Relation between intramolecular NH...S hydrogen bonds and coordination number in mercury(II) complexes with carbamoylbenzenethiol derivatives

Article abstract of DOI:10.1021/ic0481780

A novel series of bis(carbamoylthiophenolato)mercury(II) complexes, [Hg(S-RNHCOC₆H₄)₂] (1, R = 2-t-Bu; 2, R = 2-CH₃; 3, R = 2-C₆H₅CH₂; 4, R = 4-t-Bu), and a tetrakis(carbamoylthiophenolato)mercury(II) complex, (NEt ₄)₂Hg-(S-2-CH₃NHCOC₆H ₄)₄] (5), were synthesized and characterized by ¹H NMR, IR, ¹⁹⁹Hg NMR, and crystallographic analyses. The bis(carbamoylthiophenolato)mercury complexes 1-3 do not have intramolecular NH...S hydrogen bonds between the amide NH group and the sulfur atom coordinated to mercury, whereas the tetrakis(thiophenolato)-mercury complex 5 does have an intramolecular NH...S hydrogen bond. A relatively weak NH...S hydrogen bond in 5 can be seen in the ¹H NMR spectra and the IR spectra in chloroform and in the solid state. The ¹⁹⁹Hg NMR spectra in bis(carbamoylthiophenolato)mercury complexes 1-4 show a downfield shift, with an increase in the flow of electrons to mercury(II) from the oxygen atom due to the intramolecular Hg...O bonding interaction. Conversely, the ¹⁹⁹Hg NMR spectra in S show a high-field shift with a decrease in the flow of electrons to mercury(II) from the sulfur atom due to the intramolecular NH...S hydrogen bond.

Full text of DOI:10.1021/ic0481780

Inorg. Chem. 2005, 44, 4037−4044
Relation between Intramolecular NH‚‚‚S Hydrogen Bonds and
Coordination Number in Mercury(II) Complexes with
Carbamoylbenzenethiol Derivatives
Masahiro Kato,† Kazunori Kojima,† Taka-aki Okamura,† Hitoshi Yamamoto,† Takeshi Yamamura,‡ and
Norikazu Ueyama*,†
Department of Macromolecular Science, Graduate School of Science, Osaka UniVersity,
Toyonaka, Osaka 560-0043, Japan, and Department of Chemistry, Faculty of Science,
Science UniVersity of Tokyo, Kagurazaka, Shinjuku, Tokyo 162-8601, Japan
Received December 25, 2004
A novel series of bis(carbamoylthiophenolato)mercury(II) complexes, [Hg(S-RNHCOC6H4)2] (1, R
2-CH3; 3, R 2-C6H5CH2; 4, R 4-t-Bu), and a tetrakis(carbamoylthiophenolato)mercury(II) complex, (NEt4)2[Hg-
(S-2-CH3NHCOC6H4)4] (5), were synthesized and characterized by 1H NMR, IR, 199Hg NMR, and crystallographic
analyses. The bis(carbamoylthiophenolato)mercury complexes 1 3 do not have intramolecular NH‚‚‚S hydrogen
) 2-t-Bu; 2, R )
)
)
−
bonds between the amide NH group and the sulfur atom coordinated to mercury, whereas the tetrakis(thiophenolato)-
mercury complex 5 does have an intramolecular NH‚‚‚S hydrogen bond. A relatively weak NH‚‚‚S hydrogen bond
in 5 can be seen in the 1H NMR spectra and the IR spectra in chloroform and in the solid state. The 199Hg NMR
spectra in bis(carbamoylthiophenolato)mercury complexes 1−4 show a downfield shift, with an increase in the flow
of electrons to mercury(II) from the oxygen atom due to the intramolecular Hg‚‚‚O bonding interaction. Conversely,
the 199Hg NMR spectra in 5 show a high-field shift with a decrease in the flow of electrons to mercury(II) from the
sulfur atom due to the intramolecular NH‚‚‚S hydrogen bond.
Introduction
a trigonal tricoordinate structure in the chemistry of the
Hg(II) ion in vivo.6-8 Researchers have consequently begun
investigating the stabilizing factor of the tri- and tetracoodi-
nate state in vivo. Gruff et al. have synthesized and
determined the crystal structure of the di- and tricoordinate
complex with the [S-2,4,6-((CH3)2CH)3C6H2]- ligand and
reported that the Hg-S bond length increases with increasing
coordination number.1 Yamamura et al. showed that the
change from dicoordination (Hg(SR)2) to tricoordination
([Hg(SR)3]-) by the addition of the thiolate anion takes place
with a change of the peptide conformation in the Hg(Cys-
X-Y-Cys) complex (Scheme 1).9
The mercuric(II) ion has a high affinity for the sulfur atom
of thiolate, which is a soft donor having large polarizability.
Most mononuclear mercury thiolate complexes have a low
coordination number and exist as neutral linear dicoordinated
complexes (Hg(SR)2); there are several other types of
coordination environments in mononuclear anionic com-
plexes, such as [Hg(SR)3]- 1,2 and [Hg(SR)4]2-.3,4 A previous
study of mercury thiolate complexes suggests that dicoor-
dinate complexes form easily in dilute solutions, whereas
tetracoordinate complexes, with tetrahedral structure, form
with difficulty except in concentrated solutions containing
excess thiolate ligand.5 It has been suggested that MerR has
We have previously reported that the NH‚‚‚S hydrogen
bond contributes to the positive shift in the redox potential
* Author to whom correspondence should be addressed. E-mail:
ueyama@chem.sci.osaka-u.ac.jp.
(5) Wright, J. G.; Natan, M. J.; MacDonnell, F. M.; Ralston, D. M.;
O’Halloran, T. V. Prog. Inorg. Chem. 1990, 38, 323-412.
(6) Watton, S. P.; Wright, J. G.; MacDonnell, F. M.; Bryson, J. W.; Sabat,
M.; O’Halloran, T. V. J. Am. Chem. Soc. 1990, 112, 2824-2826.
(7) Wright, J. G.; Tsang, H. T.; Penner-Hahn, J. E.; O’Halloran, T. V. J.
Am. Chem. Soc. 1990, 112, 2434-2435.
† Osaka University.
‡ Science University of Tokyo.
(1) Gruff, E. S.; Koch, S. A. J. Am. Chem. Soc. 1990, 112, 1245-1247.
(2) Christou, G.; Folting, K.; Huffman, J. C. Polyhedron 1984, 3, 1247-
1253.
(3) Choudhury, S.; Dance, I. G.; Guerney, P. J.; Rae, A. D. Inorg. Chim.
Acta 1983, 70, 227-230.
(4) Silver, A.; Koch, S. A.; Millar, M. Inorg. Chem. Acta 1993, 205, 9-14.
(8) Fleissner, G.; Reigle, M. D.; O′Halloran, T. V.; Spiro, T. G. J. Am.
Chem. Soc. 1998, 120, 12690-12691.
(9) Yamamura, T.; Watanabe, T.; Kikuchi, A.; Yamane, T.; Ushiyama,
M.; Hirota, H. Inorg. Chem. 1997, 36, 4849-4859.
10.1021/ic0481780 CCC: $30.25
Published on Web 04/29/2005
© 2005 American Chemical Society
Inorganic Chemistry, Vol. 44, No. 11, 2005 4037

Kato et al.
Scheme 1
Scheme 2
Chart 1
SH‚‚‚OdC hydrogen bond, but the thiolate anion form has
an intramolecular NH‚‚‚S hydrogen bond due to the rotation
of the amide plane.19 Also, the platinum complex with this
ligand, [Pt(bpy)(S-2-CH3NHCOC6H4)2], has a structure with
a weak intramolecular NH‚‚‚S hydrogen bond.20 We have
investigated the intra- and intermolecular interaction and the
orientation of the amide plane in the Hg-thiophenolate
complexes with differing terminal substituents and differing
coordination numbers using X-ray analysis and NMR and
IR measurements.
and to the remarkable shortening or elongation of the metal-
sulfur bond distance in some transition metal complexes.10-17
The 2-(acylamino)benzenethiolate complex of mercury(II),
[Hg(S-2-RCONHC6H4)2], has a five-membered ring structure
based on a weak intramolecular NH‚‚‚S hydrogen bond,
according to X-ray analysis.18 However, 2,6-(acylamino)-
benzenethiolate, with the amide group in both o-positions
of the sulfur atom complex of mercury(II), [Hg(S-2,6-
RCONHC6H3)2], has a structure that forms not only three
intramolecular NH‚‚‚S hydrogen bonds but also one
Hg‚‚‚OdC interaction. This suggests that the carbonyl
oxygen coordinates to the mercuric ion, in view of the weak
NH‚‚‚S hydrogen bond. In fact, it is not clear whether the
mercury(II) complex prefers the NH‚‚‚S hydrogen bond. The
previous works suggest that the formation of the NH‚‚‚S
hydrogen bond decreases the electron density on the S atom
which coordinates to the metal.10-17 Consequently, it is
expected that the NH‚‚‚S hydrogen bond stabilizes the extra
negative charge on metal center in the anionic Hg complex
with a high coordination number.
This paper finds and studies a relation between the
intramolecular NH‚‚‚S hydrogen bond and the coordination
number in the bis(carbamoylthiophenolato)mercury(II) com-
plexes [Hg(S-RNHCOC6H4)2] (1, R ) 2-t-Bu; 2, R ) 2-CH3;
3, R ) 2-C6H5CH2; 4, R ) 4-t-Bu) and the tetrakis(car-
bamoylthiophenolato)mercury(II) complex (NEt4)2[Hg(S-2-
CH3NHCOC6H4)4] (5) (Chart 1). The 2-substituted thiophe-
nol ligand, 2-RNHCOC6H4SH, has been found to have
distinct conformations in the thiol form and the thiolate anion
form. The thiol form has a structure with an intramolecular
Results and Discussion
Synthesis of (NEt4)2[Hg(S-2-CH3NHCOC6H4)4] (5).
Synthesis of (NEt4)2[Hg(S-2-CH3NHCOC6H4)4] (5) was
accomplished by the ligand exchange reaction from the tris-
(thiophenolate) complex (NEt4)[Hg(SC6H5)3] in tetrahydro-
furan, as shown in Scheme 2. The resulting tricoordinate
complex forms the tetracoordinate complex in equilibrium.
Complex 5 is the most insoluble under these conditions and
was obtained as fine crystals.
Crystal Structures of the Bis(carbamoylthiopheno-
late) Complexes, [Hg(S-2-t-BuNHCOC6H4)2] (1), [Hg-
(S-2-CH3NHCOC6H4)2] (2), and [Hg(S-2-C6H5CH2NH-
COC6H4)2] (3). Figures 1 and 2 show the crystal structures
and intermolecular interactions of complexes 1-3 as deter-
mined by X-ray analysis. Table 1 shows selected bond
distances and bond angles for the three complexes. Complex
1 crystallized in the P1h space group with Z ) 4. The complex
therefore contains two distinct conformers/unit cell. Both
molecules have similar S-Hg-S angles (177.3 and 176.9°);
one conformer has 66.8° for the C11-S1-Hg1-S2-C21
torsion angle, and the other shows -89.1° for the
C31-S3-Hg2-S4-C41 torsion angle. The amide NH (H2,
H4) for one of the two thiophenolate ligands is directed to
form an intramolecular NH‚‚‚OdC hydrogen bond with the
carbonyl oxygen (O1, O3) of the other thiophenolate ligand
(N‚‚‚O ) 2.98, 3.00 Å). The other amide NH (H1, H3) is
directed to form an intermolecular NH‚‚‚OdC hydrogen
bond (N‚‚‚O ) 2.91, 2.92 Å). As a result, the crystal structure
in 1 forms one-dimension chains with the alternating intra-
and intermolecular hydrogen bonds. The carbonyl oxygen
(O1, O3) with the intramolecular hydrogen bond lies very
close to the mercury atom (2.65, 2.68 Å). In general, the
distance of Hg‚‚‚O van der Waals bonding is ca. 3.0 Å,21 so
(10) Ueyama, N.; Okamura, T.; Nakamura, A. J. Am. Chem. Soc. 1992,
114, 8129-8137.
(11) Ueyama, N.; Okamura, T.; Nakamura, A. J. Chem. Soc., Chem.
Commun. 1992, 1019-1020.
(12) Okamura, T.; Ueyama, N.; Nakamura, A.; Ainscough, E. W.; Brodie,
A. M.; Waters, J. M. J. Chem. Soc., Chem. Commun. 1993, 1658-
1660.
(13) Ueyama, N.; Nishikawa, N.; Yamada, Y.; Okamura, T.; Nakamura,
A. J. Am. Chem. Soc. 1996, 118, 12826-12827.
(14) Ueyama, N.; Yamada, Y.; Okamura, T.; Kimura, S.; Nakamura, A.
Inorg. Chem. 1996, 35, 6473-6484.
(15) Okamura, T.; Takamizawa, S.; Ueyama, N.; Nakamura, A. Inorg.
Chem. 1998, 37, 18-28.
(16) Ueyama, N.; Nishikawa, N.; Yamada, Y.; Okamura, T.; Oka, S.;
Sakurai, H.; Nakamura, A. Inorg. Chem. 1998, 37, 2415-2421.
(17) Ueyama, N.; Nishikawa, N.; Yamada, Y.; Okamura, T.; Nakamura,
A. Inorg. Chim. Acta 1998, 283, 91-97.
(18) Ueyama, N.; Taniuchi, K.; Okamura, T.; Nakamura, A.; Maeda, H.;
Emura, S. Inorg. Chem. 1996, 35, 1945-1951.
(19) Kato, M.; Kojima, K.; Inohara, M.; Okamura, T.; Yamamoto, H.;
Ueyama, N. Submitted for publication, 2005.
(20) Kato, M.; Okamura, T.; Yamamoto, H.; Ueyama, N. Inorg. Chem.
2005, 44, 1966-1972.
(21) Bondi, A. J. Phys. Chem. 1964, 68, 441-451.
4038 Inorganic Chemistry, Vol. 44, No. 11, 2005

Hg(II) Complexes with Carbamoylbenzenethiols
Figure 2. Intra- and intermolecular contacts in (a) [Hg(S-2-t-
BuNHCOC6H4)2] (1), (b) [Hg(S-2-CH3NHCOC6H4)2] (2), and (c)
[Hg(S-2-C6H5CH2NHCOC6H4)2] (3).
Figure 1. Crystal structures of (a) [Hg(S-2-t-BuNHCOC6H4)2] (1), (b)
[Hg(S-2-CH3NHCOC6H4)2] (2), and (c) [Hg(S-2-C6H5CH2NHCOC6H4)2]
(3). The hydrogen atoms except for amide proton have been omitted for
clarity. Dotted lines refer to intra- and intermolecular interactions.
Hg‚‚‚OdC interaction (Hg‚‚‚O ) 3.24 Å). In addition, the
thiophenol rings undergo an intermolecular π-π stacking
interaction.
The reported mononuclear Hg(S-2-RCONHC6H4)2 com-
plexes have a structure that forms an intramolecular NH‚‚‚S
hydrogen bond, because the amide NH binding directs to
the S atoms.18 However, these three bis(carbamoylthiophe-
nolate) complexes do not give rise to an intramolecular
NH‚‚‚S hydrogen bond. The thiolate anions (NEt4)(2-
RCONHC6H4S) and (NEt4)(2-RNHCOC6H4S) form an in-
tramolecular NH‚‚‚S hydrogen bond.19 Consequently, the
ionicity of the sulfur coordinated to mercury appears to be
low and formation of an intramolecular NH‚‚‚S hydrogen
bond is difficult.
Crystal Structure of the Tetrakis(carbamoylthiophe-
nolate) Complex, (NEt4)2[Hg(S-2-CH3NHCOC6H4)4] (5).
Figure 3 shows an ORTEP view of 5, and selected bond
distances and bond angles are listed in Table 1. Complex 5
has a tetrahedral coordination, like the reported molecular
structure of [Hg(SAr)4]2-.3,4 The distance between the
mercury atom and the sulfur atom is 2.55 Å, greater by about
0.2 Å than in the above-mentioned bis(carbamoylthiophe-
nolate) complexes. These distances are the same as in the
reported molecular structures of the bis(carbamoylthiophe-
nolate) and tetrakis(carbamoylthiophenolate) complexes,1,3
and any difference in the metal-sulfur bond lengths due to
the intramolecular NH‚‚‚S hydrogen bond is not detectable.
that the Hg‚‚‚O1 and Hg‚‚‚O3 bonding comprise the bonding
interactions of Hg‚‚‚O.
Complex 2 crystallized with the C2/c space group with Z
) 4. The complex therefore contains half of the molecule/
unit cell, and the two thiophenolate ligands have the same
structure as the center of symmetry is mercury. The carbonyl
oxygen (O1) of the thiophenolate ligand lies close to mercury
(3.06 Å). This suggests the existence of the Hg‚‚‚O binding
interactions. The angles of S1-Hg1-O1, S1-Hg1-O1′, and
O1-Hg1-O1′ are respectively 84.4, 96.5, and 158.3°, and
complex 2 has a tetrahedral-like structure due to the sulfur
and the carbonyl oxygen. The intermolecular distance of
O1-N1 is 2.81 Å, and an intermolecular NH‚‚‚OdC
hydrogen bond forms. In addition, the mercury undergoes
an intermolecular interaction with the sulfur of the neighbor-
ing molecule.
Complex 3 crystallized in the P1h space group with Z ) 1.
The complex therefore also contains half of the molecule/
unit cell, and the two thiophenolate ligands have the same
structure as the center of symmetry of mercury. The structure
in 3 does not permit an intramolecular NH‚‚‚S hydrogen bond
or Hg‚‚‚OdC interaction but does give rise to an intermo-
lecular NH‚‚‚OdC hydrogen bond (N‚‚‚O ) 2.75 Å) and
Inorganic Chemistry, Vol. 44, No. 11, 2005 4039

Kato et al.
Table 1. Selected Bond Distances (Å), Intra- and Intermolecular Contacts (Å), and Bond Angles (deg) for [Hg(S-2-t-BuNHCOC6H4)2] (1),
[Hg(S-2-CH3NHCOC6H4)2] (2), [Hg(S-2-C6H5CH2NHCOC6H4)2] (3), and (NEt4)2[Hg(S-2-CH3NHCOC6H4)4] (5)
Complex 1
Hg(1)-S(1)
2.351(4)
2.345(4)
177.3(2)
103.4(6)
101.1(4)
66.8
2.65(1)
3.358(5)
2.98(2)
2.91(1)
Hg(2)-S(3)
2.325(4)
2.321(5)
176.9(2)
102.5(5)
99.2(6)
-89.1
Hg(1)-S(2)
Hg(2)-S(4)
S(1)-Hg(1)-S(2)
Hg(1)-S(1)-C(11)
Hg(1)-S(2)-C(21)
C(11)-S(1)-Hg(1)-S(2)-C(21)
Hg(1)‚‚‚O(1)(intra)
Hg(1)‚‚‚S(3)(inter)
N(2)‚‚‚O(1)(intra)
N(1)‚‚‚O(4)(inter)
S(3)-Hg(2)-S(4)
Hg(2)-S(3)-C(31)
Hg(2)-S(4)-C(41)
C(31)-S(3)-Hg(2)-S(4)-C(41)
Hg(2)‚‚‚O(3)(intra)
Hg(2)‚‚‚S(2)(inter)
N(4)‚‚‚O(3)(intra)
N(3)‚‚‚O(2)(inter)
2.68(1)
3.625(4)
3.00(2)
2.92(2)
Complex 2
2.333(3)
Hg(1)-S(1)
S(1)-Hg(1)-S(1′)
C(11)-S(1)-Hg(1)-S(1′)-C(11′)
Hg(1)‚‚‚O(1)(intra)
S(1)-Hg(1)-O(1)
175.18(9)
109.9
3.06
84.4
158.3
Hg(1)-S(1)-C(11)
102.2(2)
N(1)‚‚‚O(1)(inter)
S(1)-Hg(2)-C(2)
2.810(7)
95.7(3)
O(1)-Hg(1)-O(1′)
Complex 3
2.338(1)
180.0
180.0
3.243(5)
Hg(1)-S(1)
S(1)-Hg(1)-S(1′)
Hg(1)-S(1)-C(11)
N(1)‚‚‚O(1)(inter)
100.9(1)
2.754(6)
C(11)-S(1)-Hg(1)-S(1′)-C(11′)
Hg(1)‚‚‚O(1)(inter)
Complex 5
Hg(1)-S(1)
2.551(3)
115.13(8)
98.67(14)
-15(2)
S(1)-Hg(1)-S(1′)
S(1)-Hg(1)-S(1′′′)
N(1)-C(17)-C(16)-C(11)
N(1)‚‚‚S(1)
S(1)-Hg(1)-S(1′′)
Hg(1)-S(1)-C(11)
115.13(8)
107.0(4)
3.02(1)
The intramolecular distances between the nitrogen atom and
the sulfur atom in the four thiophenolate ligands are about
3.00 Å. This suggests the formation of the intramolecular
NH‚‚‚S hydrogen bond. The X-ray analyses suggest that the
anionic ionicity of the sulfur atom coordinated to mercury
in tetrakis(carbamoylthiophenolate) complex 5 is greater than
in bis(carbamoylthiophenolate) anion 2, leading to rotation
of the amide plane and formation of the intramolecular
NH‚‚‚S hydrogen bond in complex 5.
[Hg(S-2-CH3NHCOC6H4)4] (5), in the solid state. Table 2
lists the IR data in the amide region ν(NH) and ν(CdO)
bands for the mercury complexes, the free ν(NH) and
ν(CdO) bands of the corresponding thiol and disulfide
compounds, and the shift values. Complex 1 exhibits two
NH bands at 3302 and 3250 cm-1 and two CO bands at 1650
IR Spectra in the Solid State and Solution. Figure 4
shows the IR spectra of the bis(carbamoylthiophenolate)
complexes, [Hg(S-2-t-BuNHCOC6H4)2] (1), [Hg(S-2-CH3-
NHCOC6H4)2] (2), and [Hg(S-2-C6H5CH2NHCOC6H4)2] (3),
and of the tetrakis(carbamoylthiophenolate) complex, (NEt4)2-
Figure 4. IR spectra of (a) [Hg(S-2-CH3NHCOC6H4)2] (1), (b) [Hg(S-
2-CH3NHCOC6H4)2] (2), (c) [Hg(S-2-C6H5CH2NHCOC6H4)2] (3), and (d)
(NEt4)2[Hg(S-2-t-BuNHCOC6H4)2] (5) in the solid state.
Figure 3. Crystal structure of (NEt4)2[Hg(S-2-CH3NHCOC6H4)2] (5).
Dotted lines refer to the intramolecular NH‚‚‚S hydrogen bond.
4040 Inorganic Chemistry, Vol. 44, No. 11, 2005

Hg(II) Complexes with Carbamoylbenzenethiols
Table 2. IR Spectral Data (cm-1) for Mercury(II) Complexes and Related Compounds in the Solid State and in Chloroform (10 mM)
in solid state
in chloroform
compd
ν(NH)
ν(CO)
ν(NH)
3450
3432
3424, 3348
ca. 3200, 3451
3429
3431
ν(CO)
1638
1637
1650, 1631
1627
1659
1658
1618
[Hg(S-2-t-BuNHCOC6H4)2] (1)
[Hg(S-2-CH3NHCOC6H4)2] (2)
[Hg(S-2-C6H5CH2NHCOC6H4)2] (3)
(NEt4)2[Hg(S-2-CH3NHCOC6H4)4] (5)
(S-2-t-BuNHCOC6H4)2
3261
3232
3302
3182
3294
3303
3154
3345
3228
1627, 1610
1634
1650, 1614
1631
1634
1632
1618
2-t-BuNHCOC6H4SH
(NEt4)(2-t-BuNHCOC6H4S)
[Hg(S-2-t-BuCONHC6H4)2]
[Hg(S-2-CH3CONHC6H4)2]
3153
1685, 1665, 1649
1658
and 1614 cm-1, as shown in Figure 4a. From the X-ray
analyses, one of the two carbonyl oxygens forms an intra-
molecular NH‚‚‚OdC hydrogen bond with the amide proton
and the bonding interaction with mercury, while the other
carbonyl oxygen forms the intermolecular NH‚‚‚OC hydro-
gen bond. It follows that the amide NH groups of the two
thiophenolate ligands in 1 are not equivalent, and the CO
band with the Hg‚‚‚OdC interaction is detected as a low-
wavenumber band (3250 cm-1).
has two distinct amide groups, and the NH and CO bands
with the intramolecular NH‚‚‚OdC hydrogen bond are
observed at 3348 and 1631 cm-1, respectively, and those
without the hydrogen bond are observed at 3424 and 1650
cm-1. Complex 2 exhibits an NH band at 3450 cm-1 and a
CO band at 1638 cm-1. Complex 3 exhibits an NH band at
3432 cm-1 and a CO band at 1637 cm-1. The NH bands in
both complexes have values rather similar to that in the
corresponding thiol compound.19 Consequently, complexes
2 and 3 do not form an NH‚‚‚OdC and NH‚‚‚S hydrogen
bond in solution.
Complex 2 exhibits an NH band at 3261 cm-1 and two
CO bands at 1627 and 1610 cm-1, as shown in Figure 4b.
From the X-ray analyses, the two carbonyl oxygens partici-
pate in the intramolecular Hg‚‚‚OdC interaction, but two
CO bands are detected because the two Hg‚‚‚O distances
are different (2.98(3) and 3.15(2) Å). Complex 3 exhibits
an NH band at 3232 cm-1 and a CO band 1634 cm-1, as
shown in Figure 4c. From the X-ray analyses, the two
thiophenolate ligands have the same structure as the center
of symmetry is mercury and are equivalent. As a result, the
NH and CO bands are each detected as a single band. The
CO band with the intermolecular Hg‚‚‚OdC interaction in
the crystal structure appears at high-wavenumber compared
with 2 with the intramolecular Hg‚‚‚OdC interaction.
The tetrakis(carbamoylthiophenolate) complex 5 exhibits
an NH band at 3182 cm-1 and a CO band at 1631 cm-1.
This large ∆ν(NH) value for 5, compared with that of the
thiol compound and bis(carbamoylthiophenolate) complexes,
is ascribed to the intramolecular NH‚‚‚S hydrogen bond and
is additional to the values detected as a result of the NH‚‚‚S
hydrogen bond in the corresponding thiophenolate anion
compounds.17 The intramolecular NH‚‚‚S hydrogen bond
does not form, because of a reduction in the ionicity for the
sulfur atom coordinated to mercury in the bis(carbamoyl-
thiophenolate) complex. However, an increase of the ionicity
for the sulfur atom with increasing coordination number gives
rise to an intramolecular NH‚‚‚S hydrogen bond in the
tetrakis(carbamoylthiophenolate) complex. The crystal struc-
ture in 5 does not form an intermolecular interaction,
suggesting that the intramolecular NH‚‚‚S hydrogen bond
is strong.
The tetrakis(carbamoylthiophenolate) complex 5 exhibits
a broad NH band at ca. 3200 cm-1, a free NH band at 3451
cm-1, and a CO band at 1631 cm-1. This large shift of the
NH band suggests that complex 5 has an intramolecular
NH‚‚‚S hydrogen bond in solution as well as in the solid
state. In view of the NH band in bis(carbamoylthiophenolate)
complex 2 (3450 cm-1), these results suggest that the NH
band with the intramolecular NH‚‚‚S hydrogen bond and the
NH band without the hydrogen bond due to rotation of the
amide plane are detected separately. The ∆ν(NH) value for
5 is ca. 100 cm-1 below that of the thiol compound. This
value is much smaller than that for the corresponding thiolate
anion (-278 cm-1) but is similar to that of the reported
platinum complex [Pt(bpy)(S-2-t-BuNHCOC6H4)2] (-126
cm-1).20 The intramolecular NH‚‚‚S hydrogen bond in the
tetrakis(carbamoylthiophenolate) complex 5 is not as strong
as that in the thiophenolate anion but is similar in strength
to that in the platinum complex in solution. The weaker
NH‚‚‚S hydrogen bond in the mercury complex is ascribed
to a lowering of the ionicity of the sulfur atom by the strongly
covalent Hg-S bond.
1
1H NMR Spectra. Table 3 summarizes the H chemical
shifts of the amide NH for the bis(carbamoylthiophenolate)
complexes, [Hg(S-2-t-BuNHCOC6H4)2] (1), [Hg(S-2-CH3-
NHCOC6H4)2] (2), [Hg(S-2-C6H5CH2NHCOC6H4)2] (3), and
[Hg(S-4-t-BuNHCOC6H4)2] (4), and the tetrakis(carbam-
oylthiophenolate) complex, (NEt4)2[Hg(S-2-CH3NHCOC6H4)4]
(5), and the corresponding disulfide, thiol, and thiolate anion
compounds. The amide NH signals appear at 6.19 ppm in
1, 6.52 ppm in 2, 6.77 ppm in 3, and 6.52 ppm in 4. These
values are similar to that of the corresponding thiol com-
pound, and the large downfield shift by the intramolecular
NH‚‚‚S hydrogen bond such as the corresponding thiophe-
nolate anion compound19 is not detectable. However, the
amide NH signal in 5 is detected at 9.20 ppm and is largely
shifted downfield compared with the bis(carbamoylthiophe-
Table 2 summarizes the IR data in the amide region
ν(NH) and ν(CdO) bands in chloroform-d1 for the mercury
complexes, free ν(NH) and ν(CdO) bands of the corre-
sponding thiol and disulfide compounds, and the shift values.
Complex 1 exhibits two NH bands at 3424 and 3348 cm-1
and two CO bands at 1650 and 1631 cm-1. This suggests
that, in solution as well as the crystal structure, complex 1
Inorganic Chemistry, Vol. 44, No. 11, 2005 4041

Kato et al.
Table 3. 1H Chemical Shifts (ppm) of Amide NHs in Chloroform-d1
and 199Hg Chemical Shifts (ppm) in Dimethylformamide-d7 of
Mercury(II) Complexes and Related Compounds
compd
1H/ppm
199Hg/ppma
[Hg(S-2-t-BuNHCOC6H4)2] (1)
[Hg(S-2-CH3NHCOC6H4)2] (2)
[Hg(S-2-C6H5CH2NHCOC6H4)2] (3)
[Hg(S-4-t-BuNHCOC6H4)2] (4)
(NEt4)2[Hg(S-2-CH3NHCOC6H4)4] (5)
(S-2-t-BuNHCOC6H4)2
6.19
6.52
6.77
5.85
9.20
5.83
5.72
12.16
8.51
-1032
-934
-1059
-1059
-466b
2-t-BuNHCOC6H4SH
(NEt4)(2-t-BuNHCOC6H4S)
[Hg(S-2-t-BuCONHC6H4)2]
Hg(SC6H5)2
-1142
-1058
a ppm from Hg(CH3)2. b In chloroform-d1.
nolate) complex and the corresponding thiol compound. This
shift is ascribed to the formation of the intramolecular
NH‚‚‚S hydrogen bond in solution expected from the IR data.
However, the 1H signals are all broad, suggesting that
complex 5 is the equilibrium state described by eq 1 in
solution.
Figure 5. Correlation of 199Hg NMR chemical shifts in dimethylformamide
with Hammett σp constants in Hg(SC6H4R)2.
thiophenol ring results in a largely downfield shift of the
199Hg signals, especially for complex 2. From NMR theoreti-
cal studies of the elements in group 12 (Zn, Cd), the chemical
shift is the sum of diamagnetic terms and paramagnetic terms,
and the chemical shift is strongly influenced by the para-
magnetic terms.23 In the case of an element in group 12,
this paramagnetic term is affected by flow of the electron in
the ligand to the unoccupied p-orbital of the metal. In the
reported mercury complexes forming the intramolecular NH‚
‚‚S hydrogen bond, the flow of an electron to the p-orbital
of Hg(II) is less, because of the overlap between the s-orbital
of the amide proton and the p-orbital of the sulfur atom.18
However, in the complexes 1 and 2 the paramagnetic term
is large because of both the flow of the electron from the
sulfur atom and also the flow of the electron from the oxygen
atom involved in the intramolecular Hg‚‚‚O bonding interac-
tions; the result suggests that the 199Hg signal shifts down-
field. The 199Hg signal is detected at -1059 cm-1 in 3
without the intramolecular interaction and at 1032 cm-1 in
1 with a single intramolecular Hg‚‚‚OdC interaction and
shifts downfield. In addition, the 199Hg signal is detected at
-934 cm-1 in 2 with two intramolecular Hg‚‚‚OdC interac-
tions and shifts further downfield.
The 199Hg signal in tetrakis(carbamoylthiophenolate) com-
plex 5 appears at -466 ppm in chloroform-d1. The value is
largely shifted downfield relative to the bis(carbamoyl-
thiophenolate) complex. As well as the results of Gruff et
al.,1 this suggests that the flow of the electron in the ligand
to the unoccupied p-orbital of the mercury atom increases
due to the increase in the coordination number, and the
paramagnetic term increases.
Biological Relevance. The high coordination number state
in the Hg2+ complex is important in reducing Hg2+ to
Hg(0) in mercuric reductase. It has been proposed that MerR
has a tricoordinate structure in the detoxification system of
(NEt4)2[Hg(SAr)4] h Hg(SAr)2 + 2(NEt4)(SAr) (1)
The amide NH signal in 5 at -30 °C is not split into two
signals by the equilibrium but is detected at 9.7 ppm and
largely shifts downfield by 0.5 ppm. It follows that the
equilibrium shifts to the tetracoordinate state forming the
intramolecular NH‚‚‚S hydrogen bond at low temperature
in solution. These findings suggest that the amide proton
detected separately in the IR measurement is observed on
the average by the rotation of the amide plane in the 1H NMR
measurement.
199Hg NMR Spectra. The 199Hg NMR spectra in com-
plexes 1-5 were measured to investigate the electronic states
around the mercury. Table 3 summarizes the results and the
199Hg chemical shifts of the reported mercury complexes.
Hg(CH3)2 was used as the external reference for the mercury
resonance. The signals appear at -1032 ppm in 1, -934
ppm in 2, and -1059 ppm in 3. The signal in p-substituted
thiophenolate complex 4, which is synthesized to take into
account the electronic effect of the substituent, is detected
at -1059 ppm and is similar or shifted downfield relative
to the o-substituted thiophenolate complexes 1-3. The signal
in the reported mercury complex Hg(S-2-RCONHC6H4)2
forming the intramolecular NH‚‚‚S hydrogen bond shifts to
high field compared with Hg(S-4-RCONHC6H4)2.18 Figure
5 plots the chemical shifts of the 199Hg signals in dimeth-
ylformamide-d7 of Hg(SC6H4R)2 with Hammett σp constants.
The plots of the p-substituents, OMe, NHCOCH3, Cl, and
NO2, follow a straight line apart from those for the
p-substituent, H. Deviation of Hg(SC6H5)2 from the line with
a high-field chemical shift is probably due to contamination
by polymeric structures with tri- and tetracoordinate geom-
etry.22
The electron contribution of the carbamoyl group at the
o-position shows an electron-withdrawing effect (σp ) 0.3).
Introduction of carbamoyl groups at the o-position of the
(23) Nakatsuji, H.; Kand, K.; Endo, K.; Yonezawa, T. J. Am. Chem. Soc.
1984, 106, 4653-4660.
(22) Canty, A. J.; Kishimoto, R. Inorg. Chim. Acta 1977, 24, 109-122.
4042 Inorganic Chemistry, Vol. 44, No. 11, 2005

Hg(II) Complexes with Carbamoylbenzenethiols
Hg2+ ion.6-8 We have synthesized tetrakis(carbamoyl-
thiophenolate) mercuric complex 5 and determined its crystal
structure. Complex 5 has a tetrahedral structure with four
intramolecular NH‚‚‚S hydrogen bonds which are undetect-
able in the bis(carbamoylthiophenolate) complex. The tet-
rahedral Hg(II) structure with a NH‚‚‚S hydrogen bond is
similar to that of rubredoxin. The four Fe-S distances of
the reduced rubredoxin are slightly longer than those of the
oxidized form, whereas the six NH‚‚‚S hydrogen bonds
between the sulfur atoms of cysteines coordinated to the Fe
atom and the neighboring amide NHs of the main chain are
shorter than in the oxidized form.24,25 As a result, the overall
positions of the backbone atoms around the [Fe-S] redox
center remain uncharged with the change in oxidation state.
The model complexes [Fe(S-2-CH3CONHC6H4)4]2- 15 and
[Fe(cys-X-Y-cys)2]2- 26 show a positive shift of redox
potential due to the NH‚‚‚S hydrogen bond. Our investigation
suggests that the NH‚‚‚S hydrogen bonds in tetrakis-
(carbamoylthiophenolato)mercuric complex stabilize the
extra negative charge due to the increase in the coordination
number.
We have also reported previously that the NH‚‚‚S hydro-
gen bond reduces the pKa of thiol.19 Lowering of the pKa
stabilizes the thiolate anion state and increases the complex-
ation constant. This effect also indicates that NH‚‚‚S
hydrogen bonds are the stabilizing factor in the tri- and
tetracoordinate mercury complexes. The present results
therefore suggest that the combined effects of NH‚‚‚S
hydrogen bonds stabilize the high coordination number of
the Hg2+ complex proposed as the intermediate in the
reduction of Hg2+ in vivo.
The tetrakis(carbamoylthiophenolate) mercury complex 5
has a tetragonal structure and forms an intramolecular
NH‚‚‚S hydrogen bond. In addition, the distance between
the mercury atom and the sulfur atom is longer by 0.2 Å
than that in bis(carbamoylthiophenolate) complexes. In the
tetrakis(carbamoylthiophenolato)mercury complex, the thiophe-
nolate ligand becomes anionic because of the increase of
ionic bonding between the mercury and the sulfur, and an
intramolecular NH‚‚‚S hydrogen bond is formed. The previ-
ous works show that the intramolecular NH‚‚‚S hydrogen
bond between the amide NH and the sulfur coordinated to
metal reduces the π-donor capacity of the thiolate ligands.
Consequently, formation of the intramolecular NH‚‚‚S
hydrogen bond in the tetrakis(carbamoylthiophenolate) com-
plex stabilizes the extra negative charge by increasing of the
coordination number and perhaps stabilizes the tri- and
tetracoordinate mercury complexes existing in vivo.
Experimental Section
Materials. All operations were performed under an argon
atmosphere. All solvents were dried and distilled under argon before
use. The syntheses of 2-mercapto-N-alkylbenzamide and 4-mer-
capto-N-alkylbenzamide were carried out using the same previously
reported procedure.19
Synthesis of [Hg(S-2-t-BuNHCOC6H4)2] (1). To a methanol
solution (10 mL) of 2-mercapto-N-(1,1-dimethylethyl)benzamide
(490 mg, 2.4 mmol) was added mercury dichloride (350 mg, 1.3
mmol) at room temperature. After being stirred for 2 h, the solution
was concentrated, and saturated NaCl(aq) was added (30 mL) to
give a white precipitate which was collected with filtration. The
resulting white solid was washed with saturated NaCl(aq) and water.
Yield: 664 mg (92%). Anal. Calcd for C22H28N2O2S2Hg‚2C4H8O:
C, 47.32; H, 5.82; N, 3.68. Found: C, 47.36; H, 5.20; N, 3.54.
ESI-MS: m/z 641.2, [M + Na]+. 1H NMR (chloroform-d1): δ 7.62
(d, 2H), 7.29 (d, 2H), 7.15 (t, 2H), 6.19 (s, 2H), 1.34 (s, 18H).
13C{H} NMR (chloroform-d1): δ 170.5, 141.0, 136.3, 131.2, 129.6,
127.3, 126.5, 52.2, 28.8.
Synthesis of [Hg(S-2-CH3NHCOC6H4)2] (2). The complex was
synthesized by the same method described above for the synthesis
of [Hg(S-2-t-BuNHCOC6H4)2]. Yield: 98%. The crude product was
recrystalized from methanol. Anal. Calcd for C16H16N2O2S2Hg‚
1/4C6H14: C, 37.90; H, 3.54; N, 5.05. Found: C, 38.17; H, 3.32;
N, 5.09. ESI-MS: m/z 556, [M + Na]+. 1H NMR (chloroform-d1):
δ 7.65 (d, 2H), 7.37 (d, 2H), 7.24 (t, 2H), 7.18 (t, 2H), 6.52 (s,
2H), 2.88 (s, 6H). 13C{H} NMR (chloroform-d1): δ 171.2, 139.8,
136.5, 131.8, 129.9, 127.8, 126.5, 26.7.
Conclusions
The bis(carbamoylthiophenolate) mercury complexes [Hg-
(S-2-t-BuNHCOC6H4)2] (1), [Hg(S-2-CH3NHCOC6H4)2] (2),
and [Hg(S-2-C6H5CH2NHCOC6H4)2] (3) and tetrakis(car-
bamoylthiophenolate) mercury complex (NEt4)2[Hg(S-2-
CH3NHCOC6H4)2] (5) were synthesized and their crystal
structures determined. The bis(carbamoylthiophenolate) mer-
cury complexes 1-3 do not form an intramolecular NH‚‚‚S
hydrogen bond because of lowering of the ionicity for the
sulfur atom by the strongly covalent Hg-S bond. The
orientation of the amide plane to the mercury atom differs
with differing terminal substituents, and the intra- and
intermolecular interactions are qualitatively different. The
199Hg signal appears at -1059 ppm in 3 without the
intramolecular interaction, at 1032 ppm in 1 with a single
Hg‚‚‚OdC interaction, and at -934 ppm in 2 with two
Hg‚‚‚OdC interactions, largely shifting downfield due to the
Hg‚‚‚OdC interaction. Differences in the orientation of the
amide group and the terminal substituent control the structure
of the mercury complex and the electronic state around the
mercury ion.
Synthesis of [Hg(S-2-C6H5CH2NHCOC6H4)2] (3). The complex
was synthesized by the same method described above for the
synthesis of [Hg(S-2-t-BuNHCOC6H4)2]. Yield: 90%. Anal. Calcd
for C28H24N2O2S2Hg: C, 49.08; H, 3.53; N, 4.09. Found: C, 48.74;
1
H, 3.33; N, 4.14. H NMR (chloroform-d1): δ 7.62 (d, 2H), 7.31
(d, 2H), 7.25 (m, 12H), 7.20 (t, 2H), 7.13 (t, 2H), 6.77 (s, 2H),
4.41 (d, 2H). 13C{H} NMR (chloroform-d1): δ 170.5, 139.7, 137.7,
136.6, 131.9, 129.9, 128.7, 128.0, 127.6, 126.5, 44.0.
Synthesis of [Hg(S-4-t-BuNHCOC6H4)2] (4). The complex was
synthesized by the same method described above for the synthesis
of [Hg(S-2-t-BuNHCOC6H4)2]. Yield: 87%. Anal. Calcd for
C22H28N2O2S2Hg: C, 42.81; H, 4.57; N, 4.54. Found: C, 42.15;
H, 4.34; N, 4.43. ESI-MS: m/z 641.2, [M + Na]+. 1H NMR
(chloroform-d1): δ 7.55 (d, 4H), 7.42 (d, 4H), 5.85 (s, 2H), 1.52
(s, 18H). 13C{H} NMR (chloroform-d1): δ 166.0, 134.2, 133.1,
129.1, 127.4, 51.8, 28.9.
(24) Day, M. W.; Hsu, B. T.; Joshua-Tor, L.; Park, J. B.; Zhou, Z. H.;
Adams, M. W. W.; Rees, D. C. Protein Sci. 1992, 1, 1494-1507.
(25) Min, T.; Ergenekan, C. E.; Eidsness, M. K.; Ichiye, T.; Kang, C.
Protein Sci. 2001, 10, 613-621.
(26) Sun, W. Y.; Ueyama, N.; Nakamura, A. Inorg. Chem. 1991, 30, 4026-
4031.
Inorganic Chemistry, Vol. 44, No. 11, 2005 4043

Kato et al.
Table 4. Crystallographic Data for [Hg(S-2-t-BuNHCOC6H4)2] (1), [Hg(S-2-CH3NHCOC6H4)2] (2), [Hg(S-2-C6H5CH2NHCOC6H4)2] (3), and
(NEt4)2[Hg(S-2-CH3NHCOC6H4)4] (5)
1
2
3
5
chem formula
fw
C22H28N2O2S2Hg
617.19
C16H16N2O2S2Hg
533.02
C28H24N2O2S2Hg
685.22
C48H72N6O4S4Hg
1125.96
T/K
296(1)
296(1)
296 (1)
296(1)
cryst system
lattice params
a/Å
b/Å
c/Å
triclinic
monoclinic
triclinic
tetragonal
10.943(4)
15.062(5)
17.238(7)
82.15(3)
86.89(3)
85.89(3)
2804(1)
4
21.993(5)
9.173(5)
8.950(5)
90
104.09(3)
90
4.696(1)
11.835(2)
12.327(2)
103.39(1)
100.94(2)
92.30(2)
651.8(2)
1
12.679(3)
12.679(3)
33.381(6)
90
90
90
R/deg
â/deg
γ/deg
V/Å3
1751(1)
4
5366(2)
4
Z
space group
P1h (No. 2)
C2/c (No. 15)
2.022
90.36
2706
2551
P1h (No. 2)
I41/a (No. 88)
1.394
30.77
2586
2358
0.053
0.181
D
calc/g‚cm-3
1.462
1.746
µ/cm-1
56.59
10 439
9852
0.073
0.224
60.91
4195
3778
0.033
reflcns collcd
indep reflcns
R for I > 2σ(I)
wR2 for all data
0.053
0.143
0.074
Synthesis of (NEt4)2[Hg(S-2-CH3NHCOC6H4)4] (5). To a
tetrahydrofuran solution (7 mL) of (NEt4)[Hg(SC6H5)3] (130 mg,
0.19 mmol) was added a tetrahydrofuran solution (3 mL) of
2-mercapto-N-methylbenzamide (97 mg, 0.58 mmol), and the
resulting solution was stirred overnight at room temperature. The
reaction mixture was concentrated and added diethyl ether to
precipitate a white powder. Yield: 98%. Anal. Calcd for
C48H72N6O4S4Hg‚3H2O: C, 48.86; H, 6.66; N, 7.12. Found: C,
48.46; H, 6.47; N, 6.78. 1H NMR (chloroform-d1): δ 9.20 (s, 4H),
7.73 (d, 4H), 7.43 (d, 4H), 6.86 (t, 8H), 2.85 (m, 28H), 1.01 (t,
24H).
Physical Measurements. 1H NMR and 13C NMR spectra were
obtained on a JEOL GSX-400 spectrometer in chloroform-d1
solution at 303 K. Tetramethylsilane (TMS) was used as the internal
reference for proton resonance. 199Hg NMR spectra were obtained
on a Varian Unityplus 600 MHz spectrometer in dimethylforma-
mide-d7 or chloroform-d1 solution at 303 K. IR spectra were taken
on a Jasco FT/IR-8300 spectrometer. Samples were prepared as
chloroform-d1 solutions or KBr pellets. ESI-mass spectrometric
analyses were performed on a Finniganmat LCQ-MS instrument
in methanol or acetonitrile.
Structure Determinations. Suitable single crystals of [Hg(S-
2-t-BuNHCOC6H4)2] (1), [Hg(S-2-CH3NHCOC6H4)2] (2), [Hg(S-
2-C6H5CH2NHCOC6H4)2] (3), and (NEt4)2[Hg(S-2-CH3NHCOC6H4)4]
(5) were shielded in a glass capillary under an argon atmosphere.
X-ray measurements were made at 300 K on a Rigaku AFC7R for
1 and AFC5R for 2, 3, and 5 diffractometer with graphite-
monochromated Mo KR radiation (0.710 69 Å). Unit cell dimen-
sions were refined with 23 reflections for 1 and 25 reflections for
2, 3, and 5. The basic crystallographic parameters for 1-3 and 5
are listed in Table 4. Three standard reflections were chosen and
monitored with every 150 reflections and did not show any
significant change. The data were collected up to 2θmax ) 55° for
1 and 5 and 60° for 2 and 3. An empirical absorption correction
based on azimuthally scans three reflections was applied. The
structures were solved by the direct method using the teXsan
crystallographic software package.27 Refinements were carried out
on F for 1 and 2 and on F2 for 3 and 5, respectively. All non-
hydrogen atoms were refined anisotropically. All hydrogen atoms
were placed on the calculated positions. The final refinement was
carried out using full-matrix least-squares techniques with non-
hydrogen atoms. The final difference Fourier map showed no
significant features. Atom-scattering factors and dispersion correc-
tions were taken from ref 28 In complex 5, tetraethylammonium
cation is disordered into two positions with site occupancy factors
of each 0.500.
Acknowledgment. This work was supported by a Grant-
in Aid for Scientific Research on Priority Area (A) (No.
12304040) from the Ministry of Education, Culture, Sports,
Science, and Technology of Japan. M.K. expresses his special
thanks for the center of excellence (21COE) program
“Creation of Integrated EcoChemistry of Osaka University”.
Supporting Information Available: X-ray crystallographic data
in CIF format. This material is available free of charge via the
Internet at http://pubs.acs.org.
IC0481780
(27) teXsan: Crystal Structure Analysis Program; Molecular Corp.: The
Woodlands, TX, 1985 and 1992.
(28) Cromer, D. T.; Waber, J. T. International Tables for X-ray Crystal-
lography; Kynoch Press: Birmingham, U.K., 1974; Vol. IV.
4044 Inorganic Chemistry, Vol. 44, No. 11, 2005