic field ∆E 209.94 228.21 Pauli (Gouss)] curve are shown in Fig. 12. The fine shape of the ∆E − 474.71 (65.72%) − 501.59 (64.80%) elstat hysteresis loop is a characteristic of a weak ferromagnetic ∆E − 239.67 (33.18%) − 267.00 (34.50%) orb behavior. ∆E − 7.96 (1.10%) − 5.45 (0.7%) disp deformation densities (Δρ) and related energy values, pro- Conclusions viding around 61 and 73.5% of the overall orbital interac- tions for both [Cu(L)(MeIm)(H O)] and [Ni(L)(MeIm)] Two new Schiff base complexes were synthesized and char - complexes, respectively. Figure 10 illustrates the deforma- acterized by the spectral and analytical techniques. The tion densities Δρ1α and 1β, Δρ2β, Δρ3β, Δρ5α, Δρ6α and crystal structures of complexes (1) and (2) were specified 6β, and Δρ7β,which come from M ← L σ donation from the by X-ray crystallography. The electrochemical reduction 2− lone pair of N and O atoms of L ligand (Schiff base ligand) of these complexes at a carbon glass electrode in CH CN to Cu metal ion in [Cu(L)(MeIm)(H O)] complex. In the last solution indicates that the redox reaction of Ni(III)/Ni(II) figure, the deformation densities, Δρ3β, and Δρ4β represent and Cu(II)/Cu(I) is irreversible. The bonding situation 2+ the M ← L π donation and Δρ4α and Δρ5β represent the π between the two interacting fragments, [Ni(MeIm)] and 2− 2+ back-donation, respectively (See Fig. 8). On the other hand, L in [Ni(L)(MeIm)] complex and [Cu(MeIm)(H O)] and 2− the visual inspection of Fig. 11 indicates that Δρ1α and 1β, L in [Cu(L)(MeIm)(H O)] complex was analyzed by NBO Δρ4β, Δρ5α, Δρ6α, Δρ7β, Δρ8α and Δρ8β come from the and energy-decomposition analysis (EDA), and its natural M ← L σ donation from the lone pair of N and O atoms of orbitals for chemical valence variation (EDA–NOCV). 2− L ligand (Schiff base ligand) to Ni metal ion in [Ni(L) The findings indicated that the values of WBIs for M → N (MeIm)] complex. Furthermore, the deformation densities bonds in the complexes are almost similar but the values Δρ3α, Δρ3β, and Δρ5β represent the M ← L π donation and of M → O bond lengths obtained for [Ni(L)(MeIm)] com- Δρ4β indicates the π back-donation. Note that the colour in plex are slightly more than the corresponding values for Figs. 8 and 9 denotes the charge flow, which is from red to [Cu(L)(MeIm)(H O)] complex. 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