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3-(Aryl)-2-sulfanylpropenoates of mercury(II) and phenylmercury(II)
Polyhedron 27 (2008) 2436–2446
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3-(Aryl)-2-sulfanylpropenoates of mercury(II) and phenylmercury(II) José S. Casas a, Alfonso Castiñeiras a, María D. Couce b, Manuel García-Vega a, Manuel Rosende a, Agustín Sánchez a, José Sordo a,*, José M. Varela a, Ezequiel M. Vázquez López b a b
Departamento de Química Inorgánica, Facultade de Farmacia, Universidade de Santiago de Compostela, 15782 Santiago de Compostela, Galicia, Spain Departamento de Química Inorgánica, Facultade de Química, Edificio de Ciencias Experimentais, Universidade de Vigo, 36310 Vigo, Galicia, Spain
a r t i c l e
i n f o
Article history: Received 10 January 2008 Accepted 23 April 2008 Available online 6 June 2008 Keywords: Sulfanylpropenoato Mercury(II) IR Phenylmercury(II) NMR Crystal structure
a b s t r a c t Compounds [HQ]2[Hg(L)2] and [HQ][PhHg(L)] [where HQ = diisopropylammonium cation; L = pspa, fspa, tspa, where p = 3-(phenyl), f = 3-(2-furyl), t = 3-(2-thienyl), and spa = 2-sulfanylpropenoato] have been prepared by the reaction of mercury(II) acetate or phenylmercury(II) acetate with the corresponding acid in the presence of diisopropylamine in ethanol. The compounds have been characterized by elemental analysis, FAB mass spectrometry and IR and NMR (1H, 13C) spectroscopy. The crystal structures of the [HQ]2[Hg(L)2] compounds show the presence of diisopropylammonium cations and [Hg(L)2]2 anions. In each anion the Hg atom is in an HgO2S2 environment and this can be described as nido-tbp. The crystal structures of the [HQ][PhHg(L)] compounds show the presence of diisopropylammonium cations and [PhHg(L)] anions in which the Hg atom adopts an HgCOS distorted T-environment. The NMR data suggest that the coordination mode of the ligand L2 determined by X-ray diffractometry in the solid remains in solution. Ó 2008 Elsevier Ltd. All rights reserved.
1. Introduction The useful properties of mercury and its compounds has as a counterpart in their toxic effects. This metal is widespread today and is emitted as a vapour into the atmosphere from both natural and anthropogenic sources. This vapour is slowly converted to Hg(II) by oxidative process and the mercury returns to the earth in rainwater [1]. Hg(II) has an extremely high affinity for compounds that contain sulfhydryl groups and in the blood and tissues of humans it is bound to these groups of cysteine-containing peptides and proteins. Often very stable forms include linear complexes with two sulfur ligands; however, the Hg–S bonds are labile and for higher coordination numbers the structures are flexible, often with distorted trigonal or tetrahedral coordination geometries [1,2]. The methylmercury(II) cation is formed in the environment in biotic processes by microbial metabolization and in abiotic processes by chemical reactions that do not involve living organisms. In marine sediments or at the bottom of lakes methylmercury(II) is concentrated in plankton and progresses up the food chain as it is readily absorbed and accumulated by living organisms. The methylmercury and phenylmercury(II) cations also have a high affinity for the S-donor atoms present in proteins, peptides and amino acids. However, the behaviour as a toxic agent is different; methylmercury is neurotoxic, whereas the phenyl derivative shows toxic effects as Hg(II). These facts are consistent with the easier breakdown of the Hg–C bond in the phenyl derivative [1–3].
The breakdown of this bond once the R–Hg fragment is Sbonded is activated by the donating ability of other donor atoms that are able to provide an additional interaction to the Hg–S bond. For the organomercurial lyase enzymes that are able to degrade methylmercury, the influence of additional S-donor atoms from cysteine [4] or O-donor atoms from either a phenolic group [5] or a carboxylate group [6] have been postulated. As alternatives to the classical chelating agents dimercaptosuccinic acid (DMSA) and dimercaptopropanesulfonic acid (DMPS) [7], the 3-(aryl)-2-sulfanylpropenoic acids (where aryl = phenyl, 2-furyl) were tested [8,9] as chelating agents against mercury intoxication through mobilization of the metal by complex formation. As these complexes have not been studied we selected these two ligands [H2L, Scheme 1], along with the 2-thienyl derivative for comparative purposes, and reacted them with Hg(II) in order to prepare and structurally characterize the respective complexes.
O 3
R
H 2L
R=
1
C OH
6
6 7
6
5
5
5 4
7
4
7
4 9
0277-5387/$ - see front matter Ó 2008 Elsevier Ltd. All rights reserved. doi:10.1016/j.poly.2008.04.034
2
C SH
8
* Corresponding author. Tel.: +34 981528074; fax: +34 981547102. E-mail address: [email protected] (J. Sordo).
CH
H2pspa
O H2fspa
S H2tspa
J.S. Casas et al. / Polyhedron 27 (2008) 2436–2446
This structural study is relevant because, although there are previous results on S-donor ligands coordinated to Hg(II) and carboxylate ‘‘inorganic” complexes, to the best of our knowledge Hg(II) complexes with an S2O2 kernel either do not contain or contain only weakly coordinated carboxylates [10]. The contrasting chelating ability of this class of ligand [11,12] should enable the preparation and study of this kernel. In addition, in the case of phenylmercury(II), an HgCSO kernel with S,O-donor bidentate chelate ligands was not found in the literature [13] or in a search of the CSD database [14] and could contribute to our understanding of Hg–C bond cleavage. As a result, we also prepared and characterized the corresponding phenylmercury(II) complexes with these ligands. The work described here involves the synthesis and characterization of compounds of the type [HQ]2[Hg(L)2], in which the Hg atom has an HgO2S2 coordination kernel, and compounds of the type [HQ][PhHg(L)], in which an HgCSO kernel was identified and characterized by X-ray diffraction. 2. Experimental 2.1. Material and methods The 3-(aryl)-2-sulfanylpropenoic acids H2pspa, H2fspa and H2tspa were prepared by condensation of the appropriate aldehyde with rhodanine, subsequent hydrolysis in an alkaline medium and acidification with HCl [15,16]. Mercury(II) acetate, phenylmercury(II) acetate and diisopropylamine (Merck) were used as supplied. Elemental analyses were performed with a Carlo-Erba 1108 microanalyser. Melting points were determined with a Büchi apparatus and are uncorrected. IR spectra (KBr pellets or Nujol mulls) were recorded on a Bruker IFS66V FT-IR spectrophotometer and are reported in Section 2.2. 1H and 13C NMR spectra were recorded in dmso-d6 or CDCl3 at room temperature on Bruker AMX 300 and AMX 500 spectrometers operating at 300.14 or 500.14 (1H) and 75.46 or 125.76 MHz (13C), using 5 mm o.d. tubes; chemical shifts are reported relative to TMS using the solvent signal (d1H = 2.50 ppm; d13C = 39.50 ppm) as reference. 199 Hg NMR were recorded in dmso-d6 and, in some cases, CDCl3 (concentration ranging from 102 to 2.6 102 M) at room temperature on a Bruker AMX 500 spectrometer operating at 89.47 MHz. Chemical shifts are reported relative to pure dimethylmercury(II) as secondary standard. Mass spectra were recorded on a Kratos MS50TC spectrometer connected to a DS90 system and operating in FAB conditions (Xe, 8 eV) using as liquid matrix 3-nitrobenzyl alcohol. 2.2. Synthesis 2.2.1. Compounds of the type [HQ]2[Hg(L)2] These compounds were prepared by reacting diisopropylamine, the appropriate H2L acid and Hg(OAc)2 in ethanol in a 2:2:1 molar ratio. The solid formed after agitation of the reaction mixture at room temperature was filtered off and vacuum dried.
2.2.2. [HQ]2[Hg(pspa)2] (1) H2pspa (0.90 g, 0.005 mmol), Hg(OAc)2 (0.80 g, 0.0025 mmol), diisopropylamine (0.51 g, 0.005 mmol), ethanol (50 mL), grey solid, yield: 73.6%, M.p.: 163 °C. Anal. Calc. for C30H44N2O4S2Hg: C, 47.3; H, 5.8; N, 3.7; S, 8.4. Found: C, 47.3; H, 5.9; N, 3.6; S, 8.9%. IR (cm1): ma(CO2) 1547s; ms(CO2) 1343vs; d(NH2+) 1618s. 1H NMR (dmso-d6, ppm): d C(3)H 7.73 (s, 2), CH3 1.18, NH2+ 8.85. 13 C NMR (dmso, ppm): d C(1) 170.7, C(2) 135.9, C(3) 131.2, CH 46.0, CH3 18.7. 199Hg NMR (dmso-d6, ppm): d 784.7. FAB peaks at m/z (%) = 662.2 (1.20) ([HQ][Hg(pspa)2] + 2H); 102.1 (100)
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(HQ). Recrystallization from an ethanol–dmso mixture gave crystals suitable for an X-ray study. 2.2.3. [HQ]2[Hg(fspa)2] (2) H2fspa (0.90 g, 0.0053 mmol), Hg(OAc)2 (0.45 g, 0.0026 mmol), diisopropylamine (0.54 g, 0.0053 mmol), ethanol (50 mL), yellow solid, yield: 48.2%, M.p.: 172 °C. Anal. Calc. for C26H40N2O6S2Hg: C, 42.1; H, 5.4; N, 3.8; S, 8.2. Found: C, 42.2; H, 5.7; N, 3.2; S, 8.6%. IR (cm1): ma(CO2) 1543s; ms(CO2) 1344vs; d(NH2+) 1620s. 1 H NMR (dmso-d6, ppm): d C(3)H 7.61 (s, 2), CH 3.27 (q, 4), CH3 1.17 (d, 24). 13C NMR (dmso-d6, ppm): d C(1) 169.9, C(2) 135.9, C(3) 141.4, CH 45.9, CH3 18.70. 199Hg NMR (dmso-d6, ppm): d 780.7. 199Hg NMR (CDCl3, ppm): d 853. FAB peaks at m/z (%) = 642.2 (0.96) ([HQ][Hg(fspa)2] + 2H); 102.1 (100.00) (HQ). Crystals suitable for an X-ray study were obtained from the mother liquor. 2.2.4. [HQ]2[Hg(tspa)2] (3) H2tspa (0.90 g, 0.0048 mmol), Hg(OAc)2 (0.77 g, 0.0024 mmol), diisopropylamine (0.49 g, 0.0048 mmol), ethanol (50 mL), white solid, yield: 68.7%, M.p.: 168 °C. Anal. Calc. for C26H40N2O4S4Hg: C, 40.4; H, 5.2; N, 3.6; S, 16.6. Found: C, 39.8; H, 5.1; N, 3.3; S, 16.1%. IR (cm1): ma(CO2) 1548s; ms(CO2) 1335vs; d(NH2+) 1612m. 1H NMR (dmso-d6, ppm): d C(3)H 7.97 (s, 2), CH 3.27 (q, 4), CH3 1.16 (d, 24), NH2+ 8.96 (s, br, 4). 13C NMR (dmso-d6, ppm): d C(1) 170.2, C(2) 134.5, C(3) 124.6, CH 45.9, CH3 18.7. 199Hg NMR (dmso-d6, ppm): d –810.2. FAB peaks at m/z (%) = 673.1 (0.82) ([HQ][Hg(tspa)2] + H); 102.1 (100) (HQ). Crystals suitable for an X-ray study were obtained by recrystallization from a dmso/dmf mixture. 2.2.5. Compounds of the type [HQ][PhHg(L)] These compounds were prepared by reacting the appropriate sulfanylpropenoic acid, diisopropylamine and PhHg(OAc) in ethanol in a 1:1:1 molar ratio. The solid formed after agitation of the mixture at room temperature was filtered off and vacuum dried. 2.2.6. [HQ][PhHg(pspa)] (4) H2pspa (0.90 g, 0.005 mmol), PhHg(OAc) (1.69 g, 0.005 mmol), diisopropylamine (0.51 g, 0.005 mmol), ethanol (50 mL), white solid, yield: 69.7%, M.p.: 183 °C. Anal. Calc. for C21H27NO2SHg: C, 45.2; H, 4.9; N, 2.5; S, 5.7. Found: C, 45.0; H, 4.8; N, 2.7; S, 5.8%. IR (cm1): ma(CO2) 1553s; ms(CO2) 1340vs; d(NH2+) 1618m. 1H NMR (dmso-d6, ppm): d C(3)H 7.66 (s, 1), CH 3.30 (q, 4), CH3 1.19 (d, 24), NH2+ 8.55 (s,br, 1). 13C NMR (dmso-d6, ppm): d C(1) 171.5, C(2) 137.9, C(3) 131.0, CH 46.0, CH3 18.9. 199Hg NMR (dmso-d6, ppm): d 755.4. 199Hg NMR (CDCl3, ppm): d 820.9. FAB peaks at m/z (%) = 558.10 (1.44) ([HQ][PhHg(pspa)] + H); 457.98 (1.68) ([PhHg(pspa)] + H); 102.09 (100.00) (HQ). Crystals suitable for an X-ray study were obtained from the mother liquor. 2.2.7. [HQ][PhHg(fspa)] (5) H2fspa (0.90 g, 0.0053 mmol), PhHg(OAc) (1.79 g, 0.0053 mmol), diisopropylamine (0.54 g, 0.0053 mmol), ethanol (50 mL), white solid, yield: 76.6%, M.p.: 172 °C. Anal. Calc. for C19H25NO3SHg: C, 41.6; H, 4.6; N, 2.6; S, 5.8. Found: C, 41.8; H, 4.6; N, 2.4; S, 5.4%. IR (cm1): ma(CO2) 1546 m; ms(CO2) 1334vs; d(NH2+) 1620m. 1H NMR (dmso-d6, ppm): d C(3)H 7.56 (s, 1), CH 3.30, CH3 1.16 (d, 12), NH2+ 8.68 (s,br). 13C NMR (dmso-d6, ppm): d C(1) 170.9, C(2) 141.4, C(3) 137.5, CH 46.0, CH3 18.8. 199Hg NMR (dmso-d6, ppm): d 776.1. (CDCl3, ppm): d 861.5. FAB peaks at m/z (%) = 549.07 (1.31) ([HQ][PhHg(fspa)]); 447.94 (2.50) ([PhHg(fspa)] + H); 102.09 (100.00) (HQ). Crystals suitable for an X-ray study were obtained from the mother liquor.
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2.2.8. [HQ][PhHg(tspa)] (6) H2tspa (0.90 g, 0.0048 mmol), PhHg(OAc) (1.63 g, 0.0048 mmol), diisopropylamine (0.49 g, 0.0048 mmol), ethanol (50 mL), white solid, yield: 78.7%, M.p.: 184 °C. Anal. Calc. for C19H25NO2S2Hg: C, 40.5; H, 4.4; N, 2.4; S, 11.4. Found: C, 40.3; H, 4.0; N, 2.3; S, 11.0%. IR (cm1): ma(CO2) 1552s; ms(CO2) 1335vs; d(NH2+) 1617m. 1H NMR (dmso-d6, ppm): d C(3)H 7.97 (s, 1), CH 3.30 (q, 2), CH3 1.20 (d, 12), NH2+ 8.84 (s, br). 13C NMR (dmso-d6, ppm): d C(1) 171.38, C(2) 134.9, C(3) 126.2, CH 45.9, CH3 18.7. 199Hg NMR (dmso-d6, ppm): d 788.8. 199Hg NMR (CDCl3, ppm): d 839.4. FAB peaks at m/z (%) = 565.06 (1.98) ([HQ][PhHg(tspa)]); 463.93 (3.21) ([PhHg(tspa)] + H); 102.09 (100.00) (HQ). Crystals suitable for an X-ray study were obtained from the mother liquor.
absorption were carried out. The structures of 1–4 were solved using direct methods but by the heavy atom Patterson method in 5 and 6 [21]. In the refinement the non-H atoms were treated anisotropically [21]. The H atoms were localized from difference Fourier maps and refined as riders (N–H 0.90, C–H 0.93–0.98 Å) [21], except in 1 and 3 where the atomic position and isotropic temperature factor were also refined. The scattering factors were taken from International Tables for Crystallography [22]. The main calculations were performed with SHELXL-97 [21] and PLATON [20] and figures were plotted with ZORTEP [23] and MERCURY [24].
3. Results and discussion 2.3. X-ray studies 3.1. Compounds of the type [HQ]2[Hg(L)2] Single crystals were mounted on glass fibres in Bruker Smart 1000 CCD (1–3) or Enraf-Nonius MACH3 (4–6) automatic diffractometers. Data were collected at 293 K using Mo Ka radiation (k = 0.71073 Å). The crystal data, experimental details and refinement results are summarized in Table 1. Corrections for Lorentz effects, polarization [17] and multi-scan (SADABS) [18] for 1–3 or semi-empirical (w scan) [19,20] for 4–6
The reaction of diisopropylamine, the corresponding H2L acid and Hg(OAc)2 in ethanol in a 2:2:1 molar ratio gave rise to solids with this composition. In all the cases the FAB spectra show peaks for the protonated [HQ][Hg(L)2] species. The compounds are soluble in dmso and dmf but insoluble or sparingly soluble in water, ethanol, acetone, chloroform and acetonitrile.
Table 1 Crystal structure and refinement data for [HQ]2[Hg(pspa)2] (1), [HQ]2[Hg(fspa)2] (2), [HQ]2[Hg(tspa)2] (3), [HQ][PhHg(pspa)] (4), [HQ2[PhHg(fspa)] (5) and [HQ][PhHg(tspa)] (6) Compound
[HQ]2[Hg(pspa)2] (1)
[HQ]2[Hg(fspa)2] (2)
[HQ]2[Hg(tspa)2] (3)
[HQ][PhHg(pspa)] (4)
[HQ][PhHg(fspa)] (5)
[HQ][PhHg(tspa)] (6)
Empirical formula Formula weight Temperature (K) Wavelength (Å) Crystal system, space group Unit cell dimensions a (Å) b (Å) c (Å) a (°) b (°) c (°) V (Å3) Z, Dcalc (Mg/m3) Absorption coefficient (mm1) F (0 0 0) Crystal size (mm) H Range for data collection (°) Index ranges
C30H44N2O4S2Hg 761.38 293(2) 0.71073 monoclinic, P2(1)/n
C26H40N2O6S2Hg 741.31 293(2) 0.71073 triclinic, P 1
C26H40N2O4S4Hg 773.43 293(2) 0.71073 monoclinic, P2(1)/c
C21H27NO2SHg 558.09 293(2) 0.71073 monoclinic, P2(1)/c
C19H25NO3SHg 548.05 293(2) 0.71073 orthorhombic, Pbca
C19H25NO2S2Hg 564.11 293(2) 0.71073 monoclinic, P2(1)/c
14.3539(11) 15.9545(13) 15.6774(12)
14.079(4) 15.321(4) 16.238(5)
8.659(2) 22.182(4) 11.092(4)
11.122(2) 17.062(4) 21.505(4)
8.300(2) 22.25(4) 11.164(2)
112.574(5)
94.80(2)
94.33(2)
94.33(2)
3345.5(5) 4, 1.512 4.759
13.9291(9) 14.712(1) 18.109(1) 92.665(1) 111.939(1) 110.151(1) 3165.5(3) 4, 1.555 5.032
3234.2(16) 4, 1.588 5.049
2123.0(8) 4, 1.746 7.362
4080.6(14) 8, 1.784 7.662
2056.1(8) 4, 1.822 7.701
1528 0.22 0.21 0.15 1.65–28.05
1480 0.04 0.15 0.08 1.64–28.01
1544 0.14 0.15 0.24 1.90–27.88
1088 0.35 0.30 0.15 2.36–27.97
2128 0.35 0.25 0.15 2.38–27.97
1096 0.40 0.30 0.25 3.07–27.98
15 6 h 6 18, 19 6 k 6 20, 19 6 l 6 20 18 192/7388 [0.0664]
14 6 h 6 18, 19 6 k 6 19, 23 6 l 6 23 18 142/12 632 [0.0488]
18 6 h 6 18, 20 6 k 6 20, 21 6 l 6 21 24 213/7415 [0.0982]
11 6 h 6 0, 29 6 k 6 0, 14 6 l 6 14 5444/5123 [0.0479]
0 6 h 6 14, 22 6 k 6 0, 0 6 l 6 28 4909/4908 [1.0764]
10 6 h 6 10, 29 6 k 6 0, 14 6 l 6 0 1575/4936 [0.0506]
91.0% (h = 28.05) multiscan
96.1% (h = 27.88) semi-empirical from equivalents 1.000 and 0.644
97.5% (h = 27.9) semi-empirical from equivalents 0.971 and 0.486
90.3% (h = 27.97) psi scan
97.5% (h = 27.98) psi scan
1.000 and 0.486
82.4% (h = 28.01°) semi-empirical from equivalents 1.000 and 0.479
0.968 and 0.515
0.982 and 0.546
full-matrix leastsquares on F2 7388/0/364 0.704 R1 = 0.0390, wR2 = 0.0460 R1 = 0.1404 wR2 = 0.0570 0.868 and 0.679
full-matrix leastsquares on F2 12632/683 0.567 R1 = 0.0467, wR2 = 0.1038 R1 = 0.1193, wR2 = 0.1327 1.290 and 1.098
full-matrix leastsquares on F2 7415/346 1.012 R1 = 0.0740, wR2 = 0.1195 R1 = 0.1661, wR2 = 0.1431 2.096 and 1.014
full-matrix leastsquares on F2 5123/239 1.018 R1 = 0.0450, wR2 = 0.1018 R1 = 0.1653, wR2 = 0.1337 1.098 and 1.359
full-matrix leastsquares on F2 4908/230 0–955 R1 = 0.0457, wR2 = 0.0892 R1 = 0.2123, wR2 = 0.1317 0.866 and 1.206
full-matrix leastsquares on F2 4936/230 0.955 R1 = 0.0466 wR2 = 0.0792 R1 = 0.1737, wR2 = 0.1043 1.536 and 0.852
Reflections collected/ unique [Rint] Completeness to theta Absorption correction Maximum and minimum transmission Refinement method Data/parameters Goodness-of-fit on F2 Final R indices [I > 2r (I)] R indices (all data) Largest difference in peak and hole (e A3)
111.280(2)
J.S. Casas et al. / Polyhedron 27 (2008) 2436–2446
3.1.1. Description of the structures of [HQ]2[Hg(pspa)2] (1), [HQ]2[Hg(fspa)2] (2) and [HQ]2[Hg(tspa)2] (3) Crystals suitable for X-ray study were obtained for compounds derived from H2pspa, H2fspa and H2tspa. As the structures have significant similarities they are discussed together. In all cases the crystals contain diisopropylammonium cations and anions of the type [Hg(L)2]2, where L (pspa2, fspa2 and tpsa2) behaves as a bidentate chelate ligand bonded to Hg through an O atom of the carboxylate group and the S atom of the deprotonated SH group. The numbering scheme for the [Hg(L)2]2 anions is shown in Fig. 1 and selected values for the bond distances (Å) and angles (°) are given in Tables 2 and 3. The Hg atom in all the anions is tetracoordinated in an HgO2S2 environment, with slightly different parameters in molecules A
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and B for [Hg(fspa)2]2 (Table 3). The Hg–S bond distances range from 2.333(2) Å for [Hg(pspa)2]2 to 2.349(3) Å for [Hg(tspa)2]2. These values are slightly shorter than those found in Hg(II) compounds with S,S0 -bidentate ligands [25] to give an HgS4 environment and are in the range found for linear S–Hg–S bis-thiolato complexes of Hg(II) [26]; the Hg–O bond distances range from 2.499(7) Å in [Hg(tspa)2] to 2.553(4) Å in [Hg(pspa)2]2. As far as the angles around the metal are concerned, the value for the bite angle of the ligand, which ranges from 77.56(17)° for [Hg(fspa)2]2 to 80.04(15)° for [Hg(tspa)2]2, is lower; the largest value is found for the S–Hg–S angle, which ranges from 168.03(9)° in [Hg(tspa)2]2 to 171.83(8)° in the fspa derivative. In order to investigate the influence that a possible Hg–S interaction between neighbouring molecules has on the S–Hg–S angle
Fig. 1. ORTEP drawing showing the structures of the [Hg(pspa)2]2 (I), the two molecules A(II) and B(III) of the [Hg(fspa)2]2 and [Hg(tspa)2]2 (IV) anions with the numbering scheme. The ellipsoids are drawn at the 30% probability level.
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Table 2 Selected bond lengths (Å) and angles (°) in [HQ]2[Hg(pspa)2] (1) and [HQ]2[Hg(tspa)2] (3)
(a) Hg environment Hg(1)–O(11) Hg(1)–O(21) Hg(1)–S(1)#1 Hg(1)–S(1) Hg(1)–S(2) O(11)–Hg(1)–S(1) O(11)–Hg(1)–S(2) S(1)–Hg(1)–S(2) S(1)#1–Hg(1)–S(2) S(1)#1–Hg(1)–S(1) O(21)–Hg(1)–S(1) O(21)–Hg(1)–S(2) O(11)–Hg(1)–O(21) O(11)–Hg(1)–S(1)#1 O(21)–Hg(1)–S(1)#1 (b) Ligand S(1)–C(12) O(11)–C(11) O(12)–C(11) S(2)–C(22) O(21)–C(21) O(22)–C(21) O(12)–C(11)–O(11) O(12)–C(11)–C(12) O(11)–C(11)–C(12) C(13)–C(12)–S(1) C(11)–C(12)–S(1) O(22)–C(21)–O(21) O(22)–C(21)–C(22) O(21)–C(21)–C(22) C(23)–C(22)–S(2) C(21)–C(22)–S(2) a
[HQ]2[Hg(pspa)2]a (1)
[HQ]2[Hg(tspa)2] (3)
2.510(4) 2.553(4) 3.427(2) 2.346(2) 2.333(2) 78.26(10) 110.53(11) 169.93(6) 79.45(5) 96.76(4) 106.62(11) 77.77(11) 96.95(14) 85.83(9) 156.55(11)
2.499(7) 2.518(6)
1.746(6) 1.258(6) 1.255(6)
1.747(10) 1.223(10) 1.259(11) 1.750(9) 1.269(10) 1.244(10) 126.1(9) 117.0(8) 116.8(9) 120.8(7) 121.5(7) 123.2(8) 118.4(9) 118.4(8) 122.0(7) 120.9(7)
2.349(3) 2.346(3) 79.35(16) 109.19(15) 168.03(9)
106.71(16) 80.04(15) 102.9(2)
123.3(7) 118.4(6) 118.3(6) 121.1(5) 121.6(5)
Symmetry operations: #1 x, y, z.
Table 3 Selected bond lengths (Å) and angles (°) in [HQ]2[Hg(fspa)2] (2) (a) Hg environment Hg(1)–O(11A) Hg(1)–O(21A) Hg(2)–O(11B) Hg(2)–O(21B) O(11A)–Hg(1)–S(11A) O(21A)–Hg(1)–S(11A) S(11A)–Hg(1)–S(21A) O(11B)–Hg(2)–S(11B) O(21B)–Hg(2)–S(11B) S(11B)–Hg(2)–S(21B) (b) Ligand S(11A)–C(12A) S(11B)–C(12B) O(11A)–C(11A) O(11B)–C(11B) O(12A)–C(11A) O(12B)–C(11B) O(12A)–C(11A)–O(11A) O(12B)–C(11B)–O(11B) O(12A)–C(11A)–C(12A) O(12B)–C(11B)–C(12B) O(11A)–C(11A)–C(12A) O(11B)–C(11B)–C(12B) C(13A)–C(12A)–S(11A) C(13B)–C(12B)–S(11B) C(11A)–C(12A)–S(11A) C(11B)–C(12B)–S(11B) C(13A)–C(14A)–O(13A) C(13B)–C(14B)–O(13B)
2.550(7) 2.536(6) 2.549(6) 2.540(6) 77.56(17) 106.95(18) 171.83(8) 79.15(16) 107.86(16) 170.90(8) 1.766(9) 1.750(9) 1.246(11) 1.282(11) 1.227(11) 1.269(10) 124.7(9) 122.8(9) 117.5(10) 119.5(9) 117.7(9) 117.6(8) 120.7(7) 120.5(7) 121.3(8) 122.9(7) 114.1(10) 113.8(9)
Hg(1)–S(11A) Hg(1)–S(21A) Hg(2)–S(11B) Hg(2)–S(21B) O(11A)–Hg(1)–S(21A) O(21A)–Hg(1)–S(21A) O(11A)–Hg(1)–O(21A) O(11B)–Hg(2)–S(21B) O(21B)–Hg(2)–S(21B) O(11B)–Hg(2)–O(21B) S(21A)–C(22A) S(21B)–C(22B) O(21A)–C(21A) O(21B)–C(21B) O(22A)–C(21A) O(22B)–C(21B) O(21A)–C(21A)–O(22A) O(21B)–C(21B)–O(22B) O(21A)–C(21A)–C(22A) O(21B)–C(21B)–C(22B) O(22A)–C(21A)–C(22A) O(22B)–C(21B)–C(22B) C(23A)–C(22A)–S(21A) C(23B)–C(22B)–S(21B) C(21A)–C(22A)–S(21A) C(21B)–C(22B)–S(21B) C(23A)–C(24A)–O(23A) C(23B)–C(24B)–O(23B)
2.337(3) 2.334(3) 2.347(2) 2.336(2) 108.03(17) 78.54(18) 98.0(2) 107.19(16) 78.09(16) 98.3(2) 1.752(9) 1.758(9) 1.245(11) 1.261(10) 1.224(11) 1.231(10) 123.0(10) 123.3(8) 117.6(9) 117.7(8) 119.4(10) 118.9(9) 120.9(7) 120.6(7) 122.7(7) 122.6(7) 113.4(9) 112.4(9)
of the Hg kernel, we analysed these distances. Only in the pspa derivative 1 were interactions found that could be considered sig-
nificant [Hg–S(1)#1 = 3.4272(16) Å]. In the other two cases the intermolecular Hg–S bond distances are greater than 4 Å. At this point we must underline the variability in the sum of the van der Waals radii for Hg and S (on using the value reported by Bondi [27] we obtained a value of 3.3 Å for the sum of the two radii, which was revised to 3.7 Å [13] or to 4.016 Å on using the van der Waals radii reported by Batsanov [28]). However, the influence of this intermolecular interaction on the bond distances and angles of the Hg kernel does not seem to be significant. The intermolecular interaction is also absent in [Hg(Htsal)2] [10] and [Hg(Htsal)2] 1,4-dioxane [29] (H2tsal = thiosalicylic acid). The former compound, which cocrystallizes with [Hg2(tsal)2(PPh3)2], has parameters [Hg–S: 2.3444(12), 2.3392(12) Å; Hg–O: 2.641(3), 2.682(3) Å; S–Hg–S: 170.12(4)°] close to those found in this work, although the Hg–O bond distances are longer and the S–Hg–S angle slightly wider. Other examples in the literature include the 2,2,6, 6-tetramethyl-3,5-heptanedione [30], the 2-dimethylamino-3-4dioxo-cyclobut-1-en-thiolate [26] and the N-(piperidylthiocarbonylcarbonyl)benzamide [31] mercury(II) complexes and these also have, as in the case of the thiosalicylic acid, wider S–Hg–S bond angles than those found in this work. For the Hg atom in the thiosalicylic acid derivative Henderson and Nicholson [10], taking into account the large tetrahedral distortion in the kernel, proposed a nido-trigonal bipyramidal coordination geometry or even an S–Hg–S linear geometry with a weak Hg O interaction. The compounds described in this work have a shorter Hg–O bond distance than that found in the thiosalicylic acid derivative, making the nido-tbp geometry the more appropriate description. The planarity of the L2 fragment is different in the three structures. In [Hg(pspa)2]2 the angle between the idealized plane of the chelate ring and that of the C(14)–C(19) phenyl ring is 22.6° and this value is 12.26° for the other L fragment. Equivalent angles are 12.68° and 10.46° in molecule A and 21.68° and 5.58° in molecule B for the fspa derivative and 10.61° and 15.52° in [HQ]2[Hg(tspa)2], although there is a lack of planarity in the chelate ring in the latter compound (rms [Hg(1)/S(1)/O(11)/C(11)/C(12)] = 0.0917° and rms [Hg(1)/S(2)/O(21)/C(21)/C(22)] = 0.0970°). The diisopropylammonium cation in each of the three structures has parameters that are comparable with other previously described examples [32,33]. Table 4 Structural parameters (Å, °) describing intermolecular hydrogen bonding in the complexes [HQ]2[Hg(L)2]a D–H
H A
D A
D–H A
[HQ]2[Hg(pspa)2] N(1)–H(1A) O(12)#1 N(1)–H(1B) O(21) N(2)–H(2A) O(11)#1 N(2)–H(2B) O(22)
0.91(5) 1.09(5) 0.87(5) 0.97(5)
1.82(5) 1.67(5) 2.00(5) 1.72(5)
2.722(6) 2.761(6) 2.806(6) 2.692(6)
170(5)° 176(4)° 155(5)° 175(5)
[HQ]2[Hg(fspa)2] N(11)–H(11A) O(12B)#2 N(11)–H(11B) O(11B) N(41)–H(41A) O(21B) N(41)–H(41B) O(12A)#4 N(21)–H(21A) O(22B) N(21)–H(21B) O(11A)#5 N(31)–H(31A) O(22A) N(31)–H(31B) O(21A)#3
0.90 0.90 0.90 0.90 0.90 0.90 0.90 0.90
1.82 1.89 1.84 1.94 1.95 1.88 1.84 1.89
2.708(9) 2.777(9) 2.719(9) 2.827(9) 2.831(9) 2.761(9) 2.737(9) 2.776(9)
169.6° 166.2° 163.8° 168.4° 166.2° 165.3° 172.1° 167.3°
[HQ]2[Hg(tspa)2] N(1)–H(11A) O(22)#6 N(1)–H(11B) O(11) N(2)–H(21A) O(21)#7 N(2)–H(21B) O(12)
0.92(9) 0.90(9) 1.01(9) 0.81(9)
1.84(9) 1.93(9) 1.79(9) 2.00(9)
2.738(10) 2.807(10) 2.769(10) 2.801(10)
164(8)° 162(8)° 163(7)° 170(9)°
a Symmetry code: #1 x + 1/2, y + 1/2, z + 1/2; #2 x + 2, y + 1, z + 1; #3 x + 2, y + 2, z + 1; #4 x 1, y 1, z; #5 x,y 1,z; #6 x,y + 1/2, z + 1/2; #7 x, y + 1/2, z + 1/2.
J.S. Casas et al. / Polyhedron 27 (2008) 2436–2446
The [Hg(L)]2 anions and the [HQ]+ cations are hydrogen bonded through the NH2 group of the cation and the O atoms of the carboxylate group. The metric parameters for these bonds are included in Table 4. In the three structures the [HQ]+ cation bridges two dianionic [Hg(L)]2 units but the final arrangement is different. In [HQ]2[Hg(pspa)2], two [HQ]+ units establish a double-bridge between two [Hg(pspa)2]2 anions to afford zig-zag chains (Fig. 2a) parallel to the crystallographic direction {1 1 2}. These chains are schematically represented in Fig. 2b using a rod as a symbol for the anion and a left/right arrow as a symbol for the cation. The chains are packed in the crystallographic c-axis, as shown in Fig. 2c, in which the hydrogen bond and the weak Hg S interaction are underlined. The same interaction in [HQ]2[Hg(fspa)2] generates rack-chains running parallel to the crystallographic b-axis (Fig. 3) and these are also represented using the same symbols. In contrast to the above situation, 2D molecular association is observed in the thiophene derivative. The crystal structure may be described in terms of the formation of the unit shown in Fig. 4a by bridge of four [HQ]+ units between four [Hg(tspa)2]2 units. The cyclic unit is associated with another of these units through interactions analogous to those described above (Fig. 4b). The resulting sheet is parallel to the crystallographic bc-plane. 3.1.2. Spectroscopy The IR spectra of the [HQ]2[Hg(L)2] complexes do not show a m(SH) band, which is located near 2550 cm1 in the spectra of
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the free ligands. Furthermore, the vibrations of the CO2H group [m(C@O) = 1670, 1665 and 1673 cm1 for H2pspa, H2fspa and H2tspa are replaced by bands typical of a carboxylate group with [mas(CO2)] observed between 1548 and 1543 cm1 and [msym(CO2)] between 1344 and 1335 cm1. As in other compounds in which the HQ cation is hydrogen bonded [12,34] to the carboxylate group the Dm (=masCO2–msymCO2) parameter has values smaller than those found for a monodentate carboxylate group [35], which was attributed [34] to the effect of the N–H O hydrogen bond on the structural parameters of the carboxylate group. A strong band at around 1610 cm1 in all the spectra was assigned [36] to the d(NH2) vibration of the diisopropylammonium cation. The 1H NMR spectra of the complexes in all cases show the typical signals of the diisopropylammonium cation and the absence of signals attibutable to SH and COOH groups is consistent with bideprotonation of the ligand. These spectra show, in general, a shift of the C(3)–H signal to higher field on complexation, which suggests the persistence of the Hg–S bond in solution. The persistence of the S-coordination is confirmed [37,38] by the shift of the C(3) signal in the 13C NMR spectra. In these spectra the C(1) signals are in positions close to those found [34,39,40] for compounds with a monodentate coordinated carboxylate group, thus suggesting the persistence in solution of the coordination mode found in the solid state. The 199Hg NMR spectra show only a signal located between 780.7 and 810.2 ppm, indicating the presence of only one type
Fig. 2. (a) A view of the polymeric structure of [HQ]2[Hg(pspa)2] (1) and (b) a schematic view of the structure; and (c) details of the hydrogen bonding and Hg S intermolecular interactions.
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Fig. 3. (a) A view of the polymeric structure of [HQ]2[Hg(fspa)2] (2) and (b) a schematic view of the structure.
Fig. 4. (a) A partial view of the polymeric structure of [HQ]2[Hg(tspa)2] (3) and (b) a schematic view of the structure.
of chemical environment for Hg(II). The position of the signal is close to the positions found for other four-coordinated Hg(II) complexes that have the HgS2N2 kernel [41]. In the case of 2 the spectrum was recorded in dmso/dmso-d6 (780.7 ppm) and in CDCl3 (853.0 ppm). The difference in the positions of the signal in these spectra is within the accepted range [42] for the influence of the solvent, suggesting the same chemical environment for the metal in both solvents, thus excluding dmso coordination. The additional coordination of these solvent molecules would increase the coordination number and should move the d (199Hg) signal to higher frequencies [41]. 3.2. Compounds of the type [HQ][PhHg(L)] Reaction of diisopropylamine, the corresponding sulfanylpropenoic acid and PhHg(OAc) in ethanol in a 1:1:1 molar ratio gave solids with this composition. The FAB mass spectra show peaks for the [HQ][HgPh(L)] molecular ion.
3.2.1. Description of the structures of [HQ][PhHg(pspa)] (4), [HQ][PhHg(fspa)] (5) and [HQ][PhHg(tspa)] (6) Single crystals suitable for X-ray studies were obtained for the three phenyl mercury complexes. The similarity between the structures, indeed the structures of 4 and 6 are isotypic, again means that these compounds will be discussed together. The three crystals contain diisopropylammonium cations and [HgPh(L)] anions that interact through hydrogen bonds. The numbering scheme for each compound is shown in Fig. 5 and selected bond distances (Å) and angles (°) are listed in Table 5. In each anion the ligand is S,O-bidentate chelate to give a HgCOS kernel. It should be noted that such an example in which O and S atoms from the same ligand has not been found previously [13,14] for phenylmercury(II) derivatives. In this kernel the metal adopts a significantly distorted T-environment. In this environment the Hg–C bond distance is about 2.065 Å, which is normal for phenylmercury(II) derivatives [13] and the Hg–O and Hg–S
J.S. Casas et al. / Polyhedron 27 (2008) 2436–2446
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Fig. 5. ORTEP drawing showing the structures of [HQ][PhHg(pspa)] (4) (I), [HQ][PhHg(fspa)] (5) (II) and [HQ][PhHg(tspa)] (6) (III) with the numbering scheme. The ellipsoids are drawn at the 30% probability level.
bond distances are close to 2.565 and 2.355 Å, respectively. The values for the O–Hg–S, C–Hg–O and C–Hg–S angles are about 76.50°, 106.0° and 174.0°, respectively. The sum of these angles is close to 360° in the three anions.
For other kernels values for the Hg–S bond distance between 2.357(3) and 2.405(1) Å were previously described for PhHg+ compounds with thiosemicarbazones [43] and ligands containing P–S bonds [44] and values larger than 2.370 Å have also been described
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Table 5 Selected bond lengths (Å) and angles (°) in [HQ][PhHg(pspa)] (4), [HQ][PhHg(fspa)] (5) and [HQ][PhHg(tspa)] (6)
(a) Hg environment Hg(1)–O(1) Hg(1)–S(1) Hg(1)–C(11) Hg(1)–S(1)#1 O(1)–Hg(1)–S(1) O(1)–Hg(1)– S(1)#1 S(1)–Hg(1)– S(1)#1 C(11)–Hg(1)–S(1) C(11)–Hg(1)– S(1)#1 C(11)–Hg(1)– O(1) (b) Ligand S(1)–C(2) O(1)–C(1) O(2)–C(1) O(2)–C(1)–O(1) O(2)–C(1)–C(2) O(1)–C(1)–C(2) C(3)–C(2)–S(1) C(1)–C(2)–S(1) a b
HQ][PhHg(pspa)]a (4)
[HQ][PhHg(fspa)] (5)
[HQ][PhHg(tspa)]b (6)
2.560(6) 2.360(3) 2.060(10) 3.381(3)a 76.04(16) 93.73(17)a
2.566(7) 2.353(3) 2.060(11) 3.316(3)b 76.49(18) 97.96(19)b
2.570(6) 2.354(2) 2.075(8) 3.593(3)a 77.23(14) 93.82(14)a
89.04(9)a
88.83(9)b
91.90(9)a
173.7(3) 95.6(3)a
174.3(3) 96.3(3)b
175.0(3) 91.4(3)a
107.9(3)
105.2(3)
106.3(3)
1.767(9) 1.259(11) 1.241(11) 123.6(9) 117.3(9) 119.1(8) 122.9(7) 119.6(7)
1.765(10) 1.260(13) 1.243(13) 124.8(10) 116.4(11) 118.8(10) 122.6(8) 119.3(8)
1.759(8) 1.261(9) 1.231(9) 123.9(8) 117.5(8) 118.6(7) 121.6(6) 121.1(6)
Table 6 Structural parameters (Å, °) describing intermolecular hydrogen bonding in the complexes [HQ][HgPh(L)]a D–H
H A
D A
D–H A
[HQ][PhHg(pspa)] N(1)–H(1A) O(1)#1 N(1)–H(1B) O(2)
0.90 0.90
1.95 1.84
2.833(10) 2.730(9)
167.1 169.1
[HQ][PhHg(fspa)] N(1)–H(1A) O(1)#2 N(1)–H(1B) O(2)
0.90 0.90
1.98 1.81
2.855(11) 2.703(10)
164.9 169.7
[HQ][PhHg(tspa)] N(1)–H(1A) O(1) #1 N(1)–H(1B) O(2)
0.90 0.90
1.93 1.84
2.809(9) 2.734(8)
165.8 169.1
a
Symmetry operation: #1 x + 1, y + 1, z + 1. Symmetry operation: #1 x + 1, y + 1, z.
[45–49]. The values found for the Hg–O bonds can be considered [50] typical of relatively strong bonds. These structures can be related with that of [HgPh(S2COEt)] [51], in which an S-donor atom is coordinated to a PhHg+ fragment to give a practically linear C–Hg–S [176.1 (4)°] environment, and with that of [HgPh(pmbp)] (pmbp = 1-phenyl-3-methyl-4benzoylpyrazol-5-onato] [50] where the pmbp ligand has two O-donor atoms, both coordinated to the Hg atom to give an
Symmetry code: #1 = x + 1, y + 1, z; #2 = x, y + 1, z.
HgCO2 environment reminiscent of the HgCOS present in this case. The structural parameters for the latter compound [Hg–O(1): 2.585(9) Å; Hg–O(2): 2.087(7) Å; Hg–C: 2.040(11) Å; C–Hg–O(1): 112.1(4)°; C–Hg–O(2): 168.6(3)°; O(1)–Hg–O(2): 78.3(3)°] have some similarities with these structures if the O(2) atom, trans to C but closest to the Hg atom, is replaced by the S atom of the sulfanylpropenoic fragment; the bite of the ligand is also similar. The parameters for the diisopropylammonium cation are unremarkable and close to those previously described. In the three crystals there are weak interactions, which are weaker in the tspa derivative, and these are depicted in the structures of the pspa and fspa derivatives shown in Fig. 6. Similar interactions in methylmercury xanthates of the type MeHgS(S)COR (R = Et, iPr, CH2Ph) [45] lead to supramolecular structures, but in this case such interactions could be hindered by the hydrogen bonds that exist between the diisopropylammonium cations and the corresponding anions. The parameters for these bonds, which involve the NH2 group and the carboxylate group, are listed in Table 6. As observed in the complexes [HQ]2[Hg(L)2], the [HQ]+ units establish two hydrogen bonds with two molecules of [HgPh(L)]
Fig. 6. The polymeric structures of: (a) [HQ][PhHg(pspa)] (4) and (b) [HQ][PhHg(fspa)] (5).
J.S. Casas et al. / Polyhedron 27 (2008) 2436–2446
to afford centrosymmetric dimers. These units are now associated in chains running parallel to crystallographic c (compounds 4 and 6) or a (compound 5) axes (see Fig. 6) through the previously described weak intermolecular Hg–S interaction (Table 5). 3.2.2. Spectroscopy As for [HQ]2[Hg(L)], the IR spectra of 4, 5 and 6 do not show the m(SH) band and the vibrations of the CO2H group are replaced by bands typical of the carboxylate group. The Dm[ma(CO2)–ms(CO2)] values are again typical of a monodentate carboxylate group involved in N–H O hydrogen bonds. The 1H NMR spectra show the typical bands of the diisopropylammonium cation, lacking signals attributable to SH and COOH. Furthermore, the spectra show a shift of the C(3)–H signal to higher field on complexation, suggesting the persistence of the Hg–S bond in solution. The position of the C(3) signals in each of the 13C NMR spectra of the complexes again supports S-coordination and the position of the C(1) signal suggests that the carboxylate group remains coordinated in solution. Thus, as in the [HQ]2[Hg(L)2] complexes, the ligand remains S,O-coordinated in solution. The 199Hg NMR spectra of the three complexes show only one signal each. In CDCl3 the signals for 4, 5 and 6 are at 820.9, 861.5 and 839.4 ppm, respectively, and in dmso the signals range between 755.4 and 788.8 ppm. The position of the signal in the spectra in chloroform is close to those found for thiosemicarbazonates of phenylmercury(II) in which the metal is tricoordinated [43]. Once again, the difference between the value in CDCl3 and dmso-d6 suggest that this latter solvent does not increase the coordination number of the metal in comparison to that found in the solid state. 4. Conclusion In summary, two types of complexes [HQ]2[Hg(L)2] and [HQ][PhHg(L)] where HQ is diisopropylammonium and L a bideprotonated 3-(aryl)-2-sulfanylpropenoic acid have been synthesized and characterized. Among the [HQ]2[Hg(L)2] complexes this study has led to the structural characterization of the unusual HgO2S2 kernel built on the basis of S,O-bidentate donor ligands. The chelating ability of the corresponding 3-(phenyl)- and 3-(2-furyl)-2-sulfanylpropenoic acids previously used as chelating agents against mercury intoxication is thus confirmed. This S,O-coordination mode was recently described for the widely used chelating agent DMSA, which contains SH and COOH groups, against the diorganotin(IV) fragment [52]. However, X-ray absorption spectroscopy and DFT calculations [7] suggest the presence of metallated species mainly supported by Hg–S bonds in the case of mercury. The same coordination mode was found for the ligands in the [HQ][PhHg(L)] complexes and this enabled us to determine the structural parameters of the CHgSO kernel, which has been identified previously for S,O-bidentate chelate ligands. Both types of complex show different supramolecular structures based on N–H O hydrogen bonds, with weak Hg S interactions also present in some cases. Acknowledgement This work was supported by the Ministerio de Educación y Ciencia, Spain, under project BQU2002-04524-C02-01. Appendix A. Supplementary data CCDC 667931, 667932, 667933, 667934, 667935 and 667936 contain the supplementary crystallographic data for 1, 2, 3, 4, 5
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[44] O. Bumbu, A. Silvestru, C. Silvestru, J.E. Drake, M.B. Hursthouse, M.E. Light, J. Organomet. Chem. 687 (2003) 118. [45] J.S. Casas, E.E. Castellano, J. Ellena, I. Haiduc, A. Sánchez, R.F. Semeniuc, J. Sordo, Inorg. Chim. Acta 329 (2002) 71. [46] T.S. Lobana, A. Sánchez, J.S. Casas, A. Castiñeiras, J. Sordo, M.S. García-Tasende, Main Group Met. Chem. 24 (2001) 61. [47] A. Castiñeiras, W. Hiller, J. Strähle, J. Bravo, J.S. Casas, M. Gayoso, J. Sordo, J. Chem. Soc., Dalton Trans. (1986) 1945.
[48] J. Zukerman-Schpector, E.M. Vázquez-López, A. Sánchez, J.S. Casas, J. Sordo, J. Organomet. Chem. 405 (1991) 67. [49] E.R.T. Tiekink, J. Organomet. Chem. 322 (1987) 1. [50] M.F. Mahon, K.C. Molloy, B.A. Omotowa, M.A. Mesubi, J. Organomet. Chem. 525 (1996) 239. [51] E.R.T. Tiekink, Acta Crystallogr., Sect. C 50 (1994) 861–862. [52] Ch. Ma, Q. Zhang, Eur. J. Inorg. Chem. (2006) 3244.
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3-(Aryl)-2-sulfanylpropenoates of mercury(II) and phenylmercury(II) José S. Casas a, Alfonso Castiñeiras a, María D. Couce b, Manuel García-Vega a, Manuel Rosende a, Agustín Sánchez a, José Sordo a,*, José M. Varela a, Ezequiel M. Vázquez López b a b
Departamento de Química Inorgánica, Facultade de Farmacia, Universidade de Santiago de Compostela, 15782 Santiago de Compostela, Galicia, Spain Departamento de Química Inorgánica, Facultade de Química, Edificio de Ciencias Experimentais, Universidade de Vigo, 36310 Vigo, Galicia, Spain
a r t i c l e
i n f o
Article history: Received 10 January 2008 Accepted 23 April 2008 Available online 6 June 2008 Keywords: Sulfanylpropenoato Mercury(II) IR Phenylmercury(II) NMR Crystal structure
a b s t r a c t Compounds [HQ]2[Hg(L)2] and [HQ][PhHg(L)] [where HQ = diisopropylammonium cation; L = pspa, fspa, tspa, where p = 3-(phenyl), f = 3-(2-furyl), t = 3-(2-thienyl), and spa = 2-sulfanylpropenoato] have been prepared by the reaction of mercury(II) acetate or phenylmercury(II) acetate with the corresponding acid in the presence of diisopropylamine in ethanol. The compounds have been characterized by elemental analysis, FAB mass spectrometry and IR and NMR (1H, 13C) spectroscopy. The crystal structures of the [HQ]2[Hg(L)2] compounds show the presence of diisopropylammonium cations and [Hg(L)2]2 anions. In each anion the Hg atom is in an HgO2S2 environment and this can be described as nido-tbp. The crystal structures of the [HQ][PhHg(L)] compounds show the presence of diisopropylammonium cations and [PhHg(L)] anions in which the Hg atom adopts an HgCOS distorted T-environment. The NMR data suggest that the coordination mode of the ligand L2 determined by X-ray diffractometry in the solid remains in solution. Ó 2008 Elsevier Ltd. All rights reserved.
1. Introduction The useful properties of mercury and its compounds has as a counterpart in their toxic effects. This metal is widespread today and is emitted as a vapour into the atmosphere from both natural and anthropogenic sources. This vapour is slowly converted to Hg(II) by oxidative process and the mercury returns to the earth in rainwater [1]. Hg(II) has an extremely high affinity for compounds that contain sulfhydryl groups and in the blood and tissues of humans it is bound to these groups of cysteine-containing peptides and proteins. Often very stable forms include linear complexes with two sulfur ligands; however, the Hg–S bonds are labile and for higher coordination numbers the structures are flexible, often with distorted trigonal or tetrahedral coordination geometries [1,2]. The methylmercury(II) cation is formed in the environment in biotic processes by microbial metabolization and in abiotic processes by chemical reactions that do not involve living organisms. In marine sediments or at the bottom of lakes methylmercury(II) is concentrated in plankton and progresses up the food chain as it is readily absorbed and accumulated by living organisms. The methylmercury and phenylmercury(II) cations also have a high affinity for the S-donor atoms present in proteins, peptides and amino acids. However, the behaviour as a toxic agent is different; methylmercury is neurotoxic, whereas the phenyl derivative shows toxic effects as Hg(II). These facts are consistent with the easier breakdown of the Hg–C bond in the phenyl derivative [1–3].
The breakdown of this bond once the R–Hg fragment is Sbonded is activated by the donating ability of other donor atoms that are able to provide an additional interaction to the Hg–S bond. For the organomercurial lyase enzymes that are able to degrade methylmercury, the influence of additional S-donor atoms from cysteine [4] or O-donor atoms from either a phenolic group [5] or a carboxylate group [6] have been postulated. As alternatives to the classical chelating agents dimercaptosuccinic acid (DMSA) and dimercaptopropanesulfonic acid (DMPS) [7], the 3-(aryl)-2-sulfanylpropenoic acids (where aryl = phenyl, 2-furyl) were tested [8,9] as chelating agents against mercury intoxication through mobilization of the metal by complex formation. As these complexes have not been studied we selected these two ligands [H2L, Scheme 1], along with the 2-thienyl derivative for comparative purposes, and reacted them with Hg(II) in order to prepare and structurally characterize the respective complexes.
O 3
R
H 2L
R=
1
C OH
6
6 7
6
5
5
5 4
7
4
7
4 9
0277-5387/$ - see front matter Ó 2008 Elsevier Ltd. All rights reserved. doi:10.1016/j.poly.2008.04.034
2
C SH
8
* Corresponding author. Tel.: +34 981528074; fax: +34 981547102. E-mail address: [email protected] (J. Sordo).
CH
H2pspa
O H2fspa
S H2tspa
J.S. Casas et al. / Polyhedron 27 (2008) 2436–2446
This structural study is relevant because, although there are previous results on S-donor ligands coordinated to Hg(II) and carboxylate ‘‘inorganic” complexes, to the best of our knowledge Hg(II) complexes with an S2O2 kernel either do not contain or contain only weakly coordinated carboxylates [10]. The contrasting chelating ability of this class of ligand [11,12] should enable the preparation and study of this kernel. In addition, in the case of phenylmercury(II), an HgCSO kernel with S,O-donor bidentate chelate ligands was not found in the literature [13] or in a search of the CSD database [14] and could contribute to our understanding of Hg–C bond cleavage. As a result, we also prepared and characterized the corresponding phenylmercury(II) complexes with these ligands. The work described here involves the synthesis and characterization of compounds of the type [HQ]2[Hg(L)2], in which the Hg atom has an HgO2S2 coordination kernel, and compounds of the type [HQ][PhHg(L)], in which an HgCSO kernel was identified and characterized by X-ray diffraction. 2. Experimental 2.1. Material and methods The 3-(aryl)-2-sulfanylpropenoic acids H2pspa, H2fspa and H2tspa were prepared by condensation of the appropriate aldehyde with rhodanine, subsequent hydrolysis in an alkaline medium and acidification with HCl [15,16]. Mercury(II) acetate, phenylmercury(II) acetate and diisopropylamine (Merck) were used as supplied. Elemental analyses were performed with a Carlo-Erba 1108 microanalyser. Melting points were determined with a Büchi apparatus and are uncorrected. IR spectra (KBr pellets or Nujol mulls) were recorded on a Bruker IFS66V FT-IR spectrophotometer and are reported in Section 2.2. 1H and 13C NMR spectra were recorded in dmso-d6 or CDCl3 at room temperature on Bruker AMX 300 and AMX 500 spectrometers operating at 300.14 or 500.14 (1H) and 75.46 or 125.76 MHz (13C), using 5 mm o.d. tubes; chemical shifts are reported relative to TMS using the solvent signal (d1H = 2.50 ppm; d13C = 39.50 ppm) as reference. 199 Hg NMR were recorded in dmso-d6 and, in some cases, CDCl3 (concentration ranging from 102 to 2.6 102 M) at room temperature on a Bruker AMX 500 spectrometer operating at 89.47 MHz. Chemical shifts are reported relative to pure dimethylmercury(II) as secondary standard. Mass spectra were recorded on a Kratos MS50TC spectrometer connected to a DS90 system and operating in FAB conditions (Xe, 8 eV) using as liquid matrix 3-nitrobenzyl alcohol. 2.2. Synthesis 2.2.1. Compounds of the type [HQ]2[Hg(L)2] These compounds were prepared by reacting diisopropylamine, the appropriate H2L acid and Hg(OAc)2 in ethanol in a 2:2:1 molar ratio. The solid formed after agitation of the reaction mixture at room temperature was filtered off and vacuum dried.
2.2.2. [HQ]2[Hg(pspa)2] (1) H2pspa (0.90 g, 0.005 mmol), Hg(OAc)2 (0.80 g, 0.0025 mmol), diisopropylamine (0.51 g, 0.005 mmol), ethanol (50 mL), grey solid, yield: 73.6%, M.p.: 163 °C. Anal. Calc. for C30H44N2O4S2Hg: C, 47.3; H, 5.8; N, 3.7; S, 8.4. Found: C, 47.3; H, 5.9; N, 3.6; S, 8.9%. IR (cm1): ma(CO2) 1547s; ms(CO2) 1343vs; d(NH2+) 1618s. 1H NMR (dmso-d6, ppm): d C(3)H 7.73 (s, 2), CH3 1.18, NH2+ 8.85. 13 C NMR (dmso, ppm): d C(1) 170.7, C(2) 135.9, C(3) 131.2, CH 46.0, CH3 18.7. 199Hg NMR (dmso-d6, ppm): d 784.7. FAB peaks at m/z (%) = 662.2 (1.20) ([HQ][Hg(pspa)2] + 2H); 102.1 (100)
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(HQ). Recrystallization from an ethanol–dmso mixture gave crystals suitable for an X-ray study. 2.2.3. [HQ]2[Hg(fspa)2] (2) H2fspa (0.90 g, 0.0053 mmol), Hg(OAc)2 (0.45 g, 0.0026 mmol), diisopropylamine (0.54 g, 0.0053 mmol), ethanol (50 mL), yellow solid, yield: 48.2%, M.p.: 172 °C. Anal. Calc. for C26H40N2O6S2Hg: C, 42.1; H, 5.4; N, 3.8; S, 8.2. Found: C, 42.2; H, 5.7; N, 3.2; S, 8.6%. IR (cm1): ma(CO2) 1543s; ms(CO2) 1344vs; d(NH2+) 1620s. 1 H NMR (dmso-d6, ppm): d C(3)H 7.61 (s, 2), CH 3.27 (q, 4), CH3 1.17 (d, 24). 13C NMR (dmso-d6, ppm): d C(1) 169.9, C(2) 135.9, C(3) 141.4, CH 45.9, CH3 18.70. 199Hg NMR (dmso-d6, ppm): d 780.7. 199Hg NMR (CDCl3, ppm): d 853. FAB peaks at m/z (%) = 642.2 (0.96) ([HQ][Hg(fspa)2] + 2H); 102.1 (100.00) (HQ). Crystals suitable for an X-ray study were obtained from the mother liquor. 2.2.4. [HQ]2[Hg(tspa)2] (3) H2tspa (0.90 g, 0.0048 mmol), Hg(OAc)2 (0.77 g, 0.0024 mmol), diisopropylamine (0.49 g, 0.0048 mmol), ethanol (50 mL), white solid, yield: 68.7%, M.p.: 168 °C. Anal. Calc. for C26H40N2O4S4Hg: C, 40.4; H, 5.2; N, 3.6; S, 16.6. Found: C, 39.8; H, 5.1; N, 3.3; S, 16.1%. IR (cm1): ma(CO2) 1548s; ms(CO2) 1335vs; d(NH2+) 1612m. 1H NMR (dmso-d6, ppm): d C(3)H 7.97 (s, 2), CH 3.27 (q, 4), CH3 1.16 (d, 24), NH2+ 8.96 (s, br, 4). 13C NMR (dmso-d6, ppm): d C(1) 170.2, C(2) 134.5, C(3) 124.6, CH 45.9, CH3 18.7. 199Hg NMR (dmso-d6, ppm): d –810.2. FAB peaks at m/z (%) = 673.1 (0.82) ([HQ][Hg(tspa)2] + H); 102.1 (100) (HQ). Crystals suitable for an X-ray study were obtained by recrystallization from a dmso/dmf mixture. 2.2.5. Compounds of the type [HQ][PhHg(L)] These compounds were prepared by reacting the appropriate sulfanylpropenoic acid, diisopropylamine and PhHg(OAc) in ethanol in a 1:1:1 molar ratio. The solid formed after agitation of the mixture at room temperature was filtered off and vacuum dried. 2.2.6. [HQ][PhHg(pspa)] (4) H2pspa (0.90 g, 0.005 mmol), PhHg(OAc) (1.69 g, 0.005 mmol), diisopropylamine (0.51 g, 0.005 mmol), ethanol (50 mL), white solid, yield: 69.7%, M.p.: 183 °C. Anal. Calc. for C21H27NO2SHg: C, 45.2; H, 4.9; N, 2.5; S, 5.7. Found: C, 45.0; H, 4.8; N, 2.7; S, 5.8%. IR (cm1): ma(CO2) 1553s; ms(CO2) 1340vs; d(NH2+) 1618m. 1H NMR (dmso-d6, ppm): d C(3)H 7.66 (s, 1), CH 3.30 (q, 4), CH3 1.19 (d, 24), NH2+ 8.55 (s,br, 1). 13C NMR (dmso-d6, ppm): d C(1) 171.5, C(2) 137.9, C(3) 131.0, CH 46.0, CH3 18.9. 199Hg NMR (dmso-d6, ppm): d 755.4. 199Hg NMR (CDCl3, ppm): d 820.9. FAB peaks at m/z (%) = 558.10 (1.44) ([HQ][PhHg(pspa)] + H); 457.98 (1.68) ([PhHg(pspa)] + H); 102.09 (100.00) (HQ). Crystals suitable for an X-ray study were obtained from the mother liquor. 2.2.7. [HQ][PhHg(fspa)] (5) H2fspa (0.90 g, 0.0053 mmol), PhHg(OAc) (1.79 g, 0.0053 mmol), diisopropylamine (0.54 g, 0.0053 mmol), ethanol (50 mL), white solid, yield: 76.6%, M.p.: 172 °C. Anal. Calc. for C19H25NO3SHg: C, 41.6; H, 4.6; N, 2.6; S, 5.8. Found: C, 41.8; H, 4.6; N, 2.4; S, 5.4%. IR (cm1): ma(CO2) 1546 m; ms(CO2) 1334vs; d(NH2+) 1620m. 1H NMR (dmso-d6, ppm): d C(3)H 7.56 (s, 1), CH 3.30, CH3 1.16 (d, 12), NH2+ 8.68 (s,br). 13C NMR (dmso-d6, ppm): d C(1) 170.9, C(2) 141.4, C(3) 137.5, CH 46.0, CH3 18.8. 199Hg NMR (dmso-d6, ppm): d 776.1. (CDCl3, ppm): d 861.5. FAB peaks at m/z (%) = 549.07 (1.31) ([HQ][PhHg(fspa)]); 447.94 (2.50) ([PhHg(fspa)] + H); 102.09 (100.00) (HQ). Crystals suitable for an X-ray study were obtained from the mother liquor.
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2.2.8. [HQ][PhHg(tspa)] (6) H2tspa (0.90 g, 0.0048 mmol), PhHg(OAc) (1.63 g, 0.0048 mmol), diisopropylamine (0.49 g, 0.0048 mmol), ethanol (50 mL), white solid, yield: 78.7%, M.p.: 184 °C. Anal. Calc. for C19H25NO2S2Hg: C, 40.5; H, 4.4; N, 2.4; S, 11.4. Found: C, 40.3; H, 4.0; N, 2.3; S, 11.0%. IR (cm1): ma(CO2) 1552s; ms(CO2) 1335vs; d(NH2+) 1617m. 1H NMR (dmso-d6, ppm): d C(3)H 7.97 (s, 1), CH 3.30 (q, 2), CH3 1.20 (d, 12), NH2+ 8.84 (s, br). 13C NMR (dmso-d6, ppm): d C(1) 171.38, C(2) 134.9, C(3) 126.2, CH 45.9, CH3 18.7. 199Hg NMR (dmso-d6, ppm): d 788.8. 199Hg NMR (CDCl3, ppm): d 839.4. FAB peaks at m/z (%) = 565.06 (1.98) ([HQ][PhHg(tspa)]); 463.93 (3.21) ([PhHg(tspa)] + H); 102.09 (100.00) (HQ). Crystals suitable for an X-ray study were obtained from the mother liquor.
absorption were carried out. The structures of 1–4 were solved using direct methods but by the heavy atom Patterson method in 5 and 6 [21]. In the refinement the non-H atoms were treated anisotropically [21]. The H atoms were localized from difference Fourier maps and refined as riders (N–H 0.90, C–H 0.93–0.98 Å) [21], except in 1 and 3 where the atomic position and isotropic temperature factor were also refined. The scattering factors were taken from International Tables for Crystallography [22]. The main calculations were performed with SHELXL-97 [21] and PLATON [20] and figures were plotted with ZORTEP [23] and MERCURY [24].
3. Results and discussion 2.3. X-ray studies 3.1. Compounds of the type [HQ]2[Hg(L)2] Single crystals were mounted on glass fibres in Bruker Smart 1000 CCD (1–3) or Enraf-Nonius MACH3 (4–6) automatic diffractometers. Data were collected at 293 K using Mo Ka radiation (k = 0.71073 Å). The crystal data, experimental details and refinement results are summarized in Table 1. Corrections for Lorentz effects, polarization [17] and multi-scan (SADABS) [18] for 1–3 or semi-empirical (w scan) [19,20] for 4–6
The reaction of diisopropylamine, the corresponding H2L acid and Hg(OAc)2 in ethanol in a 2:2:1 molar ratio gave rise to solids with this composition. In all the cases the FAB spectra show peaks for the protonated [HQ][Hg(L)2] species. The compounds are soluble in dmso and dmf but insoluble or sparingly soluble in water, ethanol, acetone, chloroform and acetonitrile.
Table 1 Crystal structure and refinement data for [HQ]2[Hg(pspa)2] (1), [HQ]2[Hg(fspa)2] (2), [HQ]2[Hg(tspa)2] (3), [HQ][PhHg(pspa)] (4), [HQ2[PhHg(fspa)] (5) and [HQ][PhHg(tspa)] (6) Compound
[HQ]2[Hg(pspa)2] (1)
[HQ]2[Hg(fspa)2] (2)
[HQ]2[Hg(tspa)2] (3)
[HQ][PhHg(pspa)] (4)
[HQ][PhHg(fspa)] (5)
[HQ][PhHg(tspa)] (6)
Empirical formula Formula weight Temperature (K) Wavelength (Å) Crystal system, space group Unit cell dimensions a (Å) b (Å) c (Å) a (°) b (°) c (°) V (Å3) Z, Dcalc (Mg/m3) Absorption coefficient (mm1) F (0 0 0) Crystal size (mm) H Range for data collection (°) Index ranges
C30H44N2O4S2Hg 761.38 293(2) 0.71073 monoclinic, P2(1)/n
C26H40N2O6S2Hg 741.31 293(2) 0.71073 triclinic, P 1
C26H40N2O4S4Hg 773.43 293(2) 0.71073 monoclinic, P2(1)/c
C21H27NO2SHg 558.09 293(2) 0.71073 monoclinic, P2(1)/c
C19H25NO3SHg 548.05 293(2) 0.71073 orthorhombic, Pbca
C19H25NO2S2Hg 564.11 293(2) 0.71073 monoclinic, P2(1)/c
14.3539(11) 15.9545(13) 15.6774(12)
14.079(4) 15.321(4) 16.238(5)
8.659(2) 22.182(4) 11.092(4)
11.122(2) 17.062(4) 21.505(4)
8.300(2) 22.25(4) 11.164(2)
112.574(5)
94.80(2)
94.33(2)
94.33(2)
3345.5(5) 4, 1.512 4.759
13.9291(9) 14.712(1) 18.109(1) 92.665(1) 111.939(1) 110.151(1) 3165.5(3) 4, 1.555 5.032
3234.2(16) 4, 1.588 5.049
2123.0(8) 4, 1.746 7.362
4080.6(14) 8, 1.784 7.662
2056.1(8) 4, 1.822 7.701
1528 0.22 0.21 0.15 1.65–28.05
1480 0.04 0.15 0.08 1.64–28.01
1544 0.14 0.15 0.24 1.90–27.88
1088 0.35 0.30 0.15 2.36–27.97
2128 0.35 0.25 0.15 2.38–27.97
1096 0.40 0.30 0.25 3.07–27.98
15 6 h 6 18, 19 6 k 6 20, 19 6 l 6 20 18 192/7388 [0.0664]
14 6 h 6 18, 19 6 k 6 19, 23 6 l 6 23 18 142/12 632 [0.0488]
18 6 h 6 18, 20 6 k 6 20, 21 6 l 6 21 24 213/7415 [0.0982]
11 6 h 6 0, 29 6 k 6 0, 14 6 l 6 14 5444/5123 [0.0479]
0 6 h 6 14, 22 6 k 6 0, 0 6 l 6 28 4909/4908 [1.0764]
10 6 h 6 10, 29 6 k 6 0, 14 6 l 6 0 1575/4936 [0.0506]
91.0% (h = 28.05) multiscan
96.1% (h = 27.88) semi-empirical from equivalents 1.000 and 0.644
97.5% (h = 27.9) semi-empirical from equivalents 0.971 and 0.486
90.3% (h = 27.97) psi scan
97.5% (h = 27.98) psi scan
1.000 and 0.486
82.4% (h = 28.01°) semi-empirical from equivalents 1.000 and 0.479
0.968 and 0.515
0.982 and 0.546
full-matrix leastsquares on F2 7388/0/364 0.704 R1 = 0.0390, wR2 = 0.0460 R1 = 0.1404 wR2 = 0.0570 0.868 and 0.679
full-matrix leastsquares on F2 12632/683 0.567 R1 = 0.0467, wR2 = 0.1038 R1 = 0.1193, wR2 = 0.1327 1.290 and 1.098
full-matrix leastsquares on F2 7415/346 1.012 R1 = 0.0740, wR2 = 0.1195 R1 = 0.1661, wR2 = 0.1431 2.096 and 1.014
full-matrix leastsquares on F2 5123/239 1.018 R1 = 0.0450, wR2 = 0.1018 R1 = 0.1653, wR2 = 0.1337 1.098 and 1.359
full-matrix leastsquares on F2 4908/230 0–955 R1 = 0.0457, wR2 = 0.0892 R1 = 0.2123, wR2 = 0.1317 0.866 and 1.206
full-matrix leastsquares on F2 4936/230 0.955 R1 = 0.0466 wR2 = 0.0792 R1 = 0.1737, wR2 = 0.1043 1.536 and 0.852
Reflections collected/ unique [Rint] Completeness to theta Absorption correction Maximum and minimum transmission Refinement method Data/parameters Goodness-of-fit on F2 Final R indices [I > 2r (I)] R indices (all data) Largest difference in peak and hole (e A3)
111.280(2)
J.S. Casas et al. / Polyhedron 27 (2008) 2436–2446
3.1.1. Description of the structures of [HQ]2[Hg(pspa)2] (1), [HQ]2[Hg(fspa)2] (2) and [HQ]2[Hg(tspa)2] (3) Crystals suitable for X-ray study were obtained for compounds derived from H2pspa, H2fspa and H2tspa. As the structures have significant similarities they are discussed together. In all cases the crystals contain diisopropylammonium cations and anions of the type [Hg(L)2]2, where L (pspa2, fspa2 and tpsa2) behaves as a bidentate chelate ligand bonded to Hg through an O atom of the carboxylate group and the S atom of the deprotonated SH group. The numbering scheme for the [Hg(L)2]2 anions is shown in Fig. 1 and selected values for the bond distances (Å) and angles (°) are given in Tables 2 and 3. The Hg atom in all the anions is tetracoordinated in an HgO2S2 environment, with slightly different parameters in molecules A
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and B for [Hg(fspa)2]2 (Table 3). The Hg–S bond distances range from 2.333(2) Å for [Hg(pspa)2]2 to 2.349(3) Å for [Hg(tspa)2]2. These values are slightly shorter than those found in Hg(II) compounds with S,S0 -bidentate ligands [25] to give an HgS4 environment and are in the range found for linear S–Hg–S bis-thiolato complexes of Hg(II) [26]; the Hg–O bond distances range from 2.499(7) Å in [Hg(tspa)2] to 2.553(4) Å in [Hg(pspa)2]2. As far as the angles around the metal are concerned, the value for the bite angle of the ligand, which ranges from 77.56(17)° for [Hg(fspa)2]2 to 80.04(15)° for [Hg(tspa)2]2, is lower; the largest value is found for the S–Hg–S angle, which ranges from 168.03(9)° in [Hg(tspa)2]2 to 171.83(8)° in the fspa derivative. In order to investigate the influence that a possible Hg–S interaction between neighbouring molecules has on the S–Hg–S angle
Fig. 1. ORTEP drawing showing the structures of the [Hg(pspa)2]2 (I), the two molecules A(II) and B(III) of the [Hg(fspa)2]2 and [Hg(tspa)2]2 (IV) anions with the numbering scheme. The ellipsoids are drawn at the 30% probability level.
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Table 2 Selected bond lengths (Å) and angles (°) in [HQ]2[Hg(pspa)2] (1) and [HQ]2[Hg(tspa)2] (3)
(a) Hg environment Hg(1)–O(11) Hg(1)–O(21) Hg(1)–S(1)#1 Hg(1)–S(1) Hg(1)–S(2) O(11)–Hg(1)–S(1) O(11)–Hg(1)–S(2) S(1)–Hg(1)–S(2) S(1)#1–Hg(1)–S(2) S(1)#1–Hg(1)–S(1) O(21)–Hg(1)–S(1) O(21)–Hg(1)–S(2) O(11)–Hg(1)–O(21) O(11)–Hg(1)–S(1)#1 O(21)–Hg(1)–S(1)#1 (b) Ligand S(1)–C(12) O(11)–C(11) O(12)–C(11) S(2)–C(22) O(21)–C(21) O(22)–C(21) O(12)–C(11)–O(11) O(12)–C(11)–C(12) O(11)–C(11)–C(12) C(13)–C(12)–S(1) C(11)–C(12)–S(1) O(22)–C(21)–O(21) O(22)–C(21)–C(22) O(21)–C(21)–C(22) C(23)–C(22)–S(2) C(21)–C(22)–S(2) a
[HQ]2[Hg(pspa)2]a (1)
[HQ]2[Hg(tspa)2] (3)
2.510(4) 2.553(4) 3.427(2) 2.346(2) 2.333(2) 78.26(10) 110.53(11) 169.93(6) 79.45(5) 96.76(4) 106.62(11) 77.77(11) 96.95(14) 85.83(9) 156.55(11)
2.499(7) 2.518(6)
1.746(6) 1.258(6) 1.255(6)
1.747(10) 1.223(10) 1.259(11) 1.750(9) 1.269(10) 1.244(10) 126.1(9) 117.0(8) 116.8(9) 120.8(7) 121.5(7) 123.2(8) 118.4(9) 118.4(8) 122.0(7) 120.9(7)
2.349(3) 2.346(3) 79.35(16) 109.19(15) 168.03(9)
106.71(16) 80.04(15) 102.9(2)
123.3(7) 118.4(6) 118.3(6) 121.1(5) 121.6(5)
Symmetry operations: #1 x, y, z.
Table 3 Selected bond lengths (Å) and angles (°) in [HQ]2[Hg(fspa)2] (2) (a) Hg environment Hg(1)–O(11A) Hg(1)–O(21A) Hg(2)–O(11B) Hg(2)–O(21B) O(11A)–Hg(1)–S(11A) O(21A)–Hg(1)–S(11A) S(11A)–Hg(1)–S(21A) O(11B)–Hg(2)–S(11B) O(21B)–Hg(2)–S(11B) S(11B)–Hg(2)–S(21B) (b) Ligand S(11A)–C(12A) S(11B)–C(12B) O(11A)–C(11A) O(11B)–C(11B) O(12A)–C(11A) O(12B)–C(11B) O(12A)–C(11A)–O(11A) O(12B)–C(11B)–O(11B) O(12A)–C(11A)–C(12A) O(12B)–C(11B)–C(12B) O(11A)–C(11A)–C(12A) O(11B)–C(11B)–C(12B) C(13A)–C(12A)–S(11A) C(13B)–C(12B)–S(11B) C(11A)–C(12A)–S(11A) C(11B)–C(12B)–S(11B) C(13A)–C(14A)–O(13A) C(13B)–C(14B)–O(13B)
2.550(7) 2.536(6) 2.549(6) 2.540(6) 77.56(17) 106.95(18) 171.83(8) 79.15(16) 107.86(16) 170.90(8) 1.766(9) 1.750(9) 1.246(11) 1.282(11) 1.227(11) 1.269(10) 124.7(9) 122.8(9) 117.5(10) 119.5(9) 117.7(9) 117.6(8) 120.7(7) 120.5(7) 121.3(8) 122.9(7) 114.1(10) 113.8(9)
Hg(1)–S(11A) Hg(1)–S(21A) Hg(2)–S(11B) Hg(2)–S(21B) O(11A)–Hg(1)–S(21A) O(21A)–Hg(1)–S(21A) O(11A)–Hg(1)–O(21A) O(11B)–Hg(2)–S(21B) O(21B)–Hg(2)–S(21B) O(11B)–Hg(2)–O(21B) S(21A)–C(22A) S(21B)–C(22B) O(21A)–C(21A) O(21B)–C(21B) O(22A)–C(21A) O(22B)–C(21B) O(21A)–C(21A)–O(22A) O(21B)–C(21B)–O(22B) O(21A)–C(21A)–C(22A) O(21B)–C(21B)–C(22B) O(22A)–C(21A)–C(22A) O(22B)–C(21B)–C(22B) C(23A)–C(22A)–S(21A) C(23B)–C(22B)–S(21B) C(21A)–C(22A)–S(21A) C(21B)–C(22B)–S(21B) C(23A)–C(24A)–O(23A) C(23B)–C(24B)–O(23B)
2.337(3) 2.334(3) 2.347(2) 2.336(2) 108.03(17) 78.54(18) 98.0(2) 107.19(16) 78.09(16) 98.3(2) 1.752(9) 1.758(9) 1.245(11) 1.261(10) 1.224(11) 1.231(10) 123.0(10) 123.3(8) 117.6(9) 117.7(8) 119.4(10) 118.9(9) 120.9(7) 120.6(7) 122.7(7) 122.6(7) 113.4(9) 112.4(9)
of the Hg kernel, we analysed these distances. Only in the pspa derivative 1 were interactions found that could be considered sig-
nificant [Hg–S(1)#1 = 3.4272(16) Å]. In the other two cases the intermolecular Hg–S bond distances are greater than 4 Å. At this point we must underline the variability in the sum of the van der Waals radii for Hg and S (on using the value reported by Bondi [27] we obtained a value of 3.3 Å for the sum of the two radii, which was revised to 3.7 Å [13] or to 4.016 Å on using the van der Waals radii reported by Batsanov [28]). However, the influence of this intermolecular interaction on the bond distances and angles of the Hg kernel does not seem to be significant. The intermolecular interaction is also absent in [Hg(Htsal)2] [10] and [Hg(Htsal)2] 1,4-dioxane [29] (H2tsal = thiosalicylic acid). The former compound, which cocrystallizes with [Hg2(tsal)2(PPh3)2], has parameters [Hg–S: 2.3444(12), 2.3392(12) Å; Hg–O: 2.641(3), 2.682(3) Å; S–Hg–S: 170.12(4)°] close to those found in this work, although the Hg–O bond distances are longer and the S–Hg–S angle slightly wider. Other examples in the literature include the 2,2,6, 6-tetramethyl-3,5-heptanedione [30], the 2-dimethylamino-3-4dioxo-cyclobut-1-en-thiolate [26] and the N-(piperidylthiocarbonylcarbonyl)benzamide [31] mercury(II) complexes and these also have, as in the case of the thiosalicylic acid, wider S–Hg–S bond angles than those found in this work. For the Hg atom in the thiosalicylic acid derivative Henderson and Nicholson [10], taking into account the large tetrahedral distortion in the kernel, proposed a nido-trigonal bipyramidal coordination geometry or even an S–Hg–S linear geometry with a weak Hg O interaction. The compounds described in this work have a shorter Hg–O bond distance than that found in the thiosalicylic acid derivative, making the nido-tbp geometry the more appropriate description. The planarity of the L2 fragment is different in the three structures. In [Hg(pspa)2]2 the angle between the idealized plane of the chelate ring and that of the C(14)–C(19) phenyl ring is 22.6° and this value is 12.26° for the other L fragment. Equivalent angles are 12.68° and 10.46° in molecule A and 21.68° and 5.58° in molecule B for the fspa derivative and 10.61° and 15.52° in [HQ]2[Hg(tspa)2], although there is a lack of planarity in the chelate ring in the latter compound (rms [Hg(1)/S(1)/O(11)/C(11)/C(12)] = 0.0917° and rms [Hg(1)/S(2)/O(21)/C(21)/C(22)] = 0.0970°). The diisopropylammonium cation in each of the three structures has parameters that are comparable with other previously described examples [32,33]. Table 4 Structural parameters (Å, °) describing intermolecular hydrogen bonding in the complexes [HQ]2[Hg(L)2]a D–H
H A
D A
D–H A
[HQ]2[Hg(pspa)2] N(1)–H(1A) O(12)#1 N(1)–H(1B) O(21) N(2)–H(2A) O(11)#1 N(2)–H(2B) O(22)
0.91(5) 1.09(5) 0.87(5) 0.97(5)
1.82(5) 1.67(5) 2.00(5) 1.72(5)
2.722(6) 2.761(6) 2.806(6) 2.692(6)
170(5)° 176(4)° 155(5)° 175(5)
[HQ]2[Hg(fspa)2] N(11)–H(11A) O(12B)#2 N(11)–H(11B) O(11B) N(41)–H(41A) O(21B) N(41)–H(41B) O(12A)#4 N(21)–H(21A) O(22B) N(21)–H(21B) O(11A)#5 N(31)–H(31A) O(22A) N(31)–H(31B) O(21A)#3
0.90 0.90 0.90 0.90 0.90 0.90 0.90 0.90
1.82 1.89 1.84 1.94 1.95 1.88 1.84 1.89
2.708(9) 2.777(9) 2.719(9) 2.827(9) 2.831(9) 2.761(9) 2.737(9) 2.776(9)
169.6° 166.2° 163.8° 168.4° 166.2° 165.3° 172.1° 167.3°
[HQ]2[Hg(tspa)2] N(1)–H(11A) O(22)#6 N(1)–H(11B) O(11) N(2)–H(21A) O(21)#7 N(2)–H(21B) O(12)
0.92(9) 0.90(9) 1.01(9) 0.81(9)
1.84(9) 1.93(9) 1.79(9) 2.00(9)
2.738(10) 2.807(10) 2.769(10) 2.801(10)
164(8)° 162(8)° 163(7)° 170(9)°
a Symmetry code: #1 x + 1/2, y + 1/2, z + 1/2; #2 x + 2, y + 1, z + 1; #3 x + 2, y + 2, z + 1; #4 x 1, y 1, z; #5 x,y 1,z; #6 x,y + 1/2, z + 1/2; #7 x, y + 1/2, z + 1/2.
J.S. Casas et al. / Polyhedron 27 (2008) 2436–2446
The [Hg(L)]2 anions and the [HQ]+ cations are hydrogen bonded through the NH2 group of the cation and the O atoms of the carboxylate group. The metric parameters for these bonds are included in Table 4. In the three structures the [HQ]+ cation bridges two dianionic [Hg(L)]2 units but the final arrangement is different. In [HQ]2[Hg(pspa)2], two [HQ]+ units establish a double-bridge between two [Hg(pspa)2]2 anions to afford zig-zag chains (Fig. 2a) parallel to the crystallographic direction {1 1 2}. These chains are schematically represented in Fig. 2b using a rod as a symbol for the anion and a left/right arrow as a symbol for the cation. The chains are packed in the crystallographic c-axis, as shown in Fig. 2c, in which the hydrogen bond and the weak Hg S interaction are underlined. The same interaction in [HQ]2[Hg(fspa)2] generates rack-chains running parallel to the crystallographic b-axis (Fig. 3) and these are also represented using the same symbols. In contrast to the above situation, 2D molecular association is observed in the thiophene derivative. The crystal structure may be described in terms of the formation of the unit shown in Fig. 4a by bridge of four [HQ]+ units between four [Hg(tspa)2]2 units. The cyclic unit is associated with another of these units through interactions analogous to those described above (Fig. 4b). The resulting sheet is parallel to the crystallographic bc-plane. 3.1.2. Spectroscopy The IR spectra of the [HQ]2[Hg(L)2] complexes do not show a m(SH) band, which is located near 2550 cm1 in the spectra of
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the free ligands. Furthermore, the vibrations of the CO2H group [m(C@O) = 1670, 1665 and 1673 cm1 for H2pspa, H2fspa and H2tspa are replaced by bands typical of a carboxylate group with [mas(CO2)] observed between 1548 and 1543 cm1 and [msym(CO2)] between 1344 and 1335 cm1. As in other compounds in which the HQ cation is hydrogen bonded [12,34] to the carboxylate group the Dm (=masCO2–msymCO2) parameter has values smaller than those found for a monodentate carboxylate group [35], which was attributed [34] to the effect of the N–H O hydrogen bond on the structural parameters of the carboxylate group. A strong band at around 1610 cm1 in all the spectra was assigned [36] to the d(NH2) vibration of the diisopropylammonium cation. The 1H NMR spectra of the complexes in all cases show the typical signals of the diisopropylammonium cation and the absence of signals attibutable to SH and COOH groups is consistent with bideprotonation of the ligand. These spectra show, in general, a shift of the C(3)–H signal to higher field on complexation, which suggests the persistence of the Hg–S bond in solution. The persistence of the S-coordination is confirmed [37,38] by the shift of the C(3) signal in the 13C NMR spectra. In these spectra the C(1) signals are in positions close to those found [34,39,40] for compounds with a monodentate coordinated carboxylate group, thus suggesting the persistence in solution of the coordination mode found in the solid state. The 199Hg NMR spectra show only a signal located between 780.7 and 810.2 ppm, indicating the presence of only one type
Fig. 2. (a) A view of the polymeric structure of [HQ]2[Hg(pspa)2] (1) and (b) a schematic view of the structure; and (c) details of the hydrogen bonding and Hg S intermolecular interactions.
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J.S. Casas et al. / Polyhedron 27 (2008) 2436–2446
Fig. 3. (a) A view of the polymeric structure of [HQ]2[Hg(fspa)2] (2) and (b) a schematic view of the structure.
Fig. 4. (a) A partial view of the polymeric structure of [HQ]2[Hg(tspa)2] (3) and (b) a schematic view of the structure.
of chemical environment for Hg(II). The position of the signal is close to the positions found for other four-coordinated Hg(II) complexes that have the HgS2N2 kernel [41]. In the case of 2 the spectrum was recorded in dmso/dmso-d6 (780.7 ppm) and in CDCl3 (853.0 ppm). The difference in the positions of the signal in these spectra is within the accepted range [42] for the influence of the solvent, suggesting the same chemical environment for the metal in both solvents, thus excluding dmso coordination. The additional coordination of these solvent molecules would increase the coordination number and should move the d (199Hg) signal to higher frequencies [41]. 3.2. Compounds of the type [HQ][PhHg(L)] Reaction of diisopropylamine, the corresponding sulfanylpropenoic acid and PhHg(OAc) in ethanol in a 1:1:1 molar ratio gave solids with this composition. The FAB mass spectra show peaks for the [HQ][HgPh(L)] molecular ion.
3.2.1. Description of the structures of [HQ][PhHg(pspa)] (4), [HQ][PhHg(fspa)] (5) and [HQ][PhHg(tspa)] (6) Single crystals suitable for X-ray studies were obtained for the three phenyl mercury complexes. The similarity between the structures, indeed the structures of 4 and 6 are isotypic, again means that these compounds will be discussed together. The three crystals contain diisopropylammonium cations and [HgPh(L)] anions that interact through hydrogen bonds. The numbering scheme for each compound is shown in Fig. 5 and selected bond distances (Å) and angles (°) are listed in Table 5. In each anion the ligand is S,O-bidentate chelate to give a HgCOS kernel. It should be noted that such an example in which O and S atoms from the same ligand has not been found previously [13,14] for phenylmercury(II) derivatives. In this kernel the metal adopts a significantly distorted T-environment. In this environment the Hg–C bond distance is about 2.065 Å, which is normal for phenylmercury(II) derivatives [13] and the Hg–O and Hg–S
J.S. Casas et al. / Polyhedron 27 (2008) 2436–2446
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Fig. 5. ORTEP drawing showing the structures of [HQ][PhHg(pspa)] (4) (I), [HQ][PhHg(fspa)] (5) (II) and [HQ][PhHg(tspa)] (6) (III) with the numbering scheme. The ellipsoids are drawn at the 30% probability level.
bond distances are close to 2.565 and 2.355 Å, respectively. The values for the O–Hg–S, C–Hg–O and C–Hg–S angles are about 76.50°, 106.0° and 174.0°, respectively. The sum of these angles is close to 360° in the three anions.
For other kernels values for the Hg–S bond distance between 2.357(3) and 2.405(1) Å were previously described for PhHg+ compounds with thiosemicarbazones [43] and ligands containing P–S bonds [44] and values larger than 2.370 Å have also been described
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Table 5 Selected bond lengths (Å) and angles (°) in [HQ][PhHg(pspa)] (4), [HQ][PhHg(fspa)] (5) and [HQ][PhHg(tspa)] (6)
(a) Hg environment Hg(1)–O(1) Hg(1)–S(1) Hg(1)–C(11) Hg(1)–S(1)#1 O(1)–Hg(1)–S(1) O(1)–Hg(1)– S(1)#1 S(1)–Hg(1)– S(1)#1 C(11)–Hg(1)–S(1) C(11)–Hg(1)– S(1)#1 C(11)–Hg(1)– O(1) (b) Ligand S(1)–C(2) O(1)–C(1) O(2)–C(1) O(2)–C(1)–O(1) O(2)–C(1)–C(2) O(1)–C(1)–C(2) C(3)–C(2)–S(1) C(1)–C(2)–S(1) a b
HQ][PhHg(pspa)]a (4)
[HQ][PhHg(fspa)] (5)
[HQ][PhHg(tspa)]b (6)
2.560(6) 2.360(3) 2.060(10) 3.381(3)a 76.04(16) 93.73(17)a
2.566(7) 2.353(3) 2.060(11) 3.316(3)b 76.49(18) 97.96(19)b
2.570(6) 2.354(2) 2.075(8) 3.593(3)a 77.23(14) 93.82(14)a
89.04(9)a
88.83(9)b
91.90(9)a
173.7(3) 95.6(3)a
174.3(3) 96.3(3)b
175.0(3) 91.4(3)a
107.9(3)
105.2(3)
106.3(3)
1.767(9) 1.259(11) 1.241(11) 123.6(9) 117.3(9) 119.1(8) 122.9(7) 119.6(7)
1.765(10) 1.260(13) 1.243(13) 124.8(10) 116.4(11) 118.8(10) 122.6(8) 119.3(8)
1.759(8) 1.261(9) 1.231(9) 123.9(8) 117.5(8) 118.6(7) 121.6(6) 121.1(6)
Table 6 Structural parameters (Å, °) describing intermolecular hydrogen bonding in the complexes [HQ][HgPh(L)]a D–H
H A
D A
D–H A
[HQ][PhHg(pspa)] N(1)–H(1A) O(1)#1 N(1)–H(1B) O(2)
0.90 0.90
1.95 1.84
2.833(10) 2.730(9)
167.1 169.1
[HQ][PhHg(fspa)] N(1)–H(1A) O(1)#2 N(1)–H(1B) O(2)
0.90 0.90
1.98 1.81
2.855(11) 2.703(10)
164.9 169.7
[HQ][PhHg(tspa)] N(1)–H(1A) O(1) #1 N(1)–H(1B) O(2)
0.90 0.90
1.93 1.84
2.809(9) 2.734(8)
165.8 169.1
a
Symmetry operation: #1 x + 1, y + 1, z + 1. Symmetry operation: #1 x + 1, y + 1, z.
[45–49]. The values found for the Hg–O bonds can be considered [50] typical of relatively strong bonds. These structures can be related with that of [HgPh(S2COEt)] [51], in which an S-donor atom is coordinated to a PhHg+ fragment to give a practically linear C–Hg–S [176.1 (4)°] environment, and with that of [HgPh(pmbp)] (pmbp = 1-phenyl-3-methyl-4benzoylpyrazol-5-onato] [50] where the pmbp ligand has two O-donor atoms, both coordinated to the Hg atom to give an
Symmetry code: #1 = x + 1, y + 1, z; #2 = x, y + 1, z.
HgCO2 environment reminiscent of the HgCOS present in this case. The structural parameters for the latter compound [Hg–O(1): 2.585(9) Å; Hg–O(2): 2.087(7) Å; Hg–C: 2.040(11) Å; C–Hg–O(1): 112.1(4)°; C–Hg–O(2): 168.6(3)°; O(1)–Hg–O(2): 78.3(3)°] have some similarities with these structures if the O(2) atom, trans to C but closest to the Hg atom, is replaced by the S atom of the sulfanylpropenoic fragment; the bite of the ligand is also similar. The parameters for the diisopropylammonium cation are unremarkable and close to those previously described. In the three crystals there are weak interactions, which are weaker in the tspa derivative, and these are depicted in the structures of the pspa and fspa derivatives shown in Fig. 6. Similar interactions in methylmercury xanthates of the type MeHgS(S)COR (R = Et, iPr, CH2Ph) [45] lead to supramolecular structures, but in this case such interactions could be hindered by the hydrogen bonds that exist between the diisopropylammonium cations and the corresponding anions. The parameters for these bonds, which involve the NH2 group and the carboxylate group, are listed in Table 6. As observed in the complexes [HQ]2[Hg(L)2], the [HQ]+ units establish two hydrogen bonds with two molecules of [HgPh(L)]
Fig. 6. The polymeric structures of: (a) [HQ][PhHg(pspa)] (4) and (b) [HQ][PhHg(fspa)] (5).
J.S. Casas et al. / Polyhedron 27 (2008) 2436–2446
to afford centrosymmetric dimers. These units are now associated in chains running parallel to crystallographic c (compounds 4 and 6) or a (compound 5) axes (see Fig. 6) through the previously described weak intermolecular Hg–S interaction (Table 5). 3.2.2. Spectroscopy As for [HQ]2[Hg(L)], the IR spectra of 4, 5 and 6 do not show the m(SH) band and the vibrations of the CO2H group are replaced by bands typical of the carboxylate group. The Dm[ma(CO2)–ms(CO2)] values are again typical of a monodentate carboxylate group involved in N–H O hydrogen bonds. The 1H NMR spectra show the typical bands of the diisopropylammonium cation, lacking signals attributable to SH and COOH. Furthermore, the spectra show a shift of the C(3)–H signal to higher field on complexation, suggesting the persistence of the Hg–S bond in solution. The position of the C(3) signals in each of the 13C NMR spectra of the complexes again supports S-coordination and the position of the C(1) signal suggests that the carboxylate group remains coordinated in solution. Thus, as in the [HQ]2[Hg(L)2] complexes, the ligand remains S,O-coordinated in solution. The 199Hg NMR spectra of the three complexes show only one signal each. In CDCl3 the signals for 4, 5 and 6 are at 820.9, 861.5 and 839.4 ppm, respectively, and in dmso the signals range between 755.4 and 788.8 ppm. The position of the signal in the spectra in chloroform is close to those found for thiosemicarbazonates of phenylmercury(II) in which the metal is tricoordinated [43]. Once again, the difference between the value in CDCl3 and dmso-d6 suggest that this latter solvent does not increase the coordination number of the metal in comparison to that found in the solid state. 4. Conclusion In summary, two types of complexes [HQ]2[Hg(L)2] and [HQ][PhHg(L)] where HQ is diisopropylammonium and L a bideprotonated 3-(aryl)-2-sulfanylpropenoic acid have been synthesized and characterized. Among the [HQ]2[Hg(L)2] complexes this study has led to the structural characterization of the unusual HgO2S2 kernel built on the basis of S,O-bidentate donor ligands. The chelating ability of the corresponding 3-(phenyl)- and 3-(2-furyl)-2-sulfanylpropenoic acids previously used as chelating agents against mercury intoxication is thus confirmed. This S,O-coordination mode was recently described for the widely used chelating agent DMSA, which contains SH and COOH groups, against the diorganotin(IV) fragment [52]. However, X-ray absorption spectroscopy and DFT calculations [7] suggest the presence of metallated species mainly supported by Hg–S bonds in the case of mercury. The same coordination mode was found for the ligands in the [HQ][PhHg(L)] complexes and this enabled us to determine the structural parameters of the CHgSO kernel, which has been identified previously for S,O-bidentate chelate ligands. Both types of complex show different supramolecular structures based on N–H O hydrogen bonds, with weak Hg S interactions also present in some cases. Acknowledgement This work was supported by the Ministerio de Educación y Ciencia, Spain, under project BQU2002-04524-C02-01. Appendix A. Supplementary data CCDC 667931, 667932, 667933, 667934, 667935 and 667936 contain the supplementary crystallographic data for 1, 2, 3, 4, 5
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and 6. These data can be obtained free of charge via www.ccdc.cam.ac.uk/conts/retrieving.html, or from the Cambridge Crystallographic Data Centre, 12 Union Road, Cambridge CB2 1EZ, UK; fax: +44 1223 336 033; or e-mail: [email protected]. Supplementary data associated with this article can be found, in the online version, at doi:10.1016/j.poly.2008.04.034. References [1] T.W. Clarkson, L. Magos, Crit. Rev. Toxicol. 36 (2006) 609. [2] R.E. Hoffmeyer, S.P. Singh, C.J. Donan, A.R.S. Ross, R.J. Hughes, I.P. Pickering, G.N. George, Chem. Res. Toxicol. 19 (2006) 753. [3] (a) J.P.K. Rooney, Toxicology 234 (2007) 145. and references therein; (b) J.P.K. Rooney, Toxicology 238 (2007) 216. [4] J.G. Melnick, G. Parkin, Science 317 (2007) 225. [5] K.E. Pitts, A.O. Summers, Biochemistry 41 (2002) 10287. [6] E. Gopinath, T.C. Bruice, J. Am. Chem. Soc. 109 (1987) 7903. [7] N.G. Geoge, R.C. Price, J. Gailer, G.A. Buttigieg, M. Bonner Denton, H.H. Harris, J.J. Pickering, Chem. Res. Toxicol. 17 (2004) 999. [8] D.N. Kachru, S. Khandelwal, B.L. Sharma, S.K. Tandon, Pharm. Toxicol. 64 (1989) 182. [9] S. Khandelwal, D.N. Kachru, S.K. Tandon, Biochem. Int. 16 (1988) 869. [10] W. Henderson, B.K. Nicholson, Inorg. Chim. Acta 357 (2004) 2231. [11] J. Wagner, P. Vitali, J. Schorm, E. Giroux, Can. J. Chem. 55 (1977) 4028. [12] E. Barreiro, J.S. Casas, M.D. Couce, A. Sánchez, R. Seoane, J. Sordo, J.M. Varela, E.M. Vázquez-López, Dalton Trans. (2007) 3074. [13] J.S. Casas, M.S. García-Tasende, J. Sordo, Coord. Chem. Rev. 193–195 (1999) 283. [14] F.H. Allen, Acta Crystallogr., Sect. B 58 (2002) 380. [15] C. Gränacher, Helv. Chim. Acta 5 (1922) 610. [16] E. Campaigne, R.E. Cline, J. Org. Chem. 21 (1956) 32. [17] (a) Bruker Analytical Instrumentation, SAINT: SAX Area Detector Integration, 1996.; (b) Enraf-Nonius, CAD-4 Express Software. Version 5.1. Enraf-Nonius, Delft, The Netherlands, 1995; A.L. Spek, HELENA. A Program for data reduction of CAD4 data. University of Utrecht, The Netherlands, 1997. [18] G.M. Sheldrick, SADABS, Version 2.03, University of Göttingen, Germany, 2002. [19] A.C.T. North, D.C. Phillips, F.S. Mathews, Acta Crystallogr., Sect. A 24 (1968) 351. [20] A.L. Spek Platon, A Multipurpose Crystallographic Tool, University of Utrecht, The Netherlands, 1997. [21] G.M. Sheldrick, SHELXS97 and SHELXL97, Programs for the Refinement of Crystal Structures, University of Göttingen, Germany, 1997. [22] International Tables for X-ray Crystallography, vol. C, Kluwer Academic Publishers, Dordrecht, The Netherlands, 1995. [23] L. Zsolnai, ZORTEP. A Program for the Presentation of THERMAL Ellipsoids, University of Heidelberg, Germany, 1997. [24] MERCURY 1.2. A Program crystal structure visualisation and exploration. The Cambridge Crystallographic Data Centre. Cambridge. UK,
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