Synthesis and Crystal Structure of Bis (N-alkyl-N-phenyl ...

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Damian C. Onwudiwe • Peter A. Ajibade. Received: 29 September 2009 / Accepted: 10 February 2011 / Published online: 25 February 2011. Ó Springer ...
J Chem Crystallogr (2011) 41:980–985 DOI 10.1007/s10870-011-0029-3

ORIGINAL PAPER

Synthesis and Crystal Structure of Bis(N-alkyl-N-phenyl dithiocarbamato)mercury(II) Damian C. Onwudiwe • Peter A. Ajibade

Received: 29 September 2009 / Accepted: 10 February 2011 / Published online: 25 February 2011 Ó Springer Science+Business Media, LLC 2011

Abstract The mixed ligand dithiocarbamate complex was synthesized by the reaction between the ammonium salt of the dithiocarbamate ligands with mercury salt. There are two mercury complexes in the asymmetric unit with a compositional disorder between an ethyl group and a methyl group. A distorted tetrahedral geometry is found for each mercury atom defined by four sulphur atoms derived from two asymmetrically chelating dithiocarbamate ligands. IR spectra show thioureide t(C–N) bands at 1491 cm-1 which is higher than observed in the simple complexes of the same ligands. The effect of alkyl substituents were observed in the magnetic unequivalence of the thioureide and phenyl units in the NMR spectroscopy. The molecules are related to each other by virtue of the compositional disorder which exists at three positions in the alkyl group across the unit. The compound crystallizes in ˚, b = the triclinic space group P-1 with a = 10.4764(10) A ˚ ˚ 11.0433(10) A, c = 18.5566(17) A, a = 97.8980(10)°, b = 95.3340(10)°, c = 110.3010(10)°, and Z = 2. Keywords Mercury  Dithiocarbamate  Metal complex  Compositional disorder

Introduction Transition metal dithiocarbamate complexes find use in diverse applications such as material science, medicine and agriculture [1, 2], and possess interesting structural chemistry [3, 4] that make their study continuously attractive. The anion [S2CNR2]- has high affinity compared with other D. C. Onwudiwe  P. A. Ajibade (&) Department of Chemistry, University of Fort Hare, Private Bag X1314, Alice, South Africa e-mail: [email protected]

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1,1-dithiolate anions and its high coordinating properties has been attributed to the significant contribution of the resonance form of the anion to the electronic structure of the dithiocarbamate ligand [5]. The relative ease of their crystallization compared to other 1,1-dithiolato complexes make them ideal candidates for systematic structural studies especially for the elucidation of the principles of crystal packing [6]. Mercury atom in alkyl-aryl dithiocarbamate exists within a four coordinate geometry defined by S4 donor set obtained from two chelating dithiocarbamate ligands. They usually crystallize as a dimeric aggregate via secondary interactions of the HgS [7, 8] given rise to a spectacular array of supramolecular architectures, which is peculiar to the zinc triad [9]. In several metal dithiocarbamates, such interactions may be mitigated by the presence of bulky R groups which makes this mode of association impossible [10]. This may be ascribed to steric hindrance. However, it has been demonstrated that steric effects may be utilized as a design element in crystal engineering especially in main group element compounds [6]. Tiekink et al. [11–13] has demonstrated that the introduction of hydrogen bonding functionality in the dithiocarbamate bound R groups is a way of mediating MS interaction thereby encouraging supramolecular aggregation. In this study, we investigate the response of the MS interaction to the alteration of the flow of thioureide electron by using different substituent’s which are resident on the dithiocarbamate ligands.

Experimental Materials and Physical Measurements Commercial reagent grade chemicals N-methyl aniline, N-ethyl aniline (Aldrich) and mercury chloride (Fluka) were

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used as received without further purification. Infrared spectra were recorded on Perkin-Elmer 2000 FT-IR spectrometer in the range 370–3600 cm-1 as KBr disc. NMR spectra were obtained on a Bruker NMR spectrometer. Proton chemical shifts are reported in parts per million (ppm) relative to Me4Si. Elemental analyses were performed by using a Fisons elemental analyzer. The ligands were prepared by modification of a literature procedure [14]. Synthesis of Sodium N-methylN-phenyldithiocarbamate (1) Sodium hydroxide (2 g, 0.05 mol) dissolved in minimum amount of distilled water was allowed to attain an ice temperature; to this cold carbon disulphide (3, 0.05 mL) was added. This was then followed by the addition of N-methyl aniline (5.44 mL, 0.05 mol). The mixture was stirred for 2 h while keeping the temperature below 4 °C. A yellowish-white solid product, which hinders the stirring process, separated out which was filtered, washed with ether and finally recrystallized from warm acetone. The white solid product was dried under vacuum over CaCl2 at room temperature giving 8.4 g (yield = 82%) (sodium N-methyl-N-phenyldithiocarbamate); mp [ 300 °C. Selected IR (KBr), t(cm-1): 3444 and 1630 (water), 1455 (C=N), 1262 (C2–N), 962 (C=S) Synthesis of Sodium N-ethyl-N-phenyldithiocarbamate (2) Sodium N-ethyl-N-phenyldithiocarbamate was prepared using similar procedure for (1) above. A round bottom flask was cooled in a freezing mixture of common salt and ice. To this, sodium hydroxide (2 g, 0.05 mol) dissolved in minimum quantity of distilled water was added followed by the addition of carbon disulphide (3, 0.05 mL). To this mixture, N-ethyl aniline (6.44 mL, 0.05 mol) cooled in ice was added and stirred for 4 h keeping the temperature below 4 °C. A yellowish-white crystalline product separated out and was filtered. The residue was dispersed in 40 mL of ether and the white sodium N-ethyl-N-phenyldithiocarbamate was isolated from the colourless crystalline impurity. The product was rinsed with ether and dried under vacuum over CaCl2 at room temperature giving 6.1 g (yield = 56%) white solid, mp = 98–100 °C. Selected IR (KBr), t(cm-1): 3435 and 1637 (water), 1453 (C=N), 1261 (C2–N), 960 (C=S) Synthesis of Complex [Hg(S2CN(C2H5)C6H5)2] [Hg(SCN(CH3)C6H5)(SCN(C2H5)C6H5)] (3) To a well stirred 20 mL aqueous solution of ligand (1) (0.256 g, 1.25 mmol) and 20 mL aqueous solution of

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ligand (2) (0.274 g, 1.25 mmol), was added 0.338 g (1.25 mmol) HgCl2 in 20 mL of the same solvent to obtain an immediate precipitation. The reaction mixture was then stirred for 1 h at room temperature. The pale green product was filtered, washed with water and dried in vacuo. Single crystals suitable for X-ray analysis were obtained by recrystallizing the product in chloroform/methanol solvent mixture. Yield: 0.520 g, (yield = 72%), mp = 218 °C. 1 H NMR (CDCl3) d = 7.42–7.33 (m, C6H5–N(C2H5)), 7.28–7.24 (m, C6H5–N(CH3)), 4.16 (q, CH2–N(C2H5)), 1.53 (s, CH3–N(CH3)), 1.26 (t, CH3–N(C2H5)). 13C NMR (CDCl3) d 206.43, 205.84 (CS2), 147.47, 145.26 (C6H5–N (C2H5)), 129.66, 128.80, 126.43, 125.34 (C6H5–N (CH3)), 55.86 (CH2-(C2H5)), 48.93 (CH3–N (CH3)), 12.26 (CH3(C2H5)). Selected IR (KBr), t(cm-1): 1459 (C=N), 1280 (C2–N), 966 (C=S). Anal. Calc. for C17H18N2S4Hg (579.17): C, 35.25; H, 3.13; N, 4.84; S, 22.14. Found: C, 30.49; H, 2.75; N, 3.97; S, 20.38.

Crystallographic Experimental Section Data Collection A yellow crystal with approximate dimensions 0.46 9 0.45 9 0.30 mm3 was selected under oil under ambient conditions and attached to the tip of a MiTeGen MicroMountÓ. The crystal was mounted in a stream of cold nitrogen at 100(2) K and centered in the X-ray beam by using a video camera. The crystal evaluation and data collection were performed on a Bruker CCD-1000 dif˚ ) radiation and fractometer with Mo-Ka (k = 0.71073 A the diffractometer to crystal distance of 4.9 cm. The initial cell constants were obtained from three series of scans at different starting angles. Each series consisted of 20 frames collected at intervals of 0.3° in a 6° range about with the exposure time of 10 s per frame. A total of 181 reflections were obtained. The reflections were successfully indexed by an automated indexing routine built in the SMART program. The final cell constants were calculated from a set of 9907 strong reflections from the actual data collection. The data were collected by using the full sphere data collection routine to survey the reciprocal space to a resolution ˚ . A total of 25094 data were harvested by colof 0.71 A lecting three sets of frames with 0.25° scans in u with an exposure time 12 s per frame. These highly redundant datasets were corrected for Lorentz and polarization effects. The absorption correction was based on fitting a function to the empirical transmission surface as sampled by multiple equivalent measurements [15].

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Structure Solution and Refinement The E-statistics strongly suggested the centrosymmetric space group P-1 that yielded chemically reasonable and computationally stable results of refinement [16]. A successful solution by the direct methods provided most nonhydrogen atoms from the E-map. The remaining nonhydrogen atoms were located in an alternating series of least-squares cycles and difference Fourier maps [16]. All non-hydrogen atoms were refined with anisotropic displacement coefficients unless otherwise specified. All hydrogen atoms were included in the structure factor calculation at idealized positions and were allowed to ride on the neighboring atoms with relative isotropic displacement coefficients. The disordered carbon atoms were refined with restraints and constraints. The final least-squares refinement of 446 parameters against 10359 data resulted in residuals R (based on F2 for I C 2r) and wR (based on F2 for all data) of 0.0400 and 0.1055, respectively. The final difference Fourier map contained eight peaks of ˚ -3) near atoms Hg1 and electron density (max ca. 4.451 e/A Hg2 which are considered noise. The molecular diagram is drawn with 50% probability ellipsoids.

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at higher frequencies in the spectrum of the complex, 3. This increased double bond character of the C=S bond and the appearance as a single peak in this region evidence for the presence of bidentate dithiocarbamates [21, 22]. The non-equivalence of the dithiocarbamate groups coordinated to the mercury atom is the primary feature of the 1H and 13C NMR. The variation of the alkyl substituent induces different electron density, creating different magnetic environment. The aromatic protons had two sets of signals depending on the type of the organic substituent. The first set of the aromatic protons were identified as multiplets between 7.42 and 7.33 ppm, while the second sets appeared between 7.28 and 7.24 ppm. The protons of the methyl group attached to nitrogen showed signals in the

Results and Discussion Spectral Studies The IR spectra of the ligands 1 and 2 exhibit prominent bands at 3354, 3351 cm-1 and 1632, 1627 cm-1 respectively characteristic of O–H stretching and vibrational bands of water. These indicate that the compounds are hydrated. Some alkali salts of dithiocarbamate are known to crystallize with lattice water molecules [17]. The thioureido bands of ligands 1 and 2 were observed as sharp peaks at 1455 and 1453 cm-1 [18]. An increase of approximately 40 cm-1 was observed for the thioureido band of the complex, 3, appearing around 1491 cm-1. The shift to higher energy upon coordination is ascribed to the increased double bond character in the CN group, caused by electron delocalization toward the metal center [19]. The electron releasing ability of the R in –NR(C6H5)-group in dithiocarbamates affects the electronic structure of the complexes. The difference in the electron donating capacity of the alkyl groups enhances the flow of electron density on to the sulphur atom, via the p-system and therefore to the Hg ion, subsequently causing greater double bond character in C=N bond. These peaks fall within the stretching frequencies of m(C–N) (1250–1350) and m(C=N) (1640–1690) [20]. The m(CS2ass) of the sodium salts of the dithiocarbamates ligands 1 and 2 which occurred at 962 and 960 cm-1 respectively were observed

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Fig. 1 A molecular drawing of the compound. All hydrogen atoms were omitted for clarity. Only the major components of the compositional and positional disorder are shown

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expected region. They were observed as singlet at 1.53 ppm, being more deshielded than the protons of the terminal methyl (-CH3) of the ethylene which appeared around 1.26 ppm as a triplet. The methylene protons appeared as quartets in the region 4-17–4-12 ppm. In the 13C NMR spectra of the complex, 3, the signals due to the carbon of the dithiocabamato moiety, CS2, appear as two peaks (207.00 and 206.00 ppm). The two peaks indicate magnetic unequivalence of the backbone carbon caused by different organic groups on the same position on the two dithiocarbamate units. An increase in the electron density on the nitrogen as a result of the higher inductive effect of the ethyl group results in more shielding effect on the –CS2 carbon [23] of the dithiocarbamate carrying the ethyl substituent. The methylene carbon of the ethyl group experiences more deshielding effect than the terminal carbon (-CH3), hence resonate at 55.86 ppm. The peak at 12.26 ppm is assigned to the terminal carbon, distinct from the resonance frequency of the nitrogen bonded methyl (N–CH3) found at 48.93 ppm. The difference has ascribed to the deshielding effect of the nitrogen and proximity to the thioureide p-system [24, 25]. The aromatic carbons resonate in two different sets with different intensities. This may be due to the difference in the

ligating strength of the dithiocarbamate units caused by the different alkyl substituent. Towards the lower field are two peaks of relatively low intensity, 147.47 and 145.26 ppm assigned to the resonance frequency of the aromatic carbons of the N-ethyl units. The high peaks between 129.66 and 125.34 ppm are assigned to the aromatic peaks of the N-methyl unit. This difference clearly indicates the substituent effect of the alkyl group on the complex.

Fig. 2 A molecular drawing of the Hg1 complex of the compound. All hydrogen atoms were omitted for clarity. Only the major components of the compositional and positional disorder are shown

Fig. 3 A molecular drawing of the Hg2 complex of the compound. All hydrogen atoms were omitted for clarity. Only the major components of the compositional and positional disorder are shown

Description of the Crystal Structure The molecular structure of the compound with the atom numbering scheme is shown in Figs 1, 2 and 3. The crystal data and structure refinement are presented in Table 1 and selected bond length and angles are given in Table 2. The structure of the compound consists of triclinic space group P-1. In the molecular structure, there are two mercury complexes in the asymmetric unit (Fig. 1). There is compositional disorder at the positions of C17, C26, and C35

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Table 1 Summary of crystal data and structure refinement for the compound Empirical formula

C17.29H18.59HgN2S4

Formula weight

583.27

Temperature, K ˚ Wavelength, A

100(2) K ˚ 0.71073 A

Crystal system

Triclinic

Space group

P-1

Unit cell dimensions ˚) a (A

10.4764(10)

˚ ) and bond angles (°) for the Table 2 Selected bond length (A compound Bond length

Bond angles

Hg(1)–S(1)

2.3784(13)

S(1)–Hg(1)–S(3)

165.36(5)

Hg(1)–S(3)

2.4087(13)

S(1)–Hg(1)–S(4)

124.52(4)

Hg(1)–S(4)

2.7763(14)

S(3)–Hg(1)–S(4)

69.98(4)

Hg(1)–S(2)

2.9403(16)

S(1)–Hg(1)–S(2)

67.49(4)

Hg(2)–S(6)

2.3641(14)

S(3)–Hg(1)–S(2)

111.91(5)

Hg(2)–S(7)

2.3866(13)

S(4)–Hg(1)–S(2)

108.71(4)

Hg(2)–S(8) Hg(2)–S(5)

2.8369(18) 2.9716(15)

S(6)–Hg(2)–S(7) S(6)–Hg(2)–S(8)

168.82(6) 122.08(5)

S(1)–C(1)

1.753(6)

S(7)–Hg(2)–S(8)

69.10(5)

S(2)–C(1)

1.689(5)

S(6)–Hg(2)–S(5)

67.44(5)

S(3)–C(10)

1.740(5)

S(7)–Hg(2)–S(5)

111.92(5)

S(4)–C(10)

1.715(5)

S(8)–Hg(2)–S(5)

103.02(4)

S(5)–C(19)

1.693(6)

C(1)–S(1)–Hg(1)

94.31(18)

S(6)–C(19)

1.759(6)

C(1)–S(2)–Hg(1)

77.55(19)

S(7)–C(28)

1.735(6)

C(10)–S(3)–Hg(1)

90.46(17)

S(8)–C(28)

1.704(6)

C(10)–S(4)–Hg(1)

79.41(19)

N(1)–C(1)

1.338(7)

C(19)–S(5)–Hg(2)

76.7(2)

N(1)–C(8)

1.458(7)

C(19)–S(6)–Hg(2)

94.80(19)

N(1)–C(2)

1.458(7)

C(28)–S(7)–Hg(2)

91.81(18)

25094

N(2)–C(10)

1.474(7)

C(28)–S(8)–Hg(2)

Independent reflection Refinement method

10359 [Rint = 0.0252] Full-matrix least-squares on F2

N(2)–C(17)

1.481(9)

C(1)–N(1)–C(2)

120.9(5)

Completeness to h = 25.00°

99.4%

N(2)–C(11) N(3)–C(19)

1.4399(6) 1.324(7)

C(1)–N(1)–C(8) C(2)–N(1)–C(8)

122.9(5) 116.1(7)

Absorption correction

Multi-scan with SADABS

N(3)–C(26A)

1.471(8)

C(10)–N(2)–C(11)

121.7(4)

10359/17/446

N(3)–C(20)

1.453(8)

C(19)–N(3)–C(20)

121.6(5)

1.084

N(4)–C(28)

1.336(7)

C(19)–N(3)–C(26)

128.2(8)

Final R indices [I [ 2r(I)]

R1 = 0.0400, wR2 = 0.0986

N(4)–C(29)

1.436(6)

C(28)–N(4)–C(29)

120.1(13)

R indices (all data)

R1 = 0.0528, wR2 = 0.1055

N(4)–C(35)

1.492(9)

C(28)–N(4)–C(29)

120.8(6)

Largest different peak and ˚ -3 hole e. A

4.491 and -2.452

˚) b (A ˚) c (A

11.0433(10)

b (°) c (°)

95.3010(10) 110.3010

Volume (A3)

1971.4(3)

Z

4

Dcalc Mg/m

18.5566(17)

3

1.965

Absorption coefficient (mm-1)

8.233

F(000)

1121

Crystal size (mm)

0.46 9 0.45 9 0.30

Theta range (°)

2.10–29.97

Index ranges

-14 B h B 14, -15 B k B 15, -25 B 1 B 25

Reflections collected

Data/restraints/parameters 2

Goodness-of-fit on F

between an ethyl group and a methyl group. At the position of atom C17, 52.5(2)% of the time an ethyl group is present and 47.5(2)% of the time a methyl group is present. At the position of atom C26, 54.37(18)% of the time a methyl group is present and 45.63(18)% of the time an ethyl group is present. At the position of atom C35, 62.46(14)% of the time an ethyl group is present and 37.54(14)% of the time a methyl group is present. The C29–C34 benzyl ring is disordered over two positions with a minor component contribution of 19.47(18)%. The mercury atom is tetrahedrally coordinated to four S atoms. The metal-sulphur bonds are of disparate length, and the carbon–sulphur distance has an inverse relation to the metal-sulphur. Two of the Hg–S bond distances are ˚ while the other short in the range 2.3641(14)–2.4087(13) A two Hg–S bond distances are long in the range 2.7763(14)– ˚ . The configuration around the mercury atom 2.9716(15) A

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78.2(2)

is a strongly distorted tetrahedron. The two mercury complexes in the asymmetric unit are essentially the same, and the two complexes are actually isomorphous (and presumably fully isostructural); the description will thus concentrate on the details of only one of the structure. The asymmetric unit consisting of one complex molecule is shown in Figs. 2 and 3. The distorted tetrahedral coordination around the mercury atom consists of two dithiocarbamate ligands acting as a bidentate chelating ligand. There is a large compression of the dithiocarbamate bite angles S(1)–Hg(1)–S(2) and S(3)–Hg(1)–S(4) in the range 67–69°. These lead to enlargement of the other angles; S(1)–Hg(1)–S(3) and S(2)–Hg(1)–S(4) around the mercury atom with respect to the ideal tetrahedral value. The deviation from the ideal tetrahedral value is probably due to the small bite angles of the dithocarbamate ligand. The deviation of the S–C–S angle from that found in the free ion is presumably due to steric constraints as a result of chelation. The C–N bond length in the dithiocarbamate

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ligands varied. While three of the N–CS2: N(1)–C(1); N(3)–C(19) and N(4)–C(28) average bond length is ˚ closer to that of C–N double bond (1.28 A ˚ ). 1.333(7) A ˚ is closer to a The other N(2)–C(10) bond length of 1.474 A ˚ ) single bond. This showed that the typical C–N (1.47 A Hg–S bond have high covalent character expected of third row transition metal series. The closeness if the N(2)– C(10) to a single C–N bond length might be due to the compositional disorder of the ethyl group at position C17. All the other C–N bond are typical single bond.

Supplementary Materials CCDC 737048 contains the supplementary crystallographic data for this paper. These data can be obtained free of charge from The Cambridge Crystallographic Data Centre via www.ccdc.cam.ac.uk/data_request/cif or from The Director, CCDC, 12 Union Road, Cambridge, CB2 1EZ, UK (Fax: ?44-1223-336-033; e-mail: [email protected]). Acknowledgments The authors gratefully acknowledge financial support from GMRDC, University of Fort Hare, South Africa. The contribution of Ilia A. Guzei and Lara C. Spencer are gratefully acknowledged.

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