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Compounds of Fe(III) and Co(II) Coordinated with Oxygen Atoms SIMONA TURCUMAN (ANTIGHIN)1, DOINA SIBIESCU1, IOAN ROSCA1, MARIUS SEBASTIAN SECULA1, IGOR CRETESCU2*, 1 ”Gh. Asachi” Technical University, Faculty of Chemical Engineering and Environmental Protection, Chemical Engineering Department, 73 D. Mangeron, 700050, Iasi, Romania 2 ”Gh. Asachi” Technical University, Faculty of Chemical Engineering and Environmental Protection, Environmental Engineering and Management Department, 73 D. Mangeron, 700050, Iasi, Romania The authors present the synthesis and characterization of some novel coordinative compounds derived from the interaction between Fe(III) and Co(II) respectively with morfolin-4-carboditioic acid-2-(3,5-dibrome,4methyl,2-hydroxy-phenyl)-2-oxo-ethyl-ester organic ligand. The synthesized compounds were characterized by using the following methods: elemental chemical analysis, thermogravimetry, IR absorption spectroscopy, Electron Spin Resonance (ESR) spectroscopy, Mössbauer spectroscopy and X-ray diffraction. From the obtained results it can be noticed that the central atoms are hexacoordinated by oxygen atoms from 〉 C = O and - O(H) groups of the organic ligand. The obtaining reactions of these novel compounds might be applied in gravimetric determination of Fe(III) and Co(II) respectively. Keywords: morfolin-4-carboditioic acid-2-(3,5-dibrome,4-methyl,2-hydroxy-phenyl)-2-oxo-ethyl-ester, Fe(III), Co(II), Mössbauer spectra, precipitating reagent. Organic ligands such as: morfolin-4-carboditioic acid-2(3,5-dibrome,4-methyl,2-hydroxy-phenyl)-2-oxo-ethyl-ester are used in the synthesis of Fe(III) and Co(II) coordination compounds. Some of these ligands can be applied in gravimetric determinations of metal ions [1-10]. In this study is presented the synthesis and study of coordinative compounds obtained from the reactions: morfolin-4-carboditioic acid-2-(3,5-dibrome,4-methyl,2hydroxy-phenyl)-2-oxo-ethyl-ester ligand with Fe(III) and Co(II) ions in the combination ratio of 3:1, in case of Fe(III), and 2:1, in case of Co(II). The novel compounds were investigated by the following methods: chemical analysis, termogravimetry, IR absorption spectroscopy, ESR and Mössbauer spectroscopy and X-ray diffraction. Experimental part As reactant were used FeCl3, CoCl2 x 6H2O (Merck A.R.) and : morfolin-4-carboditioic acid-2-(3,5-dibrome,4-methyl,2hydroxy-phenyl)-2-oxo-ethyl-ester prepared according to the directions in literature [11-13]. The syntheses of the coordination compounds presented in this work were carried out according to the method described in literature [11]. The reactant solutions of 0.2 M concentration were prepared using as solvent a mixture of ethylic alcohol (98%) and water in the ratio of 1:1 (in volumes) for the salts of Fe(III) and Co(II), and dimethyleformamide (DMF) solvent: morfolin-4-carboditioic acid-2-(3,5-dibrome,4-methyl,2-hydroxy-phenyl)-2-oxo-ethylester (noted HL herein further). The obtaining reactions of the synthesized compounds were performed by mixing and stirring at room temperature, for 70 min, 200 mL of HL with 200 mL from each solutions containing Fe(III) and Co(II) respectively. 1. FeCl3+3 (C14H15NO3S2Br2) → → Fe(C14H14 NO3S2Br2)3 + 3 HCl 2. CoCl2+ 2(C14H15NO3S2Br2)+2H2O → → Co(C14H14 NO3S2Br2)2 + 2 H2O + 2HCl The resulted precipitates were separated by filtration, washed on a funnel vacuum nozzle, and then dried at 100oC until a constant weight was reached. Under the specified conditions, efficiencies of 100 % were achieved. The contents of C, H, N, S, Fe(III) and Co(II) were determined for each synthesized compound using adequate conventional methods [11- 13]. Thermogravimetric parameters of thermal decomposing reactions [14-16] were achieved by processing the derivatograms recorded by means of a Q1500D (MOM Budapesta) derivatograph, according to the procedure described in the previously works [3,5]. The absorption spectra in the IR range 200 and 4000 cm-1, respectively were recorded and processed according to the methodology presented in the previously papers [3,5]. Results and discussions Analyzing the experimental data concerning the combination ratio of Fe(III) and Co(II): morfolin-4carboditioic acid-2-(3,5-dibrome,4-methyl,2-hydroxy-phenyl)2-oxo-ethyl-ester ligand, it results that the chemical analysis of the synthesized compounds (table 1) was performed with an error of ±0.27% in relation to the content of C,H,N,S,Br, Fe(III) and Co(II). Table 1 ELEMENTAL COMPOSITION (%) OF THE SYNTHESIZED COMPOUNDS * email: [email protected]; Tel.: + 40 0741914342 REV. CHIM. (Bucharest) ♦ 62♦ No. 2 ♦ 2011 http://www.revistadechimie.ro 189 Table 2 CHARACTERISTIC TEMPERATURES OF THERMAL DECOMPOSITION STAGES, REACTION ORDERS AND ACTIVATION ENERGIES, OF THE SYNTHESIZED COMPOUNDS. The novel compounds have the formula: Fe(C 14 H 14 NO 3S 2Br 2) 3 and Co(C 14 H 14 NO 3S 2Br 2) 2 x 2H 2 O respectively. Further, these compounds will be referred as FeL3 and CoL2 x 2H2O respectively. The characteristic temperature stages of thermal decomposing of the synthesized compounds, reaction order and activation energy values were calculated according to Freeman-Carrol method [14] and are presented in table 2. Thermal decomposition stages listed in table 2 corresponds to the thermal decomposition that follows the elimination of coordination water. Water was eliminated at 180°C from FeL3, and at 230°C from CoL2 x 2H2O. The coordination water is eliminated at higher temperatures than the crystallization and zeolitic water. Processes taking place under the action of temperature and oxygen from air are sometimes very complicated and difficult to interpret. Usually, the temperatures at the start and end of thermal decomposing stages are emphasized, and the reaction parameters, such as reaction order and activation energy, are calculated [14-18]. The thermal stability of synthesized compounds is established. After the coordination water is eliminated, two thermal decomposing stages follow. The final solid products of thermal decomposing reactions are oxides of the respective metals: FeO and CoO. The molecular structure of the gaseous products formed could not be identified. The thermal stability decreases with the increase of alkalinity of the central atom: FeL3> CoL2 [11-13, 17, 18]. In fact, the layer of substance thermally decomposed can be of a few millimeters and its thickness decreases as thermal decomposing advances step by step, and in the same time the dispersion degree increases due to the chemical reaction. Consequently, the gaseous products encounter a lower resistance during “vaporization”, and the reaction order tend to unity in accordance to the data reported in literature [11, 15, 16]. IR absorption spectra of the ligand and synthesized compounds bring important information on the chemical Fig 1 Structure of morfolin-4-carboditioic acid-2-(3,5-dibrome, 4methyl,2-hydroxy-phenyl)-2-oxo-ethyl-ester ligand bonds of the central atoms of Fe(III) and Co(II) respectively with some of the ligand atoms (table 3). By means of IR absorption spectra of the synthesized compounds, it was established whether there are absorptions corresponding to bonds such as O-M, >C = O→ M and M ← OH2, originating from the interaction of functional groups -O(H) and >C=O in ligand and respectively due to the coordination water (fig. 1). Based also on the IR adsorption spectra of the synthesized compounds, it was outlined the existence of some very important bonds between central atoms of Fe(III) and Co(II) respectively and the donor atoms in ligand, such as oxygen and nitrogen that correspond the stretch vibrations:νM-O and νM-N (table 3). In concordance with data reported by other authors [6,11], in the low frequencies range (450-1500 cm-1) occur bends corresponding both to the valence vibrations of simple bonds: C-C, C-O, Fe-O, Co-O, and to the deformation vibrations of other bonds. The bands with frequencies of 467 cm-1 and 437 cm-1 correspond to the stretch frequencies: νCo-O and ν Fe-O respectively. The bands of vibration frequency of C-O group observed in the region 1267-1287 cm -1 in the ligand spectrum are shifted towards higher wavelengths and become less intense in the spectra of the investigated compounds [19-23]. Fig. 2. Thermogram of FeL3 compound. 190 http://www.revistadechimie.ro REV. CHIM. (Bucharest) ♦ 62♦ No. 2 ♦ 2011 Table 3 IR SPECTRAL BANDS CHARACTERISTIC FOR THE SYNTHESIZED COMPOUNDS The stretch (valence) vibrations of carbonyl groups occur at 1715 cm-1, in case of ligand, while in the synthesized compounds occur at 1657 cm-1 and 1640 cm-1 for FeL3 and CoL2·2H2O respectively. This supports the assumption that the central atoms of Fe(III) and Co(II) coordinate with the oxygen atom in carbonyl group: M ← O=C< where M = Fe, Co. The spectral bands characteristics of IR absorption spectra of the synthesized compounds are presented in table 3. Full IR absorption spectra is presented only for CoL2 x 2H2O compound (fig. 3). The absorption of OH phenol group in orto position is located in the range 3277-3275 cm-1, and disappears in the investigated compounds. In case of phenols, the most important band [19-23] is located between 773-1426 cm-1 (νC-OH). By substituting the hydrogen atom with a central atom of Fe(III) or Co(II), the peaks corresponding to OH group in IR spectra of the synthesized compounds disappear. Hence, it can be stated that each central atom binds to an oxygen atom from the phenol group where, in fact, a hydrogen atom is substituted with Fe(III) and Co(II) respectively. According to ESR spectra, both synthesized compounds contain central atoms with odd electrons: 5 in case of Fe(III) and 3 in case of Co(II). The spectroscopic splitting factor takes values between 2.0225 and 2.018, hence, much higher than that of the free electron (2.0023) due to the contribution of the orbital momentum and covalence degree of bonds where central atoms such as Fe(III) and Co(II) are involved. These values are in agreement with other works reported in literature [5-9]. The conclusions based on the Mössbauer spectra [24]supports that the central atom in FeL3 is in the IIIrd oxidation state with high spin (S=5/2) which indicates a relative ionic character of Fe-O bond. The value of ΔEQ parameter (table 5) supports the octahedral encompassment of Fe(III) with electrons distributed on the last level: t32g, e2g It is of very high importance that due to the symmetric electron configuration 3 d5 of Fe(III) central atom, it was not observed any splitting of quadrupole in case of octahedral coordination only by oxygen atoms. In case of FeL3, it was observed a dependence of the isomer shift on the temperature of 0.05 mm/s 100 °C, which is higher than that obtained in case of most coordinative compounds. This behavior is in agreement with the second-order Doppler effect. It can be explained as the temperature increases from 80 to 300 K, at the same time as the oscillations of Fe(III) atoms in the crystalline network increase, it takes also place a shift of the electronic density of spin s within the ligand-central atom bond. The X-ray diffractograms of the HL ligand and synthesized compounds (FeL3, CoL2 x 2H2O) lead to the conclusion that these compounds crystallize in monoclinic Table 4 VALUES OF THE SPECTROSCOPIC SPLITTING FACTOR (g), INTENSITY OF THE MAGNETIC FIELD CORRESPONDING TO THE SPECTRUM CENTER OF THE SAMPLE (Hx, GAUSS) AND ODD ELECTRON NUMBER OF THE CENTRAL ATOM (n) Fig. 3. IR absorption spectrum of CoL2·2H2O compound REV. CHIM. (Bucharest) ♦ 62♦ No. 2 ♦ 2011 http://www.revistadechimie.ro 191 Fig. 4. Mossbauer spectrum of FeL3 recorded at 80 K Table 6 VALUES OF ELEMENTAL CELL PARAMETERS FOR HL LIGAND, FeL3 AND CoL2×2H2O COMPOUNDS Table5 PARAMETER VALUES OF MÖSSBAUER SPECTRUM OF FeL3 FeL3 CoL3 x 2H2O Fig. 5. Structural formula of the synthesized compounds 192 http://www.revistadechimie.ro REV. CHIM. (Bucharest) ♦ 62♦ No. 2 ♦ 2011 Fig. 6. Diffractograms of HL(1) ligand and CoL2·2H2O compound. system due to the crystallographic characteristics of the ligand that keeps its monoclinic crystalline structure. The elemental cell parameters are shown in table 6. Based on the elemental cell parameters of FeL3 and CoL2 x 2H2O compounds, it results that in both cases the values of a and c parameters are relatively close though they are much lower than the b value. This shows that the central atoms of Fe(III) and Co(II) coordinates with H2O respectively in the ac plan of the elemental cell towards b side accompanied by volume compression. The coordination of ligand by central atoms Fe(III) and Co(II) is achieved in the ac plane of the elemental cell accompanied by its volume compression. In the same time it can be noted a slight distortion of α angle that leads to the conclusion that water molecules coordinate with the central atoms of Fe(III) and Co(II) above and beneath the ab plane accompanied by volume compression of compound elemental cell due to coordination. In both structures of these compounds can be noted a slight distortion of β angle probably due to the distribution of water molecules and OH groups above and beneath the plane were are located the ligands derived from morfolin4-carboditioic acid-2-(3,5-dibrome,4-methyl,2-hydroxyphenyl)-2-oxoetil-ester . Based on the data obtained by means of chemical analysis, IR absorption spectroscopy, thermogravimetric analysis, electron spin resonance and Mössbauer spectroscopy and X-ray diffraction, it can be concluded that the central atoms of Fe(III) and Co(II) are hexacoordinated in octahedral structures[25-29]. Both central atoms, Fe(III) and Co(II) respectively, are hexacoordinated by oxygen atoms from >C=O and –O(H) groups of HL ligand (fig. 5). Conclusions Two novel compounds of Fe(III) and Co(II) with morfolin4-carboditioic acid-2-(3,5-dibrome,4-methyl,2-hydroxyphenyl)-2-oxo-ethyl-ester ligand in the molar ration central atom:ligand of 1:2 in case of Co(II) and 1:3 in case of Fe(III) were synthesized and characterized. The synthesized compounds were characterized by means of modern technical methods such as elemental chemical analysis,thermogravimetric analysis, IR absorption spectroscopy, ESR and Mössbauer spectroscopy and X-ray diffraction. By means of these techniques, it was shown that the synthesized compounds are of high spin REV. CHIM. (Bucharest) ♦ 62♦ No. 2 ♦ 2011 having hexacoordinated central atoms and octahedral crystalline structure. 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