- Email: [email protected]
Synthesis of α-mercury sulfide nanosheets from (1,10-phenanthroline)bis(1,2,3,4-tetrahydroquinolinecarbodithioato-S,S′)mercury(II)
Journal of Molecular Structure 1076 (2014) 382–386
Contents lists available at ScienceDirect
Journal of Molecular Structure journal homepage: www.elsevier.com/locate/molstruc
Synthesis of a-mercury sulfide nanosheets from (1,10-phenanthroline)bis(1,2,3,4-tetrahydroquinolinecarbodithioato-S, S0 )mercury(II) N. Srinivasan a, S. Thirumaran a,⇑, Samuele Ciattini b a b
Department of Chemistry, Annamalai University, Annamalainagar 608 002, India Centro di Cristallografia Strutturale, Polo Scientifio di Sesto Fiorentino, Via della Lastruccia N°3, 50019 Sesto Fiorentino, Firenze, Italy
h i g h l i g h t s
g r a p h i c a l a b s t r a c t
Complex 1 was prepared and
characterized by IR, NMR and X-ray diffraction. Complex 1 was used as single source precursor for the preparation of a-HgS. 2 min Preparation of high-quality hexagonal shaped a-HgS nanosheets was reported. Optical and structural properties of as-prepared a-HgS were evaluated. Quantum confinement effect was confirmed by UV visible spectroscopy.
a r t i c l e
i n f o
Article history: Received 23 June 2014 Received in revised form 30 July 2014 Accepted 31 July 2014 Available online 11 August 2014 Keywords: 1,2,3,4-Tetrahydroquinolinecarbodithioate Mercury(II) Single source precursor a-HgS nanosheets
a b s t r a c t (1,10-phenanthroline)bis(1,2,3,4-tetrahydroquinolinecarbodithioato-S,S0 )mercury(II); [Hg(thqdtc)2(1,10phen)] (1); has been synthesized and characterized by elemental analysis, IR and NMR spectroscopy and single crystal X-ray analysis. IR spectrum of the complex reveals the contribution of thioureide form to the structure. In the 13C NMR spectrum, [Hg(thqdtc)2(1,10-phen)] shows a single low-field resonance associated with backbone carbon of dithiocarbamate (N13CS2) at 205.7 ppm. The mononuclear structure of [Hg(thqdtc)2(1,10-phen)] exhibits monodentate and bidentate coordination by dithiocarbamate ligands and an intermediate geometry between tetragonal pyramidal and trigonal bipyramidal for mercury, defined by an N2S3 donor set. [Hg(thqdtc)2(1,10-phen)] has been found to be an effective singlesource precursor for the preparation of a-HgS nanosheets via solvothermal method. The as-prepared HgS nanosheets have been characterized by powder XRD, TEM, UV–Vis and fluorescence spectroscopy. TEM image of HgS exhibits that the as-prepared HgS particles are hexagonal shaped nanosheets. UV– Vis spectroscopy established pronounced quantum confinement effect. Ó 2014 Elsevier B.V. All rights reserved.
Introduction Dithiocarbamates have great binding potential to metals and have wide range of uses in coordination chemistry [1,2]. Metal ⇑ Corresponding author. Address: Department of Chemistry, Annamalai University, Annamalainagar 608 002, Tamil Nadu, India. Tel.: +91 9842897597. E-mail address: [email protected] (S. Thirumaran). http://dx.doi.org/10.1016/j.molstruc.2014.07.083 0022-2860/Ó 2014 Elsevier B.V. All rights reserved.
dithiocarbamate complexes have been widely studied because of their biological, agricultural, and analytical applications [3–5]. Metal dithiocarbamate complexes have proven to be very successful as single source precursors for the preparation of metal sulfide nanoparticles [6]. Mercury sulfide belongs to group II–VI material that is one of the most useful metal sulfide nanoparticles. HgS usually crystallizes in two forms: the cubic phase (b-HgS,
N. Srinivasan et al. / Journal of Molecular Structure 1076 (2014) 382–386
383
and convenient low cost solvothermal preparation of a-HgS nanoparticles and its characterization along with the synthesis, spectral and single crystal X-ray structural studies on 1. Experimental General
Scheme 1. Preparation of 1.
Table 1 Crystal data, data collection and refinement parameters for [Hg(thqdtc)2(1,10-phen)]. Empirical formula FW Crystal dimensions (mm) Crystal system Space group a/Å b/Å c/Å a/° b/° c/° U/Å3 Z DC/g cm3 l/cm1 F(0 0 0) k/Å h Range/° Index ranges Reflections collected Observed reflections F0 > 40 O(F0) Weighting scheme Number of parameters refined Final R, Rw (obs, data) GOOF
C32H28N4S4Hg 797.41 0.3 0 2 0.2 Monoclinic P21/c 11.4402(4) 17.9679(8) 14.7633(6) 90.00 93.630(4) 90.00 3028.6(2) 4 1.749 5.388 1568 Mo Ka (0.71073) 4.05–28.32 14 6 h 6 14, 22 6 k 6 22, 19 6 l 6 15 5672 4166 Calc. W = 1/(r2 (F20) + (0.0000p)2 + 26.1254p) where p = (F20 + 2F2c )/3 370 0.0546, 0.0849 1.141
metacinnabar) and the hexagonal phase (a-HgS, cinnabar). Mercury sulfide is an useful material with wide application in many fields such as ultrasonic transducers, image sensors, electrostatic image materials, and photoelectric conversion devices [7,8]. Also mercury sulfide is promising material for catalysts and infrared detectors, because of its narrow band gap [9]. Thermal decomposition in coordinating solvent is one of the most common methods to produce stable monodispersed quantum dots [10]. Other advantages of this synthetic route offers the mildness, safety and simplified fabrication procedure and equipment, when compared with other routes [11]. In this article, we report a selective simple, 2 min
1,2,3,4-Tetrahydroquinoline (Alfa Aesar), carbon disulfide (Merck), mercury chloride (Merck), 1,10-phenanthroline (Himedia), ethylenediamine (Merck) and solvents (sd fine) were commercially available high-grade materials and used as received. IR spectra were recorded on a Thermo Nicolet Avatar 330 FT-IR spectrophotometer (range; 400–4000 cm1) as KBr pellets. Elemental analysis was performed using Perkin Elmer 2400 series II CHN analyzer. The NMR spectra were recorded on AV-III 400 NMR spectrometer operating at 400 MHz. The wide-angle X-ray diffraction (XRD) was recorded using Philips X’pert Pro MPD Diffractometer. The diffraction pattern was recorded in the 2h range of 10–80° at a scan rate of 5 s/step. TEM images were recorded using a Philips CM200 (operating voltages: 20–200 kV, resolution: 2.4 Å). A Shimadzu UV-1650 PC double beam UV–Vis spectrophotometer was used for recording the electronic spectra. The spectra were recorded in chloroform and the pure solvent was used as the reference and fluorescence measurements were made using a Jasco FP550 spectrofluorimeter. Preparation of 1 The bis(1,2,3,4-tetrahydroquinolinecarbodithioato-S,S’)mercury(II); [Hg(thqdtc)2]; was prepared using the established procedure [12]. A hot solution of 1,10-phenanthroline (2 mmol, 0.40 g) in ethanol was added to a hot solution of [Hg(thqdtc)2] (1 mmol, 0.62 g) in chloroform. The resulting yellow solution was cooled and then added with petroleum ether (boiling range: 40–60 °C). Yellow precipitate of the complex separated out, which was filtered and dried (Scheme 1). Yield: 80%; m.p. 178 °C; Anal. (%) Calcd. for [C32H28N4S4Hg]: C, 48.2; H, 3.5; N, 7.0. Found: C, 48.0; H, 3.4; N, 7.0. IR (cm1): 1453 (mCAN), 965 (mCAS), 1508, 1590, 1621 (1,10-phen). 1H NMR (ppm): 4.26 (t, H-2), 2.77 (t, H-4), 2.03 (quintet, H-3), 7.93 (t, H-5, H-6, H-7), 7.16–7.27 (m, H-8), 9.21 [d, H-2 (1,10-phen)], 7.67 [t, H-3 (1,10-phen)], 8.28 [d, H-4 (1,10-phen)], 7.82 [s, H-5 (1,10-phen)]. 13 C NMR (ppm): 23.8 (C-4), 26.0 (C-3), 55.0 (C-2), 125.4, 126.3, 127.0, 128.0 (C-5, C-6, C-7, C-8), 133.2 (C-4a), 141.2 (C-8a), 205.7 (NCS2); 1,10-phen: 150.0 (C-2), 123.0 (C-3), 135.9 (C-4), 128.4 (C4a), 126.3 (C-5), 145.7 (C-10b). X-ray crystallography Details of the crystal data, data collection and refinement parameters for complex 1 are summarized in Table 1. Suitable crystals were obtained from a solution of the substance in a mixture of benzene and dichloromethane (2:1). Intensity data were collected at ambient temperature (293(2) K) on Oxford diffraction Xcalibur3 using graphite monochromated Mo Ka radiation (k = 0.71073 Å). All the non-hydrogen atoms were refined anisotropically and hydrogen atoms were refined isotropically. Preparation of HgS nanoparticles 0.5 g of 1 was dissolved in 15 mL of ethylenediamine in a flask and then heated to reflux (117 °C) and maintained at this temperature for 2 min. The red precipitate obtained was filtered off and washed with ethanol.
384
N. Srinivasan et al. / Journal of Molecular Structure 1076 (2014) 382–386
Fig. 1. IR spectrum of 1.
Fig. 2. The structures and numbering of thqdtc and 1,10-phen.
Results and discussion Spectral studies on 1 IR spectrum of 1 is shown in Fig. 1. The energy of the thioureide
mCAN band is intermediate between the stretching frequencies associated with typical single and double bonded carbon and nitro-
gen atoms [13]. [Hg(thqdtc)2(1,10-phen)] shows the mCAN (thioureide) at 1453 cm1, indicating the partial double bond character. The mCAS band appears at 965 cm1. The ring frequencies associated with 1,10-phenanthroline are observed in the range of 1600–1000 cm1 [14]. In the present study, the characteristic bands due to 1,10-phenanthroline appear at 1621, 1590 and 1508 cm1. Other bands due to 1,10-phenanthroline are masked by those due to the dithiocarbamate ligand. The structures and numbering of thqdtc and 1,10-phen are shown in Fig. 2. In complex 1, protons at C-2 and C-8 carbons undergo strong deshielding to give the signals around 4.25 and 7.16–7.27 ppm, respectively. The deshielding of protons at C-2 and C-8 is attributed to the release of electrons on the nitrogen of dithiocarbamate group toward the sulfur (or the mercury) via thioureide p-system. A quintet observed at 2.03 ppm and a triplet observed at 2.77 ppm are due to the protons at C-3 and C-4. A triplet observed at 7.93 ppm is assigned to the protons at C-5, C-6 and C-7 of thqdtc. Free 1,2,3,4-tetrahydroquinoline shows signals at 41.9 ppm due to C-2 carbon. In the case of 1, the C-2 carbon of thqdtc gets
Fig. 3. ORTEP diagram of 1.
385
N. Srinivasan et al. / Journal of Molecular Structure 1076 (2014) 382–386 Table 2 Bond distances (Å) and angles (°) for [Hg(thqdtc)2(1,10-phen)]. Bond distances (Å) Hg1AS4 Hg1AS2 Hg1AN1 Hg1AN2 Hg1AS1 N1AC1 N1AC12 N2AC10 N2AC11 N3AC13 S1AC13 S2AC13 S3AC23 S4AC23
Bond angles (°) 2.379(2) 2.450(2) 2.677(7) 2.685(7) 2.783(2) 1.308(10) 1.373(9) 1.312(12) 1.341(10) 1.331(10) 1.703(9) 1.731(9) 1.678(8) 1.739(8)
S4AHg1AS2 S4AHg1AN1 S2AHg1AN1 S4AHg1AN2 S2AHg1AN2 N1AHg1AN2 S4AHg1AS1 S2AHg1AS1 N1AHg1AS1 N2AHg1AS1 C13AS1AHg1 C13AS2AHg1 C23AS4AHg1 N2AC10AC9
Fig. 4. (a) Powder X-ray diffraction pattern of HgS nanosheets prepared from 1 and (b) Rietveld plot of the HgS nanosheets prepared from 1 shows the observed data as dots, calculated model fit as continuous line and residual in the bottom. The Bragg peaks also marked as bars.
deshielded and give signals around 55.0 ppm. The downfield shift of C-2 carbon signal in the case of the complex is due to reduction in the electron density in their vicinity, which contribute to a significant thioureide structure Nd+'Cd in the complex. The most important 13C NMR signal of the N13CS2 carbon is observed at 205.7 for 1 with very weak intensity characteristic of the quaternary carbon signal. Structural analysis 1 ORTEP diagram of 1 is shown in Fig. 3. Selected bond distances and angles are presented in Table 2. Complex 1 is monomeric with four molecules per unit cell. Mercury is pentacoordinated by three sulfur atoms from the dithiocarbamates and two nitrogen atoms from the chelating 1,10-phenanthroline ligand. In this case, one of the dithiocarbamates is a chelating ligand with asymmetry in
157.57(8) 104.39(14) 87.35(15) 82.40(15) 120.00(15) 61.2(2) 122.26(8) 68.14(7) 111.97(14) 78.06(16) 81.8(3) 92.0(3) 101.4(3) 124.1(10)
N2AC11AC7 N2AC11AC12 N1AC12AC4 N1AC12AC11 N3AC13AS1 N3AC13AS2 S1AC13AS2 C15AC14AN3 C21AC22AN3 C17AC22AN3 N4AC23AS3 N4AC23AS4 S3AC23AS4
122.6(7) 118.4(6) 122.0(7) 118.2(7) 123.1(7) 118.9(7) 118.1(5) 110.1(9) 121.0(11) 116.7(10) 122.2(6) 116.0(6) 121.8(5)
its HgAS bond distances [HgAS1 = 2.783(2) and HgAS2 = 2.450(2) Å] and another dithiocarbamate ligand is monodentate. The HgN2S3 coordination geometry is intermediate between square pyramidal (SP) and trigonal bipyramidal (TBP). To quantitatively characterize the coordination polyhedra in complexes with coordination number = 5, the parameter s = (a b)/60 is used [15] (in our case, a and b are the two largest angles, a > b). In an ideal TP (C4v), s = 0 since a = b. In a regular TBP (C3v), a is equal to 180°, while the equatorial angle (b) is 120° giving rise to s = 1. Polyhedra with contributions from both the TP and TBP correspond to the values falling within the range 0–1. In [Hg(thqdtc)2(1,10-phen)], the two largest angles are equal to 157.57(8)° and 122.26(8)°. Therefore, s = 0.59, which point to intermediate (between ideal TP and TBP) geometries of the mercury coordination polyhedra. From the s value, the coordination geometry is described as being 59% along the pathway of distortion from TP toward TBP. There is a close intramolecular Hg S(3) [3.229(2) Å] interaction. If the long Hg S(3) interaction in [Hg(thqdtc)2(1,10-phen)] is taken into account, the coordination geometry of Hg may be described as a distorted octahedral. The HgAS3 bond is associated with the shorter CAS distance [C23AS3 = 1.678(8) Å], which is close to the C@S distance of 1.61 Å. The other CAS bond lengths in [Hg(thqdtc)2(1,10-phen)] are C13AS1 = 1.703(9), C13AS2 = 1.731(9) and C23AS4 = 1.739(8) Å, which are in between the single and double bond distances [2]. Average CAN bond distance is 1.337(10) Å which clearly indicates the contribution of the thioureide form to the dithiocarbamate ligand. This contrasts well with the adjacent typical single bonded NAC distance [1.475(24) Å].
Characterization of mercury sulfide nanoparticles To study the crystalline structures of the products, XRD measurements were carried out at room temperature. The powder Xray diffraction pattern of the as-prepared HgS is shown in Fig. 4(a). The diffraction peaks could be indexed to be a pure hexagonal phase HgS (cinnabar). In the XRD pattern, no peaks of any impurities were detected, indicating the high purity of the product. The unit cell parameters were accurately calculated via Rietveld fit using Le Bail method. The Rietveld plot of prepared mercury sulfide is shown in Fig. 4(b) and the unit cell parameters are a = 4.1457(1) Å, c = 9.4888(5) Å, V = 141.23(1) Å3 and 3 D = 8.2032(6) g cm . The calculated lattice parameters are in good agreement with the literature values (JCPDS Card No. 6-0256). The dimensions and morphologies of the products were observed by TEM measurements. TEM image of as-prepared HgS particles is shown in Fig. 5. TEM micrograph shows that the as-prepared HgS particles are hexagonal nanosheets. The thickness of the
386
N. Srinivasan et al. / Journal of Molecular Structure 1076 (2014) 382–386
Fig. 5. TEM image of HgS nanosheets prepared from the 1.
Fig. 6. (a) UV–Vis and (b) fluorescence spectra (excitation at 460 nm) of HgS nanosheets prepared from 1.
synthesized hexagonal sheets is ca. 5 nm and the length is in the range 300–1300 nm. Optical properties of the nanosheets were investigated by UV– Vis and fluoresecence spectroscopy at room temperature. UV–Vis absorption spectra have been proven to be very sensitive to the formation of nanoparticles [16,17]. The absorption maxima is related to the size of semiconductor particles [18]. The UV–Vis spectrum of the as-prepared a-HgS nanosheets is shown in Fig. 6(a). There is a strong and broad absorption peak located at 275 nm (4.5 eV). A blue shift of the absorption edge of the sample from their bulk value of 620 nm (2.0 eV) is clearly observed [19]. The blue shift in the absorption maximum is a consequence of exciton confinement and confirms the as-prepared HgS particles are nanomaterial. The fluoresecence spectrum (Fig. 6(b)) of the as-prepared nanosheets was performed in order to investigate their luminescence properties. Two emission peaks have been observed for semiconductor nanomaterials and they are ascribed to the exciton and the trapped luminescence [20]. Only one emission band was observed in the spectrum of as-prepared HgS nanosheets. The asprepared HgS shows maximum at 545 nm. A red shift with respect to the absorption maximum was observed. The observed broadening of the emission peak could be attributed to both the size distribution and the increase of the surface states due to the increase in surface to volume ratio for smaller nanoparticles [21]. Conclusions Complex 1 has been synthesized and characterized by IR and NMR spectroscopy and single crystal X-ray structure analysis. This complex has been shown to be a suitable single source precursor for single phase (cinnabar) mercury sulfide nanosheets by thermolysis in ethylenediamine. The synthesis process of a-HgS is simple, facile, effective, safe and versatile method.
Appendix A. Supplementary material Crystallographic data have been deposited with the Cambridge Crystallographic Centre as supplementary publication number CCDC-673374 for 1. Copies of the data can be obtained free of charge an application to CCDC, 12 Union Road, Cambridge CBZ 1FZ UK. Supplementary data associated with this article can be found, in the online version, at http://dx.doi.org/10.1016/ j.molstruc.2014.07.083. References [1] [2] [3] [4] [5] [6] [7] [8] [9] [10] [11] [12] [13] [14] [15] [16] [17] [18] [19] [20] [21]
P.J. Heard, Prog. Inorg. Chem. 53 (2005) 1. G. Hogarth, Prog. Inorg. Chem. 53 (2005) 73. A.H. Neims, D.S. Coffey, L. Hellerman, J. Biol. Chem. 241 (1966) 5941. G.D. Thorn, R.A. Ludwig, The dithiocarbamates and Related Compounds, Elsevier, Amsterdam, 1962. K.W. Weissmahr, C.L. Houghton, D.L. Sedlak, Anal. Chem. 70 (1998) 4800. N.L. Pickette, P. O’Brien, Chem. Rec. 1 (2001) 467. N. Tokyo, J. Appl. Phys. 461 (1975) 4857. S.S. Kale, C.D. Lokhande, J. Mater. Chem. Phys. 59 (1999) 242. A.M. Fernandez, M.T.S. Nair, P.K. Nair, J. Mater. Manuf. Process. 8 (1993) 535. C.B. Murray, C.R. Kagan, M.G. Bawendi, Annu. Rev. Mater. Sci. 30 (2000) 545. Y.C. Zhang, G.Y. Wang, X.Y. Hu, J. Alloys Comp. 437 (2007) 47. B.S. Garg, R.K. Garg, M.J. Reddy, Indian J. Chem. A 32 (1993) 697. L. Ronconi, L. Giovagnini, C. Marzano, F. Bettio, R. Graziani, G. Pilloni, D. Fregona, Inorg. Chem. 44 (2005) 1867. S.P. Sinha, Spectrochim. Acta 20 (1964) 879. A.W. Addison, T.N. Rao, J. Reedijk, J.V. Rin, G.C. Verschoor, J. Chem. Soc., Dalton Trans. 7 (1984) 1349. T. Wang, Z. Li, L. Wang, C. Guo, Y. Su, Langmuir 23 (2007) 10533. D. Huang, F. Geng, Y. Liu, X. Wang, J. Jiao, L. Yu, Colloids Surfaces A: Physiochem. Eng. Aspects 392 (2011) 191. L. Yang, R. Xie, L. Liu, D. Xiao, J. Zhu, J. Phys. Chem. C 115 (2011) 19507. A.K. Mahapatra, A.K. Dash, Physica E 35 (2006) 9. B. Geng, J. Ma, F. Zhan, Mat. Chem. Phys. 113 (2009) 534. S. Biswas, S. Kar, Nanotechnology 19 (2008) 045710.
Contents lists available at ScienceDirect
Journal of Molecular Structure journal homepage: www.elsevier.com/locate/molstruc
Synthesis of a-mercury sulfide nanosheets from (1,10-phenanthroline)bis(1,2,3,4-tetrahydroquinolinecarbodithioato-S, S0 )mercury(II) N. Srinivasan a, S. Thirumaran a,⇑, Samuele Ciattini b a b
Department of Chemistry, Annamalai University, Annamalainagar 608 002, India Centro di Cristallografia Strutturale, Polo Scientifio di Sesto Fiorentino, Via della Lastruccia N°3, 50019 Sesto Fiorentino, Firenze, Italy
h i g h l i g h t s
g r a p h i c a l a b s t r a c t
Complex 1 was prepared and
characterized by IR, NMR and X-ray diffraction. Complex 1 was used as single source precursor for the preparation of a-HgS. 2 min Preparation of high-quality hexagonal shaped a-HgS nanosheets was reported. Optical and structural properties of as-prepared a-HgS were evaluated. Quantum confinement effect was confirmed by UV visible spectroscopy.
a r t i c l e
i n f o
Article history: Received 23 June 2014 Received in revised form 30 July 2014 Accepted 31 July 2014 Available online 11 August 2014 Keywords: 1,2,3,4-Tetrahydroquinolinecarbodithioate Mercury(II) Single source precursor a-HgS nanosheets
a b s t r a c t (1,10-phenanthroline)bis(1,2,3,4-tetrahydroquinolinecarbodithioato-S,S0 )mercury(II); [Hg(thqdtc)2(1,10phen)] (1); has been synthesized and characterized by elemental analysis, IR and NMR spectroscopy and single crystal X-ray analysis. IR spectrum of the complex reveals the contribution of thioureide form to the structure. In the 13C NMR spectrum, [Hg(thqdtc)2(1,10-phen)] shows a single low-field resonance associated with backbone carbon of dithiocarbamate (N13CS2) at 205.7 ppm. The mononuclear structure of [Hg(thqdtc)2(1,10-phen)] exhibits monodentate and bidentate coordination by dithiocarbamate ligands and an intermediate geometry between tetragonal pyramidal and trigonal bipyramidal for mercury, defined by an N2S3 donor set. [Hg(thqdtc)2(1,10-phen)] has been found to be an effective singlesource precursor for the preparation of a-HgS nanosheets via solvothermal method. The as-prepared HgS nanosheets have been characterized by powder XRD, TEM, UV–Vis and fluorescence spectroscopy. TEM image of HgS exhibits that the as-prepared HgS particles are hexagonal shaped nanosheets. UV– Vis spectroscopy established pronounced quantum confinement effect. Ó 2014 Elsevier B.V. All rights reserved.
Introduction Dithiocarbamates have great binding potential to metals and have wide range of uses in coordination chemistry [1,2]. Metal ⇑ Corresponding author. Address: Department of Chemistry, Annamalai University, Annamalainagar 608 002, Tamil Nadu, India. Tel.: +91 9842897597. E-mail address: [email protected] (S. Thirumaran). http://dx.doi.org/10.1016/j.molstruc.2014.07.083 0022-2860/Ó 2014 Elsevier B.V. All rights reserved.
dithiocarbamate complexes have been widely studied because of their biological, agricultural, and analytical applications [3–5]. Metal dithiocarbamate complexes have proven to be very successful as single source precursors for the preparation of metal sulfide nanoparticles [6]. Mercury sulfide belongs to group II–VI material that is one of the most useful metal sulfide nanoparticles. HgS usually crystallizes in two forms: the cubic phase (b-HgS,
N. Srinivasan et al. / Journal of Molecular Structure 1076 (2014) 382–386
383
and convenient low cost solvothermal preparation of a-HgS nanoparticles and its characterization along with the synthesis, spectral and single crystal X-ray structural studies on 1. Experimental General
Scheme 1. Preparation of 1.
Table 1 Crystal data, data collection and refinement parameters for [Hg(thqdtc)2(1,10-phen)]. Empirical formula FW Crystal dimensions (mm) Crystal system Space group a/Å b/Å c/Å a/° b/° c/° U/Å3 Z DC/g cm3 l/cm1 F(0 0 0) k/Å h Range/° Index ranges Reflections collected Observed reflections F0 > 40 O(F0) Weighting scheme Number of parameters refined Final R, Rw (obs, data) GOOF
C32H28N4S4Hg 797.41 0.3 0 2 0.2 Monoclinic P21/c 11.4402(4) 17.9679(8) 14.7633(6) 90.00 93.630(4) 90.00 3028.6(2) 4 1.749 5.388 1568 Mo Ka (0.71073) 4.05–28.32 14 6 h 6 14, 22 6 k 6 22, 19 6 l 6 15 5672 4166 Calc. W = 1/(r2 (F20) + (0.0000p)2 + 26.1254p) where p = (F20 + 2F2c )/3 370 0.0546, 0.0849 1.141
metacinnabar) and the hexagonal phase (a-HgS, cinnabar). Mercury sulfide is an useful material with wide application in many fields such as ultrasonic transducers, image sensors, electrostatic image materials, and photoelectric conversion devices [7,8]. Also mercury sulfide is promising material for catalysts and infrared detectors, because of its narrow band gap [9]. Thermal decomposition in coordinating solvent is one of the most common methods to produce stable monodispersed quantum dots [10]. Other advantages of this synthetic route offers the mildness, safety and simplified fabrication procedure and equipment, when compared with other routes [11]. In this article, we report a selective simple, 2 min
1,2,3,4-Tetrahydroquinoline (Alfa Aesar), carbon disulfide (Merck), mercury chloride (Merck), 1,10-phenanthroline (Himedia), ethylenediamine (Merck) and solvents (sd fine) were commercially available high-grade materials and used as received. IR spectra were recorded on a Thermo Nicolet Avatar 330 FT-IR spectrophotometer (range; 400–4000 cm1) as KBr pellets. Elemental analysis was performed using Perkin Elmer 2400 series II CHN analyzer. The NMR spectra were recorded on AV-III 400 NMR spectrometer operating at 400 MHz. The wide-angle X-ray diffraction (XRD) was recorded using Philips X’pert Pro MPD Diffractometer. The diffraction pattern was recorded in the 2h range of 10–80° at a scan rate of 5 s/step. TEM images were recorded using a Philips CM200 (operating voltages: 20–200 kV, resolution: 2.4 Å). A Shimadzu UV-1650 PC double beam UV–Vis spectrophotometer was used for recording the electronic spectra. The spectra were recorded in chloroform and the pure solvent was used as the reference and fluorescence measurements were made using a Jasco FP550 spectrofluorimeter. Preparation of 1 The bis(1,2,3,4-tetrahydroquinolinecarbodithioato-S,S’)mercury(II); [Hg(thqdtc)2]; was prepared using the established procedure [12]. A hot solution of 1,10-phenanthroline (2 mmol, 0.40 g) in ethanol was added to a hot solution of [Hg(thqdtc)2] (1 mmol, 0.62 g) in chloroform. The resulting yellow solution was cooled and then added with petroleum ether (boiling range: 40–60 °C). Yellow precipitate of the complex separated out, which was filtered and dried (Scheme 1). Yield: 80%; m.p. 178 °C; Anal. (%) Calcd. for [C32H28N4S4Hg]: C, 48.2; H, 3.5; N, 7.0. Found: C, 48.0; H, 3.4; N, 7.0. IR (cm1): 1453 (mCAN), 965 (mCAS), 1508, 1590, 1621 (1,10-phen). 1H NMR (ppm): 4.26 (t, H-2), 2.77 (t, H-4), 2.03 (quintet, H-3), 7.93 (t, H-5, H-6, H-7), 7.16–7.27 (m, H-8), 9.21 [d, H-2 (1,10-phen)], 7.67 [t, H-3 (1,10-phen)], 8.28 [d, H-4 (1,10-phen)], 7.82 [s, H-5 (1,10-phen)]. 13 C NMR (ppm): 23.8 (C-4), 26.0 (C-3), 55.0 (C-2), 125.4, 126.3, 127.0, 128.0 (C-5, C-6, C-7, C-8), 133.2 (C-4a), 141.2 (C-8a), 205.7 (NCS2); 1,10-phen: 150.0 (C-2), 123.0 (C-3), 135.9 (C-4), 128.4 (C4a), 126.3 (C-5), 145.7 (C-10b). X-ray crystallography Details of the crystal data, data collection and refinement parameters for complex 1 are summarized in Table 1. Suitable crystals were obtained from a solution of the substance in a mixture of benzene and dichloromethane (2:1). Intensity data were collected at ambient temperature (293(2) K) on Oxford diffraction Xcalibur3 using graphite monochromated Mo Ka radiation (k = 0.71073 Å). All the non-hydrogen atoms were refined anisotropically and hydrogen atoms were refined isotropically. Preparation of HgS nanoparticles 0.5 g of 1 was dissolved in 15 mL of ethylenediamine in a flask and then heated to reflux (117 °C) and maintained at this temperature for 2 min. The red precipitate obtained was filtered off and washed with ethanol.
384
N. Srinivasan et al. / Journal of Molecular Structure 1076 (2014) 382–386
Fig. 1. IR spectrum of 1.
Fig. 2. The structures and numbering of thqdtc and 1,10-phen.
Results and discussion Spectral studies on 1 IR spectrum of 1 is shown in Fig. 1. The energy of the thioureide
mCAN band is intermediate between the stretching frequencies associated with typical single and double bonded carbon and nitro-
gen atoms [13]. [Hg(thqdtc)2(1,10-phen)] shows the mCAN (thioureide) at 1453 cm1, indicating the partial double bond character. The mCAS band appears at 965 cm1. The ring frequencies associated with 1,10-phenanthroline are observed in the range of 1600–1000 cm1 [14]. In the present study, the characteristic bands due to 1,10-phenanthroline appear at 1621, 1590 and 1508 cm1. Other bands due to 1,10-phenanthroline are masked by those due to the dithiocarbamate ligand. The structures and numbering of thqdtc and 1,10-phen are shown in Fig. 2. In complex 1, protons at C-2 and C-8 carbons undergo strong deshielding to give the signals around 4.25 and 7.16–7.27 ppm, respectively. The deshielding of protons at C-2 and C-8 is attributed to the release of electrons on the nitrogen of dithiocarbamate group toward the sulfur (or the mercury) via thioureide p-system. A quintet observed at 2.03 ppm and a triplet observed at 2.77 ppm are due to the protons at C-3 and C-4. A triplet observed at 7.93 ppm is assigned to the protons at C-5, C-6 and C-7 of thqdtc. Free 1,2,3,4-tetrahydroquinoline shows signals at 41.9 ppm due to C-2 carbon. In the case of 1, the C-2 carbon of thqdtc gets
Fig. 3. ORTEP diagram of 1.
385
N. Srinivasan et al. / Journal of Molecular Structure 1076 (2014) 382–386 Table 2 Bond distances (Å) and angles (°) for [Hg(thqdtc)2(1,10-phen)]. Bond distances (Å) Hg1AS4 Hg1AS2 Hg1AN1 Hg1AN2 Hg1AS1 N1AC1 N1AC12 N2AC10 N2AC11 N3AC13 S1AC13 S2AC13 S3AC23 S4AC23
Bond angles (°) 2.379(2) 2.450(2) 2.677(7) 2.685(7) 2.783(2) 1.308(10) 1.373(9) 1.312(12) 1.341(10) 1.331(10) 1.703(9) 1.731(9) 1.678(8) 1.739(8)
S4AHg1AS2 S4AHg1AN1 S2AHg1AN1 S4AHg1AN2 S2AHg1AN2 N1AHg1AN2 S4AHg1AS1 S2AHg1AS1 N1AHg1AS1 N2AHg1AS1 C13AS1AHg1 C13AS2AHg1 C23AS4AHg1 N2AC10AC9
Fig. 4. (a) Powder X-ray diffraction pattern of HgS nanosheets prepared from 1 and (b) Rietveld plot of the HgS nanosheets prepared from 1 shows the observed data as dots, calculated model fit as continuous line and residual in the bottom. The Bragg peaks also marked as bars.
deshielded and give signals around 55.0 ppm. The downfield shift of C-2 carbon signal in the case of the complex is due to reduction in the electron density in their vicinity, which contribute to a significant thioureide structure Nd+'Cd in the complex. The most important 13C NMR signal of the N13CS2 carbon is observed at 205.7 for 1 with very weak intensity characteristic of the quaternary carbon signal. Structural analysis 1 ORTEP diagram of 1 is shown in Fig. 3. Selected bond distances and angles are presented in Table 2. Complex 1 is monomeric with four molecules per unit cell. Mercury is pentacoordinated by three sulfur atoms from the dithiocarbamates and two nitrogen atoms from the chelating 1,10-phenanthroline ligand. In this case, one of the dithiocarbamates is a chelating ligand with asymmetry in
157.57(8) 104.39(14) 87.35(15) 82.40(15) 120.00(15) 61.2(2) 122.26(8) 68.14(7) 111.97(14) 78.06(16) 81.8(3) 92.0(3) 101.4(3) 124.1(10)
N2AC11AC7 N2AC11AC12 N1AC12AC4 N1AC12AC11 N3AC13AS1 N3AC13AS2 S1AC13AS2 C15AC14AN3 C21AC22AN3 C17AC22AN3 N4AC23AS3 N4AC23AS4 S3AC23AS4
122.6(7) 118.4(6) 122.0(7) 118.2(7) 123.1(7) 118.9(7) 118.1(5) 110.1(9) 121.0(11) 116.7(10) 122.2(6) 116.0(6) 121.8(5)
its HgAS bond distances [HgAS1 = 2.783(2) and HgAS2 = 2.450(2) Å] and another dithiocarbamate ligand is monodentate. The HgN2S3 coordination geometry is intermediate between square pyramidal (SP) and trigonal bipyramidal (TBP). To quantitatively characterize the coordination polyhedra in complexes with coordination number = 5, the parameter s = (a b)/60 is used [15] (in our case, a and b are the two largest angles, a > b). In an ideal TP (C4v), s = 0 since a = b. In a regular TBP (C3v), a is equal to 180°, while the equatorial angle (b) is 120° giving rise to s = 1. Polyhedra with contributions from both the TP and TBP correspond to the values falling within the range 0–1. In [Hg(thqdtc)2(1,10-phen)], the two largest angles are equal to 157.57(8)° and 122.26(8)°. Therefore, s = 0.59, which point to intermediate (between ideal TP and TBP) geometries of the mercury coordination polyhedra. From the s value, the coordination geometry is described as being 59% along the pathway of distortion from TP toward TBP. There is a close intramolecular Hg S(3) [3.229(2) Å] interaction. If the long Hg S(3) interaction in [Hg(thqdtc)2(1,10-phen)] is taken into account, the coordination geometry of Hg may be described as a distorted octahedral. The HgAS3 bond is associated with the shorter CAS distance [C23AS3 = 1.678(8) Å], which is close to the C@S distance of 1.61 Å. The other CAS bond lengths in [Hg(thqdtc)2(1,10-phen)] are C13AS1 = 1.703(9), C13AS2 = 1.731(9) and C23AS4 = 1.739(8) Å, which are in between the single and double bond distances [2]. Average CAN bond distance is 1.337(10) Å which clearly indicates the contribution of the thioureide form to the dithiocarbamate ligand. This contrasts well with the adjacent typical single bonded NAC distance [1.475(24) Å].
Characterization of mercury sulfide nanoparticles To study the crystalline structures of the products, XRD measurements were carried out at room temperature. The powder Xray diffraction pattern of the as-prepared HgS is shown in Fig. 4(a). The diffraction peaks could be indexed to be a pure hexagonal phase HgS (cinnabar). In the XRD pattern, no peaks of any impurities were detected, indicating the high purity of the product. The unit cell parameters were accurately calculated via Rietveld fit using Le Bail method. The Rietveld plot of prepared mercury sulfide is shown in Fig. 4(b) and the unit cell parameters are a = 4.1457(1) Å, c = 9.4888(5) Å, V = 141.23(1) Å3 and 3 D = 8.2032(6) g cm . The calculated lattice parameters are in good agreement with the literature values (JCPDS Card No. 6-0256). The dimensions and morphologies of the products were observed by TEM measurements. TEM image of as-prepared HgS particles is shown in Fig. 5. TEM micrograph shows that the as-prepared HgS particles are hexagonal nanosheets. The thickness of the
386
N. Srinivasan et al. / Journal of Molecular Structure 1076 (2014) 382–386
Fig. 5. TEM image of HgS nanosheets prepared from the 1.
Fig. 6. (a) UV–Vis and (b) fluorescence spectra (excitation at 460 nm) of HgS nanosheets prepared from 1.
synthesized hexagonal sheets is ca. 5 nm and the length is in the range 300–1300 nm. Optical properties of the nanosheets were investigated by UV– Vis and fluoresecence spectroscopy at room temperature. UV–Vis absorption spectra have been proven to be very sensitive to the formation of nanoparticles [16,17]. The absorption maxima is related to the size of semiconductor particles [18]. The UV–Vis spectrum of the as-prepared a-HgS nanosheets is shown in Fig. 6(a). There is a strong and broad absorption peak located at 275 nm (4.5 eV). A blue shift of the absorption edge of the sample from their bulk value of 620 nm (2.0 eV) is clearly observed [19]. The blue shift in the absorption maximum is a consequence of exciton confinement and confirms the as-prepared HgS particles are nanomaterial. The fluoresecence spectrum (Fig. 6(b)) of the as-prepared nanosheets was performed in order to investigate their luminescence properties. Two emission peaks have been observed for semiconductor nanomaterials and they are ascribed to the exciton and the trapped luminescence [20]. Only one emission band was observed in the spectrum of as-prepared HgS nanosheets. The asprepared HgS shows maximum at 545 nm. A red shift with respect to the absorption maximum was observed. The observed broadening of the emission peak could be attributed to both the size distribution and the increase of the surface states due to the increase in surface to volume ratio for smaller nanoparticles [21]. Conclusions Complex 1 has been synthesized and characterized by IR and NMR spectroscopy and single crystal X-ray structure analysis. This complex has been shown to be a suitable single source precursor for single phase (cinnabar) mercury sulfide nanosheets by thermolysis in ethylenediamine. The synthesis process of a-HgS is simple, facile, effective, safe and versatile method.
Appendix A. Supplementary material Crystallographic data have been deposited with the Cambridge Crystallographic Centre as supplementary publication number CCDC-673374 for 1. Copies of the data can be obtained free of charge an application to CCDC, 12 Union Road, Cambridge CBZ 1FZ UK. Supplementary data associated with this article can be found, in the online version, at http://dx.doi.org/10.1016/ j.molstruc.2014.07.083. References [1] [2] [3] [4] [5] [6] [7] [8] [9] [10] [11] [12] [13] [14] [15] [16] [17] [18] [19] [20] [21]
P.J. Heard, Prog. Inorg. Chem. 53 (2005) 1. G. Hogarth, Prog. Inorg. Chem. 53 (2005) 73. A.H. Neims, D.S. Coffey, L. Hellerman, J. Biol. Chem. 241 (1966) 5941. G.D. Thorn, R.A. Ludwig, The dithiocarbamates and Related Compounds, Elsevier, Amsterdam, 1962. K.W. Weissmahr, C.L. Houghton, D.L. Sedlak, Anal. Chem. 70 (1998) 4800. N.L. Pickette, P. O’Brien, Chem. Rec. 1 (2001) 467. N. Tokyo, J. Appl. Phys. 461 (1975) 4857. S.S. Kale, C.D. Lokhande, J. Mater. Chem. Phys. 59 (1999) 242. A.M. Fernandez, M.T.S. Nair, P.K. Nair, J. Mater. Manuf. Process. 8 (1993) 535. C.B. Murray, C.R. Kagan, M.G. Bawendi, Annu. Rev. Mater. Sci. 30 (2000) 545. Y.C. Zhang, G.Y. Wang, X.Y. Hu, J. Alloys Comp. 437 (2007) 47. B.S. Garg, R.K. Garg, M.J. Reddy, Indian J. Chem. A 32 (1993) 697. L. Ronconi, L. Giovagnini, C. Marzano, F. Bettio, R. Graziani, G. Pilloni, D. Fregona, Inorg. Chem. 44 (2005) 1867. S.P. Sinha, Spectrochim. Acta 20 (1964) 879. A.W. Addison, T.N. Rao, J. Reedijk, J.V. Rin, G.C. Verschoor, J. Chem. Soc., Dalton Trans. 7 (1984) 1349. T. Wang, Z. Li, L. Wang, C. Guo, Y. Su, Langmuir 23 (2007) 10533. D. Huang, F. Geng, Y. Liu, X. Wang, J. Jiao, L. Yu, Colloids Surfaces A: Physiochem. Eng. Aspects 392 (2011) 191. L. Yang, R. Xie, L. Liu, D. Xiao, J. Zhu, J. Phys. Chem. C 115 (2011) 19507. A.K. Mahapatra, A.K. Dash, Physica E 35 (2006) 9. B. Geng, J. Ma, F. Zhan, Mat. Chem. Phys. 113 (2009) 534. S. Biswas, S. Kar, Nanotechnology 19 (2008) 045710.