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Synthesis and characterization of a MoO3–pyrrolidinedithiocarbamate hybrid
International Journal of Inorganic Materials 3 (2001) 931–935
Synthesis and characterization of a MoO 3 –pyrrolidinedithiocarbamate hybrid R.F. de Farias ´ , Universidade Federal de Roraima, Caixa Postal 167,69301 -970, Boa Vista, Roraima, Brazil Departamento de Quımica
Abstract By using lamellar molybdenum trioxide, MoO 3 , and ammonium pyrrolidinedithiocarbamate (1-pyrrolidinecarbodithioic acid, ammonium salt), apdc, as precursors, an inorganic–organic intercalation hybrid of formula MoO 3 ?0.54apdc was synthesized, which was characterized by CHN elemental analysis, infrared spectroscopy, X-ray diffraction and SEM microscopy. After intercalation, the interlayer distance is increased from 0.7 (MoO 3 ) to 1.2 nm (hybrid). The use of lamellar MoO 3 as a molecular sieve for apdc and similar organic species is proposed. 2001 Elsevier Science Ltd. All rights reserved. Keywords: Molybdenum oxide; Hybrids; Lamellar compounds
1. Introduction The intercalation of organic molecules into inorganic substrates have been extensively explored to obtain the so called inorganic–organic hybrids. Such hybrids could exhibit the properties of both the inorganic and organic phases [1–3]. As an example, the inorganic–organic hybrids with photochemical properties can be mentioned [3]. Molybdenum has two oxides with defined composition [4]: MoO 2 and MoO 3 . The trioxide is ortorombic, exhibiting a lamellar stucture with MoO 6 units, which exhibits a distorted octahedral geometry [5], as shown in Fig. 1. The lamellar MoO 3 matrix has been successfully used for the synthesis of inorganic organic hybrids with polyaniline [6,7] and pyrazine [8]. The ammonium pyrrolidinedithiocarbamate (1pyrrolidinecarbodithioic acid, ammonium salt), the structural formula are which is shown in Fig. 2, can be used as a sequestrating agent towards metal cations [9]. The present work reports the synthesis and characterization of a MoO 3 –pyrrolidinedithiocarbamate hybrid, named here as MoO 3 –apdc
E-mail address: [email protected] (R.F. de Farias). 1466-6049 / 01 / $ – see front matter 2001 Elsevier Science Ltd. All rights reserved. PII: S1466-6049( 01 )00082-4
Fig. 1. Lamellar structure for MoO 3 .
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R.F. de Farias / International Journal of Inorganic Materials 3 (2001) 931 – 935
Fig. 2. Structural formula for ammonium pyrrolidinedithiocarbamate, apdc.
croelemental analyser. The X-ray diffraction patterns were obtained in a Shimadzu XD-3A equipment, using CuKa radiation (35 kV, 25 mA). The infrared spectra were obtained in a Bomem apparatus in the range 4000–400 cm 21 with a resolution of 4 cm 21 by dispersing the samples in KBr discs. The SEM micrographs were taken in a Jeol equipment, model JSM T-300, with an accelerating voltage of 15 kV. To estimate the length of the apdc molecule, as well as to obtain its electrostatic potential map, quantum chemical calculations (Hartree-Fock, STO-3G) were performed by using the Spartan-Pro 1.0.3 package [10].
3. Results and discussion 2. Experimental The MoO 3 –apyrrolidinedithiocarbamate hybrid was synthesized by mixing 0.2 g of MoO 3 (Baker) with 50 cm 3 of a 0.3 mol dm 23 solution of apdc (Aldrich). The obtained suspension was stirred for 4 h at room temperature and kept as such for 48 h. The obtained hybrid was exhaustively washed with doubly-distilled water, filtered and dried under vacuum at 308C for 12 h. The occurance of a chemical reaction was indicated by a color change from pale green (MoO 3 ) to deep gray (hybrid). Carbon, nitrogen and hydrogen elemental analysis were performed in a Perkin-Elmer, model PE 2400, mi-
The carbon, hydrogen and nitrogen percentages were found as 4.1, 0.6 and 1.1, respectively, giving a total amount of 0.54 mmol of apdc per gram of hybrid matrix. It is worth noting that the calculated and experimental C / H and C / N ratios: 7.50 (6.83) and 4.29 (3.73), respectively, are not in agreement. A such fact could be explained by supposing that some NH 3 molecules (from apdc molecules dissociation) are also adsorbed on the inorganic substrate, increasing the hydrogen and nitrogen total amounts. The obtained infrared (IR) spectra (not shown) are not conclusive, since the MoO 3 IR are very large and intense, merging with the organic moiety bands. The X-ray diffraction patterns are shown in Fig. 3. In
Fig. 3. X-ray diffraction patterns for MoO 3 (a) and MoO 3 –apdc (b).
R.F. de Farias / International Journal of Inorganic Materials 3 (2001) 931 – 935
the oxide diffraction pattern, peaks at 12.68 and 25.28 are associated with the 001 and 002 diffraction planes [6–8]. Taking into account the 001 diffraction peak, the interlayer distance can be calculated as 0.7 nm. If the apdc molecules have intercalated into the inorganic substrate interlayer space, an increase of the interlayer distance could be expected. Comparing the MoO 3 and MoO 3 –apdc diffraction patterns it can be seen that for the hybrid the 001 and 002 diffraction peaks are shifted to higher 2u values of 12.88 and 25.88, respectively, which are associated with a decrease and not an increase of the interlayer distance. Such a fact could be explained by supposing the presence of new MoO 3 phases due to different hydration degrees of the inorganic substrate. Such a hypothesis is reinforced taking into account that thare are two distinct MoO 3 phases with very small d-value differences, such as [11] PDF 01-0706, d 001 50.689 nm and PDF 47-1320, d 001 50.688 nm. In the hybrid diffraction pattern, there are three diffraction peaks at 7.58, 9.88 and 10.58 with d51.2, 0.9 and 0.84 nm, respectively, not observed for the inorganic substrate. By using Spartan [10], the length of the apdc molecule was calculated as 0.5 nm. So, taking into account the interlayer distance for MoO 3 (0.7 nm) and the length of the ppdc molecule (0.5 nm), it can be seen from 0.710.551.2 nm, which is the interlayer distance for the 7.58 diffraction peak observed for the hybrid matrix. Hence, it can be concluded that a real intercalation compound was formed, despite the fact that probably some apdc molecules are simply adsorbed on the oxide grains surfaces. Such considerations are summarized and illustrated in Fig. 4.
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The SEM micrographs for the substrate and hybrid matrices are shown in Fig. 5. As can be observed, the surface of the grains for the hybrid matrix is some different in comparison with the MoO 3 grains. The elemental analysis (EDX) performed for sulphur shows that this element is homogeneously distributted on the hybrid matrix. As suggested in Fig. 4, the anion C 5 H 8 NS 22 , interacts with the Lewis acid sites on the oxide surface through the sulphur atoms. A such supposition is based on the electrostatic potential map shown in Fig. 6b. In a such map, the negatively-charged regions are shown in red and the less negatively-charged regions in blue. It is verified that the nitrogen atom is not available to interact with the acidic sites on the MoO 3 surface.
4. Conclusion Based on the obtained results, it can be concluded that a MoO 3 –apdc intercalation hybrid was obtained. Could be inferred that a larger population of apdc molecules could be intercalated by changing the experimental conditions such as the apdc / MoO 3 ratio and temparature. Taking into account the high affinity of the inorganic substrate towards the apdc molecules, the use of lamellar MoO 3 as a sequestrating (molecular sieve) agent for apdc and similar organic molecules can be proposed. Furthermore, since the nitrogen atom of apdc does not interact with the inorganic substrare, its electron pair is available to
Fig. 4. Schematic representation for apdc molecule (C 5 H 8 NS 2 2 anion), molybdenum oxide and the respective intercalation compound.
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R.F. de Farias / International Journal of Inorganic Materials 3 (2001) 931 – 935
Fig. 5. SEM micrographs for MoO 3 , 20003 (a) and MoO 3 –apdc, 35003 (b). The scale bar is in micrometers.
R.F. de Farias / International Journal of Inorganic Materials 3 (2001) 931 – 935
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Fig. 6. C 5 H 8 NS 2 2 anion: ball and spoke model (a) and electrostaic potential map (b). In the electrostaic potential map, the negatively-charged regions are shown in red and the less negatively-charged regions in blue.
interact with another acidic species, opening up a series of exciting possibilities.
References [1] [2] [3] [4]
Rao CNR. J Mater Chem 1999;9:1. Sanchez C, Ribot F, Lebeau B. J Mater Chem 1999;9:35. Ogawa M, Kuroda K. Chem Rev 1995;95:399. Greenwood NN, Earnshaw A. Chemistry of the elements, Oxford: Butterworth–Heinemann, 1995.
[5] Kihlborg L. The crystal chemistry of molybdenum oxides, Advances in chemistry series, Vol. 39, Washington, DC: Am Chem Soc, 1963. [6] de Farias RF, de Souza JM, de Melo JV, Airoldi C. J Colloid Interface Sci 1999;212:123. [7] de Farias RF. Effects of adsorption on the redox process of oxide surfaces. In: Encyclopedia of surface and colloid science, New York: Marcel Dekker, 2001. [8] de Farias RF. Int J Inorg Mater, in press. [9] Aldrich handbook of fine chemical and laboratory equipment, 2000– ˜ Paulo: Sigma–Aldrich Quımica ´ 2001 ed., Sao Brasil, 2000, p. 1453. [10] Wavefunction Inc., Irvine, CA, USA. [11] Joint Commitee on Powder Diffraction Standards. Powder diffraction file, Pensylvania: Swarthmore, 1973.
Synthesis and characterization of a MoO 3 –pyrrolidinedithiocarbamate hybrid R.F. de Farias ´ , Universidade Federal de Roraima, Caixa Postal 167,69301 -970, Boa Vista, Roraima, Brazil Departamento de Quımica
Abstract By using lamellar molybdenum trioxide, MoO 3 , and ammonium pyrrolidinedithiocarbamate (1-pyrrolidinecarbodithioic acid, ammonium salt), apdc, as precursors, an inorganic–organic intercalation hybrid of formula MoO 3 ?0.54apdc was synthesized, which was characterized by CHN elemental analysis, infrared spectroscopy, X-ray diffraction and SEM microscopy. After intercalation, the interlayer distance is increased from 0.7 (MoO 3 ) to 1.2 nm (hybrid). The use of lamellar MoO 3 as a molecular sieve for apdc and similar organic species is proposed. 2001 Elsevier Science Ltd. All rights reserved. Keywords: Molybdenum oxide; Hybrids; Lamellar compounds
1. Introduction The intercalation of organic molecules into inorganic substrates have been extensively explored to obtain the so called inorganic–organic hybrids. Such hybrids could exhibit the properties of both the inorganic and organic phases [1–3]. As an example, the inorganic–organic hybrids with photochemical properties can be mentioned [3]. Molybdenum has two oxides with defined composition [4]: MoO 2 and MoO 3 . The trioxide is ortorombic, exhibiting a lamellar stucture with MoO 6 units, which exhibits a distorted octahedral geometry [5], as shown in Fig. 1. The lamellar MoO 3 matrix has been successfully used for the synthesis of inorganic organic hybrids with polyaniline [6,7] and pyrazine [8]. The ammonium pyrrolidinedithiocarbamate (1pyrrolidinecarbodithioic acid, ammonium salt), the structural formula are which is shown in Fig. 2, can be used as a sequestrating agent towards metal cations [9]. The present work reports the synthesis and characterization of a MoO 3 –pyrrolidinedithiocarbamate hybrid, named here as MoO 3 –apdc
E-mail address: [email protected] (R.F. de Farias). 1466-6049 / 01 / $ – see front matter 2001 Elsevier Science Ltd. All rights reserved. PII: S1466-6049( 01 )00082-4
Fig. 1. Lamellar structure for MoO 3 .
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R.F. de Farias / International Journal of Inorganic Materials 3 (2001) 931 – 935
Fig. 2. Structural formula for ammonium pyrrolidinedithiocarbamate, apdc.
croelemental analyser. The X-ray diffraction patterns were obtained in a Shimadzu XD-3A equipment, using CuKa radiation (35 kV, 25 mA). The infrared spectra were obtained in a Bomem apparatus in the range 4000–400 cm 21 with a resolution of 4 cm 21 by dispersing the samples in KBr discs. The SEM micrographs were taken in a Jeol equipment, model JSM T-300, with an accelerating voltage of 15 kV. To estimate the length of the apdc molecule, as well as to obtain its electrostatic potential map, quantum chemical calculations (Hartree-Fock, STO-3G) were performed by using the Spartan-Pro 1.0.3 package [10].
3. Results and discussion 2. Experimental The MoO 3 –apyrrolidinedithiocarbamate hybrid was synthesized by mixing 0.2 g of MoO 3 (Baker) with 50 cm 3 of a 0.3 mol dm 23 solution of apdc (Aldrich). The obtained suspension was stirred for 4 h at room temperature and kept as such for 48 h. The obtained hybrid was exhaustively washed with doubly-distilled water, filtered and dried under vacuum at 308C for 12 h. The occurance of a chemical reaction was indicated by a color change from pale green (MoO 3 ) to deep gray (hybrid). Carbon, nitrogen and hydrogen elemental analysis were performed in a Perkin-Elmer, model PE 2400, mi-
The carbon, hydrogen and nitrogen percentages were found as 4.1, 0.6 and 1.1, respectively, giving a total amount of 0.54 mmol of apdc per gram of hybrid matrix. It is worth noting that the calculated and experimental C / H and C / N ratios: 7.50 (6.83) and 4.29 (3.73), respectively, are not in agreement. A such fact could be explained by supposing that some NH 3 molecules (from apdc molecules dissociation) are also adsorbed on the inorganic substrate, increasing the hydrogen and nitrogen total amounts. The obtained infrared (IR) spectra (not shown) are not conclusive, since the MoO 3 IR are very large and intense, merging with the organic moiety bands. The X-ray diffraction patterns are shown in Fig. 3. In
Fig. 3. X-ray diffraction patterns for MoO 3 (a) and MoO 3 –apdc (b).
R.F. de Farias / International Journal of Inorganic Materials 3 (2001) 931 – 935
the oxide diffraction pattern, peaks at 12.68 and 25.28 are associated with the 001 and 002 diffraction planes [6–8]. Taking into account the 001 diffraction peak, the interlayer distance can be calculated as 0.7 nm. If the apdc molecules have intercalated into the inorganic substrate interlayer space, an increase of the interlayer distance could be expected. Comparing the MoO 3 and MoO 3 –apdc diffraction patterns it can be seen that for the hybrid the 001 and 002 diffraction peaks are shifted to higher 2u values of 12.88 and 25.88, respectively, which are associated with a decrease and not an increase of the interlayer distance. Such a fact could be explained by supposing the presence of new MoO 3 phases due to different hydration degrees of the inorganic substrate. Such a hypothesis is reinforced taking into account that thare are two distinct MoO 3 phases with very small d-value differences, such as [11] PDF 01-0706, d 001 50.689 nm and PDF 47-1320, d 001 50.688 nm. In the hybrid diffraction pattern, there are three diffraction peaks at 7.58, 9.88 and 10.58 with d51.2, 0.9 and 0.84 nm, respectively, not observed for the inorganic substrate. By using Spartan [10], the length of the apdc molecule was calculated as 0.5 nm. So, taking into account the interlayer distance for MoO 3 (0.7 nm) and the length of the ppdc molecule (0.5 nm), it can be seen from 0.710.551.2 nm, which is the interlayer distance for the 7.58 diffraction peak observed for the hybrid matrix. Hence, it can be concluded that a real intercalation compound was formed, despite the fact that probably some apdc molecules are simply adsorbed on the oxide grains surfaces. Such considerations are summarized and illustrated in Fig. 4.
933
The SEM micrographs for the substrate and hybrid matrices are shown in Fig. 5. As can be observed, the surface of the grains for the hybrid matrix is some different in comparison with the MoO 3 grains. The elemental analysis (EDX) performed for sulphur shows that this element is homogeneously distributted on the hybrid matrix. As suggested in Fig. 4, the anion C 5 H 8 NS 22 , interacts with the Lewis acid sites on the oxide surface through the sulphur atoms. A such supposition is based on the electrostatic potential map shown in Fig. 6b. In a such map, the negatively-charged regions are shown in red and the less negatively-charged regions in blue. It is verified that the nitrogen atom is not available to interact with the acidic sites on the MoO 3 surface.
4. Conclusion Based on the obtained results, it can be concluded that a MoO 3 –apdc intercalation hybrid was obtained. Could be inferred that a larger population of apdc molecules could be intercalated by changing the experimental conditions such as the apdc / MoO 3 ratio and temparature. Taking into account the high affinity of the inorganic substrate towards the apdc molecules, the use of lamellar MoO 3 as a sequestrating (molecular sieve) agent for apdc and similar organic molecules can be proposed. Furthermore, since the nitrogen atom of apdc does not interact with the inorganic substrare, its electron pair is available to
Fig. 4. Schematic representation for apdc molecule (C 5 H 8 NS 2 2 anion), molybdenum oxide and the respective intercalation compound.
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R.F. de Farias / International Journal of Inorganic Materials 3 (2001) 931 – 935
Fig. 5. SEM micrographs for MoO 3 , 20003 (a) and MoO 3 –apdc, 35003 (b). The scale bar is in micrometers.
R.F. de Farias / International Journal of Inorganic Materials 3 (2001) 931 – 935
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Fig. 6. C 5 H 8 NS 2 2 anion: ball and spoke model (a) and electrostaic potential map (b). In the electrostaic potential map, the negatively-charged regions are shown in red and the less negatively-charged regions in blue.
interact with another acidic species, opening up a series of exciting possibilities.
References [1] [2] [3] [4]
Rao CNR. J Mater Chem 1999;9:1. Sanchez C, Ribot F, Lebeau B. J Mater Chem 1999;9:35. Ogawa M, Kuroda K. Chem Rev 1995;95:399. Greenwood NN, Earnshaw A. Chemistry of the elements, Oxford: Butterworth–Heinemann, 1995.
[5] Kihlborg L. The crystal chemistry of molybdenum oxides, Advances in chemistry series, Vol. 39, Washington, DC: Am Chem Soc, 1963. [6] de Farias RF, de Souza JM, de Melo JV, Airoldi C. J Colloid Interface Sci 1999;212:123. [7] de Farias RF. Effects of adsorption on the redox process of oxide surfaces. In: Encyclopedia of surface and colloid science, New York: Marcel Dekker, 2001. [8] de Farias RF. Int J Inorg Mater, in press. [9] Aldrich handbook of fine chemical and laboratory equipment, 2000– ˜ Paulo: Sigma–Aldrich Quımica ´ 2001 ed., Sao Brasil, 2000, p. 1453. [10] Wavefunction Inc., Irvine, CA, USA. [11] Joint Commitee on Powder Diffraction Standards. Powder diffraction file, Pensylvania: Swarthmore, 1973.