www.scielo.br/eq Volume 35, número 2, 2010 89Ecl. Quím., São Paulo, 35 - 2: 89 - 98, 2010 Artigo/Article tHe pHySiCo-CHemiCal propertieS of 2-metHoxypHenoxyaCetateS of mn(ii), Co(ii), ni(ii) and Cu(ii) W. Ferenc1*, M. Bernat1 and J. Sarzyński2 1Faculty of Chemistry, Maria Curie-Sklodowska University, 20-031 Lublin, Poland 2Faculty of Physics, Maria Curie-Sklodowska University, 20-031 Lublin, Poland *Author for correspondence: e-mail: wetafer@poczta.umcs.lublin.pl abstract: The complexes of 2-methoxyhenoxyacetates of Mn(II), Co(II), Ni(II) and Cu(II)with the general formula: M(C9H9O4)3·4H2O, where M(II) = Mn, Co, Ni and Cu have been synthe- sized and characterized by elemental analysis, IR spectroscopy, magnetic and thermogravi- metric studies and also X-ray diffraction measurements. The complexes have colours typical for M(II) ions (Mn(II) - a pale pink, Co(II) - pink, Ni(II) - green, and Cu(II) – blue). The carboxylate group binds as monodentate and bidentate ligands. On heating to 1273K in air the complexes decompose in the same way. At first, they dehydrate in one step to anhydrous salts, that next decompose to the oxides of respective metals with the intermediate formation of the oxycarbonates. Their solubility in water at 293K is of the order of 10-5 mol·dm-3. The magnetic moments of analysed complexes were determined in the range of 76-303K. The results reveal them to be high-spin complexes of weak ligand fields. Keywords: 2-methoxyphenoxyacetates, thermal stability, magnetic properties of Mn(II), Co(II), Ni(II), Cu(II). introduction The carboxylates play an important role in inorganic and bioinorganic chemistry. Many me- tal cations in a great number of various biologi- cal processes are a component of several vitamins and drugs [1-3]. The carboxylates of d- and 4f- ion elements may be used as electric materials in the modern branches of techniques and technology or they may have applications as precursors in su- perconducting ceramic and magnetic field produc- tions. These kind of compounds are often used as catalysts, pigments, solvents, food preservatives and plastics productions. From the survey of literature it follows that metal carboxylates may be applied for the produc- tions of high degree purity of metal oxides and polycarboxylic acids are often used for supramo- lecular compound synthesis, which in many ca- ses, form with metal ions the molecular polymers containing in their structures, pores and channels owning to them they appear catalytic and adsorp- tion properties. Therefore they may be used for the adsorption of inorganic gases such as: argon, nitrogen and hydrocarbons or small molecules of another inorganic compounds. Polycarboxylic acid may also form the molecules with two- and three – dimentional structures, yielding special magnetic and luminescence properties which let them be used in optical and electronic industries [1,4,5]. 2-Methoxyphenoxyacetic acid is a grey- white solid hardly soluble in water. A literature Ecl. Quím., São Paulo, 35 - 2: 89 - 98, 201090 Artigo Article survey indicates that its compounds with various cations have been relatively seldom studied. The complex of Cu(II) with 2-methoxyphenoxyacetic acid was synthesized and its structure determined [6]. As a continuation of our studies on carbo- xylates we decided to synthesize 2-methoxyphe- noxyacetates with Mn(II), Co(II), Ni(II) and Cu(II) and to study some of their properties not to be investigated so far, such as magnetic properties in the range of 77-303K thermal stability in air at 293-1273K, solubility in water at 293K and to record their FTIR spectra. Thermal stability investigations give infor- mations about the dehydratation process and the ways of decompositions, and the magnetic sus- ceptibility measurements let study the kinds of the way of coordination of the central ions and ligan- ds. The determination of the solubility is valuable because it informs about the practical use of acid for separation of transition metal ions by extrac- tion or ion-exchange chromatographic methods. experimental The 2-methoxyphenoxyacetates of Mn(II), Co(II), Ni(II) and Cu(II) were prepared by the addi- tion of the equivalent quantities of 0,1 mol·dm-3 ammonium 2-metoxyphenoxyacetate (pH ≈ 5) to a hot solutions containing the 0,1 mol·dm-3 Mn(II), Co(II), Ni(II) and Cu(II) chlorides and crystalli- zing at 293K. The solid formed were filtered off, washed with hot water and methanol to remove ammonium ions and dried at 303K to a constant mass. The contents of carbon and hydrogen in the complexes and in the intermediate and final pro- ducts obtained from their thermal decompositions determined by elemental analysis using a CHN 2500 Perkin-Elmer analyzer. The contents of M2+ metals were established by XRF method using spectrometer of X-ray fluorescence with energy dispersion EDXRF-1510 (CANBERRA firm). table 1. Elemental analysis data of Mn(II), Co(II), Ni(II) and Cu(II) 2-methoxyphenoxyacetates and their solubility in water at 293K Complex L- = C9H9O4 H/% C/% M/% Solubility calcd found calcd found calcd found mol/dm3 MnL2∙4H2O 5.32 5.14 44.18 44.11 11.23 11.20 2,61 ·10-5 CoL2∙4H2O 5.27 5.11 43.82 43.76 12.76 12.70 9,28 ·10-5 NiL2∙4H2O 5.28 5.04 43.84 43.04 11.90 11.70 1,50 ·10-5 CuL2∙4H2O 5.23 5.27 43.42 43.58 12.76 12.70 5,11 ·10-5 The FTIR and FIR spectra of complexes were recorded over the ranges of 4000-400cm-1 and 600-100cm-1, respectively, using M-80 and Perkin-Elmer 180 spectrometers. Samples for IR spectra me- asurements were prepared as KBr discs. FIR spectra were obtained in Nujol mulls sandwiched between polyethylene plates (Table 2). The FTIR spectra of the intermediate and final products obtained from the complex thermal decompositions were also registered. Ecl. Quím., São Paulo, 35 - 2: 89 - 98, 2010 91 Artigo Article table 2. Wavenumbers (cm-1) of COO- bands in the analysed complexes of Mn(II), Co(II), Ni(II), Cu(II), and Na(I), and of the COOH in 2-methoxyphenoxyacetic acid Complex L-=C9H9O4 ν C=O ν as OCO ν sym OCO Δν OCO ν M-O MnL2∙4H2O - 1654 1425 229 465 CoL2∙4H2O - 1619 1412 207 470 NiL2∙4H2O - 1603 1414 189 472 CuL2∙4H2O - 1597 1427 170 465 HL 1742 - - - - NaL - 1615 1427 188 454 The X-ray diffraction patterns of hydrated, intermediate and final products of complex ther- mal decompositions were taken on a HZG-4 (Carl Zeiss Jena) diffractometer using Ni filtered Cu Kα radiation. The measurements were made wi- thin the range 2Θ = 4-80o by means of the Bra- gg - Brentano method. The relationships between I/Io and 2Θ for these complexes are presented in Fig.1. Ecl. Quím., São Paulo, 35 - 2: 89 - 98, 201092 Artigo Article 2θ 10 20 30 40 I/I 0 0 20 40 60 80 100 120 2θ 10 20 30 40 50 60 70 80 I/I 0 0 20 40 60 80 100 120 2θ 10 20 30 40 50 60 70 80 I/I 0 0 20 40 60 80 100 120 2θ 5 10 15 20 25 30 35 40 45 I/I 0 0 20 40 60 80 100 120 MnL2  4H2O CoL2  4H2O NiL2  4H2O CuL2  4H2O fig.1. Dependence of I/I0 vs 2θ for Mn(II), Co(II), Ni(II) and Cu(II) complexes The thermal stability and decomposition of the analysed complexes were determined by Pau- lik-Paulik-Erday Q-1500D derivatograph with Derill converter, recording TG, DTG, and DTA curvers (Fig.2). The measurements were made at a heating rate of 10 K·min-1 with a full scale. The samples (100mg) were heated in platinum cruci- bles in static air to 1273K with a sensitivity of TG-100mg. DTG and DTA sensitivities were re- gulated by a Derill computer program. The pro- ducts of decomposition were calculated from TG curves and verified by the diffraction pattern re- gistration and IR spectra. The thermogravimetric analysis of DSC/TG was performed at temperatu- re 323-723K using a differential thermoanalyzer Netzsch STA 409C 3F. The measurements were carried out under nitrogen flow (99,995% purity) and temperature increase rates of 1-12 K·min-1. Ecl. Quím., São Paulo, 35 - 2: 89 - 98, 2010 93 Artigo Article table 3. Temperature ranges of thermal stability of Mn(II), Co(II), Ni(II) and Cu(II) 2-methoxyphenoxyac- etates in air Complex L- = C9H9O4 ΔT1 / K Mass loss / % n H2O ΔH / kJ·mol-1 OHH 21∆ / kJ·mol-1 Residuecalcd. found MnL2∙4H2O 348-443 14,73 14,69 4 128,91 32,2 MnO CoL2∙4H2O 353-433 14,61 14,70 4 113,76 28,4 CoO NiL2∙4H2O 323-433 14,61 14,54 4 128,48 32,1 NiO CuL2∙4H2O 318-393 14,47 14,48 4 117,47 29,4 CuO ΔT1 – temperature range of dehydration process, n – number of water molecules lost in the dehydra- tion process, ΔH – enthalpy of dehydration process, OHH 21∆ - enthalpy value for one molecule of water, M as s lo ss % En do ←← ←← ∆∆ ∆∆T →→ →→ E xo fig.2. TG, DTG and DTA curves for Co(II) 2-methoxyphenoxyacetate Magnetic susceptibilities of polycrystalline samples of 2-methoxyphenoxyacetates of Mn(II), Co(II), Ni(II) and Cu(II) were measured by the Gouy method using a sensitive Cahn RM-2 balan- ce. The samples were placed in a long cylindrical tube which was suspended from an analytical ba- lance. The sample tube was positioned between the poles of the magnet such that one its end was in the region of homogeneous field and the other end was in the region of zero field. The force exer- ted on the sample was a function of the volume occupied by the sample in the region of the field gradient. This force may be written in scalar form as a function of the isotropic volume susceptibili- ty. Measurements were carried out at a magnetic field strength of 9,9 kOe. The calibrant employed was Hg[Co(SCN)4] for which the magnetic sus- ceptibility was assumed to be 1,644∙10-5cm3g-1. Ecl. Quím., São Paulo, 35 - 2: 89 - 98, 201094 Artigo Article Correction for diamagnetism of the calibrant atoms was calculated by the use of Pascal’s constants [8,9]. Magnetic moments were calculated from Eq.(1): μeff = 2,83 (χM ∙ T)1/2 (1) table 4. Magnetic data for the studied complexes of Mn(II), Co(II), Ni(II) and Cu(II) MnL2∙4H2O L- = C9H9O4 CoL2∙4H2O NiL2∙4H2O CuL2∙4H2O T/K χM∙106 µeff/µB T/K χM∙106 µeff/µB T/K χM∙106 µeff/µB T/K χM∙106 µeff/µB 76 60395 6.06 76 31831 4.40 76 16750 3.19 76 5747 1.87 123 38190 6.13 123 21090 4.56 123 10150 3.16 123 3483 1.85 133 34155 6.03 133 19687 4.58 133 9434 3.17 133 3317 1.88 143 31641 6.02 143 18628 4.62 143 8986 3.21 143 3059 1.87 153 29635 6.03 153 17653 4.65 153 8461 3.22 153 2875 1.88 163 27849 6.03 163 16344 4.62 163 7937 3.22 163 2709 1.88 173 26371 6.04 173 15511 4.64 173 7489 3.22 173 2581 1.89 183 24982 6.05 183 14774 4.65 183 7093 3.22 183 2433 1.89 193 23880 6.08 193 14108 4.67 193 6747 3.23 193 2341 1.90 203 22777 6.09 203 13454 4.68 203 6440 3.24 203 2212 1.90 213 21796 6.10 213 12871 4.69 213 6108 3.23 213 2139 1.91 223 20749 6.09 223 12216 4.67 223 5788 3.22 223 1991 1.89 233 19889 6.09 233 11717 4.68 233 5532 3.21 233 1936 1.90 243 19183 6.11 243 11348 4.70 243 5340 3.22 243 1863 1.90 253 18522 6.13 253 10967 4.71 253 5148 3.23 253 1826 1.92 263 17904 6.14 263 10634 4.73 263 4982 3.24 263 1789 1.94 273 17639 6.15 273 10599 4.77 273 4918 3.25 273 1734 1.99 283 16934 6.20 283 10230 4.77 283 4803 3.27 283 1697 1.94 293 16449 6.21 293 9921 4.78 293 4649 3.27 293 1660 1.96 303 15986 6.23 303 9516 4.81 303 4419 3.27 303 1586 1.96 Ecl. Quím., São Paulo, 35 - 2: 89 - 98, 2010 95 Artigo Article fig.3. FTIR spectrum of gaseous products of thermal decomposition of Mn(II) 2-methoxyphenoxyacetate The solubilities of 2-methoxyphenoxyace- tates of Mn(II), Co(II), Ni(II) and Cu(II) in wa- ter were measured at 293K. Saturated solutions of the obtained compounds were prepared under isothermal conditions. The contents of Mn(II), Co(II), Ni(II) and Cu(II) were determined using ASA 880 spectrophotometer (Varian). The values of solubilities are presented in Table1. results and discussion 2-Methoxyphenoxyacetates of Mn(II), Co(II), Ni(II) and Cu(II) were obtained as polycrys- talline products with a metal ion to ligand ratio of 1:2 and the general formula M(C9H9O4)3·4H2O, where M(II) = Mn, Co, Ni and Cu. The colours of these complexes are typical for M(II) ions: pinkish for Mn(II), pink for Co(II), green for Ni(II), and blue for Cu(II). In these compounds the d→d elec- tron transitions of the central ions are those of the lowest energy and absorption occurs at relatively high wave lengths that depends on the nature of the metal ion [9,10]. The compounds were characterized by ele- mental analysis (Table 1), FTIR and FIR spectra (Table 2). The 2-methoxyphenoxyacetates of Mn(II), Co(II), Ni(II) and Cu(II) exhibit similar solid state IR spectra. The band at 1742 cm-1 originating from the -COOH group, seen in the acid spectrum, is replaced in the spectra of complexes by two bands at 1619-1581 cm-1 and 1355-1341cm-1, resulting from the asymmetric and symmetric vibrations of COO- group, respectively [11-14]. The bands with the maxima at 3565-3208cm-1, 1599-1505cm-1 and 971-908cm-1 confirm the presence of crystalliza- tion water molecules in the analyzed complexes. The bands of ν(C=C) ring vibrations appear at 1654-1597cm-1, 1493cm-1, 1290-1010cm-1 and 670-620cm-1. The bands attributed to asymmetric and symmetric C-H stretching modes of the CH3 groups are observed at 2969-2928cm-1 and 2924- 2901cm-1, respectively. The bands of asymmetric and symmetric valency vibrations occur at 1260- 1217 and 1060-1058cm-1, respectively. The bands Ecl. Quím., São Paulo, 35 - 2: 89 - 98, 201096 Artigo Article at 472-465cm-1 confirm the ionic metal-oxygen bond [15-21]. In the range of 472-465cm-1 they increase in the following way: Mn(II) = Cu(II) < Co(II) < Ni(II), which suggests the strongest M-O bond in the case of Ni(II) complex. The bands in the range of 336-276cm-1 are connected with the O-H…O streching vibrations and they change their shapes according to the rise of atomic number of elements in 2-methoxyphe- noxyacetates. Table 2 presents the values of the two band frequencies of asymmetrical and symmetrical vi- brations for carboxylate group of analyzed com- plexes. The separations of the νasCOO - , and νsCOO - modes in the compounds Δν(COO-) are greater or smaller than those of the sodium salt (ΔνCOO - = 188cm-1) indicating a various degree of M-O ionic bonds in 2-methoxyphenoxyacetates compared to that of the sodium salt. For the complexes the shifts of the frequencies of bands of νas(COO-), and νs(COO-) are lower and higher, respectively, than those for sodium 2-methoxyphenoxyacetate. Accordingly, taking into account the spectrosco- pic criteria [12,14,22] the carboxylate ions appear to be monodentate (Co(II), Ni(II) and Mn(II)) or bidentate (Cu(II) complex) groups. In order to estimate the crystalline forms of the 2-methoxyphenoxyacetates the X-ray powder diffraction measurements were done. The diffrac- togram values suggest them to be polycrystalline compounds with various degree of crystallinity (Fig.1) [23]. The thermal stability of Mn(II), Co(II), Ni(II), and Cu(II) 2-methoxyphenoxyacetates was studied in air at 293-1273 K (Table 3. Fig.2). When heated to 1273 K the Mn(II) complex is de- hydrated in one step. In the temperature range of 348 – 443 K it losses two water molecules in one step and forms anhydrous salt. The loss of mass calculated from TG curve is equal to 14,69% (theoretical value is 14,73%). The anhydrous salt at 603–703 K is gradually decomposed to MnO that is the final product of complex decomposi- tion. The intermediate compound formed in this range of temperature is oxycarbonate of manga- nium. The dehydration process is connected with endothermic effect whereas the combustion of the organic ligand is accompanied by exothermic one. The final product of complex decomposition was confirmed by IR spectra and X-ray powder dif- fractogram. The tetrahydrate of 2-methoxyphenoxyace- tate of Co(II) during heating in air losses the water molecules in one step at 353 – 433 K and forms the anhydrous complex. The loss of mass calcu- lated from TG curve is equal to 14,70% and calcu- lated one 14,61%. During heating the anhydrous salt 1183-1223 K is decomposed to CoO with the intermediate formation of oxycarbonate of cobalt. The final product of complex decomposition was identified by X-ray powder diffractogram as CoO. The dehydration process is accompanied with the endoeffect while that of oxidation by exothermic one (Fig.2). When heated in air to 1273 K the tetra- hydrate of Ni(II) 2-methoxyphenoxyacetate de- hydrates in one step at 323 – 433K and forms anhydrous complex. The found mass loss being equal to 14,54% corresponds to the loss of four molecules of water (theoretical value is equal to 14,61%). The anhydrous 2-methoxyphenoxyace- tate of Ni(II) at 633-713 K is decomposed to NiO, which is the final product of thermal decomposi- tion. The dehydration process is connected with an endothermic effect seen in DTA curve, while the combustion of the organic ligand is connected with exothermic one. During heating to 1273 K the Cu (II) com- plex dehydrates in one step. In the temperature range of 318 – 393 K it losses four molecules of water and forms anhydrous salt. The loss of mass calculated from TG curve is equal to 14,48% (the theoretical value is 14,47%). The anhydrous com- plex at 598-768 K is decomposed to CuO that is a final product of complex decomposition. The intermediate compounds formed in this range of temperature may contain oxycarbonate of Cu, Cu and Cu2O that being next oxidized to CuO. The final product of complex decomposition was iden- tified by X-ray powder diffractogram. The dehy- dration process, in this case, is connected with an endothermic effect seen on DTA curve, while the combustion of the organic ligand is accompanied by exothermic one. Considering the temperature of dehydration process and the way by which it proceeds it is possible to assume that the water molecules may be in the outer coordination sphere of the complex [24,25]. Ecl. Quím., São Paulo, 35 - 2: 89 - 98, 2010 97 Artigo Article Taking into account the temperature val- ues of the initial dehydration process it appears that Co(II) complex is the most thermally stable while Cu(II) compound has the least thermal sta- bility because it starts to release water molecule at 318K. The values of enthalpy of dehydration pro- cess were determined with the use of DSC/TG system under nitrogen atmosphere. They are in the range of 128,9 – 113,7 kJ∙mol-1 and 32,2 – 28,4 kJ∙mol-1 per one molecule of water. These values indicate that the water molecule is the strongest bounded in the Mn(II) complex while that the weakest in Co(II) compound. The decomposition process with the gas product analysis was recorded for 2-methoxy- phenoxyacetates of Mn(II), Co(II), Ni(II) and Cu(II). For example the FTIR spectrum of gas- eous products of decomposition process of Mn(II) 2-methoxyphenoxyacetate is presented in Fig.3. FTIR spectra of the gas phase products indicate that the decomposition of complexes is connected with the release of CO2, CO, H2O, alcohols and hydrocarbons. The characteristic valence and de- formation vibration bands of water molecules in FTIR spectra appear in the wavenumber ranges of 4000-3500cm-1 and 2000cm-1. The bands char- acterictic for CO2 molecule vibrations occur in the following ranges: 2700 – 2500 cm-1 and 1000 cm-1. The bands of hydrocarbon vibrations are ob- served at 2250 cm-1- and the band characteristic for CO molecule vibrations appears at 2060 cm-1. The bands typical for alcohol molecule vibrations are observed at 4000 – 3500 cm-1 and 1700-1500 cm-1 [26-28]. The solubility of analyzed compounds was measured (Table 1). It is in the order of 10-5 mol·dm-3. The Co(II) 2-methoxyphenoxyacetate is the most soluble salt, while that of Ni(II) the least soluble one. The compounds are hardly soluble in water and the order value is not sufficient to use 2-methoxyphenoxyacetic acid for the separation of some metal ions by ion-exchange chromatog- raphy method. The magnetic susceptibility of 2-meth- oxyphenoxyacetates of Mn(II), Co(II), Ni(II) and Cu(II) was measured in the temperature range of 77-303K (Table 4. Fig.4). Temperature (K) 50 100 150 200 250 300 350 χ( cm 3 /m ol ) 1000 2000 3000 4000 5000 6000 fig.4. Dependence between magnetic susceptibility values vs temperatures for 2-methoxyphenoxyac- etate of Cu(II) The values of the Weiss constant, Θ, for all complexes were found to have a negative sign which probably arises from antiferromagnetic spin interaction or from a crystal field splitting of the paramagnetic spin state [29-34]. The magnetic moment values experimen- tally determined at 76-303K for Mn(II), Co(II), Ni(II) and Cu(II) compounds change from 6,06 µB (at 76K) to 6,23 µB (at 303K) for Mn(II) complex, from 4,40 µB (at 76K) to 4.81 µB (at 303K) for Co(II), from 3,19 µB (at 76K) to 3.27 µB (at 303K) for Ni(II) and from 1.87 µB (at 76K) to 1,96 µB (at 303K) for Cu(II) 2-methoxyphenoxyacetates. The magnetic moment data are very close to the spin only values for the respective ions cal- culated from the equation μeff = [4s(s+1)]1/2 in the absence of the magnetic interactions for present spin-system. The magnetic moment values cal- culated at room temperature for Mn(II), Co(II), Ni(II) and Cu(II) ions are equal to 5,9 µB, 3,88 µB, 2,83µB, and 1,73µB, respectively. For Mn(II), Co(II), Ni(II) and Cu(II) ions the magnetic mo- ment values may be different than the spin-only. These values are higher than the spin-only worth which results from a spin-orbital coupling. The experimental data suggest that these compounds are high-spin complexes with weak ligand field [29-34]. From the obtained results it appears that in 2-methoxyphenoxyacetates of Mn(II), Co(II), Ni(II) and Cu(II) the coordination numbers may Ecl. Quím., São Paulo, 35 - 2: 89 - 98, 201098 Artigo Article be equal to 5 and 6 depending on the dentates of carboxylate group and the position of water mol- ecules in the complex. The coordination numbers of Mn(II), Co(II), Ni(II) and Cu(II) ions could be established on the basis of the complete crystal structure determination of monocrystals but they have not been obtained so far. Conclusions On the basis of the results it appears that 2-methoxyphenoxyacetates of Mn(II), Co(II), Ni(II), and Cu(II) were synthesized as tetrahydra- tes. Their colours are typical for M(II) ions. 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