Reactions of a methylmercury zwitterionic thiolate complex [MeHg(Tab)]PF6 with various donor ligands: Relevance to methylmercury detoxification

Article abstract of DOI:10.1039/c2dt12219g

Reaction of MeHgI with Ag₂O in H₂O followed by addition of equimolar TabHPF₆ in MeCN gave rise to a methylmercury zwitterionic thiolate complex [MeHg(Tab)]PF₆ (1) (TabH = 4-(trimethylammonio)benzenethiol) in a high yield. Treatment of 1 with KI and KSCN afforded an anion exchange product [MeHg(Tab)]I·0.25H₂O (2·0.25H₂O) and [MeHg(Tab)]SCN (3), respectively, while that of 1 with equimolar Tab resulted in the formation of another MeHg/Tab compound [MeHg(Tab)₂]PF₆ (4). The cation of 2 or 3 shows an approximately linear structure in which the central Hg(ii) is coordinated by one C atom of one CH₃ group and one S atom of a Tab ligand. The Hg(ii) center of the cation of 4 is trigonally coordinated by one C atom of the CH ₃ group and two S atoms of two Tab ligands. The analogous reaction of 1 with NH₄SCN led to the cleavage of the Hg-C bond of 1 and the formation of a known four-coordinated Hg(ii)/Tab complex [Hg(Tab) ₂(SCN)₂] (5). When 4 was treated with 4,6-Me ₂pymSH or EtSH, another four-coordinated Hg(ii)/Tab complex [Hg(Tab)₄]₃(PF₆)₆ (6) was generated in a high yield. The Hg(ii) center of each cation of 6 is tetrahedrally coordinated by four S atoms of four Tab ligands. The results suggested that cleavage of the Hg-C bond in the methylmercury complex 1 could be completed by increasing the coordination number of its Hg(ii) center by S-donor ligands and protonating the methyl group by weak acids. The Royal Society of Chemistry 2012.

Full text of DOI:10.1039/c2dt12219g

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PAPER
Reactions of a methylmercury zwitterionic thiolate complex [MeHg(Tab)]PF6
with various donor ligands: relevance to methylmercury detoxification†
Ai-Xia Zheng,a Hong-Xi Li,a Kai-Peng Hou,a Jing Shi,a Hui-Fang Wang,a Zhi-Gang Rena and
Jian-Ping Lang*a,b
Received 19th November 2011, Accepted 4th December 2011
DOI: 10.1039/c2dt12219g
Reaction of MeHgI with Ag2O in H2O followed by addition of equimolar TabHPF6 in MeCN gave rise to
a methylmercury zwitterionic thiolate complex [MeHg(Tab)]PF6 (1) (TabH = 4-(trimethylammonio)
benzenethiol) in a high yield. Treatment of 1 with KI and KSCN afforded an anion exchange product
[MeHg(Tab)]I·0.25H2O (2·0.25H2O) and [MeHg(Tab)]SCN (3), respectively, while that of 1 with
equimolar Tab resulted in the formation of another MeHg/Tab compound [MeHg(Tab)2]PF6 (4). The
cation of 2 or 3 shows an approximately linear structure in which the central Hg(II) is coordinated by one
C atom of one CH3 group and one S atom of a Tab ligand. The Hg(II) center of the cation of 4 is
trigonally coordinated by one C atom of the CH3 group and two S atoms of two Tab ligands. The
analogous reaction of 1 with NH4SCN led to the cleavage of the Hg–C bond of 1 and the formation of a
known four-coordinated Hg(II)/Tab complex [Hg(Tab)2(SCN)2] (5). When 4 was treated with 4,6-
Me2pymSH or EtSH, another four-coordinated Hg(II)/Tab complex [Hg(Tab)4]3(PF6)6 (6) was generated
in a high yield. The Hg(II) center of each cation of 6 is tetrahedrally coordinated by four S atoms of four
Tab ligands. The results suggested that cleavage of the Hg–C bond in the methylmercury complex 1
could be completed by increasing the coordination number of its Hg(II) center by S-donor ligands and
protonating the methyl group by weak acids.
that involve the cleavage of the Hg–C bond and the reduction of
the mercuric residues to elemental mercury, Hg(0). The relevant
Introduction
The high affinity of organomercurials for thiols and their lipophi-
lic nature make them highly toxic to living organisms, causing
irreversible damage to the central nervous system.1 Owing to the
relatively high stability of the Hg–CH3 bond under physiological
conditions,2 the methylmercury ion, MeHg+, is probably the
most ubiquitous compound and one of most dangerous pollutant
agents, which has the ability to bio-accumulate and bio-magnify
in aquatic food webs.3 As a result, fishes in numerous lakes
worldwide contain ever-increasing MeHg concentrations.4 For
humans, the main pathway of exposure to MeHg is the consump-
tion of fish and sea mammals.5 For example, it has caused the
death of almost 2000 people by Minamata disease.6
catalysts that perform the above reactions are MerB, organomer-
curial lyase, and MerA, mercuric ion reductase.7,8 Much atten-
tion has been devoted, in the literature, to the study of the
mechanism of the Hg–C cleavage.9 Parkin et al. suggested that
the Hg–C bonds of the mercury alkyl complexes are readily
cleaved by a thiol which may be ascribed to the consequence of
the mercury center of two-coordinate being able to access higher
coordination numbers.10 Barbaro et al. also have demonstrated
that a higher coordination number of mercury can contribute to
the activation of the Hg–C bonds.11 Bencini et al. showed the
mechanism of the Hg–C bond cleavage by halogenic acids via
theoretical calculation.12
Therefore, it becomes critically important to find suitable
approaches to detoxification of organomercury compounds. In
nature, bacteria respond to the toxicity of the organomercurial
compounds by developing two peculiar resistance mechanisms
On the other hand, we are interested in the preparation of
metal complexes of a zwitterionic thiolate, 4-(trimethylammo-
nio)benzenethiol (TabH) which bears an ammonium group and a
sulfhydryl group and to some extent is similar to cysteine.13 As
an extension of this study, we carried out the reaction of MeHgI
with Ag2O and TabHPF6, and isolated a unique complex
[MeHg(Tab)]PF6 (1) in a high yield. In our previous reports, we
employed [Hg(Tab)2](PF6)2 to react with donor ligands (inor-
ganic anions, organic amines, nitrogen heterocyclic compounds
and organic carboxylic acids). In most of these reactions, the
linear coordination geometry of the Hg atom in [Hg(Tab)2](PF6)2
was further fulfilled by additional donor ligands. Do some donor
aCollege of Chemistry, Chemical Engineering and Materials Science,
Soochow University, Suzhou, 215123, P. R. China. E-mail: jplang@-
suda.edu.cn; Fax: 86-512-65880089
bState Key Laboratory of Coordination Chemistry, Nanjing University,
Nanjing, 210093, P. R. China
†Electronic supplementary information (ESI) available. CCDC reference
numbers 853202–853205. For ESI and crystallographic data in CIF or
other electronic format see DOI: 10.1039/c2dt12219g
This journal is © The Royal Society of Chemistry 2012
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ligands such as I−, SCN−, Tab and other weak acids react with
the Hg center of 1? Does the introduction of these ligands
change the linear structure of 1? Can the methyl group be readily
cleaved by these ligands? With these questions in mind, we
carried out the reactions of 1 with KI, KSCN, Tab, NH4SCN,
4,6-dimethylpyrimidine-2-thione (4,6-Me2pymSH) or EtSH, and
isolated two anion exchange products 2 and 3, one three-coordi-
nated MeHg/Tab complex 4, and two methyl-free products 5 and
6. These reactions along with the structural characterization of 2,
3, 4 and 6 may provide an interesting insight into detoxification
of organomercury compounds, which will be described below.
(w) cm−1. UV-Vis (MeCN; λmax, nm (ε, M−1 cm−1)): 246
(74200), 270 (45000). 1H NMR (400 MHz, DMSO-d6): δ
7.57–7.68 (m, 4H, Ph), 3.55 (s, 9H, NMe3), 0.71 (s, 3H, MeHg).
Synthesis of [MeHg(Tab)]SCN (3). Compound 3 was prepared
as colorless blocks in a similar way to that described for the
preparation of 2, except KSCN (10 mg, 0.1 mmol) was used in
place of KI. Yield: 36 mg (82% based on Hg). Anal. Calcd. for
C11H16HgN2S2: C, 29.96; H, 3.66; N, 6.35; S, 14.54. Found: C,
29.58; H, 3.41; N, 6.72; S, 14.83. IR (KBr disc): 3024 (w), 2054
(s), 1582 (w), 1491 (m), 1413 (w), 1126 (w), 1009 (w), 958 (w),
833 (w), 738 (w), 555 (w) cm−1. UV-Vis (MeCN; λmax, nm (ε,
1
M−1 cm−1)): 234 (67100), 272 (87200). H NMR (400 MHz,
Experimental
DMSO-d6): δ 7.55–7.70 (m, 4H, Ph), 3.54 (s, 9H, NMe3), 0.70
(s, 3H, MeHg).
Materials and methods
Synthesis of [MeHg(Tab)2](PF6) (4). Compound 4 was pre-
pared as colorless flakes in a similar way to that described for
the preparation of 2, except Tab (34 mg, 0.2 mmol) was used in
place of KI. Yield: 56 mg (80% based on Hg). Anal. Calcd. for
C19H29F6HgN2PS2: C, 32.82; H, 4.20; N, 4.03; S, 9.22. Found:
C, 32.45; H, 4.42; N, 3.93; S, 9.47. IR (KBr disc): 2963 (w),
1579 (w), 1488 (m), 1416 (w), 1126 (w), 1009 (w), 959 (w),
853 (s), 746 (w), 559 (m) cm−1. UV-Vis (MeCN; λmax, nm (ε,
TabHPF6 and 4,6-Me2pymSH were prepared according to the lit-
erature method.14 Tab was obtained from reactions of TabHPF6
with Et3N in MeCN followed by filtration and dried in vacuo.
Other chemicals and reagents were obtained from commercial
sources and used as received. IR spectra were recorded on Varian
Scamiter-1000 spectrometer (4000–400 cm−1) as the KBr disk.
The elemental analyses for C, H, N and S were performed on a
Carlo-Erba CHNO-S microanalyzer. 1H NMR spectra were
recorded at ambient temperature on a Varian UNITY-400 spec-
trometer. Chemical shifts are quoted relative to the solvent signal
in DMSO-d6. UV-vis spectra in MeCN were measured on a
Hitachi U-2810 spectrophotometer. ESI mass spectra were per-
formed on a DECAX-30000 LCQ Deca XP mass spectrometer
using MeCN as mobile phase.
1
M−1 cm−1)): 286 (48300). H NMR (400 MHz, DMSO-d6): δ
7.39–7.51 (m, 8H, Ph), 3.52 (s, 18H, NMe3), 0.64 (s, 3H, CH3).
Synthesis of [Hg(Tab)2(SCN)2] (5). Compound 5 was prepared
as colorless blocks in a similar way to that described for the
preparation of 2, except NH4SCN (10 mg, 0.2 mmol) was used
in place of KI. Yield: 23 mg (35% based on Hg). Anal. Calcd.
for C20H26HgN4S4: C, 36.88; H, 4.02; N, 8.60; S, 19.69. Found:
C, 36.54; H, 4.25; N, 8.39; S, 19.92. IR (KBr disc): 2080 (s),
1581 (w), 1489 (m), 1126 (w), 1010 (w), 953 (m), 831 (s), 740
(w), 555 (m) cm−1. UV-Vis (MeCN; λmax, nm (ε, M−1 cm−1)):
Caution! All mercury compounds are toxic and appropriate
safety precautions must be taken in handling these compounds.
Synthesis of [MeHg(Tab)]PF6 (1). To a solution of MeHgI
(116 mg, 0.2 mmol) in H2O (5 mL) was added Ag2O (23 mg,
0.1 mmol). The resulting mixture was stirred for 48 h to form a
yellow precipitation of AgI and filtered. The resulting colorless
solution was then treated with a solution containing TabHPF6
(62 mg, 0.2 mmol) in MeCN and the mixture was stirred for 2 h,
forming in a large amount of a white precipitate. The precipitate
was dried in vacuo to give 1 as a white powder. Yield: 98 mg
(92% based on Hg). Anal. Calcd. for C10H16F6HgNPS: C,
22.75; H, 3.06; N, 2.65; S, 6.07. Found: C, 22.43; H, 3.27; N,
2.98; S, 6.25. IR (KBr disc): 2916 (w), 1586 (w), 1490 (m),
1417 (w), 1127 (w), 1010 (w), 956 (m), 840 (s), 746 (w), 558
(m) cm−1. UV-Vis (MeCN; λmax, nm (ε, M−1 cm−1)): 272
1
271 (17400). H NMR (400 MHz, DMSO-d6): δ 7.51–7.63 (m,
4H, Ph), 3.58 (s, 9H, NMe3).
Synthesis of [Hg(Tab)4]3(PF6)6·MeOH·2MeCN (6·MeOH·2-
MeCN). A solution of 4,6-Me2pymSH (14 mg, 0.1 mmol) in
MeOH (2 mL) was treated with a solution of 4 (69 mg,
0.1 mmol) in MeCN (5 mL) to form a colorless solution. A
workup similar to that used in the isolation of 2 afforded color-
less flakes of 6·MeOH·2MeCN. Yield: 45 mg (42% based on
Hg). Anal. Calcd. for C36H52F12HgN4P2S4: C, 37.29; H, 4.52;
N, 4.83; S, 11.06. Found: C, 37.42; H, 4.39; N, 4.68; S, 11.36.
IR (KBr disc): 1580 (w), 1482 (s), 1127 (s), 1011 (m), 960 (w),
841 (s), 559 (s) cm−1. UV-Vis (MeCN; λmax, nm (ε, M−1
cm−1)): 284 (73500). 1H NMR (400 MHz, DMSO-d6): δ
7.57–7.72 (m, 4H, Ph), 3.52 (m, 9H, NMe3).
1
(74600). H NMR (400 MHz, DMSO-d6): δ 7.50–7.64 (m, 4H,
Ph), 3.54 (s, 9H, NMe3), 0.71 (s, 3H, MeHg).
Synthesis of [MeHg(Tab)]I·0.25H2O (2·0.25H2O). To a sol-
ution of 1 (53 mg, 0.1 mmol) in MeCN (5 mL) was added KI
(17 mg, 0.1 mmol) in MeOH (2 mL). The resulting mixture was
stirred for 1 h to form a colorless solution and filtered. Diethyl
ether (20 mL) was layered onto the filtrate to form colorless
prisms of 2·0.25H2O in several days, which were collected by
filtration, and washed with Et2O and dried in vacuo. Yield:
44 mg (87% based on Hg). Anal. Calcd. for C10H16HgINS: C,
23.56; H, 3.16; N, 2.75; S, 6.29. Found: C, 23.87; H, 3.52; N,
2.41; S, 6.03. IR (KBr disc): 3012 (w), 2910 (w), 1587 (w),
1487 (s), 1411 (w), 1125 (m), 1009 (m), 966 (w), 822 (w), 551
X-ray crystallography
Single crystals of 2·0.25H2O, 3, 4 and 6·MeOH·2MeCN suitable
for X-ray analysis were obtained directly from the above prep-
arations. All measurements were made on a Rigaku Mercury
CCD X-ray diffractometer by using graphite monochromated
Mo-Kα (λ = 0.71073 Å) radiation. Crystals of 2·0.25H2O, 3, 4
and 6·MeOH·2MeCN were mounted with grease at the top of a
glass fiber and cooled at 223 K in a liquid nitrogen stream.
2700 | Dalton Trans., 2012, 41, 2699–2706
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Diffraction data were collected at ω mode with a detector-to-
crystal distance of 35 mm. Cell parameters were refined by using
the program Crystalclear (Rigaku and MSc, Ver. 1.3, 2001) on
all observed reflections. The collected data were reduced by
using the program CrystalClear (Rigaku and MSc, version 3.6,
2004), and an absorption correction (multi-scan) was applied.
The reflection data were also corrected for Lorentz and polariz-
ation effects.
82% yield (Scheme 1). When a solution of 1 was combined with
a solution of Tab in a 1 : 1∼3 molar ratio, a unique three-coordi-
nated MeHg/Tab complex 4 was isolated in various yields
(Scheme 1). These results showed that, if any, the interaction
−
between [MeHg(Tab)]+ and PF6 was quite weak. In addition, 1
is readily soluble in MeCN, DMF and DMSO, which implies
that 1 could be a two-coordinate complex, not a coordination
polymer.
The crystal structures of 2·0.25H2O, 3, 4 and 6·MeOH·2-
MeCN were solved by direct methods and refined on F2 by full-
matrix least-squares techniques with SHELXTL-97 program.15
Because of the partial evaporation of the solvent molecules, we
could not locate any more solvent molecules in the potential
solvent area of 156 Å3 per unit cell (18.1% of the total cell
volume calculated by the Platon program15c) in 6·MeOH·2-
MeCN. For 6·MeOH·2MeCN, the methyl groups of one Tab
ligand were found to be disordered over two positions with an
occupancy factor of 0.49/0.51 for C79–C82/C79A-C82A. All
non-hydrogen atoms, except for those of the MeOH molecules
(C113, C116, O1, O2) in 6·MeOH·2MeCN were refined aniso-
tropically. Hydrogen atoms of the disordered water molecule
(O1) in 2·0.25H2O and the MeOH molecules (C116, O1, O2) in
6·MeOH·2MeCN were not located. All other hydrogen atoms
were placed in geometrically idealized positions (C–H = 0.98 Å
for methyl groups; C–H = 0.95 Å for phenyl groups) and con-
strained to ride on their parent atoms with Uiso(H) = 1.5Ueq (C)
for methyl groups and Uiso(H) = 1.2Ueq(C) for phenyl groups.
Pertinent crystal data and collection and refinement parameters
for 2·0.25H2O, 3, 4 and 6·MeOH·2MeCN are given in Table 1.
On the other hand, similar reaction of 1 with 2 equiv. of
NH4SCN did not yield the expected [MeHg(Tab)(SCN)] or the
anion-exchange product 3 but generated a four-coordinate Hg/
Tab complex 5 in 35% yield (Scheme 1). The crystal structure of
5 is the same as that of the previously reported one.13a In this
case, the methyl group of 1 was protonated by the weak acid,
+
NH4 , and the whole structure may be decomposed. The remain-
ing species such as Hg2+, Tab, and NCS− in the solution might
re-organize into compound 5. The reason for the decomposition
of 1 and the formation of 5 may be attributed to the weak acidity
+
of NH4 ions. This is in accordance with the fact that the Hg–C
bond of the RHgX compounds could be broken by the acids.12a
We also attempted the analogous reactions of 1 with NH4Cl,
NH4Br or NH4I, but the cleavage of Hg–C bond of 1 and the for-
mation of the similar compounds like 2 did not occur. Such a
phenomena may be ascribed to the fact that the Hg–C bond of
the mercury alkyl complexes are readily cleaved by S-donor
ligands and the formation of three- or four-coordinated Hg(II)
complexes of S-donor ligands.9a,10 According to the literature,10b
cleavage of the Hg–C bonds of both PhSHgEt and {LHgEt}
[BF4] by PhSH could be promoted by addition of L (L = 2-mer-
capto-1-t-butylimidazole). Parks et al. also suggested that
coordination of R–Hg(II) by two equivalents of cysteine thiolate
is necessary and sufficient to activate the Hg–C bond toward pro-
tonolysis.9a Thus we carried out the reaction of 4 with 4,6-
Me2pymSH and isolated another Hg(II)/Tab product
[Hg(Tab)4]3(PF6)6 (6) (Scheme 1). In this reaction, the methyl
group of 4 might be acidified by 4,6-Me2pymSH and sub-
sequently eliminated. The initial mercury product was assumed
to be [Hg(Tab)2(4,6-Me2pymS)]PF6 (Scheme 1). This complex
could not be isolated because it may quickly disproportionate
Results and discussion
Synthetic and spectral aspects
Treatment of MeHgI with excess silver oxide for 48 h in water
developed a large amount of yellow solid (AgI), which was
removed by filtration (Scheme 1). The resulting colorless sol-
ution was mixed with equimolar TabHPF6, forming a large
amount of colorless precipitate, which was filtered, washed with
Et2O, and dried in vacuo. The elemental analysis, the IR spec-
into
6 and a known Hg(II)/thiolate complex [Hg(4,6-
1
trum and the H NMR spectrum of the white solid were all well
Me2pymS)2].16 The later complex was identified by ESI mass
spectrometry (m/z = 480.0 {M + 1}+) (Fig. 1a). Both products
were also observed when 4 was treated with EtSH. We attempted
the direct reactions of 1, 2, or 3 with 4,6-Me2pymSH, EtSH and
other thiols, but no evident Hg–Me cleaving reactions were
taking place, and only the starting complexes were recovered. It
is evident that the Hg–C bond of the trigonally-coordinated
complex 4 might be more readily activated than those of the
linear coordinated complexes 1–3.
consistent with the chemical formula [MeHg(Tab)]PF6 (1).
However, attempts to grow its single crystals always failed.
Since methylmercury(II) was regarded as an essentially uni-
functional cation to give coordination number 2 for mercury(II),
we tentatively assumed the Hg(II) center of 1 to be two-coordi-
nate. Considering that access to geometries of the Hg(II) center
with a coordination number greater than two is required for the
efficient activity of MerB, the two-coordinated Hg atom of 1
may be further coordinated by other donor ligands such as halide
or pseudohalide or Tab ligand to afford a three- or four-coordi-
nation environment. We thus carried out the reaction of 1 with
equimolar KI in MeCN/MeOH. To our surprise, no expected
product [MeHg(Tab)I], but an anion-exchanged product
2·0.25H2O, was isolated in 87% yield (Scheme 1). Compound
2·0.25H2O could be also prepared in a quantitative yield when
MeHgI was treated with equimolar TabHPF6 in the presence of
Et3N. An analogous reaction of 1 with one or more equivalents
of KSCN also produced another anion-exchange product 3 in
Solids 2–6 are relatively stable toward oxygen and moisture
and readily soluble in MeCN, DMF and DMSO but almost inso-
luble in MeOH, EtOH, CH2Cl2, benzene and H2O. The elemen-
tal analyses of 1–6 were consistent with their chemical formulas.
The IR spectra of 1, 4, and 6 showed the characteristic P–F
−
stretching vibrations of PF6 at 840 and 559 cm−1. The peak at
2054 cm−1 for 3 and 2080 cm−1 for 5 in the IR spectrum indi-
1
cated the presence of the SCN− anion. The H NMR spectra of
1–6 in DMSO-d6 at room temperature featured multiplets in the
region of 7.39–7.72 ppm for phenyl groups and a singlet at
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Table 1 Crystal data and structure refinement parameters for 2·0.25H2O, 3, 4 and 6·MeOH·2MeCN
Compounds
2·0.25H2O
40H66Hg4I4N4OS4
2057.21
Monoclinic
P21/c
14.339(3)
7.3906(15)
28.086(8)
109.38(3)
2807.7(11)
2.433
3
4
6·MeOH·2MeCN
Formula
Formula weight
Crystal system
Space group
a/Å
b/Å
c/Å
C
C11H16HgN2S2
440.99
Monoclinic
P21/c
6.9713(14)
21.564(4)
10.158(4)
113.92(2)
1395.9(7)
2.098
C19H29F6HgN2PS2
695.12
Monoclinic
P21/c
17.975(4)
11.308(2)
12.905(3)
105.36(3)
2529.3(9)
1.825
C113H166F36Hg3N14OP6S12
3592.91
Monoclinic
Pc
27.196(5)
12.152(2)
23.754(5)
99.35(3)
7746(3)
1.540
β/°
V/Å3
Dc/g cm−3
Z
2
4
4
2
μ(Mo-Kα)/mm−1
F(000)
13.282
1876
11.302
832
6.367
1352
3.279
3592
Total reflections
Unique reflection
No. observations
No. parameters
Ra
12787
7765
14147
47515
6388 (Rint = 0.0526)
4858 [I > 2.00 σ(I)]
272
0.0411
0.0927
3116 (Rint = 0.0496)
2877 [I > 2.00 σ(I)]
151
0.0457
0.1298
5770 (Rint = 0.0499)
4153 [I > 2.00 σ(I)]
282
0.0653
0.1787
28302 (Rint = 0.0569)
23614 [I > 2.00 σ(I)]
1711
0.0688
0.1750
wRb
GOFc
0.924
1.142
1.075
1.049
a R = Σ∥Fo|−|Fc∥/Σ|Fo|. b wR = {Σw(Fo −Fc ) /Σw(Fo ) }1/2
numbers of parameters refined.
.
c GOF = {Σw((Fo −Fc ) )/(n-p)}1/2, where n = number of reflections and p = total
2
2 2
2 2
2
2 2
Scheme 1
3.54 ppm for the methyl protons of the NMe3 unit of the Tab
ligands. The peak related to the methyl protons of MeHg was
observed at 0.70 ppm for 1–4.
In order to gain more insight into the behaviors of 1–4 and 6
in solution, their positive-ion ESI mass spectra were examined.
The assignments were made through the inspection of peak pos-
itions and isotopic distributions. The positive-ion ESI-MS of 1–3
in MeCN exhibited the parent cation [MeHg(Tab)]+ at m/z =
384.1 (Fig. 1b), the patterns of which match well with its theor-
etical isotopic distributions. For 4, the positive ESI-MS showed
not only a parent cation peak at m/z = 551.2 for [MeHg(Tab)2]+
(Fig. 1c), but also a [Hg(Tab)2]2+ fragment peak at m/z = 268.1
(Fig. 1d). The positive-ion ESI-MS of
6 exhibited a
[Hg(Tab)2]2+ fragment peak at m/z = 268.1, implying that 6 was
dissociated under the mass conditions.
As shown in Fig. 2, the electronic spectra of 1–4 and 6 in
MeCN exhibited a strong and broad absorption with maxima
values ranging from 234 to 286 nm and a long absorption tail to
ca. 400 nm. Because the absorption spectrum of the free Tab in
MeCN had a broad absorption band at 314 nm, the main peaks
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Fig. 3 (a) Perspective view of one of the two [MeHgTab]+ cations of
2. (b) Dimeric structure formed by the Hg⋯I secondary interactions and
Hg⋯C interactions in 2. All hydrogen atoms are omitted for clarity.
observed in the spectra of 1–4 and 6 were blue-shifted and may
be due to the ligand(Tab)-to-metal charge transfer (LMCT).17
The peaks observed in the spectra of 4 and 6 were red-shifted
relative to the peak of 1–3, which may be ascribed to the differ-
ent coordination environments about the Hg atoms in these com-
pounds. The identities of 2, 3, 4 and 6 were further confirmed by
X-ray crystallography.
Fig. 1 (a) The observed (upper) and the calculated (lower) isotopic pat-
terns for [Hg(4,6-Me2pymS)2]. (b) The observed (upper) and the calcu-
lated (lower) isotopic patterns for the [MeHg(Tab)]+ cation in 1–3. (c)
The observed (upper) and the calculated (lower) isotopic patterns for the
[MeHg(Tab)2]+ cation in 4. (d) The observed (upper) and the calculated
(lower) isotopic patterns for the [Hg(Tab)2]2+ cation in 4 and 6.
Crystal structure of [MeHg(Tab)]I·0.25H2O (2·0.25H2O) and
[MeHg(Tab)]SCN (3). Compounds 2·0.25H2O and 3 crystallize
in the monoclinic space group P21/c and the asymmetric unit of
2
consists of two crystallographically independent
[MeHg(Tab)]+ cations, two iodides and half a water solvent mol-
ecule, while that of 3 contains one [MeHg(Tab)]+ cation and one
SCN− anion. Because the two cations of 2 and the cation of 3
are structurally very similar, only a perspective view of one of
the two cations of 2 is shown in Fig. 3a and the pertinent bond
lengths and angles of the two cations are compared in Table 2.
In the [MeHg(Tab)]+ cations of 2 and 3, each Hg(II) center is
coordinated by one S atom from one Tab ligand and one C atom
of the methyl group to afford an approximately linear coordi-
nation geometry. The Hg–C bond length of 3 (2.056(8) Å) is
shorter than that of 2 (2.076(9) Å) and [LHgEt](BF4) (2.092(5)
Å; L = 2-mercapto-1-t-butylimidazole),10b but comparable to
that of [PhSHgMe] (2.06(2) Å).18 The mean Hg–S bond lengths
of 2 (2.348(3) Å) and 3 (2.3500(15) Å) are slightly shorter than
those of the corresponding ones found in other two-coordinated
methylmercury thiolate compounds such as [LHgMe] (2.396(2)
Å,
L =
tris(2-mercapto-1-t-butylimidazolyl)hydroborato),10a
[PhSHgEt] (2.369(2) Å),18a [PhSHgMe] (2.383(2) Å), [MeHgL]
(2.375(6) Å, HL = 2-mercaptobenzothiazole),18b and [MeHg
(S2CC5H6NH2-2)] (2.393(3) Å).18c
Fig. 2 Electronic spectra of 1 (2.0 × 10−5 M), 2 (2.5× 10−5 M), 3 (1.8
× 10−5 M), 4 (3.3 × 10−5 M) and 6 (2.2 × 10−5 M) in MeCN in a 1 cm–
thick glass cell.
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Table 2 Selected bond distances (Å) and angles (°) for 2, 3, 4 and 6
Compound 2
Hg(1)–C(10)
Hg(1)⋯I(1)
Hg(2)–S(2)
C(10)–Hg(1)–S(1)
S(1)–Hg(1)⋯I(1)
C(20)–Hg(2)⋯I(2)
Compound 3
2.089(9)
3.3819(13)
2.349(3)
175.6(3)
83.50(7)
99.8(3)
Hg(1)–S(1)
Hg(2)–C(20)
Hg(2)⋯I(2)
C(10)–Hg(1)⋯I(1)
C(20)–Hg(2)–S(2)
S(2)–Hg(2)⋯I(2)
2.347(3)
2.062(9)
3.4014(9)
100.8(3)
177.7(3)
82.38(7)
Hg(1)–C(10)
C(10)–Hg(1)–S(1)
Compound 4
2.056(8)
175.3(3)
Hg(1)–S(1)
2.3500(15)
Hg(1)–C(19)
Hg(1)–S(2)
C(19)–Hg(1)–S(2)
Compound 6
2.051(12)
2.737(2)
121.4(5)
Hg(1)–S(1)
C(19)–Hg(1)–S(1)
S(1)–Hg(1)–S(2)
2.422(2)
160.0(5)
78.54(6)
Hg(1)–S(2)
Hg(1)–S(1)
Hg(2)–S(8)
Hg(2)–S(6)
Hg(3)–S(11)
Hg(3)–S(9)
S(2)–Hg(1)–S(4)
S(4)–Hg(1)–S(1)
S(4)–Hg(1)–S(3)
S(8)–Hg(2)–S(7)
S(7)–Hg(2)–S(6)
S(7)–Hg(2)–S(5)
S(11)–Hg(3)–S(10)
S(10)–Hg(3)–S(9)
S(10)–Hg(3)–S(12)
2.4903(11)
2.5074(10)
2.4801(10)
2.5668(9)
2.4693(11)
2.5627(10)
113.35(4)
109.88(3)
91.72(3)
123.00(3)
101.50(3)
111.32(3)
120.82(3)
99.63(4)
Hg(1)–S(4)
Hg(1)–S(3)
Hg(2)–S(7)
Hg(2)–S(5)
Hg(3)–S(10)
Hg(3)–S(12)
S(2)–Hg(1)–S(1)
S(2)–Hg(1)–S(3)
S(1)–Hg(1)–S(3)
S(8)–Hg(2)–S(6)
S(8)–Hg(2)–S(5)
S(6)–Hg(2)–S(5)
S(11)–Hg(3)–S(9)
S(11)–Hg(3)–S(12)
S(9)–Hg(3)–S(12)
2.5014(10)
2.5921(11)
2.4821(10)
2.5788(10)
2.4840(12)
2.5757(10)
118.02(3)
107.00(4)
113.88(3)
108.32(3)
101.09(3)
111.77(3)
112.97(3)
102.63(3)
110.27(3)
Fig. 4 (a) View of the [MeHgTab]SCN structure of 3. (b) 2D structure
formed by hydrogen-bonding interactions in 3 (looking along the b
axis). All H atoms except those involved in hydrogen-bonding inter-
actions were omitted.
110.60(4)
Although the two independent cations of 2 are not parallel to
each other, the MeHgS species of one cation is almost parallel to
one Tab unit of the neighboring cation (Fig. 3b). The Hg atom
interacts with the phenyl ring of Tab ligand with Hg⋯C contact
of 3.7149(12) and 3.8645(7) Å, thereby forming a dimeric struc-
ture. Due to the existence of Hg⋯I secondary interactions
(3.3819(13) and 3.4014(9) Å) in 2 and Hg⋯S secondary inter-
actions (3.2308(7) Å) in 3, the Hg centers in 2 and 3 may be
considered as having a pseudo-three-coordinated T-shaped geo-
metry. For 3, there exist several intermolecular hydrogen-
bonding interactions among the H atoms of the methyl groups of
Tab ligands and the S atom of SCN− anions [C7⋯S2 (x, y, 1 +
z)], the N atoms of SCN− anions [C9⋯N2 (−1 + x, 1/2 − y,
1/2 + z); C9⋯N2 (−1 + x, y, 1 + z)], which lead to the formation
of a 2D hydrogen-bonded network (Fig. 4b).
Crystal structure of [MeHg(Tab)2]PF6 (4). Compound 4 crys-
tallizes in the monoclinic space group P21/c and its asymmetric
−
unit consists of a [MeHg(Tab)2]+ cation and one PF6 anion. In
the cation of 4, the central Hg1 atom is coordinated by two S
atoms of the two Tab ligands and one C atom of the methyl
group, forming a unique distorted trigonal-planar coordination
geometry (Fig. 5a). The two Tab ligands take a trans configur-
ation with a dihedral angle of 65.6°. The Hg–C length (2.051
(12) Å) is similar to that of the three-coordinated methylmercury
complex [MeHg(2,2′-bpy)]NO3 (2.066(58) Å).19 It is noted that
the Hg1–S1 bond distance (2.422(2) Å) is significantly longer
than the Hg–S2 bond length (2.737(2) Å). The two C–Hg–S
bond angles are 160.0(5)° and 121.4(5)°, which are much
smaller than the linear coordinated compounds. The smaller
Fig. 5 (a) View of the [MeHg(Tab)2]+ cation of 4. (b) 2D network
formed by hydrogen-bonding interactions in 4 (looking along the b
axis). All H atoms except those involved in hydrogen-bonding inter-
actions were omitted.
S–Hg–C angle corresponds to the longer Hg–S distance.
Because the PF6− anions are located between the [MeHg(Tab)2]+
cations, several F atoms interact with the H atoms of the methyl
groups [C18⋯F1 (−x, 1 − y, 2 − z); C18⋯F3 (−x, −1/2 + y, 5/2
− z); C18⋯F4 (x, 1/2 − y, −1/2 + z)] and the H atoms of the
2704 | Dalton Trans., 2012, 41, 2699–2706
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(SCN− and RS−) and protonation of the methyl group via weak
+
acids like NH4 , 4,6-Me2pymSH or EtSH in a cooperative
way, which may provide a simple approach to detoxification of
organomercury compounds.
Acknowledgements
The authors thanked the National Natural Science Foundation of
China (90922018 and 21171124), the Nature Science Key Basic
Research of Jiangsu Province for Higher Education
(09KJA150002), the Specialized Research Fund for the Doctoral
Program of higher Education of Ministry of Education
(20093201110017), the State Key Laboratory of Coordination
Chemistry of Nanjing University for financial support. J. P. Lang
also highly appreciated the support for the Qin-Lan and the
“333” Projects of Jiangsu Province, the Priority Academic
Program Development of Jiangsu Higher Education Institutions,
and the “SooChow Scholar” Program and Program for Innova-
tive Research Team of Suzhou University. The authors also
greatly appreciate the helpful comments from the editor and the
reviewers.
Fig. 6 View of one of the three independent [Hg(Tab)4]2+ cations of 6.
All hydrogen atoms have been omitted for clarity.
phenyl groups [C11⋯F1] of the Tab ligands, forming a 2D
hydrogen-bonded network (Fig. 5b).
Crystal structure of [Hg(Tab)4]3(PF6)6·MeOH·2MeCN
(6·MeOH·2MeCN). Compound 6·MeOH·2MeCN crystallizes in
the monoclinic space group Pc and its asymmetric contains three
crystallographically independent [Hg(Tab)4]2+ dications, six
PF6− anions, two halves of methanol solvent molecules, one and
two halves of MeCN solvent molecules. The structure of the [Hg
(Tab)4]2+ dication (Fig. 6) resembles those observed in (Me4N)2
[Hg(SPhCl-p)4],20a [Hg(SpyH)4(ClO4)2] (Spy− = pyridine-4-
thiolate),20b (NEt4)2[Hg(S-2-CH3NHCOC6H4)4].20c Each Hg
atom is coordinated by four S atoms from four Tab ligands,
forming a strongly distorted tetrahedral coordination geometry
with the S–Hg–S angles in the range of 91.72(3)–123.00(3)°.
The average Hg–S distance (2.5242(12) Å) is close to that of
(Me4N)2[Hg(SPhCl-p)4] (2.540(5) Å), but substantially longer
than those of the corresponding ones in [Hg(Tab)2](PF6)2 (2.331
(3) Å) and [Hg2(Tab)6](PF6)4 (2.4242(14) Å).13a In the crystal of
6·MeOH·2MeCN, there exist very complicated hydrogen-
bonding interactions among the methyl groups of Tab ligands,
References
1 (a) H. R. Sunshine and S. J. Lippard, Nucleic Acids Res., 1974, 1, 673;
(b) J. W. Sekowski, L. H. Malkas, Y. T. Wei and R. J. Hickey, Toxicol.
Appl. Pharmacol., 1997, 145, 268; (c) I. Onyido, A. R. Norris and
E. Buncel, Chem. Rev., 2004, 104, 5911; (d) B. N. Ahamed,
M. Arunachalam and P. Ghosh, Inorg. Chem., 2010, 49, 4447.
2 (a) H. Strasdeit, A. Döllen, W. Saak and M. Wilhelm, Angew. Chem.,
2000, 112, 803; (b) L. Magos, Metal Ions in Biological Systems, (ed.,
(A. Sigel and H. Sigel), Dekker, New York, 1997, 34, 327.
3 (a) R. E. Hecky, D. J. Ramsey, R. A. Bodaly and N. E. Strange, Advances
in Mercury Toxicology, 1991, 33; (b) C. A. Kelly, J. W. M. Rudd, R.
A. Bodaly, N. P. Roulet, V. L. Louis, A. Heyes, T. R. Moore, S. Schiff,
R. Aravena, K. J. Scott, B. Dyck, R. Harris, B. Warner and G. Edwards,
Environ. Sci. Technol., 1997, 31, 1334; (c) J. G. Wiener, D.
P. Krabbenhoft, G. H. Heinz and A. M. Scheuhammer, Handbook of Eco-
toxicology, 2003, 409; (d) J. G. Wiener, D. P. Krabbenhoft, G. H. Heinz
and A. M. Scheuhammer, Handbook of Ecotoxicology, 2003, 409;
(e) F. M. M. Morel, A. M. L. Krepiel and M. Amyot, Annu. Rev. Ecol.
Syst., 1998, 29, 543.
−
the F atoms of the PF6 anions, and MeOH solvent molecules,
which may not be described in this paper.
4 W. F. Fitzgerald and T. W. Clarkson, Environ. Health Perspect., 1991, 96,
159.
5 (a) T. W. Clarkson, L. Magos and G. J. Myers, N. Engl. J. Med., 2003,
349, 1731; (b) P. A. D’Itri and F. M. D’Itri, Environ. Manage., 1978, 2,
3.
6 (a) M. Uchino, Y. Tanaka, Y. Ando, T. Yonehara, A. Hara, I. Mishima,
T. Okajima and M. Ando, J. Environ. Sci. Health, Part B, 1995, 30, 699;
(b) T. W. Clarkson and L. Magos, Crit. Rev. Toxicol., 2006, 36, 609;
(c) D. L. Rabenstein, Acc. Chem. Res., 1978, 11, 100.
7 (a) T. W. Clarkson and L. Magos, Crit. Rev. Toxicol., 2006, 36, 609;
(b) J. Mutter, J. Naumann and C. Guethlin, Crit. Rev. Toxicol., 2007, 37,
537; (c) T. W. Clarkson, Environ. Health Perspect., 2002, 110, 11;
(d) T. W. Clarkson, Crit. Rev. Clin. Lab. Sci., 1997, 34, 369;
(e) N. J. Langford and R. E. Ferner, J. Hum. Hypertens., 1999, 13, 651;
(f) D. W. Boening, Chemosphere, 2000, 40, 1335; (g) L. Magos, Met.
Ions Biol. Sys., 1997, 34, 321; (h) A. R. Hutchison and D. A. Atwood,
J. Chem. Crystallogr., 2003, 33, 631; (i) L. Alessio, M. Campagna and
R. Lucchini, Am. J. Ind. Med., 2007, 50, 779; ( j) T. W. Clarkson, J.
B. Vyas and N. Ballatorl, Am. J. Ind. Med., 2007, 50, 757; (k) J. F. Risher
and C. T. De Rosa, J. Environ. Health, 2007, 70, 9; (l) I. Onyido,
A. R. Norris and E. Buncel, Chem. Rev., 2004, 104, 5911;
(m) P. O. Ozuah, Current Probl. Pediatr., 2000, 30, 91.
Conclusions
In the work reported here, we demonstrate the isolation of the
two-coordinated methylmercury complex 1 from reactions of
MeHgI with Ag2O and TabHPF6. The Hg–C bond of 1 was inert
when 1 was treated with KI and KSCN to form two anion-
exchange products 2 and 3. In the case of Tab, the linear coordi-
nation geometry of the Hg(II) center of 1 was converted into the
trigonal-planar coordination geometry of the Hg(II) center of 4.
However, the Hg–C bond of 1 was readily cleaved by a weak
acid NH4SCN to give a tetrahedrally-coordinated Hg(II) complex
5. When complex 4 was treated with other weak acids such as
4,6-Me2pymSH or EtSH, the cleavage of the Hg–C bond of 4
was also observed to form another tetrahedrally-coordinated
Hg(II) complex 6. These results revealed that in our system,
increasing the coordination number of the Hg(II) center by donor
ligands like Tab may not promote the cleaving Hg–C bond in the
methylmercury complexes. The cleavage of the Hg–C bond in
MeHg complexes 1 and 4 could be completed by enhancement
of Hg(II) coordination number through S-donor ligands
8 (a) M. J. Moore, M. D. Distefano, L. D. Zydowsky, R. T. Cummings and
C. T. Walsh, Acc. Chem. Res., 1990, 23, 301; (b) C. T. Walsh, M.
D. Distefano, M. J. Moore, L. M. Shewchuk and G. L. Verdine, FASEB
J., 1988, 2, 124.
This journal is © The Royal Society of Chemistry 2012
Dalton Trans., 2012, 41, 2699–2706 | 2705

View Article Online
9 (a) J. M. Parks, H. Guo, C. Momany, L. Liang, S. M. Miller,
A. O. Summers and J. C. Smith, J. Am. Chem. Soc., 2009, 131, 13278;
(b) J. G. Omichinski, Science, 2007, 317, 205; (c) H. Strasdeit, Angew.
Chem., Int. Ed., 2008, 47, 828; (d) X. C. Li, R. Z. Liao, W. C. Zhou and
G. J. Chen, Phys. Chem. Chem. Phys., 2010, 12, 3961; (e) Y. W. Chen,
C. F. Huang, K. S. Tsai, R. S. Yang, C. C. Yen, C. Y. Yang, S. Y. Lin-
Shiau and S. H. Liu, Chem. Res. Toxicol., 2006, 19, 1080;
(f) A. J. Canty, N. Chaichit, B. M. Gatehouse and E. E. George, Inorg.
Chem., 1981, 20, 4293.
10 (a) J. G. Melnick and G. Parkin, Science, 2007, 317, 225;
(b) J. G. Melnick, K. Yurkerwich and G. Parkin, Inorg. Chem., 2009, 48,
6763; (c) F. R. Jensen and B. Rickborn, Electrophilic Substitution of
Organomercurials, McGraw-Hill, New York, 1968.
Inorg. Chem., 2009, 48, 2639; (g) X. Y. Tang, A. X. Zheng, H. Shang,
R. X. Yuan, H. X. Li, Z. G. Ren and J. P. Lang, Inorg. Chem., 2011, 50,
503; (h) A. X. Zheng, Z. G. Ren, L. L. Li, H. Shang, H. X. Li and
J. P. Lang, Dalton Trans., 2011, 40, 589.
14 (a) B. V. DePamphilis, B. A. Averill, T. Herskovitz, L. Que, Jr. and
R. H. Holm, J. Am. Chem. Soc., 1974, 96, 4159; (b) A. Rodríguez,
A. Sousa-Pedrares, J. A. García-Vázquez, J. Romero and A. Sousa, J.
Organomet. Chem., 2010, 695, 1271.
15 (a) G. M. Sheldrick, SHELXS-97, Program for Solution of Crystal Struc-
tures, University of Göttingen, Germany, 1997; (b) G. M. Sheldrick,
SHELXL-97, Program for Refinement of Crystal Structures, University of
Göttingen, Germany, 1997; (c) A. L. Spek, J. Appl. Crystallogr., 2003,
36, 7.
11 (a) P. Barbaro, F. Cecconi, C. A. Ghilardi, S. Midollini, A. Orlandini and
A. Vacca, Inorg. Chem., 1994, 33, 6163; (b) J. S. Casas, M. S. García-
Tasende and J. Sordo, Coord. Chem. Rev., 1999, 193, 283;
(c) C. E. Holloway and M. Melník, J. Organomet. Chem., 1995, 495, 1.
12 (a) V. Barone, A. Bencini, F. Totti and M. G. Uytterhoeven, Organome-
tallics, 1996, 15, 1465; (b) M. Wilhelm, S. Deeken, E. Berssen,
W. Saak, A. Lützen, R. Koch and H. Strasdeit, Eur. J. Inorg. Chem.,
2004, 2301.
13 (a) J. X. Chen, W. H. Zhang, X. Y. Tang, Z. G. Ren, Y. Zhang and
J. P. Lang, Inorg. Chem., 2006, 45, 2568; (b) J. X. Chen, Q. F. Xu, Y. Xu,
Y. Zhang, Z. N. Chen and J. P. Lang, Eur. J. Inorg. Chem., 2004, 4247;
(c) J. X. Chen, Q. F. Xu, Y. Zhang, Z. N. Chen and J. P. Lang,
J. Organomet. Chem., 2004, 689, 1071; (d) J. X. Chen, W. H. Zhang,
X. Y. Tang, Z. G. Ren, H. X. Li, Y. Zhang and J. P. Lang, Inorg. Chem.,
2006, 45, 7671; (e) X. Y. Tang, J. X. Chen, G. F. Liu, Z. G. Ren,
Y. Zhang and J. P. Lang, Eur. J. Inorg. Chem., 2008, 2593;
(f) X. Y. Tang, R. X. Yuan, Z. G. Ren, H. X. Li, Y. Zhang and J. P. Lang,
16 (a) A. K. Das and S. Seth, J. Inorg. Biochem., 1997, 65, 207;
(b) A. Rodríguez, A. Sousa-Pedrares, J. A. García-Vázquez, J. Romero
and A. Sousa, Eur. J. Inorg. Chem., 2005, 2242.
17 (a) W. Y. Guo, Z. H. Peng, D. C. Li and Y. H. Zhou, Polyhedron, 2004,
23, 1701; (b) A. Armas, V. Sonois, E. Mothes, H. Mazarguil and
P. Faller, J. Inorg. Biochem., 2006, 100, 1672.
18 (a) J. G. Melnick, K. Yurkerwich, D. Buccella, W. Sattler and G. Parkin,
Inorg. Chem., 2008, 47, 6421; (b) J. Bravo, J. S. Casas, M. V. Castaro,
M. Gayoso, Y. P. Mascarenhas, A. Sanchez, C. O. P. Santos and
J. Sordoi, Inorg. Chem., 1985, 24, 3435; (c) C. S. Lai and
E. R. T. Tiekink, CrystEngComm, 2003, 5, 253.
19 A. J. Canty and A. Marker, Inorg. Chem., 1976, 15, 425.
20 (a) S. Choudhury, I. G. Dance, P. J. Guerney and A. D. Rae, Inorg. Chim.
Acta, 1983, 70, 227; (b) K. S. Anjali, J. J. Vittal and P. A. W. Dean,
Inorg. Chim. Acta, 2003, 351, 79; (c) M. Kato, K. Kojima, T. Okamura,
H. Yamamoto, T. Yamamura and N. Ueyama, Inorg. Chem., 2005, 44,
4437.
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