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Synthesis, structural characterization and chromotropism of a copper(II) complex containing a bidentate ligand
Accepted Manuscript Synthesis, structural characterization and chromotropism of a copper(II) complex containing a bidentate ligand Hamid Golchoubian, Mahbobeh Tarahomi, Ehsan Rezaee, Giuseppe Bruno PII: DOI: Reference:
S0277-5387(14)00642-1 http://dx.doi.org/10.1016/j.poly.2014.09.035 POLY 11004
To appear in:
Polyhedron
Received Date: Accepted Date:
19 July 2014 16 September 2014
Please cite this article as: H. Golchoubian, M. Tarahomi, E. Rezaee, G. Bruno, Synthesis, structural characterization and chromotropism of a copper(II) complex containing a bidentate ligand, Polyhedron (2014), doi: http://dx.doi.org/ 10.1016/j.poly.2014.09.035
This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
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Synthesis, structural characterization and chromotropism of a copper(II) complex containing a bidentate ligand
Hamid Golchoubian*1, Mahbobeh Tarahomi1, Ehsan Rezaee1, Giuseppe Bruno2 1
Department of Chemistry, University of Mazandaran, Babol-sar; Iran. Postal Code 4741695447.
2
Dipartimento di Chimica Inorganica, Vill. S. Agata, Salita Sperone 31, Università di Messina 98166 Messina, Italy e-mail: [email protected]
Reprint requests to Dr. H. Golchoubian. Tel/Fax: (98)-1125342350, E-mail: [email protected] Abstract A
new
coordination
compound,
[Cu(L)2(OH2)](ClO4)2
where
L
=
N-(pyridin-2-
ylmethyl)propane-2-amine, was prepared and characterized by elemental analysis, molar conductance and IR and UV-Vis spectroscopic techniques. X-ray crystal analysis of the complex confirmed that the copper(II) ion has a distorted square pyramidal environment. The complex is chromotropic in solution. The chromotropic properties of the complex, including solvato-, thermo-, halo- and ionochromism, were investigated in detail. The complex displayed strongly pronounced reversible thermochromism in solution due to dissociation and of re-coordination of a water molecule.
Keywords: Diamine ligand; Copper(II) complex; Thermochromism; Solvatochromism; Ionochromism; Halochromism 1
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1. Introduction Recently, the chromotropic behaviors of inorganic complexes have been investigated due to their potentially versatile applications [1-3]. Chromotropism is a reversible change in the color of a substance caused by some form of stimulus. One of the stimuli is temperature (thermochromism), which involves a change in color of a compound induced by temperature change. This phenomenon has many applications, such as temperature sensors, thermochromic pigments, temperature indicators, security and novelty printing, coating, as well as in thermography [4-7]. Solvatochromism is another important chromotropic property, which is defined as a reversible color change of a transition metal complex due to variation of a solvent‟s properties [8]. Recent studies have demonstrated that solvatochromic materials can be used as a Lewis-acid base color indicator [9] and to develope of optical sensor materials to monitor pollutant levels in the environment [10,11]. Solvatochromism also provides a quantitative method to identify the solvent behavior for different solvents and the function of solvents in physicochemical studies [12-23]. In addition to thermochromism and solvatochromism, ionochromism, a reversible color change caused by the addition of ions, is another important property of transition metal complexes which has attracted great attention due to their important applications in analytical chemistry and in high technology fields such as carbonless copying paper, direct thermal printing and sensor materials [7]. The pH effect on the visible absorption spectrum is defined as halochromism and can be regarded as one of the simplest external stimulations and can induce switching properties such as visible absorption for pH sensors. pH sensors are especially attractive since various living organisms, like enzymes, function within a narrow pH range, and their actions or behaviors can be explained as being “on-off” switched as a
2
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function of pH [24]. The visual detection of CO2 gas [25] and the preparation of smart and interactive textiles [26] are other applications of halochromic dyes. However, the majority of pH sensors are based on organic molecules and less attention has been focused on metal complexes [27]. Among the transition metal complexes, copper(II) ions with a combination of chelate ligands have been recognized as the most encouraging candidates for practical applications of chromotropism due to their high thermodynamic stabilities, unsaturated coordination number and also the existence of simple and regular changes in their electronic spectra in accord to the power of the stimuli imposed on the system. In this work the new bidentate ligand N-(pyridin-2-ylmethyl)propane-2-amine and its copper(II) complex, as shown in Scheme 1, were prepared and fully characterized. The chromotropic behaviors of the complex, including thermochromism, solvatochromism, ionochromism and halochromism, were investigated. Based on our knowledge after our first report [28], this is the second time that a compound has shown all these properties collectively.
2. Experimental 2.1. Materials and methods All solvents were spectral-grade and all other reagents were used as received. Caution! Perchlorate salts are potentially explosive and should be handled with appropriate care. Elemental analyses were performed on a LECO CHN-600 elemental analyzer. Absolute metal percentages were determined with a Varian-spectra A-30/40 atomic absorption-flame spectrometer. The sample was dried to a constant weight under a high vacuum prior to analysis. Conductance measurements were made at 25 °C with a Jenway 400 conductance meter on 3
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concentrations of 10.0 × 10-4, 6.00 × 10-4, 4.00 × 10-4 and 2.00 × 10-4 M of samples in selected solvents. Then for each solvent, a curve was plotted by drawing the molar conductance versus the concentration of the sample. The curve was then extrapolated to an infinitely dilute solution to obtain the molar conductance value. The infrared spectrum (potassium bromide disk) was recorded using a Bruker FT-IR instrument. 1H and
13
C NMR spectra were measured with a
Bruker 400 DRX Fourier Transform spectrometer at room temperature. The electronic absorption spectra were measured using Braic2100 model UV-Vis spectrophotometers. The buffer solution of pH = 7.2 for the ionochromic study was prepared by mixing 100 mL of ammonium chloride (1.1 M) and 100 mL of aqueous ammonia solution (0.05 M). The following solvents were used for the solvatochromic study: nitromethane (NM), nitrobenzene (NB), benzonitrile (BN), acetone (AC), acetonitrile (AN), propionitrile (PN), methanol (MeOH), ethanol (EtOH), water (H2O), dimethylformamide (DMF), dimethylsulfoxide (DMSO) and hexamethylphosphorictriamide (HMPA). 2.2. Synthesis 2.2.1. N-(pyridin-2-ylmethyl)propane-2-amine (L) A mixture of pyridine-2-carbaldehyde (2.7 ml, 30 mmol), tert-butylamine (3.5 ml, 30 mmol) and a few drops of acetic acid in methanol (35 ml) was prepared and refluxed for 10 min. The solvent was then evaporated under reduced pressure. NaBH4 (1.7 g, 45 mmol) was added gradually to the resultant yellow oil dissolved in methanol (30 mL). The resulting mixture was allowed to stand overnight. After heating the solution to near the boiling point, HCl (10 ml, 17 M) was added to it, while placing the solution in an ice bath, and then it was heated again to the boiling temperature. The mixture was then made alkaline by adding NaOH (4 M). The sodium borate
4
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precipitate was removed by filtration. Evaporation of the solvent from the filtrate resulted in a yellow oil which was subsequently extracted with dichloromethane (3 15 mL). The combined CH2Cl2 fractions were dried over anhydrous Na2SO4. Evaporation of the solvent under reduced pressure resulted in the desired product as a brown oil. The yield was 45%. Selected IR data (ν/cm-1 using KBr disk): 3308 (m, N–H str.), 2964 (s, C–H str. aliphatic), 1595 (s, C=N str.), 1433 (s, CC str. aromatic), 1227 (s, NC str. aliphatic). 1H NMR (400 MHz, CDCl3) : 1.15 (s, 9H, ((CH3)3C-), 1.92 (s, br, H, tert-Butyl-NH), 3.83 (s, 2H, CH2Py), 7.80 (d,d, J = 5.2, 1.6 Hz, H, Py), 7.27 (s, H, Py), 7.57 (t,d, J = 7.6, 2.0 Hz, H, Py), 8.48 (d, J = 4.4 Hz, H, Py). When one drop of D2O was added to the 1H NMR sample, the broad signal at 1.92 ppm disappeared. C NMR (100 MHz in CDCl3) : 29.06 (CH3CN), 48.53 (CH3CN), 50.48
13
(NHCH2Py), 121.71, 122.46, 136.41, 149.08, 160.46 (PyC). 2.2.2. Preparation of [Cu(L)2(OH2)](ClO4)2 To a solution of the ligand L (0.328 g, 2 mmol) in ethanol (6 mL) was slowly added Cu(ClO4)2·6H2O (0.37 g, 1 mmol) in ethanol (6 mL). The resultant purple color mixture was stirred for 2 h at room temperature. The desired compound precipitated from the solution as a blue solid. The compound was recrystallized by diffusion of diethylether into an acetonitrile solution. The typical yield was 43%. The crystals were suitable for X-ray crystallography. Anal. calcd for C20H34N4CuCl2O9 (MW= 608.96 g mol-1): C, 39.45; H, 5.63; N, 9.20; Cu, 10.44; Found: C, 39.72; H, 5.62; N, 9.22; Cu, 10.53 %. Selected IR data (ʋ/cm-1 using KBr disk): 3448 (m, O-H str.), 3275 (m, N-H str), 2974 (m C-H str.), 1649 (s, C=N str.), 1476 (m, N-H bend.), 1112 (s, O-ClO3 str.), 625 (s, O-ClO3 bend.), 427 (w, Cu-O str.), 449 (w, Cu-N str.). 2.3.1. X-ray structure determination
5
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The X-ray measurements of the complex were made on a Bruker Apex-II CCD single crystal diffractometer at room temperature using graphite-monochromated Mo-Kα radiation. Data were collected and reduced by SMART and SAINT software [29] in the Bruker packages. The structure was solved by direct method [30,31] and subsequent Fourier difference techniques and refined using the full-matrix weighted least-squares procedure on F2 [32] with anisotropic thermal parameters for all non-hydrogen atoms. Several hydrogen atoms were located on the final difference map, the ligand H atoms were included in the refinement via the "riding model" method with the X---H bond geometry and the H isotropic displacement parameter depending on the parent X atom. The oxygen displacement ellipsoids are very large due to a significant rotational disorder of the perchlorate anion, but each attempt to treat it by a suitable overlap of two rotated conformations was unsuccessful. The last difference Fourier maps have shown the largest electron density residuals around the disordered perchlorate anion. A summary of the crystal data and structure determination is reported in Table 1. 3. Results and discussion 3.1 Synthesis The ligand was prepared by the condensation of equimolar amounts of tert-butylamine and pyridine-2-carbaldehyde and further reduction of the resulting diimine by sodium borohydride. The copper(II) complex was synthesized by mixing Cu(ClO4)·6H2O and the ligand in a molar ratio of 1:2, respectively, in ethanol. Thermochromism and solvatochromism in coordination compounds 3.2.3. X-ray structure The complex was crystallized in the monoclinic space group P21/n. A perspective view together with the atom labelling scheme for the complex is given in Fig. 1 and selected bond parameters
S0277-5387(14)00642-1 http://dx.doi.org/10.1016/j.poly.2014.09.035 POLY 11004
To appear in:
Polyhedron
Received Date: Accepted Date:
19 July 2014 16 September 2014
Please cite this article as: H. Golchoubian, M. Tarahomi, E. Rezaee, G. Bruno, Synthesis, structural characterization and chromotropism of a copper(II) complex containing a bidentate ligand, Polyhedron (2014), doi: http://dx.doi.org/ 10.1016/j.poly.2014.09.035
This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65
Synthesis, structural characterization and chromotropism of a copper(II) complex containing a bidentate ligand
Hamid Golchoubian*1, Mahbobeh Tarahomi1, Ehsan Rezaee1, Giuseppe Bruno2 1
Department of Chemistry, University of Mazandaran, Babol-sar; Iran. Postal Code 4741695447.
2
Dipartimento di Chimica Inorganica, Vill. S. Agata, Salita Sperone 31, Università di Messina 98166 Messina, Italy e-mail: [email protected]
Reprint requests to Dr. H. Golchoubian. Tel/Fax: (98)-1125342350, E-mail: [email protected] Abstract A
new
coordination
compound,
[Cu(L)2(OH2)](ClO4)2
where
L
=
N-(pyridin-2-
ylmethyl)propane-2-amine, was prepared and characterized by elemental analysis, molar conductance and IR and UV-Vis spectroscopic techniques. X-ray crystal analysis of the complex confirmed that the copper(II) ion has a distorted square pyramidal environment. The complex is chromotropic in solution. The chromotropic properties of the complex, including solvato-, thermo-, halo- and ionochromism, were investigated in detail. The complex displayed strongly pronounced reversible thermochromism in solution due to dissociation and of re-coordination of a water molecule.
Keywords: Diamine ligand; Copper(II) complex; Thermochromism; Solvatochromism; Ionochromism; Halochromism 1
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1. Introduction Recently, the chromotropic behaviors of inorganic complexes have been investigated due to their potentially versatile applications [1-3]. Chromotropism is a reversible change in the color of a substance caused by some form of stimulus. One of the stimuli is temperature (thermochromism), which involves a change in color of a compound induced by temperature change. This phenomenon has many applications, such as temperature sensors, thermochromic pigments, temperature indicators, security and novelty printing, coating, as well as in thermography [4-7]. Solvatochromism is another important chromotropic property, which is defined as a reversible color change of a transition metal complex due to variation of a solvent‟s properties [8]. Recent studies have demonstrated that solvatochromic materials can be used as a Lewis-acid base color indicator [9] and to develope of optical sensor materials to monitor pollutant levels in the environment [10,11]. Solvatochromism also provides a quantitative method to identify the solvent behavior for different solvents and the function of solvents in physicochemical studies [12-23]. In addition to thermochromism and solvatochromism, ionochromism, a reversible color change caused by the addition of ions, is another important property of transition metal complexes which has attracted great attention due to their important applications in analytical chemistry and in high technology fields such as carbonless copying paper, direct thermal printing and sensor materials [7]. The pH effect on the visible absorption spectrum is defined as halochromism and can be regarded as one of the simplest external stimulations and can induce switching properties such as visible absorption for pH sensors. pH sensors are especially attractive since various living organisms, like enzymes, function within a narrow pH range, and their actions or behaviors can be explained as being “on-off” switched as a
2
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function of pH [24]. The visual detection of CO2 gas [25] and the preparation of smart and interactive textiles [26] are other applications of halochromic dyes. However, the majority of pH sensors are based on organic molecules and less attention has been focused on metal complexes [27]. Among the transition metal complexes, copper(II) ions with a combination of chelate ligands have been recognized as the most encouraging candidates for practical applications of chromotropism due to their high thermodynamic stabilities, unsaturated coordination number and also the existence of simple and regular changes in their electronic spectra in accord to the power of the stimuli imposed on the system. In this work the new bidentate ligand N-(pyridin-2-ylmethyl)propane-2-amine and its copper(II) complex, as shown in Scheme 1, were prepared and fully characterized. The chromotropic behaviors of the complex, including thermochromism, solvatochromism, ionochromism and halochromism, were investigated. Based on our knowledge after our first report [28], this is the second time that a compound has shown all these properties collectively.
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65
concentrations of 10.0 × 10-4, 6.00 × 10-4, 4.00 × 10-4 and 2.00 × 10-4 M of samples in selected solvents. Then for each solvent, a curve was plotted by drawing the molar conductance versus the concentration of the sample. The curve was then extrapolated to an infinitely dilute solution to obtain the molar conductance value. The infrared spectrum (potassium bromide disk) was recorded using a Bruker FT-IR instrument. 1H and
13
C NMR spectra were measured with a
Bruker 400 DRX Fourier Transform spectrometer at room temperature. The electronic absorption spectra were measured using Braic2100 model UV-Vis spectrophotometers. The buffer solution of pH = 7.2 for the ionochromic study was prepared by mixing 100 mL of ammonium chloride (1.1 M) and 100 mL of aqueous ammonia solution (0.05 M). The following solvents were used for the solvatochromic study: nitromethane (NM), nitrobenzene (NB), benzonitrile (BN), acetone (AC), acetonitrile (AN), propionitrile (PN), methanol (MeOH), ethanol (EtOH), water (H2O), dimethylformamide (DMF), dimethylsulfoxide (DMSO) and hexamethylphosphorictriamide (HMPA). 2.2. Synthesis 2.2.1. N-(pyridin-2-ylmethyl)propane-2-amine (L) A mixture of pyridine-2-carbaldehyde (2.7 ml, 30 mmol), tert-butylamine (3.5 ml, 30 mmol) and a few drops of acetic acid in methanol (35 ml) was prepared and refluxed for 10 min. The solvent was then evaporated under reduced pressure. NaBH4 (1.7 g, 45 mmol) was added gradually to the resultant yellow oil dissolved in methanol (30 mL). The resulting mixture was allowed to stand overnight. After heating the solution to near the boiling point, HCl (10 ml, 17 M) was added to it, while placing the solution in an ice bath, and then it was heated again to the boiling temperature. The mixture was then made alkaline by adding NaOH (4 M). The sodium borate
4
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precipitate was removed by filtration. Evaporation of the solvent from the filtrate resulted in a yellow oil which was subsequently extracted with dichloromethane (3 15 mL). The combined CH2Cl2 fractions were dried over anhydrous Na2SO4. Evaporation of the solvent under reduced pressure resulted in the desired product as a brown oil. The yield was 45%. Selected IR data (ν/cm-1 using KBr disk): 3308 (m, N–H str.), 2964 (s, C–H str. aliphatic), 1595 (s, C=N str.), 1433 (s, CC str. aromatic), 1227 (s, NC str. aliphatic). 1H NMR (400 MHz, CDCl3) : 1.15 (s, 9H, ((CH3)3C-), 1.92 (s, br, H, tert-Butyl-NH), 3.83 (s, 2H, CH2Py), 7.80 (d,d, J = 5.2, 1.6 Hz, H, Py), 7.27 (s, H, Py), 7.57 (t,d, J = 7.6, 2.0 Hz, H, Py), 8.48 (d, J = 4.4 Hz, H, Py). When one drop of D2O was added to the 1H NMR sample, the broad signal at 1.92 ppm disappeared. C NMR (100 MHz in CDCl3) : 29.06 (CH3CN), 48.53 (CH3CN), 50.48
13
(NHCH2Py), 121.71, 122.46, 136.41, 149.08, 160.46 (PyC). 2.2.2. Preparation of [Cu(L)2(OH2)](ClO4)2 To a solution of the ligand L (0.328 g, 2 mmol) in ethanol (6 mL) was slowly added Cu(ClO4)2·6H2O (0.37 g, 1 mmol) in ethanol (6 mL). The resultant purple color mixture was stirred for 2 h at room temperature. The desired compound precipitated from the solution as a blue solid. The compound was recrystallized by diffusion of diethylether into an acetonitrile solution. The typical yield was 43%. The crystals were suitable for X-ray crystallography. Anal. calcd for C20H34N4CuCl2O9 (MW= 608.96 g mol-1): C, 39.45; H, 5.63; N, 9.20; Cu, 10.44; Found: C, 39.72; H, 5.62; N, 9.22; Cu, 10.53 %. Selected IR data (ʋ/cm-1 using KBr disk): 3448 (m, O-H str.), 3275 (m, N-H str), 2974 (m C-H str.), 1649 (s, C=N str.), 1476 (m, N-H bend.), 1112 (s, O-ClO3 str.), 625 (s, O-ClO3 bend.), 427 (w, Cu-O str.), 449 (w, Cu-N str.). 2.3.1. X-ray structure determination
5
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The X-ray measurements of the complex were made on a Bruker Apex-II CCD single crystal diffractometer at room temperature using graphite-monochromated Mo-Kα radiation. Data were collected and reduced by SMART and SAINT software [29] in the Bruker packages. The structure was solved by direct method [30,31] and subsequent Fourier difference techniques and refined using the full-matrix weighted least-squares procedure on F2 [32] with anisotropic thermal parameters for all non-hydrogen atoms. Several hydrogen atoms were located on the final difference map, the ligand H atoms were included in the refinement via the "riding model" method with the X---H bond geometry and the H isotropic displacement parameter depending on the parent X atom. The oxygen displacement ellipsoids are very large due to a significant rotational disorder of the perchlorate anion, but each attempt to treat it by a suitable overlap of two rotated conformations was unsuccessful. The last difference Fourier maps have shown the largest electron density residuals around the disordered perchlorate anion. A summary of the crystal data and structure determination is reported in Table 1.