Syntheses and structural characterizations of 24-membered dimetal (Mn, Ni, Fe) macrocyclic complexes and the C-S bond formation between acetylacetone and a mercapto N-heterocycle

Article abstract of DOI:10.1039/b604579k

An organic ligand 2,5-di(3-pentanedionylthio)-1,3,4-thiadiazole (H ₂L) reacts with metal (Mn, Ni, Fe) salts, resulting in 24-membered dimetal macrocyclic complexes [MnL(H₂O)(dmso)]₂· 2dmso (1), [NiL(H₂O)(dmf)]₂·2dmf (2), [MnL(dmf)₂]₂ (3) and [Fe₂L₂(solvent) ₂(SO₄)] (solvent = dmso (6); H₂O (7); dmf (8)). Di-manganese macrocyclic complexes [MnL(dmf)(dmso)]₂ (4) and [MnL(H₂O)₂]₂·6H₂O (5) can also be obtained directly by aerobic assembly reaction of MnCl₂, dipotassium 1,3,4-thiadiazole-2,5-dithiolate (K₂tdadt) and acetylacetone (H₂acac) in various solvents, accompanying a C-S bond formation between acetylacetone and the mercapto N-heterocycle. Disulfide has been considered as the intermediate in the assembly reaction. Meanwhile an assembly reaction including MnCl₂, 2-mercaptobenzimidazole and H ₂acac has produced an organic compound 2-(3-pentanedionylthio) benzimidazole with a new C-S bond. These dimetal complexes have similar macrocyclic structures, in which solvent molecules and sulfate coordinate to the octahedral metal in trans-configuration, whereas a pair of water molecules are located in octahedral cis-positions for 5 owing to a small steric effect. A host cavity of sufficiently large size exists in the macrocyclic structure to trap the solvent molecules and the sulfate anion. The IR spectra have been used to assign the solvent molecules trapped and the sulfate anion which is shown as a bridged bidentate ligand. Thermal analyses show the stability of the macrocyclic backbone below 200 °C and gradual release processes of the trapped solvent molecules. Decomposition and oxidation of the dimetal macrocycle backbone occur at 300-500 °C, resulting in a metal sulfate. Further decomposition led to metal oxide at 500-600 °C. The Royal Society of Chemistry 2006.

Full text of DOI:10.1039/b604579k

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Syntheses and structural characterizations of 24-membered dimetal
(Mn, Ni, Fe) macrocyclic complexes and the C–S bond formation
between acetylacetone and a mercapto N-heterocycle†‡
Xiaofeng Zhang, Hui Chen, Chengbing Ma, Changneng Chen and Qiutian Liu*
Received 29th March 2006, Accepted 31st May 2006
First published as an Advance Article on the web 14th June 2006
DOI: 10.1039/b604579k
An organic ligand 2,5-di(3-pentanedionylthio)-1,3,4-thiadiazole (H2L) reacts with metal (Mn, Ni, Fe)
salts, resulting in 24-membered dimetal macrocyclic complexes [MnL(H2O)(dmso)]2·2dmso (1),
[NiL(H2O)(dmf)]2·2dmf (2), [MnL(dmf)2]2 (3) and [Fe2L2(solvent)2(SO4)] (solvent = dmso (6); H2O (7);
dmf (8)). Di-manganese macrocyclic complexes [MnL(dmf)(dmso)]2 (4) and [MnL(H2O)2]2·6H2O (5)
can also be obtained directly by aerobic assembly reaction of MnCl2, dipotassium
1,3,4-thiadiazole-2,5-dithiolate (K2tdadt) and acetylacetone (H2acac) in various solvents,
accompanying a C–S bond formation between acetylacetone and the mercapto N-heterocycle. Disulfide
has been considered as the intermediate in the assembly reaction. Meanwhile an assembly reaction
including MnCl2, 2-mercaptobenzimidazole and H2acac has produced an organic compound
2-(3-pentanedionylthio)benzimidazole with a new C–S bond. These dimetal complexes have similar
macrocyclic structures, in which solvent molecules and sulfate coordinate to the octahedral metal in
trans-configuration, whereas a pair of water molecules are located in octahedral cis-positions for 5
owing to a small steric effect. A host cavity of sufficiently large size exists in the macrocyclic structure to
trap the solvent molecules and the sulfate anion. The IR spectra have been used to assign the solvent
molecules trapped and the sulfate anion which is shown as a bridged bidentate ligand. Thermal analyses
show the stability of the macrocyclic backbone below 200 ◦C and gradual release processes of the
trapped solvent molecules. Decomposition and oxidation of the dimetal macrocycle backbone occur at
300–500 ◦C, resulting in a metal sulfate. Further decomposition led to metal oxide at 500–600 ◦C.
pentanedionylthio)-1,3,4-thiadiazole (H2L), which has been used
Introduction
to prepare a series of 24-membered dimetal macrocyclic complexes
in this work. This work also reports a C–S bond formation
between acetylacetone and a mercapto N-heterocycle leading to
dimanganese 24-membered macrocyclic complexes.
The assembly of metallamacrocyclic complexes has become an
area of particular interest since the appealing structures of the
metallamacrocycles can act as highly specific hosts used for
selective recognition1 of neutral molecules, cations and anions.
Metallamacrocycles have also been reported to have diverse
possible applications in switchable electron-transfer,2 catalysis3
and magnetism.4 Some important review articles5 have discoursed
at great length on the self-assembly of metallamacrocycles. Poly-
dentate bridging ligands1–14 are generally used as a spacer to
combine polyhedral metal nodes forming the metallamacrocycle.
Many interesting synthetic designs have been performed.10,13,14
Among the metallamacrocyclic complexes, dimetal macrocyclic
complexes have attracted great interest in recent years and
become an important type of metallamacrocycles,15,16 of which
b-diketonate-based ligands as one of the organic spacers have
been used.16 Here, we report a novel bridging ligand 2,5-di(3-
Results and discussion
Synthesis
The ligand 2,5-di(3-pentanedionylthio)-1,3,4-thiadiazole (H2L)
has been synthesized by reaction of ClHacac with dipotassium 2,5-
dimercapto-1,3,4-thiadiazole in high yield. Two b-diketone units
existing in both sides of this molecule afford a possibility to chelate
a pair of metal ions, constructing a macrocyclic dimetallic complex
[ML]2 as shown in Scheme 1.
The dimetal 24-membered macrocyclic complexes synthesized
were as follows: [MnL(H2O)(dmso)]2·2dmso (1), [NiL(H2O)-
(dmf)]2·2dmf (2), [MnL(dmf)2]2 (3), [MnL(dmf)(dmso)]2 (4),
[MnL(H2O)2]2·6H2O (5), [Fe2L2(dmso)2(SO4)]·2H2O (6), [Fe2L2-
(H2O)2(SO4)]·2H2O (7) and [Fe2L2(dmf)2(SO4)]·2CH2Cl2 (8).
Metal salts, Mn(OAc)2, Ni(NO3)2 and FeSO4 react with H2L
resulting in 24-membered dimetal (Mn, Ni, Fe) macrocyclic
complexes. The reaction of FeSO4 with H2L only resulted in di-
Fe(III) macrocycle complexes 6, 7 and 8, showing the oxidation
from Fe(II) to Fe(III). It is noted that the di-Mn macrocycles, such
as 4 and 5, can also be prepared from an assembly reaction of
State Key Laboratory of Structural Chemistry, Fujian Institute of Research
on the Structure of Matter, Chinese Academy of Sciences, Fuzhou, Fujian,
350002, China. E-mail: lqt@ms.fjirsm.ac.cn
† The HTML version of this article has been enhanced with colour images.
‡ Electronic supplementary information (ESI) available: Fig. S1: packing
diagram of H2L; Fig. S2–S4: structure and packing diagram of 1·2dmso;
Fig. S5 and S6: structure and packing digram of 4; Fig. S7: rough structure
of 7; Fig. S8–S14: DTA and TG curves determined for H2L, 2, 4 and 5
under dinitrogen or air atmosphere; and the data of IR spectra for all the
complexes. See DOI: 10.1039/b604579k
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intermediate.20 An early example reported the C–S bond formation
between a metal acetylacetonate and a disulfide (thiocyanogen),21
while preparation of 2-C5H4N(acac–S)Pd(Hacac) is a recent
example of C–S bond formation between disulfide and palla-
dium acetylacetonate.22 The disulfide is therefore proposed as
an intermediate in the assembly of the di-Mn macrocycles. It
is noted that the standard potential (1.51 V) of MnIII/MnII is
obviously higher than that (0.77 V) of FeIII/FeII, implying that
MnIII has stronger ability to oxidize the sulfide to give the disulfide.
Such considerations may also explain why Fe(III) is unable to
induce the assembly of dimetal macrocycles in the same way as
Mn(III) species do. The Mn(III) species can oxidise the thiolate
to form the disulfide with concomitant reduction of Mn(III) to
Mn(II) and then the Mn(II) species is aerobically reoxidised.
The aerial oxidation of the Mn(II) is necessary for the synthesis
of dimanganese macrocycle 5. A parallel anaerobic assembly
reaction using MnCl2·4H2O was performed and did not lead to
any separable product from the reaction solution during a long
period (two months). However, the di-Mn macrocyclic complex
5 was rapidly produced when exposing the reaction solution to
air (see Experimental section). Compared to Mn(II), the reaction
starting from MnIII(Hacac)3 successfully afforded 5 (Experimental
section, method 2). These experiments indicate that the Mn(II)
→ Mn(III) oxidation is important for the formation of the di-Mn
macrocycle. When 4,6-dimethyl-2-mercaptopyrimidine reacts with
MnCl2·4H2O and H2acac under aerobic conditions, a disulfide
bis-(4,6-dimethylpyrimidine) 2,2ꢀ-disulfide was obtained in 42.5%
yield and was identified by X-ray diffraction,23 indicating the exis-
tence of the disulfide as an intermediate. Meanwhile, the disulfide
can be also obtained in 77.9% yield by the oxidation of 4,6-
dimethyl-2-mercaptopyrimidine in the presence of Mn(Hacac)3.
However, eqn (8) and (9) show no evidence for the further product
of C–S bond fusion, implying the limitation of the disulfide
for further reaction. Even so, a successful C–S bond formation
between H2acac and 2-mercaptobenzimidazole in the presence of
MnCl2 under aerobic conditions has been performed (eqn (10))
accompanying the formation of an organic compound HLꢀ.
Scheme 1 Dimetal 24-membered macrocyclic complexes were obtained
from the reaction of a metal(II) salt (metal = Mn, Ni, Fe) with H2L.
the precursors H2acac, K2tdadt and MnCl2·4H2O. The reaction of
Mn(Hacac)3 with K2tdadt has also led to the di-Mn(II) macrocycle
3. Obviously, C–H bond activation of H2acac accompanied with
C–S bond formation between H2acac and the tdadt anion has
occurred in the assembly reaction. Related reactions are showed
as follows:
MnCl2 + H2L → [Mn2L2(solvent)2]
NiCl2 + H2L → [Ni2L2(solvent)2]
(1)
(2)
(3)
(4)
FeSO4 + H2L → [Fe2L2(SO4)(solvent)2]
Mn(Hacac)3 + H2L → [Mn2L2(solvent)2]
(5)
(6)
(7)
of which, eqn (1)–(4) represent the reactions of metal salt with H2L
to give Mn(II), Ni(II) and Fe(III) macrocycles, while eqn (5) and
(6) indicate the C–S bond fusion accompanying the formation of
the Mn(II) macrocycles in the assembly reaction. However, similar
assembly reaction of ferrous or ferric chloride only led to the
formation of Fe(Hacac)3 (eqn (7)) under aerobic conditions and
further C–S bond fusion between H2acac and tdadt anion had
not been found. Other assembly reactions with Ni, Co and Cu
salts have not yet produced separable products. Therefore, the
participation of Mn salts is considered to be essential for the
formation of the C–S bond in preparing 4 and 5. C–H bond
activation accompanying with C–S bond formation is attractive
in organometallic chemistry. Researches17,18 have mentioned the
catalysis of Mn ion and disulfide as a possible intermediate.
Metal acetylacetonates have an activable C–H bond and can
be expected to easily react with S-electrophiles, forming C–S
bonds. As reported in the literature Mn(III) complexes can be
obtained from Mn(II) reactants by aerial oxidation,19 while the
Mn(III) ion is reduced in oxidation of thiolate to get a disulfide
(8)
(9)
(10)
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Structures
H2L. The structure of H2L shown in Fig. 1 contains two
enolic six-membered rings at each end of the molecule. A pseudo-
C2 axis passes through S2 and the middle of the N1–N2 bond.
Eight non-hydrogen atoms (5C + 2O + 1S) in the Hacac–S unit
˚
are coplanar with a largest deviation of 0.0202 A from the least
square plane. The dihedral angles between the Hacac–S and the
1,3,4-thiadiazole planes are 83.7 and 85.9◦, which are connected
by C6–S1–C3 and C7–S3–C10A to form a cambered molecule.
Intermolecular hydrogen-bonding interaction was not found in
the packing diagram (ESI, Fig. S1‡), in which neighboring 1,3,4-
thiadiazole rings align parallel along the b axis. The closest
˚
distance between the thiadiazole planes is 3.4074 A, indicating
face to face p–p stacking interactions.24
Fig. 3 Structure of 2 showing thermal ellipsoids at 30% probability. Two
dmso ligands extend to the inner space of the macrocycle (symmetry code:
A: −x + 2, −y + 2, −z + 2).
Fig. 1 An enolic structure of 2,5-di(3-pentanedionylthio)-1,3,4-thiadiazole
(H2L) with independent atom-labeling showing thermal ellipsoids at 30%
probability.
24-Membered dimetal macrocyclic complexes. Complexes 1–
4 with a common formula [ML(solvent)2]2 have similar dimetal
macrocyclic structures shown in Fig. 2–4 (see also Fig. S2–S6,
ESI‡). A crystallographically imposed symmetrical center exists
within each the macrocycle. Eight non-hydrogen atoms (5C +
2O + 1S) in each the acac-S units are coplanar with deviation
˚
of 0.025–0.0633 A from the least square plane. The metal ion is
chelated by the acac groups forming two non-planar six-membered
Fig. 4 Structure of 3 with two dmf ligands at opposed positions in the
coordination sphere of the Mn ion showing thermal ellipsoids at 30%
probability (symmetry code: A: −x + 1, −y + 2, −z + 1).
chelating rings. The acac oxygen atoms occupy the equatorial
plane of the octahedral metal with rather small dihedral angles
between the O1–M–O2 and O3A–M–O4A planes (1, 5.5◦, 2, 3.0◦,
3, 2.2◦ and 4, 5.8◦). The dihedral angles between the thiadiazole
ring and the acac-S planes are 94.2, 104.6◦ for 1; 84.3, 83.1◦ for
2; 80.3, 82.6◦ for 3 and 97.7, 100.5◦ for 4, which are fairly similar
to those of the free ligand. It is worthwhile to notice that both the
thiadiazole ring planes in these complexes are exactly parallel.
Two solvent ligands are located at opposed positions with a
solvent molecule extending to the inner space of the macrocy-
cle. Selected bond distances and angles and other comparable
structural parameters for all 24-membered dimetal macrocyclic
complexes in this work are listed in Table 1.
Fig. 2 Structure of 1 showing thermal ellipsoids at 30% probability. Two
dmso ligands extend to the inner space of the macrocycle. The other
two solvate dmso molecules lying outside the macrocycle are omitted for
simplify (symmetry code: A: −x + 2, −y + 2, −z + 2).
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◦
˚
Table 1 Summary of selected bond distances (A) and angles ( ) together with other structural parameters for 24-membered dimetal macrocyclic
complexes
Compound
1
2
3
4
5
8
M–O1
M–O2
M–O3A
M–O4A
M–O5
M–O6
2.121(6)
2.135(6)
2.113(6)
2.009(5)
2.009(5)
1.995(5)
2.138(4)
2.121(3)
2.133(4)
2.112(4)
2.137(4)
2.133(4)
2.138(3)
1.968(6)
1.972(7)
1.986(6)
1.967(6)
2.135(3)
2.158(4) (H2O)a
2.121(6)
1.998(5)
2.134(4)
2.146(4)
2−
a
2.197(7) (dmso)a
2.178(7) (H2O)a
2.045(7) (dmf)a
2.071(5) (H2O)a
2.150(5) (dmf)a
2.199(4) (dmf)a
2.189(5) (dmso)a
2.231(5) (dmf)a
1.912(6) (SO4
)
2.022(7) (dmf)a
86.4(3)–93.6(3)
O–Mn–O (cis)
O–M–O (trans)
80.4(2)–111.2(3)
166.4(3); 167.6(3)
172.5(3)
86.3(3)–95.2(3)
177.2(2); 177.4(2)
177.4(3)
80.99(14)–95.7(2)
80.6(2)–111.1(2)
79.6(1)–102.0(2)
167.70(10); 167.75(16) 166.90(17); 167.29(17) 159.85(19); 168.82(17) 174.0(3); 175.5(3)
172.1(2)
Osol–M–Osol
174.68(19)
85.0(2)
178.4(3)
M · · · M
S · · · S
6.806
8.381
6.901
8.073
6.604
8.457
6.939
8.444
8.212
8.120
6.201
8.287
Angle between thiadiazole rings
Angle between acac–S and
thiadiazole ring planes
0
0
0
0
24.9
96.0; 99.0
0
104.6; 94.2
84.3; 83.1
80.3; 82.6
97.7; 100.5
92.4; 89.9
a The oxygen atom belongs to that solvent molecule. Symmetry code: A: 1: x + 2, −y + 2, −z + 2; 2: −x + 2, −y + 2, −z + 2; 3: −x + 1, −y + 2, −z +
1; 4: −x, −y + 1, −z; 5: −x, y, −z + 1/2; 6: −x + 1, −y + 1, −z.
In contrast with the trans-manner coordination of the solvent
ligands in 1–4, both the H2O molecules are in a cis-manner in
the aqua dimanganese macrocycle [MnL(H2O)2]2 (5) (Fig. 5).
Complex 5 with Z = 4 in space group Ccca has crystallographi-
cally imposed 222-symmetry. The molecular structure possesses
the highest C2h symmetry among all the mentioned dimetal
macrocycles, though its coordination sphere of the Mn(II) ion
has a substantial distortion from octahedral geometry. The acac
in the enol-form chelates to the Mn ion forming non-planar
six-membered chelate rings. The dihedral angle between both
planes (O1–Mn–O2 and O1A–Mn–O2A) is 78.5◦ and is obviously
larger than those in 1–4, giving rise to a larger Mn · · · MnA
Diiron complexes 6, 7 and 8 can also be considered as 24-
membered macrocyclic complexes though a sulfate anion bridges
between both the Fe(III) ions, dividing the macrocycle into two
parts. In the structure of 8 the central sulfate moiety is disordered
about the inversion centre. The structural parameters of 8 are listed
in Table 1, showing shorter metal–O distances than those in the
Mn and Ni analogues. The sulfate ion exists inside the macrocycle
and coordinates to both the Fe(III) ions by symmetrically related
O5 and O5A as shown in Fig. 6. A rough structure of 7 is shown
in Fig, S7, ESI.‡ The sulfate bridge shortens the separation of
˚
Fe · · · FeA to 6.201 A, the shortest metal · · · metal separation
among all the dimetal macrocycles, while the S2 · · · S2A separation
˚
˚
˚
separation of 8.210 A, while the S2 · · · S2A separation of 8.120 A
is comparable to those in other dimetal macrocyclic complexes.
Both the thiadiazole rings in 5 are inclined to each other with an
angle of 25.8◦. It is considered that all the differences in structure
should stem from the two small H2O ligands which coordinate
to the Mn ion in cis-manner. Otherwise, dmf or dmso ligands
preferably coordinate to the octahedral metal ion in trans-manner
owing to steric factors.
of 8.287 A is comparable to those of other dimetal (Mn, Ni)
macrocycles. Meanwhile bond valence sum (BVS) analysis25 has
been performed to calculate the oxidation state of the metal centre.
Fig. 6 Structure of 8 showing thermal ellipsoids at 30% probability. A
sulfate ion inside the macrocycle coordinates to both the Fe(III) ions. The
solvate CH2Cl2 molecules are outside the macrocycle and omitted for
clarity (symmetry code: A: −x + 1, −y + 1, −z).
Fig. 5 Structure of 5 showing thermal ellipsoids at 30% probability. Two
H2O molecules are enclosed (symmetry mode: A: −x, y, −z + 1/2; B: x,
−y + 3/2, −z + 5/2).
4050 | Dalton Trans., 2006, 4047–4055
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The bond valences (s) were calculated according to the following
equation,
channels and the trapped solvent molecules were also found in
other compounds (see Fig. S4, ESI‡). Interestingly, the adjacent
thiadiazole rings overlap in a parallel manner in a head-to-tail
s = exp[(r0 − r)/B]
˚
manner with a face-to-face distance of 3.54 A, indicating p–p
staking interactions.
where r is the observed Fe–O bond length and r0 and B are
empirically determined parameters. This calculation gave a BVS
value of 3.3+ for complex 8, supporting the Fe(III) oxidation
state. There are three types of Fe–O distances, Fe–Oacac (1.968(6)–
Infrared spectra and the trapped molecules
IR spectra display characteristic features of the coordinated H2L
ligand and the trapped solvent molecules. In Table 2 the relevant
absorptions for these complexes are listed and the empirical
assignments are given. Typical absorptions of the 24-membered
dimetal macrocyclic complexes are three strong peaks between
˚
˚
˚
1.986(6) A), Fe–Odmf (2.022(7) A) and Fe–OSO (1.912(6) A). These
4
Fe–O bond lengths are consistent with those of other FeIII(acac)
complexes26 (1.97–2.02 A) and shorter than those of Fe (acac)
II
˚
complexes27 reported (2.00–2.33 A).
˚
˚
The size of host cavity is estimated by M · · · MA (6.20–8.21 A)
1591 and 1333 cm−1 assignable to C O and C N bonds of
the L ligand. Complexes 2–4 containing ligated and solvate dmf
=
=
˚
and S2 · · · S2A (8.07–8.46 A) separations for these macrocycles.
These host cavities of sufficiently large size allow the solvent
molecules to exist inside the macrocycle as the guest molecules.
Two H2O molecules are enclosed in the cavity of 5 and one sulfate
anion in 7 and 8. Hydrogen bonding interactions were observed
between the solvent molecules in the cavity. In the structure of 2
two dmf molecules are hydrogen-bonded to the aqua ligand with
=
molecules show the C O vibrations as sharp signals at 1674–
1649 cm−1. The coordinated and solvate H2O molecules were
easily assigned to the broad peaks at 3419–3373 cm−1 with medium
intensity for the complexes containing aqua molecules. Free dmso
has a strong absorption at 1055 cm−1. However the dmso ligand
=
coordinates to the metal giving rise to a weakening of the S
O
˚
an O6 · · · O7 separation of 2.728(7) and 2.796(8) A. Also, hydrogen
bond and red shift of the infrared frequency. It should be noted
that the peaks of dmso are coincident with several peaks (1060(s)
and 1022(m) cm−1) of the free H2L and they thus overlap each
other. The spectra of complexes 1, 4 and 6 exhibit relevant strong
absorptions in this area as follows: 1053(m), 1026(s) cm−1 for
1; 1014(s) cm−1 for 4; 1020(s) cm−1 for 6. These absorptions
should contain the contribution of the dmso ligands since the
peaks in the region 1026–1014 cm−1 are obviously enhanced. An
uncoordinated SO42− group with Td symmetry has infrared active
m3 and m4 fundamentals at 1104 and 613 cm−1.28 If the sulfate
coordinates to a metal ion in a bidentate and/or bridged mode,
the spectra will undergo marked change28 with the lowering of
the symmetry of the sulfate ion, the m1 fundamental will appear
with medium intensity, and moreover, the m3 and m4 will split.29
In di-Fe(III) macrocyclic complexes the sulfate acts as a bidentate
bridged ligand and its absorption bands in the sulfate region are
shown in Table 3, exhibiting several split peaks, such as 1225, 1128,
1065 cm−1 and 1221, 1126, 1065 cm−1 for 6 and 7, respectively. This
spectral feature is consistent with the fact reported in refs. 28–30
that the free sulfate peaks at 1104 cm−1 undergo splitting into three
bands.
bonds were found between the H2O ligand and neighboring solvate
˚
H2O molecules (OH2O · · · OH2O 2.703 A) in 5, as well as between the
˚
H2O and carbonyl O atom (OH2O · · · Ocarbonyl 2.835 A). In addition,
the solvate H2O molecule is hydrogen-bonded to the N atom
˚
of thiadiazole ring with an N · · · OH separation of 2.924 A.
O
2
A packing diagram of 5 (Fig. 7) shows these H2O molecules
existing in the channels formed by the overlapping cavities. Similar
Thermal analyses
Fig. 7 Packing diagram of 5. Solvate and ligated H2O molecules exist
in the channels formed by the overlapping cavities. Hydrogen bonding
interactions are shown as dotted lines.
The thermal stability of the macrocyclic complexes has been
examined by thermogravimetric analyses. The TGA curves were
Table 2 Relevant infrared data (cm−1) for dimetal macrocyclic compounds and ligand H2L
2−
m(l-SO4
)
=
=
=
=
m(H2O)
m(C O)dmf
m(C O, C N)L
m(S O)dmso
m1
m3
m4
H2L
1549, 1390
[MnL(H2O)(dmso)]2·2dmso (1)
[NiL(H2O)(dmf)]2·2dmf (2)
[MnL(dmf)2]2 (3)
[MnL(dmf)(dmso)]2 (4)
[MnL(H2O)2]2·6H2O (5)
[Fe2L2(dmso)2(SO4)]·2H2O (6)
[Fe2L2(H2O)2(SO4)]·2H2O (7)
3419
3400
1587, 1383, 1336
1587, 1383, 1336
1589, 1373, 1336
1591, 1383, 1335
1578, 1375, 1333
1566, 1367, 1338
1564, 1365, 1338
1053, 1026
1674, 1649
1676, 1653
1660
1014
1020
3400
3394
3373
980
985
1225, 1128, 1065
1221, 1126, 1065
667, 619, 600
652
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determined in nitrogen atmosphere in the range from 25 to
◦
1200 C. Free H2L showed relatively high thermal stability with
an insignificant weight loss (0.21%) before 188 ◦C (ESI,‡Fig.
S8 and S9). Then rapid decomposition occurred accompanying
a weight loss of >50% (188–225 ◦C). It is expected that the L
ligand in these complexes should have thermal stability below
180 ◦C. The TGA and DTA curves (Fig. 8) of di-Mn complex
3 showed a first weight loss of 26.4% (177–242 ◦C) with an
endothermic peak corresponding to the release of all the four
dmf molecules (calc. 26.8%). With increasing of the temperature
to 321 ◦C the collapse of the macrocyclic backbone led to a
further weight loss of 50%. Di-Ni complex 2 showed similar
thermal behavior (ESI,‡Fig. S10) including a first weight loss of ca.
4.7% (below 101 ◦C) corresponding to the release of two trapped
water molecules (calc. 3.17%), and a weight loss of 29.2% (below
272 ◦C) attributed to the removal of solvate and coordinated
solvent molecules (calc. 2H2O, 3.17%; 4dmf, 25.77%). Then a
rapid weight loss (ca. 65%) was observed from 272 to 400 ◦C
accompanying the collapse of the macrocyclic backbone. Complex
5 was observed to have a weight loss of 18.48% from 150 to
241 ◦C (ESI,‡ Fig. S12) which is consistent with its release of
the solvate and ligated H2O molecules (calc. 10H2O, 18.40%).
Rapid weight loss was observed at >241 ◦C indicating the collapse
of the backbone. The thermogravimetric analyses have displayed
the desolvation and decomposition processes of the complexes.
However, the final products after continuing heating were uniden-
tified under dinitrogen atmosphere. As a comparison, the TGA
curves were determined in air in the range from 25 to 700 ◦C
in order to observe the oxidation reaction in the participation
of dioxygen. The thermogravimetric analyses of these complexes
display occurrence of three consecutive processes: desolvation,
decomposition/oxidation of the ligand and inorganic residue
formation. Complex 2 lost its coordination water molecules at
104 ◦C and its dmf molecules at 213 ◦C with the expected
endothermic peaks (Figure S11). The subsequent decomposition
and oxidation were in the range 270–480 ◦C and 480–530 ◦C with
two strong exothermic peaks and drastic ◦weight loss. The final
residue in the temperature range 530–700 C remained constant
weight (11.92%) and could be considered as the metal oxide NiO
(calc. 13.1%) Similar thermal behaviors for di-Mn complexes 4
and 5 in air atmosphere were observed (ESI,‡Fig. S13 and S14).
The final residue of the di-Mn complexes with constant weight
Fig. 8 DTA and TG curves determined under dinitrogen atmosphere for
[MnL(dmf)2].
4052 | Dalton Trans., 2006, 4047–4055
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Fig. 9 DTA and TG curves determined under air atmosphere for 2, 4 and 5 in the temperature range 450–700 ◦C. A common exothermic peak was
observed.
◦
(4, 16.2%; 5, 20.8%) at 580–700 ◦C was tentatively considered as
MnO2 when compared to calculated values (4, 15.8%; 5, 18.8%).
Interestingly a similar weight loss (Fig. 9) has been found for these
macrocycle complexes in the temperature range 500–600 ◦C with a
strong exothermic reaction. It may stem from a common thermal
behavior, in which a metal sulfate formed in the decomposition of
the macrocyclic backbone at 300–500 ◦C. This has been supported
by the weight loss values. The thermal decomposition/oxidation
of the macrocycle appears to produce Mn2(SO4)3 with 64.78%
(calc. 63.86%) or 58.36% (calc. 56.97%) weight loss, respectively,
for 4 and 5, and NiSO4 with 72.34% (calc. 72.68%) weight loss for
di-Ni complex 2. These sulfates were further oxidized to result in
the metal oxide MnO2 or NiO after continuing heating.
between 80 and 240 C mainly correlated to the trapped solvent
molecules.
Experimental
All manipulations were performed under aerobic conditions with
materials as received. IR spectra were recorded on a Magna-75-
FT-IR spectrophotometer as KBr pellets (4000–400 cm−1). The 1H
NMR spectra were recorded on a Bruker-Am 500 spectrometer
with TMS as standard. Thermal analysis was performed on
NETZSCH STA449C thermogravimetric instrument. Elemental
analyses were performed using a Germany Elemental Analyzer
Vario EL III.
2,5-Di(3-pentanedionylthio)-1,3,4-thiadiazole (H2L)
Conclusions
Dipotassium 1,3,4-thiadiazole-2,5-dithiolate (K2tdadt, 2.26 g,
10 mmol) was dissolved in 50 mL of MeOH. To the solution
2.69 g (20 mmol) of ClHacac was added and stirred for 6 h.
After filtration 3.1 g of white powder was collected in 90% yield,
which was recrystallized in CH2Cl2 to get square crystals of
H2L. Elemental analysis: calc. for C12H14N2O4S3 (%): C 41.60, H
4.07, N 8.09, S 27.77; found: C 41.38, H 3.98, N 7.95, S 27.39. 1H
(1) 2,5-Di(3-pentanedionylthio)-1,3,4-thiadiazole (H2L) has been
used to synthesize new 24-membered dimetal (Mn(II), Ni(II) and
Fe(III)) macrocycle complexes. The reaction of H2L with either
Mn(OAc)2 or Mn(Hacac)3 produces only di-Mn(II) macrocycles,
while the reaction with FeSO4 affords di-Fe(III) macrocycles in
which a sulfate ion bridges between both the Fe(III) ions.
(2) C–H bond activation and C–S bond formation have been ob-
served in an aerobic assembly system of MnCl2, dipotassium 1,3,4-
thiadiazole-2,5-dithiolate (K2tdadt) and acetylacetone (H2acac) in
various solvents, leading to the di-Mn(II) macrocycle complexes.
The participation of the manganese ion is essential for the C–S
bond fusion. Disulfide has been considered as a possible interme-
diate. A similar assembly using 2-mercaptobenzimidazole has led
to an organic compound 2-(3-pentanedionylthio)benzimidazole.
(3) The 24-membered dimetal macrocycle complexes provide a
host cavity correlating to the molecular recognition. The solvents
(dmso, dmf and H2O) and the sulfate ion are trapped inside
the cavity and have been assigned by IR spectra. Meanwhile,
the thermogravimetric analyses of these complexes show the
occurrence of three consecutive processes: desolvation, decompo-
sition/oxidation of the ligand and inorganic residue formation,
indicating the thermal stability of the macrocycle backbone
when the temperature is below 240 ◦C. The thermal behavior
=
NMR (CDCl3, d/ppm): 2.417 (6H, CH3), 17.33 (1H, C C–OH).
[MnL(H2O)(dmso)]2·2dmso (1). H2L (0.20 g, 0.5 mmol) was
dissolved in 25 mL of mixed solvent (CH2Cl2–dmso–MeOH, 2 :
1 : 2, v/v/v) and 0.063 g (0.5 mmol) of Mn(OAc)2·4H2O was
added under stirring. After filtration, the slight yellow filtrate
was allowed to stand for several days to deposit yellow rhombic
crystals of 1 (0.18 g, yield 31%). Elemental analysis: calc. for
C32H52Mn2N4O14S10 (%): C 33.50, H 4.57, N 4.88, S 27.94, Mn
9.58; found: C 33.41, H 4.61, N 4.82, S 27.68, Mn 10.13.
[NiL(H2O)(dmf)]2·2dmf (2). The above synthetic procedure of
1 was used for the synthesis of 2 with Ni(NO3)2·6H2O and dmf was
used as the solvent. Light-blue crystals (0.10 g, yield 18%) were
collected. Elemental analysis: calc. for C36H56Ni2N8O14S6 (%): C
38.10, H 4.97, N 9.88, S 16.95; found: C 37.44, H 4.77, N 9.63, S
17.00.
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[MnL(dmf)2]2 (3). A solution of 0.125 g of Mn(Hacac)3
(0.36 mmol) in 10 mL of dmf was added with stirring to 10 mL
of CH2Cl2 containing H2L (0.20 g, 0.5 mmol). The solution was
stirred for 1 h and filtered. The filtrate was allowed to stand
for several days to deposit yellow rhombic crystals which were
collected to obtain 0.10 g of 3 (yield 51%). Elemental analysis:
calc. for C36H52Mn2N8O12S6 (%): C, 39.62; H, 4.80; N, 10.27; S,
17.64; found: C, 39.71; H, 4.68; N, 10.26; S, 17.45.
[Fe2L2(dmf)2(SO4)]·2CH2Cl2 (8). The synthetic procedure of 6
was used with a change of the solvent for FeSO4·7H2O (10 mL of
dmf–dmso, 1 : 1 v/v). A few red rhombic crystals were selected
from the dark red impure powder and identified as 8 by X-ray
diffraction.
Assembly reaction of FeSO4·7H2O with K2tdadt and H2acac.
The procedure for 5 (method 1) was used with the use of
FeSO4·7H2O (or FeCl2·4H2O). The filtrate was allowed to stand
for several days to deposit black crystals, which were collected in
moderate yield and identified as Fe(Hacac)3 by X-ray diffraction,
indicating that the experiment did not lead to the formation of
C–S bond and the di-Fe macrocycle.
[MnL(dmf)(dmso)]2 (4). A solution of 0.4 g (2 mmol) of
MnCl2·4H2O in 10 mL of dmf–dmso (1 : 1, v/v) was added to
15 mL of an MeOH solution containing 0.36 g (3.6 mmol) of
H2acac and 0.45 g (1.99 mmol) of K2tdadt, and stirred for 12 h.
The filtrate was allowed to stand for several days affording 0.21 g
(yield 21%) of yellow block crystals. Elemental analysis: calc. for
C34H50Mn2N6O12S8 (%): C, 37.08; H, 4.58; N, 7.63; S, 23.29; Mn,
9.98; found: C, 36.58; H, 4.66; N, 7.34; S, 23.60; Mn, 10.48.
2-(3-Pentanedionylthio)benzimidazole (HLꢀ). To a CH3OH so-
lution (15 mL) of 0.4 g (2 mmol) of MnCl2·4H2O and 0.36 g
(3.6 mmol) of acetylacetone (H2acac), 0.30 g (2 mmol) of 2-
mercaptobenzimidazole was added and stirred for 12 h. The filtrate
was reduced to ca. 10 mL by volatilization at room temperature
to deposit yellow needle crystals (62 mg, yield 13%). Elemental
analysis: calc. for C12H12N2O2S (%): C 58.04, H 4.87, N 11.28,
[MnL(H2O)2]2·6H2O (5).
Method 1. The synthetic procedure of 4 was used with a change
of the solvent for MnCl2·4H2O (20 mL of H2O–MeOH, 1 :
1, v/v). Yellow rhombic crystals (0.43 g, yield 49%) were collected.
Elemental analysis: calc. for C24H44Mn2N4O18S6 (%): C, 29.42; H,
4.49; N, 5.72; S, 19.61; Mn, 11.24; found: C, 31.44; H, 4.66; N,
5.74; S, 19.74; Mn, 12.06. The amount of the hydrate molecules
may change in the product giving rise to analysis deviation.
1
S 12.91; found: C 58.46, H 4.61, N 10.85, S 12.45. H NMR
(CDCl3, d, ppm): 2.38 (6H, CH3), 7.40 (1H, NH), 7.88 (broad, 4H,
=
CH benzene ring), 17.63 (1H, C C–OH). The structure has been
determined by X-ray diffraction and is the same to that reported
in literature.32
Method 2. 0.45 g (1.99 mmol) of K2tdadt was added to 20 mL
of MeOH to obtain a yellow solution to which HOAc was added
dropwise to adjust the pH of the reaction mixture to 6.0. To the
yellow solution 0.70 g (1.99 mmol) of Mn(Hacac)3 was added and
the solution stirred for 2 h. After filtration the filtrate was allowed
to stand for two weeks at room temperature to deposit yellow
rhombic crystals which were collected to obtain 0.59 g of 5 (yield
61%).
X-Ray structure determinations
All the crystals suitable for X-ray diffraction were selected
from the reaction solutions. The diffraction data were collected
on a Siemens SMART CCD diffractometer with graphite-
monochromated Mo-Ka radiation (k = 0.71073 A) using x-scan
˚
mode at 293 K. The intensity data were corrected for Lorentz-
polarization factors and empirical absorption correction was
applied. The structures were solved by direct methods and Fourier
techniques for each compound and refined by full-matrix least-
squares calculation with the SHELXL-97 program package.33
All the non-hydrogen atoms were refined anisotropically. One
oxygen atom (O4) in the solvate H2O molecule for complex 5
was found to be disordered in two positions with occupancy of
0.5. For complex 8, the sulfur atom S4 and the oxygen atoms
O6 and O7 are disordered in two positions with occupancy of
0.5. Only a rough structure was solved31 for complex 7 with
similar features found to that of complex 8. For all compounds,
hydrogen atoms were geometrically located and added to the
structure factor calculations but their positions were not refined.
The crystallographic data were compiled in Table 3, in which the
data of complex 7 was omitted.31
Parallel anaerobic experiment. The synthetic procedure of
method 1 was used but the procedure was performed under
dinitrogen atmosphere. The filtrate was allowed to stand for
several days accompanying the concentration of the filtrate
sometimes. We failed to obtain any isolable product during two
months, indicating that anaerobic conditions did not lead to
complex 5. Then exposure of the solution to air gave rise to the
rapid deposition of yellow rhombic crystals which were collected
in moderate yield and identified as 5 by X-ray diffraction.
[Fe2L2(dmso)2(SO4)]·2H2O (6). To a solution of H2L (0.20 g,
0.5 mmol) in 10 mL of CH2Cl2, 0.14 g (0.5 mmol) of FeSO4·7H2O
in 10 mL of dmso was added under stirring. The deep red solution
was filtered and the filtrate was allowed to stand for days to
deposit red crystals (0.15 g, yield 56%). Elemental analysis: calc.
for C28H40Fe2N4O16S9 (%): C, 30.88; H, 3.70; N, 5.14; S, 26.50;
found: C, 30.76; H, 3.90; N, 5.15; S, 26.21.
CCDC reference numbers 281993–281997 for complexes 1–5,
281998 for 8 and 281999 for H2L.
For crystallographic data in CIF or other electronic format see
DOI: 10.1039/b604579k
[Fe2L2(H2O)2(SO4)]·3H2O (7). The synthetic procedure of 6
was used with a change of the solvent for FeSO4·7H2O (10 mL
of CH3OH). Red hexagonal crystals of [Fe2L2(H2O)2(SO4)]·3H2O
(0.08 g, yield 32%) were collected. Elemental analysis: calc. for
C24H34Fe2N4O17S7 (%): C, 29.19; H, 3.47; Fe, 11.32; N, 5.68; S,
22.74; found: C, 28.94; H, 3.46; Fe, 11.20; N, 5.61. S, 22.70. A
rough structure of complex 7 was solved (see ESI,‡ Fig. S7).31
Acknowledgements
This work was supported by NNSFC (No. 20471061) and The Sci.
& Tech. Innovation Foundation for the Young Scholar of Fujian
Province (No. 2005J059).
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Schulze-Isfort, W. W. Seidel, T. Lugger, R. Frohlich, O. Kataeva and
F. E. Hahn, Chem. Eur. J., 2002, 8, 1327–1335.
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31 Crystallographic data for 7: C24H34Fe2N4O17S7, Mr = 986.67, mono-
clinic, space group◦P21/n, a = 12.1447(3), b = 10.9276(3), c = 16.555(1)
3
A, b = 103.085(1) , V = 2139.97(8) A , Z = 2, l = 1.087 mm−1, R =
˚
˚
0.1188 and Rw = 0.2493 for 3209 reflections (I > 2r(I)). Fe–Oacac
,
˚
˚
1.960(7)–1.995(8) A; Fe–OH O, 2.054(8) A.
2
32 L. Smrcˇok, D. Tunega, V. Langer and M. Koo´sˇ, Z. Kristallogr., 2002,
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33 G. M. Sheldrick SHELXTL-97, Universita¨t Go¨ttingen, 1997.
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The Royal Society of Chemistry 2006
Dalton Trans., 2006, 4047–4055 | 4055
©