INTRODUCTION

Many Schiff bases were used as ligands in preparation of complexes with copper, nickel, cobalt, and iron [1, 2]. Synthetic organic semiconductors are widely used in electronic industry [3–5]. In this study, newly synthesized organic oxime-containing metal complexes were synthesized and their temperature-dependent electrical parameters studied.

RESULTS AND DISCUSSION

Earlier, we have studied reactions of isonitrosomethyl-p-tolyl ketone with 1,2-diaminobenzene and its metal complexes [6]. Herein, we report reactions of isonitroso-p-chloroacetophenone 2a and isonitroso-p-methylacetophenone 2b with 3,4-diaminotoluene in ethanol that led to formation of oximes 3a, 3b [7, 8]. Structures of the synthesized ligands were supported by IR, UV–Vis, and NMR spectroscopy, LC/MS-MS, elemental analysis, thermal analyses. In mononuclear complexes 4a and 4b Cu(II) ion was coordinated to nitrogen and oxygen atoms of the imine and oxime groups of the ligands. The compounds 4a and 4b were reacted with Cu(II) and Ni(II) perchlorates to obtain complexes 5a, 5b, 6a, 6b, 7a, and 7b (Scheme 1). In the homodinuclear 5a and 5b and heterodinuclear 6a and 6b complexes, second metal ions [Cu(II) or Ni(II)] coordinated with 1,10-phenanthroline nitrogen atoms. Homotrinuclear copper complexes 7a and 7b were formed by the combination of three Cu(II) ions with diimine-dioximes [9, 10]. Mononuclear complexes had the square pyramidal geometry, but we could not suggest any coordination geometry for the other complexes. The resulting complexes were readily soluble in methanol, ethanol, acetone, and chloroform but poorly soluble in water and ether [11]. Electrical conductivity of the synthesized complexes was studied in the temperature range of 300–400 K [12].

Scheme 1.
scheme 1

Synthetic approaches to the complexes.

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1H and 13C NMR spectra supported the structures of the ligands [13–17]. In IR spectra the bands of the (C=N)imine and (C=N)oxime groups recorded for 3a and 3b ligands in the ranges of 1608–1620 and 1576–1593 cm−1 were shifted to the lower frequencies upon complexation indicating that oxime and imine nitrogen atoms were coordinated to the metal ions [28]. Due to the fact that the mononuclear complexes were coordinated via nitrogen atoms, the M–O band was not observed.

In TGA experiments all complexes demonstrated the gradual weight loss upon heating. Generally, thermograms of the complexes were characterized by three or four decomposition steps within the temperature range 35–900°C. The first and second weight losses (75–175°C)–(175–240°C) were assigned to the lattice and coordinated water molecules. The third step in the range of 240–340°C indicated decomposition of the coordinated ligands. The fourth weight loss (400–900°C) indicated formation of the corresponding metal oxides [18–20].

Molar conductivity measurements were carried out at 25°C and used 2×10–5 mol methanol solutions, and the accumulated data for the complexes fall between 174 and 642 Ω–1 cm2 mol–1 which did not allow to establish a correlation between the copper-nickel ratios and molar conductivity [21].

The magnetic moments measured for mononuclear Cu(II) complexes 4a, 4b (1.84 and 1.90 B.M.) corresponded to one unpaired electron. The magnetic moments measured for homodinuclear complexes 5a and 5b (2.01 and 2.16 B.M.), heterodinuclear complexes 6a and 6b (2.91 B.M. and 2.94 B.M.) and trinuclear complexes 7a and 7b (1.71 and 1.81 B.M.) indicated their paramagnetic character. The data accumulated for trinuclear and dinuclear complexes were lower than magnetic moments equivalent to three and two electrons, which could be due to the strong intramolecular antiferromagnetic effect [22].

In UV-Vis spectra of 3a and 3b ligands the bands were recorded at 276 and 285 nm (ɛ = 32120 and 30960 mol–1 L cm–1) and assigned to the aromatic rings n–π* transitions. The bands at 314 and 333 nm (ɛ = 22340 and 25520 mol–1 L cm–1) were attributed to the imine and oxime π–π* transitions [21]. The absorption bands between 337 and 983 nm were attributed to ligand-to-metal charge transfer bands of the d-orbitals of copper and nickel metal centers [23–25].

According to Figs. 1a, 1b, electrical conductivity of the samples increased exponentially upon heating, indicating their semiconducting behavior. The higher Cu rate resulted in increased conductivity of the samples. Electrical conductivity of the complexes of the 3b series indicated their more stable behavior than that of the 3a series being dependent upon Cu content and temperature.

Fig. 1.
figure 1

Temperature dependence of electrical conductivity of 3a (a) and 3b (b) series.

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Activation energies were calculated for the samples in the temperature range of 300–400 K. Resistivity and conductivity values determined for complexes of 3a and 3b series measured at room temperature are given in Table 1 [26].

Table 1. Some electrical parameters and activation energies of 3a and 3b series complexes measured at room temperature
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EXPERIMENTAL

All reagents were purchased from Merck or Sigma-Aldrich and used without further purification. FT-IR spectra (400–4000 cm–1) were recorded on a Perkin Elmer FTIR Spectrophotometer. UV-Vis spectra were recorded in chloroform on Shimadzu UV-1800 spectrophotometer within the wavelength range of 200–800 nm. NMR spectra were measured on a Varian 400 MHz NMR Spectrometer. Mass spectra [ESI] were measured on an Agilent Micromass Quattro LC-MS/MS spectrometer. Thermo Finnigan Flash EA 1112 Model analyzer was used to carry out elemental analysis. Quantitative analysis of copper and nickel ions was carried out on a PerkinElmer Inc. Optima 2000 DV ICP-OES device. Melting points were determined by a Stuart melting point SMP10 apparatus. Conductivity was measured in methanol on a WTW Conductivity 7110 meter. Magnetic moments were measured on a Sherwood Scientific MX1 Model. TGA was carried out on a Perkin-Elmer Diamond TGA System. Temperature-dependent electrical measurements were carried out on a Janis brand cryostat. Temperature control was provided by a LakeShore 331 temperature control unit.

İsonitroso-p-methylacetophenone 2a and isonitroso-p-chloroacetophenone 2b were prepared according to the published methods [8, 27, 28]. N,N′-Bis[(1Z,2E)-1-(4-methylphenyl)-2-(hydroxyimino)-1-phenylethylidene]-4-methylbenzene-1,2-diamine 3a and N,N′-bis[(1Z,2E)-1-(4-chlorophenyl)-2-(hydroxyimino)ethylidene]-4-methylbenzene-1,2-diamine 3b were obtained according to the procedure described in [29]. All complexes were obtained by the modified previously reported method [6].

N,N′-Bis[(1Z,2E)-1-(4-methylphenyl)-2-(hydroxyimino)-1-phenylethylidene]-4-methylbenzene-1,2-diamine (3a). Yield 69%, mp 120–122°C. IR spectrum, ν, cm–1: 3227 (OH), 1671 (C=N, imine), 1606 (C=N, oxime), 1057 (=N–O). 1H NMR spectrum (CDCl3), δ, ppm: 2.45 s (6H) (Ar-CH3), 2.60 s (3H) (Aramine–CH3), 7.35–8.08 m (11H, Harom), 8.09 s (1H, H–C=N), 8.10 s (1H, H–C=N), 9.24 s (1H, OH), 9.26 s (1H, OH). 13C NMR spectrum, δС, ppm: 21.40, 21.80, 21.84, 126.96, 127.27, 127.35, 127.93, 128.38, 128.55, 129.02, 129.83, 131.58, 132.47, 134.13, 139.80, 139.91, 140.18, 140.31, 140.68, 140.75, 141.46, 142.37, 143.16, 151.03, 151.73. Found, %: C 72.74; H 5.82; N 13.64. C25H24N4O2. Calculated, %: C 72.80; H 5.86; N 13.58. MS (MM): m/z: 412.48 [M – 2]+. UV–Vis spectrum (CH2Cl2): 276 (32120), 314 (22340).

N,N′-Bis[(1Z,2E)-1-(4-chlorophenyl)-2-(hydroxyimino)ethylidene]-4-methylbenzene-1,2-diamine (3b). Yield 67%, mp 150–152°C. IR spectrum, ν, cm–1: 3247 (OH), 1669 (C=N, imine), 1592 (C=N, oxime), 1011 (=N–O). 1H NMR spectrum (CDCl3), δ, ppm: 2.59 s (3H) (Aramine–CH3), 7.55–8.02 m (11H, Harom), 8.04 s (1H, H–C=N), 8.05 s (1H, H–C=N), 9.19 s (1H, OH), 9.21 s (1H, OH). 13C NMR spectrum, δС, ppm: 21.88, 124.66, 124.78, 127.97, 128.38, 128.61, 128.81, 128.89, 129.06, 132.11, 132.25, 132.77, 135.73, 140.13, 140.41, 140.62, 141.03, 141.68, 141.84, 142.23, 142.64, 149.74, 150.46. Found, %: C 60.75; H 3.83; N 12.44. C23H18Cl2N4O2. Calculated, %: C 60.94; H 4.00; N 12.36. MS (MM): m/z: 453.32 [M – 3]+. UV–Vis spectrum (CH2Cl2): 285 (30960), 333 (25520).

[Cu(L1)(H2O)](ClO4)2·2H2O (4a). Yield 59%, mp 200–202°C. IR spectrum, ν, cm–1: 3705 (OH or H2O), 2323 (O···H–H), 1610 (C=N, imine), 1576 (C=N, oxime), 1434 (=N–O), 1107, 1052, 619 (ClO4), 481 (M–N). Found, %: C 42.02; H 4.31; N 7.74; Cu 8.78. C25H30Cl2CuN4O12. Calculated, %: C 42.11, H 4.24, N 7.86, Cu 8.91. μeff B.M.: 1.84. ΛMb: 174. UV–Vis spectrum (CH2Cl2): 352 (41140), 636 (5340).

[Cu(L2)(H2O)](ClO4)2·2H2O) (4b). Yield 59%, mp 209–212°C. IR spectrum, ν, cm–1: 3370 (H2O or OH), 2323 (O···H–H), 1620 (C=N, imine), 1593 (C=N, oxime), 1492 (=N–O), 1089, 1046, 619 (ClO4), 481 (M–N). Found, %: C 35.76; H 3.06; N 7.35; Cu 8.35. C23H24Cl4CuN4O13. Calculated, %: C 35.88; H 3.14; N 7.28; Cu 8.25. μeff B.M.: 1.90. ΛMb: 393. UV–Vis spectrum (CH2Cl2): 349 (34890), 599 (41360), 780 (29630), 983 (8280).

[Cu(L1)(H2O)Cu(phen)](ClO4)2·(H2O) (5a). Yield 61%, mp 278–281°C. IR spectrum, ν, cm–1: 3542 (H2O or OH), 1610 (C=N, imine), 1585 (C=N, oxime), 1432 (=N–O), 1091, 1050, 619 (ClO4), 576 (M–O), 481 (M–N). Found, %: C 58.68; H 4.75; N 11.20; Cu 16.76. C34H24Br2Cl2Cu2N6O11. Calculated, %: C 58.80; H 4.80; N 11.12; Cu 16.82. μeff B.M.: 2.01. ΛMb: 334. UV–Vis spectrum (CH2Cl2): 356 (33530), 635 (1560), 735 (12680), 766 (29610).

[Cu(L2)(H2O)Cu(phen)](ClO4)2 (5b). Yield 67%, mp 226–229°C. IR spectrum, ν, cm–1: 3512 (H2O or OH), 1620 (C=N, imine), 1591 (C=N, oxime), 1491 (=N–O), 1089, 1044, 620 (ClO4), 572 (M–O), 484 (M–N). Found, %: C 43.11; H 2.79; N 8.49; Cu 12.89. C35H28Cl4Cu2N6O11. Calculated, %: C 43.00; H 2.89; N 8.60; Cu 13.00. μeff B.M.: 2.16. ΛMb: 438. UV–Vis spectrum (CH2Cl2): 344 (31530), 599 (7620), 642 (7860), 833 (16980).

[Cu(L1)(H2O)Ni(phen)](ClO4)2·(H2O) (6a). Yield 65%, mp >300°C. IR spectrum, ν, cm–1: 3547 (H2O or OH), 1608 (C=N, imine), 1582 (C=N, oxime), 1494 (=N–O), 1064, 620 (ClO4), 573 (M–O), 497 (M–N). Found, %: C 46.71; H 3.76; N 8.75; Cu 6.59; Ni 6.12. C37H36Cl2CuNiN6O12. Calculated, %: C 46.79; H 3.82; N 8.85; Cu 6.69; Ni 6.18. μeff B.M.: 2.91. ΛMb: 357. UV–Vis (CH2Cl2): 346 (23400), 635 (19450),735 (9680), 766 (12590).

[Cu(L2)(H2O)Ni(phen)](ClO4)2 (6b). Yield 65%. mp 240–243°C. IR spectrum, ν, cm–1: 3505 (H2O or OH), 1620 (C=N, imine), 1592 (C=N, oxime), 1492 (=N–O), 1089, 1044, 620 (ClO4), 571 (M–O), 493 (M–N). Found, %: C 43.37; H 3.02; N 8.50; Cu 6.42; Ni 5.94. C35H28Cl4CuNiN6O11. Calculated, %: C 43.22; H 2.90; N 8.64; Cu 6.53, Ni 6.03. μeff B.M.: 2.94. ΛMb: 524. UV–Vis spectrum (CH2Cl2): 338 (17590), 596 (11840), 958 (2560).

[Cu3(L1)2(H2O)2](ClO4)2·(H2O)2 (7a). Yield 60%, mp 236–238°C. IR spectrum, ν, cm–1: 3563 (H2O or OH), 1618 (C=N, imine), 1536 (C=N, oxime), 1465 (=N–O), 1096, 1047, 620 (ClO4), 576 (M–O), 484 (M–N). Found, %: C 46.75; H 4.16; N 8.67; Cu 14.78. C50H52Cl2Cu3N8O16. Calculated, %: C 46.82; H 4.09; N 8.74; Cu 14.86. μeff B.M.: 1.71. ΛMb: 507. UV–Vis spectrum (CH2Cl2): 347 (15890), 594 (7260), 883 (22670), 980 (1450).

[Cu3(L2)2(H2O)2](ClO4)2·(H2O) (7b). Yield 57%. mp 238–240°C. IR spectrum, ν, cm–1: 3582, 3550, 3511 (H2O or OH), 1620 (C=N, imine), 1593 (C=N, oxime), 1491 (=N–O), 1089, 1047, 621 (ClO4), 575 (M–O), 482 (M–N). Found, %: C 41.11; H 2.92; N 8.26; Cu 14.08. C46H38Cl6Cu3N8O15. Calculated, %: C 41.04; H 2.85; N 8.32; Cu 14.16. μeff B.M.: 1.81. ΛMb: 642. UV–Vis spectrum (CH2Cl2): 337 (7500), 596 (1200), 650 (17650), 964 (960).

CONCLUSIONS

Structures of the synthesized compounds are confirmed by spectroscopic and stoichiometric studies. The mononuclear complexes are formed via nitrogen atoms of the imine and oxime groups of the ligands. The initially produced complexes have been reacted with Cu(II) and Ni(II) perchlorates to give the corresponding homodinuclear, heterodinuclear and homotrinuclear complexes. Electrical conductivity of the synthesized complexes indicates that all complexes have semiconductor properties.