Copper(II)-mercury(II) heterometallic complexes derived from a salen-type ligand: A new coordination mode of the old Schiff base ligand

Article abstract of DOI:10.1021/om201033q

Three heterometallic copper(II)-mercury(II) complexes, [(CuL-CH ₃)HgCl₂] (1), [(CuL-CH₃)₂HgCl ₂] (2), and [(CuL-CH₂-HgCl)₂] (3), have been synthesized by reacting the "complex as ligand" [CuL-CH₃] with HgCl₂ by varying the reaction conditions and stoichiometry of the reactants, where H₂L-CH₃ = the di-Schiff base of 1,3-propanediamine and 2-hydroxyacetophenone. All three complexes have been characterized by X-ray single-crystal structure, elemental, and spectroscopic analyses. In complex 1, the Hg(II) ion is bonded by two phenoxido oxygen atoms of a [CuL-CH₃] moiety and two terminal chloride ions to form a dinuclear species. In the trinuclear complex 2, the central Hg(II) ion is coordinated by two terminal [CuL-CH₃] units through one phenoxido oxygen from each unit and two chloride ions. On the other hand, in the tetranuclear complex 3, the Hg(II) ion has a distorted-tetrahedral geometry, being bonded to one chloride, two phenoxido oxygen atoms of one [CuL-CH ₂] unit, and a methyl carbon atom of another [CuL-CH₂] unit. The structure of complex 3 reveals an unprecedented heptadentate coordination mode (1-κ⁴NN′OO′:2- κ²OO′:3-κC) of the Schiff base ligand that resulted in a unique organomercury metallamacrocycle.

Full text of DOI:10.1021/om201033q

Article
pubs.acs.org/Organometallics
Copper(II)−Mercury(II) Heterometallic Complexes Derived from a
Salen-Type Ligand: A New Coordination Mode of the Old Schiff Base
Ligand
Saptarshi Biswas,† Rajat Saha,‡ and Ashutosh Ghosh*,†
†Department of Chemistry, University College of Science, University of Calcutta, 92, APC Road, Kolkata 700 009, India
‡Department of Physics, Jadavpur University, Jadavpur, Kolkata 700 032, India
S
* Supporting Information
ABSTRACT: Three heterometallic copper(II)−mercury(II) complexes, [(CuL-
CH3)HgCl2] (1), [(CuL-CH3)2HgCl2] (2), and [(CuL-CH2-HgCl)2] (3), have
been synthesized by reacting the “complex as ligand” [CuL-CH3] with HgCl2 by
varying the reaction conditions and stoichiometry of the reactants, where H2L-
CH3 = the di-Schiff base of 1,3-propanediamine and 2-hydroxyacetophenone. All
three complexes have been characterized by X-ray single-crystal structure,
elemental, and spectroscopic analyses. In complex 1, the Hg(II) ion is bonded by
two phenoxido oxygen atoms of a [CuL-CH3] moiety and two terminal chloride
ions to form a dinuclear species. In the trinuclear complex 2, the central Hg(II)
ion is coordinated by two terminal [CuL-CH3] units through one phenoxido
oxygen from each unit and two chloride ions. On the other hand, in the
tetranuclear complex 3, the Hg(II) ion has a distorted-tetrahedral geometry,
being bonded to one chloride, two phenoxido oxygen atoms of one [CuL−CH2]
¯ unit, and a methyl carbon atom of another [CuL−CH2]¯ unit. The structure of complex 3 reveals an unprecedented
heptadentate coordination mode (1-κ4NN′OO′:2-κ2OO′:3-κC) of the Schiff base ligand that resulted in a unique organomercury
metallamacrocycle.
several metal chelates. A CSD (updated May 2011) search
reveals that to date 14 heteronuclear complexes of Hg(II) have
been reported with various “complex as ligand” species; among
them 10 are copper(II) chelates. Out of these 10 complexes, 4
are dinuclear, 2 are trinuclear, 2 are tetranuclear, and 2 are
INTRODUCTION
■
Since Hugo Schiff first synthesized the “Schiff bases”,1 by the
condensation of an amine with an aldehyde, their complexes
with transition-metal ions have been one of the most
exhaustively studied topics in coordination chemistry because
of the ease with which they can be synthesized, their wide range
of complexing ability, and their uses in various fields of
chemistry: e.g. inorganic biochemistry, catalysis, and magnet-
ism.2 Among the Schiff bases, “salen-types”, which are formed
by the condensation of various diamines and salicylaldehyde
derivatives, are arguably the most popular ones. In general, the
dinegative anionic form of this type of Schiff base acts as a
tetradentate chelating ligand with two nitrogen and two oxygen
atoms as donor sites to produce a mononuclear complex.3
However, in several cases it has been found4 that the oxygen
atoms of such metal complexes can coordinate to a second
metal ion and generate multinuclear complexes.5 As a result,
the mononuclear complexes of such ligands with dipositive
first-row transition elements can conveniently be used as a
“complex as ligand” for the synthesis of heterometallic
complexes in which the coordinating modes of these di-Schiff
bases are penta- or hexadentate with the nitrogen and oxygen
atoms as donor centers. Recently, we have incorporated Na(I),
Cd(II), Pb(II), and Mn(II) ions with the help of such Cu(II)
chelates, to result in tri- and tetranuclear heterometallic
complexes.6 Mercury is well known to form an adduct with
polynuclear.
Herein, we report the synthesis and crystal structure of the
dinuclear complex [(CuL-CH3)HgCl2] (1), the trinuclear
complex [(CuL-CH3)2HgCl2] (2), and the tetranuclear cyclic
organomercurial complex [(CuL-CH2-HgCl)2] (3), where the
di-Schiff base H2L-CH3 = N,N′-bis(α-methylsalicylidene)-1,3-
propanediamine (Scheme 1). We show here that upon
changing the molar ratios of [CuL-CH3] to the Hg(II) salt,
dinuclear and trinuclear complexes can conveniently be
prepared. Both of the complexes convert slowly into the
tetranuclear complex 3, in which the methyl group of [CuL-
CH3] undergoes direct mercuration. To our knowledge,
complex 3 is the first report of an organomercurial species
where a methyl carbon at the α position of a imine nitrogen of a
metal-bound Schiff base undergoes direct mercuration by C−H
bond activation.
Received: October 25, 2011
Published: May 9, 2012
© 2012 American Chemical Society
3844
dx.doi.org/10.1021/om201033q | Organometallics 2012, 31, 3844−3850

Organometallics
Article
Scheme 1. Synthetic Route to Complexes 1−3
did not get dissolved was removed by filtration, and the filtrate was
allowed to stand at room temperature. Overnight, deep green X-ray-
quality single crystals appeared at the bottom of the vessel. The
crystals were isolated, washed with Et2O, and dried in a vacuum
desiccator containing anhydrous CaCl2. Yield: 0.652 g (64%). Anal.
Calcd for C38H40Cu2Hg1N4O4Cl2 (1015.31): C, 44.95; H, 3.97; N,
5.52. Found: C, 45.18; H, 3.96; N, 5.42. HRMS (m/z, ESI+): found for
HgCl2 + H + CH3CN 311.9276 (calcd 311.9404), [CuL-CH3] + H
372.1049 (calcd 372.0999), [CuL-CH3] + Na 394.0813 (calcd
394.0818), [CuL-CH3]2 + H 743.1896 (calcd 743.1920), [CuL-
CH3]2 + Na = 765.1735 (calcd 765.1739).
Synthesis of the Complex [(CuL-CH2-HgCl)2] (3). An aqueous
solution (10 mL) of HgCl2 (0.5 mmol, 0.136 g) was added to a
methanolic solution (40 mL) of [CuL-CH3] (0.5 mmol, 0.186 g)
followed by the addition of triethylamine (0.5 mmol, 0.07 mL), and
the mixed solution was stirred well for about 15 min. There was no
immediate precipitation. The solution was allowed to stand at room
temperature for slow evaporation of solvent. Deep brown X-ray-quality
single crystals started to appear as the volume was reduced. The
crystals were isolated when the volume of the solution was reduced to
about 5 mL, washed with Et2O, and dried in a desiccator containing
anhydrous CaCl2. Yield: 0.185 g (61%). Anal. Calcd for
C38H38Hg2Cu2N4O4Cl2 (1213.88): C, 37.60; H, 3.16; N, 4.62.
Found: C, 37.45; H, 3.28; N, 4.29. HRMS (m/z, ESI+): found for
HgCl 236.93 (calcd 236.94), HgCl + 2MeOH 301.01 (calcd 300.99),
[CuL-CH3] + H 372.09 (calcd 372.10), [CuL-CH3] + Na 394.09
(calcd. 394.08), [CuL-CH2-HgCl] + H 608.02 (calcd 608.03), [CuL-
CH2-HgCl] + Na 630.00 (calcd 630.01), [CuL-CH2-HgCl] + H +
MeOH 672.09 (calcd 672.09), [CuL-CH3]2 + H 743.14 (calcd
743.19), [CuL-CH3]2 + Na 767.16 (calcd 767.16), [(CuL-CH2-
HgCl)(CuL-CH3)] + H 979.12 (calcd 979.12), [(CuL-CH2-HgCl)-
(CuL-CH3)] + Na 1001.11 (calcd 1001.11), [(CuL-CH2-HgCl)2] + H
1213.13 (calcd 1213.05).
EXPERIMENTAL SECTION
■
Starting Materials. 2-Hydroxyacetophenone and 1,3-propanedi-
amine were purchased from Lancaster and were of reagent grade. They
were used without further purification.
Caution! Organomercurials are extremely toxic, and appropriate
handling conditions should be used for their generation and disposal.
Perchlorate salts of metal complexes with organic ligands are
potentially explosive. Only a small amount of material should be
prepared, and it should be handled with care.
Synthesis of the Schiff Base Ligand H2L-CH3 and Its Copper
Complex [CuL-CH3]. The di-Schiff base ligand H2L-CH3 was
prepared by the reported method.7 Briefly, 5 mmol of 1,3-
propanediamine (0.42 mL) was mixed with 10 mmol of the required
2-hydroxyacetophenone (1.20 mL) in methanol (20 mL). The
resulting solution was refluxed for ca. 2 h and cooled. The yellow
methanolic solution was used directly for complex formation.
A methanolic solution (10 mL) of Cu(ClO4)2·6H2O (5 mmol,
1.855 g), was added to a methanolic solution of H2L-CH3 (5 mmol, 20
mL) in the presence of Et3N (1.40 mL, 10 mmol) to prepare the
complex [CuL-CH3] as reported earlier.7
Synthesis of the Complex [CuL-CH3-HgCl2] (1). An aqueous
solution (5 mL) of HgCl2 (1 mmol, 0.271 g) was added to a
methanolic solution (20 mL) of [CuL-CH3] (1 mmol, 0.372 g).
Microcrystalline greenish brown solid started to separate immediately
on stirring the mixture. The stirring was continued for 30 min, and the
solid product was isolated by filtration, washed with Et2O, and dried in
a vacuum desiccator containing anhydrous CaCl2. X-ray-quality single
crystals were obtained by layering a methanolic solution of this
compound with diethyl ether. Yield: 0.519 g (81%). Anal. Calcd for
C19H20HgCuN2O2Cl2 (643.41): C, 35.47; H, 3.13; N, 4.35. Found: C,
35.18; H, 3.16; N, 4.52. HRMS (m/z, ESI+): found for HgCl2 + H +
CH3CN 311.9379 (calcd 311.9404), [CuL-CH3] + H 372.1117 (calcd
372.0999), [CuL-CH3] + Na 394.1055 (calcd 394.0818), [CuL-CH3]2
+ H 743.1989 (calcd 743.1920), [CuL-CH3]2 + Na 765.1672 (calcd
765.1739).
Alternative Method for the Synthesis of Complex 3. Complex
3 has also been synthesized by dissolving complex 1 (0.25 mmol, 0.161
g) in 50 mL of methanol in the presence of triethylamine (0.25 mmol,
0.035 mL). The solvent was allowed to evaporate slowly at ambient
temperature. When the volume of the solution was reduced to ca. 10
mL (after about 4 days), the crystalline product of 3 started to appear,
which was collected by filtration. Yield: 0.090 g, 59%.
Synthesis of the Complex [(CuL-CH3)2HgCl2] (2). A methanolic
solution (20 mL) of [CuL-CH3] (2 mmol, 0.744 g) was mixed with 5
mL of an aqueous solution of HgCl2 (1 mmol, 0.271 g). The solution
was warmed in a water bath for 10 min to redissolve most of the
precipitate that appeared on mixing. A small amount of precipitate that
3845
dx.doi.org/10.1021/om201033q | Organometallics 2012, 31, 3844−3850

Organometallics
Article
Table 1. Crystal Structure and Refinement Data for Complexes 1−3
1
2
3
formula
formula wt
space group
cryst syst
a (Å)
C19H20CuHgN2O2Cl2
643.41
Pbca
C38H40Cu2HgN4O4Cl2
1015.31
P2/c
C38H38Cu2Hg2N4O4Cl2
1213.88
P21/c
orthorhombic
15.976(2)
13.598(2)
18.897(2)
90
monoclinic
20.640(1)
10.304(1)
17.955(1)
90
monoclinic
9.378(5)
9.902(5)
20.420(5)
90
b (Å)
c (Å)
α = γ (deg)
β (deg)
V (Å3)
90
91.095(2)
3818.1(3)
4
91.009(5)
1895.9(2)
2
4105.2(8)
8
Z
dcalcd (g cm−3
)
2.082
1.766
2.126
μ (mm−1
)
8.783
5.300
9.366
Rint
0.0612
4291
0.1229
0.0277
no. of unique data
no. of data with I > 2σ(I)
R1 on I > 2σ(I)
wR2 on I > 2σ(I)
GOF
7388
3866
3058
4002
3540
0.0469
0.0942
1.025
0.0861
0.1074
0.2271
0.2985
1.024
1.178
Physical Measurements. Elemental analyses (C, H, and N) were
performed using a Perkin-Elmer 2400 Series II CHN analyzer. IR
spectra in KBr pellets (4500−500 cm−1) were recorded using a Perkin-
Elmer RXI FT-IR spectrophotometer. Electronic spectra in methanolic
solutions (800−220 nm) were recorded with a Hitachi U-3501
spectrophotometer. High-resolution mass spectra (HRMS) electro-
spray ionization (ESI) was recorded on a Qtof Micro YA263 high-
resolution mass spectrometer. For HRMS (ESI), compounds 1 and 2
were taken up in CH3CN and compound 3 was taken up in MeOH.
Powder X-ray diffraction patterns were recorded on a Bruker D-8
Advance diffractometer operated at 40 kV voltage and 40 mA current
and calibrated with a standard silicon sample, using Ni-filtered Cu Kα
(α = 0.154 06 nm) radiation. Experimental and simulated powder
XRD plots are given in Figure S4 (Supporting Information).
crystalline complex [CuL-CH3-HgCl2] (1). When the
proportion of [CuL-CH3] was increased to make it the double
the molar concentration of HgCl2, the deep green complex
[(CuL-CH3)2HgCl2] (2) was obtained from the MeOH/H2O
medium. Formation of mono-, bis-, and tris-complex species of
metal ions with increased proportions of the bidentate chelating
ligand is a usual phenomenon in coordination chemistry.
However, isolation of di- and trinuclear heterometallic
complexes simply by varying the proportion of [CuL-CH3]
seems to be a very rare phenomenon. On the other hand, when
HgCl2 and [CuL-CH3] were allowed to react in the same
medium (MeOH/H2O) but in low concentration and in the
presence of Et3N, the brown tetranuclear complex [(CuL-CH2-
HgCl)2] (3) resulted after 4−5 days. The concentration was
kept low in order to avoid immediate precipitation of complex
1. Complexes 1 and 2 both slowly transformed into compound
3 when triethylamine was added to their methanol solutions
and the resulting solution was kept for several days. For 2
transformation takes a longer time and the yield is lower
compared to that for 1; moreover, the product contains both 3
and crystals of [CuL-CH3]. The conversion of the dinuclear
compound [CuL-CH3-HgCl2] (1) into the tetranuclear [(CuL-
CH2-HgCl)2] (3) clearly shows that in the presence of
triethylamine the methyl group of 1 slowly undergoes
mercuration and consequently two dinuclear units join together
through the C−Hg bond to form the cyclic tetranuclear
organomercurial compound 3. The added triethylamine helps
to remove the liberated HCl molecule and thus facilitate the
formation of 3.
Crystallographic Data Collection and Refinement. Suitable
single crystals of the three complexes were mounted on a Bruker-AXS
SMART APEX II diffractometer equipped with a graphite mono-
́
chromator and Mo Kα (λ = 0.710 73 Å) radiation. The crystal was
positioned at 60 mm from the CCD. A total of 360 frames were
measured with a counting time of 10 s. The structure was solved using
Patterson methods by using SHELXS-97. Subsequent difference
Fourier synthesis and least-squares refinement revealed the positions
of the remaining non-hydrogen atoms. Non-hydrogen atoms were
refined with independent anisotropic displacement parameters.
Hydrogen atoms were placed in idealized positions, and their
displacement parameters were fixed to be 1.2 times larger than
those of the attached non-hydrogen atom. Successful convergence was
indicated by the maximum shift/error of 0.001 for the last cycle of the
least-squares refinement. Absorption corrections were carried out
using the SADABS program.8 All calculations were carried out using
SHELXS-97,9 SHELXL-97,10 PLATON 99,11 ORTEP-32,12 and
WinGX system version 1.64.13 Data collection and structure
refinement parameters and crystallographic data for the complexes
are given in Table 1. The relatively high R value of complex 3 is due to
the poor quality of the crystal. Three different crystals were diffracted
to get a better result. However, we were unable to get a lower R value.
In addition to elemental analysis, the complexes were initially
characterized by IR spectra. A strong and sharp band due to the
azomethine ν(CN) group of the Schiff base appears at 1598,
1601, and 1596 cm−1 for complexes 1−3, respectively. The
electronic spectra of the complexes (measured in methanol
solution) display a single absorption band for 1 and 3 at 534
nm. In complex 2, this band appears at 545 nm. These
absorption bands may be attributed to the d−d transitions in
copper(II) ions with a square-based geometry. The intense
broad band at about 350, 344, and 354 nm for complexes 1−3,
respectively, is due to a ligand-to-metal charge transfer
RESULTS AND DISCUSSION
■
Syntheses and IR, UV−Vis, and Mass Spectra of the
Complexes. The Schiff base ligand H2L-CH3 and its Cu(II)
complex [CuL-CH3] were synthesized using the reported
procedure.7 The neutral complex [CuL−CH3] on reaction with
HgCl2 in a 1/1 molar ratio in MeOH/H2O medium (4/1, v/v)
resulted in an immediate precipitation of the greenish
3846
dx.doi.org/10.1021/om201033q | Organometallics 2012, 31, 3844−3850

Organometallics
Article
a
transition. A higher energy band at about 269, 269, and 270 nm
for complexes 1−3, respectively, is due to the π−π* transition
of aromatic rings (Figure S5 and Table S1, Supporting
Information).
Table 2. Bond Angles and Distances of Complexes 1 and 3
distance (Å)
angle (deg)
atoms
1
3
1
3
The HRMS-ESI of 1 and 2 were recorded in acetonitrile
solution while that of complex 3 was measured in methanolic
solution (Figures S1−S3, Supporting Information). The spectra
of complexes 1 and 2 show a similar pattern. It seems that both
complexes dissociate into [CuL-CH3] and HgCl2 in solution
and the dimeric species [CuL-CH3]2 is formed. On the other
hand, the spectra of complex 3 are quite different. The
existence of tetranuclear species is confirmed by the presence of
a peak at m/z [M + H]+ 1213.13. Several fragments were
observed in the mass spectra of complex 3. The fragments
[CuL-CH2-HgCl + H]+, [CuL-CH2-HgCl + Na]+, [CuL-CH2-
HgCl + H + 2MeOH]+, [(CuL-CH2-HgCl)(CuL-CH3) + H]+
and [(CuL-CH2−HgCl)(CuL-CH3) + Na]+ from the tetranu-
clear species show distinct peaks at m/z 608.02, 630.00, 672.09,
979.12, and 1001.11, respectively. The peaks due to [HgCl]+
and [HgCl + 2MeOH]+ are also observed at m/z 236.93 and
301.01, respectively, which are absent in the spectra of 1 and 2.
The appearance of peaks at m/z 372.09 and 743.14 may be
attributed to the presence of [CuL-CH3] and [CuL-CH3]2,
respectively, as in 1 and 2.
Hg1−
2.322(2)
2.536(4)
2.439(4)
2.316(2)
2.322(8)
Cl1−Hg1−
98.0(1)
97.5(1)
160.8(1)
62.9(1)
94.2(4)
95.1(4)
162.9(6)
61.1(4)
Cl1
O1
Hg1−
2.610(14) Cl1−Hg1−
O1
O2
Hg1−
2.624(13) Cl1−Hg1−
Cl2/Cl2*
2.05(2)
O2
Hg1−
O1−Hg1−
Cl2/
O2
Cl2*
Cu1−O1 1.879(4)
Cu1−O2 1.883(3)
Cu1−N1 1.938(4)
Cu1−N2 1.959(5)
1.873(13) O1−Hg1−
Cl2/Cl2*
1.887(12) O2−Hg1−
Cl2/Cl2*
94.8(1)
101.0(1)
87.3(2)
93.2(2)
157.4(2)
161.0(2)
91.6(2)
95.1(2)
101.6(6)
98.2(6)
90.1(6)
92.6(6)
157.1(6)
154.6(6)
93.2(6)
94.0(6)
1.978(15) O1−Cu1−
O2
1.938(14) O1−Cu1−
N1
O1−Cu1−
N2
O2−Cu1−
N1
O2−Cu1−
N2
N1−Cu1−
Structure Description of the Complexes. [(CuL-CH3)-
HgCl2] (1). The asymmetric unit of complex 1 consists of one
[CuL-CH3] unit, one Hg(II) ion, and two chloride ions (Figure
1). The copper atom shows a distorted-square-planar geometry,
N2
a
Symmetry code: (*) 1 − x, −y, 1 − z for complex 3.
[(CuL-CH3)2HgCl2]. The two units are equivalent, with only
some minor differences in bond angles and distances. The
ORTEP view of unit A is shown in Figure 2, and the bond
Figure 1. ORTEP diagram of complex 1. Ellipsoids are drawn at the
20% probability level.
being coordinated by the two phenoxido oxygen atoms O(1)
and O(2) and the two imine nitrogen atoms N(1) and N(2)
(Table 2). The rms deviation of the four coordinating atoms
from the mean plane passing through them is 0.338 Å. The
metal atom is 0.028(1) Å from this plane.
Figure 2. ORTEP diagram of unit A of complex 2. Ellipsoids are
drawn at the 20% probability level. The open bonds show the weak
Hg(1)···O(2) interactions.
The Hg(II) atom is tetracoordinated, being bonded to two
terminal chloride ions (Cl1 and Cl2) and two bridging
phenoxido oxygens (O1 and O2) of the copper chelate (Figure
1). The environment around Hg(II) may be viewed as a
distorted-tetrahedral geometry with ∠Cl(1)−Hg(1)−Cl(2) =
160.8(1)° and ∠O(1)−Hg(1)−O(2) = 62.9(1)°.
[(CuL-CH3)2HgCl2] (2). The structure of complex 2 contains
two trinuclear units (A and B) with an Cu2Hg core, both of
which contain a crystallographic 2-fold axis passing through the
Hg atom. Both units consist of two [CuL-CH3] groups, one
mercury(II) ion, and two chloride ions and have the formula
distances and angles of both units are given in Table 3. The two
terminal Cu(II) ions possess a pentacoordinate, square-
pyramidal coordination sphere. The basal plane in the copper
ion is constituted by the four coordinating atoms (two oxygen
and two nitrogen) from the di-Schiff base. Two [CuL-CH3]
units in the molecule are also joined together through the
coordination of one of the phenoxido oxygens, O(2A)a or
O(2B)b, to the axial position of the other unit to complete the
square-pyramidal geometry (symmetry code: (a) 1 − x, y, 3/2 −
5
z; (b) −x, y,
/ − z). The rms deviations of the four
2
3847
dx.doi.org/10.1021/om201033q | Organometallics 2012, 31, 3844−3850

Organometallics
Article
a
two additional long bonds formed by the other oxygen atoms,
O(2), of the two terminal [CuL-CH3] units (Table 3). Note
that this O(2) atom is the one that is semicoordinated to the
axial position of the other copper atom in the trinuclear unit.
Each discrete unit is connected by C(8B)−H(8B3)···Cl(1A)
hydrogen-bonding interactions to form 1D supramolecular
chains along the crystallographic a axis, as shown in Figure 3A.
The hydrogen-bonding interactions are summarized in Table 4.
Table 3. Bond Angles and Distances of Complex 2
A unit
B unit
atoms
distance (Å)
atoms
distance (Å)
Hg1A−O1A
Hg1A−Cl1A
Hg1A−O2A
Cu1A−O1A
Cu1A−N1A
Cu1A−N2A
Cu1A−O2A
Cu1A−O2Aa
2.307(8)
2.466(6)
3.117(8)
1.954(8)
1.967(12)
1.976(9)
1.915(8)
2.321(7)
Hg1B−O1B
Hg1B−Cl1B
Hg1B−O2B
Cu1B−O2B
Cu1B−N1B
Cu1B−N2B
Cu1B−O1B
Cu1B−O2Bb
2.341(8)
2.451(13)
3.007(8)
1.893(8)
1.967(12)
1.974(12)
1.926(7)
2.483(9)
Table 4. Hydrogen-Bonding Interaction of Complex 2
∠D−
D−H
H···A
(Å)
H···A
A unit
B unit
D−H···A
C8B−
(Å)
D···A (Å)
(deg)
symmetry
atoms
angle (deg)
atoms
angle (deg)
0.9600
2.6900
3.613(15)
161.00
x, 1 − y,
1/2 + z
H8B3···Cl1A
O1A−Cu1A−N2A
O1A−Cu1A−N1A
O1A−Cu1A−O2A
O2Aa−Cu1A−N1A
O1A−Cu1A−O2Aa
Cl1A−Hg1A−O1A
Cl1A−Hg1A−O1Aa
O2A−Cu1A−N1A
O2A−Cu1A−N2A
O2A−Cu1A−O2Aa
O2Aa−Cu1A−N2A
N1A−Cu1A−N2A
Cl1A−Hg1A−Cl1Aa
O1A−Hg1A−O1Aa
154.5(3)
88.6(4)
90.9(4)
101.8(3)
85.9(3)
100.0(2)
112.0(2)
177.2(3)
86.7(4)
75.3(3)
117.8(3)
95.0(4)
118.0(2)
O1B−Cu1B−N2B
O1B−Cu1B−O2Bb
O2B−Cu1B−N1B
O2B−Cu1B−N2B
O1B−Cu1B−O2B
Cl1B−Hg1B−O1B
Cl1B−Hg1B−Cl2b
Cl1B−Hg1B−O1Bb
O1B−Hg1B−O1Bb
O2B−Cu1B−O2Bb
N1B−Cu1B−N2B
O2Bb−Cu1B−N1B
O2Bb−Cu1B−N2B
152.5(4)
84.4(3)
166.7(4)
88.5(4)
88.7(4)
103.7(4)
115.4(3)
108.4(4)
117.8(3)
75.6(3)
98.0(5)
91.1(4)
121.2(4)
90.8(4)
These 1D supramolecular chains are further connected by C−
H···π interactions to form 2D supramolecular sheets in the ab
plane (Figure 3B). The hydrogen atom H(4B) interacts with
one of the phenyl rings of the CuL-CH3 unit. All these
dimensions are given in Table 5.
Table 5. C−H···π Interaction of Complex 2
H···R1
a
C···R1
∠C−H···R1
C−H···R1
C4B−
(Å)
(Å)
(deg)
symmetry
2.910
3.746
151
1 − x, 2 − y, 2 − z
H4B···R1
115.6(3)
O1B−Cu1B−N1B
a
R1 = C14A−C15A−C16A−C17A−C18A−C19A.
a
3
5
Symmetry code: (a) 1 − x, y, /2 − z; (b) −x, y, /2 − z.
[(CuL-CH2-HgCl)2] (3). Complex 3 is a tetranuclear metal
equatorially coordinating atoms from the mean plane passing
through them are 0.242 and 0.330 Å for the A and B units,
respectively. The metal atoms Cu(1A) and Cu(1B) are
0.067(1) and 0.115(2) Å from this plane, respectively.
The mercury atom, which sits on a 2-fold axis, is bonded with
two oxygen atoms from two different [CuL-CH3] units and two
chloride ions. In addition to these four short bonds, there are
cluster. The asymmetric unit contains one [CuL-CH2]− ion,
one Hg(II) ion, and one chloride ion (Figure 4). The Cu(II)
atom has a distorted-square-planar geometry, being coordinated
by the two phenoxido oxygen atoms O(1) and O(2) and the
two imine nitrogen atoms N(1) and N(2). The rms deviations
of the four coordinating atoms from the mean plane passing
through them is 0.399 Å, indicating significant distortion
Figure 3. (A) Supramolecular chain formed by C(8B)−H(8B3)···Cl(1A) hydrogen-bonding interactions along the crystallographic a axis. (B) 2D
supramolecular sheets formed by both hydrogen-bonding and C−H···π interactions within the crystallographic ab plane of complex 2.
3848
dx.doi.org/10.1021/om201033q | Organometallics 2012, 31, 3844−3850

Organometallics
Article
bond activation is of considerable importance, because it can
lead to the formation of unexpected products through reactive
organometallic intermediates.21 In the rich and diverse
chemistry of Hg(II), the formation of various new organo-
metallic materials by the interaction of mercury(II) with alkynyl
compounds deserves special mention.22 Usually organolithium
or Grignard reagents are used for the formation of Hg−C
bonds.14 Direct mercuration is reported to occur in some
compounds that contain acidic hydrogen atoms.15 In the metal-
bound substrate, however, such examples are found in very few
systems: e.g., in a Ni(II)-bound tetraaza macrocycle,15b
a
platinum(II)-bound [acac],23 and a Cu(II)-bound 8-hydrox-
yquinoline complex.15c,d Very recently, a Cu(II)-bound Schiff
base ligand has been reported to undergo C-mercuration at the
phenyl ring.16 Complex 3 is thus the first example of methyl
carbon mercuration in a metal-bound Schiff base complex.
Figure 4. ORTEP diagram of complex 3. Ellipsoids are drawn at the
20% probability level. Hydrogen atoms are omitted for simplicity.
CONCLUSIONS
■
In summary, we have presented here an unique example for the
synthesis of heterometallic dinuclear CuII-HgII, bent trinuclear
CuII HgII, and cyclic tetranuclear CuII HgII complexes by
toward tetrahedral geometry. The metal atom is 0.022(2) Å
from this plane.
The Hg(II) atom has a distorted-tetrahedral coordination
geometry. The chloride ion (Cl1) and the carbon atom (C12*)
(symmetry code: (*) 1 − x, −y, 1 − z) of the methylene group
from another [CuL-CH2]− coordinate to Hg(II) in nearly
linear positions, and the two oxygen atoms O(1) and O(2) of
the Schiff base bridge the Cu(II) and Hg(II) at angular
positions (Figure 4). The organomercury bond (C12*−Hg1)
distance is 2.05(2) Å and is in the range of other C−Hg
bonds.14−16 The Cu(1)···Hg(1) and Cu(1)···Hg(1)* bond
distances are 3.545 and 5.519 Å and Cu(1)···Cu(1)* and
Hg(1)···Hg(1)* bond distances are 5.343 and 7.583 Å,
respectively.
A CSD search reveals that only 10 heterometallic complexes
have been reported to incorporate Hg(II) ion with the help of a
“complex as ligand”, [CuL] (H2L = any salen type Schiff base).
Among them, four16,17 resemble complex 1 in the present
paper, where one [CuL] unit on chelation with a mercuric
halide (chloride/bromide) results in a dinuclear compound.
However, the geometry around Hg is distorted tetrahedral as in
1 in only two complexes.17a,b The Hg atom is pentacoordinated
in one,17c having a close contact with the solvent molecule, and
is hexacoordinated16 in the other one. Of the remaining six
compounds, one pair each of trinuclear,18 tetranuclear,19 and
polymeric16,20 compounds have been reported. However,
unlike compound 2, both of the reported trinuclear compounds
are linear, whereas the reported tetranuclear complexes are
formed by the dimerization of dinuclear units; one through μ2-
chloro bridges19a and other by μ3-phenoxido bridges.19b
Compound 3 is also formed by dimerization of the dinuclear
complex 1. However, here the dimerization takes place, very
unexpectedly, through the mercuration of the methyl group of
the Schiff base ligand. Hence, the structure of 3 is very different
from that of the two reported tetranuclear complexes.
2
2
2
reacting the same “complex as ligand” [CuL-CH3] with HgCl2
simply by controlling the molar ratios and reaction conditions
(i.e., concentration of reactants and addition of triethylamine).
The nuclearity of similar heterometallic complexes is known to
be modulated by anionic coligands.6d The uniqueness of the
present examples lies in the fact that the same reactants, [CuL−
CH3] and HgCl2, have been used to synthesize three different
complexes. Moreover, we have shown here for the first time
that the methyl group of a Cu(II)-bound Schiff base complex
can undergo direct mercuration under ambient conditions to
make the coordination mode of the salen-type di-Schiff base
heptadentate. Such a coordination mode enabled us to produce
the novel tetranuclear organomercuiral Cu(II)−Hg(II) metal-
lamacrocycle.
ASSOCIATED CONTENT
* Supporting Information
■
S
HRMS (ESI) spectra of complexes 1−3 (Figures S1−S3),
powder X-ray spectrum of complex 3 (Figure S4), UV−vis
spectra (Figure S5) and data (Table S1), and CIF files giving
crystallographic data for complexes 1−3. This material is
available free of charge via the Internet at http://pubs.acs.org.
CCDC 835847 contains the supplementary crystallographic
data for 3. These data can be also obtained free of charge via
http://www.ccdc.cam.ac.uk/conts/retrieving.html or from the
Cambridge Crystallographic Data Centre, 12 Union Road,
Cambridge CB2 1EZ, U.K. (fax, (+44) 1223-336-033; e-mail,
deposit@ccdc.cam.ac.uk).
AUTHOR INFORMATION
Corresponding Author
*E-mail: ghosh_59@yahoo.com (A.G.).
Notes
■
The flexidentate behavior of the di-Schiff base ligand H2L-
CH3 is well known, generally through the donor centers N and
O. However, the most important aspect of complex 3 is the
coordination of the Schiff base to the metal centers through
carbon atoms that makes it heptadentate with the 1-
κ4NN′OO′:2-κ2OO′:3-κC coordination mode. To our knowl-
edge, this is the first example of such a coordination mode of
salen-type Schiff base ligands. The methyl group of the
coordinated Schiff base undergoes direct mercuration in the
presence of HgCl2 to form complex 3. Metal-mediated C−H
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
We thank the CSIR of India for awarding a senior research
fellowship (Sanction No. 09/028(0732)/2008-EMR-I) to S.B.
Crystallography was performed at the DST-FIST, India-funded
Single Crystal Diffractometer Facility, at the Department of
Chemistry, University of Calcutta.
3849
dx.doi.org/10.1021/om201033q | Organometallics 2012, 31, 3844−3850

Organometallics
Article
(19) (a) Ercan, I.; Ercan, F.; Arici, C.; Atakol, O. Acta Crystallogr.,
Sect. C 2002, 58, m137−m138. (b) Nayak, M.; Sarkar, S.; Hazra, S.;
Sparkes, H. A.; Howard, J. A. K.; Mohanta, S. CrystEngComm 2011, 13,
124−132.
REFERENCES
■
(1) Schiff, H. Ann. Suppl. 1864, 3, 343.
(2) (a) Srinivasan, K.; Michaud, P.; Kochi, J. K. J. Am. Chem. Soc.
1986, 108, 2309−2320. (b) Zhang, W.; Loebach, J. L.; Wilson, S. R.;
Jacobsen, E. N. J. Am. Chem. Soc. 1990, 112, 2801−2803. (c) Miyasaka,
H.; Saitoh, A.; Abe, S. Coord. Chem. Rev. 2007, 251, 2622−2664.
(3) (a) Cheng, X.; Gao, S.; Huo, L.; Ng, S. W. Acta Crystallogr., Sect.
E 2005, 61, 385−386. (b) Xiong, R.; Song, B.; Zuo, J.; You, X.
Polyhedron 1996, 15, 903−907. (c) Drew, M. G. B.; Prasad, R. N.;
Sharma, R. P. Acta Crystallogr., Sect. C 1985, 41, 1755−1758.
(d) Baker, E. N.; Hall, D.; Waters, T. N. J. Chem. Soc. A 1970,
406−409.
(20) Gheorghe, R.; Costes, J.-P.; Shova, S.; Andruh, M. Rev. Roum.
Chim. 2007, 52, 753−758.
(21) (a) Halder, S.; Drew, M. G. B.; Bhattacharya, S. Organometallics
2006, 25, 5969−5972. (b) Nishikata, T.; Abela, A. R.; Huang, S.;
Lipshutz, B. H. J. Am. Chem. Soc. 2010, 132, 4978−4979. (c) Oblad, P.
F.; Bercaw, J. E.; Hazari, N.; Labinger, J. A. Organometallics 2010, 29,
789−794.
(22) Wong, W.−Y. Coord. Chem. Rev. 2007, 251, 2400−2427.
́
(23) Ara, I.; Falvello, L. R.; Fornies, J.; Sicilia, V.; Villarroya, P.
(4) (a) O’Bryan, N. B.; Maier, T. O.; Paul, I. C.; Drago, R. S. J. Am.
Chem. Soc. 1973, 95, 6640−6645. (b) Gruber, S. J.; Harris, C. M.; Sinn,
E. J. Inorg, Nucl. Chem. 1968, 30, 1805−1830.
Organometallics 2000, 19, 3091−3099.
(5) (a) Epstein, J. M.; Figgis, B. N.; White, A. H.; Willis, A. C. J.
Chem. Soc., Dalton Trans. 1974, 1954−1961. (b) Brewer, G. A.; Sinn,
E. Inorg. Chim. Acta 1987, 134, 13−14. (c) Bencini, A.; Benelli, C.;
Caneschi, A.; Carlin, R. L.; Dei, A.; Gatteschi, D. J. Am. Chem. Soc.
1985, 107, 8128−8136. (d) Novitchi, G.; Shova, S.; Caneschi, A.;
Costes, J.-P.; Gdaniec, M.; Stanica, N. Dalton Trans. 2004, 1194−1200.
(e) Mukherjee, P.; Biswas, C.; Drew, M. G. B.; Ghosh, A. Polyhedron
2007, 26, 3121−3128. (f) Mukherjee, P.; Drew, M. G. B.; Tangoulis,
V.; Estrader, M.; Diaz, C.; Ghosh, A. Polyhedron 2009, 28, 2989−2996.
(6) (a) Biswas, S.; Naiya, S.; Drew, M. G. B.; Estarellas, C.; Frontera,
A.; Ghosh, A. Inorg. Chim. Acta 2011, 366, 219−226. (b) Biswas, S.;
Ghosh, A. Polyhedron 2011, 30, 676−681. (c) Biswas, S.; Ghosh, A.
Indian J. Chem., Sect. A 2011, 50A, 1356−1362. (d) Biswas, S.; Naiya,
́
S.; Gomez-García, C. J.; Ghosh, A. Dalton Trans. 2012, 41, 462−473.
(7) Iida, K.; Oonishi, I.; Nakahara, A.; Komoyama, Y. Bull. Chem. Soc.
Jpn. 1970, 43, 2347−2354.
(8) SAINT, version 6.02, and SADABS, version 2.03; Bruker AXS, Inc.,
Madison, WI, 2002.
(9) Sheldrick, G. M. SHELXS 97, Program for Structure Solution;
University of Gottingen, Gottingen, Germany, 1997.
̈
̈
(10) Sheldrick, G. M. SHELXL 97, Program for Crystal Structure
Refinement; University of Gottingen, Gottingen, Germany, 1997.
̈
̈
(11) Spek, A. L. PLATON, Molecular Geometry Program. J. Appl.
Crystallogr. 2003, 36, 7−13.
(12) Farrugia, L. J. J. Appl. Crystallogr. 1997, 30, 565.
(13) Farrugia, L. J. J. Appl. Crystallogr. 1999, 32, 837−538.
(14) (a) Gabbai, F. P.; Burress, C. N.; Melaimi, M.-A.; Taylor, T. J. In
Comprehensive Organmetallic Chemistry III; Mingos, D. M. P., Crabtree,
R. H., Eds.; Elsevier: Oxford, U.K., 2007; Chapter 2.07, p 419.
(b) Wong, W.-Y.; Lu, G.-L.; Liu, L.; Shi, J.-X.; Lin, Z. Eur. J. Inorg.
Chem. 2004, 2066−2077. (c) Bai, S.-Z.; Lou, X.-H.; Li, H.-M.; Shi, H.
Acta Crystallogr., Sect. E 2009, 65, m842−m843. (d) Flower, K. R.;
Howard, V. J.; Naguthney, S.; Pritchard, R. G.; Warren, J. E.;
McGown, A. T. Inorg. Chem. 2002, 41, 1907−1912. (e) Chandrasekhar,
V.; Kumar, A.; Pandey, M. D. J. Organomet. Chem. 2010, 695, 74−81.
(f) Flower, K. R.; Pritchard, R. G. Acta Crystallogr., Sect. E 2006, 62,
m1467−m1468. (g) Flower, K. R.; Pritchard, R. G. Acta Crystallogr.,
Sect. E 2006, 62, m1469−m1470.
(15) (a) Larock, R. C. In Comprehensive Organometallic Chemistry II;
Abel, E. W., Stone, F. G. A., Wilkinson, G., Eds.; Elsevier: Oxford,
U.K., 1995; Chapter 9, p 389. (b) Kajiwara, T.; Murao, R.; Ito, T. J.
Chem. Soc., Dalton Trans. 1997, 2537−2538. (c) Kline, R. J.; Wardeska,
J. G. Inorg. Chem. 1969, 8, 2153−2155. (d) Chawla, N. K.; Jones, M.
M. Inorg. Chem. 1964, 3, 1549−1553.
(16) Constable, E. C.; Zhang, G.; Housecroft, C. E.; Zampese, J. A.
Dalton Trans. 2010, 39, 1941−1947.
(17) (a) Atakol, O.; Arici, C.; Tahir, M. N.; Kenar, A.; Ulku, D. Acta
Crystallogr., Sect. C 1999, 55, 1416−1418. (b) Kaynak, F. B.; Ulku, D.;
Atakol, O.; Durmus, S. Acta Crystallogr., Sect. C 1999, 55, 1784−1785.
(c) Colon, M. L.; Qian, S. Y.; Vanderveer, D.; Bu, X. R. Inorg. Chim.
Acta 2004, 357, 83−88.
(18) Yildirim, L. T.; Kurtaran, R.; Namli, H.; Azaz, A. D.; Atakol, O.
Polyhedron 2007, 26, 4187−4194.
3850
dx.doi.org/10.1021/om201033q | Organometallics 2012, 31, 3844−3850