научная статья по теме SYNTHESIS AND CHARACTERIZATION OF NI(II) AND CO(II) COMPLEXES OF SCHIFF BASES DERIVED FROM 3,4-DIMETHYL- 3-TETRAHYDROBENZALDEHYDE AND 4,6-DIMETHYL- 3-TETRAHYDROBENZALDEHYDE AND GLYCINE Химия

Текст научной статьи на тему «SYNTHESIS AND CHARACTERIZATION OF NI(II) AND CO(II) COMPLEXES OF SCHIFF BASES DERIVED FROM 3,4-DIMETHYL- 3-TETRAHYDROBENZALDEHYDE AND 4,6-DIMETHYL- 3-TETRAHYDROBENZALDEHYDE AND GLYCINE»

КООРДИНАЦИОННАЯ ХИМИЯ, 2007, том 33, № 8, с. 618-621

УДК 541.49

SYNTHESIS AND CHARACTERIZATION OF Ni(II) AND Co(II) COMPLEXES OF SCHIFF BASES DERIVED FROM 3,4-DIMETHYL-A3-TETRAHYDROBENZALDEHYDE AND 4,6-DIMETHYL-A3-TETRAHYDROBENZALDEHYDE AND GLYCINE

© 2007 E. Guler and O. Ko?yigit

Faculty of Science and Arts, Department of Chemistry, Selcuk University, 42075 Kampus Selquklu, Konya, Turkey

Received June 14, 2006

The Schiff bases derived from 3,4-dimethyl-A3-tetrahydrobenzaldehyde or 4,6-dimethyl-A3-tetrahydrobenzal-dehyde and glycine and their complexes with nickel(II) and copper(II) were synthesized and investigated. All compounds were characterized by elemental analyses, conductivity measurements, and FT-IR spectroscopy. The Schiff base ligands and their complexes were further characterized by XH NMR. The results suggest that the Schiff base acts as a bidentate ligand, which bonds to the metal ions through the imino nitrogen and carbox-ylate oxygen. The potassium salts of the Schiff bases are 1 : 1 electrolytes but all the complexes are nonelec-trolytes.

INTRODUCTION

Schiff base derivates of 2-chlorobenzaldehyde and glycine and A3-tetrahydrobenzaldehyde or 2-methyl-A3-tetrahydrobenzaldehyde and glycine and their metal ligand complexes have been studied previously, and their structures were characterized [1-3]. In these works, the complex formation constants, availability as carriers for ligand membrane transport, and their reaction properties and mechanisms of reactions with epoxy compounds of Schiff bases were investigated in detail. In addition, these Schiff bases can be usable as reference material for the identification of Schiff bases that can be obtained by the extraction of some lipids. Some oximes can be used for many applications due to their importance from the point of physiological or biological characteristics. Synthesis of new oxime compounds and investigation of their application are very important for the new research.

In this paper, we present the synthesis and characterization of ligands - the Schiff bases derived from 3,4-dimethyl-A3-tetrahydrobenzaldehyde or 4,6-dime-thyl-A3-tetrahydrobenzaldehyde and glycine - and their complexes with nickel(II) and copper(II).

The potassium salts of the ligands (KL1 • H2O and KL2 • H2O) are the following:

K[^-CH=^-CH2-

V

-C— O]

H2O

EXPERIMENTAL

Chemicals and materials. All chemicals used were of reagent grade. Metal chlorides and glycine were purchased from Sigma Chemical. 3,4-dimethyl-A3-tetrahydrobenzal-dehyde and 4,6-dimethyl-A3-tetrahydrobenzaldehyde were prepared according to published methods [4].

Melting points were measured on a Gallenkamp melting point apparatus and are uncorrected. Elemental analyses were performed at the Tubitak Laboratory (Gebze, Kocaeli). 1HNMR analyses were performed at the M.E.T.U. Laboratory (Ankara, Turkey). IR spectra were recorded in KBr pellets (Perkin Elmer Model 1605 FT-IR spectrometer) in the range 4000-400 cm-1. All conductivity measurements were performed in methanol using a Shanghai DDS-11A apparatus at 25°C; the concentration of the solution was 1.0 x 10-4 mol l-1. The magnetic moments of the complexes were measured by the Gouy method with a Newport Instruments type D-104 magnet power supply (293 K). Data on H2O analysis were obtained using a TAS-100 thermoanalysis instrument. The metal content of each complex was determined on a

SYNTHESIS AND CHARACTERIZATION OF Ni(II) AND Co(II) COMPLEXES Table 1. Analytical data and some physical properties of compounds

Compound (empirical formula), M Color Yield, M.p., M-eff, Mb Contents (found/calcd), % Conductivity

% °C C H N M Ohm1 cm2 mol1

KL1 ■ H2O (CnH18NO3K), 251.1 White 71 >300 51.85/52.57 6.58/7.17 6.10/5.58 91.58

NiL^ ■ 6H2O (C22H44N201gNi), 554.8 Green 70 >300 Diamagnetic 46.75/47.58 7.67/7.93 5.61/5.05 11.45/10.58 5.52

CuLl■2H2O (C22H36N2O6Cu) Blue 71 >300 1.67 48.44/54.15 7.28/7.38 5.84/5.74 12.01/13.02 5.54

487.5

KL2 ■ H2O (C11H18NO3K), 251.1 White 72 >300 51.78/52.57 6.53/7.17 6.05/5.58 91.63

NiL^ ■ 6H2O (C22H44N201gNi), Green 74 >300 Diamagnetic 46.82/47.58 7.71/7.93 5.58/5.05 11.34/10.58 5.51

554.8

CuL^ ■2H2O (C22H36N2O6Cu), 487.5 Blue 73 >300 1.65 48.32/54.15 6.22/7.38 5.91/5.74 11.98/13.02 5.56

Varian, Vista AXCCD Simultaneous model ICP-AES spectrophotometer.

Synthesis of N-(3,4-dimethyl)-A3-tetrahydroben-zylideneglycinatopotassium monohydrate salt (KL1 •

• H2O) and N-(4,6-dimethyl)-A3-tetrahydroben-zylideneglycinatopotassium monohydrate salt (KL2 •

• H2O) [1, 2]. An ethanolic solution (80 ml) of glycine (2.25 g, 30 mmol) and potassium hydroxide (1.68 g, 30 mmol) was stirred magnetically at room temperature for 1 h and then filtered. The colorless solution of potassium glycinate was added dropwise to an ethanolic solution (80 ml) of 3,4-dimethyl-A3-tetrahydrobenzalde-hyde or 4,6-dimethyl-A3-tetrahydrobenzaldehyde (4.14 g, 30 mmol). The mixture was stirred magnetically at room temperature for 1 h. After white solid particles appeared in the solution, precipitation was gradually increased by stirring. The resulting white solid product was filtered, washed with 95% ethanol, and dried in a vacuum desiccator; the yield of KL1 ■ H2O and KL2 ■ H2O were 5.04 (71) and 4.97 g (70%), respectively.

Synthesis of NiLl • 6H2O and CuL^ • 2H2O. An

ethanolic solution (60 ml) of nickel chloride (2.378 g, 10 mmol) or copper chloride (1.706 g, 10 mmol) was mixed with KL1 (5.02 g, 20 mmol) in a 1 : 2 molar ratio. The mixture was stirred magnetically at room temperature for 2 h and then concentrated to ~10 ml at 65-70°C in a water bath. Addition of 7 ml of distilled water to the concentrated reaction mixture precipitated green or blue products, respectively. The precipitate was collected by

filtration, washed with diethyl ether and then 95% eth-anol, and dried in a vacuum desiccator; the yields of the Ni(II) and Cu(II) complexes were 3.95 (71) and 4.05 g (72%), respectively.

2 2 Synthesis of NiL2 • 6H2O and CuL2 • 2H2O were

performed in an analogous manner as the preparation of the complexes of L1; the yields of the Ni(II) and Cu(II) complexes were 4.12 (74) and 4.10 g (73%), respectively.

Table 2. Infrared spectral data of the compounds (cm x)

Compounds v(H2O) v(C=N) VjCOO) Vs(COO)

KL1 ■ H2O KL2 ■ H2O 3325 m, br 3325 m, br 1645 s 1645 s 1595 s 1595 s 1390 m 1390 m

CuLl ■2H2O 3335w,br 1630 s 1600 s 1380 s

NiLl ■ 6H2O 3330w, br 1625 s 1605 s, br 1380 m

CuL^ ■2H2O 3335 w, br 1630 s 1605 s 1385 s

NiL^ ■ 6H2O 3335 w, br 1625 s 1600 s, br 1380 m

620 GULER, KOCYIGIT

Table 3. Selected 1H NMR chemical shift (5) signal data in DMSO

Compounds 5, ppm

L1K ■ H2O 8.30 s. (1H, CH=N); 4.15 s. (2H, CH2); 0.95 s. (6H, CH3)

L2K ■ H2O 8.25 s. (1H, CH=N,); 4.10 s. (2H, CH2); 0.95 d. (6H, CH3, J = 6.0 Hz)

NiL2 ■ 6H2O 8.75 s. (2H, CH=N); 4.80 s. (4H, CH2); 1.00 s. (12H, CH3)

NiL2 ■ 6H2O 8.80 s. (2H, CH=N); 4.75 s. (4H, CH2); 0.95 d. (12H, CH3, J = 6.5 Hz)

RESULTS AND DISCUSSION

The elemental analyses (Table 1) are in agreement with the chemical formulas of the compounds. Molar conductivities in methanol (Table 1) indicate that the Schiff base potassium salts are 1 : 1 electrolytes but all the complexes behave as nonelectrolytes.

The IR spectra of the potassium salts of the Schiff base ligands and their complexes (Table 2) provide insight into the mode of bonding of the ligands to the metal ions. The strong and broad absorption in the region 3300-3350 cm1 of all the compounds substantiates the presence of water. The coordination of the imino nitrogen to the metal ion can be inferred from the shift of v(C=N) from 1645 to 1625 cm-1. This is in agreement with the results of Nakamoto et al. [5]. These authors showed that for selected metal complexes of glycine in the same physical state the asymmetrical carboxylate stretching frequency increased, while the symmetrical one decreased from Cu and Ni. Probably, the carboxy-late oxygen takes part in coordination according to the changes of vas(COO) and vs(COO) of these complexes.

1H NMR spectra of the Schiff base ligands and complexes. The 1H NMR spectra of the synthesized ligand and metal complexes are given in Table 3. When the 1H NMR spectra of KL1 and KL2 are compared, the spectra are quite similar to each other. The peak seen at 8.25 ppm belongs to the protons in the CH=N groups and those at 4.15 ppm belong to the CH2 groups. Mor-ever, the peaks for the CH3 group of ligands were observed at 0.95 ppm.

When the 1H NMR spectra of the complexes are compared with those of the ligands, the observed peaks for the ligands, generally, were shifted to a lower field. This shift indicates that the complexes formed. However, the largest shifts were observed for the CH=N and CH2COO- protons. This was expected because of the charge transfer from these groups to the metal. When the 1H NMR spectra of the Ni(II) complexes were compared with the 1H NMR spectra of free KL2, the CH=N and CH2COO- protons were shifted by 0.45 and 0.55 ppm, respectively.

Magnetic susceptibility measurements provided sufficient data to characterize the structure (Table 1). The mononuclear complexes of Ni(II) are diamagnetic as expected for a d metal in a square-planar field [6-9]. The magnetic moments of the mononuclear complexes of

Cu(II) are ~1.67-1.65 which is comparable with the values reported for slightly distorted square-planar Co(II) complexes [10].

The obtained results are in agreement with the data of papers [1, 2].

Structure of metal complexes. From the above discussion, it is seen that the metal ions in the complexes are bonded to the ligands through the imino nitrogen and carboxylate oxygen atoms. As the complexes are presumed to be tetracoordinate, the proposed structures of the Ni(II) and Cu(II) complexes with the ligands L1 and L2 (n = 6 for M = Ni and n = 2 for M = Cu) and their coordination modes [8] are shown below:

R—HC=N

/CH^C^

O

O

O

C-CH2

/

,N = CH-R

nH2O

KL1: R =

KL2: R

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