Coordination behaviors of a 23-membered NO4S2-macrocycle: Mononuclear silver(I) complex and conformational isomers of tetranuclear bis(macrocycle) mercury(II) complexes exhibiting exo- and endo/exocyclic coordination modes

Article abstract of DOI:10.1016/j.ica.2018.07.012

A ditopic 23-membered NO₄S₂-macrocycle (L) incorporating both semi-rigid and flexible binding sites was synthesized and its silver(I) and mercury(II) complexes exhibiting different stoichiometries and coordination modes were prepared. First, silver(I) perchlorate reacts with L to afford an endocyclic mononuclear complex [Ag(L)]ClO₄ (1) in which the silver(I) ion locates at the semi-rigid binding site in the cavity. The solution study for the silver(I) complexation via the ¹H NMR titration agrees with the corresponding solid state data that show the endo-mode. Interestingly, the reaction of L with HgI₂ led to the isolation of two conformational isomers with a tetranuclear bis(macrocycle) composition, [(^exoHgLI₂)₂(μ-Hg₂I₄)] (2a) and [(^endoHgLI₂)₂(μ-Hg₂I₄)] (2b), which are dominated by the coordination modes of L toward the mercury(II) center. In both conformers, two exocyclic mercury(II) complex units (^exoHgLI₂)₂ in 2a or two endocyclic complex units [(^endoHgLI₂)₂ in 2b are linked by tetraiododimercury(II) core (μ-Hg₂I₄) to give a 4:2 (metal-to-ligand) stoichiometry. Based on the packing structures and high temperature experiment, the intermolecular interactions might be responsible for the formation of 2a and 2b which are kinetically and thermodynamic controlled, respectively.

Full text of DOI:10.1016/j.ica.2018.07.012

InorganicaChimicaActa482(2018)749–755
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Research paper
Coordination behaviors of a 23-membered NO4S2-macrocycle: Mononuclear
silver(I) complex and conformational isomers of tetranuclear bis
(macrocycle) mercury(II) complexes exhibiting exo- and endo/exocyclic
coordination modes
Mingyeong Shina, Huiyeong Jua, Yoichi Habatab,⁎, Shim Sung Leea,⁎
a
Department of Chemistry and Research Institute of Natural Science, Gyeongsang National University, Jinju 52828, South Korea
Department of Chemistry and Research Center for Materials with Integrated Properties, Toho University, 2-2-1 Miyama, Funabashi, Chiba 274-8510, Japan
b
A R T I C L E I N F O
A B S T R A C T
Keywords:
Macrocyclic complex
Tetranuclear bis(macrocycle) complex
Exocyclic coordination
Conformational isomer
A ditopic 23-membered NO4S2-macrocycle (L) incorporating both semi-rigid and flexible binding sites was
synthesized and its silver(I) and mercury(II) complexes exhibiting different stoichiometries and coordination
modes were prepared. First, silver(I) perchlorate reacts with L to afford an endocyclic mononuclear complex [Ag
(L)]ClO4 (1) in which the silver(I) ion locates at the semi-rigid binding site in the cavity. The solution study for
the silver(I) complexation via the 1H NMR titration agrees with the corresponding solid state data that show the
endo-mode. Interestingly, the reaction of L with HgI2 led to the isolation of two conformational isomers with a
tetranuclear bis(macrocycle) composition, [(exoHgLI2)2(μ-Hg2I4)] (2a) and [(endoHgLI2)2(μ-Hg2I4)] (2b), which
are dominated by the coordination modes of L toward the mercury(II) center. In both conformers, two exocyclic
mercury(II) complex units (exoHgLI2)2 in 2a or two endocyclic complex units [(endoHgLI2)2 in 2b are linked by
tetraiododimercury(II) core (μ-Hg2I4) to give a 4:2 (metal-to-ligand) stoichiometry. Based on the packing
structures and high temperature experiment, the intermolecular interactions might be responsible for the for-
mation of 2a and 2b which are kinetically and thermodynamic controlled, respectively.
Kinetic and thermodynamic products
1. Introduction
process is required. In practice, dibenzo-30-crown-10 offers a bent form
accommodating potassium(I) in a 3-D configuration [18,19]. Our group
Coordination chemistry of the crown ether type macrocycles in-
cluding heterocrowns are not limited to Group I and II metal ions but
extend to diverse ionic and neutral guests [1–5]. Based on the well-
established cation-to-cavity size ratio for the selectivity of the en-
docyclic complexations [6], the macrocyclic complexes can be divided
by three categories. In the first category, the cavity is too small to fit the
metal ion to its inside, and therefore, the metal ion lies above the cavity
in a perching mode to form a sandwich [7–13] or a club-sandwich
[14–17] type complex. The second category includes the complexes in
which the cation fits properly in the cavity to form a stable endocyclic
mononuclear species (optimal spatial fit). In the last category, when the
cavity is larger than the cation it is hard to isolate the solid complexes
due to the lower stability.
have also reported the silver(I) complexation of a 21-membered di-
benzo-O4S2 macrocycle with a twist-and-squeeze fashion via a synergic
cooperation of multiple contacts [20].
Apart from the oxygen-bearing crown ethers, the sulfur-containing
heterocrowns such as thiaoxa- or thiaaza-macrocycles frequently form
not only endocyclic complexes but also exocyclic complexes due to the
exo-orientation of the sulfur donors [22,23]. A range of the exocyclic
complexes based on the thia- and thiaaza macrocycles with from 13- to
24-membered macrocycles have been reported by Schröder [24,25],
Sheldrick [26–29], Heller [30], and our groups [31–38]. Thus, the
larger macrocycles incorporating aromatic subunits and some sulfur
donors with conformational flexibility can provide a potential design
tool for engineering new coordination products in terms of stoichio-
metries, topologies and coordination modes.
Generally, the flexible large macrocycle in the last category wraps
around the metal ion [18–20] and could act as a receptor in the areas of
sensors and carriers [21] when the ‘bind-detect’ or ‘transport-release’
In this work, we propose a 23-membered NO4S2-macrocycle L in-
corporating a semi-rigid binding site and a flexible binding site due to
⁎
Corresponding authors.
E-mail addresses: habata@chem.sci.toho-u.ac.jp (Y. Habata), sslee@gnu.ac.kr (S.S. Lee).
https://doi.org/10.1016/j.ica.2018.07.012
Received 15 May 2018; Received in revised form 4 July 2018; Accepted 4 July 2018
Availableonline05July2018
0020-1693/©2018PublishedbyElsevierB.V.

M. Shin et al.
InorganicaChimicaActa482(2018)749–755
70.3 69.6, 69.0, 33.7, 33.6. MS (ESI) m/z: 520.25 [L·Na]+
.
2.3. Preparation of complexes
2.3.1. [Ag(L)]ClO4 [1]
AgClO4 (4.3 mg, 0.021 mmol) in methanol (1 mL) was added to a
solution of L (9.9 mg, 0.019 mmol) in dichloromethane (1 mL). Slow
evaporation of the solution afforded colorless crystalline product 1
suitable for X-ray analysis (yield 60%). IR (KBr pellet): 2921, 2845,
1592, 1490, 1451, 1411, 1367, 1286, 1237, 1187, 1129 (ClO4−), 1095,
1045, 1024, 780, 747 cm−1. Anal. Calcd for [C27H31AgClNO8S2]: C,
45.65; H, 4.48; N, 1.97; S, 9.03. Found: C, 45.66; H, 4.33; N, 1.99; S,
8.86. 1H NMR (see Fig. S3a, 300 MHz, CDCl3, δ): 8.12–7.83 (11H,
aromatic), 5.32 (s, 4H, PyCH2O), 4.05 (s, 4H, OCH2CH2O), 3.56 (t, 4H,
OCH2CH2S), 3.42 (s, 4H, ArCH2S), 2.84(t, 4H, SCH2CH2O); 13C NMR
(see Fig. S3a, 75 MHz, CDCl3, δ) 156.5, 156.2, 137.6, 130.8, 128.4,
127.7, 121.6, 121.4, 110.9, 71.1, 70.7, 69.6, 30.6, 30.0. MS (ESI) m/z:
Scheme 1. Ditopic macrocycle L with semi-rigid and flexible domains.
three aromatic subunits and an -S-O-O-S- segment, respectively
(Scheme 1). Considering the relative metal ion binding affinities of the
donor atoms in L, the presence of one pyridine subunit is expected to
promote coordination of the metal ion inside the cavity [38].
Herein, we report the synthesis of the ditopic macrocycle L and its
silver(I) and mercury(II) complexes. Related solution studies for the
silver(I) complexation including 1H NMR titration is also reported. In
the mercury(II) complexations, an interesting feature is the isolation of
two tetramercury(II) bis(macrocycle) complex isomers whose co-
ordination modes are exocyclic and endocyclic respect to the macro-
cyclic ring cavity. The strategies to control the endocyclic and exocyclic
coordination modes for the macrocyclic complexes by variation of in-
terdonor (S⋯S) distance [10], anion [32,39], ring rigidity [37], and
ligand isomer [40] have been introduced by us. However, such con-
formational isomers with different coordination modes have not en-
countered in the macrocyclic complexes so far.
604.08 [AgL]+
.
2.3.2. [(exoHgLI2)2(μ-Hg2I4)] [2a] and [(endoHgLI2)2(μ-Hg2I4)] [2b]
A solution of HgI2 (8.9 mg, 0.020 mmol) in methanol (1 mL) was
layered onto a solution of L (10.3 mg, 0.021 mmol) in dichloromethane
(1 mL). Slow evaporation of the solution in the capillary tube afforded a
lump of the needle-shaped pale yellow crystals of 2a (below 2% yield)
suitable for the X-ray analysis. No further analysis were possible due to
the extremely low yield.
A solution of HgI2 (8.7 mg, 0.019 mmol) in methanol (1 mL) was
added to the stirred solution of L (10.7 mg, 0.022 mmol) in di-
chloromethane (1 mL). Slow evaporation of the solution in the vial for
two days afforded needle-shaped pale yellow crystals of 2b (60% yield)
suitable for the X-ray analysis. For 2b: Mp: 135–136 °C. Anal. Calcd for
[C54H62Hg4I8N2O8S4]: C, 23.06; H, 2.22; N, 1.00; S, 4.56. Found: C,
23.23; H, 2.14; N, 1.24; S, 4.84. 1H NMR (see Fig. S4a, 300 MHz, CDCl3,
δ): 7.98–6.96 (11H, aromatic), 5.20 (s, 4H, PyCH2O), 3.83 (s, 4H,
OCH2CH2O), 3.29 (t, 4H, OCH2CH2S), 3.14 (s, 4H, ArCH2S), 2.47 (t, 4H,
SCH2CH2O); 13C NMR (see Fig. S4a, 75 MHz, CDCl3, δ) 156.6, 156.5,
138.3, 131.1, 128.9, 127.9, 122.0, 121.6, 112.9, 71.2, 70.3, 69.4, 30.9,
29.9.
2. Experimental
2.1. General considerations
All chemicals and solvents used in the syntheses were of reagent
grade and were used without further purification. Mass (ESI) spectra
were obtained employing a Thermo Scientific LCQ Fleet spectrometer.
The FT-IR spectra were measured using a Thermo Fisher Scientific
Nicolet iS 10 FT-IR spectrometer. The elemental analysis was carried
out using a Thermo Scientific Flash 2000 Series elemental analyzer.
NMR spectra were recorded on a Bruker 300 spectrometer (300 MHz).
2.4. X-ray crystallography
PXRD experiments were performed with
a Bruker GADDS dif-
fractometer equipped with graphite-monochromated Cu Kα radiation.
Caution! The perchlorate-containing complexes are potentially ex-
plosive and should be handled with great care.
All data were collected on a Bruker SMART APEX2 ULTRA dif-
fractometer equipped with graphite monochromated Mo Kα radiation
(λ = 0.71073 Å) generated by a rotating anode. Data collection, data
reduction, and semiempirical absorption correction were carried out
using the software package APEX2 [41]. All of the calculations for the
structure determination were carried out using the SHELXTL package
[42]. Relevant crystal data collection and refinement data for the
crystal structures are summarized in Table. S1.
2.2. Synthesis and characterization of L
Cs2CO3 (6.4 g, 18.1 mmol) was dissolved in DMF (2 L) in a 3 L
round-bottom flask. 3,6-Dioxa-1,8-octane-dithiol (2.3 g, 12.8 mmol)
and dichloride 6 (5.1 g, 13.1 mmol) were dissolved in DMF (1.0 L) and
placed in a dropping funnel. The contents of the dropping funnel were
added dropwise into the DMF solution under a nitrogen atmosphere at
50–60 °C for 12 h. After being cooled to room temperature, the reaction
mixture was filtered and the solvent evaporated. Water was added, and
the mixture was extracted with dichloromethane. The organic phase
was dried over anhydrous sodium sulfate and filtered and the solvent
was removed to give a yellow crude mixture. Flash column chromato-
graphy (SiO2, n-hexane/ethyl acetate = 7:3) afforded the product as a
white solid in 20% yield. Mp: 120–121 °C. IR (KBr, pellet) 2923, 2859,
2362, 2343, 1654, 1597, 1493, 1449, 1246, 1105, 1091, 1047, 1020,
781, 749 cm−1. Anal. Calcd for [C27H31NO4S2]: C, 65.16; H, 6.28; N,
2.81; S, 12.88. Found: C, 65.22; H, 6.24; N, 2.85; S, 13.27. 1H NMR (see
Fig. S1a, 300 MHz, CDCl3, δ): 7.88–6.96 (11H, aromatic), 5.22 (s, 4H,
PyCH2O), 3.87 (s, 4H, OCH2CH2O), 3.37 (t, 4H, OCH2CH2S), 3.22 (s,
4H, ArCH2S), 2.56 (t, 4H, SCH2CH2O); 13C NMR (see Fig. S1b, 75 MHz,
CDCl3, δ) 156.6, 155.9, 139.9, 131.7, 129.8, 125.4, 125.1, 121.7, 113.0,
3. Results and discussion
3.1. Synthesis of macrocycle L
Synthesis of the target macrocycle L involves four steps starting
from ditosylate 3 (Scheme 2). Dichloride 6 was prepared from dialde-
hyde 4 and dialcohol 5 using known procedures [43–45]. L was ob-
tained by a coupling cyclization reaction between dichloride 6 and
dithiol in the presence of CS2CO3 under high dilution condition in di-
methylformamide (DMF) (20% yield). The 1H and 13C NMR spectra
(Fig. S1) together with the microanalysis and the mass spectra were all
in clear agreement with the proposed structures.
For the complexation of L, AgClO4 was used. In this reaction, a di-
chloromethane solution of L was allowed to diffuse slowly into a me-
thanol solution of one equivalent of AgClO4. Slow evaporation of the
solution afforded a colorless crystalline product 1 suitable for single
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M. Shin et al.
InorganicaChimicaActa482(2018)749–755
donors, whereas the smaller downfield shifts for H1 and H5 near the O
donors indicate a weaker contribution of the O donors to the co-
ordination to the silver(I) center. The downfield shifts of the pyridyl
protons (Δδ: 0.13 ppm for Ha and 0.06 ppm for Hb) also show the
contribution of the hetero N donor to the coordination, reflecting the
metal ion position inside the cavity similar to its endocyclic mono-
nuclear complex in the solid state shown in Fig. 2. From the titration
data in Fig. 2b, the stability constant (at 23 °C) for the 1:1 complexation
between silver(I) and L was obtained by using HyperNMR2008 soft-
ware [47] and this yields the log K value of 8.9, suggesting the for-
mation of a stable endocyclic mononuclear complex due to the collec-
tive effect of Ag-S, Ag-N and Ag-O bonds in solution.
Scheme 2. Synthesis of L.
crystal X-ray diffraction (SC-XRD) analysis. The SC-XRD analysis re-
vealed that 1 crystallizes in the monoclinic space group P21/n and
adopts a typical endocyclic mononuclear structure of the type [Ag
(L)]ClO4 (Fig. 1). In the macrocyclic complex cation, the silver(I) center
binds to NO2S2 donors at the semi-rigid site of L (Scheme 1) in a twisted
conformation, preventing coordination from the anion or solvent. The
coordination sphere adopts a distorted square pyramidal coordination
geometry (τ = 0.1) [46] with the S1, S2, N1 and O2 atoms defining a
square plane, and the O1 atom as an apex. The bond lengths of Ag-O
[2.710(2), 2.718(2) Å] and Ag-S [2.481(8), 2.519(9) Å] are typical.
Two oxygen donors in the flexible site remain uncoordinated (Ag1⋯O3
3.821(3) Å and Ag1⋯O4 4.315(3) Å) due to the stronger affinity of
pyridine toward the silver(I) center (Ag1-N1 2.325(3) Å). Hence, the
metal center in 1 is effectively shielded by the bound macrocycle from
the anion and solvent. Consequently, the preferred formation of the
endocyclic structure of 1 is in keeping with the coordination ability of
the NO2S2 donors in the semi-rigid domain which provide a favorable
conformation in the aids of the flexible domain of L.
3.3. Mercury(II) iodide complexes: kinetic product (2a) and
thermodynamic product (2b)
As depicted in Scheme 3, we found that a reaction of L with mercury
(II) iodide at room temperature afforded a kinetically controlled (see
later) tetranuclear bis(macrocycle) complex 2a; this was followed by
formation of a thermodynamically stable product 2b whose formula is
identical but its conformation is different. Since, 2a and 2b seem to be
interconvertible via a flip-flop, they could be considered conformational
isomers. Furthermore, 2a and 2b show exocyclic and endocyclic co-
ordination modes, respectively. Details of the two isomers are described
below mainly in terms of the coordination modes. We also provide
some evidences for the two isomers as the kinetic and thermodynamic
products.
Slow diffusion of HgI2 in methanol to L in dichloromethane and
allowing the solution to evaporate afforded a small amount of 2a as a
pale yellow crystalline product (Route I in Scheme 3). The SC-XRD
analysis revealed that 2a has a tetranuclear bis(macrocycle) arrange-
ment with the formula [(exoHgLI2)2(μ-Hg2I4)] in which two exo-type
3.2. NMR titration of L with silver(I) perchlorate
macrocyclic complex units,
(
exoHgLI2), are bridged by tetra-
iododimercury(II) core, (μ-Hg2I4) (Fig. 3). In CCDC [48], 155 hits for
the (Hg2I4) unit have been found, however, only two examples of such
core bridging two thiamacrocycles via Hg-S bonds have been reported
so far [32,49]. Since an inversion center locates in the middle of 2a, the
asymmetric unit contains one L, two Hg atoms (Hg1 and Hg2) and four
iodide atoms.
1H NMR titration of L with AgClO4 was performed to obtain further
information on the complexation behavior in solution (Fig. 2a). On
stepwise addition of AgClO4 to the ligand solution, the signals for all
aliphatic protons (H1 – H5) shift downfield, in keeping with the complex
formation with a fast ligand exchange rate. The titration shows that the
plots for all proton signals exhibit no further shifts above a mole ratio of
1.0 (Fig. 2b), indicating that the complex formed has a stable 1:1 metal-
to-ligand species. The silver(I)-induced shifts for the aliphatic protons
follow the order H3 (Δδ 0.35 ppm) > H2,4 (0.27 ppm) > H5
(0.19 ppm) > H1 (0.09 ppm). The largest downfield shift for H3 ad-
jacent to the S donor is due to the silver(I) being strongly bound to the S
As mentioned above, we found that the exo-mode of the Hg1 atom
(
exoHg) in 2a was converted to the endo-mode (endoHg) in 2b (Fig. 4).
When the reaction solution was left undisturbed for 5 days; at the end of
this period only crystals of 2b were left, and these had formed in much
higher yield (60%) than occurred initially for 2a.
Some modified approaches were also carried out, affording isolation
Fig. 1. Crystal structure of 1, [Ag(L)]ClO4. Selected
bond lengths (Å) and bond angles (°): Ag1-S1
2.481(8), Ag1-S2 2.519(9), Ag1-N1 2.325(3), Ag1-
O1 2.710(2), Ag1-O2 2.718(2), S1-Ag1-S2
118.68(3), S1-Ag1-O1 135.94(6), S1-Ag1-O2
78.69(5),
S2-Ag1-O1
76.94(5),
S2-Ag1-O2
123.16(5), N1-Ag1-S1 125.70(7), N1-Ag1-S2
114.77(7), N1-Ag1-O1 65.12(8), N1-Ag1-O2
64.70(8), O1-Ag1-O2 129.77(7).
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M. Shin et al.
InorganicaChimicaActa482(2018)749–755
Fig. 2. (a) 1H NMR spectra of L (1.0 × 10−2 M) following the stepwise addition of AgClO4 in CD3CN and (b) their titration curves for each proton in L.
Scheme 3. Two mercury(II) iodide complex isomers (2a and 2b) obtained in this work.
Fig. 4. Crystal structure of 2b, [(endoHgLI2)2(μ-Hg2I4)] showing an endocyclic
coordination mode of the endoHg1 atom.
Fig. 3. Crystal structure of 2a, [(exoHgLI2)2(μ-Hg2I4)] showing an exocyclic
methanol was allowed on standing at 50 °C and was cooled down to
coordination mode of the exoHg1 atom.
room temperature to evaporate, a pale yellow crystalline product 2b
was afforded. Considering the above results, the conversion of 2a to 2b
at the room temperature is in accord with the exocyclic product 2a
being a kinetic product, while the endocyclic product 2b being a
thermodynamic product. The selected geometric parameters of 2a and
2b are presented in Table 1. The structural characteristics of both
products are compared and discussed below
of 2b both in crystal and powder form directly. For example, under the
identical reaction condition but with stirring at 50 °C for 10 min (Route
II in Scheme 3), a pale yellow precipitate was obtained. The powder X-
ray diffraction (PXRD) pattern confirmed that this solid is a pure pro-
duct 2b (Fig. S2). When a mixture of HgI2 and L in dichloromethane/
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M. Shin et al.
InorganicaChimicaActa482(2018)749–755
en-
intermetallic distance between exoHg1⋯Hg2 (9.64 Å) in 2a and
Table 1
Comparison of the selected bond lengths (Å) and bond angles (°) for 2a and 2b.
doHg1⋯Hg2 (4.78 Å) in 2b is also remarkable. In the overlapped top
views of the macrocyclic complex units (Fig. 5a), the inward form of the
endoHg1 atom in 2b (dark green) could be occurred not by hindered
rotation about a particular bond but rather hindered rotation through
the flipping of an S1-C-C-O3 fragment bound to the exoHg1 atom in 2a
(light blue) or by the packing stability via the intermolecular interac-
tions (Fig. 5b).
2a
2b
Hg1-O3
Hg1-S1
Hg1-I1
Hg1-I2
Hg2-S2
Hg2-I3
Hg2-I3A
Hg2-I4
2.741(4)
2.671(14)
2.647(5)
2.626(5)
2.564(14)
2.728(5)
3.397(5)
2.635(5)
2.740(3)
2.799(13)
2.615(5)
2.596(5)
2.573(12)
2.760(6)
3.158(5)
2.664(5)
In practice, the packing structures confirmed that both products
feature pseudo polymeric arrangements with different connectivity and
dimensions (Fig. 6). In 2a, the complex molecules interact via face-to-
face type aromatic π-π stacking (orange dashed lines in Fig. 6a, cen-
troid⋯centroid 4.04 Å) to form a pseudo 1D polymeric chain and no
further interactions exist between the chains. In 2b, the intermolecular
edge-to-face type π-π interactions (yellow dashed lines in Fig. 6b,
3.16 Å) form pseudo 1D chains which are further cross-linked by C-
H⋯O hydrogen bonds between the chains (red dashed lines, 2.46 Å),
resulting in the pseudo 2-D network. Thus, unlike 2a, the compact
network structure of 2b is reinforced by π-π interactions as well as by
hydrogen bonds. As a consequence, the packing for 2b is more favor-
able because of (i) a minimization of the steric repulsion between ad-
jacent two molecules and (ii) maximization of their attraction via the
edge-to-face π-π interactions as well as van der Walls interactions. Al-
though the origin of the formations of two conformers associated with
the different coordination modes is not clear, the close packing of 2b
may play a role in forming a more stable thermodynamic product in-
corporating the endocyclic conformation of the S1-C-C-O3 segment
toward Hg1 atom.
Since 2a was obtained in a very low yield under the layered con-
dition, the reversibility test between 2a and 2b was not possible.
Sometimes mole-ratio of the reactants for the complexation could be a
controlling factor to give different topological products (supramole-
cular isomers or polymorph) with an identical composition [52]. In
order to examine the mole-ratio effect on the resulting complexes, the
concentration of HgI2 was varied (2–5 equiv.) relative to the ligand
concentration under the homogenous condition. According to the PXRD
patterns for these products (Fig. 7), all the reactions solely yielded 2b,
suggesting that no mole-ratio dependency was observed in this case.
Consequently, the results from the mole-ratio experiments also support
that 2b is a thermodynamically stable.
S1-Hg1-O3
S1-Hg1-I1
S1-Hg1-I2
O3-Hg1-I1
O3-Hg1-I2
I1-Hg1-I2
S2-Hg2-I3
S2-Hg2-I4
S2-Hg2-I3A
I3-Hg2-I3A
I4-Hg2-I3
I4-Hg2-I3A
71.74(8)
96.16(3)
114.92(3)
93.74(9)
96.21(8)
148.92(16)
104.79(3)
124.58(3)
90.40(3)
93.69(12)
129.82(15)
94.29(13)
69.11(8)
99.94(3)
101.86(3)
89.65(7)
104.50(7)
157.13(16)
114.24(3)
123.60(3)
88.45(3)
96.97(13)
117.98(15)
104.63(15)
2a and 2b both of which crystallize in the triclinic space group P-1
also share structural similarities featuring a tetranuclear bis(macro-
cycle) arrangement. Each Hg1 atom in both products is four-coordinate,
being bound to one sulfur atom, one oxygen atom from L in a highly
twisted and bent conformation. The coordination sphere is completed
by two iodide atoms adopting a distorted tetrahedral geometry with the
tetrahedral angles falling in the range 71.74(8)° (S1-Hg1-O3) to
148.92(16)° (I1-Hg1-I2) in 2a and 69.11(8)° (S1-Hg1-O3) to
157.13(16)° (I1-Hg1-I2) in 2b. The large deviations are due to the
formation of the pentagonal ring via Hg1-S1 and Hg1-O3 chelation as
well as the repulsive interaction between two spacious iodo ligands.
The exoHg1-S1 in 2a [2.671(14) Å] is typical, while that of endoHg1-S1 in
2b [2.799(13) Å] falls on the longer end of the reported values in lit-
eratures for such bonds (2.5–2.8 Å) [50,51]. Oppositely, the exoHg1-I
bond distances in 2a [2.647(5), 2.626(5) Å] are slightly longer than
those of endoHg1-I in 2b [2.615(5), 2.596(5) Å] but all values are
comparable with those reported previously [32,49].
On complexation, the flexible domain (S1-O3-O4-S2) incorporating
an S1-C-C-O3 fragment shows a larger conformational change than the
semi-rigid domain (Fig. 5). The associated difference of the
Fig. 5. Structural comparison of exoHg1 complex unit (2a, light blue) and endoHg1 complex (2b, dark green): (a) top views (overlapped) and (b) side views. (For
interpretation of the references to color in this figure legend, the reader is referred to the web version of this article.)
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InorganicaChimicaActa482(2018)749–755
Fig. 6. Packing arrangement of (a) 2a showing in-
termolecular face-to-face π-π interactions (orange
dashed lines, centroid-to-centroid distance =
4.036 Å) and (b) 2b showing intermolecular edge-
to-face π-π interactions (yellow dashed lines) and
interchain hydrogen bonds (red dashed lines). (For
interpretation of the references to color in this
figure legend, the reader is referred to the web
version of this article.)
which mercury(II) exist inside and outside the macrocyclic cavity. As
supported by their relative abundances in functions of reaction time
and temperature, the minor exocyclic complex is the kinetically favored
product, and the major endocyclic complex is the thermodynamically
favored product. The results serve to exemplify the rich and diverse
coordination modes documented so far for the formation of con-
formational isomers incorporating the endocyclic and exocyclic co-
ordination.
Acknowledgements
This work was supported by NRF (2016R1A2A205918799 and
2017R1A4A1014595), South Korea, and the Support Program for
Strategic Research Foundation at Private Universities (2012-2016) and
JSPS KAKENHI Grant Number JP17K05844, Japan.
Appendix A. Supplementary data
Supplementary data associated with this article can be found, in the
online version, at https://doi.org/10.1016/j.ica.2018.07.012.
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