УДК 541.49
SYNTHESIS, CRYSTAL STRUCTURE, CHROMATOGRAPHIC SEPARATION, AND THERMOGRAVIMETRIC INVESTIGATION OF A ONNO TYPE ASYMMETRIC SCHIFF BASE AND ITS TRINUCLEAR COMPLEXES
© 2014 S. Oz1 *, U. Ergun2, M. Yakut3, I. Svoboda4, A. Atakol3, E. Kubra i nal3,
N. Yilmaz3, and O. Atakol3
1Ahi Evran University, Faculty of Science and Arts, Department of Chemistry, Kirçehir, 40100 Turkey 2Dtizce University, Faculty of Science and Arts, Department of Chemistry, Dtizce, 81620 Turkey 3Ankara University, Faculty of Science, Department of Chemistry, Ankara, 06100 Turkey 4Strukturforschung, FB Materialwissenschaft, TU-Darmstadt, Petersenstrasse 23, D-64287Darmstadt, Germany *E-mail: drsevioz@gmail.com; soz@ahievran.edu.tr Received November 22, 2013
1,3- Propanediamine was put to react with 2-hydroxybenzaldehyde and 2-hydroxyacetophenone sequentially in aprotic medium. The crystalline product was examined by high performance liquid chromatography. The composition was 66% asymmetric Schiff base N(2-hydroxybenzylidene)-N'(2-hydroxyacetophenone)-1,3-pro-panediamine (SALLACH2) and 33% ¿is-N,N'(2-hydroxyacetophenylidene)-1,3-propanediamine (LACH2). As the crystals were uniform and of appropriate size, the molecular model of the material was revealed by X-ray diffraction. It was seen that two molecules of SALLACH2 and one molecule of LACH2 formed the mixed crystals. The substance was separated to its components and the asymmetric Schiff base was purified with a silica column. The substance was characterized with elemental analysis, FT-IR, MS, 'HNMR, and 13CNMR. In addition, six tri-nuclear complex with the nuclear structure of NiII—NiII—NiI1, NiII—CuII—NiI1, NiII—MnII—NiI1 were prepared from this Schiff base and stoichiometry was determined by elemental analysis, FT-IR and thermogravimetry. Finally, the molecular structures of two complexes were brought to light by XRD which highlights the asymmetry of the ligand more clearly.
DOI: 10.7868/S0132344X14080088
INTRODUCTION
The Schiff bases that were made up of diamines and aldehydes have been in the literature of coordination chemistry since 1930s [1—6]. The mentioned Schiff bases have symmetric structures established by single type aldehyde components. Among those, bis-N,N' (2-hydroxyphenylidene)-1,2-diaminoethane and biS-N,N'(2-hydroxyphenylidene)-1,3-propanedi-amine (LH2) hold an important place as tetradentate ONNO type ligands. Especially, LH2 and its derivatives, that form poly-nuclear complexes with interesting structures, are often noticed [7—13].
On the other hand, studies involving asymmetric Schiff bases prepared from diamines are not too much seen. The studies on the asymmetrical ONNO type Schiff bases have increased in recent years in literature [14—20]. In these studies, Schiff bases are prepared from symmetrical diamine and different two aldehyde compounds or an asymmetrical diamine and an aldehyde compound.
Generally, the template synthesis method was employed in the preparation of these complexes and without preferably preparing the asymmetric Schiff
base, the aldehyde and amine components were put to react in the presence of the metal ion of interest.
The first complex that involves an asymmetric Schiff base was reported in 1973 [21]. However, despite the fact that the name "asymmetric Schiff base" and the idea beyond it have been long known, there has not been any report on the synthesis and characterization of such a substance. This study has been designed to fill this gap.
The Schiff base made up of 1,3-propanediamine and 2-hydroxybenzaldehyde has a tendency to form polynuclear complexes of bis-N,N'(2-hydroxyphe-nylidene)-1,3-propanediamine (LACH2). Despite the resemblance, a poly-nuclear complex involving bis-N,N'(2-hydroxyacetophenylidene)-1,3-propanedi-amine was absent in the literature. In this context, an asymmetric Schiff base of 1,3-propanediamine with one amino group condensed with 2-hydroxybenzalde-hyde and the other amino group with 2-hydroxyace-tophenone (SALLACH2) was designed. Sketch for preparation of asymmetrical Schiff base SALLACH2:
Step 1 H3C.
P - 3 ^C=N NH2
H3C. _ - OH
,C-O Expected monocondensed Schiff base
+ I I in MeCN +
H2N NH2 1 h -H2O
OH ^ 2 1 h —H2O
SteP 2 LACH
2
3 C=O
. .. 20°C
+
in MeCN
H2O ^ -OH HO' SALLACH2
To this end, the molar equivalent carbonyl component was put to react with one mole of amine in aprotic medium and under cold conditions. After a certain time, the other aldehyde component was added to the mixture. It was clear that the obtained product was going to be a mixture. Therefore, every solid substance obtained by this method was analyzed by high performance liquid chromatography (HPLC). Because that the mixture contained symmetric Schiff bases, they were also prepared accordingly to be used as HPLC standards. It is very likely that the symmetric Schiff bases are thermodynamically more stable than their asymmetric counterparts since during the synthesis when two of the carbonyl components were added jointly onto the amine component, asymmetric Schiff base formation was not observed. On the other hand, if metal ions are present in the environment, there are studies attesting the asymmetric Schiff base complex formation [15—18].
In this study the asymmetric Schiffbase of 1,3-pro-panediamine with one amino group condensed with 2-hydroxybenzaldehyde and the other amino group with 2-hydroxyacetophenone was successfully synthesized and isolated SALLACH2. The product was a crystalline solid. It was analyzed by X-ray diffraction methods and the molecular structure was determined. Later on, the mixture was purified by column chromatography and the asymmetric Schiff base was isolated. The elemental analysis and characterization study were done by means of FT-IR, 1H NMR, 13C NMR, MS and DSC. The abbreviation SALLACH2 will be used for the isolated Schiff base from now on.
The transformation of the isolated Schiff base to its symmetric counterparts by hydrolization in am-phiprotic solvents was observed. In addition, six trinu-
clear complexes were prepared from asymmetrical Schiff base. The complex structure also contains acetate (AcO) or nitrite (NO-) anions as ^ bridges [22]. The formulas of the complexes are given below.
If NiSALLAC is described as the complex between Ni2+ ion and SALLACH2 Schiff base, formulas of six trinuclear complexes are as follows: {(NiSALLAC)Ni(AcO)2(DMF)2} (I); {(NiSALLAC)2 Cu(AcO)2(DMF)2} (II); (NiSALLAC)2Mn(AcO)2 (DMF)2} (III); {(NiSALLAC)2Ni(NO2)2(DMF)2} (IV); {(NiSALLAC)2Cu(NO2)2(DMF)2} (V); {(NiSALLAC)2Mn(NO2)2(DMF)2} (VI).
EXPERIMENTAL
Materials and apparatus. Used reactives were of Merck or Fluka brands and they were used without further purification. In this study, Shimadzu Infinity FTIR-Spectrometer equipped with three reflectional ATR unit was used for IR spectra. The C, H, and N analyses were performed on Elemantar Vario Micro Cube instrument. Metal analyses were recorded on GBC Avanta PM Model atomic absorption spectrometer using FAAS mode. Complex (2—3 mg) was dissolved in 1 mL HNO3 (63%) with heating, diluted to 100 mL and given to nebulizer of atomic absorpion spectroscopy (AAS) for metal analysis. The mass spectra were obtained by Shimadzu, 2010 plus with direct inlet (DI) unit with an electron impact ionizer. DI temperature was varied between 40—140°C and ionization was done with electrons with 70 eV energy. The NMR spectra were recorded on the Bruker Ultrashield 300 MHz NMR spectrometer. DMSO-d6 solution was
the solvent. The thermogravimetric analyses were performed by Shimadzu DTG-60H. In thermogravimetric analyses, temperature was varied between 30— 600°C. These analyses were performed at 10°C/min rate and under N2 atmosphere in Pt pans. Calibration of the instrument was done with metallic In, Pb or Zn.
Synthesis of N(2-hydroxybenzylidene)-N'(2-hydroxy-acetophenone)-1,3-propanediamine (SALLACH2). The
asymmetric Schiff base was prepared in MeCN that was dehydrated by CaH2. 1,3-Diaminopropane (3.7 g, 0.05 mol) was dissolved in 50 mL MeCN and the temperature was decreased to — 10°C in a salt-ice bath. 2-Hydroxyacetophenone (6.80 g, 0.05 mol) was added with constantly stirring for 5 min. This solution was kept in ice-water mixture for half an hour and the temperature was kept under 1°C. After the duration, salycilaldehyde (2-hydroxybenzaldehyde) (6.10 g, 0.05 mol) was added to the solution and again the solution was kept in ice-water mixture for half an hour, stirring. After that, this solution was kept in the deep freeze at —20°C for 12 h. A yellow crystalline substance was obtained and filtered by vacuum. The filtrate was rinsed with MeCN and Et2O and air-dried. The yield was 72-75%, m.p. = 88-89°C.
This crystalline substance was chromatographically investigated. In chromatographic studies, the concentration of the asymmetric Schiff base within the mixture was determined by using symmetric Schiff bases (LH2 and LACH2) as HPLC standards. The mobile phase was selected as 85% MeCN : 15% H2O in which the resolution was at its maximum. The chromato-grams obtained by using 100 ppm stock LH2, LACH2 and SALLACH2 can be seen in Fig. 1.
A silica column (Merck silica gel 60, 40-63 ^m) with 50 cm height and 2.0 cm diameter was used to separate the mixture. 50% EtAcO : 50% «-C6H14 was selected as the most suitable solvent for separation. It was observed that LACH2 moved rapidly within this solvent. In addition, the ratio of the R value of LACH2 and Rf value of SALLACH2 was approximately two. Both substances being yellow, their locations in the column were noted easily and the eluates were collected. The compounds were obtained separately by evaporating the solvent. SALLACH2 was recrystallized in a little volume of MeCN and its purity was checked by HPLC.
C18H20N2O2 (SALLACH2)
anal. calcd., %: C, 72.94; H, 6.80; N, 9.44. Found, %: C, 73.34; H, 6.55; N, 9.86.
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Fig. 1. Obtained ch
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